The Papua New Guinea University of Technology

Department of Open and Distance Learning

ADULT MATRICULATION

BIOLOGY 2

Prepared by:
Department of Open and Distance Learning
The PNG University of Technology
 MATRICULATION BIOLOGY 2

Matriculation Biology 2
Paul Nongur
Copyright 2013

Published by:
The Papua New Guinea University of Technology
Lae, Morobe Province

All rights reserved. No part of this document may be reproduced, stored in retrieval
system, or transmitted by any form or by any means electronic, electrostatic,
magnetic tape, mechanical, photocopying, recording or otherwise without permission
in writing from the publisher.

__________________________________

Copyright 2013 by
The Papua New Guinea University of Technology
Lae, Morobe Province

Printed 2013
ISBN

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 MATRICULATION BIOLOGY 2

ACKNOWLEDGMENT

The author and publisher would like to acknowledge all those that have contributed in
advice and encouragement, many of whom have assisted in the draft and compilation
of the course book.

Many thanks to:

Dr. Gariba Danbaro for having proofread the course book,

Mr. Eduardo Banzon for editing, formatting and content improvements,
Mr. William Kerua for producing resource materials
My wife Jennifer Nongur for typing the manuscripts,
My sons Daniel and Melton for assisting and being there for me when needed at
home,

The many resource persons and producers of resource materials used in this course
book.

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 MATRICULATION BIOLOGY 2

TABLE OF CONTENTS

PAGE
Course Overview 9
Unit 1.0 Ecology 19
Introduction 20
1.1 The Earth‘s Biosphere 21
1.2 Climate and Biomes 21
1.3 Climatic Regions 27
1.4 Climatic Zones of Papua New Guinea 42
1.5 Plant Adaptations 54
1.6 Animal Adaptation 63
1.7 Controls of Ecosystems Functions 74
Summary 76
Student Learning Activity 1 77
Student Learning Activity 2 78

Unit 2.0 Tropical Rainforest 80

Introduction 81
2.1 Tropical Rainforests 82
2.2 Abiotic Factors of the Rainforest 84
2.3 Abiotic Factors affect Plants and Animals 85
2.4 Plant Adaptations 86
2.5 Rainforest Animal Adaptations 90
2.6 Types of Rainforests 93
2.7 Structure of a Rainforest 94
2.8 Precipitation and Climate 96
Summary 98
Student Learning Activity 3 100

Unit 3.0 The Soil 102

Introduction 103
3.1 What is soil? 104
3.2 Soil Formation 104
3.3 Soil Composition 104

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3.4 Organic Activity 105

3.5 Physical Properties 106
3.6 Soil Texture 106
3.7 Soil Acidity 107
3.8 Soil Colour 108
3.9 Soil Profiles 108
3.10 Influence on Soil Quality 110
3.11 Inherent and Dynamic Quality of Soil 111
3.12 Human Impact 111
3.13 Keeping Soil Healthy 113
Summary 115
Student Learning Activity 4 117

Unit 4.0 Measuring Climate 119

Introduction 120
4.1 Early Measurements and Ideas 121
4.2 Instruments for Measuring Climate Change 121
4.3 Climate Change 124
Summary 125
Student Learning Activity 5 128

Unit 5.0 Aquatic Ecosystems 129

Introduction 130
5.1 Aquatic Ecosystems 131
5.2 Functions 134
5.3 Abiotic Characteristics 135
5.4 Biotic Characteristics 135
5.5 Autotrophic Organisms 136
5.6 Heterotrophic Organisms 136
5.7 Osmosis 138
5.8 Basic Adaptation to Life in Water 141
Summary 152
Student Learning Activity 6 153

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Unit 6.0 Food Chains and Food Webs 154

Introduction 155
6.1 Food Chains 156
6.2 Food Webs 157
6.3 Pyramid of Numbers 158
6.4 Pyramid of Energy 159
6.5 Pyramid of Biomass 160
6.6 Ecological Pyramids 161
Summary 163
Student Learning Activity 7 165

Unit 7.0 Nutrient Cycles 167

Introduction 168
7.1 What is a nutrient cycle? 169
7.2 The Nutrient Cycle 169
7.3 Water Cycle 171
7.4 Carbon Cycle 172
7.5 Nitrogen Cycle 174
7.6 Environmental Problems 176
7.7 Greenhouse Effect 179
7.8 Climate Change 181
Summary 183
Student Learning Activity 8 185

Unit 8.0 Population 187

Introduction 188
8.1 What is population? 189
8.2 Population Structure 191
8.3 Investigating Population 192
8.4 Population Size 193
8.5 Population Growth 195
Summary 200
Student Learning Activity 9 201

Unit 9.0 Evolution 202

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Introduction 203
9.1 What is Evolution? 204
9.2 The Theory of Evolution 204
9.3 History of Evolutionary Ideas 204
9.4 Voyage of the Beagle 205
9.5 The Mechanism of Evolution 206
9.6 Speciation 211
9.7 Role of Competition in Evolution 211
9.8 Artificial and Sexual Selection 211
9.9 Evidence for Evolution 213
9.10 Embryology 215
9.11 Fossils (Palaeontology) 217
9.12 The Nature of the Fossil Record 219
Summary 222
Student Learning Activity 10 223

Unit 10.0 Geological Continental Drift 225

Introduction 226
10.1 Continental Drift Hypothesis 228
10.2 Earth's Major Plates 229
Summary 236
Student Learning Activity 11 237

Unit 11.0 Classification 238

Introduction 239
11.1 Classification and Naming of Living Things 240
11.2 The Three Domains 241
11.3 The Six Kingdoms 242
11.4 Origins of Diversity 244
11.5 Phylogeny, Cladistics and Cladogram 245
11.6 Classification of Living Things and Viruses 246
Summary 249
Student Learning Activity 12 250

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Unit 12.0 Biochemistry 252

Introduction 253
12.1 What is Biochemistry 254
12.2 Relationship to Other "Molecular-Scale" Biological Sciences 254
12.3 Similarities between Organisms 255
12.4 Chemical Composition of Living Matter 256
12.5 Genetics 258
Summary 263
Student Learning Activity 13 264

Unit 13.0 Early Views on Creation 265

Introduction 266
13.1 Myths 267
13.2 Creationism 267
13.3 Theological and Philosophical Doctrines 268
Summary 271
Student Learning Activity 14 273
Answers to Student Learning Activities 274
Assignments 311
Bibliography 324
Appendix 1 Glossary 325

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 MATRICULATION BIOLOGY 2

COURSE OVERVIEW AND STUDY GUIDE

INTRODUCTION

Matriculation Biology 2 is the Part Two of the Biology course in Matriculation Studies
equivalent to Grade 12 Biology. This Course Guide intends to explain what this
course involves in terms of content and organization and follows with exercises and
assignments. You will get answers to the following questions in the succeeding
pages:

Who is the course intended for?

What study materials are supplied?
What does it cover?
What sort of work is involved?
What help is available?
How is the course assessed?
Your review exercises

WHO IS THE COURSE INTENDED FOR?

Matriculation Biology 2 is a course designed for students who have completed

Matriculation Biology 1 with at least a D grade or better. It is intended for students
who wish to study Biology or Biology related courses after completing Matriculation
Studies. Hence, you should pass this course with a B grade or better should you plan
on studying Biology or a Biology related discipline such as Agriculture, Applied
Sciences, Medicine, Environmental Science, Food Technology, Forestry, etc.
Matriculation Biology 1 (Grade 11 equivalent) is a pre-requisite for Biology 2 (Grade
12 equivalent).

WHAT STUDY MATERIALS ARE SUPPLIED?

The Course Guide forms part of the Unit covered in Biology. These units are not
based on any particular text book. Nevertheless, some good reading references are
included for reference purposes. There are 13 units containing all your study material.
In addition to this study material provided by the Department of Open and Distance
Learning, you should also provide for yourself:

- A scientific calculator,
- drawing pencil and pen (blue, black etc)
- ruler marked in centimetres and millimetres and
- note pads to attempt written assignments,
- exercise book to do exercises and solve self-test,

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- folder to keep marked assignments,

- extra textbooks to aid in your understanding of the topics (Optional)

WHAT DOES THE COURSE COVER?

In Biology 2 there are 13 Units:

Unit 1.0 Ecology

Unit 2.0 Tropical Rainforest
Unit 3.0 The Soil
Unit 4.0 Measuring Climate
Unit 5.0 Aquatic Ecosystems
Unit 6.0 Food Chains and Food Webs
Unit 7.0 Nutrient Cycles
Unit 8.0 Population
Unit 9.0 Evolution
Unit 10.0 Geological Continental Drift
Unit 11.0 Classification
Unit 12.0 Biochemistry
Unit 13.0 Early Views on Creation

However this course covers a selection of topics in Ecology, some of which you may
have already studied but some of which will or may be new to you. You will get more
details in the Study Notes which are found in this Course and Study Guide.

At the end of each topic/unit there are activities/exercises. Attempt them for revision
purposes. You will get a written assignment at the end of one or two units depending
on the tutor. You should expect to spend about 1 and half hours to two hours on each
unit each day. Of course, time spent for each unit may vary from student to student.
Many students obtain better results when they study more slowly. Most importantly
spend enough time on each topic to thoroughly understand the course materials
provided for that topic of study before you go on to the next topic of study.

STUDY NOTES/ READINGS

The study notes or readings in each unit try what ordinarily a tutor would do in a
classroom situation. Read and study the notes carefully and understand them. Note
that you are to study the materials that are presented to you not just reading it like a
story book.
A good way to use the study notes is to firstly, read the material thoroughly; and
secondly, read the material slowly and carefully while paying special attention to each
key word(s) and phrase(s). You should make sure that you understand all the

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definitions, figures, diagrams, examples and reasoning. Use the glossaries provided
at the end of the study guide for word usage in text. Sometimes you may have to use
another dictionary to find out the meaning of difficult words.

Throughout the study material you will find questions and exercises. The purpose of
these questions and exercises is to help you play an active part in learning the study
materials. By answering the questions you will discover for yourself results, which will
then be discussed in the material following the questions. It is more interesting and
meaningful when you discover new results for yourself rather than to be told about
them. So be sure to answer them, when you come to questions of this type during the
course of the study.

It is advisable to have a pencil and paper handy when you are reading. You may also
want to write down questions, which occur to you, as you read and later ask your
tutor or other students.

SELF-TEST

After you have thoroughly studied the material, you should attempt to answer
exercises given for each topic/section. These exercises are practice exercises and
will help you to assess your progress and understanding of this unit of study. All
questions should be attempted. If you have any difficulty with a certain question, do
not go on, go back and revise the topic and/or relevant section and try answering the
questions once again. If you still cannot answer it, you should ask your tutor. He will
be most willing to help you.

WRITTEN ASSIGNMENT

The written assignment should only be attempted after the course notes had been
read carefully. All assignment questions must be attempted before a written
assignment is handed over for marking. Your effort to answering the questions will
help the tutor to assess you and to understand your difficulties so that amendments
will be made to correct some of your mistakes. Sample assignments are included
within this handbook. Do not attempt them until you are told to by your tutor.

MARKS

At the end of each exercise or assignment you will get your marked scripts. This will
enable you to determine your performance and understanding of each topic of study.
Keep your marked script for future revision. They can become very helpful when you
are preparing for your examination.

HOW IS THE COURSE ASSESSED?

The course is assessed in two parts: compulsory assignments and a final

examination. The compulsory assignments form 30% of the assessment while the
remaining 70% comes from the final examination. Therefore, assignments must be
submitted regularly according to the timetable or schedules provided by your tutor.

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If for any reason you are going to submit the assignments late, you should write to
your Centre Coordinator or Biology tutor explaining your reasons for the lateness and
suggesting a revised schedule that will help getting your assignments submitted
before the examinations are due. Assignments submitted late or after the
examination will not be marked. It is in your own interest to send in assignments on
time so that tutors can give you feedback on your progress before it is too late.
Tutors have the right to deduct marks for lateness or refuse to mark assignments
submitted late.

WHAT HELP IS AVAILABLE?

The study units or topics in this course are designed for self-study; meaning that you
can study the course without the help of a teacher/tutor. Furthermore, to make
studying for this material easier there will be tutorial sessions organised in the
University Study Centres. Your Biology II tutor at the study centres will tell you about
the frequency of the Biology II tutorials.

Feel free to ask your tutor questions about the study materials or the problems you
are having with the study materials. Your tutor will devote some time of tutorials in
discussing your difficulties. You should not expect the tutor to teach the whole unit
during those limited times. Therefore learning of Biology from the units is going to be
your own responsibility. The presence of the tutor is only to guide you through the
unit or study guide.

We learn so many things in life from different persons in different forms and methods.
Our colleagues doing a similar course are very useful resource person to assisting
you learn new things. Therefore, whenever opportunity arises discuss your Biology
problems with other students doing the same course. You may arrange time to meet
every week at a place with other students to share your problems. The difficulties
discussed in such a group can be later discussed with your tutor in the next tutorial.

Because some of the study centres are located within the High and Secondary
Schools and colleges, it is a good idea to make acquaintances with the staff
members and the students there and sometimes discuss your difficulties in Biology II
with them. You should also become a member of a Public Library in your province.
You could get some help from text books at the same or lower level. If you cannot
find any assistance or help, please make sure that the assignments you sent in for
marking and assessment purposes are your own work. Cheating will not help you in
any way or form. Remember you will be on your own in the final examination room.

LEARNING OUTCOMES

After completing this unit, students can:

* define ecology and explain its composition

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* describe and explain the different types of ecosystems (terrestrial, aquatic and
desert)
* describe the adaptation of plants and animals living within their respective
ecosystems
* determine the interdependency of living organisms within each environment
* explain the composition of tropical rainforest
* state morphological adaptations of plants in the tropical rainforest
* explain confidently the structure of rainforest
* understand that soil is an abiotic factor of ecology
* explain the different stages of soil formation
* describe with confidence properties of soil composition
* confidently name the instruments used for measuring climate
* understand the complex interactive climatic system
* identify and understand the composition the importance of the aquatic
ecosystems to human life
* identify and describe different adaptations of organisms
* understand the differences between food chains and food webs
* understand the process of succession
* understand the different nutrient cycles
* define and explain population
* name the earth's major and minor plates
* identify and describe evidence for continental drift in the form of plant and animal
fossils of the same age found around different continent shores
* describe the different classifications, kingdoms of all living things
* describe the schematic relationship between biochemistry, genetics, and
molecular biology
* describe the relationship to other "molecular-scale" biological sciences
* explain the theological and philosophical doctrines of creation

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TEXTBOOKS

Recommended for students:

GCSE Biology, Mackean, John Murray, 1986

Biology, GCSE Edition, Jones, Jones, Cup, 1984
Introduction to Biology, Tropical Edition, Mackean, John Murray, 1984
Life Study, Mackean, John Murray, 1981
Biology, Longman, Terry Parkins, John Simpkins, 1999

Recommended for teachers:

Biology, A Functional Approach, M.B.V. Roberts, 1993

Biology, Beckett, OUP, 1986
Biology, Cadogan, Green, Heinemann, 1985
NEW Care Biology, Practical Manual. Hill, Coben, McDonnell Heinemann, 1983
Biology for the IB Diploma, Oxford, Andrew Allot, 2007

SUBJECT STUDY GUIDE SCHEDULE

Week Topic
1&2 Unit 1.0 Ecology
1.1 The Earth‘s Biosphere
1.2 Biomes
1.3 Climatic Regions
1.4 Climatic Zones of Papua New Guinea
1.6 Plant Adaptations
1.7 Animal Adaptation
3&4 Unit 2.0 Tropical Rainforest
2.1 Tropical Rainforests
2.2 Abiotic Factors of the Rainforest
2.3 Abiotic Factors Affect Plants and Animals
2.4 Plant Adaptations
2.5 Rainforest Animal Adaptations
2.6 Types of Rainforests
2.7 Precipitation and Climate

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2.8 Structure of a Rainforest

5&6 Unit 3.0 The Soil
3.1 What is soil?
3.2 Soil Formation
3.3 Soil Composition
3.4 Organic Activity
3.5 Physical Properties
3.6 Soil Texture
3.7 Soil Acidity
3.8 Soil Colour
3.9 Soil Profiles
3.10 Influence on Soil Quality
3.11 Inherent and Dynamic Quality of Soil
3.12 Human Impact
3.13 Keeping Soil Healthy
7 Unit 4.0 Measuring Climate
4.1 Early Measurements and Ideas
4.2 Instruments for Measuring Climate Change
4.3 Climate Change
7 Unit 5.0 Aquatic Ecosystems
5.1 Aquatic Ecosystems
5.2 Functions
5.3 Abiotic Characteristics
5.4 Biotic Characteristics
5.5 Autotrophic Organisms
5.6 Heterotrophic Organisms
5.7 Osmosis
5.8 Basic Adaptation to Life in Water
8 Unit 6.0 Food Chains and Food Webs
6.1 Food Chains
6.2 Food Webs
6.3 Ecological Pyramids
6.4 Pyramid of Biomass
6.5 Pyramid of Numbers

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6.6 Pyramid of Energy

6.7 Pyramid of Biomass
6.8 Ecological Pyramids
9 Unit 7.0 Nutrient Cycles
7.1 What is a Nutrient Cycle?
7.2 The Nutrient Cycle
7.3 Water Cycle
7.4 Carbon Cycle
7.5 Nitrogen Cycle
7.6 Environmental Problems
7.7 Greenhouse Effect
7.8 Climate Change
10 Unit 8.0 Population
8.1 What is population?
8.2 Population Structure
8.3 Investigating Population
8.4 Population Size
8.5 Population Growth
10 & 11 Unit 9.0 Evolution
9.1 What Is Evolution?
9.2 The Theory of Evolution
9.3 History of Evolutionary Ideas
9.4 Voyage of the Beagle
9.5 The Mechanism of Evolution
9.6 Speciation
9.7 Role of Competition in Evolution
9.8 Artificial and Sexual Selection
9.9 Evidence for Evolution
9.10 Embryology
9.11 Fossils (Palaeontology)
9.12 The Nature of the Fossil Record
12 Unit 10.0 Geological Continental Drift
10.1 Continental Drift Hypothesis
10.2 Earth's Major Plates

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12 Unit 11.0 Classification

11.1 Classification and Naming of Living Things
11.2 The Three Domains
11.3 The Six Kingdoms
11.4 Origins of Diversity
11.5 Phylogeny, Cladistics and Cladogram
11.6 Classification of Living Things/Viruses
13 Unit 12.0 Biochemistry
12.1 What is biochemistry?
12.2 Relationship to other "Molecular-Scale" Biological
Sciences
12.3 Similarities between Organisms
12.4 Chemical Composition of Living Matter
12.5 Genetics
13 Unit 13.0 Early Views on Creation
13.1 Myths
13.2 Creationism
13.3 Theological and Philosophical Doctrines

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QUESTIONNAIRE

Course Code and Title __________________________________________

Dear Student,
We would like to seek your views about this course module, its strengths, and its
weaknesses in order for us to improve it. We therefore request you to fill in this questionnaire
and submit it when you finish this course. If the space provided is insufficient, kindly use a
separate sheet. Do not write your name. Thank you for your cooperation.
Please tick the appropriate box.

Items Excellent Very Good Good Poor Give

specific
examples if poor.
(e.g. Units & pages)

1. Logical presentation of content ____________

2. The use of language ____________

3. The style of language? ____________

4. Explanation of concepts ____________

5. Use of tables ____________

6. Use of graphs ____________

7. Use of diagrams/illustrations ____________

8. How are the student activities? ____________

9. How is feedback to questions? ____________

10. Do the units cover the course

syllabus? ____________

11. If not, which of the topics are not covered?

________________________________________________________________________________
12. Comment on the depth of the coverage of the content.
________________________________________________________________________________
13. Is there anything especially good or bad about this course module?
________________________________________________________________________________
14. How do you think the module could be improved?
________________________________________________________________________________
15. Any other comments you wish to make?
_______________________________________________________________________________

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UNIT 1.0

ECOLOGY

Learning Outcomes

At end of this Unit, you can:

1 define ecology and explain its composition

2 describe and explain the different types of ecosystems (terrestrial, aquatic and
desert)

3 describe the adaptation of plants and animals living within their respective
ecosystems

4 determine the interdependency of living organisms within each environment

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INTRODUCTION

Ecology is the study of the relationships between organisms and their environments,
including: the interactions of living organisms with one another and with their non-
living surroundings, the flow of matter and energy in an environment, and the
structure and functions of nature. The environment is all the factors in the
surroundings of organisms that directly or indirectly have an effect on them. These
factors are either biotic or abiotic. Biotic factors are all the living organisms in the
environment. Abiotic are physical or non-living factors such as soil, rain, temperature
etc. Community is where all the organisms in a particular area at a given time. And
the number of a particular species in an area at a specific time is referred to as
population. Habitat is the area in which an organism lives.

Plants and animals inhabit land up to a height of about 6km above sea level. In water
they live as far down as 11km below the surface. The total volume of the earth in
which life permanently exists is called the biosphere, in which there are four major
habitats – marine, estuarine, freshwater and terrestrial. The biosphere is the
collective interaction of all the biomes on the Earth. On the land there are several bio-
geographical zones, in each of which there is characteristic plant and animal life.
Climate is one of the main factors that determine what living organism will be found in
any given environment.

No living thing in the world lives entirely on its own or is independent. Every living
organism depends on its surroundings and other plants and animals. A community of
living things in a particular area, along with the soil, water and other non-living
materials, forms an ecosystem. An ecosystem is any environment containing living
organisms interacting with each other and with their non-living parts of the
environment. Ecosystem can be as small as water –filled hollow in a tree or as large
as a forest. This system involves the exchange of materials and energy between
organisms and their environment. Ecosystems are largely self-sustaining.

Environments have abiotic and biotic features. Abiotic means non-living; biotic
means living. Abiotic features include physical and chemical factors such as
temperature, rainfall, type of soil, atmosphere and the salinity of water. Biotic features
include all the living organisms, their population, distribution and interactions.

The habitat of organism is the place where it lives. A niche is a specific limited
habitat of a particular species plus its own unique position. For example, leaf canopy,
tree truck, etc. The study of relationships of living organisms with each other and
with the physical environment is called ecology.

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1.1 THE EARTH’S BIOSPHERE

The earth‘s biosphere contains numerous complex ecosystems that collectively

contain all of the living organisms of the planet. Unique perspectives of the earth
help suggest the immensity and complexity of the planet‘s biosphere. The thin
mantle of life that covers the Earth is called the biosphere.

The biosphere is the space on and near the Earth's surface that contains and
supports living organisms and ecosystems. It is typically subdivided into the
lithosphere, atmosphere, and hydrosphere. The lithosphere is the earth's surrounding
layer composed of solid soil and rock, the atmosphere is the surrounding gaseous
envelope, and the hydrosphere refers to liquid environments such as lakes and
oceans, occurring between the lithosphere and atmosphere. The biosphere's creation
and continuous evolution result from physical, chemical, and biological processes.

Figure 1.1 The component of Biosphere

Source: users.rcn.com/jkimball.ma.ultranet/BiologyPages

1.2 CLIMATE AND BIOMES

The broad units of vegetation are called plant formations or biomes. Biomes are
associated with plants and animals life, and are influenced by many factors, including
climate, latitude, altitude, moisture and temperature.

The major biomes are desert, tropical rainforest, savannah grassland, temperate
deciduous forest and coniferous forest. All biomes vary geographically from each
other. Other minor biomes includes the associated freshwater communities (streams,
lakes, ponds, wetlands) and marine environment (Open Ocean, littoral-shallow water
regions, benthic-bottom regions, rocky shores, sandy shores, estuaries, and
associated tidal marshes.

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Types of biomes

Geography is interested in how people and cultures relate to the physical

environment. The largest environment of which we are part is the biosphere. The
biosphere is the part of the earth's surface and its atmosphere where organisms exist.
It has also been described as the life-supporting layer that surrounds the Earth.

The biosphere we live in is made up of biomes. A biome is a large geographical

region where certain types of plants and animals thrive. Each biome has a unique set
of environmental conditions and plants and animals that have adapted to those
conditions. The major land biomes have names like tropical rainforest, grasslands,
desert, temperate deciduous forest, taiga (also called coniferous or boreal forest),
and tundra.

There are quite a few different types of biomes in the world. Each of them has unique
characteristics. Due to the climate and features, there are different plants and
animals that are able to thrive in them. Learning about the types of biomes helps us
to make sense of why certain animals and plants are found in one location and not
the next.

It also helps us to fully understand why the different plants and animals within a given
biome are so dependent upon each other. There is a balance that has to be
maintained in order for all to continue surviving there. The dependence that they
have upon each other is very detailed. It is also interesting to explore.

The classifications of these biomes help us to understand the world. Too often we are
caught up in only what goes on around us. By identifying the different factors that
take place throughout the world, you can get the sense of what is really going on
around us. It is fascinating information. Each of the biomes by themselves is worth
exploring in great detail.

Biomes of the World

There are twelve types of Biomes in the world.

1 Tundra Biome
2 Desert Biome
3 Taiga Biome
4 Tropical Rainforest Biome
5 Chaparral Biome
6 Coral Reef Biome
7 Freshwater Biome
8 Grassland Biome
9 Ocean Biome

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10 Savannah Biome
11 Temperate Deciduous Forest Biome
12 Wetland Biome

Terrestrial Biomes

Biomes that are found on land and that have an abundance of vegetation are known
as terrestrial biomes. There are many variations though depending on the climate,
vegetation, and location of them. Some of the popular terrestrial biomes include the
tundra biome, the forest biome, the grassland biome, and the desert biome.

Tundra biomes are extremely cold and have very harsh conditions. They include
areas of Russian and the Arctic. Only a few types of plants and animals are able to
survive here. Even humans find it to be very hard to live in such conditions. With the
forest biome you are talking about the tropical and subtropical areas. They are the
ones that have lots of humidity, ample rainfall, and plenty of thick forest regions in
them.

In the grassland biome there are plenty of plants, grass, and flowers that grow. There
is a rainy season and a dry season. This is a type of environment with decent
temperatures throughout the year. As a result it is easier for the plants and animals
that live here to be able to survive. However, in some locations there is a long
drought season. During this period of time it is harder for them to survive.

The desert biome is the hottest and the driest of all the terrestrial biomes out there.
The extreme temperatures and lack of rainfall can really take a toll. The risk of fire is
very high too which can result in many areas being burned.

Freshwater Biomes

Freshwater biomes are those that are found in the water. It is unbelievable the
amount of aquatic life that exists out there. The depth of the water will determine
what lives there as well as the temperature. If the water moves or if it stands still it will
also be something that is taken into consideration. When you think about freshwater
biomes, they don‘t have to be large bodies of water to count.

They include lakes, rivers, streams, ponds, and the wetlands. Sometimes, the
organism that lives there is only a single cell. They often rely on the water for food
and for survival. When you look at such freshwater you may see areas of moss. That
is a big indicator that there are organisms living in the water. They feed on that moss
as a means of surviving in their given biome.

Marine Biomes

When you think about extremely large bodies of water such as the ocean, those are
marine biomes. They contain saltwater instead of freshwater. They also include coral
reefs and estuaries. The ocean biome is the biggest of all of them in the world. That
makes sense because so much of the surface of the Earth is made up of water.

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Due to the mass size of the ocean biome, there are many subcategories offered as
well. This makes it possible for further evaluation of all of them to be considered. It is
amazing what can take place in the marine biomes. The technology we have today
allows us to use underwater cameras to see those magnificent relationships among
the plants and animals living there.

Endolithic Biomes

Some argue if the endolithic biome is really a separate classification. Yet many
experts believe that these living things don‘t fall into any other categorization
properly. You will find endolithic biomes in all of these other types of biomes though.
This reference is to various forms of microscopic life. They live in the rocks and pores
so they are very difficult to identify and to categorize.

Anthropogenic Biomes

Perhaps the most complicated element of biomes is wrapped up with anthropogenic

biomes. This is one that takes all of the human efforts into it. The fact that we use
land for planting food through farming efforts falls into this category. The forms of
vegetation that will be offered can be evaluated. Based on that information, we are
able to determine what will grow best in a given type of environment.

The use of the land in different biomes depends on what it has to offer. You can‘t
fight nature but you can certainly benefit from all that it offers. Anthropogenic biomes
explain why certain activities are possible in one biome but not in others. It is very
interesting to explore in more detail how all of this helps to maintain the ultimate
balance among plants and animals that live in a given biome.

There is no doubt that the actions of humans have continued to alter the natural
patterns of climate. Take the issue of global warming for example. It has causes
certain areas to be much warmer than they normally would be. As a result there are
shifts in the way plants and animals living in those biomes are able to survive.

Being able to manage what is best for plants and animals doesn‘t always come with
such easy answers. However, the fact that we do understand the biomes in detail
allows for action to be taken against humans. If their efforts could result in a location
being destroyed, then there can be actions taken to prevent humans from building in
that area or destroying it. Such efforts can be complicated and time consuming. Yet
they are for the overall good of a given biome.

Anthropogenic biomes also give us the opportunity to do what is right within any
given biome as well. They allow us to make good choices about how our movements
will affect all other living things. Being able to see the whole picture instead of only
reaching for what we want is very important. There are too many plants and animals
out there at risk of being extinct due to the selfish efforts of humans.

To give them credit, for a long time it wasn‘t understood how everything fit and was
interconnected. However, now that we have that information it is wrong to ignore it.

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Being able to identify your own role in any biome is important. However, never lose
track of the fact that we depend on plants and animals for our ultimate survival as
well.

Importance of Biomes

All of the biomes in the world are very important for all of us. The animals and plants
that live in them are a delicate balance. The efforts of humans though often upset
that balance. As a result there can be serious problems in any of the biomes. Now
that we are fully aware of what our actions do, it is time to correct them. By doing all
we can in the way of conservation and preservation of the biomes, we can help to
ensure that the plants and animals in their respective biomes have a chance to thrive.

Every single biome out there is very important to the overall structure of the Earth.
Even though these biomes have undergone a variety of changes in the past, what
the future holds for them is uncertain. It all depends on what we want to do for the
betterment of our world. In the past, humans have taken action that will help them.
Yet they failed to see the negative impact that it had on other living elements around
them.

Ignorance is no longer an excuse though for allowing it to continue. All of us have the
ability, the opportunity, and the responsibility to learn the facts. When we do so, we
will have a clear picture of what these biomes offer, too often their value is
underestimated and taken for granted. Steps have to be put into motion now to make
sure that they are able to continue to survive.

Tundra Biome

Tundra is a biome in the Northern Hemisphere lying above the zone of northern
coniferous forest (taiga) and below the polar oceans and terrestrial regions of
permanent ice and snow. Alternate freezing and thawing of the ground on a seasonal
cycle and the presence of a permanently frozen subsoil layer called permafrost.
Annual precipitation is generally less than 380mm over most of the Arctic Tundra.
Plant growth is limited by the cold temperatures and lack of available water. Lichens,
mosses, and low shrubs pre-dominate the tundra biome. Plants have adapted to the
basic problem of cold weather by having a very short growing seasons with soil that
only thaw to a depth of a few centimetres.

The Arctic Tundra occurs in the northern parts of Alaska, Canada, Norway, Finland
Russia and Siberia and in some parts of Iceland and Greenland.

Producers/Plants

Green plants can make their own energy containing chemicals using simple
chemicals from the air and soil. Plants are able to produce their own food so they are
called producers.

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To produce food plants need energy. Where does this energy come from? Although
vast amount of energy from the sun reaches the earth, plants use only a very small
amount of it for making their food through a process called photosynthesis.

The glucose produced during photosynthesis can be used immediately to give the
plants energy to stay alive. Excess glucose produced can be converted into other
substances required by the plant for growth and reproduction. Surplus glucose that is
not required immediately for energy or growth and production, can be converted to
starch or lipid (usually oils). These can be stored in the plant cells so they are easily
available for future consumption.

Examples of plant adaptations of the tundra biome

1 The Arctic Willow is a tiny tree that grows very slowly due to the cold conditions.

Morphological adaptation: grows horizontally to the ground where it is warmest and

protected from the cold.

Physiological Adaptation: produces antifreeze chemicals in the sap to prevent the

cells from freezing in the winter.

2 The Arctic Poppy is a small annual plant with large yellow flowers growing close
to the ground.

Morphological Adaptation: large flower attract the few insects and trap weak sunshine
to raise the temperature slightly.

Physiological Adaptation: fast growing, pollinating and setting of seeds to beat the
start of winter.

Consumers/Animals

Animals cannot make their own food. They must eat other organisms to obtain their
nutrients and energy so they are called consumers.

There are four different types of consumers.

1 Herbivores eat only plant material such as; leaves, nectar, and fruits.
Herbivores spend a lot of time eating because plants are not a concentrated
source of protein and also contain a large proportion of cellulose which is
difficult to digest.
2 Carnivores eat other animals. Meat is a good source of protein and energy so
carnivores do not spend much time eating as herbivores.
3 Omnivores eat both plants and animals.
4 Parasites live and feed on or inside another living organism called its host.

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Adaptation of some consumers

1 Lemming is a rodent that eats the young grass and willows. It reproduces
rapidly when the conditions are favourable.

Morphological adaptation: thick fur to keep warm.

Physiological Adaptation: stores food as fat to survive the winter.
Behavioural Adaptation: hibernation or dormancy i.e. the lemming sleeps
underground during the winter, particularly to slow down metabolism to a
minimum to conserve the food reserves stored as fat.

2 The Snowy Owl is a large owl that feeds on lemmings.

Morphological adaptation: During the winter months, the snowy owl‘s white
plumage camouflages it perfectly, allowing it to swoop down undetected on
small mammals and fish. It turns white in winter. Legs are covered in feathers
to keep them warm.
Behavioural Adaptation: Breed more chicks when the population of lemmings
rises in a good season.
Physiological Adaptation: excellent eye sight and hearing which enables it to
find and catch food.

Conserving of Heat

Still air is a good insulator and prevents the conduction of heat. Feathers and fur hold
a layer of still air close to the skin which prevents heat loss and keeps the animal
warm.

Most animals in the tundra are birds and mammals. They are homoeothermic with a
constant, warm, body temperature. Animals that are poikilothermic have a variable
body temperature of the environment. Amphibian and reptiles are poikilothermic and
are able to survive the cold tundra conditions.

1.3 CLIMATIC REGIONS

There are series of climatic regions namely, Tropical (tropical lowlands and
highlands), Arid (desert and scrub forest), Temperate (deciduous, coniferous forest,
grassland) and Polar (tundra, permanent ice and snow).

Have you ever wondered why one area of the world is a desert, another a grassland,
and another a rainforest? Why are there different forests and deserts, and why are
there different types of life in each area? The answer is climate.

Climate is the characteristic condition of the atmosphere near the earth's surface at a
certain place on earth. It is the long-term weather of that area (at least 30 years). This
includes the region's general pattern of weather conditions, seasons and weather
extremes like hurricanes, droughts, or rainy periods. Two of the most important
factors determining an area's climate are air temperature and precipitation.

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World biomes are controlled by climate. The climate of a region will determine what
plants will grow there, and what animals will inhabit it. All three components, climate,
plants and animals are interwoven to create the fabric of a biome.

Figure 1.2 showing World’s Climatic Regions

NORTH AMERICA

Greenland
arctic to subarctic; cool summers, cold winters

Canada
varies from temperate in south to subarctic and arctic in north

United States of America

mostly temperate, but tropical in Hawaii and Florida, arctic in Alaska, semiarid in the
great plains west of the Mississippi River, and arid in the Great Basin of the
southwest; low winter temperatures in the northwest are ameliorated occasionally in
January and February by warm chinook winds from the eastern slopes of the Rocky
Mountains

United Mexican States

varies from tropical to desert

Republic of Cuba
tropical; moderated by trade winds; dry season (November to April); rainy season
(May to October)

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Republic of Panama
tropical maritime; hot, humid, cloudy; prolonged rainy season (May to January), short
dry season (January to May)

SOUTH AMERICA

Federative Republic of Brazil

mostly tropical, but temperate in south

Republic of Colombia
tropical along coast and eastern plains; cooler in highlands

Republic of Peru
varies from tropical in east to dry desert in west; temperate to frigid in Andes

Republic of Ecuador
tropical along coast, becoming cooler inland at higher elevations; tropical in
Amazonian jungle lowlands

Republic of Bolivia
varies with altitude; humid and tropical to cold and semiarid

Republic of Paraguay
subtropical to temperate; substantial rainfall in the eastern portions, becoming
semiarid in the far west

Republic of Chile
temperate; desert in north; Mediterranean in central region; cool and damp in south

Argentine Republic
mostly temperate; arid in southeast; subantarctic in southwest

AFRICA

People's Democratic Republic of Algeria

arid to semiarid; mild, wet winters with hot, dry summers along coast; drier with cold
winters and hot summers on high plateau; sirocco is a hot, dust/sand-laden wind
especially common in summer

Kingdom of Morocco
Mediterranean, becoming more extreme in the interior

Islamic Republic of Mauritania

desert; constantly hot, dry, dusty

Republic of Mali
sub-tropical to arid; hot and dry February to June; rainy, humid, and mild June to
November; cool and dry November to February

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Republic of Niger
desert; mostly hot, dry, dusty; tropical in extreme south

Federal Republic of Nigeria

varies; equatorial in south, tropical in centre, arid in north

Republic of Cameroon
varies with terrain, from tropical along coast to semiarid and hot in north

Great Socialist People's Libyan Arab Jamahiriya

Mediterranean along coast; dry, extreme desert interior

Arab Republic of Egypt

desert; hot, dry summers with moderate winters

Republic of Chad
tropical in south, desert in north

Republic of the Sudan

tropical in south; arid desert in north; rainy season varies by region (April to
November)

Federal Democratic Republic of Ethiopia

tropical monsoon with wide topographic-induced variation

Democratic Republic of the Congo

tropical; hot and humid in equatorial river basin; cooler and drier in southern
highlands; cooler and wetter in eastern highlands; north of Equator - wet season April
to October, dry season December to February; south of Equator - wet season
November to March, dry season April to October

Republic of Angola
Semi-arid in south and along coast to Luanda; north has cool, dry season (May to
October) and hot, rainy season (November to April)

Federal Democratic Republic of Ethiopia

tropical monsoon with wide topographic-induced variation

Republic of Uganda
tropical; generally rainy with two dry seasons (December to February, June to
August); semiarid in northeast

Republic of Kenya
varies from tropical along coast to arid in interior

United Republic of Tanzania

varies from tropical along coast to temperate in highlands

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Republic of Zambia
tropical; modified by altitude; rainy season (October to April)

Republic of Namibia
desert; hot, dry; rainfall sparse and erratic

Republic of Zimbabwe
tropical; moderated by altitude; rainy season (November to March)

Republic of South Africa

mostly semi-arid; subtropical along east coast; sunny days, cool nights

Republic of Madagascar
tropical along coast, temperate inland, arid in south

EUROPE

Republic of Iceland
temperate; moderated by North Atlantic Current; mild, windy winters; damp, cool
summers

Kingdom of Norway
temperate along coast, modified by North Atlantic Current; colder interior with
increased precipitation and colder summers; rainy year-round on west coast
Kingdom of Sweden
temperate in south with cold, cloudy winters and cool, partly cloudy summers;
subarctic in north

Republic of Finland
cold temperate; potentially subarctic, but comparatively mild because of moderating
influence of the North Atlantic Current, Baltic Sea, and more than 60,000 lakes

Russian Federation
ranges from steppes in the south through humid continental in much of European
Russia; subarctic in Siberia to tundra climate in the polar north; winters vary from cool
along Black Sea coast to frigid in Siberia; summers vary from warm in the steppes to
cool along Arctic coast

Federal Republic of Germany

temperate and marine; cool, cloudy, wet winters and summers; occasional warm
foehn wind

French Republic
generally cool winters and mild summers, but mild winters and hot summers along
the Mediterranean; occasional strong, cold, dry, north-to-north westerly wind known
as mistral

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Kingdom of Spain
temperate; clear, hot summers in interior, more moderate and cloudy along coast;
cloudy, cold winters in interior, partly cloudy and cool along coast

Italian Republic
predominantly Mediterranean; Alpine in far north; hot, dry in south

Ukraine
temperate continental; Mediterranean only on the southern Crimean coast;
precipitation disproportionately distributed, highest in west and north, lesser in east
and southeast; winters vary from cool along the Black Sea to cold farther inland;
summers are warm across the greater part of the country, hot in the south

Republic of Poland
temperate with cold, cloudy, moderately severe winters with frequent precipitation;
mild summers with frequent showers and thundershowers

MIDDLE EAST

Republic of Turkey
temperate; hot, dry summers with mild, wet winters; harsher in interior

Syrian Arab Republic

mostly desert; hot, dry, sunny summers (June to August) and mild, rainy winters
(December to February) along coast; cold weather with snow or sleet periodically in
Damascus

Kingdom of Saudi Arabia

harsh, dry desert with great temperature extremes

Republic of Yemen
mostly desert; hot and humid along west coast; temperate in western mountains
affected by seasonal monsoon; extraordinarily hot, dry, harsh desert in east

Islamic Republic of Iran

mostly arid or semiarid, subtropical along Caspian coast

Islamic Republic of Pakistan

mostly hot, dry desert; temperate in northwest; arctic in north

Turkmenistan
subtropical desert

Republic of Uzbekistan
mostly midlatitude desert, long, hot summers, mild winters; semiarid grassland in
east

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Kyrgyz Republic
dry continental to polar in high Tien Shan; subtropical in southwest (Fergana Valley);
temperate in northern foothill zone

ASIA

Russian Federation
ranges from steppes in the south through humid continental in much of European
Russia; subarctic in Siberia to tundra climate in the polar north; winters vary from cool
along Black Sea coast to frigid in Siberia; summers vary from warm in the steppes to
cool along Arctic coast

Republic of Kazakhstan
continental, cold winters and hot summers, arid and semiarid

Mongolia
desert; continental (large daily and seasonal temperature ranges)

Democratic People's Republic of Korea

temperate with rainfall concentrated in summer

Republic of Korea
temperate, with rainfall heavier in summer than winter

Republic of India
varies from tropical monsoon in south to temperate in north

People's Republic of China

extremely diverse; tropical in south to subarctic in north

Republic of Bangladesh
tropical; mild winter (October to March); hot, humid summer (March to June); humid,
warm rainy monsoon (June to October)

Democratic Socialist Republic of Sri Lanka

tropical monsoon; northeast monsoon (December to March); southwest monsoon
(June to October)

Republic of Singapore
tropical; hot, humid, rainy; two distinct monsoon seasons - North eastern monsoon
from December to March and South western monsoon from June to September;
inter-monsoon - frequent afternoon and early evening thunderstorms

Republic of Indonesia
tropical; hot, humid; more moderate in highlands

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Malaysia
tropical; annual southwest (April to October) and northeast (October to February)
monsoons

Republic of Indonesia
tropical; hot, humid; more moderate in highlands

Republic of the Philippines

tropical marine; northeast monsoon (November to April); southwest monsoon (May to
October)

Japan
varies from tropical in south to cool temperate in north

AUSTRALIA

Commonwealth of Australia
generally arid to semiarid; temperate in south and east; tropical in north

OCEANIA

Independent State of Papua New Guinea

tropical; northwest monsoon (December to March), southeast monsoon (May to
October); slight seasonal temperature variation

New Zealand
temperate with sharp regional contrasts

Territory of New Caledonia and Dependencies

tropical; modified by southeast trade winds; hot, humid

Solomon Islands
tropical monsoon; few extremes of temperature and weather

Republic of the Fiji Islands

tropical marine; only slight seasonal temperature variation

Federated States of Micronesia

tropical; heavy year-round rainfall, especially in the eastern islands; located on
southern edge of the typhoon belt with occasionally severe damage

Territory of French Polynesia

tropical, but moderate

Kingdom of Tonga
tropical; modified by trade winds; warm season (December to May), cool season
(May to December)

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Republic of Kiribati
tropical; marine, hot and humid, moderated by trade winds

Some facts about climate

The sun's rays hit the equator at a direct angle between 23°N and 23°S latitude.
Radiation that reaches the atmosphere here is at its most intense.

In all other cases, the rays arrive at an angle to the surface and are less intense. The
closer a place is to the poles, the smaller the angle and therefore the less intense the
radiation.

Our climate system is based on the location of these hot and cold air-mass regions
and the atmospheric circulation created by trade winds and westerlies.

Trade winds north of the equator blow from the northeast. South of the equator, they
blow from the southeast. The trade winds of the two hemispheres meet near the
equator, causing the air to rise. As the rising air cools, clouds and rain develop. The
resulting bands of cloudy and rainy weather near the equator create tropical
conditions.

Westerlies blow from the southwest on the Northern Hemisphere and from the
northwest in the Southern Hemisphere. Westerlies steer storms from west to east
across middle latitudes.

Both westerlies and trade winds blow away from the 30 ° latitude belt. Over large
areas centred at 30 ° latitude, surface winds are light. Air slowly descends to replace
the air that blows away. Any moisture the air contains evaporates in the intense heat.
The tropical deserts, such as the Sahara of Africa and the Sonoran of Mexico, exist
under these regions.

Seasons

The Earth rotates about its axis, which is tilted at 23.5 degrees. This tilt and the sun's
radiation result in the Earth's seasons. The sun emits rays that hit the earth's surface
at different angles. These rays transmit the highest level of energy when they strike
the earth at a right angle (90°). Temperatures in these areas tend to be the hottest
places on earth. Other locations, where the sun's rays hit at lesser angles, tend to be
cooler.

As the Earth rotates on its tilted axis around the sun, different parts of the Earth
receive higher and lower levels of radiant energy. This creates the seasons. Three
major climate groups show the dominance of special combinations of air-mass
source regions.

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Climate Group 1
Low-latitude Climates: These climates are controlled by equatorial a tropical air
masses.

Tropical Moist Climates Rainforest

Rainfall is heavy in all months. The total annual rainfall is often more than 250 cm.
(100 in.). There are seasonal differences in monthly rainfall but temperatures of 27°C
(80°F) mostly stay the same. Humidity is between 77 and 88%.
High surface heat and humidity cause cumulus clouds to form early in the afternoons
almost every day.
The climate on eastern sides of continents is influenced by maritime tropical air
masses. These air masses flow out from the moist western sides of oceanic high-
pressure cells, and bring lots of summer rainfall. The summers are warm and very
humid. It also rains a lot in the winter
 Average temperature: 18°C (°F)
 Annual Precipitation: 262 cm. (103 in.)
 Latitude Range: 10°S to 25°N
 Global Position: Amazon Basin; Congo Basin of equatorial Africa; East Indies,
from Sumatra to New Guinea.

Wet-Dry Tropical Climates Savannah

A seasonal change occurs between wet tropical air masses and dry tropical air
masses. As a result, there is a very wet season and a very dry season. Trade winds
dominate during the dry season. It gets a little cooler during this dry season but will
become very hot just before the wet season.

Figure 1.3 showing Tropical Moist Climates Rainforest

 Temperature Range: 16°C
 Annual Precipitation: 0.25 cm. (0.1 in). All months less than 0.25 cm. (0.1 in)
 Latitude Range: 15° to 25°N and S

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 Global Range: India, Indochina, West Africa, southern Africa, South America
and the north coast of Australia

Figure 1.4 showing Wet-Dry Tropical Climates Savannah

Dry Tropical Climate Desert biome

These desert climates are found in low-latitude deserts approximately between 18° to
28° in both hemispheres. These latitude belts are centred on the tropics of Cancer
and Capricorn, which lie just north and south of the equator. They coincide with the
edge of the equatorial subtropical high pressure belt and trade winds. Winds are
light, which allows for the evaporation of moisture in the intense heat. They generally
flow downward so the area is seldom penetrated by air masses that produce rain.
This makes for a very dry heat. The dry arid desert is a true desert climate, and
covers 12% of the Earth's land surface.

Figure 1.5 showing Dry Tropical Climate Desert Biome

 Temperature Range: 16°C

 Annual Precipitation: 0.25 cm (0.1 in). All months less than 0.25 cm (0.1 in)
 Latitude Range: 15°- 25°N and S.
 Global Range: south-western United States and northern Mexico; Argentina;
north Africa; south Africa; central part of Australia

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Climate Group 2

Mid-latitude Climates: Climates in this zone are affected by two different air-masses.
The tropical air-masses are moving towards the poles and the polar air-masses are
moving towards the equator. These two air masses are in constant conflict. Either air
mass may dominate the area, but neither has exclusive control.

Dry Mid-latitude Climates Steppe

Characterized by grasslands, this is a semiarid climate. It can be found between the

desert climate (BW) and more humid climates of the A, C, and D groups. If it received
less rain, the steppe would be classified as an arid desert. With more rain, it would be
classified as a tall grass prairie.

This dry climate exists in the interior regions of the North American and Eurasian
continents. Moist ocean air masses are blocked by mountain ranges to the west and
south. These mountain ranges also trap polar air in winter, making winters very cold.
Summers are warm to hot.
 Temperature Range: 24°C (43°F).
 Annual Precipitation: less than 10 cm (4 in) in the driest regions to 50 cm (20
in) in the moister steppes.
 Latitude Range: 35°- 55°N.
 Global Range: Western North America (Great Basin, Columbia Plateau, Great
Plains); Eurasian interior, from steppes of eastern Europe to the Gobi Desert
and North China.

Figure 1.6 showing Dry Mid-latitude Climates Steppe

Mediterranean Climate Chaparral biome
This is a wet-winter, dry-summer climate. Extremely dry summers are caused by the
sinking air of the subtropical highs and may last for up to five months.
Plants have adapted to the extreme difference in rainfall and temperature between
winter and summer seasons. Sclerophyll plants range in formations from forests, to
woodland, and scrub. Eucalyptus forests cover most of the chaparral biome in
Australia.
Fires occur frequently in Mediterranean climate zones.
 Temperature Range: 7°C (12°F)
 Annual Precipitation: 42 cm (17 in).

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 Latitude Range: 30°- 50°N and S

 Global Position: central and southern California; coastal zones bordering the
Mediterranean Sea; coastal Western Australia and South Australia; Chilean
coast; Cape Town region of South Africa

Figure 1.7 showing Mediterranean Climate Chaparral Biome

Dry Mid-latitude Climates Grasslands biome

These dry climates are limited to the interiors of North America and Eurasia. Ocean
air masses are blocked by mountain ranges to the west and south. This allows polar
air masses to dominate in winter months. In the summer, a local continental air mass
is dominant. A small amount of rain falls during this season.

Annual temperatures range widely. Summers are warm to hot, but winters are cold.

 Temperature Range: 31°C (56°F)

 Annual Precipitation: 81 cm. (32 in.).
 Latitude Range: 30°- 55°N and S
 Global Position: western North America (Great Basin, Columbia Plateau,
Great Plains); Eurasian interior

Figure 1.8 showing Dry Mid-latitude Climates Grasslands Biome

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Moist Continental Climate Deciduous Forest biome

This climate is in the polar front zone - the battleground of polar and tropical air
masses. Seasonal changes between summer and winter are very large. Daily
temperatures also change often. Abundant precipitation falls throughout the year. It is
increased in the summer season by invading tropical air masses. Cold winters are
caused by polar and arctic masses moving south.

 Temperature Range: 31°C (56°F)

 Average Annual Precipitation: 81 cm (32 in).
 Latitude Range: 30°- 55°N and S (Europe: 45°- 60°N).
 Global Position: eastern parts of the United States and southern Canada;
northern China; Korea; Japan; central and eastern Europe.

Figure 1.9 showing Moist Continental Climate Deciduous Forest Biome

Climate Group 3
High-latitude climates: Polar and arctic air masses dominate these regions. Canada
and Siberia are two air-mass sources which fall into this group. A southern
hemisphere counterpart to these continental centers does not exist. Air masses of
arctic origin meet polar continental air masses along the 60th and 70th parallels.
Boreal forest Climate taiga biome
This is a continental climate with long, very cold winters, and short, cool summers.
This climate is found in the polar air mass region. Very cold air masses from the
arctic often move in. The temperature range is larger than any other climate.
Precipitation increases during summer months, although annual precipitation is still
small.
Much of the boreal forest climate is considered humid. However, large areas in
western Canada and Siberia receive very little precipitation and fall into the subhumid
or semiarid climate type.
 Temperature Range: 41°C (74°F), lows; -25°C (-14°F), highs; 16°C (60°F).
 Average Annual Precipitation: 31 cm (12 in).

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 Latitude Range: 50°- 70°N and S.

 Global Position: central and western Alaska; Canada, from the Yukon Territory
to Labrador; Eurasia, from northern Europe across all of Siberia to the Pacific
Ocean

Figure 1.10 showing Boreal forest Climate Taiga Biome

Tundra Climate Tundra biome

The tundra climate is found along arctic coastal areas. Polar and arctic air masses
dominate the tundra climate. The winter season is long and severe. A short, mild
season exists, but not a true summer season. Moderating ocean winds keep the
temperatures from being as severe as interior regions.
 Temperature Range: -22°C to 6°C (-10°F to 41°F).
 Average Annual Precipitation: 20 cm (8 in).
 Latitude Range: 60°- 75°N.
 Global Position: arctic zone of North America; Hudson Bay region; Greenland
coast; northern Siberia bordering the Arctic Ocean.

Figure 1.11 showing Tundra Climate Tundra Biome

Highland Climate Alpine Biome

Highland climates are cool to cold, found in mountains and high plateaus. Climates
change rapidly on mountains, becoming colder the higher the altitude gets. The
climate of a highland area is closely related to the climate of the surrounding biome.
The highlands have same seasons and wet and dry periods as the biome they are in.

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Mountain climates are very important to mid-latitude biomes. They work as water
storage areas. Snow is kept back until spring and summer when it is released slowly
as water through melting.
 Temperature Range: -18°C to 10°C (-2°F to 50°F)
 Average Annual Precipitation: 23 cm (9 in.)
 Latitude Range: found all over the world
 Global Position: Rocky Mountain Range in North America, the Andean
mountain range in South America, the Alps in Europe, Mt. Kilimanjaro in
Africa, the Himalayas in Tibet, Mt. Fuji in Japan.

Figure 1.12 showing Highland Climate Alpine Biome

1.4 CLIMATIC ZONES OF PAPUA NEW GUINEA

The main variable of Papua New Guinea's climate is not temperature or air pressure,
but rainfall. Papua New Guineas climate can be described as tropical climate, with
the coastal plains averaging a temperature of 28°C, the inland and mountain areas
averaging 26°C, and the higher mountain regions, 23°C. The area's relative humidity
is quite high, and ranges between 70 and 90 percent.

The extreme variations in rainfall are linked with the monsoons. Generally speaking,
there is a dry season (June to September), and a rainy season (December to March).
Western and northern parts of Papua New Guinea experience the most precipitation,
since the north- and westward-moving monsoon clouds are heavy with moisture by
the time they reach these more distant regions.

The habitat and distribution of plants and animals in the country is not by chance and
a number of factors combine to control this distribution are explained in the following
chapter.

Generally the climatic zones of Papua New Guinea are categorized as follows:

1 Lowlands ranges from 0 – 600m above sea level (a.s.l). It is further divided
into four zones.

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(a) Lowland dry sub-humid e.g. National Capital District (Port Moresby) with
natural vegetation of savanna grassland with kunai grasses (Imperata spp.)
and main trees are Eucalyptus spp.

(b) Lowland sub humid e.g. Western Province (Daru) with natural vegetation of
Monsoon forest dominated by Bombax, Erythrina, Pterygota, palms etc.

(c) Lowland humid e.g. East Sepik (Ambunti), East New Britain (Rabaul) and
Madang with natural vegetation of lowland rainforest

(d) Lowland per-humidity e.g. Morobe (Lae) also with natural vegetation of
lowland rainforest
2 Pre-montane ranges from 600 – 1500m above sea level (a.s.l). It is divided
into further three zones.

a) Pre-montane sub-humid e.g. Bulolo with natural vegetation of pre-montane

grassland with Imperata and Theineda.

b) Pre-montane humid e.g. Lumi, Panguna, Garaina with natural vegetation of

pre-montane forest with Araucariz or mixed forest.

c) Pre-montane pre-humid e.g. Kutubu also with natural vegetation of pre-

montane forest with Araucariz or mixed forest

3 Lower montane ranges from 1500 – 1800m above sea level (a.s.l). It is
divided into further three zones.

a) Lower-montane sun-humid e.g. Goroka

b) Lower-montane humid e.g. Mt. Hagen

c) Lower-montane pre-humid e.g. Jimi

4 Mid- Montane ranges from 1800 – 2700m above sea level (a.s.l). It is further
classed into Mid-montane humid e.g. Tambul (Western Highlands) and pre-
montane pre-humid with mid-montane forest Nathofagus

5 Upper-montane (2700 – 3200m) a.s.l with upper-montane forest with cloud or

moss forest e.g. Mt. Whelm in the Simbu Province.

Climate and Biomes

The differences in these biomes can be traced to differences in climate and where
they are located in relation to the Equator. Global temperatures vary with the angle at
which the sun's rays strike the different parts of the Earth's curved surface. Because
the sun's rays hit the Earth at different angles at different latitudes, not all places on
Earth receive the same amount of sunlight. These differences in the amount of
sunlight cause differences in temperature.

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Biomes located in the high latitudes (60° to 90°) farthest from the Equator (taiga and
tundra) receive the least amount of sunlight and have lower temperatures. Biomes
located at middle latitudes (30° to 60°) between the poles and the Equator
(temperate deciduous forest, temperate grasslands and cold deserts) receive more
sunlight and have moderate temperatures. At the low latitudes (0° to 23°) of the
Tropics the sun's rays strike the Earth most directly. As a result, the biomes located
there (tropical rain forest, tropical grassland and the warm desert) receive the most
sunlight and have the highest temperatures.

Another notable difference among biomes is the amount of precipitation. In the low
latitudes, the air is warm, due to the amount of direct sunlight, and moist, due to
evaporation from warm sea waters and ocean currents. Storms produce so much rain
that the tropical rain forest receives 200 plus inches per year, while the tundra,
located at a higher latitude, is much colder and dryer, and receives just ten inches.

Soil moisture, soil nutrients, and length of growing season also affect what kinds of
plants can grow in a place and what kinds of organisms the biome can sustain. Along
with temperature and precipitation, these are factors that distinguish one biome from
another and influence the dominant types of vegetation and animals that have
adapted to a biome's unique characteristics.

As a result, different biomes have different kinds and quantities of plants and animals,
which scientists refer to as biodiversity. Biomes with greater kinds or quantities of
plants and animals are said to have high biodiversity. Biomes like the temperate
deciduous forest and grasslands have better conditions for plant growth. Ideal
conditions for biodiversity include moderate to abundant precipitation, sunlight,
warmth, nutrient-rich soil, and a long growing season. Because of the greater warmth,
sunlight and precipitation in the low latitudes, the tropical rain forest has greater
numbers and kinds of plants and animals than any other biome.

Low Biodiversity Biomes

Biomes with low precipitation, extreme temperatures, short growing seasons, and
poor soil have low biodiversity--fewer kinds or amounts of plants and animals-due to
less than ideal growing conditions and harsh, extreme environments. Because desert
biomes are inhospitable to most life, plant growth is slow and animal life is limited.
Plants there are short and the burrowing, nocturnal animals are small in size. Of the
three forest biomes, the taiga has the lowest biodiversity. Cold year-round with harsh
winters, the taiga has low animal diversity.

In the tundra, the growing season lasts a mere six to eight weeks, and plants there
are few and small. Trees can't grow due to permafrost, where only the top few inches
of the ground thaw during the short summer. The grasslands biomes are considered
to have more biodiversity, but only grasses, wildflowers, and a few trees have
adapted to its strong winds, seasonal droughts, and annual fires. While biomes with
low biodiversity tend to be inhospitable to most life, the biome with the highest
biodiversity is inhospitable to most human settlement.

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A particular biome and its biodiversity have both potential and limitations for human
settlement and meeting human needs. Many of the important issues facing modern
society are the consequences of the way humans, past and present, use and change
biomes and how that has affected the biodiversity in them.

Ecosystems

An ecosystem is a living community of plant and animals sharing an environment with

non-living elements such as climate and soil. Ecosystems exist on a variety of scales.
An example of a small scale ecosystem (micro) is a pond. A medium scale
ecosystem (messo) could be a forest. The tropical rainforest is an example of a very
large ecosystem (biome). The boundaries are not fixed in any objective way,
although sometimes they seem obvious, as with the shoreline of a small pond.

Sunlight is the main source of energy. This allows plants to convert energy by
photosynthesis. This provides food for some animals, birds and fish. These are called
Herbivores. The other animals eat the animals that have eaten the plants. These are
Carnivores. This process is called the Food Chain.

The world has many different ecosystems. Each one has its own climate, soil, plants
and animals. Very few ecosystems are natural today because of human activities.
More ecosystems are under threat than ever before and need protecting.

Components of an Ecosystem

You are already familiar with the parts of an ecosystem. You have learned about
climate and soils. From this course and from general knowledge, you have a basic
understanding of the diversity of plants and animals, and how plants and animals and
microbes obtain water, nutrients, and food. We can clarify the parts of an ecosystem
by listing them under the headings "abiotic" and "biotic".

ABIOTIC COMPONENTS BIOTIC COMPONENTS

Sunlight Primary producers
Temperature Herbivores
Precipitation Carnivores
Water or moisture Omnivores
Soil or water chemistry (e.g., P, NH4+) Detritivores
Edaphic factors Decomposers

All of these vary over space/time.

By and large, this set of environmental factors is important almost everywhere, in all
ecosystems.

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Abiotic Characteristics

An ecosystem is composed of biotic communities that are structured by biological

interactions and abiotic environmental factors. Some of the important abiotic
environmental factors of aquatic ecosystems include substrate type, water depth,
nutrient levels, temperature, salinity, and flow. It is often difficult to determine the
relative importance of these factors without rather large experiments. There may be
complicated feedback loops. For example, sediment may determine the presence of
aquatic plants, but aquatic plants may also trap sediment, and add to the sediment
through peat.

The amount of dissolved oxygen in a water body is frequently the key substance in
determining the extent and kinds of organic life in the water body. Fish need
dissolved oxygen to survive, although their tolerance to low oxygen varies among
species; in extreme cases of low oxygen some fish even resort to air gulping. Plants
often have to produce aerenchyma, while the shape and size of leaves may also be
altered. Conversely, oxygen is fatal to many kinds of anaerobic bacteria.

Nutrient levels are important in controlling the abundance of many species of algae.
The relative abundance of nitrogen and phosphorus can affect determine which
species of algae come to dominate. Algae are a very important source of food for
aquatic life, but at the same time, if they become over-abundant, they can cause
declines in fish when they decay. Similar over-abundance of algae in coastal
environments such as the Gulf of Mexico produces, upon decay, a hypoxic region of
water known as a dead zone.

The salinity of the water body is also a determining factor in the kinds of species
found in the water body. Organisms in marine ecosystems tolerate salinity, while
many freshwater organisms are intolerant of salt. The degree of salinity in an estuary
or delta may is an important control upon the type of wetland (fresh, intermediate, or
brackish), and the associated animal species. Dams built upstream may reduce
spring flooding, and reduce sediment accretion, and may therefore lead to saltwater
intrusion in coastal wetlands.

Freshwater used for irrigation purposes often absorb levels of salt that are harmful to
freshwater organisms.

Biotic Characteristics

The biotic characteristics are mainly determined by the organisms that occur. For
example, wetland plants may produce dense canopies that cover large areas of
sediment or snails or geese may graze the vegetation leaving large mud flats.
Aquatic environments have relatively low oxygen levels, forcing adaptation by the
organisms found there. For example, many wetland plants must produce
aerenchyma to carry oxygen to roots. Other biotic characteristics are more subtle and
difficult to measure, such as the relative importance of competition, mutualism or
predation. There are a growing number of cases where predation by coastal

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herbivores including snails, geese and mammals appears to be a dominant biotic

factor.

Biotic Factors of Deserts

A desert is a region that obtains incredibly less amount of precipitation or it can be

also defined as an area where more water is lost by evaporation than water received
by precipitation. Most deserts receive an average precipitation of less than 400 mm
annually.

Figure 1.13 Typical Desert; Source: Answers.com

Biotic, meaning of or related to life, are living factors. Plants, animals, fungi, protist
and bacteria are all biotic or living factors.

Biotic factors are, in entirety, anything that affects a living organism that is itself alive.
Such things include animals which consume the organism in question, or the food
that the organism consumes. As opposed to abiotic factors (non-living components of
an organism's environment, such as temperature, light, moisture, air currents, etc.),
biotic factors are the living components of an organisms environment, such as
predators and prey.

For example, if one were to examine a desert ecosystem for biotic and abiotic factors,
one would observe things like the extreme temperatures of the day and night, the fast
winds, the heavy amount of sunlight, and scarcity of water as abiotic, or NON-living
factors in the environment. One would observe that for a quail living in the desert,
living elements like the quail's prey (insects, seeds, etc.) and predators (coyotes,
sparrow hawk, gold eagles, etc.) make up the biotic factors of the quail's environment.

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Desert Plants

Figure 1.14 Desert plants and wildflowers

Source: Fotolia.com

The drought-tolerant plants in the desert include wildflowers, cactus and succulents,
trees, shrubs, grasses, creosote shrubs, riverside cottonwoods and willows. With
minimal water, desert plants, wildflowers, trees and shrubs utilize the abundant
energy of the desert sun to produce more plant life, which serves to fuel the desert
animals and insects.

Desert Mammals
Desert mammals such as bears, bobcats, coyotes, kit foxes, mule deer, raccoons,
rabbits, gophers and squirrels stay cool in the peak desert heat by hiding out in trees
or digging burrows underground.

Mountain lions and bobcats are the elusive carnivores of the desert, hunting deer,
rabbits, birds, snakes and rodents primarily at night. Coyotes, kit foxes and raccoons
are omnivores that survive in the desert by eating cacti, frogs, toads, fish, rabbits,
squirrels and anything else they can scavenge.

Figure1.15 Eastern Coyote (Canis latrans) Coyotes stay cool in desert dens.
Source: Fotolia.com

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Mule deer, rabbits and gophers are herbivores that eat roots, tubers, grasses and
prickly pear.

Desert Birds and Fish

The desert is home to a variety of birds, such as hawks, owls, ostriches,

woodpeckers, cactus wrens and turkey vultures (also known as buzzards).

Desert hawks and owls are carnivores that hunt small mammals, insects and other
birds primarily at night, while turkey vultures are carnivores that feed on the dead
carcasses of other animals. Ostriches are omnivores that feed on plants, insects,
small vertebrates and invertebrates. Woodpeckers and cactus wrens are omnivores
that eat ants, beetles and other insects, as well as plants and tree bark.

Desert fish live in the warm pools that are remnants of ancient lakes. The desert pup
fish is a low-desert stream fish that feeds on algae and often dies off when the pools
dry up during the hottest months. The Sonoran Desert has more than 100 species of
freshwater fish. These fish live in what little freestanding water remains from rivers
that existed a century ago. Fish such as the loach minnow live in shallow riffles of
water only 6 inches deep over gravel beds, feeding almost exclusively on fly larvae.
Lower-elevation desert lands still maintain large populations of native fish, including
the top minnow, long squawfish, Yaqui chub, desert suckers, razorback sucker and
the bonytail chub.

Figure 1.16 Hawks survive by hunting smaller animals. Source: Fotolia.com

Desert Reptiles and Amphibians

The heat-loving, thick-skinned reptiles and amphibians of the desert include

rattlesnakes, lizards, toads and tortoises. Rattlesnakes eat lizards, rodents and small
mammals such as rabbits. Desert toads, such as the Sonoran Desert toad, feed on
insects, spiders and small mice. Desert lizards, such as the Texas horned lizard, eat
vegetation, ants, grasshoppers, insects and small animals. Desert tortoises are
herbivores, although occasionally they eat carrion and insects.

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Figure 1.17 Tortoises survive in the desert eating by desert plants.

Source: Fotolia.com

Desert Insects and Spiders

Insects and spiders that reside in the desert include bees, ants, butterflies, wasps,
mosquitoes and black widow spiders. Bees and butterflies feed on available plant
nectar. Wasps and black widow spiders feed on insects and other spiders, while ants
eat whatever they can scavenge.

Figure 1.18 Desert bees feed on plant nectar.

Source: Fotolia.com

Desert Biome

Desert refers to the regions of the Earth that are characterized by less than 250 mm
of annual rainfall, and, in most cases, an evaporation rate that exceeds precipitation,
and a high average temperature. Because of a lack of moisture in the soil and low
humidity in the atmosphere, most of the sunlight penetrates to the ground. Daytime
temperatures can reach 550C. At night the desert floor radiates heat back to the
atmosphere, and the temperature can drop to near freezing. Deserts are caused by a
combination of climate patterns, geological features, and human impact.

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Some of the deserts are: Gobi in China, Sahara in North Africa, and the Arabian and
Iranian deserts in the Middle East and the Great Victoria and Great Sandy deserts of
Australia. In sandy deserts such as the Sahara and parts of the North American
desert, sand dunes are typical features. Sand dunes are caused by winds literally
sandblast rocks into unusual shapes.

Abiotic Factors of Deserts

Rainfall

A desert receives less than 400mm of rain per year. The rainfall is often very irregular.
It may rain for several years and then a deluge of rain comes in just a few days.

Temperature

The mean daily temperature is approximately 200C but ranges from 400C by the
afternoon and fall through the night to 00C by dawn. The great fluctuations in the
temperature are caused by two main factors:

(i) Lack of cloud cover and low humidity allows the full power of solar radiation to
strike the earth during daylight. At night this lack of cloud cover allows the heat
of the day to be rapidly lost back into the space. Clouds act like a blanket
providing shade in the day and keeping animals warm at night.

(ii) Lack of vegetation. Bare rocks and sand heat up fast under the desert sun in
turn heat the air above. (in contrast, the thick vegetation, of a jungle absorbs
the sun‘s heat and warms up slowly).

The deserts in the world are divided into three types.

1 Subtropical deserts - they are the hottest deserts with dry terrain and rapid
evaporation rate.

2 Cool coastal deserts - the average temperature in these deserts is much

cooler because of cold offshore oceanic currents.

3 Cold winter deserts - they are striking with harsh temperature differences
ranging from 38°C in summers to -12°C in winters.

Apart from these the Polar Regions are also measured as deserts because virtually
all the moisture in these parts is accumulated in the form of ice.

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Figure 1.19 Showing the Deserts of the world

Source: Image by USGS; geology.com
Desert Ecology

In ecology, desert ecology is the sum of the interactions between both biotic and
abiotic processes in arid regions, and it includes the interactions of plant, animal, and
bacterial populations in a desert habitat, ecosystem, and community. Some of the
abiotic factors also include latitude and longitude, soil, and climate. Each of these
factors has caused adaptations to the particular environment of the region. The biotic
processes include animals and plants and the way they interact. Although deserts
have severe climates, some plants still manage to grow. In hot deserts plants are
called xerophytic meaning they are able to survive long dry periods. They may close
their pores in daytime; they store water in their stems and leaves. Some of these
plants include popcorn flower, barrel cactus and Saguaro cactus.

Deserts are most notable for their dry climates resulting from rain-blocking mountain
ranges and remoteness from oceanic moisture. Deserts occupy one-fifth of the
Earth's land surface and occur in two belts: between 15° and 35° latitude in both the
southern and northern hemispheres. These bands are associated with the high solar
intensities that all areas in the tropics receive, and being too far from the equator to
receive rain from the Intertropical Convergence Zone.

Deserts support diverse communities of plant and animals that have evolved
resistance to and methods of circumventing the extreme temperatures and arid
conditions. Desert ecology is characterized by dry, alkaline soils, low net production
and opportunistic feeding patterns by herbivores and carnivores. Lichens and blue-
green algae are significant primary producers in the desert. The detrital food chain is
less important in desert ecology than in the ecology of other regions.

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DESERT SIZE LOCATION FACTS

SUBTROPICAL DESERTS
Egypt, Algeria, Eritrea,
Chad, Libya,
The world's largest hot desert. The desert
9,400,000 Mauritania, Mali,
Sahara climate is very extreme with scorching
km2 Morocco, Sudan, Niger,
days and frigid nights.
Tunisia, Djibouti &
Western Sahara
930,000 Namibia, Botswana &
Kalahari It's a huge semi-arid sandy savannah.
km2 South Africa.
Eastern Libya,
1,100,000 This desert is mostly sandy or stony
Libyan 2 northwestern Sudan &
km plain.
southwestern Egypt.
400,000 It's an arid region with virtually no rainfall
Nubian northeastern Sudan
km2 and oases.
northeast Ethiopia, It's known as the "Cruelest Place on
150,000
Danakil south Eritrea and Earth" the desert is known for its extreme
km2
Djibouti heat and in-hospitability atmosphere.
Saudi Arabia, United The largest sand desert in the world. The
650,000
Rub al Khali Arab Emirates, Oman desert is the most oil-rich site in the
km2
and Yemen. world.
500,000 Iraq, Jordan, Syria and It's also known as the Syro-Arabian. The
Syrian
km2 Saudi Arabia. desert is very rocky and flat.
103,600 It's known as the great arc of reddish
An Nafud Saudi Arabia
km2 sand desert in central Saudi Arabia.
2 With frequent sandstorms the desert is known
Ad Dahna 650,000 km Saudi Arabia
for its sudden violent winds.
2 Largely a barren region of shifting sand
Thar 200,000 km India, Pakistan
dunes, scrub flora and a rural economy.
2
Great Victoria 424,400 km Australia It's the largest desert in Australia.
2
Great Sandy 284,993 km Australia It's the second largest desert in Australia
2 It's a large area of dry, red sandy plain and
Simpson 176,500 km Australia
dunes
2 It is the home of Aboriginal Indigenous
Gibson 155,000 km Australia
Australians, Red Kangaroos and Emu.
2 The desert has basins, plains, mountain
Sonoran 311,000 km United States, Mexico
ridges & is home to the Saguaro cactus.
Although the desert is sparsely populated,
2
Mojave 124,000 km United States several cities can be found here, including the
largest 'Las Vegas'.
2
Sechura 188,735 km Peru Desert composed of equatorial dry forests.

COLD WINTER DESERTS

2
Great Basin 492,000 km United States It's the largest United States desert.

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2 It is the largest desert in Argentina and is the

Patagonian 670,000 km Argentina and Chile
7th largest desert in the world.
Karakum / 2 As the name says 'black sand', the area has
350,000 km Turkmenistan
Garagum significant oil and natural gas deposits.
Kazakhstan,
Kyzyl Kum / 2 Important natural-gas deposits are found in
298,000 km Turkmenistan &
Qizilqum this red sand desert.
Uzbekistan
2 People's Republic of The desert has very little water making it is
Taklamakan 337,000 km
China hazardous to cross.
It is the largest cold winter desert and is made
1,300,000 People's Republic of
Gobi 2 up of diverse geographic regions based on
km China and Mongolia
difference in climate and topography.
Scant rainfall makes Leh/Ladakh a high-
2
Leh / Ladakh 86,904 km India altitude desert with extremely scarce
vegetation.

COOL COASTAL DESERTS

It is the driest desert in the world. The land is

2 Chile, Peru, Bolivia,
Atacama 140,000 km often compared with the land on the planet
Argentina
Mars.
Most of the precipitation is from fog from the
2 Angola, Namibia and
Namib 81,000 km Atlantic Ocean. Unusual species of plants
South Africa.
and animals are found only in this desert.

1.5 PLANT ADAPTATIONS

Plants have adaptations to help them survive (live and grow) in different areas.
Adaptations are special features that allow a plant or animal to live in a particular
place or habitat. These adaptations might make it very difficult for the plant to survive
in a different place. This explains why certain plants are found in one area, but not in
another. For example, you wouldn't see a cactus living in the Arctic. Nor would you
see lots of really tall trees living in grasslands.

Desert plants have had to develop different ways of capturing water in order to
survive in their habitat. These changes are called adaptation. Most arid desert lands
support life that is frequently abundant and well adapted to the scarcity of water and
the daytime heat. Desert plants have evolved ways of conserving and efficiently
using the water available to them.

Desert plants usually have small leaves. These conserves water by reducing surface
area from which transpiration can take place. Other plants drop their leaves during
the dry period. The process of photosynthesis (by which sunlight is converted to
energy usually conducted primarily in leaves) is taken over by the stems in the desert.

A common adaptation is the development of ways to store water in the roots, stems,
leaves or fruit. Plants that store water in this way are called succulents, one of which
is the cactus. Thorns and spines (which are modified leaves) as in cactus plants;

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serve to guard the water from animal invaders. These plants take in and store and
store carbon dioxide only in the night; during the day their stomata or pores close up
to prevent evaporation. Desert plants growing on saline soils may concentrate salt in
their sap and then secrete the salt through their leaves.

Figure 1.20 Showing the Desert Marigold Baileya multiradiata

Source: Arizona-Sonora Desert Museum

Some flowering plants are ephemeral (they live for a few days utmost). Their seeds
lie dormant in the soil, sometimes for years, until a soaking rain enables them to
germinate and quickly bloom.

Some Woody desert plants have developed very long roots that go deep into the
ground to reach underground water. Others have developed spreading root systems
lying just below the surface and stretching widely. This gives the plant many tiny
roots that capture water from occasional rains and are able to take up surface
moisture quickly from heavy dew.

Another desert adaptation is seen in the leaves. Desert plants limit water loss through
their leaf surface by the size, sheen, or texture of their leaves. Small or spiny leaves
limit the surface area exposed to the drying heat. Glossy leaves reflect the sun's rays,
reducing leaf temperatures and evaporation rates. Waxy leaves prevent moisture
from escaping. Some plants only open their leaf pores at night when it is cool and
water loss from leaves is low.

Figure 1.21 Showing the

Engellman prickly pear
cactus Opuntia
engelmannii.
Source: Arizona-Sonora
Desert Museum

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The desert is very dry and often hot. Annual rainfall averages less than 10 inches per
year, and that rain often comes all at the same time. The rest of the year is very dry.
There is a lot of direct sunlight shining on the plants. The soil is often sandy or rocky
and unable to hold much water. Winds are often strong, and dry out plants. Plants
are exposed to extreme temperatures and drought conditions. Plants must cope with
extensive water loss.

 Some plants, called succulents, store water in their stems or leaves.

 Some plants have no leaves or small seasonal leaves that only grow after it
rains. The lack of leaves helps reduce water loss during photosynthesis.
Leafless plants conduct photosynthesis in their green stems.
 Long root systems spread out wide or go deep into the ground to absorb water.
 Some plants have a short life cycle, germinating in response to rain, growing,
flowering, and dying within one year. These plants can evade drought.
 Leaves with hair help shade the plant, reducing water loss. Other plants have
leaves that turn throughout the day to expose a minimum surface area to the
heat.
 Spines to discourage animals from eating plants for water
 Waxy coating on stems and leaves help reduce water loss.
 Flowers that open at night lure pollinators who are more likely to be active
during the cooler night.
 Slower growing requires less energy. The plants do not have to make as much
food and therefore do not lose as much water.

This cactus displays several This cactus displays light- This plant has a waxy
desert adaptations: it has colored hair that helps coating on its leaves.
spines rather than leaves and it shade the plant.
stores water in its stem.

Figure 1.22 plants displaying desert adaptations.

The temperate grasslands, also called prairie, feature hot summers and cold winters.
Rainfall is uncertain and drought is common. The temperate grasslands usually
receive about 10 to 30 inches of precipitation per year. The soil is extremely rich in
organic material due to the fact that the above-ground portions of grasses die off

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annually, enriching the soil. The area is well-suited to agriculture, and few original
prairies survive today.

 During a fire, while above-ground portions of grasses may perish, the root
portions survive to sprout again
 Some prairie trees have thick bark to resist fire
 Prairie shrubs readily re-sprout after fire
 Roots of prairie grasses extend deep into the ground to absorb as much
moisture as they can
 Extensive root systems prevent grazing animals from pulling roots out of the
ground
 Prairie grasses have narrow leaves which lose less water than broad leaves
 Grasses grow from near their base, not from tip, thus are not permanently
damaged from grazing animals or fire
 Many grasses take advantage of exposed, windy conditions and are wind
pollinated
 Soft stems enable prairie grasses to bend in the wind

Soft stems enable prairie grasses to bend Many grasses are wind pollinated and are well-
in the wind. Narrow leaves minimize water suited to the exposed, windy conditions of the
loss. grasslands.

Figure 1.23 plants displaying wind pollination

The tropical rainforest is hot and it rains a lot, about 80 to 180 inches per year. This
abundance of water can cause problems such as promoting the growth of bacteria
and fungi which could be harmful to plants. Heavy rainfall also increases the risk of
flooding, soil erosion, and rapid leaching of nutrients from the soil (leaching occurs
when the minerals and organic nutrients of the soil are "washed" out of the soil by
rainfall as the water soaks into the ground). Plants grow rapidly and quickly use up
any organic material left from decomposing plants and animals. This results in a soil
that is poor. The tropical rainforest is very thick, and not much sunlight is able to
penetrate to the forest floor. However, the plants at the top of the rainforest canopy
must be able to survive 12 hours of intense sunlight every day of the year. There is a
great amount of diversity in plant species in the tropical rainforest.

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 drip tips and waxy surfaces allow water to run off, to discourage growth of
bacteria and fungi
 buttresses and prop and stilt roots help hold up plants in the shallow soil
 some plants climb on others to reach the sunlight
 some plants grow on other plants to reach the sunlight
 flowers on the forest floor are designed to lure animal pollinators since there is
relatively no wind on the forest floor to aid in pollination
 smooth bark and smooth or waxy flowers speed the run off of water
 plants have shallow roots to help capture nutrients from the top level of soil.
 many bromeliads are epiphytes (plants that live on other plants); instead of
collecting water with roots they collect rainwater into a central reservoir from
which they absorb the water through hairs on their leaves
 epiphytic orchids have aerial roots that cling to the host plant, absorb minerals,
and absorb water from the atmosphere

Drip-tips on leaves help shed Prop roots help support plants Some plants collect rainwater
excess water. in the shallow soil. into a central reservoir.

Figure 1.24 Plant survival

The temperate rain forest features minimal seasonal fluctuation of temperature: the
winters are mild and the summers cool. The temperate rain forest receives a lot of
precipitation, about 80 to 152 inches per year. Condensation from coastal fogs also
adds to the dampness. The soil is poor in nutrients. Large evergreen trees, some
reaching 300 feet in height, are the dominant plant species.
 Epiphytes such as mosses and ferns grow atop other plants to reach light.
 Cool temperatures lead to slow decomposition but seedlings grow on "nurse
logs" to take advantage of the nutrients from the decomposing fallen logs.
 Trees can grow very tall due to amount of precipitation.

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Epiphytes live on other plants to reach the Trees can grow very tall in this very moist
sunlight. environment.

Figure 1.25 Displaying plants for light

There are four distinct seasons in the temperate deciduous forest: spring, summer,
autumn, and winter. The temperature varies from hot in the summer to below freezing
in the winter. Rain is plentiful, about 30 to 50 inches per year. The temperate
deciduous forest is made up of layers of plants; the number of layers depends upon
factors such as climate, soil, and the age of the forest. The tallest trees make up the
forest canopy which can be 100 feet or more above the ground. Beneath the canopy,
the understory contains smaller trees and young trees. These understory trees are
more shade tolerant than canopy trees. Below the understory is a shrub layer.
Carpeting the forest floor is the herb layer made up of wildflowers, mosses, and ferns.
Fallen leaves, twigs, and dried plants cover the ground, decompose, and help add
nutrients to the topsoil.

 Wildflowers grow on forest floor early in the spring before trees leaf-out and
shade the forest floor.
 Many trees are deciduous (they drop their leaves in the autumn, and grow new
ones in spring). Most deciduous trees have thin, broad, light-weight leaves that
can capture a lot of sunlight to make a lot of food for the tree in warm weather;
when the weather gets cooler, the broad leaves cause too much water loss
and can be weighed down by too much snow, so the tree drops its leaves.
New ones will grow in the spring.
 Trees have thick bark to protect against cold winters.

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Broad leaves can capture a Many trees have thick bark to In the autumn, deciduous
lot of sunlight for a tree. protect against the cold winters in trees drop their leaves to
the temperate deciduous forest. minimize water loss.

Figure 1.26 Survival of plants in temperate deciduous forest

Also known as boreal forests, the taiga is dominated by conifers (cone-bearing
plants), most of which are evergreen (bear leaves throughout the year). The taiga
has cold winters and warm summers. Some parts of the taiga have a permanently
frozen sub-layer of soil called permafrost. Drainage is poor due to the permafrost or
due to layers of rock just below the soil surface, and together with the ground carved
out by receding glaciers, lead to the development of lakes, swamps, and bogs. The
taiga receives about 20 inches of precipitation per year. The soil is acidic and
mineral-poor.

It is covered by a deep layer of partially-decomposed conifer needles.

 many trees are evergreen so that plants can photosynthesize right away when
temperatures rise
 many trees have needle-like leaves which shape loses less water and sheds
snow more easily than broad leaves
 waxy coating on needles prevent evaporation
 needles are dark in color allowing more solar heat to be absorbed
 many trees have branches that droop downward to help shed excess snow to
keep the branches from breaking

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Needle-like leaves help reduce The shape of many conifer

water loss and aids in the trees helps shed heavy snow
shedding of snow. to save branches from
breaking.

Figure 1.27 Displaying plants types

The tundra is cold year-round—it has short cool summers and long, severe winters.
The tundra has a permanently frozen sub-layer of soil called permafrost. Drainage is
poor due to the permafrost and because of the cold, evaporation is slow. The tundra
receives little precipitation, about 4 to 10 inches per year, and what it does receive is
usually in the form of snow or ice. It has long days during the growing season,
sometimes with 24 hours of daylight, and long nights during the winter. There is little
diversity of species. Plant life is dominated by mosses, grasses, and sedges.

 Tundra plants are small (usually less than 12 inches tall) and low-growing due
to lack of nutrients, because being close to the ground helps keep the plants
from freezing, and because the roots cannot penetrate the permafrost.
 Plants are dark in color—some are even red—this helps them absorb solar
heat.
 Some plants are covered with hair which helps keep them warm.
 Some plants grow in clumps to protect one another from the wind and cold.
 Some plants have dish-like flowers that follow the sun, focusing more solar
heat on the center of the flower, helping the plant stay warm.

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These tundra plants are low-growing. This plant grows in a clump to help
conserve heat.

Figure 1.28 Displaying tundra plants

Plant Adaptations in Water

Adaptations in Water
 Underwater leaves and stems are flexible to move with water currents
 Some plants have air spaces in their stems to help hold the plant up in the
water
 Submerged plants lack strong water transport system (in stems); instead water,
nutrients, and dissolved gases are absorbed through the leaves directly from
the water.
 Roots and root hairs reduced or absent; roots only needed for anchorage, not
for absorption of nutrients and water.
 Some plants have leaves that float atop the water, exposing themselves to the
sunlight and some plants produce seeds that can float.

In floating plants, chlorophyll is Aquatic plants must be flexible to

restricted to the upper surface. withstand the pressures of moving
water.

Figure 1.29 Displaying plant adaptation in water

 In floating plants chlorophyll is restricted to upper surface of leaves (part that

the sunlight will hit) and the upper surface is waxy to repel water.

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1.6 ANIMAL ADAPTATION

Deserts are home to many reptiles, insects, birds, and small mammals. Animals in the
desert must survive in a hostile environment. Intense heat, searing sun, and lack of
water are just a few of the challenges facing desert animals. The two main
adaptations that desert animals must make are how to deal with lack of water and
how to deal with extremes in temperature.
Animals that live in the hot desert have many adaptations. Some animals never drink,
but get their water from seeds (some can contain up to 50% water) and plants. Many
animals are nocturnal, sleeping during the hot day and only coming out at night to eat
and hunt. Some animals rarely spend any time above ground. Spade-foot toads
spend nine months of every year underground. Few large animals have adapted to
desert life because their size makes it difficult to find shelter from the heat and they
are not able to store water.
In order to survive, desert animals have developed a number of ways of adapting to
their habitat. The most common adaptation in behaviour is staying in the shade of
plants or rocks or by burrowing underground in the heat of the day. Many desert
animals are nocturnal: they stay inactive in shelter during the day and hunt at night
when it is cool.
Some animals get all the moisture they need from the insects, plants and seeds they
eat, and do not need to drink water. Most pass little moisture out of their bodies. They
do not have sweat glands and pass only small amounts of concentrated urine. Fat
increases body heat, so some desert animals have concentrated the body's fat in one
place, such as a hump or tail, rather than having it all through the body.
Some animals develop unique ways of surviving. The Thorny Devil, a lizard that lives
in Australian desert areas, has a body that channels raindrops directly into its mouth
when rain falls. The water-holding frog spends most of the year under the ground in
Australian desert areas, and develops a sort of cocoon that enables them to store
water to keep them going through the dry times.
Australia's bilby and kowari, the African gerbil, the Oryx and the kangaroo mice of
North America are just a few examples of small mammals that live in the desert.
Among the desert animals, the few amphibian species are capable of long term
dormancy or aestivate during dry periods. When the rain comes, they mature rapidly,
mate, and lay eggs.
Many birds and rodents reproduce only during or following periods of rain that
stimulate the growth of vegetation.

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Figure 1.30 Showing Australia’s Bilby

Some desert rodents, such as the North American Kangaroo mice and the African
gerbil, feed on dry seeds; their metabolic processes are extremely efficient at
conserving and recycling water, and their urine is highly concentrated.
A number of desert mammals (animals) and reptiles are nocturnal, remaining in cool
underground burrows or in the shade by the day. Some desert reptiles, such as the
horned toad, can control their metabolic heat production by varying their rate of
heartbeat and rate of body metabolism.
Some mammals, among them the desert Oryx, vary their body temperatures, storing
heat by day and releasing it at night.
Camels are one of the few large mammals to survive in the desert, and have many
special adaptations to help them.

Figure 1.31 Showing a camel in the desert

Plant and animal bodies are made up of a number of complex biological processes.
These processes can take place within a narrow range of temperatures. If the range
is exceeded the organism dies. The problem with the desert regions is that
temperatures reach extreme limits. Adding to the problem of extreme temperature is
the scarcity of water in the desert. Water is the major constituents of the living bodies.
To survive such harsh conditions, desert animals have developed certain features
that have enabled them to survive in the desert.

Adaptations that the desert animals have undergone are for the following purposes:

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To Avoid Heat

Most of the desert animals avoid being out in the sun during the hottest part of the
day. Many desert mammals, reptiles and amphibians live in burrows to escape the
intense desert heat. Rodents also plug the entrance of their burrows to keep the hot
and dry desert winds out. Most of the animals of the desert either come out during
the early morning or in the evening. Some of them like snakes, foxes and most
rodents are nocturnal. They sleep during the daytime in their burrows or dens and
hunt only during the night when the temperatures are low. Certain animals like the
Round-tailed Ground Squirrel restore to estivation when they slow down their
metabolism to conserve water and energy when the days become very hot.

To Dissipate Heat

Due to constant exposure to high temperatures, desert animals need to maintain their
body temperatures at an optimum level so that the various processes that are
important for their survival can be carried on. For this reason, some of them have
developed long body parts that provide greater body surface to dissipate heat. For
example, jackrabbits have large ears that are supplied with a large number of blood
vessels from which excess heat can be easily lost. It is a known fact that light colours
are better absorbers of heat than dark colours. Most desert animals are pale in colour.
This prevents their bodies from absorbing more heat from the Sun. However, turkeys
and black vultures are dark in colour and hence they absorb considerable amount of
heat during the day. To prevent their bodies from getting overheated, they have
evolved the process of urohydrosis. In this process, they urinate on their legs that
have numerous blood vessels. As the urine evaporates it absorbs the heat from the
blood in the blood vessels of the legs.

To Absorb Water

In deserts where water is scarce, plants like cactus are a main source of water.
These succulent plants have developed their own ways of storing water to help them
tide through the dry days of the desert. Certain insects also depend upon nectar from
flowers and sap from stems to get water. Kangaroo rats are known to be able to
manufacture water by some metabolic process from the digestion of dry seeds. Many
rodents of the desert have extra tubules in their kidneys that help them to extract
most of the water from their urine and return it to the bloodstream. They also filter the
moisture out of their exhaled breath through specialized organs in their nasal cavities.

To Preserve Water

Animals like the Gila Monster are known to store water in the fatty tissues in their tails
and other parts of the body. Also, the hump of the camel has fatty tissue. When this
fatty tissue is metabolized, it produces both energy as well as water. Desert animals
like reptiles have minimized loss of water by excreting waste in the form of an
insoluble white compound uric acid. This adaptation ensures very little wastage of
water. Most of the scavengers and the predators have evolved ways of extracting
water from the food that they eat.

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The following are just few examples of the amazing adaptations that the desert
animals have evolved to survive the extreme conditions of the desert. Without these
adaptations of the animals, the deserts would have been absolutely lifeless with no
living creature or thing around.

Addax

With its heavy head and shoulders and slender hindquarters, the addax is a clumsy-
looking animal. Its coloration varies widely between individuals, but there is always a
mat of dark-brown hair on the forehead, and both sexes have thin, spiral horns.
Addaxes are typical desert-dwellers, with their large, wide-spreading hoofs, adapted
to walking on soft sand, and they never drink, obtaining all the moisture they need
from their food, which includes succulents. Their nomadic habits are closely linked to
the sporadic rain for the addax appears to have a special ability to find patches of
desert vegetation that suddenly sprout after a downpour. They are normally found in
herds of 20 to 200. The female produces one young after a gestation of 8 1/2 months.

Class: Mammalia: Mammals Diet: Plants

Order: Artiodactyla: Even-toed Ungulates

Size: body:1.3 m (4 1/4 ft), tail: 25 - 35 cm (9 3/4 - 13 3/4 in)

Family: Bovidae: Bovids Conservation Status: Critically endangered

Scientific Name: Addax nasomaculatus Habitat: sandy and stony desert

Range: Africa: E. Mauritania, W. Mali; patchy distribution in Algeria, Chad, Niger and Sudan

Cactus Wren
The largest North American wren, the cactus wren has a distinctive white stripe over
each eye and a longer-than-usual tail, which it does not normally cock up. Cactus
wrens frequent areas with thorny shrubs, cacti and trees and forage mostly on the
ground around vegetation for insects, such as beetles, ants, wasps, and
grasshoppers, and occasionally lizards or small frogs. Some cactus fruit and berries
and seeds are also eaten. The wrens can run swiftly but usually fly if traveling any

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distance. Nests are made for roosting in at night and for shelter in bad weather. The
breeding season begins in March or April, and there may be two or three broods. The
nest is a bulky, domed structure, made of plant fibers, twigs and dead leaves, with a
tube-like side entrance that can be up to 15 cm (6 in) long; it is lined with fur or
feathers. The nest is situated on a prickly cholla cactus or amid the sharp leaves of a
yucca or other thorny bush. From 3 to 7 eggs, usually 4 to 5, are laid and then
incubated by the female for about 16 days.

Class: Aves: Birds Diet: Insects

Order: Passeriformes: Perching birds

Size: body:18 - 22 cm (7 - 8 1/2 in)

Family: Troglodytidae: Wrens Conservation Status: Non-threatened

Scientific Name: Campylorhynchus brunneicapillus Habitat: desert, arid scrubland

Range: Southwestern U.S.A. to central Mexico

Desert Lark

The plumage of the desert lark perfectly matches the color of the desert soil and is
the best example of soil camouflage in birds. The very dark subspecies, A. d. annae,
blends with the black larval sand of central Arabia, while the pale race, A. d.
isabellina, does not stray from areas of white sand.

The nest is usually built up against a rock or tuft of grass and is reinforced on the
windward side by small decorative pebbles. In the harsh desert interior, 3 eggs are
laid, while 4 or 5 may be produced at the desert edge.

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Class: Aves: Birds Diet: Seeds

Order: Passeriformes: Perching birds

Size: body:15 cm (6 in)

Family: Alaudidae: Larks Conservation Status: Non-threatened

Scientific Name: Ammomanes deserti Habitat: stony, hilly desert, dry wooded slopes

Range: Africa: Sahara; Middle East, through Iran to Afghanistan

Dingo

The dingoes are descended from domesticated dogs introduced by the aboriginal
human inhabitants of Australia many thousands of years ago. In anatomy and
behavior, dingoes are indistinguishable from domestic dogs, but the two have
interbred for so long that there are now few pure dingoes. They live in family groups
but may gather into bigger packs to hunt large prey. Originally they fed on kangaroos,
but when white settlers started to kill off the kangaroos, dingoes took to feeding on
introduced sheep and rabbits. A litter of 4 or 5 young is born in a burrow or rock
crevice after a gestation of about 9 weeks. The young are suckled for 2 months and
stay with their parents for at least a year.

Class: Mammalia: Mammals Diet: Large mammals

Order: Carnivora: Carnivores

Size: body: about 1.5 m (5 ft), tail: about 35 cm (13 3/4 in)

Family: Canidae: Dogs, Foxes Conservation Status: Non-threatened

Scientific Name: Canis dingo Habitat: sandy desert to wet and dry sclerophyll forest

Range: Australia

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Fat Sand Rat

The fat sand rat overcomes the problem of the unpredictability of desert food supplies
by laying down a thick layer of fat all over its body when food is abundant. It then
lives off this fat when food is short. Active day and night, this gerbil darts about
collecting seeds and other vegetation which it carries back to its burrow. In early
spring, a brood chamber is made and lined with finely shredded vegetation, and the
first litter of the year is born in March. There are usually 3 to 5 young in a litter, and
the breeding season continues until late summer.

Class: Mammalia: Mammals Diet: Seeds, vegetation

Order: Rodentia: Rodents

Size: body:14 - 18.5 cm (5 1/2 - 7 1/4 in), tail: 12 - 15 cm (4 3/4 - 6 in)

Family: Gerbillinae: Gerbils Conservation Status: Non-threatened

Scientific Name: Psammomys obesus Habitat: sandy desert

Range: Algeria, east to Saudi Arabia

Fennec Fox
The smallest of the foxes, the fennec fox is identified by its relatively huge ears. It
shelters in burrows it digs in the sand and is generally active at night, when it preys
on small rodents, birds, insects and lizards. Fennec foxes are sociable animals which
mate for life; each pair or family has its own territory. A litter of 2 to 5 young is born in
spring after a gestation of 50 to 51 days.

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Class: Mammalia: Mammals Diet: Small mammals

Order: Carnivora: Carnivores

Size: body: 37 - 41 cm (14 1/2 - 16 in), tail: 19 - 21 cm (7 1/2 - 8 1/4 in)

Family: Canidae: Dogs, Foxes Conservation Status: Data deficient

Scientific Name: Vulpes zerda Habitat: desert, semidesert

Range: North Africa: Morocco to Egypt, south to Northern Niger, Sudan; east to Sinai
Peninsula and Kuwait

Gila Monster

This formidable, heavy-bodied lizard has a short, usually stout tail, in which it can
store fat for use in periods of food shortage. It is gaudily patterned and has brightly
colored beadlike scales on its back. The gila lives on the ground and shelters under
rocks or in a burrow, which it digs itself or takes over from another animal. It is
primarily nocturnal but may emerge during the day in spring. The two members of the
gila monster family are the only venomous lizards. The venom is produced in glands
in the lower jaw and enters the mouth via grooved teeth at the front of the lower jaw;
it flows into the victim as the lizard chews. The gila also eats the eggs of birds and
reptiles. Gila monsters mate in the summer, and the female lays 3 to 5 eggs some
time later, in the autumn or winter.

Class: Reptilia: Reptiles Diet: Small mammals, eggs

Order: Squamata: Lizards and Snakes

Size: body:45 - 61 cm (17 3/4 - 24 in)

Family: Helodermatidae: Gila Monster Conservation Status: Vulnerable

Scientific Name: Heloderma Habitat: arid and semiarid areas with some
suspectum vegetation

Range: Southwestern U.S.A.: Southern Utah, Arizona to New Mexico; Mexico

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Great Jerboa

The great jerboa and 8 of the 9 other species in the genus Allactaga have five toes
on each hind foot. Great jerboas feed on seeds and insects, which they find by
combing through the sand with the long slender claws on their front feet. They are
nocturnal, spending the day in burrows; they also hibernate in burrows. One or two
litters are produced each year.

Class: Mammalia: Mammals Diet: Seeds, insects

Order: Rodentia: Rodents

Size: body:19 - 15 cm (3 1/2 - 6 in), tail: 16 - 22 cm (6 1/4 - 8 1/2 in)

Family: Dipodidae: Jerboas Conservation Status: Non-threatened

Scientific Name: Allactaga major Habitat: Allactaga major

Range: Russia: Ukraine, east to China

Great Mouse-Tailed Bat

Colonies of thousands of mouse-tailed bats occupy roosts in large ruined buildings,

often palaces and temples. They feed exclusively on insects, and in those areas
where a cool season temporarily depletes the food supply, the bats may enter a deep
sleep resembling torpor. Prior to this, they lay down thick layers of fat which may
weigh as much as the bats themselves, and with this they survive for many weeks
with neither food nor water. As they sleep, the accumulated fat is used up, and by the
time the cold season is passed, nothing of it remains. Mouse-tailed bats mate at the
beginning of spring, and the female produces a single offspring after a gestation of
about 4 months. The young bat is weaned at 8 weeks but does not attain sexual
maturity until its second year.

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Class: Mammalia: Mammals Diet: Flying insects

Order: Chiroptera: Bats

Size: body:6-8 cm (2 1/4-3 in), wingspan: 17-25 cm (6 3/4 -10 in), tail: 6-8 cm (2 1/4-3 in)

Family: Rhinopomatidae: Mouse-tailed Bats Conservation Status: Non-threatened

Scientific Name: Rhinopoma microphyllum Habitat: treeless arid land

Range: Middle and Near East

Lappet-faced Vulture

The lappet-faced is a typical Old World vulture with perfect adaptations for a
scavenging life. Its powerful hooked bill cuts easily into carrion, and its bare head and
neck save lengthy feather-cleaning after plunging deep into a messy carcass. The
immense broad wings, with widely spaced primary feathers, are ideal for soaring and
gliding for long periods, using few winged beats. No real mating display has been
observed. A huge stick nest is made at the top of a tree or on a crag, and the female
lays 1 egg.

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Class: Aves: Birds Diet: Carrion

Order: Falconiformes: Birds of Prey

Size: body:100 - 115 cm (39 - 45 in)

Family: Accipitridae: Vultures, Eagles, Hawks Conservation Status: Non-threatened

Scientific Name: Torgos tracheliotus Habitat: bush, desert

Range: Northern, southern, and eastern Africa

Sidewinder

A small agile snake, the sidewinder has a distinctive hornlike projection over each
eye. It is chiefly nocturnal and takes refuge in the burrow of another animal or under
a bush during the day. At night it emerges to hunt its prey, mainly small rodents, such
as pocket mice and kangaroo rats, and lizards. A desert inhabitant, this snake moves
with a sideways motion, known as side winding, thought to be the most efficient
mode of movement for a snake on sand. It throws its body into lateral waves, only
two short sections of it touching the ground. All of the snake's weight, therefore, is
pushing against the ground at these points, and this provides the leverage to move it
sideways. As it travels, the snake leaves a trail of parallel J-shaped markings. An
ideal form of movement in open, sparsely vegetated country, side winding has the
advantage of reducing contact between the snake's body and the hot sand.
Sidewinders mate in April or May, and the female gives birth to 5 to 18 live young
about 3 months later.

Class: Reptilia: Reptiles Diet: Small mammals

Order: Squamata: Lizards and Snakes
Size: body: 43 - 82 cm ( 17 - 32 1/4 in)
Family: Crotalidae: Pit Vipers Conservation Status: Non-threatened
Scientific Name: Crotalus cerastes Habitat: desert, rocky hillsides
Range: Southwestern U.S.A.: Southern California, Nevada and Utah, south to Mexico

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Thorny Devil

The grotesque thorny devil is the only species in its genus and one of the strangest
of lizards. Its body bristles with large, conical spines, and it has spines above each
eye and a spiny hump behind its head. The tail, too, is spiny. It is a slow-moving
creature, which forages for its food, mainly ants and termites, on the ground. The
female thorny devil lays 3 to 10 eggs, usually 8, in November or December. The
newly hatched young are tiny, spiny replicas of their parents.

Class: Reptilia: Reptiles Diet: Ants, termites

Order: Squamata: Lizards and Snakes

Size: body:16 cm (6 1/4 in)

Family: Agamidae: Agamid Lizards Conservation Status: Non-threatened

Scientific Name: Moloch horridus Habitat: arid scrub, desert

Range: Australia: Western, North and South, Queensland

1.7 Controls on Ecosystem Function

Now that we have learned a lot of things about how ecosystems are put together and
how materials and energy flow through ecosystems, we can now confidently address
the question of "what controls ecosystem function"? There are two dominant theories
of the control of ecosystems. The first of these theories is called bottom-up control,
which states that it is the nutrient supply to the primary producers that ultimately
controls how ecosystems function. If the nutrient supply is increased, the resulting
increase in production of autotrophs is propagated through the food web and all of
the other trophic levels will respond to the increased availability of food (meaning that
flow of energy and materials will cycle faster).

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The second theory, called top-down control, states that predation and grazing by
higher trophic levels on lower trophic levels ultimately controls ecosystem function.
That is, if you have an increase in predators, that increase will result in fewer grazers,
and that decrease in grazers will result in turn in more primary producers because
fewer of them are being eaten by the grazers. Thus the control of population numbers
and overall productivity "cascades" from the top levels of the food chain down to the
bottom trophic levels.
So, you can now again confidently question, which theory is correct? Well, as is often
the case when there is a clear dichotomy to choose from, the answer lies somewhere
in the middle. There is evidence from many ecosystem studies that both controls are
operating to some degree, but that neither control is complete. For example, the "top-
down" effect is often very strong at trophic levels near to the top predators, but the
control weakens as you move further down the food chain. Similarly, the "bottom-up"
effect of adding nutrients usually stimulates primary production, but the stimulation of
secondary production further up the food chain is less strong or is absent.

Therefore, we find that both of these controls are operating in any system at any time,
and we must understand the relative importance of each control in order to help us to
predict how an ecosystem will behave or change under different circumstances, such
as in the face of a changing climate.

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SUMMARY

Ecosystems consist of life forms existing in a symbiotic relationship with their

environment. Life forms in ecosystems compete with one another to become the
most successful at reproducing and surviving in a given niche, or environment. Two
main components exist in an ecosystem: abiotic and biotic. The abiotic components
of an ecosystem consist of the nonorganic aspects of the environment that determine
what life forms can thrive. Examples of abiotic components are temperature, average
humidity, topography and natural disturbances. Temperature varies by latitude;
locations near the equator are warmer than are locations near the poles or the
temperate zones. Humidity influences the amount of water and moisture in the air
and soil, which, in turn, affect rainfall. Topography is the layout of the land in terms of
elevation.

The biotic components of an ecosystem are the life forms that inhabit it. The life
forms of an ecosystem aid in the transfer and cycle of energy. They are grouped in
terms of the means they use to get energy. Producers such as plants produce their
own energy without consuming other life forms; plants gain their energy from
conducting photosynthesis via sunlight. Consumers exist on the next level of the food
chain. There are three main types of consumers: herbivores, carnivores and
omnivores. Herbivores feed on plants, carnivores get their food by eating other
carnivores or herbivores, and omnivores can digest both plant and animal tissue.

Biotic components and abiotic components of an ecosystem interact with and affect
one another. If the temperature of an area decreases, the life existing there must
adapt to it. Global warming, or the worldwide increase in temperature due to the
greenhouse effect, will speed up the metabolism rates of most organisms. Metabolic
rate increases with temperature because the nutrient molecules in the body are more
likely to contact and react with one another when excited by heat. According to
"Science News," tropical ectothermic -- cold-blooded -- organisms could experience
increased metabolic rates from an increase of as little as 5 degrees Celsius because
their internal temperature is almost entirely dependent on external temperature. To
adapt to these circumstances, cold-blooded life forms could reside in the shade and
not actively search for food during daylight hours when the sun is at its brightest.

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Student Learning Activity 1

1 State at least three different biomes of the world.

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2 Outline the main adaptations that plants in tundra possess in order to survive
the harsh cold and icy environment.
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3 Name the four types of consumers?

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4 Why do forests, deserts, and types of life in each area differ for each other?
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5 List the different types of deserts and their proprieties?

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Student Learning Activity 2

1 Outline the main adaptations that both plants and animals in the desert
possess in order to survive the harsh, hot and dry climate.

1.1 The adaptation for animals

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1.2 The adaptation for plants

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2 What is an ecosystem?
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3 What are the major parts of an ecosystem?

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4 Name the types of deserts and their distinct characteristics.

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5 What are the two main adaptations that desert animals must make?
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6 How do desert animals prevent water from leaving their bodies?

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UNIT 2.0

TROPICAL RAINFOREST

Learning Outcomes

At the end of this unit, you can:

1 explain the composition of tropical rainforest

2 state morphological adaptations of plants in the tropical rainforest

3 describe some of the adaptations used by plants and animals to obtain food

4 explain confidently the structure of rainforest

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INTRODUCTION

In general, rainforests are categorized into two types - the first being the tropical
rainforests (which are restricted to the tropics) while the temperate rainforests (which
are found in the temperate regions of the world). These rainforests - which are
typically characterized by heavy rainfall that they receive, span across the regions of
South America, Central America, Africa, Asia and Australia. Even though the
rainforest biome merely covers 6 percent of the total surface of the Earth, it is home
to half the species of plants and animals found on the planet. While the biotic factors
of the rainforest include living things, i.e. the plants and animals to be precise, the
abiotic factors include precipitation, sunlight, temperature, and other nonliving factors.

The trees in this biome typically grow on to attain a height of 60-100 meters; (though
trees as tall as 150-160 meters are not rare). Being close to the Equator, rainforests
receive sunlight in abundance. However, only 1 percent of this sunlight penetrates
through to the ground. This - in turn, makes it difficult for short plants to grow in this
region. Heavy rain often washes off the top layer of soil, and leaves the soil here
deficient in terms of nutrients. Nutrient deficient soil and lack of sunlight - together,
are responsible for the lack of vegetation at ground level. That being said, there do
exist some species of moss and ferns which have adapted themselves to the
seemingly harsh conditions that prevail here.

These forests receive somewhere around 1750-2000 mm of rainfall every year.

Similarly, the humidity levels of these forests often fluctuate between 77 – 88 percent,
with the cloud cover having an important role to play when it comes to high humidity
levels in the rainforests. Evapo-transpiration is one of the most important climatic
factors in this region, and the fact that it accounts for half of the precipitation in the
rainforest speaks in volumes about it. The temperature in these forests often
fluctuates between 68°F and 93°F, and this contributes to the high humidity levels
and evapo-transpiration that one gets to see here. Around 28 percent of the annual
oxygen turnover on the planet can be attributed to these forests which cover 6
percent of the total surface of the planet.

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2.1 TROPICAL RAINFORESTS

Tropical rainforests have a latitudinal range of 10 degrees and 25 degrees North and
South of the equator.

The altitudes of rainforests range from 0-1000 meters in elevation.

Rainforest now make up about 6% of the Earth's surface. They are typically divided
into four distinct layers. These layers are: the forest floor, the understory (lower
canopy), the upper canopy, and the emergent.

Figure 2.1 showing a typical Tropical Rainforest

Source:"http://www.tropical-rainforest-animals.com

The forest floor (Herb Layer) is almost always covered in shade and hit with very little
sunlight. Every so often, a tree will collapse and there will be a large opening of
sunlight for a few months until new plants quickly cover the gap. Less than 1% of
sunlight over the forest penetrates through the towering trees and onto the dark
forest floor. The topsoil is very thin and poor when it comes to growing plants. The
forest floor is covered with bits of litter, leaves and small animal carcases.
Decomposers like fungi and earthworms quickly break down the litter with help from
the heat and humidity of the air. It is then absorbed into the roots of trees as
minerals.

The understory is made up of small trees usually about 60 feet tall. There is very
dense growth here with thousands of entangled vines and shrubs. Many of the trees
in this layer have extremely large leaves because of the lack of sunlight. Some of
these leaves can grow to be as large as a large beach umbrella. There is little air
movement and in cause, is very, very humid.

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Figure 2.2 showing the four distinct layers of the rainforest

Source:"http://www.tropical-rainforest-animals.com

The canopy consists of a thick, layering branch system of vines and limbs that create
sort of a natural vista. This layer is important for absorbing ultra-violet waves from the
sun and protecting the organisms beneath its leafy maze. It also serves as a natural
shield against rain during the rainy season. This prevents "washouts" or floods on the
forest floor which could be disastrous to the natural food chain.

The emergent layer is the highest layer of the rainforest. It is very common for trees
here to well exceed 180-200 feet in height. This layer obviously receives the most
sunlight and is commonly covered by a thick layer of condensation and mist that
forms into clouds of humid air that drop into the dark, lower layers of the rainforest.

This level is home to 1/3 of all the bird species of the planet. It also holds many other
safe-seeking animals from the predators lurking in the lower layers.
Characterised by the warmth and wet all year round, rainforest is a large biome
located in the earth‘s equatorial zone. Dominant plants including broadleaf evergreen
trees, palms and tree ferns and climbing vines which form dense layered stands,
often exceeding 50m in height.

Although the trees themselves are not evergreen, they retain their leaves throughout
the year because temperature and precipitation are sufficiently high for continuous
growth. These trees develop their own rhythms for flowering, fruiting and leave
shedding. Within and below the canopy there is a diversity of plants and animal
species that exploit the many ecological niches that occur with the rainforest.

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Examples of common animals are Amphibians, bats, insects, colourful birds (big and
small), snakes and monkeys. The ways in which plants and animals in a biome
interact with each other determine their niche in the biome. A niche refers to the
ecological function and habitat of an organism. For example, grazing is a major
function of such animals in the grassland biome.

2.2 ABIOTIC FACTORS OF THE RAINFOREST

Rainforests are home to half the plants and animals found of the planet, and the
abiotic factors of these rainforests play a crucial role in adding to their biodiversity.
Abiotic factors, i.e. the non-living elements such as sunlight and precipitation, play an
important role in determining the biodiversity of a region. For a species of plant or
animal to survive in any region, it has to adapt itself to the abiotic conditions which
exist there.

On one hand, we have rainforests of South America which boast of thousands of

animal species to its credit, and on the other we have the harsh tundra in Antarctica,
wherein spotting a single animal during the winter season is nothing short of a
miracle. This difference in the levels of biodiversity can be attributed to the abiotic
factors of these biomes.

In a broad sense, rainforests are categorized into two types - the tropical rainforests
(which are restricted to the tropics) and temperate rainforests (which are found in the
temperate regions of the world). These forests - which are typically characterized by
heavy rainfall that they receive, span across the regions of South America, Central
America, Africa, Asia and Australia. Even though the rainforest biome merely covers
6 percent of the total surface of the Earth, it is home to half the species of plants and
animals found on the planet. While the biotic factors of the rainforest include living
things, i.e. the plants and animals to be precise, the abiotic factors include
precipitation, sunlight , temperature, and so on.

The trees in this biome typically grow on to attain a height of 60-100 meters; though
trees as tall as 150-160 meters are not rare. Being close to the Equator, rainforests
receive sunlight in abundance. However, only 1 percent of this sunlight penetrates to
the ground. This - in turn, makes it difficult for short plants to grow in this region.
Heavy rain often washes off the top layer of soil, and leaves the soil here deficient in
terms of nutrients. Nutrient deficient soil and lack of sunlight - together, are
responsible for the lack of vegetation at ground level. That being said, there do exist
some species of moss and ferns which have adapted themselves to the seemingly
harsh conditions that prevail here.

These forests receive somewhere around 1750-2000 mm of rainfall every year.

Similarly, the humidity levels of these forests often fluctuate between 77-88 percent,
with the cloud cover having an important role to play when it comes to high humidity
levels in the rainforests. Evapo-transpiration is one of the most important climatic
factors in this region, and the fact that it accounts for half of the precipitation in the
rainforest speaks in volumes about it. The temperature in these forests often
fluctuates between 68°F and 93°F, and this contributes to the high humidity levels

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and evapo-transpiration that one gets to see here. Around 28 percent of the annual
oxygen turnover on the planet can be attributed to these forests which cover 6
percent of the total surface of the planet.

2.3 ABIOTIC FACTORS AFFECT PLANTS AND ANIMALS

Harsh as these conditions may seem, the plants and animals of this region have
adapted themselves very well to them, and that becomes all the more obvious when
you have a look at biodiversity of the rainforest biome. While the trees in the upper
canopy here have short leaves which make sure that the amount of water lost to
evapo-transpiration is minimal, those which make up the understory have large
leaves to make the most of whatever little sunlight they get. The climatic conditions of
the rainforest cause the plant and animal matter here to decay quickly, and as soon
as it decays the same is absorbed by the plants and stored in their roots. As the soil
here lacks essential nutrients, the ability of plants to absorb and store nutrients
comes as a blessing in disguise.

Warm and wet conditions that prevail in these rainforests provide ideal conditions for
the growth of trees. The gigantic height that these trees attain can be attributed to
these very conditions in this biome. Not just the vegetation, but even the animals
found here have altered their way of life in accordance with prevailing conditions. As
the temperatures in this region often fluctuate between 68°F and 93°F, animal
species which inhabit the rainforests don't have to spend much energy in keeping
themselves warm. Instead, they can simply utilize the same energy for other activities
such as hunting and reproduction. The fact that most of the species here channelize
their energy in the process of reproduction explains why the population of species in
this biome is far more as compared to the same in other biomes.

If these rainforests are home to millions of plant and animals species today, it is only
because of the abiotic factors that they boast of. That being said, we also need to
understand the balance which we are talking about here is very delicate, such that it
can easily get disrupted and result in destruction of the biome. The destruction has
already begun with 40 percent of the rainforests in South America falling prey to
deforestation caused by human activities such as logging and agriculture. Losing
these forests is something which we can't really afford to, and the sooner we realize it
the better it is for us.

The rainforest is a key abiotic factor. The soil has little nutrients to give and is mostly
acidic so the trees provide most of the nutrients for other plants which is why they are
so big. The elevation is a key abiotic factor. The trees are so tall that certain plants of
the rainforest get less sunlight and have different organisms living there. The top
layer or canopy has different species living there than at the bottom. Different animals
and plant life live at different elevations in the rainforest.
Abiotic, meaning not alive, are nonliving factors that affect living organisms.
Environmental factors such as habitat (pond, lake, ocean, desert, mountain) or
weather such as temperature, cloud cover, rain, snow, hurricanes, etc. are abiotic
factors.

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The abiotic factors of this rainforest biome are-the amount of water and sunlight,
climate, weather and precipitation. These things affect the trees and animals that live
there. These are very important because without the right amount of water and
sunlight the trees in the rainforest would not be able to grow and would die. These
factors also affect the types of plants and animals that can live in this area. A good
example is that a lot of small bushes and shrubs would not be able to live here
because all the really tall trees would block most of the sunlight causing a lack in
sunlight to the bushes and shrubs below them. This will cause the bushes and shrubs
to die.

2.4 PLANT ADAPTATIONS

The tropical rainforests have billions of species (kinds) of plants and animals, more
than anywhere else on earth. Scientists do not yet know all the species that are to be
found in a tropical rainforest and new ones are still being discovered.

The reason there are so many species is because rainforests are very old, some
almost 100 million years old, which means dinosaurs probably lived in them. About
10,000 years ago the ice caps at the poles spread out in an Ice Age, but the ice didn't
reach the Equator so tropical rainforests survived and their plant and animal species
continued to evolve when other places on earth had to start growing plants all over
again.

In the tropics it is always hot and it rains every day. Tropical rainforests are the
wettest places on earth.

Some canopy trees grow over to over 100 metres high. Many have fruit that provides
food for animals and people. Many rainforest plants are gathered for food or
medicines. This is done without harming the rainforest.

Many 'every day' foods originated in rainforests, including tomatoes, peppers, corn,
rice, coconut, banana, coffee, cocoa, cassava (tapioca), beans and sweet potatoes.

Figure 2.3 Dry coconut

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In order to survive in the hot, wet tropics, plants of the tropical rainforest have had to
develop special features. This is called adaptation.

Because the weather is hot and wet, trees do not need thick bark to slow down
moisture loss and have instead thin, smooth bark. The layers of rainforest are
connected by vines and ferns, and mosses grow on the trees. Liana is a climbing
vine that grows on rainforest trees, climbing into the canopy so its leaves get more
sunlight.

Figure 2.4 Buttress roots

Source: Jupiter images Corporation

The leaves of rainforest trees have adapted to cope with the large amount of rain.
The leaves are big, thick and waxy, and have 'drip tips' to let the rain drain off quickly.

Many large trees have huge ridges called buttresses near the base. They may be 10-
12 metres high where they join into the trunk. They increase the surface area of a
tree so that it can 'breathe in' more carbon dioxide and 'breathe out' more oxygen.
Nutrients in the soil are near the surface, so the big rainforest trees have quite
shallow roots. The buttresses support the trees. Some trees have above-ground
roots called prop or stilt roots which give extra support to the trees. These roots can
grow about 85 cm in a month.

Figure 2.5 Showing samples of epiphytes: Orchid growing on banyan tree

Source: Jupiter images Corporation

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Some tropical rainforest plants are carnivorous, or meat-eating. They have a cavity
filled with either sweet or terrible smelling nectar that attracts insects, especially ants
and flies. Inside, the sides are steep and lined with downward pointing hairs. Insects
enter and lose their footing or are prevented from leaving because of the hairs.
Rafflesia , in Indonesian rainforests, produces the biggest flower in the world.
Thousands of flowering plants grow onto trees so they get sunshine. Their roots are
not in soil, and the plants get their food from air and water. Plants that do this are
called epiphytes (say epp-ee-fights), and include orchids, philodendrons, ferns and
bromeliads.:
The rainforest are distinctive in their variety of plant and animal life and complex
ecosystem structure. Due to the high levels of water and solar energy available, they
are among the most productive ecosystems of the world.

Figure 2.6 Showing components of plant adaptation in the rainforest

1 Bark

In drier, temperate deciduous forests a thick bark helps to limit moisture evaporation
from the tree's trunk. Since this is not a concern in the high humidity of tropical
rainforests, most trees have a thin, smooth bark. The smoothness of the bark may
also make it difficult for other plants to grow on their surface.

2 Lianas

Lianas are climbing woody vines that drape rainforest trees. They have adapted to
life in the rainforest by having their roots in the ground and climbing high into the tree
canopy to reach available sunlight. Many lianas start life in the rainforest canopy and
send roots down to the ground.

3 Drip Tips

The leaves of forest trees have adapted to cope with exceptionally high rainfall. Many
tropical rainforest leaves have a drip tip. It is thought that these drip tips enable rain

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drops to run off quickly. Plants need to shed water to avoid growth of fungus and
bacteria in the warm, wet tropical rainforest.

4 Buttresses

Many large trees have massive ridges near the base that can rise 30 feet high before
blending into the trunk. Why do they form? Buttress roots provide extra stability,
especially since roots of tropical rainforest trees are not typically as deep as those of
trees in temperate zones.

5 Prop and Stilt Roots

Prop and stilt roots help give support and are characteristic of tropical palms growing
in shallow, wet soils. Although the tree grows fairly slowly, these above-ground roots
can grow 28 inches a month.

6 Epiphytes

Epiphytes are plants that live on the surface of other plants, especially the trunk and
branches. They grow on trees to take advantage of the sunlight in the canopy. Most
are orchids, bromeliads, ferns, and Philodendron relatives. Tiny plants called
epiphylls, mostly mosses, liverworts and lichens, live on the surface of leaves.

7 Bromeliads

Bromeliads are found almost exclusively in the Americas. Some grow in the ground,
like pineapple, but most species grow on the branches of trees. Their leaves form a
vase or tank that holds water. Small roots anchor plants to supporting branches, and
their broad leaf bases form a water-holding tank or cup. The tank's capacity ranges
from half a pint to 12 gallons or more. The tanks support a thriving eco-system of
bacteria, protozoa, tiny crustaceans, mosquito and dragonfly larvae, tadpoles, birds,
salamanders and frogs.

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8 Mangroves

On tropical deltas and along ocean edges and river estuaries, trees have adapted to
living in wet, marshy conditions. These trees, called mangroves, have wide-spreading
stilt roots that support the trees in the tidal mud and trap nutritious organic matter.

9 Nepenthes
Pitcher plant vines in the family Nepenthaceae have leaves that form a pitcher,
complete with a lid. Sweet or foul-smelling nectar in the pitcher attracts insects,
especially ants and flies that lose their grip on the slick sides and fall into the liquid.
Downward-pointing hairs inside the pitcher prevent the insects' escape. The insects
are digested by the plants and provide nutrients. Pitcher plants are not epiphytes but
climbers rooted in the soil.

2.5 RAINFOREST ANIMAL ADAPTATIONS

There are billions of species (kinds) of mammals, insects, birds and reptiles found in
tropical rainforests. There are so many that there are many that have not been
named or even identified yet.
About half of all of the world's animal species live in tropical rainforests, in all the
layers of the forest. Different animals are found in different countries.
It is estimated that there are more than 50 million different kinds of insects alone in
tropical rainforests. Almost 50 different species of ants were found on one tree in
Peru.

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Tropical rainforests are almost perfect for animal survival. It is always warm, and
there are no season changes bringing times when there is little food. There is shade
from the heat and shelter from the rain. There is no shortage of food and water.
Because there are so many creatures living in the rainforest, there is a great deal of
competition for food, sunlight and space. Animals have developed special features in
order to survive. This is called adaptation.

Figure 2.7 A tree kangaroo found in tropical rainforests of Papua New Guinea

Some animals became very specialized. This means that they adapted to eating a
specific plant or animal that few others eat. For example, parrots and toucans eat
nuts, and developed big strong beaks to crack open the tough shells of Brazil nuts.
Leafcutter ants climb tall trees and cut small pieces of leaves which they carry back
to their nest. The leaf pieces they carry are about 50 times their weight. The ants
bury the leaf pieces, and the combination of the leaves and the ants' saliva
encourages the growth of a fungus, which is the only food these ants eat.

Figure 2.8 Showing a Leafcutter Ant at work

Sometimes there are relationships between animals and plants that benefit both.
Some trees depend on animals to spread the seeds of their fruit to distant parts of the
forest. Birds and mammals eat the fruits, and travel some distance before the seeds
pass through their digestive systems in another part of the forest.
One problem with specialization is that if one species becomes extinct, the other is in
danger too unless it can adapt in time. One example is that of the dodo and the
calvaria tree. The dodo, a flightless bird of Mauritius, became extinct in 1681.

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Today there are just 13 calvaria trees left on the island, each over 300 years old and
nearly at the end of their life. Scientists realized that the seeds had to pass through a
dodo's digestive system before they could germinate (begin to grow). It seemed that
the tree species would also become extinct, but scientists tried domestic turkeys and
have successfully managed to germinate some seeds.
Many rainforest animals use camouflage to 'disappear' in the rainforest. Stick insects
are perfect examples of this. There are some butterflies whose wings look like leaves.
Camouflage is of course useful for predators too, so that they can catch prey that
hasn't seen them. The Boa Constrictor is an example of a camouflaged predator.

Figure 2.9 Showing a Stick insect

The South American three-toed sloth uses camouflage and amazing slowness to
escape predators. Green algae grow in the sloth's fur, which helps camouflage it in
the forest canopy. Sloths are among the slowest moving animals of all (inside too, as
it takes about a month to digest food). They hang from branches in the canopy, and
are so still that predators such as jaguars don't see them.

Figure 2.10 Showing a three-toed sloth

Some animals are poisonous, and use bright colors to warn predators to leave them
alone. There are several species of brightly colored poison arrow frogs. Native
Central and South American tribes used to wipe the ends of their arrows onto the
frog's skin to make their arrows deadly poisonous.

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2.6 TYPES OF RAINFORESTS

Figure 2.11 Tall trees shelter many plant and animal species in the rainforest.

The tropical rainforest is a wet, warm forest of trees that grow very closely together.
The canopy (tallest tress) in the rainforest can release 200 gallons of water each year
into the atmosphere. The resulting moisture hangs over the forest, keeping the
interior warm and humid. Animals living in the rainforest have had to adapt to these
wet, warm conditions and have had to find niches that allow them to thrive. They do
this by altering species characteristics to fit the tall trees, the constant humidity and
the quiet rainforest floor.
There are two types of rainforests of the world, tropical and temperate. Tropical and
temperate rainforests share certain characteristics; however, the diversity of plants
and animals in the tropical rainforest is greater. For example, most trees flare at the
base. Vegetation is dense, tall and very green. Both types of rainforests are rich in
plant and animal species, although the diversity is greater in the tropical rainforest.

Both of them are very wet. In the tropical rainforest it rains about 400 inches a year.
In the temperate rainforest it rains about 100 inches a year. Both tropical and
temperate rainforests are very moist because the trees trap the moisture in and make
fog. The tropical rainforest is warm and the temperate is cool.

Montane forests are a type of temperate rainforest. Montane forests are found in
mountainous areas and may contain plants such as oaks, rhododendrons, and pines,
which are characteristic of temperate deciduous forests. At higher altitudes,
temperatures are cooler. Even close to the equator, frost and snow can occur.

There are hundreds of broadleaf trees that age to 50-100 years old in the tropical
rainforest. In the temperate rainforest there are also evergreen trees that can be 500-
1000 years old.

The three characteristics of the tropical rainforests are:

1. They are between the Tropic of Cancer and the Tropic of Capricorn.

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2. They receive between 80-400 inches of rain per year.

3. The temperatures range between 70-85 degrees daily.

The three Characteristics of the temperate rainforest are:

1. Located anywhere
2. They receive between 50-140 inches of rain per year.
3. The temperatures range between 50-80 degrees daily.

Sometime the forests between the Tropic of Cancer and the Tropic of Capricorn are
not rainforests. Those forests aren‘t as moist and might drop their leaves in dry
weather.

2.7 STRUCTURE OF A RAINFOREST

The Emergent Layer

This layer describes the umbrella-like upper branches of the very tallest rainforest
trees, which emerge from the main canopy of leaves and branches and often reach
heights of greater than 60m (200ft). The emergent trees can be quite far apart and do
not form a continuous layer like the canopy. Despite extreme weather conditions,
such as intense heat, strong winds and heavy rain, the emergent layer is home to
many forms of life, including butterflies, gliders, eagles, small monkeys, bats, snakes
and insects.

The Canopy Layer

Canopy trees grow to around 30-40m (100-130 ft). These trees‘ branches are packed
very closely together, creating a ‗ceiling‘ of foliage, or canopy, below the emergent
layer. Although branches from several trees may overlap, they never actually touch
each other, which some scientists believe may have evolved to hinder the passage of
infectious disease and parasites. The canopy consists not just of trees, but also of
lianas (climbing vines, such as rattan) and epiphytes, plants that root on tree trunks
and branches, including many species of orchids.

The billions of leaves in the canopy compete for sunlight, resulting in dense foliage
that shades the forest floor from sunlight, as well as protecting it from heavy rains
and possible soil erosion. The leaves act as mini solar panels, using the energy in
sunlight for converting atmospheric carbon dioxide and water into oxygen and simple
sugars, a process called photosynthesis. This exchange of gases means that the
canopy layer has an effect on both local and global climates, removing carbon from
the atmosphere and storing it.

The canopy layer contains a multitude of fruit and seeds, providing an excellent food
source for the many animals that dwell there, including insects, primates, bats and
birds, many of which are unknown to science. For example, a canopy crane set up in

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Australia enabled the identification of over 15,000 new insects in just four years. An
estimated 70-90 percent of rainforest life lives in the canopy layer.

The Understory Layer

From halfway to two thirds down the height of the tallest trees is the understorey
layer, where little sunlight, perhaps only 3% of that reaching the canopy, penetrates.
Because of the lack of light, the understorey is quite sparse. The smaller trees with
thin trunks found in this layer remain at around 20m (66ft) tall, often ―waiting‖
decades for a big tree to die and leave a gap that provides them with the light they
need to grow into the canopy. The conditions of the understorey are quite sheltered
and the dark humid environment is a haven for insects as well as birds, butterflies,
frogs, lizards and snakes and predators such as jaguars and leopards.

The Shrub Layer

This layer, sometimes considered to be part of the understorey layer, lies between
the understorey and the forest floor, at around 8m (25ft) high. A plethora of tree ferns,
ferns and shrubs thrive here and many of these plant species have medicinal
properties.
The Floor Layer

As only around 2% of available sunlight reaches the dark, humid forest floor, this
layer can be relatively free from dense vegetation, with just a few vines and tree
seedlings thriving. Instead, detritus feeders (or detritivores), such as millipedes,
woodlice, dung flies, fungi and a host of micro-organisms consume and decompose
dead plants and animal parts on the forest floor. By breaking down this organic
matter, nutrients are released back into the soil, and can be absorbed by the roots of
the rainforest trees as part of an ongoing nutrient recycling system.

The moist, dark climate of the forest floor provides a habitat for many species,
including, beetles, frogs, lizards, snakes (such as the giant Anaconda), termites,
insects, and many larger animals such as the giant anteater, apes and even
elephants.

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Figure 2.12 Layers of the forest

2.8 PRECIPITATION AND CLIMATE

Both tropical and temperate rainforests are very lush and wet. Rainfall falls regularly
throughout the year. The tropical rainforest receives 80-400 inches of rainfall per year.
It rains a lot in the temperate rainforest too; about 100 inches per year. And even
more moisture comes from the coastal fog that hovers among the trees.
Tropical rainforests are warm and moist; while temperate rainforests are cool.

Tropical Temperate

Temperatures warm cool

Number of tree species many (hundreds) few (10-20)

Types of leaves broadleaf needles

Age of trees 50-100 years 500-1000 years

lots of different kinds including orchids mostly mosses and

Epiphytes
and bromeliads ferns

Decomposition rate rapid slow

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Only a small percentage of the tropical forests are rainforests. To be a tropical

rainforest, forested areas must:
 Lie between the Tropic of Cancer and the Tropic of Capricorn.

Figure 2.13 Location of rainforest in the world

 Receive rainfall regularly throughout the year (80-400 inches per year).
 Remain warm and frost free all year long (mean temperatures are between
70° and 85°F) with very little daily fluctuation.

Consequently, many forested areas in the tropics are not rainforests. Forests that
receive irregular rainfall (monsoons followed by a dry season) are moist deciduous
forests. Trees in these forests may drop their leaves in the dry season.

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SUMMARY

Rainforests are often called the lungs of the planet for their role in absorbing carbon
dioxide, a greenhouse gas, and producing oxygen, upon which all animals depend
for survival. Rainforests also stabilize climate, house incredible amounts of plants
and wildlife, and produce nourishing rainfall all around the planet.

Rainforests:
 help stabilize the world‘s climate;
 provide a home to many plants and animals;
 maintain the water cycle
 protect against flood, drought, and erosion;
 are a source for medicines and foods;
 support tribal people; and
 are an interesting place to visit

Rainforests have an abundance of plants and animals for the following reasons:

 Climate: because rainforests are located in tropical regions, they receive a lot
of sunlight. The sunlight is converted to energy by plants through the process
of photosynthesis. Since there is a lot of sunlight, there is a lot of energy in the
rainforest. This energy is stored in plant vegetation, which is eaten by animals.
The abundance of energy supports an abundance of plant and animal
species.
 Canopy: the canopy structure of the rainforest provides an abundance of
places for plants to grow and animals to live. The canopy offers sources of
food, shelter, and hiding places, providing for interaction between different
species. For example, there are plants in the canopy called bromeliads that
store water in their leaves. Frogs and other animals use these pockets of
water for hunting and laying their eggs.

It is important to note that many species in the rainforest, especially insects and
fungi, have not even been discovered yet by scientists. Every year new species of
mammals, birds, frogs, and reptiles are found in rainforests.
There are four very distinct layers of trees in a tropical rain forest. These layers have
been identified as the emergent, upper canopy, understory, and forest floor.

 Emergent trees are spaced wide apart, and are 100 to 240 feet tall with
umbrella-shaped canopies that grow above the forest. Because emergent
trees are exposed to drying winds, they tend to have small, pointed leaves.
Some species lose their leaves during the brief dry season in monsoon
rainforests. These giant trees have straight, smooth trunks with few branches.
Their root system is very shallow, and to support their size they grow
buttresses that can spread out to a distance of 30 feet.

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 The upper canopy of 60 to 130 foot trees allows light to be easily available at
the top of this layer, but greatly reduced any light below it. Most of the
rainforest's animals live in the upper canopy. There is so much food available
at this level that some animals never go down to the forest floor. The leaves
have "drip spouts" that allows rain to run off. This keeps them dry and
prevents mould and mildew from forming in the humid environment.

 The understory, or lower canopy, consists of 60 foot trees. This layer is made
up of the trunks of canopy trees, shrubs, plants and small trees. There is little
air movement. As a result the humidity is constantly high. This level is in
constant shade.

 The forest floor is usually completely shaded, except where a canopy tree has
fallen and created an opening. Most areas of the forest floor receive so little
light that few bushes or herbs can grow there. As a result, a person can easily
walk through most parts of a tropical rain forest. Less than 1 % of the light that
strikes the top of the forest penetrates to the forest floor. The top soil is very
thin and of poor quality. A lot of litter falls to the ground where it is quickly
broken down by decomposers like termites, earthworms and fungi. The heat
and humidity further help to break down the litter. This organic matter is then
just as quickly absorbed by the trees' shallow roots.

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Student Learning Activity 3

1 List at least three components of an ecosystem.

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2 Name the distinct layers of the rain forest.

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3 List some of the abiotic factors of the rain forest.

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4 List some of the abiotic factors that affect plants and animals.
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5 Refer to the picture of a destructive rainforest and answer the questions that
follow.

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A Explain why deforestation can reduce soil fertility.

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B How can deforestation affect people who live in these areas?

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6 What are the three animal adaptations in the rainforest biome?

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UNIT 3.0

THE SOIL

LEARNING OUTCOMES

At the end of this Unit, the students can:

1 understand that soil is a abiotic factor of ecology

2 explain the different stages of soil formation

3 explain the properties of soil

4 describe with confidence properties of soil composition

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INTRODUCTION

Soil in general is the collection of natural bodies on the earth's surface, in places
modified or even made by man of earthy materials, containing living matter and
supporting or capable of supporting plants out-of-doors. Its upper limit is air or
shallow water. At its margins it grades to deep water or to barren areas of rock or ice.
Its lower limit to the not-soil beneath is perhaps the most difficult to define. Soil
includes the horizons near the surface that differ from the underlying rock material as
a result of interactions, through time, of climate, living organisms, parent materials,
and relief. In the few places where it contains thin cemented horizons that are
impermeable to roots, soil is as deep as the deepest horizon. More commonly soil
grades from at its lower margin to hard rock or to earthy materials virtually devoid of
roots, animals, or marks of other biological activity. The lower limit of soil, therefore,
is normally the lower limit of biological activity, which generally coincides with the
common rooting depth of native perennial plants. Yet in defining mapping units for
detailed soil surveys, lower layers that influence the movement and content of water
and air in the soil or the root zone must also be considered.

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3.1 WHAT IS SOIL?

The definition of soil varies depending on the person(s) considering it. To a civil
engineer planning a construction site, soil is whatever unconsolidated material
happens to be found at the surface. To a miner, soil is just some worthless material
that is in the way and must be removed. To a farmer, soil is the medium that will
nourish and supply water to the crops. Even soil scientists may hold differing
definitions, depending on their area of study.

For our purpose, soil is a mixture of broken rocks and minerals, living organisms, and
decaying organic matter called humus. Humus is dark, soft and rich in nutrients. Soil
also includes air and water.

An important factor influencing the productivity of our planet's various ecosystems is

the nature of their soils. Soils are vital for the existence of many forms of life that
have evolved on our planet. For example, soils provide vascular plants with a
medium for growth and supply these organisms with most of their nutritional
requirements. Further, the nutrient status of ecosystem's soils does not only limit both
plant growth, but also the productivity of consumer type organisms further down the
food chain.

3.2 SOIL FORMATION

A number of conceptual models of soil formation have been postulated over the
years. The two that have been keys in our basic understanding of soils and soil
formation are those of Hans Jenny (1941) and Roy W. Simonson (1959). Jenny
(1941) addressed the question of which environmental factors are responsible for the
soils we have today. Recognizing these factors is extremely useful for field scientists
when looking over a landscape and predicting the soil types that are found upon it.
These factors include the following:

1 Parent Material - What was there before soil formation began? (Possibilities
include mud deposited by a river, sand deposited by ocean, rock that weathers
and breaks down, etc.);
2 Organisms - usually refers to vegetation and microorganisms, but includes the
complete biological community;
3 Climate- on both large and small scales;
4 Relief, or landscape position;
5 Time

3.3 SOIL COMPOSITION

While a nearly infinite variety of substances may be found in soils, they are
categorized into four basic components: minerals, organic matter, air and water. Most
introductory soil textbooks describe the ideal soil (ideal for the growth of most plants)
as being composed of 45% minerals, 25% water, 25% air, and 5% organic matter. In

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reality, these percentages of the four components vary tremendously. Soil air and
water are found in the pore spaces between the solid soil particles.

Figure 3.1: Most soils contain four basic components: mineral particles, water,
air, and organic matter. The values given above are for an average soil.
(Source: PhysicalGeography.net)

Soil itself is very complex. It would be very wrong to think of soils as just a collection
of fine mineral particles. Soil also contains air, water, dead organic matter, and
various types of living organisms. Organic matter can be further sub-divided into
humus, roots, and living organisms. The formation of a soil is influenced by
organisms, climate, topography, parent material, and time.

Organisms in the soil need air and water to survive. Having these essential materials
- air, water, and organic matter - makes it possible for plants, bacteria, fungi and
small animals like earthworms and insects to live in the soil.

3.4 ORGANIC ACTIVITY

A mass of mineral particles alone do not constitute a true soil. True soils are
influenced, modified, and supplemented by living organisms. Plants and animals aid
in the development of a soil through the addition of organic matter. Fungi and
bacteria decompose this organic matter into a semi-soluble chemical substance
known as humus. Larger soil organisms, like earthworms, beetles, and termites,
vertically redistribute this humus within the mineral matter found beneath the surface
of a soil.

Humus is the biochemical substance that makes the upper layers of the soil become
dark. It is coloured dark brown to black. Humus is difficult to see in isolation because
it binds with larger mineral and organic particles. Humus provides soil with a number
of very important benefits:

 It enhances a soil's ability to hold and store moisture.

 It reduces the eluviation of soluble nutrients from the soil profile.

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 It is the primary source of carbon and nitrogen required by plants for their
nutrition.
 It improves soil structure which is necessary for plant growth.

Organic activity is usually profuse in the near surface layers of a soil. For instance,
one cubic centimeter of soil can be the home to more than 1,000,000 bacteria. A
hectare of pasture land in a humid mid-latitude climate can contain more than a
million earthworms and several million insects. Earthworms and insects are
extremely important because of their ability mix and aerate soil. Higher porosity,
because of mixing and aeration, increases the movement of air and water from the
soil surface to deeper layers where roots reside. Increasing air and water availability
to roots has a significant positive effect on plant productivity. Earthworms and insects
also produce most of the humus found in a soil through the incomplete digestion of
organic matter.

All the living things in the soil, plus essential materials that these organisms use to
survive, form the soil ecosystem. Scientists study the soil ecosystem because they
want to understand how organisms relate to one another and to the environment that
surrounds them.

3.5 PHYSICAL PROPERTIES

Soils are a complex three phase system composed of solids, liquids and gases. The
study of the physical behaviour of these phases is called soil physics and includes:

 Density and porosity

 texture
 structure
 colour
 soil water

Although most of these properties are inherited from the soil's parent material with
some effort man can adjust some properties to improve or maintain the soil's fertility.

3.6 SOIL TEXTURE

The texture of a soil refers to the size distribution of the mineral particles found in a
representative sample of soil. Almost any mineral that exists may be found in some
soil, somewhere. The mineral portion of soil is divided into three particle-size classes:
sand, silt, and clay. Sand, silt, and clay are collectively referred to as the fine earth
fraction of soil. They are less than 2mm in diameter. Larger soil particles are referred
to as rock fragments and have their own size classes (pebbles, cobbles, and
boulders). The three particle size classes are defined as follows:

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Particle Name Size Range

Sand 2mm - 0.05mm
Silt 0.05 mm - 0.02mm
Clay Less than 0.02mm

Mineralogically, sand, and silt are just small particles of rock and are largely inert.
The two important differences among them are their relative capacity to hold water
that is available for uptake by plants and their effects on soil drainage.

Clay particles are mineralogically different and are probably the most important type
of mineral particle found in a soil.

Clay minerals form at or near earth's surface, in soil or in water. Most clay belong to a
class of minerals called phyllosilicates. Despite their small size, clay particles have a
very large surface area relative to their volume. This large surface is highly reactive
and has the ability to attract and hold positively charged nutrient ions. These
nutrients are available to plant roots for nutrition. Clay particles are also somewhat
flexible and plastic because of their lattice-like design. This feature allows clay
particles to absorb water and other substances into their structure.

3.7 SOIL ACIDITY

Soil as is made up of tiny particles of rock, plant, and animal matter. Soils support a
number of inorganic and organic chemical reactions. Many of these reactions are
dependent on some particular soil chemical properties. One of the most important
chemical properties influencing reactions in a soil is pH. Soil acidity can be expressed
using the pH scale. The pH scale ranges from 0 to 14 (see figure below). Soils with a
pH above 7 are basic. Soils with a pH below 7 are acidic. A soil with a pH of 7 is
neither acidic nor basic, but is neutral. The pH and water absorption of soil help to
determine which plants will grow well in it. The pH of soil helps to decide which
minerals are available for plants. Most plants grow best in soil with a pH of 6.5.
Erosion is controlled by how well the soil retains water.

The soil is often sandy and rocky with little organic matter and poor fertility due to
leaching. Soils with a relatively large concentration of hydrogen ions tend to be acidic.
Alkaline soils have a relatively low concentration of hydrogen ions.

Soil is a poor conductor of heat so when the surface temperature is 50 0C it can only
be 200C just a few centimetres below the surface. Soil fertility is directly influenced by
pH through the solubility of many nutrients. At a pH lower than 5.5, many nutrients
become very soluble and are readily leached from the soil profile. At high pH,
nutrients become insoluble and plants cannot readily extract them. Maximum soil
fertility occurs in the range 6.0 to 7.2.

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Figure 3.2: The pH scale (Source: PhysicalGeography.net)

The illustration above also describes the pH of some common substances. A value
of 7.0 is considered neutral. Values higher than 7.0 are increasingly alkaline or basic
while values lower than 7.0 are increasingly acidic.

3.8 SOIL COLOR

Soils tend to have distinct variations in colour both horizontally and vertically. The
colouring of soils occurs because of a variety of factors. Soils of the humid tropics are
generally red or yellow because of the oxidation of iron or aluminium, respectively. In
the temperate grasslands, large additions of humus cause soils to be black. The
heavy leaching of iron causes coniferous forest soils to be gray. High water tables in
soils cause the reduction of iron, and these soils tend to have greenish and gray-blue
hues. Organic matter colours the soil black. The combination of iron oxides and
organic content gives many soil types a brown colour. Other colouring materials
sometimes present include white calcium carbonate, black manganese oxides, and
black carbon compounds.

3.9 SOIL PROFILES

As soil develops over time horizons (layers) form and collectively constitute a soil
profile. Most soil profiles cover the earth as two main layers—topsoil and subsoil.

The properties of horizons are used to distinguish between soils and are critical for
determining land-use potential.

Most soils exhibit three main horizons including:

 A horizon-humus-rich topsoil (where most plant roots, earthworms, insects and

micro-organisms are active)
 B horizon-clay-rich subsoil
 C horizon-underlying weathered rock (from which the A and B horizons form).

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Most soils have a distinct profile or sequence of horizontal layers. Generally, these
horizons result from the processes of chemical weathering, eluviation, illuviation, and
organic decomposition. Up to five layers can be present in a typical soil: O, A, B, C,
and R horizons.
The O horizon is the topmost layer of most soils. It is composed mainly of plant litter
at various levels of decomposition and humus.
A horizon is found below the O layer. This layer is composed primarily of mineral
particles and has two characteristics: it is the layer in which humus and other organic
materials are mixed with mineral particles, and it is a zone of translocation from which
eluviation has removed finer particles and soluble substances, both of which may be
deposited at a lower layer. Thus the A horizon is dark in colour and usually light in
texture and porous. The A horizon is commonly differentiated into a darker upper
horizon or organic accumulation, and a lower horizon showing loss of material by
eluviation.
The B horizon is a mineral soil layer which is strongly influenced by illuviation.
Consequently, this layer receives material eluviated from the A horizon. The B
horizon also has a higher bulk density than the A horizon due to its enrichment of
clay particles. The B horizon may be coloured by oxides of iron and aluminium or by
calcium carbonate illuviated from the A horizon.
The C horizon is composed of weathered parent material. The texture of this material
can be quite variable with particles ranging in size from clay to boulders. The C
horizon has also not been significantly influenced by the pedogenic processes,
translocation, and/or organic modification. The final layer in a typical soil profile is
called the R horizon. This soil layer simply consists of unweathered bedrock.

Figure 3.3 Hypothetical soil profile

(Source: PhysicalGeography.net)

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3.10 INFLUENCE ON SOIL QUALITY

Ecosystems can normally cope with most types of disturbance. However, human
disturbance often occurs too quickly for the environment to respond, negatively
affecting the soils and the plants and animals that depend upon them. Soils are living
environments, providing habitat for a host of microorganisms necessary for plant
growth. Impacts on soils, therefore, can affect the entire ecosystem.

Soil quality is based on how well the soil does what we want it to do. More specifically,
soil quality is the capacity of a specific kind of soil to function, within natural or
managed ecosystem boundaries, to sustain plant and animal productivity, maintain or
enhance water and air quality, and support human health and habitation.

Indicators of Soil Quality

Indicator Relationship to Soil Health

SOIL ORGANIC SOM Soil fertility, structure, stability, nutrient

MATTER (SOM) retention: soil erosion.

PHYSICAL Soil structure, depth of Retention and transport of water and nutrients:
soil, Infiltration and bulk habitat for microbes: estimate of crop
density: water holding productivity potential: compaction, plow pan,
capacity water movement: porosity: workability.

CHEMICAL pH: electrical conductivity: Biological and chemical activity thresholds:

extractable N-P-K plant and microbial activity thresholds: plant
available nutrients and potential for N and P
loss.

BIOLOGICAL Microbial biomass C and Microbial catalytic potential and repository for
N: potentially C and N: soil productivity and N supplying
mineralizable N: soil potential: microbial activity measure
respiration.

People have different ideas of what quality soil is.

 For people active in production agriculture - highly productive land, sustaining

or enhancing productivity, maximizing profits, or maintaining the soil resource
for future generations.
 For consumers - plentiful, healthful, and inexpensive food for present and
future generations.
 For naturalists - soil in harmony with the landscape and its surroundings.
 For the environmentalist - soil functioning at its potential in an ecosystem with
respect to maintenance or enhancement of biodiversity, water quality, nutrient
cycling, and biomass production.

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3.11 INHERENT AND DYNAMIC QUALITY OF SOIL

Inherent soil quality is a soil‘s natural ability to function. For example, sandy soils
drain faster than clayey soils. Deep soils will have more room for roots than soils with
bedrock near the surface. These characteristics do not change easily.

Dynamic soil quality is how soil changes depending on how it is managed.

Management choices affect the amount of soil organic matter, soil structure, soil
depth, water and nutrient holding capacity. One goal of soil quality research is to
learn how to manage soil in a way that improves soil function. Soils respond
differently to management depending on the inherent properties of the soil and the
surrounding landscape.

3.12 HUMAN IMPACT

Mankind has changes the world around us every day. Sometimes, our actions can
have unintended consequences on the soil and the critters that live there. Pollution
and the dumping of waste, as well as the loss of agricultural land and other soil
habitats to development, can cause significant changes in the environment. Such
actions can make soils much less hospitable to life and reduce the biodiversity in the
area. Our actions can also have a positive impact on the soil. Restoration and
preservation efforts, such as replanting native plants, changing land use and
preserving wetlands, have reclaimed lost habitats and protected valuable existing
habitats. Many people have begun to support a native plant industry, selecting these
plants rather than non-native species for their landscaping. These native plants offer
natural habitats for many soil creatures. The increasing popularity of organic farming
and organic produce has begun to lessen the impact of pesticides and chemical
fertilizers on the soil. All of these efforts make a difference in keeping and protecting
the soil habitats that soil critters need.

Soil quality may be defined as the capacity of a soil to function for human survival
and for the related bio-geo-cycling. Four basic soil functions contribute to such
ecosystem maintenance:

1 Sustenance of biological activity, diversity, and productivity

2 Storage and cycling of nutrients
3 Water and solute partition and regulation
4 Filtration, buffering, decomposition, immobilization and detoxification of
organic and inorganic materials

These functions apply to any ecosystem that comprises soil as a component,

whether directly or indirectly altered by man. When any of these functions are
hampered, soil quality decreases.

Soil degradation is a major consequence of ecosystem destruction and soil

disturbance. It refers to the decline in soil productivity through adverse changes in
nutrient states, organic matter, structural stability and concentrations of electrolytes
and toxic chemicals.

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Soil degradation incorporates a number of environmental problems, some of which

are interrelated. The extent of soil degradation is influenced by a number of factors,
namely soil characteristics, relief, climate, land use and socio-economic and political
controls. Management of soil degradation represents one of the most challenging
environmental problems existing today. Emphasis needs to be placed on sustainable
rather than exploitative land use.
Listed below are the physical, chemical and the anthropogenic causes of soil
degradation.

A Physical Causes

Climate and soil are important factors in determining the distribution of plants and
animals everywhere on Earth, including your neighborhood. Changes in local
weather affect when seeds will begin to sprout from the soil and when animals will
burrow underground to settle down for the winter months. Therefore, to understand
the soil in your area, it is important to understand the local weather and to monitor
any changes that might occur. Some weather events and forces, like flooding and
erosion, can have dramatic and lasting effects on the soil. Such events can change
the composition of the soil and affect the kinds of soil critters that can live there. In
addition, normal weather conditions, such as rain, can affect the kinds of soil critters
you see on any given day.

Agriculture is the primary source of negative human impact on soils. However, the
urban landscape is not exempt. Urban environments include vast regions of
impervious surfaces which water cannot penetrate. During a severe weather event,
water washes over these impenetrable surfaces, eroding stream banks and
displacing soils. Depending upon the adjacent land use, these soils may contain
toxins which can negatively impact surface water and groundwater resources. Soil
erosion feeds upon itself. As stream banks erode, water flow increases during floods,
causing more soil erosion in the process.

1 Erosion - rate of removal of soil by water/wind exceeds the rate of soil

formation
2 Compaction - compression of a mass of soil into a smaller volume and is
usually expressed in terms of dry bulk density, porosity and resistance to
infiltration Ex. Heavy agricultural machinery
3 Water excess and deficit - either can have a detrimental effect on soil
performance

B Chemical Causes

Even human activity not directly associated with soils can affect these natural
resources. Air pollution releases contaminants such as sulfur dioxide into the
atmosphere. This compound combines with moisture present in the air to create
acidic precipitation. Soils receiving this acid rain become acidic. Microorganisms die
off, impacting the health of the soils. Left unchecked, soils become ecological dead
zones, unable to support neither plant nor animal life.

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1 Acidification- the main causes are long term leaching and microbial respiration.
2 Salinisation- the accumulation of salts in the soil (e.g. irrigation)
3 Sodification- alkalization, the dominance of the soil exchange complex by Na +
ions

C Anthropogenic Causes

We humans change the world around us every day. Sometimes, our actions can
have unintended consequences on the soil and the critters that live there. Pollution
and the dumping of waste, as well as the loss of agricultural land and other soil
habitats to development, can cause significant changes in the environment. Such
actions can make soils much less hospitable to life and reduce the biodiversity in the
area

1 Deforestation
2 Misuse of agricultural land
3 Overgrazing
4 Needle-leaf afforestation
5 Excessive use of inorganic nitrogen fertilizers
6 Poor land drainage
7 Acid Deposition/Acid Rain
8 Improper Irrigation techniques
9 Construction and demolition waste
10 Metalliferous Wastes/Heavy Metals
11 Power generation emissions- Sulfur dioxide, Radionuclides

3.13 KEEPING SOIL HEALTHY

Each of us, humans can do simple things to help keep the soil healthy. Composting
organic waste instead of sending it to the landfill helps to return valuable nutrients to
the soil. Gardening with native plants, organic fertilizers, and limited pesticides helps
to protect your soil. Choosing to buy products from companies that support soil
conservation efforts lets them and their competitors know that soil health is important
to you. What other ways can you think of to help keep the soil around you healthy?

Understanding soil quality means assessing and managing soil so that it functions
optimally now and is not degraded for future use. By monitoring changes in soil
quality, a land manager can determine if a set of practices are sustainable.

Soil quality is an assessment of how well soil performs all of its functions. It cannot be
determined by measuring only crop yield, water quality, or any other single outcome.
The quality of a soil is an assessment of how it performs all of its functions now and
how those functions are being preserved for future use.

Soil quality cannot be measured directly, so we evaluate indicators. Indicators are

measurable properties of soil or plants that provide clues about how well the soil can
function. Indicators can be physical, chemical, and biological characteristics.
Useful indicators:

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 are easy to measure

 measure changes in soil functions
 encompass chemical, biological, and physical properties
 are accessible to many users and applicable to field conditions
 are sensitive to variations in climate and management

Indicators can be assessed by qualitative or quantitative techniques. After

measurements are collected, they can be evaluated by looking for patterns and
comparing results to measurements taken at a different time or field.

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SUMMARY

As soil develops over time horizons (layers) form and collectively constitute a soil
profile. Most soil profiles cover the earth as two main layers—topsoil and subsoil.

The properties of horizons are used to distinguish between soils and are critical for
determining land-use potential.

Most soils exhibit three main horizons including:

 A horizon—humus-rich topsoil (where most plant roots, earthworms, insects and
micro-organisms are active)
 B horizon—clay-rich subsoil
 C horizon—underlying weathered rock (from which the A and B horizons form).

Many soils also have an O horizon which mainly consists of plant litter which has
accumulated on the soil surface.

Soil forms continuously, but slowly, from the gradual break-up of rocks through
physical, chemical and biological processes—known as weathering. The
accumulation of material through the action of water, wind and gravity also
contributes to soil formation.

These processes can be very slow, taking many thousands of years. Five main
interacting factors affect the formation of soil including:

 parent material – minerals forming the basis of soil

 living organisms – influencing soil formation
 climate – affecting the rate of weathering and organic decomposition
 topography – grade of slope affecting drainage, erosion and deposition
 time – influencing soil properties.

Interactions between these factors cause an infinite variety of soils across the earth‘s
land surface.

Parent materials

Soil minerals form the basis of soil. They are produced from rocks (parent material)
through the processes of weathering and natural erosion. Water, wind, temperature
change, gravity, chemical interaction, living organisms and pressure differences all
help break down parent material.

The types of parent materials and the conditions under which they break down will
influence the properties of the soil formed. For example, soils formed from granite are
often sandy and infertile. On the other hand, basalt under moist conditions breaks
down to form fertile, clay soils.

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Organisms

Soil formation is influenced by organisms (e.g. plants), micro-organisms (e.g. bacteria

or fungi), burrowing insects, animals and humans.

As soil forms, plants begin to grow in it; they mature, die and regrow. Their leaves
and roots are added to the soil. Animals eat plants; their wastes and eventually their
bodies are added to the soil. This begins to change the soil. Bacteria, fungi, worms
and other burrowers break down plant litter and animal wastes and remains, to
eventually become organic matter. This may take the form of peat, humus or
charcoal.

Climate

Climate (rainfall, temperature and wind) influences the rate of weathering and also
affects plant growth. Temperature affects the rate of weathering and organic
decomposition. With a colder and drier climate, these processes can be slow, but
with heat and moisture they are relatively rapid.

Rainfall dissolves some of the soil materials and holds others in suspension. The
water carries these materials down through the soil. This is known as leaching. Over
time this process can change the soil, making it less fertile.

Topography

The shape, length and grade of slope affects drainage. Aspect determines the type of
vegetation on a slope and the amount of rainfall received. These factors cause
variation in soil formation.

Time

The length of time that soil materials have been weathered influences soil properties.
Minerals weathered from rocks are further weathered to form materials such as clays
and oxides of iron and aluminium.

Natural erosion

Soil materials are progressively moved within the natural landscape by the action of
water, gravity and wind eg. heavy rains erode soils from the hills and deposit it in
lower areas, forming deep soils. The soils left on steep hills are usually shallower.
Transported soils include alluvial (water transported), colluvial (gravity transported)
and aeolian (wind transported) soils

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Student Learning Activity 4

1 Define soil.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

2 What does Horizon A primarily compose of?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

3 List the factors that influence soil degradation?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

4 What is soil quality based on?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

5 Why are soils in the tropical rainforest region infertile?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

6 Name the distinct profile or sequence of horizontal layers of soil.

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

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7 List the processes that result in the formation of horizons.

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

8 What influences soil fertility?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

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UNIT 4.0

MEASURING CLIMATE

Learning Outcomes

At the end of this Unit, you can:

1 confidently name the instruments used for measuring climate

2 understand the complex interactive climatic system

3 understand the chemical composition of air or water

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INTRODUCTION

The climate system is a complex, interactive system consisting of the atmosphere,

land surface, snow and ice, oceans and other bodies of water, and living things. The
atmospheric component of the climate system is what we generally refer to as
climate: climate is often defined as ‗average weather‘. Climate is usually described in
terms of the mean and variability of temperature, precipitation and wind over a period
of time, ranging from months to millions of years.
Countless empirical tests of numerous different hypotheses have now built up a
massive body of Earth science knowledge. This repeated testing has refined the
understanding of many aspects of the climate system, from deep oceanic circulation
to stratospheric chemistry. Sometimes a combination of observations and models
can be used to test planetary-scale hypotheses. For example, the global cooling and
drying of the atmosphere observed after the eruption of Mt. Pinatubo in the
Philippines provided key tests of particular aspects of climate models.
Conditions of the atmosphere at a particular location over a long period of time; it is
the long-term summation of the atmospheric elements (and their variations) that, over
short time periods, constitute weather. These elements are solar radiation,
temperature, humidity, precipitation (type, frequency, and amount), atmospheric
pressure, and wind (speed and direction).
There are a number of key factors in measuring climate change, and they are broadly
categorized below. The range of instrumentation used to observe and measure
climate is truly amazing.
Temperature When measuring climate change this is a primary and can be
measured or reconstructed for the Earth‘s surface, and sea surface temperature
(SST).
Precipitation (rainfall, snowfall etc) offers another indicator of relative climate
variation and may include humidity or water balance, and water quality.
Biomass and vegetation patterns may be discerned in a variety of ways and provide
evidence of how ecosystems change to adapt to climate change.
Sea Level measurements reflect changes in shoreline and usually relate to the
degree of ice coverage in high latitudes and elevations.
Solar Activity can influence climate, primarily through changes in the intensity of
solar radiation.
Volcanic Eruptions like solar radiation can alter climate due to the aerosols that are
emitted into the atmosphere and alter climate patterns.
Chemical composition of air or water can be measured by tracking levels of
greenhouse gases such as carbon dioxide and methane, and measuring ratios of
oxygen isotopes. Research indicates a strong correlation between the percent of
carbon dioxide in the atmosphere and the Earth‘s mean temperature.

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4.1 EARLY MEASUREMENTS AND IDEAS

The Greek philosophers had much to say about meteorology, and many who
subsequently engaged in weather forecasting no doubt made use of their ideas.
Unfortunately, they probably made many bad forecasts, because Aristotle, who was
the most influential, did not believe that wind is air in motion. He did believe,
however, that west winds are cold because they blow from the sunset.

The scientific study of meteorology did not develop until measuring instruments
became available. Its beginning is commonly associated with the invention of the
mercury barometer by Evangelista Torricelli, an Italian physicist-mathematician, in
the mid-17th century and the nearly concurrent development of a reliable
thermometer. (Galileo had constructed an elementary form of gas thermometer in
1607, but it was defective; the efforts of many others finally resulted in a reasonably
accurate liquid-in-glass device.)

A succession of notable achievements by chemists and physicists of the 17th and

18th centuries contributed significantly to meteorological research. The formulation of
the laws of gas pressure, temperature, and density by Robert Boyle and Jacques-
Alexandre-César Charles, the development of calculus by Isaac Newton and
Gottfried Wilhelm Leibniz, the development of the law of partial pressures of mixed
gases by John Dalton, and the formulation of the doctrine of latent heat (i.e., heat
release by condensation or freezing) by Joseph Black are just a few of the major
scientific breakthroughs of the period that made it possible to measure and better
understand theretofore unknown aspects of the atmosphere and its behaviour.
During the 19th century, all of these brilliant ideas began to produce results in terms
of useful weather forecasts.

4.2 INSTRUMENTS FOR MEASURING CLIMATE CHANGE

There is no single instrument measuring climate change. Instead there are hundreds
of measuring devices spread across the globe, on land, under the sea and in the air.

Climate is measured in many ways. The table on the next page shows the type of
measurement, what it says and what you use to measure.

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How can it be What instruments can we

What is it?
measured? use to measure it?
Degrees
This is a
Celsius or Thermometers
Temperature measurement of heat
Fahrenheit
Wind sock,
This measures the
Knots Anemometer
Wind movement or air
Ventimeters
This is the
Intensity of Campbell-Stokes sunshine
Sun measurement of light
sunlight recorder
and heat
This is the
Rain and snow
measurement of
(Precipitation) Millimetres Rain Gauge
moisture from the
clouds
Humidity This is the moisture Psychrometer,
Percentages
in the air humidity gauge
This is the moisture
Cloud Oktas Cloud Mirror
built up in air
This is the
measurement of Map, ruler
Visibility Kilometres
things being visible or binoculars
not
This is the
Barometer,
measurement of the Millibars and
Pressure aneroid barometer, mercury
force exerted on the hectopascals
barometer
earth

Fig 4.1 Measuring Instruments

Thermometer Anemometer

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Rain Gauge

Barometer Campbell Stokes sunshine recorder

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4.3 CLIMATE CHANGE

Periodic modification of Earth's climate brought about as a result of changes in the

atmosphere as well as interactions between the atmosphere and various other
geologic, chemical, biological, and geographic factors within the Earth system.

The atmosphere is a dynamic fluid that is continually in motion. Both its physical
properties and its rate and direction of motion are influenced by a variety of factors,
including solar radiation, the geographic position of continents, ocean currents, the
location and orientation of mountain ranges, atmospheric chemistry, and vegetation
growing on the land surface. All these factors change through time. Some factors,
such as the distribution of heat within the oceans, atmospheric chemistry, and
surface vegetation, change at very short timescales. Others, such as the position of
continents and the location and height of mountain ranges, change over very long
timescales. Therefore, climate, which results from the physical properties and motion
of the atmosphere, varies at every conceivable timescale.

Climate is often defined loosely as the average weather at a particular place,

incorporating such features as temperature, precipitation, humidity, and windiness. A
more specific definition would state that climate is the mean state and variability of
these features over some extended time period. Both definitions acknowledge that
the weather is always changing, owing to instabilities in the atmosphere. And as
weather varies from day to day, so too does climate vary, from daily day-and-night
cycles up to periods of geologic time hundreds of millions of years long. In a very real
sense, climate variation is a redundant expression—climate is always varying. No
two years are exactly alike, nor are any two decades, any two centuries, or any two
millennia.

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SUMMARY

Climate as described is the average weather patterns existing throughout several

years over a large portion of Earth's surface. Usually, climate is measured for a
specific area or region based on weather patterns over a time period. Climate
therefore varies from weather because weather is concerned only with short term
events. A simple way to remember the distinction between the two is the saying,
"Climate is what you expect, but weather is what you get."

Since climate is composed of long-term average weather patterns, it encompasses

the average measurements of various meteorological elements like
humidity, atmospheric pressure, wind, precipitation and temperature. In addition to
these components, Earth's climate is also composed of a system consisting of its
atmosphere, oceans, land masses and topography, ice and biosphere. Each of these
is a part of the climate system for their ability to influence long-range weather
patterns. Ice for example, is significant to climate because it has a high albedo, or is
highly reflective, and covers 3% of the Earth's surface, therefore helping to reflect
heat back into space.

Climate Record

Although an area's climate is normally a result of a 30-35 year average, scientists

have been able to study past climate patterns for a large part of Earth's history
through paleo-climatology. In order to study past climates, paleo-climatologists use
evidence from ice sheets, tree rings, sediment samples, coral and rocks to determine
how much Earth's climate has changed through time. With these studies, scientists
have found that Earth has experienced various periods of stable climate patterns as
well as periods of climate change.

Today, scientists determine the modern climate record through measurements taken
via thermometers, barometers (an instrument measuring atmospheric pressure) and
anemometers (an instrument measuring wind speed) over the past few centuries.

Climate Classification

Climatologists studying Earth's past and modern climate record do so in an attempt

to establish useful climate classification schemes. In the past for example, climates
were determined based on travel, regional knowledge and latitude. An early attempt
the classify Earth's climates was Aristotle's Temperate, Torrid and Frigid Zones.
Today, climate classifications are based on the causes and effects of climate. A
cause for example would be the relative frequency over time of a specific type of air
mass over an area and the weather patterns it causes. A climate classification based
on an effect would be one concerned with vegetation types present an area.
The Köppen System

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The most widely used climate classification system in use today is the Köppen
System, which was developed over a period from 1918 to 1936 by Vladimir Köppen.
The Köppen System (map) classifies the Earth's climates based on natural
vegetation types as well as the combination of temperature and precipitation.

In order to classify different regions based on these factors, Köppen used a multi-
tiered classification system with letters ranging from A-E (chart). These categories
are based on temperature and precipitation but generally line up based on latitude. In
the Köppen System, the A-E climates are then subdivided into smaller zones which
are represented by a second letter, which can then be further subdivided to show
more detail.

Thornthwaite's Climate System

Although Köppen's System is the most widely used climate classification system,
there are several others that have been used as well. One of the more popular of
these is the climatologist and geographer C.W. Thornthwaite's system. This method
monitors the soil water budget for an area based on evapo-transpiration and
considers that along with total precipitation used to support an area's vegetation over
time. It also uses a humidity and aridity index to study an area's moisture based on
temperature, rainfall and vegetation type. The moisture classifications in
Thornthwaite's system are based on this index and the lower the index is, the drier an
area is. Classifications range from hyper-humid to arid.

Temperature is also considered in this system with descriptors ranging from micro-
thermal (areas with low temperatures) to mega-thermal (areas with high
temperatures and high rainfall).

Climate Change

A major topic in climatology today is that of climate change which refers to the
variation of Earth's global climate over time. Scientists have discovered that Earth
has undergone several climate changes in the past which include various shifts from
glacial periods or ice ages to warm, interglacial periods.

Today, climate change is mainly to describe the changes occurring in modern climate
such as an increase in sea surface temperatures and global warming.

The climate of Earth is able to support life in large part because of the atmospheric
greenhouse effect and the workings of the hydrological cycle. Water in the gaseous
phase, water vapour, is a key element in both of these. This report provides a basic
description of the scientific understanding of the roles water vapour plays in the
climate system.

The hydrological cycle describes the movement of water, in all three phases, within
and between the Earth's atmosphere, oceans, and continents. In the vapour phase,
water moves quickly through the atmosphere and redistributes energy associated
with its evaporation and recondensation. The movement of water vapour through the

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hydrological cycle is strongly coupled to precipitation and soil moisture, which have
important practical implications. The basic operation of the hydrologic cycle is well
known, but some details are poorly understood, mainly because we do not have
sufficiently good observations of water vapour.

There are many atmospheric greenhouse gases, some naturally occurring and some
resulting from industrial activities, but probably the most important greenhouse gas is
water vapour. Water vapour is involved in an important climate feedback loop. As the
temperature of the Earth's surface and atmosphere increases, the atmosphere is
able to hold more water vapour. The additional water vapour, acting as a greenhouse
gas, absorbs energy that would otherwise escape to space and so causes further
warming. This basic picture is complicated by important interactions between water
vapour, clouds, atmospheric motion, and radiation from both the Sun and the Earth.
There are some aspects of the role of water vapour as a greenhouse gas that are not
well understood, again mainly because we lack the necessary observations to test
theoretical models.

Monitoring long-term changes in water vapour, which are closely linked to other
climate variations and trends, is needed to both predict and detect changes. This
report describes traditional measurement systems and promising new technologies
that together may provide the continuity and quality of observations needed to
improve our understanding of water vapour in the climate system.

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Student Learning Activity 5

1 How is climate usually described?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

2 List the instruments that are used to measure

i) humidity ___________________________________________
ii) wind direction ___________________________________________
iii) sunlight ___________________________________________

3 Define climate.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

4 What is climate change?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

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UNIT 5.0

AQUATIC ECOSYSTEMS

Learning Outcomes

At the end of this Unit, you can:

1 distinguish and describe the ecosystem function

2 understand the composition aquatic ecosystems

3 identify the importance of the aquatic ecosystems to human life

4 identify and describe different adaptations of organisms

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INTRODUCTION

An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms

that are dependent on each other and on their environment live in aquatic
ecosystems. The two main types of aquatic ecosystems are marine ecosystems and
freshwater ecosystems.

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5.1 AQUATIC ECOSYSTEMS

Marine ecosystem

Marine ecosystems cover approximately 71% of the Earth's surface and contain
approximately 97% of the planet's water. They generate 32% of the world's net
primary production. They are distinguished from freshwater ecosystems by the
presence of dissolved compounds, especially salts, in the water. Approximately 85%
of the dissolved materials in seawater are sodium and chlorine. Seawater has an
average salinity of 35 parts per thousand (ppt) of water. Actual salinity varies among
different marine ecosystems.

Figure 5.1 A classification of marine habitats

Source: Wikipedia, the free encyclopaedia

Marine ecosystems can be divided into many zones depending upon water depth
and shoreline features. The oceanic zone is the vast open part of the ocean where
animals such as whales, sharks, and tuna live. The benthic zone consists of
substrates below water where many invertebrates live. The intertidal zone is the area
between high and low tides; in this figure it is termed the littoral zone. Other near-
shore (neritic) zones can include estuaries, salt marshes, coral reefs and mangrove
swamps. In the deep water, hydrothermal vents may occur where chemosynthetic
sulfur bacteria form the base of the food web.

Classes of organisms found in marine ecosystems include brown algae,

dinoflagellates, corals, cephalopods, echinoderms, and sharks. Fishes caught in
marine ecosystems are the biggest source of commercial foods obtained from wild
populations.

Environmental problems concerning marine ecosystems include unsustainable

exploitation of marine resources (for example overfishing of certain species), marine
pollution, climate change, and building on coastal areas.

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Freshwater ecosystem

.Figure 5.2 Showing Lake Kutubu, Southern Highlands, PNG

Freshwater ecosystems cover 0.80% of the Earth's surface and inhabit 0.009% of its
total water. They generate nearly 3% of its net primary production. Freshwater
ecosystems contain 41% of the world's known fish species.

There are three basic types of freshwater ecosystems.

 Lentic: slow-moving water, including pools, ponds, and lakes.

 Lotic: rapidly-moving water, for example streams and rivers.
 Wetlands: areas where the soil is saturated or inundated for at least part of the
time.

Lentic

Lake ecosystems can be divided into zones. One common system divides lakes into
three zones (see figure). The first, the littoral zone, is the shallow zone near the
shore. This is where rooted wetland plants occur. The offshore is divided into two
further zones, an open water zone and a deep water zone. In the open water zone
(or photic zone) sunlight supports photosynthetic algae, and the species that feed
upon them. In the deep water zone, sunlight is not available and the food web is
based on detritus entering from the littoral and photic zones. Some systems use
other names. The off shore areas may be called the pelagic zone, and the aphotic
zone may be called the profundal zone. Inland from the littoral zone one can also
frequently identify a riparian zone which has plants still affected by the presence of
the lake—this can include effects from windfalls, spring flooding, and winter ice
damage. The production of the lake as a whole is the result of production from plants
growing in the littoral zone, combined with production from plankton growing in the
open water.

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Figure 5.3 The three primary zones of a lake

Source: Wikipedia,

Wetlands can be part of the lentic system, as they form naturally along most
lakeshores, the width of the wetland and littoral zone being dependent upon the
slope of the shoreline and the amount of natural change in water levels, within and
among years. Often dead trees accumulate in this zone, either from windfalls on the
shore or logs transported to the site during floods. This woody debris provides
important habitat for fish and nesting birds, as well as protecting shorelines from
erosion.

Two important subclasses of lakes are ponds, which typically are small lakes that
intergrade with wetlands, and water reservoirs. Over long periods of time, lakes, or
bays within them, may gradually become enriched by nutrients and slowly fill in with
organic sediments, a process called succession. When humans use the watershed,
the volumes of sediment entering the lake can accelerate this process. The addition
of sediments and nutrients to a lake is known as eutrophication.

Ponds are small pools with shallow water, marsh, and aquatic plants. They can be
further divided into four zones: vegetation zone, open water, bottom mud and surface
film. The size and depth of ponds often varies greatly with the time of year; many
ponds are produced by spring flooding from rivers. Food webs are based both on
free-floating algae and upon aquatic plants. There is usually a diverse array of
aquatic life, with a few examples including algae, snails, fish, beetles, water bugs,
frogs, turtles, otters and muskrats. Top predators may include large fish, herons, or
alligators. Since fish are a major predator upon amphibian larvae, ponds that dry up
each year, thereby killing resident fish, provide important refugia for amphibian
breeding. Ponds that dry up completely each year are often known as vernal pools.
Some ponds are produced by animal activity, including alligator holes and beaver
ponds, and these add important diversity to landscapes.

Lotic

The major zones in river ecosystems are determined by the river bed's gradient or by
the velocity of the current. Faster moving turbulent water typically contains greater

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concentrations of dissolved oxygen, which supports greater biodiversity than the slow
moving water of pools. These distinctions form the basis for the division of rivers into
upland and lowland rivers. The food base of streams within riparian forests is mostly
derived from the trees, but wider streams and those that lack a canopy derive the
majority of their food base from algae. Anadromous fish are also an important source
of nutrients. Environmental threats to rivers include loss of water, dams, chemical
pollution and introduced species. A dam produces negative effects that continue
down the watershed. The most important negative effects are the reduction of spring
flooding, which damages wetlands, and the retention of sediment, which leads to loss
of deltaic wetlands

Wetlands

Wetlands are dominated by vascular plants that have adapted to saturated soil.
There are four main types of wetlands: swamp, marsh, fen and bog. Wetlands are the
most productive natural ecosystems in the world because of the proximity of water
and soil. Hence they support large numbers of plant and animal species. Due to their
productivity, wetlands are often converted into dry land with dykes and drains and
used for agricultural purposes. The construction of dykes, and dams, has negative
consequences for individual wetlands and entire watersheds. Their closeness to
lakes and rivers means that they are often developed for human settlement. Once
settlements are constructed and protected by dykes, the settlements then become
vulnerable to land subsidence and ever increasing risk of flooding. The Louisiana
coast around New Orleans is a well known example; the Danube Delta in Europe is
another.

5.2 FUNCTIONS

Aquatic ecosystems perform many important environmental functions. For example,

they recycle nutrients, purify water, attenuate floods, recharge ground water and
provide habitats for wildlife. Aquatic ecosystems are also used for human recreation,
and are very important to the tourism industry, especially in coastal regions.

The health of an aquatic ecosystem is degraded when the ecosystem's ability to

absorb a stress has been exceeded. A stress on an aquatic ecosystem can be a
result of physical, chemical or biological alterations of the environment. Physical
alterations include changes in water temperature, water flow and light availability.
Chemical alterations include changes in the loading rates of bio-stimulatory nutrients,
oxygen consuming materials, and toxins. Biological alterations include over-
harvesting of commercial species and the introduction of exotic species. Human
populations can impose excessive stresses on aquatic ecosystems. There are many
examples of excessive stresses with negative consequences. Consider three. The
environmental history of the Great Lakes of North America illustrates this problem,
particularly how multiple stresses, such as water pollution, over-harvesting and
invasive species can combine. The Norfolk Broadlands in England illustrate similar
decline with pollution and invasive species. Lake Pontchartrain along the Gulf of
Mexico illustrates the negative effects of different stresses including levee
construction, logging of swamps, invasive species and salt water intrusion.

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5.3 ABIOTIC CHARACTERISTICS

An ecosystem is composed of biotic communities that are structured by biological

interactions and abiotic environmental factors. Some of the important abiotic
environmental factors of aquatic ecosystems include substrate type, water depth,
nutrient levels, temperature, salinity, and flow. It is often difficult to determine the
relative importance of these factors without rather large experiments. There may be
complicated feedback loops. For example, sediment may determine the presence of
aquatic plants, but aquatic plants may also trap sediment, and add to the sediment
through peat.

The amount of dissolved oxygen in a water body is frequently the key substance in
determining the extent and kinds of organic life in the water body. Fish need
dissolved oxygen to survive, although their tolerance to low oxygen varies among
species; in extreme cases of low oxygen some fish even resort to air gulping. Plants
often have to produce aerenchyma, while the shape and size of leaves may also be
altered. Conversely, oxygen is fatal to many kinds of anaerobic bacteria.

Nutrient levels are important in controlling the abundance of many species of algae.
The relative abundance of nitrogen and phosphorus can affect determine which
species of algae come to dominate. Algae are a very important source of food for
aquatic life, but at the same time, if they become over-abundant, they can cause
declines in fish when they decay. Similar over-abundance of algae in coastal
environments such as the Gulf of Mexico produces, upon decay, a hypoxic region of
water known as a dead zone.

The salinity of the water body is also a determining factor in the kinds of species
found in the water body. Organisms in marine ecosystems tolerate salinity, while
many freshwater organisms are intolerant of salt. The degree of salinity in an estuary
or delta may is an important control upon the type of wetland (fresh, intermediate, or
brackish), and the associated animal species. Dams built upstream may reduce
spring flooding, and reduce sediment accretion, and may therefore lead to saltwater
intrusion in coastal wetlands.

Freshwater used for irrigation purposes often absorb levels of salt that are harmful to
freshwater organisms.

5.4 BIOTIC CHARACTERISTICS

The biotic characteristics are mainly determined by the organisms that occur. For
example, wetland plants may produce dense canopies that cover large areas of
sediment—or snails or geese may graze the vegetation leaving large mud flats.
Aquatic environments have relatively low oxygen levels, forcing adaptation by the
organisms found there. For example, many wetland plants must produce
aerenchyma to carry oxygen to roots. Other biotic characteristics are more subtle and
difficult to measure, such as the relative importance of competition, mutualism or
predation. There are a growing number of cases where predation by coastal

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herbivores including snails, geese and mammals appears to be a dominant biotic

factor.

5.5 AUTOTROPHIC ORGANISMS

Autotrophic organisms are producers that generate organic compounds from

inorganic material. Algae use solar energy to generate biomass from carbon dioxide
and are possibly the most important autotrophic organisms in aquatic environments.
Of course, the more shallow the water, the greater the biomass contribution from
rooted and floating vascular plants. These two sources combine to produce the
extraordinary production of estuaries and wetlands, as this autotrophic biomass is
converted into fish, birds, amphibians and other aquatic species.

Chemosynthetic bacteria are found in benthic marine ecosystems. These organisms

are able to feed on hydrogen sulphide in water that comes from volcanic vents. Great
concentrations of animals that feed on these bacteria are found around volcanic
vents. For example, there are giant tube worms (Riftia pachyptila) 1.5m in length and
clams (Calyptogena magnifica) 30 cm long.

5.6 HETEROTROPHIC ORGANISMS

Heterotrophic organisms consume autotrophic organisms and use the organic

compounds in their bodies as energy sources and as raw materials to create their
own biomass. Euryhaline organisms are salt tolerant and can survive in marine
ecosystems, while stenohaline or salt intolerant species can only live in freshwater
environments.

The mode of taking food varies from one group of animal to another. Some take food
in liquid form, whereas other takes it in solid form. The plants synthesize their own
food from raw materials like carbon dioxide and water in the presence of sunlight and
chlorophyll. Thus plants are autotrophic organisms because they synthesize their
own food themselves.

There are organisms like animals that are not capable of making their food from
sunlight and carbon dioxide and water. Animals get their food from plants and other
animals. They are called heterotrophic organisms.

Nutrition in Autotrophic Organisms

In this, organisms synthesize the essential organic compounds from inorganic

compounds like carbon dioxide and water in the presence of radiant energy of
sunlight trapped by magnesium ions (Mg2+) containing green pigment, chlorophyll.
The process is called photosynthesis.

Photosynthesis is the conversion of light energy into chemical bond energy.

6CO2 + 12 H2O ---> C6H12O6 + 6O2 + 6 H2O

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Photoautotrophic nutrition is found in all green plants and some protists having
chloroplasts like Euglena, Volvox etc. called photoautotrophs.

Some non green bacteria manufacture their organic food from inorganic substances
in the presence of energy derived from the oxidation of simple inorganic compounds
of sulphur and iron etc. For example sulphur and iron bacteria. This process is called
chemosynthesis.

And organisms are called chemoautotroph. It is also found in nitrifying bacteria like
nitosomona and nitrobacteria. Both chemosynthetic and photosynthetic organisms
are collectively called autotrophs or self nourishing.

Nutrition in Heterotrophic Organisms

This is characteristic of all animals and fungi, some protists (for example
Trypanosona, Paramecium, Amoeba), many bacteria, (for example pseudomonas)
and some non green plants (for example Parasitic plants like cuscuta) they take
readymade organic food from other dead or living plants and animals. It is so
because these have no chlorophyll so these cannot trap the radiant energy of
sunlight. The living organisms sowing heterotrophic nutrition are called heterotrophs.

On the basis of nature of food heterotrophic nutrition is of following types:

A Holozoic nutrition: in this, the organism feed exclusively on the solid food
materials. The food may be a whole plant or whole animals or their plants.

Depending upon the source of food, holozoic are of following types:

 Herbivores: These are direct plant feeding heterotrophs, for example rabbit,
cow, buffalo, etc.
 Carnivores: These derive organic food from their animal food, for example lion,
tiger and cheetah, etc.
 Omnivores: These take both plant and animal food for example, human beings,
cockroaches, etc.
 Cannibals: In this, living organisms eat upon the member of their own species,
for example some fishes.
 Detritivores: When animals feed chiefly upon dead organic matter present in
the mud, for example earth worm.
 Predators: When the larger animals feed upon the smaller animal species, for
example words like eagle, kite, etc.
 Insectivores: These feed on insects, for example frog, lizard, etc.

B Saprophytic nutrition: Organisms like fungi and many bacteria etc. take
dissolved decaying organic materials from their environment. Organism
releases some enzyme to digest the dead organic food and then the nutrients
are absorbed through the body surface.

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C Parasitic nutrition: In this a smaller organism derives pre-digested organic

food from another organism. It is shown by many bacteria, viruses, fungi,
some on green plants, for example Puccinia, cuscuta and many animals, for
example round worms, etc.

Figure 5.4 Showing a food chain for autotrophic and heterotrophic organism nutrient
flow

5.7 OSMOSIS

Osmosis is the net movement of solvent molecules through a partially permeable

membrane into a region of higher solute concentration, in order to equalize the solute
concentrations on the two sides. It may also be used to describe a physical process
in which any solvent moves, without input of energy, across a semi permeable
membrane (permeable to the solvent, but not the solute) separating two solutions of
different concentrations. Although osmosis does not require input of energy, it does
use kinetic energy and can be made to do work.

Figure 5.5 Water passing through a semi-permeable membrane to create an isotonic

environment

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Net movement of solvent is from the less concentrated (hypotonic) to the more
concentrated (hypertonic) solution, which tends to reduce the difference in
concentrations. This effect can be countered by increasing the pressure of the
hypertonic solution, with respect to the hypotonic. The osmotic pressure is defined to
be the pressure required to maintain equilibrium, with no net movement of solvent.
Osmotic pressure is a colligative property, meaning that the osmotic pressure
depends on the molar concentration of the solute but not on its identity.

Large quantities of water molecules constantly move across cell membranes by

simple diffusion, but, in general, net movement of water into or out of cells is
negligible.

There are, however, many cases in which net flow of water occurs across cell
membranes and sheets of cells. An example of great importance to you is the
secretion of and absorption of water in your small intestine. In such situations, water
still moves across membranes by simple diffusion, but the process is important
enough to warrant a distinct name - osmosis.

Osmosis is the net movement of water across a selectively permeable membrane

driven by a difference in solute concentrations on the two sides of the membrane. A
selectively permeable membrane is one that allows unrestricted passage of water,
but not solute molecules or ions.

Different concentrations of solute molecules lead to different concentrations of free

water molecules on either side of the membrane. On the side of the membrane with
higher free water concentration (i.e. a lower concentration of solute), more water
molecules will strike the pores in the membrane in a give interval of time. More
strikes equates to more molecules passing through the pores, which in turn results in
net diffusion of water from the compartment with high concentration of free water to
that with low concentration of free water.

The key to remember about osmosis is that water flows from the solution with the
lower solute concentration into the solution with higher solute concentration. This
means that water flows in response to differences in molarity across a membrane.
The size of the solute particles does not influence osmosis. Equilibrium is reached
once sufficient water has moved to equalize the solute concentration on both sides of
the membrane, and at that point, net flow of water ceases.

Here is a simple example to illustrate these principles:

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Two containers of equal volume are separated by a membrane that allows free
passage of water, but totally restricts passage of solute molecules. Solution A has 3
molecules of the protein albumin (molecular weight 66,000) and Solution B contains
15 molecules of glucose (molecular weight 180).

Into which compartment will water flow, or will there be no net movement of water?

Yes, you are right, water will move from Solution A into Solution B because Solution
B has a higher concentration of particles than Solution A.

It doesn't matter that the albumin molecules in Solution A are huge compared to the
glucose molecules - osmotic flow depends on the concentration of particles (particles
per volume) NOT on the size of the particles.

Suppose an animal or a plant cell is placed in a solution of sugar or salt in water.

1 If the medium is hypotonic — a dilute solution, with a higher water

concentration than the cell — the cell will gain water through osmosis.

2 If the medium is isotonic — a solution with exactly the same water

concentration as the cell — there will be no net movement of water across the
cell membrane.

3 If the medium is hypertonic — a concentrated solution, with a lower water

concentration than the cell — the cell will lose water by osmosis.
Essentially, this means that if a cell is put in a solution which has a solute
concentration higher than its own, then it will shrivel up, and if it is put in a solution
with a lower solute concentration than its own, the cell will expand and burst.

Figure 5.6 Plant cell under different environments

Osmotic pressure

As mentioned before, osmosis may be opposed by increasing the pressure in the

region of high solute concentration with respect to that in the low solute concentration
region. The force per unit area, or pressure, required to prevent the passage of water

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through a selectively permeable membrane and into a solution of greater

concentration is equivalent to the osmotic pressure of the solution, or turgor. Osmotic
pressure is a colligative property, meaning that the property depends on the
concentration of the solute, but not on its identity.

Osmotic gradient

The osmotic gradient is the difference in concentration between two solutions on

either side of a semi permeable membrane, and is used to tell the difference in
percentages of the concentration of a specific particle dissolved in a solution.
Usually the osmotic gradient is used while comparing solutions that have a semi
permeable membrane between them allowing water to diffuse between the two
solutions, toward the hypertonic solution (the solution with the higher concentration).
Eventually, the force of the column of water on the hypertonic side of the semi
permeable membrane will equal the force of diffusion on the hypotonic (the side with
a lesser concentration) side, creating equilibrium. When equilibrium is reached, water
continues to flow, but it flows both ways in equal amounts as well as force, therefore
stabilizing the solution.

5.8 BASIC ADAPTATION TO LIFE IN WATER

Ocean

There are thousands of species of marine life, from tiny zooplankton to enormous
whales. Each is adapted to the specific habitat it occupies.
Throughout the oceans, marine organisms must deal with several things that are less
of a problem for life on land:

 Regulating salt intake

 Obtaining oxygen
 Adapting to water pressure
 Dealing with wind, waves and changing temperatures
 Getting enough light

Highlighted below are some of the ways marine life survives in this environment that
is so different from ours.

Salt Regulation

Fish can drink salt water, and eliminate the salt through their gills. Seabirds also drink
salt water, and the excess salt is eliminated via the nasal, or ―salt glands‖ into the
nasal cavity, and then is shaken, or sneezed out by the bird. Whales don‘t drink salt
water, instead getting the water they need from the organisms they eat.

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Oxygen

Fish and other organisms that live underwater can take their oxygen from the water,
either through their gills or their skin.

Marine mammals need to come to the water surface to breathe, which is why the
deep-diving whales have blowholes on top of their heads, so they can surface to
breathe while keeping most of their body underwater.
Whales can stay underwater without breathing for an hour or more because they
make very efficient use of their lungs, exchanging up to 90% of their lung volume with
each breath, and also store unusually high amounts of oxygen in their blood and
muscles when diving.

Temperatures

Many ocean animals are cold-blooded (ectothermic) and their internal body
temperature is the same as their surrounding environment.

Marine mammals, however, have special considerations because they are warm-
blooded (endothermic), meaning they need to keep their internal body temperature
constant no matter the water temperature.
Marine mammals have an insulating layer of blubber (made up of fat and connective
tissue) under their skin. This blubber layer allows them to keep their internal body
temperature about the same as ours, even in the cold ocean.

Water Pressure

In the oceans, water pressure increases 15 pounds per square inch for every 33 feet
of water. While some ocean animals do not change water depths very often, far-
ranging animals such as whales, sea turtles and seals sometimes travel from shallow
waters to great depths several times in a single day. How can they do it?

The sperm whale is thought to be able to dive over 1 ½ miles below the ocean
surface. One adaptation is that lungs and rib cages collapse when diving to deep
depths.

The leatherback sea turtle can dive to over 3,000 feet. Its collapsible lungs and
flexible shell help it stand the high water pressure.

Wind and Waves

Animals in the intertidal zone do not have to deal with high water pressure, but need
to withstand the high pressure of wind and waves. Many marine invertebrates and
plants in this habitat have the ability to cling on to rocks or other substrates so they
are not washed away, and have hard shells for protection.

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Light

Organisms that need light, such as tropical coral reefs and their associated algae, are
found in shallow, clear waters that can be easily penetrated by sunlight.

Since underwater visibility and light levels can change, whales do not rely on sight to
find their food. Instead, they locate prey using echolocation and their hearing.

In the depths of the ocean abyss, some fish have lost their eyes or pigmentation
because they are just not necessary. Other organisms are bioluminescent, using
light-giving bacteria or their own light-producing organs to attract prey or mates.

Some general adaptations for marine organisms in the ocean

Fish have several important adaptations that allow them to live in their ocean
environment.

 Gills take oxygen out of the water so that the fish can "breathe" underwater.
(Many other marine organisms, like shrimp and sea slugs also have gills.)
 Most fish have a streamlined shape as well as a tail and fins to help them
move easily and quickly through the water.
 A swim bladder (or the liver) helps the fish control its buoyancy and stay at a
certain depth.

Marine mammals also have adaptations for life underwater

 Mammals do not have gills and cannot breathe underwater; however, they can
hold their breath for long periods of time. Some seals can hold their breath for
45 minutes and some whales can hold their breath for over an hour!
 Most marine mammals have either tails or webbed feet and their "arms" have
evolved into flippers. Their bodies also have a streamlined shape.
 Mammals are warm-blooded and need insulation to keep their body
temperature from dropping. They have either a thick layer of blubber (fat) or
very thick fur.

Wetlands

Wetlands are areas of land that are covered with fresh water or saltwater and feature
species adapted to life in a saturated environment. They are shallow and allow the
growth of rooted or anchored plants such as water lilies but also free floating plants
like duckweed.

Wetlands represent the meeting of two habitats (land and water) and are therefore
some of the most bio-diverse areas in the world (some say more than rainforests)
with many land and water species, and some that are unique only to the wetlands.

Currently, wetlands exist on all the world's continents except Antarctica, but because
of increasing pollution and a reduction in open land, they are all threatened.

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Examples include the Mahavavy-Kinkony Wetlands in Madagascar, and the

Everglades in Florida.

Wetland Formation

Wetlands begin with the saturation of a land habitat. Many were formed at the end of
the last ice age when glaciers retreated and the shallow depressions left over filled
with water. Over time, sediment and organic debris collected in the depressions and
the water became shallower until the accumulated sediment and debris filled in the
water and left behind shallow wetland ponds surrounded by dry land.

Wetlands can also form when a river overflows its banks or when changes in sea
level make once dry areas saturated. Additionally, climate can impact wetland
formation as high rainfall in normally dry areas with poor drainage causes the ground
to become saturated.
Once wetlands form, they are constantly changing. Just as growing sediment and
debris levels cause the wetlands to form, they along with roots and dead plant matter,
can cause the wetland to become more shallow, eventually to the point where the
upper layers rise above the water table and dry out. When this happens, terrestrial
plant and animal species can colonize the area.

Types of Wetlands

There are two main types of wetlands -- the coastal tidal wetlands and salt marshes,
and inland freshwater wetlands and ponds.

Coastal wetlands are along the coastlines of mid to high latitude areas worldwide,
but they are most common along the Atlantic, Pacific, Alaskan and Gulf Coasts.
Coastal wetlands form near estuaries, the area where a river meets the sea, and are
prone to varying levels of salinity and water levels because of tidal action. Because of
the varying nature of these locations, most tidal wetlands consist of unvegetated mud
and sand flats.

Some plants however, have been able to adapt to such conditions. These include the
grasses and grass-like plants of the tidal salt marshes on the coasts of the United
States. In addition, mangrove swamps consisting of salt loving trees or shrubs are
common in tropical coastal areas.

By contrast, inland wetlands are along rivers and streams (these are sometimes
called riparian wetlands), in isolated depressions, along the edges of lakes and
ponds, or in other low-lying areas where the groundwater meets the soil's surface or
when runoff is significant enough to allow formation. Precipitation can also
sometimes saturate the soil and create bogs or temporary wetlands called vernal
pools.

Unlike coastal wetlands, inland wetlands are always comprised of freshwater. They
include marshes and wet meadows that are filled with herbaceous plants and
swamps dominated by shrubs and wooded swamps full of trees.

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Significance of Wetlands

Because wetlands are among the most biologically productive ecosystems in the
world, they are of extreme significance to scores of species, many of which are
endangered. In the United States for example, one-third of the nation's threatened
and endangered species live only in wetlands, while half use wetlands during a
portion of their lives. Without the wetlands, these species would go extinct.

Estuarine and marine fish and shellfish, and some mammals must have wetlands to
survive as they are breeding grounds and/or provide a rich source of food via
decomposing plant matter. Some of the species that live in wetlands include wood
ducks and muskrats. Other fish, mammals, reptiles and birds visit wetlands
periodically because they provide food, water and shelter. Some of these are otters,
black bears and raccoons.
In addition to being unique ecosystems, wetlands also act as a filter for pollution and
excess sediment. This is important because rainwater runoff is normally laden with
dangerous pesticides and other pollutants. By going through a wetland prior to
reaching open water, this is filtered out and often, excess sediment naturally builds
up in the wetland instead of in rivers or other water bodies.

Wetlands also aid in flood protection as they act as sponges that absorb rain and
floodwater. Furthermore, wetlands are significant to the reduction of coastal erosion
as they can act as a buffer between land and the sea- an important thing to have in
areas prone to storm surges and hurricanes. Inland wetlands also prevent erosion
because the roots of the wetland's vegetation hold soil in place.

Human Impacts and Conservation

Today, wetlands are incredibly sensitive ecosystems and because of human activities,
they have been degraded considerably. Development along waterways and even
draining of wetlands has caused increased pollution (to the extent that natural
absorption cannot keep up), a decrease in available water and water quality. In
addition, the introduction of non-native species has changed the natural species
composition and sometimes crowded out native species. Recently, many places have
come to realize the importance of wetlands for their economic and biological benefits.
As a result, efforts are now being made to protect existing wetlands, restore
damaged ones, and even develop new, artificial wetlands in viable areas.

Interdependence of living organisms and their environments

In the wild one habitat will support many different populations. The group of
organisms sharing a habitat is called its community.

In a tropical river, the community is made up of fish, water snails, water birds and
crocodiles. The different species present in a community will depend on others for
their survival. For example, bees feed on pollen and nectar from flowers. Flowers
depend on bees for pollination. This is called the interdependence of living organisms.

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Some organisms will be predators that hunt other animals, their prey.

Factors affecting the size of a population include but not limited to:

- Competition for nutrients - Competition for food

- Competition for water - Competition for space
- Competition for light - Disease
- Competition for space - Predators
- Grazing land - Migration

Grazing animals affect the population of different plants. Fences keep grazing
animals out and this has an effect on plant life.

In a pond or river community, the plants are very important to the survival of the
animals. They produce oxygen when they photosynthesise. They provide food and
shelter for animals and a place for them to lay their eggs (reproduction).

Food chains, Interdependence and Adaptation

All creatures need a source of energy to stay alive. Plants get their energy from the
sun and animals get energy from eating plants or other animals.

A food chain shows what eats what in a habitat. This is a simple food chain for a
garden.

Figure 5.7 A simple food chain in a garden

There may be lots of food chains in a habitat, because lots of animals eat grass,
other animals eat snails and birds get eaten too!
A food web shows how all the living things in a habitat can be connected.

Here are a few more living things that you might find in a garden, connected together
as a food web.

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Figure 5.8 A simple food web

Every habitat will have its own food chains and webs. Most habitats have lots of
plants, and fewer animals. Do you know why? Plants use the energy from sunlight to
make food in their leaves by a process called photosynthesis. They are called
producers because they produce their own food.

Most animals cannot make their own food. They must eat something else in order to
get the energy to live and grow. They are called consumers.

Some animals eat plants. They are called herbivores. They need to eat a lot of
plants, because plants contain relatively little energy.

Animals that eat meat are called carnivores. They get their meat by eating other
animals, usually smaller than themselves.

Omnivores (like humans) eat both plants and animals. Some animals, like
earthworms, eat bits of plants and animals that are dead, rotten or are other animal‘s
droppings! They are called decomposers. They are important for recycling nutrients.
Fungi and micro organisms are also decomposers. The nutrients go back into the soil
where they can be used again by plants to help them grow.

Figure 5.9 Orange fungi - one of the decomposers

Decomposers are important in a habitat. They feed on the dead and dying bits of
plants and animals and help the nutrients and the remaining energy to be recycled.

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Decomposers also play an important part in the ecosystem. They get energy by
breaking down the dead plant and animal material and at the same time they release
nutrients necessary for plant growth. Without decomposers, such as worms, there
would be a shortage of in minerals in the soil. The plants would not grow well and
then there would be less food for all.

Pyramid of numbers

Plants are the starting point for most food chains as they are the only organisms that
can bring energy into the system. Of course not every bit of plant gets eaten so there
are many more plants than there are animals. In the same way, not every animal
(prey) is eaten by a carnivore (predator), so there are more herbivores than there are
carnivores. There are relatively few animals at the very top of the food chain like
tigers or golden eagles.

If you counted the numbers of living things in the layers of a food web you would get
a ‗pyramid‘ of numbers. If you weighed the living things then you get a similar
pyramid of ‗biomass‘.

Figure 5.10 Pyramid of numbers

Interdependence
The organisms in a habitat depend on each other. Animals need plants for food, for
shelter from the weather and as hiding places from predators. Without plants there
would be no animals for the carnivores to eat.
Plants need animals to pollinate their flowers, to spread (disperse) their seeds and to
help keep the soil fertile. Squirrels like to eat acorns, but they are also good at taking
them away and burying them. Often the young or larvae of a species will eat different
things to the adults. Caterpillars usually eat leaves whereas the butterflies feed on
nectar (pollinating the flowers by accident at the same time).
Some plants and animals live in more than one habitat. Some plants are good at
growing anywhere (we call many of these weeds!). Animals are able to move around
so they can graze or hunt in more than one habitat. The fox will hunt in woods and
fields. Dragonflies spend their larval stage in the stream eating water animals. Adult
dragonflies leave the water and fly, catching and eating other flying insects in the
meadow. Both the stream and the meadow habitat are necessary for their survival.

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Figure 5.11 Orange tip butterfly in for the nectar

Adaptation

Habitats are different. Some have too much water and others are very dry. Some
soils have chalk or salt in them. Others are very hard or soft. South facing hills are
very sunny, hot and dry. North facing slopes are cooler, damper and often shaded.

The plants and animals that live in a habitat are adapted to the conditions there.
Plants growing on sand dunes need to be able to cope with very dry and exposed
conditions. Salt marsh plants have to tolerate salt. Plants in streams have to cope
with living in water and the risk of being washed away.

Herbivores are adapted to live on plants by having teeth that can grind leaves up into
small pieces so that they can be more easily digested. Some animals like cows have
several stomachs because it takes so long to digest grass.

Some carnivores actively hunt their food so they have legs to run, wings to fly or are
able to swim. They also tend to have sharp teeth and jaws that are able to deal with
eating meat. Other animals stay in one place and eat what comes past them. For
example sea anemones can stick fast to a rock and put out tentacles to filter the
water and catch anything edible.

Competition

Competition is a struggle between organisms for the same supply of food, water,
space, mates, nesting sites and other environmental resources that are in limited
supply. Competition may occur between members of the same species (intra specific
competition) or between the members of the different species (inter specific
competition) that dwell in the community.

For example; in the intra specific competition, it can be witnessed in the courtship
behaviour of a Bird of Paradise through its spectacular display of song and dance to
attract the attention of the female Bird of Paradise. Intra specific competition is only
beneficial for the survival of a species as it ensures that the fittest or the most
desirable characteristics are passed onto the next generation.

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Symbiosis

Symbiosis is a close ecological relationship between the individuals of two (or more)
different species. Sometimes a symbiotic relationship benefits both species,
sometimes one species benefits at the other's expense, and in other cases neither
species benefits.

Ecologists use a different term for each type of symbiotic relationship:

 Mutualism - both species benefit

 Commensalism - one species benefits, the other is unaffected
 Parasitism - one species benefits, the other is harmed
 Competition - neither species benefits
 Neutralism - both species are unaffected

Varieties of Symbiosis

When two species—that is, at least two individuals representing two different
species—live and interact closely in such a way that either or both species benefit, it
is symbiosis. It is also possible for a symbiotic relationship to exist between two
organisms of the same species. Organisms engaging in symbiotic relationships are
called symbionts.

There are three basic types of symbiosis, differentiated as to how the benefits (and
the detriments, if any) are distributed. These are commensalism, parasitism, and
mutualism. In the first two varieties, only one of the two creatures benefits from the
symbiotic relationship, and in both instances the creature who does not benefit—who
provides a benefit to the other creature—is called the host.

In commensalism, the organism known as the commensal benefits from the host
without the host's suffering any detriment. An example of this is found plants; one
non woody (orchid or ferns) growing on the branches of the tree so it gets enough
sunlight for photosynthesis. By contrast, in parasitism the parasite benefits at the
expense of the host. A parasitic relationship is one in which one member of the
association benefits while the other is harmed. This is also known as antagonistic or
antipathetic symbiosis. Parasitic symbioses take many forms, from endoparasites
that live within the host's body to ectoparasites that live on its surface. In addition,
parasites may be necrotrophic, which is to say they kill their host, or biotrophic,
meaning they rely on their host's surviving. Biotrophic parasitism is an extremely
successful mode of life. An example of a biotrophic relationship would be a tick
feeding on the blood of its host.

Mutualism is distinguished from the other two types of symbiosis, because in this
variety both creatures benefit. Thus, there is no host, and theoretically the partners
are equal, though in practice one usually holds dominance over the other. An
example of this inequality is the relationship between humans and dogs. In this
relationship, both human and dog clearly benefit: the dog by receiving food, shelter,

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and care and the human by receiving protection and loving companionship—the last
two being benefits the dog also receives from the human.

Additionally, some dogs perform specific tasks, such as fetching slippers, assisting
blind or disabled persons, or tracking prey for hunting or crime-solving purposes.

Another classic is a bee which eats the nectar of flowers and in turn spreads the
pollen which allows the flower to reproduce.

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SUMMARY

A key question to ask when studying growth and productivity in ecosystems is which
factors limit ecosystem activity. Availability of resources, such as light, water, and
nutrients, is a key control on growth and reproduction. Some nutrients are used in
specific ratios. To understand how a specific ecosystem functions, it thus is important
to identify what factors limit ecosystem activity.

Resources influence ecosystem activity differently depending on whether they are

essential, substitutable, or complementary. Essential resources limit growth
independently of other levels: if the minimum quantity needed for growth is not
available, then growth does not occur. In contrast, if two resources are substitutable,
then population growth is limited by an appropriately weighted sum of the two
resources in the environment. Resources may also be complementary, which means
that a small amount of one resource can substitute for a relatively large amount of
another, or can be complementary over a specific range of conditions.

Resource availability serves as a so-called "bottom-up" control on an ecosystem: the

supply of energy and nutrients influences ecosystem activities at higher trophic levels
by affecting the amount of energy that moves up the food chain. In some cases,
ecosystems may be more strongly influenced by so-called "top-down" controls –
namely, the abundance of organisms at high trophic levels in the ecosystem. Both
types of effects can be at work in an ecosystem at the same time, but how far
bottom-up effects extend in the food web, and the extent to which the effects of
trophic interactions at the top of the food web are felt through lower levels, vary over
space and time and with the structure of the ecosystem.

Variability and change are natural processes in aquatic ecosystems, and ecosystem
communities and individual organisms have in many cases adapted to different
environmental conditions.

Human effects on aquatic ecosystems can result from pollution, changes to the
landscape or hydrological systems, and larger-scale impacts such as global climate
change. The complexity of aquatic ecosystems and the linkages within them can
make the effect of disturbances on them difficult to predict. These linkages mean that
damage to one component of the ecosystem can lead to impacts on other ecosystem
components. Increasing our understanding of aquatic ecosystems can lead to better
practices that minimize impacts on aquatic environments.

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Student Learning Activity 6

1 Explain what is meant by osmosis?

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2 When does osmotic gradient become useful?

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3 What is meant by Osmotic pressure?

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4 In which way do animals depend on plants for their survival?

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UNIT 6.0

FOOD CHAINS AND FOOD WEBS

Learning Outcomes

At the end of this Unit, you can:

1 understand the differences between food chains and food webs

2 identify the levels of food chains and food webs

3 distinguish between different tropical levels

4 understand the process of succession

5 confidently identify environmental problems and issues

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INTRODUCTION

Every plant and animal species, no matter how big or small, depends to some extent
on another plant or animal species for its survival. It could be bees taking pollen from
a flower, photosynthesis of plants, deer eating shrub leaves or lions eating the deer.

A food chain shows how energy is transferred from one living organism to another via
food. It is important for us to understand how the food chain works so that we know
what are the important living organisms that make up the food chain and how the
ecology is balanced.

Photosynthesis is only the beginning of the food chain. There are many types of
animals that will eat the products of the photosynthesis process. Examples are deer
eating shrub leaves, rabbits eating carrots, or worms eating grass. When these
animals eat these plant products, food energy and organic compounds are
transferred from the plants to the animals.

A food chain describes how energy and nutrients move through an ecosystem. At the
basic level there are plants that produce the energy, then it moves up to higher-level
organisms like herbivores. After that when carnivores eat the herbivores, energy is
transferred from one to the other.

Therefore we should understand the ecology of the environment with respect to

plants. What is their number in terms of individuals (the population), and with respect
to other living beings in the environment.

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6.1 FOOD CHAINS

The source of all food is the activity of autotrophs, mainly photosynthesis, by plants.

 They are called producers because only they can manufacture food from
inorganic raw materials.
 This food feeds herbivores, called primary consumers.
 Carnivores that feed on herbivores are called secondary consumers.
 Carnivores that feed on other carnivores are tertiary (or higher) consumers.

Such a path of food consumption is called a food chain.

Each level of consumption in a food chain is called a trophic level.

The table below gives one example of a food chain and the trophic levels
represented in it.
food chain
Grasshopper Toad Snake Hawk Bacteria of
Grass
→ → → → → decay

In general
Autotrophs(Producers) Herbivores Carnivores
→ (Primary (Secondary, tertiary, etc.
Decomposers
Consumers) consumers)
trophic levels → →
Decomposers (such as bacteria and fungi) break down organic matter in the soil to
dark coloured humus. This organic matter also supports earthworms and soil insects.
As the decomposers breakdown soil organic matter, mineral nutrients such as nitrate
ions, phosphate ions and magnesium ions are released into the soil. These become
available for plants which are absorbed with water through the root hairs on the root
system of the plants.

A simple food chain shows how energy is transferred from the sun through living
organisms. The carnivore at the end of the food chain is known as the top carnivore
or tertiary consumer.

Figure 6.1 Simple Food Chain

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6.2 FOOD WEBS

Most food chains are interconnected. Animals typically consume a varied diet and, in
turn, serve as food for a variety of other creatures that prey on them. These
interconnections create food webs.

Most animals eat more than one kind of food and so in any ecosystem food chains
connect to form a food web.

Figure 6.2 Food Web

Where two animals are feeding on the same food source competition may occur.
Competition occurs between animals and also plants when any resource is limited.

Figure 6.3 Competition with food web

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6.3 PYRAMID OF NUMBERS

The pyramid of numbers represents the number of organisms in each trophic level.
This pyramid consists of a plot of relationships between the number herbivores
(primary consumers), first level carnivore (secondary consumers), second level
carnivore (tertiary consumers) and so forth. This shape varies from ecosystem to
ecosystem because the number of organisms at each level is variable. Upright, partly
upright and inverted are the three types of pyramids of numbers. An aquatic
ecosystem is an example of upright pyramid where the number of organisms
becomes fewer and fewer higher up in the pyramid. A forest ecosystem is an
example of a partially upright pyramid, as fewer producers support more primary
consumers, but there are less secondary and tertiary consumers. An inverted
pyramid of numbers is one where the number of organisms depending on the lower
levels grows closer toward the apex. A parasitic food chain is an example.
In a food chain the members at the successive higher levels are smaller in
number. For example, in a pond the lowest trophic level is represented by algae and
diatoms, which are largest in number. The second trophic level is represented by
herbivorous zooplankton, such as copipods, ranatra, etc. which are less abundant in
number while the third and fourth trophic levels are occupied by smaller and larger
fish, respectively. There is a considerable reduction in the number of individuals from
the base to the top of the pyramid. Another example may be coated of a forest. In a
forest, the small herbivorous insects are more abundant than the insectivorous
birds. Similarly, the preying birds, such as hawks are fewer than insectivorous birds.
Figure 6.4 Upright pyramid of numbers

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6.4 PYRAMID OF ENERGY

The pyramid of energy represents the total amount of energy consumed by each
trophic level. An energy pyramid is always upright as the total amount of energy
available for utilization in the layers above is less than the energy
The amount of energy and matter transferred through food to successive higher
levels become less and less. Greater amount of energy is available at the producer
level than at the primary consumer level (herbivores). The energy production of the
primary consumer is greater than that of the secondary consumers (i.e., primary
carnivores) which form next link in the energy chain. The energy at the tertiary
consumer level (secondary carnivores) is produced in minimum amount. The actual
fractions or percentages of energy from food at one level converted to energy from
food at the next level may be more than 10% or less than 10%. This general pattern
forms an energy pyramid, because each successive trophic level has less energy
available to it.

Figure 6.5 the ecological pyramid of energy

The ecological pyramid of energy is the representation of the energy flow in an

ecosystem with the help of a pyramid.
 The trophic level at the base denotes the position of the highest amount of
energy while the amount of energy at the trophic level situated at the apex is
the lowest.
 The energy flow in ecosystem occurs according to the law of thermodynamics
which states that energy is neither created nor destroyed and can be
transformed from one form to another while some amount of energy is lost in
the form of heat energy.
 Ecological pyramid of energy is always upright as a gradual decline of energy
takes place from the initiation to the termination of a food chain.
 The main source of energy is sun. Energy never goes back to its source, i.e.
solar energy never returns to the sun and transformation of energy occurs.
Green plants capture the solar energy to synthesize food having potential
energy stored within its chemical bonds. Such potential energy transforms into
kinetic energy during respiration. A part of the kinetic energy is released as
heat in the environment that subsequently passes into the space so that the
total energy of the universe remains constant.
 As energy flows through different trophic levels, some energy is always
dissipated as heat at each step which is of no use. According to Lindemann‘s

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ten percent law, about 10% of total energy is transmitted during energy flow
through several trophic levels indicating a gradual diminution in the amount of
energy.

6.5 PYRAMID OF BIOMASS

Biomass is renewable organic (living) material. A pyramid of biomass is a

representation of the amount of energy contained in biomass, at different trophic
levels for a particular time. It is measured in grams per square meter, or calories per
square meter. This demonstrates the amount of matter lost between trophic levels.
Each level is dependent on its lower level for energy, hence the lower level
determines how much energy will be available to the upper level. Also, energy is lost
in transfer so the amount of energy is less higher up the pyramid.
There are two types of biomass pyramids: upright and inverted. An upright pyramid is
one where the combined weight of producers is larger than the combined weight of
consumers. An example is a forest ecosystem. An inverted pyramid is one where the
combined weight of producers is smaller than the combined weight of consumers. An
example is an aquatic ecosystem.

The biomass is defined as the total weight of dry matter (dry weight) present in the
ecosystem at any one time. The biomass can be measured graphically. This graph
represents the shape of a pyramid which is known as pyramid of biomass. This
pyramid shows the total mass of organisms and gives a rough picture of the overall
effect of food chain relationships for the ecological group as a whole.

Figure 6.6 showing the pyramid of biomass

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6.6 ECOLOGICAL PYRAMIDS

An ecological pyramid is a graphical representation designed to show the number of

organisms, energy relationships, and biomass of an ecosystem. They are also called
Eltonian pyramids after Charles Elton, who developed the concept of ecological
pyramids. Producer organisms (usually green plants) form the base of the pyramid,
with succeeding levels above representing the different trophic levels (respective
position of the organisms within ecological food chains). Succeeding levels in the
pyramid represent the dependence of the organisms at a given level on the
organisms at lower level. There are three types of pyramids: of numbers, of biomass,
and of energy.

In studies of energy flow, the number of organisms at any trophic level depends upon
the availability of organisms which serve as food at the lower level. For example, the
number of particular herbivorous insects would increase if more plant food was
available to them. In this way, a large amount of food would be available not only to
its prey, such as the frog but also to other animals such as a bird which feeds on that
insect as a second choice which leads to an increase in their number. With the result
of the increased predation, the number of herbivorous insects is decreased and this
in turn leads to a reduction in the number of their predators. Thus the balance of
nature is maintained by the availability of food

Ecological pyramids are graphical representations of the trophic structure of

ecosystems. Ecological pyramids are organized with the productivity of plants on the
bottom, that of herbivores above the plants, and carnivores above the herbivores. If
the ecosystem sustains top carnivores, they are represented at the apex of the
ecological pyramid of productivity.

A fact of ecological energetics is that whenever the fixed energy of biomass is

passed along a food chain, substantial energy losses occur during each transfer.
These energy losses are a necessary consequence of the so-called second law of
thermodynamics. This universal principle states that whenever energy is transformed
from one state to another, the entropy of the universe must increase (entropy refers
to the randomness of distributions of matter and energy). In the context of transfers of
fixed biological energy along the trophic chains of ecosystems, increases in entropy
are represented by losses of energy as heat (because energy is converted from a
highly ordered state in biomass, to a much less-ordered condition as heat). The end
result is that transfers of energy between organisms along food chains are inefficient,
and this causes the structure of productivity in ecological food webs to always be
pyramid shaped.

The ecological pyramid of energy is the representation of the energy flow in an

ecosystem with the help of a pyramid.

 The trophic level at the base denotes the position of the highest amount of
energy while the amount of energy at the trophic level situated at the apex is
the lowest.

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 The energy flow in ecosystem occurs according to the law of thermodynamics

which states that energy is neither created nor destroyed and can be
transformed from one form to another while some amount of energy is lost in
the form of heat energy.
 Ecological pyramid of energy is always upright as a gradual decline of energy
takes place from the initiation to the termination of a food chain.
 The main source of energy is sun. Energy never goes back to its source, i.e.
solar energy never returns to the sun and transformation of energy occurs.
Green plants capture the solar energy to synthesize food having potential
energy stored within its chemical bonds. Such potential energy transforms into
kinetic energy during respiration. A part of the kinetic energy is released as
heat in the environment that subsequently passes into the space so that the
total energy of the universe remains constant.
 As energy flows through different trophic levels, some energy is always
dissipated as heat at each step which is of no use. According to Lindemann‘s
ten percent law, about 10% of total energy is transmitted during energy flow
through several trophic levels indicating a gradual diminution in the amount of
energy.

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SUMMARY

Every organism needs to obtain energy in order to live. Plants get energy from the
sun, some animals eat plants, and some animals eat other animals.

A food chain is the sequence of who eats whom in a biological community (an
ecosystem) to obtain nutrition. A food chain starts with the primary energy source,
usually the sun or boiling-hot deep sea vents. The next link in the chain is an
organism that makes its own food from the primary energy source -- an example is
photosynthetic plants that make their own food from sunlight (using a process
called photosynthesis) and chemosynthetic bacteria that make their food energy from
chemicals in hydrothermal vents. These are called autotrophs or
primary producers.

Next come organisms that eat the autotrophs. These organisms are
called herbivores or primary consumers -- an example is a rabbit that eats grass.
The next link in the chain is animals that eat herbivores - these are called secondary
consumers -- an example is a snake that eats rabbits.

In turn, these animals are eaten by larger predators -- an example is an owl that eats
snakes.

The tertiary consumers are eaten by quaternary consumers -- an example is a hawk

that eats owls. Each food chain end with a top predator, and animal with no natural
enemies (like an alligator, hawk, or polar bear).

The arrows in a food chain show the flow of energy, from the sun or hydrothermal
vent to a top predator. As the energy flows from organism to organism, energy is lost
at each step. A network of many food chains is called a food web.

Trophic Levels:

The trophic level of an organism is the position it holds in a food chain.

1 Primary producers (organisms that make their own food from sunlight and/or
chemical energy from deep sea vents) are the base of every food chain -
these organisms are called autotrophs.
2 Primary consumers are animals that eat primary producers; they are also
called herbivores (plant-eaters).
3 Secondary consumers eat primary consumers. They are carnivores (meat-
eaters) and omnivores (animals that eat both animals and plants).
4 Tertiary consumers eat secondary consumers.
5 Quaternary consumers eat tertiary consumers.

Food chains "end" with top predators, animals that have little or no natural enemies.

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When any organism dies, it is eventually eaten by detrivores (like vultures, worms
and crabs) and broken down by decomposers (mostly bacteria and fungi), and the
exchange of energy continues.

Some organisms' position in the food chain can vary as their diet differs. For
example, when a bear eats berries, the bear is functioning as a primary consumer.
When a bear eats a plant-eating rodent, the bear is functioning as a secondary
consumer. When the bear eats salmon, the bear is functioning as a tertiary consumer
(this is because salmon is a secondary consumer, since salmon eat herring that eat
zooplankton that eat phytoplankton, that make their own energy from sunlight). Think
about how people's place in the food chain varies - often within a single meal.

Numbers of Organisms

In any food web, energy is lost each time one organism eats another. Because of
this, there have to be many more plants than there are plant-eaters. There are more
autotrophs than heterotrophs, and more plant-eaters than meat-eaters. Although
there is intense competition between animals, there is also interdependence. When
one species goes extinct, it can affect an entire chain of other species and have
unpredictable consequences.

Equilibrium

As the number of carnivores in a community increases, they eat more and more of
the herbivores, decreasing the herbivore population. It then becomes harder and
harder for the carnivores to find herbivores to eat, and the population of carnivores
decreases. In this way, the carnivores and herbivores stay in a relatively stable
equilibrium, each limiting the other's population. A similar equilibrium exists between
plants and plant-eaters.

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Student Learning Activity 7

1 Give three examples of food chains that exist in nature.

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2 In an ecological pyramid, what happens to energy, biomass and the number of

species as you move up? Why?
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3 What is biomass?
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4 In an ecosystem, can there be more carnivores than herbivores? Why?

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5 What is the 10% rule? What is its significance? Why is energy lost?
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6 What is the difference between food chain and a food web?

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7 Who do the skunks depend on for survival?

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8 Using the same food web, which organism may not increase in population if all
the toads were removed from this ecosystem?
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9 Using the same food web, which organisms would be affected if the deer were
to overproduce?
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10 From the food web, sketch out a food chain.

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UNIT 7.0

NUTRIENT CYCLES

Learning Outcomes

At the end of this Unit, you can:

1 understand the different nutrient cycles

2 understand how nutrients move from the physical environment into living
organisms and back into the physical environment

3 understand the composition of elements of each cycle

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INTRODUCTION

Composting within agricultural systems capitalizes upon the natural services of

nutrient recycling in ecosystems. Bacteria, fungi, insects, earthworms, bugs, and
other creatures dig and digest the compost into fertile soil. The minerals and nutrients
in the soil is recycled back into the production of crops.

A nutrient cycle (or ecological recycling) is the movement and exchange of organic
and inorganic matter back into the production of living matter. The process is
regulated by food web pathways that decompose matter into mineral nutrients.
Nutrient cycles occur within ecosystems. Ecosystems are interconnected systems
where matter and energy flows and is exchanged as organisms feed, digest, and
migrate about. Minerals and nutrients accumulate in varied densities and uneven
configurations across the planet. Ecosystems recycle locally, converting mineral
nutrients into the production of biomass, and on a larger scale they participate in a
global system of inputs and outputs where matter is exchanged and transported
through a larger system of biogeochemical cycles.

Particulate matter is recycled by biodiversity inhabiting the detritus in soils, water

columns, and along particle surfaces (including 'aeolian dust'). Ecologists may refer
to ecological recycling, organic recycling, bio-cycling, cycling, biogeochemical
recycling, natural recycling, or just recycling in reference to the work of nature
whereas the global bio-geochemical cycles describe the natural movement and
exchange of every kind of particulate matter through the living and non-living
components of the Earth. Nutrient cycling refers to the biodiversity within community
food web systems that loop organic nutrients or water supplies back into production.
The difference is a matter of scale and compartmentalization with nutrient cycles
feeding into global biogeochemical cycles. Solar energy flows through ecosystems
along unidirectional and non-cyclic pathways, whereas the movement of mineral
nutrients is cyclic. Mineral cycles include carbon cycle, sulphur cycle, nitrogen cycle,
water cycle, phosphorus cycle, oxygen cycle, among others that continually recycle
along with other mineral nutrients into productive ecological nutrition. Global
biogeochemical cycles are the sum product of localized ecological recycling
regulated by the action of food webs moving particulate matter from one living
generation onto the next. Earths ecosystems have recycled mineral nutrients
sustainably for billions of years.

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7.1 WHAT IS A NUTRIENT CYCLE

It is true that a nutrient cycle (or ecological recycling) is the movement and exchange
of organic and inorganic matter back into the production of living matter. The process
is regulated by food web pathways that decompose matter into mineral nutrients.
Nutrient cycles occur within ecosystems. Ecosystems are interconnected systems
where matter and energy flows and is exchanged as organisms feed, digest, and
migrate about. Minerals and nutrients accumulate in varied densities and uneven
configurations across the planet. Ecosystems recycle locally, converting mineral
nutrients into the production of biomass, and on a larger scale they participate in a
global system of inputs and outputs where matter is exchanged and transported
through a larger system of biogeochemical cycles.

Figure 7.1 A simplified food web illustrating the movement of mineral nutrients through the
food chain, into the mineral nutrient pool, and back into the trophic system illustrates
ecological recycling.

Solar energy flows through ecosystems along unidirectional and non-cyclic pathways,
whereas the movement of mineral nutrients is cyclic. Mineral cycles include carbon
cycle, sulphur cycle, nitrogen cycle, water cycle, phosphorus cycle, oxygen cycle,
among others that continually recycle along with other mineral nutrients into
productive ecological nutrition. Global biogeochemical cycles are the sum product of
localized ecological recycling regulated by the action of food webs moving particulate
matter from one living generation onto the next. Earths ecosystems have recycled
mineral nutrients sustainably for billions of years.

7.2 THE NUTRIENT CYCLE

The nutrient cycle describes how nutrients move from the physical environment into
living organisms, and subsequently is recycled back to the physical environment.
This movement of nutrients, essential for life, from the environment into plants and

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animals and back again, is a vital function of the ecology of any region. In any
particular environment, the nutrient cycle must be balanced and stable if the
organisms that live in that environment are to flourish and be maintained in a
constant population. Currently, large parts of humankind influence the nutrient cycle
in such a way that we remove nutrients from the land and discharge them into
aquatic environments. On the one hand, this leads to soil depletion on the land, and
on the other hand, an overabundance of nutrients and pollution of water sources.

Figure 7.2 The basic nutrient cycle. Source: USDA NRCS & NSTA (2010)

Nutrients – the Fuel of Life

Nutrients are chemical elements that all plants and animals require for growth. On the
earth, there is a constant and natural cycle how these elements are incorporated
when an organism grows, and degraded if an organism dies. The nutrients used in
the largest amounts are the non-mineral elements, i.e. carbon (C), hydrogen (H) and
oxygen (O). These elements are mainly taken up as carbon dioxide (CO 2) from the
air, and water (H2O) by the roots. They make up 95-98% of the mass of all living
beings. But they are, however, not sufficient for life to exist. Further elements are
important to fuel life on earth: Nitrogen (N) and Phosphorus (P), Potassium (K) as
well as Calcium (Ca) and Magnesium (Mg) are highly important, in particular for plant
growth and agriculture. These elements are often referred to as macro nutrients.
Their uptake is about 100 times that of micro nutrients. Further nutrients, that plants
take up in a much smaller amount and that are essentially consumed by humans,
include Boron (Bh), Copper (Cu), Iron (Fe), Chloride (Cl), Manganese (Mn),
Molybdenum (Mo) and Zinc (Zn) and others. These are called micro nutrients.

Natural Nutrient Cycles

These nutrients – essentially chemical elements – are continuously in a circular

movement, the nutrient cycle. The nutrient cycle is hence a general term that
describes how nutrients move from the physical environment into living organisms,
and is subsequently recycled back to the physical environment . Nutrients in the soil
are taken up by plants, which are consumed by humans or animals, and excreted

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again by them - or they are released back into the environment when organisms die
(e.g. plants lose their leaves). Microorganisms in the soil break this matter down, and
again make nutrients available in their mineral form, which makes it possible for
plants to take them up again (see also nutrient requirements of plants).

Essentially, all nutrients that plants and also human beings require to survive are
cycled in this way. In relation to water management and sanitation, it is mainly N, P
and K that are of high priority. They are the most important nutrients to sustain plant
growth and agriculture, and thus humanity.

7.3 WATER CYCLE

Water is always on the move. Rain falling where you live may have been water in the
ocean just days before. And the water you see in a river or stream may have been
snow on a high mountaintop.

Water can be in the atmosphere, on the land, in the ocean, and even underground. It
is recycled over and over through the water cycle. In the cycle, water changes state
between liquid, solid (ice), and gas (water vapor).

Figure 7.3 The Earth's Water Cycle

Source: University Corporation for Atmospheric Research

This cycle is made up of a few main parts:

 evaporation (and transpiration)

 condensation
 precipitation
 collection

Most water vapour gets into the atmosphere by a process called evaporation. This
process turns the water that is at the top of the ocean, rivers, and lakes into water
vapour in the atmosphere using energy from the Sun. Water vapour can also form

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from snow and ice through the process of sublimation and can evaporate from plants
by a process called transpiration.

The water vapour rises in the atmosphere and cools, forming tiny water droplets by a
process called condensation. Those water droplets make up clouds. If those tiny
water droplets combine with each other they grow larger and eventually become too
heavy to stay in the air. Then they fall to the ground as rain, snow, and other types of
precipitation.

Most of the precipitation that falls becomes a part of the ocean or part of rivers, lakes,
and streams that eventually lead to the ocean. Some of the snow and ice that falls as
precipitation stays at the Earth surface in glaciers and other types of ice. Some of the
precipitation seeps into the ground and becomes a part of the groundwater.

Water stays in certain places longer than others. A drop of water may spend over
3,000 years in the ocean before moving on to another part of the water cycle while a
drop of water spends an average of just eight days in the atmosphere before falling
back to Earth.

When water falls back to earth as precipitation, it may fall back in the oceans, lakes
or rivers or it may end up on land. When it ends up on land, it will either soak into the
earth and become part of the ―ground water‖ that plants and animals use to drink or it
may run over the soil and collect in the oceans, lakes or rivers where the cycle starts
all over again.

7.4 CARBON CYCLE

Organic chemicals are made from carbon more than any other atom, so the Carbon
Cycle is a very important one. Carbon between the biological to the physical
environment as it moves through the carbon cycle.

Earth's atmosphere contains 0.035% carbon dioxide, CO2, and the biological
environment depends upon plants to pull carbon into sugars, proteins, and fats.
Using photosynthesis, plants use sunlight to bind carbon to glucose, releasing
oxygen (O2) in the process.
Through other metabolic processes, plants may convert glucose to other sugars,
proteins, or fats. Animals obtain their carbon by eating and digesting plants, so
carbon moves through the biotic environment through the trophic system. Herbivore
eats plants, but are themselves eaten by carnivores.
Carbon returns to the physical environment in a number of ways. Both plants and
animals respire, so they release CO2 during respiration. Luckily for animals, plants
just happen to consume more CO2 through photosynthesis than they can produce.
Another route of CO2 back to the physical environment occurs through the death of
plants and animals. When organisms die, decomposers consume their bodies. In the
process, some of the carbon returns to the physical environment by way of
fossilization. Some of it remains in the biological environment as other organisms eat
the decomposers. But by far, most of the carbon returns to the physical environment
through the respiration of CO2

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Figure 7.4 Simple Carbon Cycle

Carbon is an element. It is part of oceans, air, rocks, soil and all living things. Carbon
doesn‘t stay in one place. It is always on the move!

Figure 7.5 the carbon cycle. Source: NCAR

 Carbon moves from the atmosphere to plants. In the atmosphere, carbon is

attached to oxygen in a gas called carbon dioxide (CO2). With the help of the
Sun, through the process of photosynthesis, carbon dioxide is pulled from the
air to make plant food from carbon.
 Carbon moves from plants to animals. Through food chains, the carbon that is
in plants moves to the animals that eat them. Animals that eat other animals
get the carbon from their food too.
 Carbon moves from plants and animals to the ground. When plants and
animals die, their bodies, wood and leaves decay bringing the carbon into the
ground. Some become buried miles underground and will become fossil fuels
in millions and millions of years.
 Carbon moves from living things to the atmosphere. Each time you exhale,
you are releasing carbon dioxide gas (CO2) into the atmosphere. Animals and
plants get rid of carbon dioxide gas through a process called respiration.
 Carbon moves from fossil fuels to the atmosphere when fuels are burned.
When humans burn fossil fuels to power factories, power plants, cars and
trucks, most of the carbon quickly enters the atmosphere as carbon dioxide
gas. Each year, five and a half billion tons of carbon is released by burning
fossil fuels. That‘s the weight of 100 million adult African elephants! Of the

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huge amount of carbon that is released from fuels, 3.3 billion tons enters the
atmosphere and most of the rest becomes dissolved in seawater.
 Carbon moves from the atmosphere to the oceans. The oceans, and other
bodies of water, soak up some carbon from the atmosphere.

Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and
other greenhouse gases, the Earth would be a frozen world. But humans have
burned so much fuel that there is about 30% more carbon dioxide in the air today
than there was about 150 years ago. The atmosphere has not held this much carbon
for at least 420,000 years according to data from ice cores. More greenhouse gases
such as carbon dioxide in our atmosphere are causing our planet to become warmer.

Carbon moves through our planet over longer time scales as well. For example, over
millions of years weathering of rocks on land can add carbon to surface water which
eventually runs off to the ocean. Over long time scales, carbon is removed from
seawater when the shells and bones of marine animals and plankton collect on the
sea floor. These shells and bones are made of limestone, which contains carbon.
When they are deposited on the sea floor, carbon is stored from the rest of the
carbon cycle for some amount of time. The amount of limestone deposited in the
ocean depends somewhat on the amount of warm, tropical, shallow oceans on the
planet because this is where prolific limestone-producing organisms such as corals
live. The carbon can be released back to the atmosphere if the limestone melts or is
metamorphosed in a subduction zone.

7.5 NITROGEN CYCLE

The Importance of Nitrogen and the Nitrogen Cycle

Nitrogen is an important component of all proteins, and thus is vital to all plant and
animal life. Just as plants are vital because of their ability to convert carbon dioxide
and water into plant organic matter (food for animals) in the carbon cycle, they are
also vital because of their ability to convert inorganic nitrogen in the soil into organic
nitrogen (plant proteins).

Figure 7.6 Simple Nitrogen Cycle

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The cycle of processes that is called the simple nitrogen cycle in this article consists
of dead, decaying organic nitrogen breaking down to release ammonia, which is
oxidized by microbes to nitrite and then to nitrate, which can be taken up by plants to
produce organic nitrogen again.

An additional route for creation of organic nitrogen from inorganic nitrogen is fixation
of atmospheric nitrogen by the class of plants called legumes. This process and the
conversions between nitrogen gas and the other forms of nitrogen will be added in to
create the more comprehensive nitrogen cycle diagram also presented in this article.

The Many Different Forms of Nitrogen

Nitrogen may well have the distinction of being the element that can exist in the
greatest number of different oxidation states. There are nitrogen species with nine
different oxidation states, having all the possible oxidation states (valences) from -3
to +5, as shown in the table below. Three of these nine species of nitrogen
(ammonia, nitrate, and nitrite) are included in an easy diagram of the nitrogen cycle
illustrating a simple nitrogen cycle in the next section. A fourth species, nitrogen gas,
is included in the more comprehensive nitrogen cycle diagram in the following
section.
In addition to the importance of the simple nitrogen cycle in making continuous
creation of plant protein possible, some of the conversions are important in
wastewater treatment, when ammonia and/or nitrate are present in the wastewater.
Some of the other species (nitrous oxide, nitric oxide, and nitrogen dioxide) have
another environmental engineering application, because they are important reactants
in the type of air pollution known as photochemical smog.
The simple diagram of the nitrogen cycle shown in two versions here (and above) is
for the simple nitrogen cycle that applies to plants other than legumes. It involves
ammonia, nitrite, nitrate, and protein.

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Figure 7.7 Simple Nitrogen Cycle

We can start consideration of this simple nitrogen cycle with any of the nitrogen
species, as for example, with nitrate in the soil serving as fertilizer for plant growth.
The inorganic nitrate is taken up by the plants and used to synthesize proteins. The
plants either serve as food for animals, with the plant protein thus becoming animal
protein, or else the plants eventually die and become dead organic matter. Animals
give off waste containing protein and ammonia and at some time they die and
become dead organic matter. Dead organic matter will typically be oxidized by
aerobic bacteria converting the carbon, hydrogen, and oxygen to carbon dioxide and
water, and releasing ammonia from the proteins. Ammonia is oxidized to nitrite ion by
nitrosomonas bacteria and nitrite is oxidized to nitrate by nitrobacter bacteria. This
takes us back to the beginning with the nitrate available to be utilized by growing
plants.

7.6 ENVIRONMENTAL PROBLEMS

Air Pollution
Air pollution means the presence of one or more unwanted substances in air. Air
pollutants have a negative impact on humans, animals and plants, and on air quality.

The most frequently present categories of air pollutants are sulphur oxides, nitrogen
oxides, Volatile Organic Compounds (VOC) and small dust particles (aerosols).
The main sources of air pollution are the industries, agriculture and traffic, as well as
energy generation. During combustion processes and other production processes air
pollutants are emitted. Some of these substances are not directly damaging to air
quality, but will form harmful air pollutants by reactions with other substances that are
present in air. Examples of large-scale air pollutants are VOC (Volatile Organic
Compounds) and small dust particles. When large concentrations of these
substances are emitted this negatively affects ecosystems, materials and public
health.

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The Importance of Air

Other planets have sunlight, but the Earth is the only planet we know that has air and
water. Without air and water, the Earth would be unable to sustain life.
A diverse community of plant and animal life has thrived on this planet for millions of
years, sustained by the sun and supported by the soil, water and air.
Definition of air pollution
Air pollution occurs when the air contains gases, dust, fumes or odour in harmful
amounts. That is, amounts which could be harmful to the health or comfort of humans
and animals or which could cause damage to plants and materials.
The substances that cause air pollution are called pollutants. Pollutants that are
pumped into our atmosphere and directly pollute the air are called primary pollutants.
Primary pollutant examples include carbon monoxide from car exhausts and sulphur
dioxide from the combustion of coal.
Further pollution can arise if primary pollutants in the atmosphere undergo chemical
reactions. The resulting compounds are called secondary pollutants. Photochemical
smog is an example of this.
More about pollutants
Air pollutants mainly occur as a result of gaseous discharges from industry and motor
vehicles. There are also natural sources such as wind-blown dust and smoke from
fires.
Some forms of air pollution create global problems, such as upper atmosphere ozone
depletion and global warming. These problems are very complex, and require
international cooperative efforts to find solutions.
The table below gives you more detailed information about air pollutants, their sources and how they
affect humans.

Pollutant Source Human Health Effects

 Internal combustion Long term exposure is linked to:
engines (e.g., cars and trucks);  Lung Cancer;
Particles (API) - Air  Industry (e.g., factories);  Heart Disease;
Particle Index  Burning wood;  Lung Disease;
 Cigarette smoke; and  Asthma Attacks; and Other health
Bushfires. problems.
Motor Vehicles are the biggest Exposure to high levels of NO2 may
contributors; lead to:
Other combustion processes;  Lung damage; or
Nitrogen Dioxide
 Respiratory Disease.
(NO2)
It has also been linked to:
 Increased hospital admissions for
asthma and respiratory problems;
Increased mortality.
Formed by various complex Ozone affects the
chemical reactions involving the  lining of the lungs;
Ozone (O3)
exposure of the oxides of  lining of the respiratory tract; and
nitrogen and some hydro-  causes eye irritation.
carbons.

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Ozone is the main ingredient of Ozone also damages plants, buildings

photochemical smog in summer and other materials.
and early autumn.
Motor vehicle exhaust and When inhaled Carbon Monoxide
burning of materials such as enters the bloodstream and disrupts
Carbon Monoxide
coal, oil and wood. It is also the supply of oxygen to the body‘s
(CO)
released from industrial tissues.
processes and waste A range of health effects may result
incineration depending on the extent of exposure.
Is largely derived from the Lead retards learning in children and
combustion of lead additives in the development of their nervous
motor fuels as well as lead system;
smelting. Lead affects almost every organ in the
Lead pollution from vehicle body, whether it is inhaled or
emissions is declining due to the ingested. Young children are
Lead (Pb)
introduction of unleaded fuels particularly susceptible.
and reductions in lead levels in
leaded fuel.
Other atmospheric sources of
lead include waste incineration
and renovation of old houses
(from leaded paint).
Most fuel combustion processes Exposure can cause headaches or
result in the release of hydro nausea, while some compounds may
Hydro-carbons (HC) - carbons to the environment. The cause cancer. Some may also
chemical compounds largest fuel sources are natural gas damage plants.
composed of and petrol. Note that hydrocarbons
Hydrogen and Carbon can enter the environment both as
atoms evaporative emissions from vehicle
fuel systems, or in exhaust
emissions or as a component of the
smoke from wood fires.

Historical explanation

In the days before the proliferation of large cities and industry, nature's own systems
kept the air fairly clean. Wind mixed and dispersed the gases, rain washed the dust
and other easily dissolved substances to the ground and plants absorbed carbon
dioxide and replaced it with oxygen.

With increasing urbanisation and industrialisation, humans started to release more

wastes into the atmosphere than nature could cope with.

Since then, more pollution has been added to the air by industrial, commercial and
domestic sources. As these sources are usually found in major cities, the gases that
are produced are usually concentrated in the air around them. The adverse effects of
air pollution were graphically illustrated in London in 1952 when, in just a few days,
an estimated 4000 people died from effects of fine particle pollution.

It is when these concentrated gases exceed safe limits that we have a pollution
problem. Nature can no longer manage air pollution without our help.

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7.7 GREENHOUSE EFFECT

The sun radiates solar energy on earth. The larger part of this energy (45%) is
radiated back into space. Greenhouse gases in the atmosphere contribute to global
warming by adsorption and reflection of atmospheric and solar energy. This natural
phenomenon is what we call the greenhouse effect. It is agreed that the greenhouse
effect is correlated with global temperature change. If greenhouse gases would not
exist earthly temperatures would be below -18oC. After the industrial revolution of the
1700‘s the greenhouse effect was enhanced by greenhouse gas emissions of
anthropogenic nature. The main source of anthropogenic greenhouse gas emissions
is fossil fuel combustion. The contribution of greenhouse gases to the greenhouse
effect varies. The enhanced greenhouse effect is said to cause a cascade of impacts
on both environment and society. How and when these effects will take place is still
under discussion.

Greenhouse gases

The greenhouse effect is the process by which absorption and emission of infrared
radiation by gases in the atmosphere warm a planet's lower atmosphere and surface.

Bubble diagram showing the share of global cumulative energy-related carbon

dioxide emissions for major emitters between 1890 and 2007.

Figure 7.8 Annual world greenhouse gas emissions, in 2005, by sector

Source: USA: World Resources Institute

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Naturally occurring amounts of greenhouse gases have a mean warming effect of

about 33°C (59°F). The major greenhouse gases are water vapour, which causes
about 36–70% of the greenhouse effect; carbon dioxide (CO2), which causes 9–26%;
methane (CH4), which causes 4–9%; and ozone (O3), which causes 3–7%. Clouds
also affect the radiation balance through cloud forcings similar to greenhouse gases.

Human activity since the Industrial Revolution has increased the amount of
greenhouse gases in the atmosphere, leading to increased radioactive forcing from
CO2, methane, tropospheric ozone, CFCs and nitrous oxide. The concentrations of
CO2 and methane have increased by 36% and 148% respectively since 1750. These
levels are much higher than at any time during the last 800,000 years, the period for
which reliable data has been extracted from ice cores. Less direct geological
evidence indicates that CO2 values higher than this were last seen about 20 million
years ago. Fossil fuel burning has produced about three-quarters of the increase in
CO2 from human activity over the past 20 years. The rest of this increase is caused
mostly by changes in land-use, particularly deforestation.

Global Warming

Global warming is the rise in the average temperature of Earth's atmosphere and
oceans since the late 19th century and its projected continuation. Since the early
20th century, Earth's mean surface temperature has increased by about 0.8°C
(1.4°F), with about two-thirds of the increase occurring since 1980. Warming of the
climate system is unequivocal, and scientists are more than 90% certain that it is
primarily caused by increasing concentrations of greenhouse gases produced by
human activities such as the burning of fossil fuels and deforestation.

There are many gases which contribute to global warming. Some have a more potent
effect than others. The number after the name indicates the equivalent greenhouse
gas effect compared to carbon dioxide (the principal man-made greenhouse gas):

 Water vapour (H2O) = ?

 Carbon dioxide (CO2) = 1
 Methane (CH4) = 21
 Nitrous oxide (N2O) = 298
 Sulphur Hexafluoride (SF6) = 22,200
 Chlorinated fluorocarbons (CFC's) = 1000 to 9000

Water vapour is an odd one in the list. It contributes to global warming because as
the atmosphere warms (from CO2 and the other greenhouse gases) the warmer
atmosphere is able to hold more water vapour, which in turn captures more heat,
thus adding to the warming through the feedback effect. Most models though ignore
the cooling effect that is also associated with water vapour.

The forcing numbers for all significant green houses gases are as follows:

 water vapour 36-72%

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 carbon dioxide 9-26%

 methane 4-9%
 ozone 3-7%

7.8 CLIMATE CHANGE

Climate change is the consequence of unchecked pollution. When carbon emissions

caused by human activity enter the air they have dangerous effects on the
environment, the economy, and our wellbeing. But just as humans cause it, we can
halt its progress.

Causes of climate change

Climate change is caused by trapping excess carbon in Earth‘s atmosphere. This

trapped carbon pollution heats up, altering the Earth's climate patterns. The largest
source of this pollution is the burning of fossil fuels (such as coal and oil) for energy.

While carbon has entered the atmosphere for millions of years through natural events
such as forest fires and volcanoes, the burning of fossil fuels and clearing of land has
resulting in the highest levels of greenhouse pollution in our atmosphere in the last
800,000 years.

Why it is getting warmer?

The Earth‘s atmosphere has evolved to retain sufficient warmth from the sun to
encourage a healthy, dynamic ecosystem, while shielding us from its harsher effects.
The introduction of huge amounts of excess pollutants thickens this blanket of
protective gases, causing heat to remain trapped within, rather than harmlessly
escaping skywards. These gases can remain in our atmosphere for up to 90 years,
contributing to long-term warming.

As the world warms, there are flow-on effects that can make things worse. For
instance, warmer water melts polar ice caps each summer. Sea ice normally reflects
heat from the sun, while water absorbs it. Less ice means more heat which in turn
means less ice, leading to a cycle of warming from which it is hard to escape.
Temperatures are already rising quickly, with the last decade being the hottest on
record.

Why this is bad?

Decades of climate science has found that if we fail to reduction carbon pollution,
climate change will have profound impacts on our planet. Climate change isn‘t just a
temperature change.

Sea level rise affects coastal property, people and ecosystems. By 2050 and a 4°C
or 0.48m sea-level rise, 130 million people per year are expected to be flooded, 3/4
of them in Asia.

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Warming also affects rainfall and seasons. This in turn threatens food security.
Inaction in cutting emissions and a temperature increase of just 4°C would cause rice
and maize yields in Asia to drop by 30%, cutting off food supply to millions. Warming
also increases the severity of extreme weather events such as tropical cyclones,
bushfires, droughts and flooding.

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SUMMARY
A nutrient cycle (or ecological recycling) is the movement and exchange
of organic and inorganic matter back into the production of living matter. The process
is regulated by food web pathways that decompose matter into mineral nutrients.
Nutrient cycles occur within ecosystems. Ecosystems are interconnected systems
where matter and energy flows and is exchanged as organisms feed, digest, and
migrate about. Minerals and nutrients accumulate in varied densities and uneven
configurations across the planet. Ecosystems recycle locally, converting mineral
nutrients into the production of biomass, and on a larger scale they participate in a
global system of inputs and outputs where matter is exchanged and transported
through a larger system of biogeochemical cycles.

Particulate matter is recycled by biodiversity inhabiting the detritus in soils, water

columns, and along particle surfaces(including 'aeolian dust'). Ecologists may refer to
ecological recycling, organic recycling, biocycling, cycling, biogeochemical recycling,
natural recycling, or just recycling in reference to the work of nature. Whereas
the global biogeochemical cycles describe the natural movement and exchange of
every kind of particulate matter through the living and non-living components of the
Earth, nutrient cycling refers to the biodiversity within community food web systems
that loop organic nutrients or water supplies back into production. The difference is a
matter of scale and compartmentalization with nutrient cycles feeding into global
biogeochemical cycles. Solar energy flows through ecosystems along unidirectional
and noncyclic pathways, whereas the movement of mineral nutrients is cyclic.
Mineral cycles include carbon cycle, sulfur cycle, nitrogen cycle, water cycle,
phosphorus cycle, oxygen cycle, among others that continually recycle along with
other mineral nutrients into productive ecological nutrition. Global biogeochemical
cycles are the sum product of localized ecological recycling regulated by the action of
food webs moving particulate matter from one living generation onto the next. Earths
ecosystems have recycled mineral nutrients sustainably for billions of years.

The nutrient cycle is nature's recycling system. All forms of recycling have feedback
loops that use energy in the process of putting material resources back into use.
Recycling in ecology is regulated to a large extent during the process
of decomposition. Ecosystems employ biodiversity in the food webs that recycle
natural materials, such as mineral nutrients, which includes water. Recycling in
natural systems is one of the many ecosystem services that sustain and contribute to
the well-being of human societies.

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A nutrient cycle of a typical terrestrial ecosystem

There is much overlap between the terms for biogeochemical cycle and nutrient
cycle. Most textbooks integrate the two and seem to treat them as synonymous
terms. However, the terms often appear independently. Nutrient cycle is more often
used in direct reference to the idea of an intra-system cycle, where an ecosystem
functions as a unit. From a practical point it does not make sense to assess a
terrestrial ecosystem by considering the full column of air above it as well as the
great depths of Earth below it. While an ecosystem often has no clear boundary, as a
working model it is practical to consider the functional community where the bulk of
matter and energy transfer occurs. Nutrient cycling occurs in ecosystems that
participate in the "larger biogeochemical cycles of the earth through a system of
inputs and outputs."

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Student Learning Activity 8

1 List the major components of the following:

A Nutrient Cycle
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B Nitrogen Cycle
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C Carbon Cycle
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D Water Cycle
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2 What are the 3 processes of water cycle?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

3 Why are bacteria important components of the Nitrogen Cycle?

___________________________________________________________________
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___________________________________________________________________

4 What are the main greenhouse gases causing global warming?

___________________________________________________________________
___________________________________________________________________
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5 What is global warming?

___________________________________________________________________
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6 What is air pollution?

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UNIT 8.0

POPULATION

Learning Outcomes

At the end of this Unit, you can:

1 define and explain population

2 explain the different capacity of investigating the population size

3 review the structure and growth rate of population

4 use and read different population graphs

5 describe models that describe the characteristics of a population

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INTRODUCTION

Population biology is a study of populations of organisms, especially the regulation of

population size, life history traits such as clutch size, and extinction. The term
population biology is often used interchangeably with population ecology, although
'population biology' is more frequently used when studying diseases, viruses, and
microbes, and 'population ecology' is used more frequently when studying plants and
animals.

Although Reverend Malthus's book, An Essay on the Principle of Population, dealt

only with the economy of human population fluctuations, which he theorized as being
related to finite food resources, abundance and decadence, it gave inspiration to
Charles Darwin for the theoretical basis of his seminal work, The Origin of Species.

"In October 1838, that is, fifteen months after I had begun my systematic
inquiry, I happened to read for amusement Malthus on Population, and
being well prepared to appreciate the struggle for existence which
everywhere goes on from long- continued observation of the habits of
animals and plants, it at once struck me that under these circumstances
favourable variations would tend to be preserved, and unfavourable ones to
be destroyed. The results of this would be the formation of a new species.
Here, then I had at last got a theory by which to work; but I was so anxious
to avoid prejudice, that I determined not for some time to write even the
briefest sketch of it. In June 1842 I first allowed myself the satisfaction of
writing a very brief abstract of my theory in pencil in 35 pages; and this was
enlarged during the summer of 1844 into one of 230 pages, which I had
fairly copied out and still possess."
Charles Darwin, from his autobiography. (1876), pp34–35

A population is all the organisms of the same group or species who live in the same
geographical area and are capable of interbreeding. In ecology the population of a
certain species in a certain area is estimated using the Lincoln Index. The area that is
used to define a sexual population is such that inter-breeding is possible between
any pair within the area and more probable than cross-breeding with individuals from
other areas. Normally breeding is substantially more common within the area than
across the border.

In sociology, population refers to a collection of human beings. Demography is a

social science which entails the statistical study of human populations. This article
refers mainly to human population.

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8.1 WHAT IS POPULATION?

The word 'population' has a few different meanings:

1 the people who inhabit a territory or state;

2 a group of organisms of the same species inhabiting a given area;
3 the act of populating (causing to live in a place);
4 the number of inhabitants (either the total number or the number of a particular
race or class) in a given place (country or city etc.);
5 (statistics) the entire aggregation of items from which samples can be drawn

One of the most fundamental problems faced by community and population

ecologists is that of measuring population sizes and distributions. These data are
important for comparing differences between communities and species. They are
necessary for impact assessments (measuring effects of disturbance) and restoration
ecology (restoring ecological systems). They are also used to set harvest limits on
commercial and game species (e.g. fish, deer, etc.).

In most cases it is either difficult or simply not possible to census all of the individuals
in the target area. The only way around this problem is to estimate population size
using some form of sampling technique. There are numerous types of sampling
techniques. Some are designed for specific types of organisms (e.g. plants vs. mobile
animals). As well there are numerous ways of arriving at estimates from each
sampling technique. All of these procedures have advantages and disadvantages. In
general, the accuracy of an estimate depends on:

1 the number of samples taken,

2 the method of collecting the samples,
3 the proportion of the total population sampled.

Sampling is viewed by statistical ecologists as a science in its own right. In most

cases, the object is to collect as many randomly selected samples as possible (so as
to increase the proportion of the total population sampled). The accuracy of an
estimate increases with the number of samples taken. This is because the number of
individuals found in any given sample will vary from the number found in other
samples. By collecting numerous samples, the effect of these variations can be
averaged out. The purpose for collecting the samples randomly is to avoid biasing
the data. Data become biased when individuals of some species are sampled more
frequently, or less frequently, than expected at random. Such biases can cause the
population size to be either over estimated or under estimated, and can lead to
erroneous estimates of population size.

Population size generally refers to the number of individuals present in the population,
and is self-explanatory. Density refers to the number of individuals in a given area.
For ecologists density is usually a more useful measure. This is because density is
standardized per unit area, and therefore, can be correlated with environmental
factors or used to compare different populations.

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The spatial distribution of a population is a much more complicated matter. Basically,

there are three possible types of spatial distributions (dispersions) (see diagrams
below). In a random dispersion, the locations of all individuals are independent of
each other. In a uniform dispersion, the occurrence of one individual reduces the
likelihood of finding another individual nearby. In this case the individuals tend to be
spread out as far from each other as possible. In a clumped dispersion, the
occurrence of one individual increases the likelihood of finding another individual
nearby. In this case, individuals tend to form groups (or clumps).

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Random Clumped Uniform

Ecologists are often interested in the spatial distribution of populations because it

provides information about the social behaviour and/or ecological requirements of the
species. For example, some plants occur in clumped distributions because they
propagate by rhizomes (underground shoots) or because seed dispersal is limited.
Clumped distributions in plants may also occur because of slight variations in soil
chemistry or moisture content. Many animals exhibit rather uniform distributions
because they are territorial (especially birds), expelling all intruders from their
territories. Random distributions are also common, but their precise cause is more
difficult to explain.

Unfortunately, it is often difficult to visually assess the precise spatial distribution of a

population. Furthermore, it is often useful to obtain some number (quantitative
measure) that describes spatial distribution in order to compare different populations.
For this reason, there are a variety of statistical procedures that are used to describe
spatial distributions.

Communities are assemblages of many species living in a common environment.

Interactions between species can have profound influences of their distributions and
abundances. Comprehensive understanding of how species interact can contribute to
understanding how the community is organized. One way to look at species
interactions is to evaluate the level of association between them. Two species are
said to be positively associated if they are found together more often than expected
by chance. Positive associations can be expected if the species share similar
microhabitat needs or if the association provides some benefit to one
(commensalisms) or both (mutualism) of the species involved. Two species are
negatively associated if they are found together less frequently than expected by
chance. Such a situation can arise if the species have very different microhabitat
requirements, or if one species, in some way, inhibits the other. For example, some

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plants practice allelopathy, the production and release of chemicals that inhibit the
growth of other plant species. Allelopathy results in a negative association between
the allelopathic species and those species whose growth is inhibited.

In human biology, the whole number of inhabitants occupying an area (such as a

country or the world) and continually being modified by increases (births and
immigrations) and losses (deaths and emigrations). As with any biological population,
the size of a human population is limited by the supply of food, the effect of diseases,
and other environmental factors. Human populations are further affected by social
customs governing reproduction and by the technological developments, especially
in medicine and public health that have reduced mortality and extended the life span.

Figure 8.1 Population Structure - Developing Countries

However, it is seen, population may be generally defined as a group of individuals of

the same species occupying a particular geographic area. Populations may be
relatively small and closed, as on an island or in a valley, or they may be more diffuse
and without a clear boundary between them and a neighbouring population of the
same species. For species that reproduce sexually, the members of a population
interbreed either exclusively with members of their own population or, where
populations integrate, to a greater degree than with members of other populations.

8.2 POPULATION STRUCTURE

The population structure of a country is how it is made up of people of different ages,

and of males and females. The common method to show the structure is by a
population pyramid. This diagram is made up by putting two bar graphs (one for male,
one for female) side by side (See figure 8.2). From this you can read off what
percentage of a population is of a certain gender and age range. In the example
below about 3% of the population are females aged between 60 and 64.

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This population pyramid is wide at the base, which means there are a large
proportion of young people in the country. It tapers very quickly as you go up into the
older age groups, and is narrow at the top. This shows that a very small proportion of
people are elderly.

This shape of pyramid is typical of a developing country, such as Papua New Guinea,
Kenya or Vietnam.

Figure 8.2 Population Structure - Developed Countries

This shape is typical of a developed country. It is narrow at the base, wider in the
middle, and stays quite wide until the very top, as there is a sizable percentage of
older people. Note that there are more old women than men. Italy and Japan have
population structures that are of this shape.

8.3 INVESTIGATING POPULATION

In studying population, it is easier studying plant populations than animal for the
reason that plants do not migrate (from place to place). Ecologist need to know the
estimated size of the populations and how the sizes change over time. Population
often remains stable but changes over time due to many other reasons or
circumstances. Some of these reasons or circumstances are:

 migration
 change in the climate
 pollution
 habitat destruction
 introduction of new species

When ecologists know that the population of plants has been affected by human
activity then it is possible to introduce some management scheme to prevent the
extinction of the species or further destruction.

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The size of population is determined by the rate of input; that is number of births,
immigration and introduction of new species) and output; that is deaths, emigration
and destruction. The physiological and the behavioural abilities of the individual
species in the environment determine the birth and death rates of the species.

8.4 POPULATION SIZE

There are two ways the measuring the population size; the first being the use of
quadrates and the second is capture and re-capture methods.

The quadrat method is used primarily in studies of plant populations, or where

animals are immobile. The principal assumptions of this technique are that the
quadrats are chosen randomly, the organisms do not move from one quadrat to
another during the census period, and that the samples taken are representative of
the population as a whole. It is often conducted by dividing the census area into a
grid. Each square within the grid is known as a quadrat and represents the sample
unit. Quadrats are chosen at random by using a random number generator or a
random number table to select coordinates. The number of individuals of the target
species is then counted in each of the chosen quadrats.

Quadrate is a square-frame used to mark out an area in which the plants and animals
are to be studied. The area can be from 50 cm sides to string square with 10 m sides
for sampling grass or tress in the forest area. Quadrates are used to estimate the
total population of a species in a given area and to estimate it percentage area cover.

Figure 8.3 showing a quadrate of three species

To calculate the percentage coverage of the species w, x, and y, use the following
formula:

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For example:

Species w = 10, Species x =9, Species y = 8

Therefore, 33% of species x is found in the 4 m by 4 m quadrate. The second method

is mostly used in determining the population of animals because they have the ability
to move far and wide. It is widely used in the ringing of birds and tagging of fish and
mammals. Here a fixed amount of time is used to catch individuals of the same
species of animals. Each individual is then marked in a suitable way, so that it can be
identified at a later time.

For example, the shells of snails, beetles or grasshoppers can be marked with a spot
of paint, and then released into their habitat. After a certain period of time, a sample
of these animals is caught or captured randomly. Upon checking the captured, some
will be marked and others will be unmarked. Therefore, to be able to calculate the
size of the population, the following formula can be used:

Worked example:

In a given habitat 25 beetles were captured, marked and released. After 6 months
some beetles numbering 35 were captured marked and released again the second
time from the same habitat. After a further 3 months, some 20 snails with marked
shells were captured.

Using the above formula, calculate the size of the population:

TP = T1 x T2
T2M
= 25 x 35
20
= 44

Therefore, the size of population is 44.

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8.5 POPULATION GROWTH

Taking quadrates and the capture - recapture method are two simple methods or
ways of estimating the number of individuals that make up the population of a
particular plant or animal species living in the area or habitat. In a natural
environment the size of a population remains about over long period of time although
there may be changes over short periods of time. When the population increases in
size, this is known as population growth.

If populations are able to grow without being controlled by death, food supply,
competition and diseases, then they would soon reach very large sizes. Population
growth increased significantly as the Industrial Revolution gathered pace from 1700
onwards. The last 50 years have seen a yet more rapid increase in the rate of
population growth due to medical advances and substantial increases in agricultural
productivity, particularly beginning in the 1960s, made by the Green Revolution. In
2007 the United Nations Population Division projected that the world's population will
likely surpass 10 billion in 2055.

In the future, world population has been expected to reach a peak of growth, then it
will decline due to economic reasons, health concerns, land exhaustion and
environmental hazards. According to one report, it is very likely that the world's
population will stop growing before the end of the 21st century. Further, there is some
likelihood that population will actually decline before 2100. Population has already
declined in the last decade or two in Eastern Europe, the Baltics and in the
Commonwealth of Independent States.

The population pattern of less-developed regions of the world in recent years has
been marked by gradually declining birth rates. These followed an earlier sharp
reduction in death rates. This transition from high birth and death rates to low birth
and death rates is often referred to as the demographic transition.

Figure 8.4 Predicted growth and decline

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Birth rates, death rates, immigration and emigration

All species of living things; new individuals must be born and older species must die.
This process or the rate at which new species are born is known as the birth rate,
while the rate at which the older species die out is known as the death rate. In some
text books the birth rate is referred to as natality while the death rate is referred to as
mortality. Whichever term is used, they mean the same, and these rates are
expressed in percentages.

If it is reported that the birth rate for a particular species of organism was 5% per year,
then, it simply means that 5 more individuals of the species was born and added to
the population for every 100 individuals in the original total population. Hence, the
original population is increased by 5 from the original 100 to 105 as the new total
population. While the death rate of the same population was 2% per year, means that
two (2) individuals died out of every 100 individuals.

In most cases, generally the birth rate is normally higher than the death rate in most
species populations. This results in more individuals being added to the population
than being lost through deaths of the species. Therefore, the overall number of
individuals within that population increases resulting in the population growth.
Nevertheless, the growth of a population also depends on the number of animals that
are entering or leaving a particular habitat of the species. The movement of
individuals from one habitat to another is called migration. Naturally, there are two
types of migration: Immigration occurs when one species of animal moves into the
population while emigration occurs when species of animal moves out of the
population. The net migration is the difference between immigration and emigration of
individuals of the species in a particular population of a particular habitat.

Therefore, the following formulae can be used to calculate different characteristics

(growth rate, death rate, net migration and birth rate) of a population.

Population Distribution

Populations of organisms (animal) are found in specific habitats. However, the

distribution or spread of individuals throughout the area is not always even. It

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depends largely on the types of environmental conditions present in that specific area.
The spread of plant population within a given area will be dependent on abiotic
environmental factors like sunlight, water, soil nutrients and temperature.

Natural disasters like droughts, landslides, frosts, bush fires and floods etc affect
population numbers and sizes in those areas. In any given natural environment it is
not usually possible to say whether changes in the numbers and sizes of populations
are mainly due to one particular factor as there are many possible factors that may
be responsible for those changes.

Population Density

Some of the factors that affect the sizes of populations have already been described.
Simply knowing the size of a population in not so useful, but some form of
comparison of size of population of various species from time to time is needed to
monitor the movement of the species population.
Population Density refers to the total number of individuals of a particular species in a
given unit area. Population density makes comparisons of population sizes in
different places or areas or even time to time in the same area much more useful.

For example: it is possible to relate the number of frogs to the number of beetles in a
particular area or the number of caterpillars to the percentage cover of cabbages at
different times.

To calculate the population density, the following information is vital: the total number
of individuals in a particular population and the total area coverage by the population.
Once the information is known, the following formula is used:

Example:

A fish pond of 200 square metres has 4000 fish in it. What is the population density?

4000
200
20 fish per square metre

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Population genetics

In population genetics a sexual population is a set of organisms in which any pair of

members can breed together. This means that they can regularly exchange gametes
to produce normally-fertile offspring, and such a breeding group is also known
therefore as a gamodeme. This also implies that all members belong to the same of
species, such as humans. If the gamodeme is very large (theoretically, approaching
infinity), and all gene alleles are uniformly distributed by the gametes within it, the
gamodeme is said to be panmictic.

Unfortunately, this seldom occurs in nature: localisation of gamete exchange –

through dispersal limitations, or preferential mating, or cataclysm, or other cause –
may lead to small actual gamodemes which exchange gametes reasonably uniformly
within themselves, but are virtually separated from their neighbouring gamodemes.
However, there may be low frequencies of exchange with these neighbours. This
may be viewed as the breaking up of a large sexual population (panmictic) into
smaller overlapping sexual populations. This failure of panmixia leads to two
important changes in overall population structure: (1).the component gamodemes
vary (through gamete sampling) in their allele frequencies when compared with each
other and with the theoretical panmictic original (this is known as dispersion, and its
details can be estimated using expansion of an appropriate binomial equation); and
(2). the level of homozygosity rises in the entire collection of gamodemes. It is most
important to note, however, that some dispersion lines will be superior to the
panmictic original, while some will be about the same, and some will be inferior.

In plant and animal breeding, procedures have been developed which deliberately
utilise the effects of dispersion (such as line breeding, pure-line breeding, back-
crossing). It can be shown that dispersion-assisted selection leads to the
greatest genetic advance (ΔG = change in the phenotypic mean), and is much more
powerful than selection acting without attendant dispersion. This is so for both
allogamous (random fertilization) and autogamous (self-fertilization) gamodemes.

Predicted growth and decline

As of today's date, the world population is estimated by the United States Census
Bureau to be 7.102 billion. The US Census Bureau estimates the 7 billion number
was surpassed on 12 March 2012. According to a separate estimate by the United
Nations, Earth‘s population exceeded seven billion in October 2011, a milestone that
offers unprecedented challenges and opportunities to all of humanity, according
to UNFPA, the United Nations Population Fund, July 6, 2013 - Latest Overpopulation
Statistics 31.12.2012, 24:00 h: 8,301,283,002

According to papers published by the United States Census Bureau, the world
population hit 6.5 billion on 24 February 2006. The United Nations Population
Fund designated 12 October 1999 as the approximate day on which world population
reached 6 billion. This was about 12 years after world population reached 5 billion in
1987, and 6 years after world population reached 5.5 billion in 1993. The population

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of some countries, such as Nigeria, is not even known to the nearest million, so there
is a considerable margin of error in such estimates.

Population growth increased significantly as the Industrial Revolution gathered pace

from 1700 onwards. The last 50 years have seen a yet more rapid increase in
the rate of population growth due to medical advances and substantial increases in
agricultural productivity, particularly beginning in the 1960s, made by the Green
Revolution. In 2007 the United Nations Population Division projected that the world's
population will likely surpass 10 billion in 2055.

In the future, the world's population is expected to peak after which it will decline due
to economic reasons, health concerns, land exhaustion and environmental hazards.
According to one report, it is very likely that the world's population will stop growing
before the end of the 21st century. Further, there is some likelihood that population
will actually decline before 2100. Population has already declined in the last decade
or two in Eastern Europe, the Baltics and in the Commonwealth of Independent
States.

The population pattern of less-developed regions of the world in recent years has
been marked by gradually declining birth rates. These followed an earlier sharp
reduction in death rates. This transition from high birth and death rates to low birth
and death rates is often referred to as the demographic transition.

Control

Human population control is the practice of artificially altering the rate of growth of a
human population. Historically, human population control has been implemented by
limiting the population's birth rate, usually by government mandate, and has been
undertaken as a response to factors including high or increasing levels
of poverty, environmental concerns, religious reasons, and over population. While
population control can involve measures that improve people's lives by giving them
greater control of their reproduction, many programs have exposed them to
exploitation.

Worldwide, the population control movement was active throughout the 1960s and
1970s, driving many reproductive health and family planning programs. In the 1980s,
tension grew between population control advocates and women's health activists
who advanced women's reproductive rights as part of a human rights-based
approach. Growing opposition to the narrow population control focus led to a
significant change in population control policies in the early 1990s.

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SUMMARY

In sociology, population refers to a collection of human beings. Demography is

a social science which entails the statistical study of human populations.
A population is a summation of all the organisms of the same group or species, that
live in the same geographical area, and has the capability of interbreeding. In
ecology the population of a certain species in a certain area is estimated using the
Lincoln Index. The area that is used to define a sexual population is defined as the
area where inter-breeding is potentially possible between any pair within the area.
The probability of interbreeding is greater than the probability of cross-breeding with
individuals from other areas. Under normal conditions, breeding is substantially more
common within the area than across the border.

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Student Learning Activity 9

1 What is a population?
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2 Why do you need to know who or what are in a population?

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3 When is a population identified?

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UNIT 9.0

EVOLUTION

Learning Outcomes

At the end of this Unit, you can:

1 State the scientific basis of the origin of life.

2 outline the Charles Darwin‘s theory of evolution.

3 describe the mechanisms and evidence of evolution.

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INTRODUCTION

Have you ever wondered how life on earth began? There are many different kinds of
plants and animals on Earth. Have they always been there? If not, how did they get
there? Have they always been the same or have they changed? The only honest
answer to these questions is that we don‘t know and will probably never know for
sure.

Most scientists believed that organisms present in the world today originate from
some simpler forms in an earlier age. These organisms changed or evolved theories
but failed to establish facts.

Evolution, simply put, is descent with modification. This definition encompasses

small-scale evolution (changes in gene frequency in a population from one
generation to the next) and large-scale evolution (the descent of different species
from a common ancestor over many generations). Evolution helps us to understand
the history of life.

Evolution is not simply a matter of change over time. Lots of things change over time:
trees lose their leaves, mountain ranges rise and erode, but they aren't examples of
biological evolution because they don't involve descent through genetic inheritance.

The central idea of evolution is that all life on Earth shares a common ancestor, just
as you and your cousins share a common grandmother.

Through the process of descent with modification, the common ancestor of life on
Earth gave rise to the fantastic diversity that we see documented in the fossil record
and around us today. Evolution means that we're all distant cousins: humans and oak
trees, hummingbirds and whales.

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9.1 WHAT IS EVOLUTION?

Evolution is a slow process of change from one form to another that takes place over
generations in animals and plants. These changes lead to new kinds or species of
living things being formed. Many people had ideas about how this happened, but it
was Darwin who first worked out how evolution occurred through his theory of natural
selection.

9.2 THE THEORY OF EVOLUTION

The theory suggests that at one time there was no living organism of any kind on the
Earth, possibly because it was too hot. As the Earth cooled, the theory supposes that
condition were just right for certain kinds of chemical reactions to take place in the
water. These chemical reactions might have produced compounds like amino acids
and enzymes, which could make the other reactions takes place. If these chemicals
somehow came together inside a membrane, they would form the first single-celled
creatures such as bacteria, which could feed, grow and reproduce. There is a great
deal of argument as bacterial, which could feed, grow and reproduce. There is a
great deal of argument among biologist about how this could happen or whether it
could have happened at all.

However, according to the experiment done by the two scientists namely, Urey and
Miller, many biologists accept their ‗Theory of Chemical Soup‘.

The atmosphere of the early earth probable contained methane, ammonia, carbon
dioxide, and other gases still abundant today on other planets in the solar system.
Chemists have experimentally reconstructed these ancient conditions in the
laboratory. If possible gases are mixed in a flask with water, and energy is added by
an electric discharge (simulated primordial lightning) substances are spontaneously
synthesized. These include, most significantly, amino acids (the building blocks of
proteins, including the all-important enzymes that control the chemical processes of
life), and purines and pyrimidines (the building blocks of RNA and DNA). It seems
probable that something like this happened on the early Earth. Consequently, the sea
would have become a ―chemical soup‖ of pre-biological organic compounds.

9.3 HISTORY OF EVOLUTIONARY IDEAS

The idea of continuous evolution was traced back as 1st century BC, but it did not
gain wide acceptance until 19th century following the work of Charles Darwin, he
assigned the major role in evolutionary change to natural selection acting on
randomly occurring variation (now know to be produced by spontaneous changes or
mutations in the genetic material of organisms).

In 1859 he published his ‗Origin of Species by Means of Natural Selection or the

Preservation of Favoured Races in the Struggle for Life, usually abbreviated to ―The
Origin of Species’. Modern molecular biology illustrated that all species can be

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traced back to a single common ancestor. For all known life forms share the same
genetic origin.

9.4 VOYAGE OF THE BEAGLE

After graduating from Cambridge in 1831, the 22 year-old Darwin was taken abroad
the English survey ship HMS Beagle, as an unpaid naturalist on a scientific
expedition round the world. This voyage, which began on December 27, 1831,
determined Darwin‘s whole future career.

Figure 9.1 Charles Darwin Figure 9.2 HMS Beagle set sail

HMS Beagle set sail with the purpose of charting further the South American coast.
It was captained by Robert Fitzroy and included in its crew the young naturalist
Charles Darwin.

Figure 9.3 The HMS Beagle's most famous expedition route on the 27th of
December 1831

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The Beagle spent on the east and west coasts of South America, Darwin was able to
leave the ship for two extended periods on the mainland. In September 1835 the
Beagle headed west for Australia, returning to England via the Cape of Good Hope.
Darwin‘s job as naturalist gave him the opportunity to observe a variety of geological
formations in different continents and islands along the way, as well as a vast array of
fossils and living organisms. In his geological observations, Darwin was most
impressed by the effect that natural forces gave on shaping the Earth‘s surface.

Discoveries of Charles Darwin’s Voyage

When Darwin was on the Galapagos Islands, he discovered 13 species of finches

that are believed to have evolved from a single species. The ancestral finch, with its
short, stout, conical bill specialized for crushing seeds, probably migrated from the
mainland to the Galapagos Islands. Its descendants share with warblers,
woodpeckers, and other birds by adapting to the available range of habitats (tree,
cactus, or ground) and food (seeds, cactus, fruit, or insects). The size and shape of
their bills reflect the specializations in seeds, fruits and insect eating.

There are now at least 13 species of finches on the Galapagos Islands, each filling a
different niche on different islands. All of them evolved from one ancestral species,
which colonized the islands only a few million years ago. This process, whereby
species evolve rapidly to exploit empty ecospace, is known as adaptive radiation.

Figure
9.4 showing some of the 13 species of finches on the Galapagos Islands

9.5 THE MECHANISM OF EVOLUTION

In evolution, the unit of study is not the species but the population or more specifically,
the total number of genes present in the gametes of the population called Gene Pool.
Gene Pools do change composition especially when the environment is changing.
Evolution has several mechanisms to prove that.

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Theories of Natural Selection

Natural Selection is process where favourable organisms survive and can reproduce
to pass on their genes to the next generation while the harmful ones are eliminated
by natural means. It can also be termed as, ―Survival of the Fittest‖. Natural selection
tends to promote adaptation in organisms where necessary for survival.

There are four basic principles of evolution through Natural Selection. These are:

1 In any population there are variations; all the members of one species are not
identical
2 In any generation there are offspring that do not reach maturity and reproduce;
the characteristics of these organisms are removed from the population.
3 Those organisms that survive and reproduce are well adapted to that
environment; they have favourable variations (survival of the fittest)
4 Favourable variations are passed onto offsprings; they become more and
more common in the population.

The main contributions by Darwin and Wallace to the theory of evolution were:

(a) the idea that species can change and (b) the mechanism of natural selection to
explain how changes take place.

Darwin's theory of evolution by natural selection is one of the best substantiated

theories in the history of science, supported by evidence from a wide variety of
scientific disciplines, including palaeontology, geology, genetics and developmental
biology.

Evolution by means of natural selection is the process by which genetic mutations

that enhance reproduction become and remain, more common in successive
generations of a population. It has often been called a "self-evident" mechanism
because it necessarily follows from three simple facts:

 Heritable variation exists within populations of organisms.

 Organisms produce more progeny than can survive.
 These offspring vary in their ability to survive and reproduce.

These conditions produce competition between organisms for survival and

reproduction. Consequently, organisms with traits that give them an advantage over
their competitors pass these advantageous traits on, while traits that do not confer an
advantage are not passed on to the next generation.

The central concept of natural selection is the evolutionary fitness of an organism.

Fitness is measured by an organism's ability to survive and reproduce, which
determines the size of its genetic contribution to the next generation. However,
fitness is not the same as the total number of offspring: instead fitness is indicated by

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the proportion of subsequent generations that carry an organism's genes. For

example, if an organism could survive well and reproduce rapidly, but its offspring
were all too small and weak to survive, this organism would make little genetic
contribution to future generations and would thus have low fitness.

If an allele increases fitness more than the other alleles of that gene, then with each
generation this allele will become more common within the population.

Figure 9.5 Mutation, followed by natural selection, results in a population with darker
colouration.

These traits are said to be "selected for". Examples of traits that can increase fitness
are enhanced survival and increased fecundity. Conversely, the lower fitness caused
by having a less beneficial or deleterious allele results in this allele becoming rarer-
they are "selected against". Importantly, the fitness of an allele is not a fixed
characteristic; if the environment changes, previously neutral or harmful traits may
become beneficial and previously beneficial traits become harmful. However, even if
the direction of selection does reverse in this way, traits that were lost in the past may
not re-evolve in an identical form.

Natural selection can change a species in small ways, causing a population to

change colour or size over the course of several generations. This is called
"microevolution."

But natural selection is also capable of much more. Given enough time and enough
accumulated changes, natural selection can create entirely new species. It can turn
dinosaurs into birds, apes into humans and amphibious mammals into whales.

Mutation

A mutation is a mistake in copying the organic base (namely adenine, cytosine,

thymine and guanine) on a chromosome during replication to make up the genetic
code. This mistake can cause organisms to change in their behaviour and

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morphology. The physical and behavioural changes that make natural selection
possible happen at the level of DNA and genes. Such changes are called
"mutations."

The organism carrying a mutation is called MUTANT. If a new gene increased the
chances of survival of the mutant, it will tend to leave more offspring than other
organisms in the populations. As a result, the genes will spread to the other
members of the next generation, causing distinct changes in the look of those
organisms. Mutations occur regularly in all biological populations.

Mutations can be caused by chemical or radiation damage or errors in DNA

replication. Such agents are called Mutagens. Mutations can even be deliberately
induced in order to adapt to a rapidly changing environment. The Ultra violet
radiation, X-rays, nitric acid and nuclear explosions are all examples of mutagens.

Most times, mutations are either harmful or neutral but in rare instances, a mutation
might prove beneficial to the organism. If so, it will become more prevalent in the next
generation and spread throughout the population.

In this way, natural selection guides the evolutionary process, preserving and adding
up the beneficial mutations and rejecting the bad ones.

Some examples of the observed and measured natural selection through mutation:

(a) Pesticides and Drug Resistance

Many insects population throughout the world have evolved resistance or high
degree of tolerance to DDT (dichlorodiphenyltrichloroethane) and a variety of
chemical agents. This is due to the mutations experienced over time had given rise to
resistance to certain chemicals, drugs, pesticides etc. That is why the research is
moving away from the use of chemical pest control agents to biological controls, like
natural predators, parasites and genetic engineering.

This sort of resistance has evolved in many pathogens (diseases causing

microorganisms). Example of diseases like malaria plasmodium is now largely
resistant to chloroquine and syphilis is now impossible to kill with penicillin.

(b) Industrial Melanism

In the 19th century, the English Peppered Moths (Biston betularia) lives in the
Southern English forests undergo a colour change. Before the Industrial Revolution
took place in Britain in the late 18th century, the light-coloured moths blended with the
lichen-covered bark of trees and were more prevalent than dark-coloured peppered
moths. However, pollution from the industrial revolution killed the lichen on trees,
leaving their dark bark exposed, and the contrasting light-coloured moths became
easy prey for birds. The dark peppered moths easily camouflaged on the dark bark
and soon became more common than the lighter varieties. Now that pollution is
decreasing, the light coloured peppered moths are increasing again. This is due to
the natural selections where the individuals adapted better to a particular
environment and reproduce more.

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(c) Sickle-cell Anaemia

Sickle-Cell anaemia (sickle-cell disease) is a hereditary in which haemoglobin
oxygen –carrying protein in the blood, is altered, leading to periodic interruptions in
blood circulations. These symptoms are due to the altered haemoglobin, which
changes shape when the amount of oxygen in the blood is reduced for any reason.
The red blood cell in which the haemoglobin is contained also changes its shape,
from round to crescent (sickle shaped). The sickle-shaped red cells interfere with
normal blood flow by plugging up small blood vessels. Sickle-cell anaemia occurs
when an individual inherits a sickle-cell gem from each parent.
Symptoms of the condition appear at about six months of age and may include
enlargement of the abdomen and heart and painful swelling of the hands and feet.
In adolescence, sexual maturation may be delayed.
Variation
An individual organism's phenotype results from both its genotype and the influence
from the environment it has lived in. A substantial part of the variation in phenotypes
in a population is caused by the differences between their genotypes. The modern
evolutionary synthesis defines evolution as the change over time in this genetic
variation. The frequency of one particular allele will become more or less prevalent
relative to other forms of that gene. Variation disappears when a new allele reaches
the point of fixation — when it either disappears from the population or replaces the
ancestral allele entirely.

Figure 9.6 White peppered moth Figure 9.7 Black morph in peppered moth
evolution

Natural selection will only cause evolution if there is enough genetic variation in a
population. Before the discovery of Mendelian genetics, one common hypothesis was
blending inheritance. But with blending inheritance, genetic variance would be rapidly
lost, making evolution by natural selection implausible. The Hardy-Weinberg principle
provides the solution to how variation is maintained in a population with Mendelian
inheritance. The frequencies of alleles (variations in a gene) will remain constant in
the absence of selection, mutation, migration and genetic drift.

Variation comes from mutations in genetic material, reshuffling of genes through

sexual reproduction and migration between populations (gene flow). Despite the
constant introduction of new variation through mutation and gene flow, most of the
genome of a species is identical in all individuals of that species. However, even
relatively small differences in genotype can lead to dramatic differences in

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phenotype: for example, chimpanzees and humans differ in only about 5% of their
genomes.

9.6 SPECIATION

Evolution, whether under the influence of natural selection or not, leads to divergence
and diversity. From a single ancestor, many of millions of separate species have, at
one time or another, evolved. The process where one species splits into two is called
speciation. Subsequently divergence leads to ever wider separation of taxonomic
units such as genera, families, orders, classes, etc.

It is widely accepted that the first step in speciation is normally Geographical

Separation (isolation). A species is accidentally divided into two geographically
separated populations. Often there may be subpopulations isolated on islands due
to Geographical isolation means no gene flow, no sexual contamination of each gene
pool by the other. Under these conditions the average gene frequencies in the two
gene pools can change because of different selection pressures.

For example, a Nepalese hairy goat is geographically isolated from the less hairy
lowlands goats by adapted to high altitudes. Geographic isolation may be on a very
small scale such as the human head louse and the pubic-hair louse are
geographically isolated by one meter or so of hairless skin on the host.

After sufficient genetic divergence while geographical isolation, the two

subpopulations are no longer capable of interbreeding even if later circumstances
chance to reunite them. When they can no longer interbreed, speciation is said to be
reproductive (Genetic) isolation have occurred and a new species (or two) is said to
have come into being. This ―biological‖ definition of the species cannot be used for
organisms that do not reproduce sexually. For example, interbreeding between a
horse and a donkey will produce a mule that is infertile or sterile, thus the gene flow
between the two populations will cease. Even if geographically reunited, such
populations will continue to evolve separately.

9.7 ROLE OF COMPETITION IN EVOLUTION

Competition is the driving force of evolution. Competition allows for more offspring to
be born, hatch, and germinate than can survive due to limited resources. Therefore,
only the stronger offsprings are able to live and the weaker ones are eliminated from
the population. Hence, in any case there must be struggle for existence, either one
individual with another of the same species or with the individual of the different
species.

9.8 ARTIFICIAL AND SEXUAL SELECTION

Artificial Selection

Man has a major influence in the crossing of plants and animals to produce breeds
with characteristics desired by man.

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Long before Darwin and Wallace, farmers and breeders were using the idea of
selection to cause major changes in the features of their plants and animals over the
course of decades. Farmers and breeders allowed only the plants and animals with
desirable characteristics to reproduce, causing the evolution of farm stock. This
process is called artificial selection because people (instead of nature) select which
organisms get to reproduce.
As shown below, farmers have cultivated numerous popular crops from the wild
mustard, by artificially selecting for certain attributes.

Figure 9.8 Common vegetables cultivated from wild mustard

These common vegetables were cultivated from forms of wild mustard. This is
evolution through artificial selection.

Sexual Selection

Sexual Selection is a type of natural selection where reproductive success among individuals
is determined by the way in which mating occurs. Competition between individuals of the
same sex for mates can favour individuals with certain hereditary characters or traits. These
characters are completed only if reproduction is successful and their frequently tends to
increase. Examples include antlers on male deer, brightly coloured patterns on male birds,
and size differences between sexes.

There are two main forms of sexual selection; intra-sexual selection and epigamic selection.
In intra-sexual selection males (or more rarely females) compete through display or physical
contest for mates. In epigamic selection females accept males (or more rarely the reverse)
with certain traits. In some instance, individuals of one sex can monopolies many individuals
of the other during the breeding season of mating purposes.

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Sexual selection is a ―special case‖ of natural selection. Sexual selection acts on an

organism's ability to obtain (often by any means necessary!) or successfully copulate with a
mate.

Selection makes many organisms go to extreme lengths for sex: peacocks (top left) maintain
elaborate tails, elephant seals (top right) fight over territories, fruit flies perform dances, and
some species deliver persuasive gifts. After all, what female Mormon cricket (bottom right)
could resist the gift of a juicy sperm-packet? Going to even more extreme lengths, the male
redback spider (bottom left) literally flings itself into the jaws of death in order to mate
successfully.

Figure 9.9 Peacock performing its dance Figure 9.10 Elephant Seals fighting over territories

Figure 9.11 Male red back spider literally flings Figure 9.12 Mormon cricket showing the
off itself into the jaws of death in order to gift of a juicy sperm-packet
mate successfully

Sexual selection is often powerful enough to produce features that are harmful to the
individual‘s survival. For example, extravagant and colourful tail feathers or fins are
likely to attract predators as well as interested members of the opposite sex.

9.9 EVIDENCE FOR EVOLUTION

Evolutionary evidence is the study of how evolution acts on the shape and form of
any individual organism during the process of development. However, the mutations
in genes affect the development, thus causing alterations to shape and form and they
seemed to have a common ancestor due similarities in them.

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Homologous Structures

Structures that are similar due to evolutionary origin, such as the forearm bones of
humans, birds, porpoises, elephants are called homologous. Structures that evolve
separately to perform a similar function are analogous. The analogous wings of birds,
bats, and insects, for example, have different embryogical origins but are all designed
for flight.

Figure 9.13 showing the homologous structures of different organisms

The hands humans, wings of bats, and insects are superficially similar but their
internal structures are quite different. The bones are homologous with those of the
other vertebrates; those in bats wings are homologous with digits two to five with a
common design called pentadactyl limb.

Comparative Anatomy

Comparative anatomy is establishing evolutionary relationships on the basis of

structural similarities and differences. Animals and plants do share a common
ancestry. In fact, the degree of resemblance between them indicate how closely
related they are in evolution; groups with little in common are assumed to have
diverged from a common ancestor much earlier in geographical history. Evolutionary
relationships are worked out by homologies; for example, the lower skeletal structure
of human and of frog and ostrich or kingomshin and shark. The dolphin and the shark
look more alike because of their streamlined shape but vary in their structures and
anatomy. The ostrich and human seem to have similar anatomy such as breath air by
means of lungs, have homologous limb-bones.

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Figure 9.14 Human and Ostrich: the comparative anatomy of the animals

Figure 9.15 Shark

Figure 9.16 Dolphin

9.10 EMBRYOLOGY

The similarity between embryos of many organisms suggests a common ancestry.

All vertebrates begin their development with fish-like structure; mammals also have
reptilian features during development. This stage suggests that organisms descend
from a common ancestor.

The fertilized eggs (a), or zygotes, are very similar, though they differ slightly in the
size of the cell nucleus. The orderly division of the single-celled zygote into a multi
celled blastocyst is referred to as cleavage. By the late cleavage stage (b), the
embryos look very similar and differ only in their cleavage patterns, which vary due to
the presence of differing amounts of yolk in the egg.

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As the body segments form (c), all three mammals remain almost identical. Notice
the ancestral gill slits, which in the mammals will later develop into parts of the ear
and pharynx. The mammals possess an umbilical cord that leads to the placenta. In
contrast, the salamander and the chicken are nourished by yolk.

Figure 9.17 shows the similarities in the embryos which suggests a common ancestry

The early forelimbs begin as buds (d). By the late fetal stage (e), limbs take on their
adult shapes. The striking similarities in the late fetal stage between monkey and
human reflect their close phylogenetic relationship.

The main difference lies in the absence of a tail in the human fetus. (If an ape fetus
were substituted for this monkey, it too would lack a tail). The chicken has developed
its specialized shell breaker.

The salamander has just hatched into its larval stage (e). It spends the first part of its
life in the water, taking in life-giving oxygen through its feathery gill slits and using its
limbs as paddles. Later, the salamander undergoes metamorphosis and acquires its
adult form with terrestrial limbs and lungs for breathing air. Only then, as an adult,
can it leave the water to live, but not reproduce, on dry land.

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The newborn of each species receive quite different treatment. The salamander
abandons the eggs after she lays them, and the larvae receive no parental care at all.
The hen incubates her eggs with body heat while sitting on them in a nest. The newly
hatched chicks receive some protection from the mother hen, but begin immediately
to find their own food. After gestation times of four (pig), six (monkey), and nine
months (human), newborn mammals are nourished by their mother's milk and require
extended care before they become independent adults.

9.11 FOSSILS (Palaeontology)

Fossils are the remains of animals and plants preserved in certain kinds of rocks
(sedimentary rocks). Figure 9.18 shows how the skeleton of a shell become
embedded in a mud or sand which was setting down on a bottom of the sea or lake.
After a few million years, with the pressure of more layers building up on top of it,
mud or sand becomes rock.

The physical evidence of a prehistoric organism, after comprising a shell, bone, or

other durable skeletal part belongs to an extinct species. Fossils also include the
imprints of organisms that have dissolved or eroded away; preserved footprints and
tracks; remarkably unaltered remains preserved in peat bogs, asphalt lakes or tar pits
and frozen ground.

Palaeontology is the study of fossils, the remains of once-living organisms which are
preserved in the sedimentary rock. There are three major conditions that allow
organisms to become a fossil. The organism itself must have hard parts. The
environment where it comes to rest must be covered with fine-grained sediment, like
mud, rapidly. The fossils only represent a small fraction of the biological life that the
fossils come from.

As the fossil is buried and becomes a rock, the conditions that a rock goes through
will on whether the fossil will be recognized. For example, if many shells are
preserved in a sedimentary rock, they will probably be preserved. But if the area is
metamorphosed, then the rock will change and you may never know there were
fossils buried in the rock

Fossilization Process

Fossils are clues to the type of organisms that roamed the Earth. Fossils, however,
provide us with more information. They can tell us about the palaeoecology or the
relationship between organisms and their environments, if we can decipher the clues
presented. Palaeontologists want to determine the physical, chemical and biological
interactions that can limit the distribution and abundance of different species. They
are always searching as to why an organism may have gone extinct. Today we know
that when an organism‘s environment changes or when other organisms invade
another habit, extinction can occur.

Fossils also indicate that organisms have changed through time. As we learn which
fossils lived in what time, we can retrace how the environment looked and assign

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periods of time to each fossil group. There are three major conditions that allow
organisms to become a fossil. The organism itself must have hard parts. The
environment where it comes to rest must be covered with fine-grained sediment, like
mud, rapidly. The fossils only represent a small fraction of the biological life that the
fossils come from.

As the fossil is buried and becomes a rock, the conditions that a rock goes through
will on whether the fossil will be recognized. For example, if many shells are
preserved in a sedimentary rock, they will probably be preserved. But if the area is
metamorphosed, then the rock will change and you may never know there were
fossils buried in the rock.

Figure 9.18 showing a simple process of fossilization

Fossilised fern.

Rock containing fossilised fronds of a fern dating from the Carboniferous Period of
354-290 million years ago. This was a time when ferns dominated the land and, when
they died, they formed large beds of coal (a form of carbon). This led to the name of
this geological period: the Carboniferous. Fossils form by a more delicate process
than coal formation. Ferns are flowerless plants that reproduce using spores. This
fossil is from the Netherlands

Figure 9.19 shows the fossilized fern

A fossil feather of Archaeopteryx, preserved in limestone, is the first specimen of the

winged dinosaur ever found. Researchers used it to determine the animal‘s feather
colour, which in turn provided clues about its potential for flight.

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Figure 9.20 shows the fossilized Archaeopteryx

Credit: Museum für Naturkunde Berlin

Example of Evolutionary fossils

Archaeopteryx (Greek meaning, ―ancient wing‖) is the first known bird, the remains of
which were found in the 19th century in limestone in Germany.
Archaeopteryx lithographical (Figure 9.20 above), is the earliest bird in the fossil
record, coming from the Late Jurassic lithographic limestone near Solnhofen,
Germany. The first specimen was found in 1891, almost coincident with Darwin's
publication of Origin of Species two years later, and ten more have since been found.
Archaeopteryx was about the size of a crow with short, broad wings and a long tail.
While its feathers were similar to those of living birds, it had jaws lined with sharp
teeth, three fingers ending in curving claws, and a long bony tail, in stark contrast to
modern birds.
Archaeopteryx's many features of dinosaurs such as the jaws with teeth, tiny
forelimbs with three claws, a long tail and a head covered with scales while body,
wings and tail were covered with feathers as in a bird provides strong evidence of the
dinosaur ancestry of birds, and, more generally, of the validity of the Theory of
Evolution.

Archaeopteryx had well-developed wings and could probable fly. The bird‘s size
probably ranged from that of a pigeon to that of a small crow. In many ways it
resembled a dinosaur; it had teeth, well developed hind limbs and a long tail. Unlike
a dinosaur, the entire body was covered with feathers. Archaeopteryx is one of the
best examples of evolution. Archaeopteryx lived during the Late Jurassic period.

9.12 THE NATURE OF THE FOSSIL RECORD

Origins to the present

The history of the Earth is recorded in its rocks and these provide the means of
identifying the multitude of events that occurred during its lifetime of more than four
billion years. See below the geological timescale.

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Figure 9.21 Geologic time scale showing major mass extinctions and the occurrence in time of the
main groups of vascular plants on land.
1 = spore-bearing plants including lycopsids and ferns;
2 = gymnosperms;
3 = angiosperms (numerical ages from ref. 1 and Geologic Time Scale, Geological Society of America,
http://www.geosociety.org/pubs/index.htm). (Ma) millions of years. Red line indicates time discussed
by Looy et al. (1).

Geologic time correlates rocks and time. The scale, developed before absolute dating
techniques were discovered, is a relative geologic scale that provides a standard of
reference for dating rocks throughout the world. It lists the succession of rock
depositions that are recognized on and immediately beneath the Earth's surface. The
standard stratigraphic column, based on fossil plant and animal assemblages from
different European strata, is used to date fossils in strata from other parts of the Earth
and is the foundation of the geologic time scale.

The application of radiometric dating techniques began early in the 20th century. The
quantitative methods provided by these techniques had the potential for dating
divisions of the geologic time scale and for estimating the age of the Earth itself. The
age of the Earth now is estimated to be between 5 billion and 4.7 billion years and
estimates of the duration of the geologic time scale divisions have been made.

Originally, geologic time scale divisions were based on the natural breaks in the
stratigraphic column. The breaks were thought to have resulted from worldwide
events of mountain building during which no sedimentation occurred and left gaps in
the record of rocks, that is, an unconformity. It is now realized that mountain building
events were not necessarily worldwide, but may be limited to a single continent or
even part of a continent during one interval of geologic time.

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The longest divisions of geologic time are the eras. Most geologic time scales
recognize four eras, three of which have been named for the fossils in the associated
strata. Thus, the Palaeozoic Era refers to ‗‗ancient life,‘‘ the Mesozoic Era to
‗‗medieval life‘‘ and the Cenozoic Era to ‗‗modern life.‘‘ Rocks older than Palaeozoic
generally lack diagnostic fossils and are widely known as belonging to the
Precambrian Era. This era included about 80 percent of Earth's history, that is, from
nearly 5 billion years to 800 million or 700 million years ago.

The eras are divided into periods of time. Rock deposits that relate to or were formed
during a certain period of time constitute a system of rocks. Periods are divided
further into epochs of time and rock systems into series.

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SUMMARY

The theory in biology postulating that the various types of plants, animals, and other
living things on Earth have their origin in other pre-existing types and that the
distinguishable differences are due to modifications in successive generations. The
theory of evolution is one of the fundamental keystones of modern biological theory.

The diversity of the living world is staggering. More than 2 million existing species of
organisms have been named and described; many more remain to be discovered-
from 10 million to 30 million, according to some estimates.

Darwin and other 19th-century biologists found compelling evidence for biological
evolution in the comparative study of living organisms, in their geographic
distribution, and in the fossil remains of extinct organisms. Since Darwin's time, the
evidence from these sources has become considerably stronger and more
comprehensive, while biological disciplines that emerged more recently genetics,
biochemistry, physiology, ecology, animal behaviour (ethnology), and especially
molecular biology have supplied powerful additional evidence and detailed
confirmation. The amount of information about evolutionary history stored in the DNA
and proteins of living things is virtually unlimited; scientists can reconstruct any detail
of the evolutionary history of life by investing sufficient time and laboratory resources.

Evolutionists no longer are concerned with obtaining evidence to support the fact of
evolution but rather are concerned with what sorts of knowledge can be obtained
from different sources of evidence. The following sections identify the most
productive of these sources and illustrate the types of information they have
provided.

When an organism dies, it is usually destroyed by other forms of life and by

weathering processes. On rare occasions some body parts-particularly hard ones
such as shells, teeth, or bones are preserved by being buried in mud or protected in
some other way from predators and weather. Eventually, they may become petrified
and preserved indefinitely with the rocks in which they are embedded. Methods such
as radiometric dating – measuring the amounts of natural radioactive atoms that
remain in certain minerals to determine the elapsed time since they were
constituted – make it possible to estimate the time period when the rocks, and the
fossils associated with them, were formed.

The skeletons of turtles, horses, humans, birds, and bats are strikingly similar, in
spite of the different ways of life of these animals and the diversity of their
environments. The correspondence, bone by bone, can easily be seen not only in the
limbs (as shown in the figures 9.13 to 9.16) but also in every other part of the body.

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Student Learning Activity 10

1 Briefly explain why birds have different sized beaks.

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2 List at least 4 (four) evidence of evolution of the vertebrates from a common

ancestor.
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3 Darwin‘s Theory of Evolution by Natural Selection has four main points.

Describe any two.
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4 Define natural selection.

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5 What does Darwin's Theory of Evolution as presented in 'The Origin of Species'

mainly concern of?
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6 Why are Darwin's Finches important?

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7 What is meant by Geological Timescale?

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8 What was the significance of the carboniferous period?

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9 Explain what relationship has Embryology with evolution.

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10 Explain how Evolutionary relationships are worked out.

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UNIT 10.0

GEOLOGICAL CONTINENTAL DRIFT

Learning Outcomes

At the end of this unit, you can:

1 name the earth's major and minor plates

2 identify the three types of plate boundaries characterized by the way the plates
move relative to each other

3 explain continental Drift, geological theory that the relative positions of the
continents on the earth's surface have changed considerably through geologic
time

4 explain the continental drift hypothesis

5 identify and describe evidence for continental drift in the form of plant and
animal fossils of the same age found around different continent shores

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INTRODUCTION

Particular types of plants and animals are found in certain continents and not others.
For example animals and plants of Asia and Australia are different. This was first
described by Alfred Wallace who suggested Wallace Line to demarcate the
distribution of these animals. It is believed that Australia‘s unique mammals and
angiosperms results from periods of evolution in isolation which is provided by the
theory of continental drift. It is believed that continents were not the same as today.
They were seemed to have fitted together. For example, the Gondwana and Pangae
land Sahul and Sunda land seemed to have fitted together.

Therefore, these continents seemed to have similar plants and animals.

Continental Drift is the geological theory that the relative positions of the continents
on the earth's surface have changed considerably through geologic time. Though first
proposed by American geologist Frank Bursley Taylor in a lecture in 1908, the first
detailed theory of continental drift was put forth by German meteorologist and
geophysicist Alfred Wegener in 1912. On the basis of geology, biology, climatology,
and the alignment of the continental shelf rather than the coastline, he believed that
during the late Paleozoic and early Mesozoic eras, about 275 to 175 million years
ago, all the continents were united into a vast supercontinent, which he called
Pangaea. Later, Pangaea broke into two super-continental masses – Laurasia to the
north, and Gondwanaland to the south. The present continents began to split apart in
the later Mesozoic era about 100 million years ago, drifting to their present positions.

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Figure 10.1 The sequence of maps shows how a large supercontinent, known as Pangaea
was fragmented into several pieces, each being part of a mobile plate of the lithosphere.
These pieces were to become Earth's current continents. The time sequence show through
the maps traces the paths of the continents to their current positions.

The theory of continental drift was not generally accepted, particularly by American
geologists, until the 1950s and 60s, when a group of British geophysicists reported
on magnetic studies of rocks from many places and from each major division of
geologic time. They found that for each continent, the magnetic pole had apparently
changed position through geologic time, forming a smooth curve, or pole path,
particular to that continent. The pole paths for Europe and North America could be
made to coincide by bringing the continents together.

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10.1 CONTINENTAL DRIFT HYPOTHESIS

Continental drift is the movement of the Earth's continents relative to each other. The
hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596
and was fully developed by Alfred Wegener in 1912 when he noticed that the shapes
of continents on either side of the Atlantic Ocean seem to fit together (for example,
Africa and South America). Francis Bacon, Antonio Snider-Pellegrini, Benjamin
Franklin, and others had noted much the same thing earlier. However, it was not until
the development of the theory of plate tectonics in the 1960s, that a sufficient
geological explanation of that movement was found.

The similarity of southern continent fossil faunas and some geological formations had
led a relatively small number of Southern hemisphere geologists to conjecture as
early as 1900 that all the continents had once been joined into a supercontinent
known as Pangaea.

The concept was initially ridiculed by most geologists, who felt that an explanation of
how a continent drifted was a prerequisite and that the lack of one made the idea of
drifting continents wholly unreasonable.

The theory received support through the controversial years from South African
geologist Alexander Du Toit as well as from Arthur Holmes. The idea of continental
drift did not become widely accepted as theory until the 1950s in Europe.

By the 1960s, geological research conducted by Robert Dietz, Bruce Heezen, and
Harry Hess along with a rekindling of the theory including a mechanism by J. Tuzo
Wilson led to acceptance among North American geologists.

The hypothesis of continental drift became part of the larger theory of plate tectonics.
This article deals mainly with the historical development of the continental drift
hypothesis before 1950.

Evidence

Evidence for continental drift is now extensive, in the form of plant and animal fossils
of the same age found around different continent shores, suggesting that these
shores were once joined, for example the fossils of the freshwater crocodile found in
Brazil and South Africa.

Another illustrative example is the discovery of fossils of the aquatic reptile

Lystrosaurus from rocks of the same age from locations in South America, Africa,
and Antarctica. There is also living evidence - the same animals being found on two
continents. An example of this is a particular earthworm found in South America and
South Africa.

The complementary shapes of the facing sides of South America and Africa are
obvious, but are a temporary coincidence. In millions of years, seafloor spreading,
continental drift, and other forces of tectonophysics will further separate and rotate

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those two continents. It was this temporary feature which inspired Alfred Wegener to
study what he defined as continental drift.

10.2 EARTH'S MAJOR PLATES

The current continental and oceanic plates include: the Eurasian plate, Australian-
Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos
plate, North American plate, Caribbean plate, South American plate, African plate,
Arabian plate, the Antarctic plate, and the Scotia plate. These plates consist of
smaller sub-plates.

Figure 10.2 The Earth's major plates

(Image courtesy of US Geological Survey)

When viewed from the perspective of geological time, the Earth is a very dynamic
place. Over the course of millions of years, the face of the Earth has changed as
continents move and mountain ranges are formed and eroded.

Land masses have coalesced and separated in several cycles over Earth's
geological history. In the most recent cycle, all land masses formed a single
supercontinent, Pangaea, by the end of the Paleozoic. Pangaea gradually separated
during the Mesozoic into two smaller supercontinents, Laurasia in the north and
Gondawanaland in the south, separated by the Tethys Sea in the east.

The Earth‘s surface consists of large crustal plates which move and jostle against
each other. There are seven large plates and many smaller plates (100 to 150 km
thick) that drift around the Earth‘s surface, highlighted in the diagram.
The continents move as a consequence of volcanic processes in oceanic areas
known as mid oceanic ridges where basalt oozes out onto the sea floor, forcing
adjacent plates apart. As the oceanic crust moves away from the ridge it cools,
becoming denser and may eventually sink back into the mantle at a subduction zone,
pulling the plate along with it. A further mechanism driving the movement of the
Earth‘s plates are large convection currents within the Earth‘s mantle. Modern

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continental masses are recognizable by the beginning of the Cenozoic, but were
joined in different patterns than at present. For example, Australia and South America
were joined through Antarctica in the early Cenozoic, the Indian subcontinent joined
Eurasia only ~10MYBP, North and South America became joined for the first time 4 ~
5 MYBP, and the Bering Strait between western North America and eastern Eurasia
opened 3 ~ 4 MYBP. Continents continue to drift: the Bering Strait has been a land
bridge at various times in the Holocene.

Figure 10.3 Geological History of Continental Drift

Figure 10.4 showing the earth's major and minor plates

Major Plates

-Australian Plate

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Minor Plates

There are dozens of smaller plates, the seven largest of which are:

Plate tectonics, from Greek "builder" or "mason", is a theory of geology that has been
developed to explain the observed evidence for large scale motions of the Earth's
lithosphere. The theory encompassed and superseded the older theory of continental
drift from the first half of the 20th century and the concept of seafloor spreading
developed during the 1960s.

Plate tectonics is a theory of geology that has been developed to explain the
observed evidence for large scale motions of the Earth's lithosphere. The theory
encompassed and superseded the older theory of continental drift from the first half
of the 20th century and the concept of seafloor spreading developed during the
1960s.

The outermost part of the Earth's interior is made up of two layers: above is the
lithosphere, comprising the crust and the rigid uppermost part of the mantle. Below
the lithosphere lies the asthenosphere. Although solid, the asthenosphere has
relatively low viscosity and sheer strength and can flow like a liquid on geological
time scales. The deeper mantle below the asthenosphere is more rigid again. This is,
however, not due to cooler temperatures but due to high pressure.
The lithosphere is broken up into what are called tectonic plates, in the case of Earth,
there are seven major and many minor plates (See list above.).The lithospheric
plates ride on the asthenosphere. These plates move in relation to one another at
one of three types of plate boundaries: convergent or collision boundaries, divergent
or spreading boundaries, and transform boundaries. Earthquakes, volcanic activity,
mountain-building, and oceanic trench formation occur along plate boundaries. The
lateral movement of the plates is typically at speeds of 0.66 to 8.50 centimeters per
year.

The lithosphere essentially "floats" on the asthenosphere and is broken-up into ten
major plates: African, Antarctic, Australian, Eurasian, North American, South
American, Pacific, Cocos, Nazca, and the Indian plates. These plates (and the more
numerous minor plates) move in relation to one another at one of three types of plate

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boundaries: convergent (two plates push against one another), divergent (two plates
move away from each other), and transform (two plates slide past one another).
Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur
along plate boundaries (most notably around the so-called Pacific Ring of Fire).

Plate tectonic theory arose out of two separate geological observations: continental
drift, noticed in the early 20th century, and seafloor spreading, noticed in the 1960s.
The theory itself was developed during the late 1960s and has since almost
universally been accepted by scientists and has revolutionized the Earth sciences
(akin to the development of the periodic table for chemistry, the discovery of the
genetic code for genetics, or evolution in biology).

Key Principles

The division of the Earth's interior into lithospheric and asthenospheric components is
based on their mechanical differences. The lithosphere is cooler and more rigid,
whilst the asthenosphere is hotter and mechanically weaker. This division should not
be confused with the chemical subdivision of the Earth into (from innermost to
outermost) core, mantle, and crust. The key principle of plate tectonics is that the
lithosphere exists as separate and distinct tectonic plates, which "float" on the fluid-
like asthenosphere. The relative fluidity of the asthenosphere allows the tectonic
plates to undergo motion in different directions.

One plate meets another along a plate boundary, and plate boundaries are
commonly associated with geological events such as earthquakes and the creation of
topographic features like mountains, volcanoes and oceanic trenches. The majority of
the world's active volcanoes occur along plate boundaries, with the Pacific Plate's
Ring of Fire being most active and famous. These boundaries are discussed in
further detail below.

Tectonic plates are comprised of two types of lithosphere: continental and oceanic
lithospheres; for example, the African Plate includes the continent and parts of the
floor of the Atlantic and Indian Oceans. The distinction is based on the density of
constituent materials; oceanic lithospheres are denser than continental ones due to
their greater mafic mineral content. As a result, the oceanic lithospheres generally lie
below sea level (for example the entire Pacific Plate, which carries no continent),
while the continental ones project above sea level.
There are three types of plate boundaries, characterized by the way the plates move
relative to each other. They are associated with different types of surface
phenomena. These different types of plate boundaries are:

 Transform boundaries occur where plates slide, or perhaps more accurately

grind, past each other along transform faults. The relative motion of the two
plates is therefore either sinistral or dextral.
 Divergent boundaries occur where two plates slide apart from each other.

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Figure 10.5 showing the three types of plate boundaries, characterized by the way the
plates move relative to each other.

 Convergent boundaries (or active margins) occur where two plates slide
towards each other commonly forming either a subduction zone (if one plate
moves underneath the other) or an orogenic belt (if the two simply collide and
compress).
 Plate boundary zones occur in more complex situations where three or more
plates meet and exhibit a mixture of the above three boundary types.

Transform (conservative) boundaries

The left- or right-lateral motion of one plate against another along transform or strike
slip faults can cause highly visible surface effects. Because of friction, the plates
cannot simply glide past each other. Rather, stress builds up in both plates and when
it reaches a level that exceeds the slipping-point of rocks on either side of the
transform-faults the accumulated potential energy is released as strain, or motion
along the fault. The massive amounts of energy that are released are the cause of
earthquakes, a common phenomenon along transform boundaries.

A good example of this type of plate boundary is the San Andreas Fault complex,
which is found in the western coast of North America and is one part of a highly
complex system of faults in this area. At this location, the Pacific and North American
plates move relative to each other such that the Pacific plate is moving north with
respect to North America.

Divergent (constructive) boundaries

At divergent boundaries, two plates move apart from each other and the space that
this creates is filled with new crustal material sourced from molten magma that forms
below. The genesis of divergent boundaries is sometimes thought to be associated
with the phenomenon known as hotspots. Here, exceedingly large convective cells

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bring very large quantities of hot asthenospheric material near the surface and the
kinetic energy is thought to be sufficient to break apart the lithosphere. The hot spot
believed to have created the Mid-Atlantic Ridge system currently underlies Iceland
which is widening at a rate of a few centimetres per century. Such hot spots can be
very productive of geothermal power and Iceland is actively developing this resource
and is expected to be the world's first hydrogen economy within twenty years.

Divergent boundaries are typified in the oceanic lithosphere by the rifts of the oceanic
ridge system, including the Mid-Atlantic Ridge, and in the continental lithosphere by
rift valleys such as the famous East African Great Rift Valley. Divergent boundaries
can create massive fault zones in the oceanic ridge system. Spreading is generally
not uniform, so where spreading rates of adjacent ridge blocks are different massive
transform faults occur. These are the fracture zones, many bearing names that are a
major source of submarine earthquakes. A sea floor map will show a rather strange
pattern of blocky structures that are separated by linear features perpendicular to the
ridge axis. If one views the sea floor between the fracture zones as conveyor belts
carrying the ridge on each side of the rift away from the spreading centre the action
becomes clear. Crest depths of the old ridges, parallel to the current spreading
centre, will be older and deeper (due to thermal contraction and subsidence).

It is at mid-ocean ridges that one of the key pieces of evidence forcing acceptance of
the sea-floor spreading hypothesis was found. Airborne geomagnetic surveys
showed a strange pattern of symmetrical magnetic reversals on opposite sides of
ridge centres. The pattern was far too regular to be coincidental as the widths of the
opposing bands were too closely matched. Scientists had been studying polar
reversals and the link was made. The magnetic banding directly corresponds with the
Earth's polar reversals. This was confirmed by measuring the ages of the rocks within
each band. In reality the banding furnishes a map in time and space of both
spreading rate and polar reversals.

Convergent (destructive) Boundaries

The nature of a convergent boundary depends on the type of lithosphere in the plates
that are colliding. Where a dense oceanic plate collides with a less-dense continental
plate, the oceanic plate is typically thrust underneath, forming a subduction zone. At
the surface, the topographic expression is commonly an oceanic trench on the ocean
side and a mountain range on the continental side.

An example of a continental-oceanic subduction zone is the area along the western

coast of South America where the oceanic Nazca Plate is being subducted beneath
the continental South American Plate. As organic material from the ocean bottom is
transformed and heated by friction a liquid magma with a great amount of dissolved
gasses will be created. This can erupt to the surface, forming long chains of
volcanoes inland from the continental shelf and parallel to it. The continental spine of
South America is dense with this type of volcano.

In North America the Cascade mountain range, extending north from California's
Sierra Nevada, is also of this type. Such volcanoes are characterized by alternating

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periods of quiet and episodic eruptions that start with explosive gas expulsion with
fine particles of glassy volcanic ash and spongy cinders, followed by a rebuilding
phase with hot magma. The entire Pacific Ocean boundary is surrounded by long
stretches of volcanoes and is known collectively as The Ring of Fire.

Where two continental plates collide the plates either crumple and compress or one
plate burrows under or (potentially) overrides the other. Either action will create
extensive mountain ranges. The most dramatic effect seen is where the northern
margins of the Indian sub-continental plate is being thrust under a portion of the
Eurasian plate, lifting it and creating the Himalaya.

When two oceanic plates converge they form an island arc as one oceanic plate is
subducted below the other. A good example of this type of plate convergence would
be Japan.

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SUMMARY

There is great variation in the sizes of continents; Asia is more than five times as
large as Australia. The largest island in the world, Greenland, is only about one-fourth
the size of Australia. The continents differ sharply in their degree of compactness.
Africa has the most regular coastline and, consequently, the lowest ratio of coastline
to total area. Europe is the most irregular and indented and has by far the highest
ratio of coastline to total area.

The continents are not distributed evenly over the surface of the globe. If a
hemisphere map centred in northwestern Europe is drawn, most of the world's land
area can be seen to lie within that hemisphere. More than two-thirds of the Earth's
land surface lies north of the Equator, and all the continents except Antarctica are
wedge shaped, wider in the north than they are in the south.

The distribution of the continental platforms and ocean basins on the surface of the
globe and the distribution of the major landform features have long been among the
most intriguing problems for scientific investigation and theorizing. Among the many
hypotheses that have been offered as explanation are:

(1) the tetrahedral (four-faced) theory, in which a cooling earth assumes the
shape of a tetrahedron by spherical collapse;
(2) the accretion theory, in which younger rocks attached to older shield areas
became buckled to form the landforms;
(3) the continental-drift theory, in which an ancient floating continent drifted apart;
and
(4) the convection-current theory, in which convection currents in the Earth's
interior dragged the crust to cause folding and mountain making.

As plate tectonics changes the shape of ocean basins, it fundamentally affects long-
term variations in global sea level. For example, the geologic record in which thick
sequences of continental shelf sediments were deposited demonstrates that the
breakup of Pangea resulted in the flooding of continental margins, indicating a rise in
sea level. There are several contributing factors. First, the presence of new ocean
ridges displaces seawater upward and outward across the continental margins.
Second, the dispersing continental fragments subside as they cool. Third, the
volcanism associated with breakup introduces greenhouse gases in the atmosphere,
which results in global warming, causing continental glaciers to melt.

The continuous rearrangement over time of the size and shape of ocean basins and
continents, accompanied by changes in ocean circulation and climate, has had a
major impact on the development of life on Earth.

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Student Learning Activity 11

1 Name the major plates.

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2 Name the minor plates.

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3 What happens when two oceanic plates converge?

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4 What are the three types of plate boundaries as characterized by the way the
plates move relative to each other?

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5 What are the names of the two outermost parts of the Earth's interior?
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UNIT 11.0

CLASSIFICATION

Learning Outcomes

At the end of this unit, you can:

1 understand the number of living things on the planet and how scientists
organise them into groups, like 'the animals' or 'the plants'.

2 understand that plants contain a chemical called chlorophyll that they use to
make their own food (it also makes them green).

3 describe the different classifications, kingdoms of all living things

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INTRODUCTION

At any one time in history, there are millions of different kinds of plants and animals in
the world. In 1753, a scientist in Sweden named Carolus Linnaeus thought of an
orderly system for classifying plants and animals. He grouped all organisms
according to a two-part name (binomial). The first part of the name is the "generic"
grouping or genus. The second part is the "specific" grouping or species. Scientists
today still use the basic idea of this system, but modern classifications systems are
much more complicated having many levels of hierarchical organization. For example,
taxonomic systems group organisms according to structure and physiological
connections between organisms. Phylogenic systems classify based on genetic
connections. Evolution theories have impacted modern classification.

Scientists believe that there are over 10 million different kinds of life forms, or species,
on Earth. Imagine trying to study and understand the lives, patterns, behaviors and
evolution of so many different kinds of organisms. In order to make their job easier,
scientists classify living things into groups based on how they are the same and how
they are different.

Based on similarities and structures, living things are grouped together in a

hierarchical system. This system suggests relationship between organisms; they are
related they have descended from a common ancestor.

Classification provides scientists and students a way to sort and group organisms for
easier study. There are millions of organisms on the earth! (Approximately 1.5 million
have been already named.)

Organisms are classified by their:

 physical structure (how they look)

 evolutionary relationships
 embryonic similarities (embryos)
 genetic similarities (DNA)
 biochemical similarities

In one classification system, there are 2 main groups. In others, there are 3. In the
one used by most of the world's scientists, which we will also use, there are 5 main
groups. All living things are placed in one of the five Kingdoms, which are the most
general group. They are then broken down into smaller groups, then smaller groups,
then smaller and so on until there is just one.

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11.1 CLASSIFICATION AND NAMING OF LIVING THINGS

With so many flora and fauna on planet Earth, there must be a method to classify
each organism to distinguish it from others so it can be correctly identified.
Classification does not only apply to biology. For example, supermarkets and grocery
stores organise their products by classifying them. Beverages may occupy one aisle,
while cleaning supplies may occupy another. In science, the practice of classifying
organisms is called taxonomy (Taxis means arrangement and nomos means law).
The modern taxonomic system was developed by the Swedish botanist Carolus (Carl)
Linneaeus (1707-1788). He used simple physical characteristics of organisms to
identify and differentiate between different species.

Linneaeus developed a hierarchy of groups for taxonomy. To distinguish different

levels of similarity, each classifying group, called taxon (pl. taxa) is subdivided into
other groups. To remember the order, it is helpful to use a mnemonic device.

The taxa in hierarchical order:

 Domain - Archea, Eubacteria, Eukaryote

 Kingdom-Plants, Animals, Fungi, Protists, Eubacteria (Monera),
Archaebacteria
 Phylum
 Class
 Order
 Family
 Genus
 Species

The domain is the broadest category, while species is the most specific category
available. The taxon Domain was only introduced in 1990 by Carl Woese, as
scientists reorganise things based on new discoveries and information. For example,
the European Hare would be classified as follows:

Eukaryote Animal Chordata Mammalia Lagomorpha Leporidae

Lepus Lepus europaeus.

Binomial nomenclature is used to name an organism, where the first word beginning
with a capital is the genus of the organism and the second word beginning with
lower-case letter is the species of the organism. The name must be in italics and in
Latin, which was the major language of arts and sciences in the 18th century. The
scientific name can be also abbreviated, where the genus is shortened to only its first
letter followed by a period. In our example, Lepus europaeus would become L.
europaeus'.

Taxonomy and binomial nomenclature are both specific methods of classifying an

organism. They help to eliminate problems, such as mistaken identity and false
assumptions, caused by common names. An example of the former is the fact that a
North American robin is quite different from the English robin. An example of the

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latter is the comparison between crayfish and catfish, where one might believe that
they both are fish when in fact, they are quite different.

Nomenclature is concerned with the assignment of names to taxonomic groups in

agreement with published rules.

Eukaryotes and Prokaryotes

Recall that there are two basic types of cells: eukaryotes and prokaryotes.

Eukaryotes are more complex in structure, with nuclei and membrane-bound

organelles. Some characteristics of eukaryotes are:

 Large (100 - 1000 μm)

 DNA in nucleus, bounded by membrane
 Genome consists of several chromosomes.
 Sexual reproduction common, by mitosis and meiosis
 Mitochondria and other organelles present
 Most forms are multi-cellular
 Aerobic

Prokaryotes refer to the smallest and simplest type of cells, without a true nucleus
and no membrane-bound organelles. Bacteria fall under this category.

Some characteristics:

 Small (1-10 μm)

 DNA circular, unbounded
 Genome consists of single chromosome.
 Asexual reproduction common, not by mitosis or meiosis.
 No general organelles
 Most forms are singular.
 Anaerobic

11.2 THE THREE DOMAINS

The three domains are organised based on the difference between eukaryotes and
prokaryotes. Today's living prokaryotes are extremely diverse and different from
eukaryotes. This fact has been proven by molecular biological studies (e.g. of RNA
structure) with modern technology. The three domains are as follows:

Archea (Archeabacteria) consists of archeabacteria, bacteria which live in extreme

environments. The kingdom Archaea belongs to this domain.

Eubacteria consists of more typical bacteria found in everyday life. The kingdom
Eubacteria belongs to this domain.

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Eukaryote encompasses most of the world's visible living things. The kingdoms
Protista, Fungi, Plantae, and Animalia fall under this category.

11.3 THE SIX KINGDOMS

Under the three domains are six kingdoms in taxonomy. The first two, Plants and
Animals, are commonly understood and will not be expounded here.

Protista, the third kingdom, was introduced by the German biologist Ernst Haeckel in
1866 to classify micro-organisms which are neither animals nor plants. Since protists
are quite irregular, this kingdom is the least understood and the genetic similarities
between organisms in this kingdom are largely unknown. For example, some protists
can exhibit properties of both animals and plants.

Fungi are organisms which obtain food by absorbing materials in their bodies.
Mushrooms and moulds belong in this kingdom. Originally, they were part of the plant
kingdom but were recategorised when they were discovered not to photosynthesise.

Eubacteria are bacteria, made up of small cells, which differ in appearance from the
organisms in the above kingdoms. They lack a nucleus and cell organelles. They
have cell walls made of peptidoglycan.

Archae (or Archaebacteria) are bacteria which live in extreme environments, such as
salt lakes or hot, acidic springs. These bacteria are in their own category as detailed
studies have shown that they have unique properties and features (ex. unusual lipids
that are not found in any other organism)which differ them from other bacteria and
which allow them to live where they live. Their cell walls lack peptidoglycan.

Organisms are groups among these five kingdoms by:

 the presence or absence of a nuclear membrane

 unicellular (one cell) or multi-cellular (many cells)
 the type of nutrition used by the organism (heterotrophic or autotrophic)

We will also go into the main phyla (next subgroup) for each kingdom.

I Kingdom Monera

 has a primitive cell structure lacking a nuclear membrane – Prokaryote

 most of this kingdom are unicellular (some exist in multicellular clusters)

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 two main phyla

A Bacteria (heterotrophic)
B Blue-green algae (autotrophic)

II Kingdom Protista

 has a membrane around the nucleus of the cell – Eukaryotic

 predominantly unicellular
 two main phyla

A Protozoa--animal like nutrition (heterotrophic)

Example: paramecia, amoeba

B Algae--plant like nutrition (autotrophic)

Example: spirogyra

III Kingdom Fungi

 has a membrane around the nucleus of the cell—Eukaryotic

 absorbs food from its environment (heterotrophic), does Not ingest it!
 organized into branched, multinucleated filaments

Example: bread molds (multicellular)

mushrooms (multicellular)
yeast (unicellular)

IV Kingdom Plants

 has a membrane around the nucleus of the cell—Eukaryotic

 multicellular organisms
 photosynthetic organisms (autotrophic)
(photo=light) (synthesis=to make)
Photosynthesis=To Make From Light

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V Kingdom Animal

 largest of 5 kingdoms
 has a membrane around the nucleus of the cell—Eukaryotic
 multi-cellular
 ingests their food (heterotrophic)
 four main phyla

A Coelenterates (soul-en-ter-ates)

i) has only two layers of cells

ii) has a hollow body cavity

Example: hydra, jellyfish

B Annelids

i) has segmented body walls (rings)

Example: earthworm, sandworm

C Arthropods

i) has an exoskeleton (exo=outside)

ii) has jointed appendages

Example: grasshopper, lobster, spiders, insects

D Chordates

i) has a dorsal (back) nerve cord

ii) have an endoskeleton (endo=inside)

Example: sharks, frogs, humans, cats

Chordates have many Classes (the next subgroup)

 Pisces (ex. fish)

 Amphibians (ex. frogs)
 Reptiles (ex. lizards)
 Aves (ex. birds)
 Mammalia (ex. humans, cats, dogs, whales)
Classification provides scientists and students a way to sort and group organisms for
easier study.

11.4 ORIGINS OF DIVERSITY

The diversity in our planet is attributed to diversity within a species. As the world
changed in climate and in geography as time passed, the characteristics of species
diverged so much that new species were formed. This process, by which new

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species evolve, was first described by British naturalist Charles Darwin as natural
selection.

For an organism to change, genetic mutations must occur. At times, genetic

mutations are accidental, as in the case of prokaryotes when they undergo asexual
reproduction. For most eukaryotes, genetic mutations occur through sexual
reproduction, where meiosis produces haploid gametes from the original parent cells.
The fusion of these haploid gametes into a diploid zygote results in genetic variation
in each generation. Over time, with enough arrangement of genes and traits, new
species are produced. Sexual reproduction creates an immense potential of genetic
variety.

One goal of taxonomy is to determine the evolutionary history of organisms. This can
be achieved by comparing species living today with species in the past. The
comparison in anatomy and structure is based on data from development, physical
anatomy, biochemistry, DNA, behaviour, and ecological preferences.

The following are examples of how such data is used:

 Anatomy

Although a horse and a human may look different, there is evidence that their arm
structures are quite similar. Their arms' sizes and proportions may be different, but
the anatomical structures are quite similar. Such evidence reveals that animals in
different taxa may not be that different. Biological features from a common
evolutionary origin are known as homologous.

 Development

 Biochemistry

Biochemical analyses of animals similar in appearance have yielded surprising

results. For example, although guinea pigs were once considered to be rodents, like
mice, biochemistry led them to be in the taxon of their own.

11.5 PHYLOGENY, CLADISTICS AND CLADOGRAM

Modern taxonomy is based on many hypotheses' of the evolutionary history of

organisms, known as phylogeny. As with the Scientific Method, scientists develop a
hypothesis on the history of an animal and utilise modern science and technology to
prove the phylogeny.

Cladistics is a classification system which is based on phylogeny. Expanding on

phylogeny, cladistics is based on the assumption that each group of related species
has one common ancestor and would therefore retain some ancestral characteristics.
Moreover, as these related species evolve and diverge from their common ancestor,
they would develop unique characteristics. Such characteristics are known as derived
characteristics

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The principles of phylogeny and cladistics can be expressed visually as a cladogram,

a branching diagram which acts as a family (phylogenetic) tree for similar species. A
cladogram can also be used to test alternative hypotheses for an animal's phylogeny.
In order to determine the most likely cladogram, the derived characteristics of similar
species are matched and analysed.

11.6 CLASSIFICATION OF LIVING THINGS AND VIRUSES

Viruses are the smallest biological particle (the tiniest are only 20 nm in diameter).
However, they are not biological organisms so they are not classified in any kingdom
of living things. They do not have any organelles and cannot respire or perform
metabolic functions. Viruses are merely strands of DNA or RNA surrounded by a
protective protein coat called a capsid. Viruses only come to life when they have
invaded a cell. Outside of a host cell, viruses are completely inert.

Since first being identified in 1935, viruses have been classified into more than 160
major groups. Viruses are classified based on their shape, replication properties, and
the diseases that they cause. Furthermore, the shape of a virus is determined by the
type and arrangement of proteins in its capsid. Viruses pathogenic to humans are
currently classified into 21 groups.
Viruses can also attack bacteria and infect bacterial cells. Such viruses are called
bacteriophages.

Viral Replication

As previously stated, viruses are not a biological life form so they cannot reproduce
by themselves. They need to take over a functioning eukaryotic or prokaryotic cell to
replicate its DNA or RNA and to make protein coat for new virus particles.

In order to enter a cell, a virus must attach to a specific receptor site on the plasma
membrane of the host cell. The proteins on the surface of the virus act as keys which
fit exactly into a matching glycoprotein on the host cell membrane. In some viruses,
the attachment protein is not on the surface of the virus but is in the capsid or in the
envelope.

There are two forms of viral replication: the lytic cycle and the lysogenic cycle.

Lytic Cycle

1 Attachment: The virus binds to specific receptors on the host cell.

2 Entry: There are two ways in which a virus can enter cells. Firstly, the virus
can inject its nucleic acid into the host cell. Secondly, if a virus is contained in
an envelope, the host cell can phagocytosise the entire virus particle into a
vacuole. When the virus breaks out of the vacuole, it then releases its nucleic
acid into the cell.

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3 Replication: The virus's nucleic acid instructs the host cell to replicate the
virus's DNA or RNA.

4 Assembly: New virus particles are assembled.

5 Lysis and Release: The virus directs the production of an enzyme which
damages the host cell wall, causing the host cell to swell and burst. The newly
formed virus particles are now released.

Lysogenic Cycle

1 Attachment: Similar to Lytic Cycle

2 Entry: Similar to Lytic Cycle

3 Incorporation: The viral nucleic acids is not replicated, but instead integrated
by genetic combination (crossing over) into the host cell's chromosome. When
integrated in a host cell this way, the viral nucleic acid as part of the host cell's
chromosome is known as a prophage.

4 Host Cell Reproduction: The host cell reproduces normally. Subsequent cell
divisions, daughter cells, contain original father cell's chromosome embedded
with a prophage.

5 Cycle Induction: Certain factors now determine whether the daughter cell
undergoes the lytic or lysogenic cycle. At any time, a cell undergoing the
lysogenic cycle can switch to the lytic cycle.

The reproduction cycle of viruses with RNA and no DNA is slightly different. A
notable example of a RNA-based virus is HIV, a retrovirus.

Retrovirus reproductive cycle

1 The retrovirus force RNA into cell, by either one of the two methods of entry
(See above).
2 In the retrovirus are reverse transcriptase enzymes, which catalyses the
synthesis of a DNA strand complementary to the viral RNA.

3 Reverse transcriptase catalyses a second DNA strand complementary to the

first. With these two strands, the double-stranded DNA can be created.

4 DNA is then incorporated into the host cell's chromosomes. Similar to the
concept of a prophage, this incorporated DNA is called a provirus. However,
the provirus never leaves the host cell, unlike a prophage.

5 The infected host cell undergoes the lytic or lysogenic cycle.

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Viral Genome

The genome of a virus consists of DNA or RNA, whose size and configuration vary.
The entire genome can exist as a single nucleic acid molecule or several nucleic acid
segments. Also, the DNA or RNA may be single-stranded or double-stranded, and
either linear or circular.

Not all viruses can reproduce in a host cell by themselves. Since viruses are so
small, the size of their genome is limiting. For example, some viruses have coded
instructions for only making a few different proteins for the viruses' capsid. On the
other hand, the human genome codes for over 30,000 different proteins. Therefore,
the lack of coded instructions causes some viruses to need the presence of other
viruses to help them reproduce themselves. Such viruses are called replication
defective.

Lastly, it is worthy to note that 70% of all viruses are RNA viruses. As the process of
RNA replication (with enzymes and other organelles of the host cell) is more prone to
errors, RNA viruses have much higher mutation rates than do DNA viruses.

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SUMMARY

In a broad sense, the science of classification is more strictly the classification of

living and extinct organisms – i.e., biological classification. Popularly, classifications
of living organisms arise according to the need and are often superficial. Anglo-
Saxon terms such as worm and fish have been used to refer, respectively, to any
creeping thing – snake, earthworm, intestinal parasite, or dragon – and to any
swimming or aquatic thing. Although the term fish is common to the names shellfish,
crayfish, and starfish, there are more anatomical differences between a shellfish and
a starfish than there are between a bony fish and a man. Vernacular names vary
widely.

Biologists, however, have attempted to view all living organisms with equal
thoroughness and thus have devised a formal classification. A formal classification
provides the basis for a relatively uniform and internationally understood
nomenclature, thereby simplifying cross-referencing and retrieval of information.

The usage of the terms taxonomy and systematics with regard to biological
classification varies greatly. Classification is used in biology for two totally different
purposes, often in combination, namely, identifying and making natural groups. The
specimen or a group of similar specimens must be compared with descriptions of
what is already known. This type of classification, called a key, provides as briefly
and as reliably as possible the most obvious characteristics useful in identification.
Very often they are set out as a dichotomous key with opposing pairs of characters.

Unfortunately, little is known about many of the vast variety of living things. In poorly
known groups—and most living things are poorly known – the first objective is
identification.

A natural classification is advantageous in that it groups together forms that seem

fundamentally to be related. Information utilized in the definition of a group thus need
not be repeated for each constituent. This provides concision and efficient
information storage. A certain amount of prediction is also possible—a new form with
a few ascertained characters similar to those of a natural group probably has other
similar characters. As long as no difficult intermediary forms are found, all of the
different types can be classified into definite discrete categories.

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Student Learning Activity 12

1 Why do we classify things?

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2 How many organisms have been already named of the millions of organisms
found on earth?
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3 How are organisms classified?

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4 Which branch of science is responsible for the naming and classification of

organisms?
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5 Name the oceanic and continental plates?
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6 How do we divide the animal kingdom?

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7 What was Alfred Wegener's proposal on the continental drifts based on? Was
it accepted? Why?
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8 What does the theory of evolution suggest of life on earth?

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9 How many living things are there on the planet?

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10 What are kingdoms?

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11 How do scientists classify living things?

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UNIT 12.0

BIOCHEMISTRY

Learning Outcomes

At the end of this unit, you can:

1 define Biochemistry

2 describe the schematic relationship between biochemistry, genetics, and

molecular biology

3 describe the relationship to other "molecular-scale" biological sciences

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INTRODUCTION

Biochemistry is the study of the chemical substances and processes that occur in
plants, animals, and microorganisms and of the changes they undergo during
development and life. It deals with the chemistry of life, and as such it draws on the
techniques of analytical, organic, and physical chemistry, as well as those of
physiologists concerned with the molecular basis of vital processes. All chemical
changes within the organism – either the degradation of substances, generally to
gain necessary energy or the build up of complex molecules necessary for life
processes - are collectively termed metabolism. These chemical changes depend on
the action of organic catalysts known as enzymes, and enzymes, in turn, depend for
their existence on the genetic apparatus of the cell. It is not surprising therefore, that
biochemistry enters into the investigation of chemical changes in disease, drug action,
and other aspects of medicine, as well as in nutrition, genetics, and agriculture.

The term biochemistry is synonymous with two somewhat older terms: physiological
chemistry and biological chemistry. Those aspects of biochemistry that deal with the
chemistry and function of very large molecules (e.g., proteins and nucleic acids) are
often grouped under the term molecular biology. Biochemistry is a young science,
having been known under that term only since about 1900. Its origins, however, can
be traced much further back; its early history is part of the early history of both
physiology and chemistry.

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12.1 WHAT IS BIOCHEMISTRY

Biochemistry, sometimes called biological chemistry, is the study of chemical

processes in living organisms, including, but not limited to, living matter. The laws of
biochemistry govern all living organisms and living processes. By controlling
information flow through biochemical signalling and the flow of chemical energy
through metabolism, biochemical processes give rise to the complexity of life.
Much of biochemistry deals with the structures, functions and interactions of cellular
components such as proteins, carbohydrates, lipids, nucleic acids and other bio-
molecules although increasingly processes rather than individual molecules are the
main focus. Among the vast number of different bio-molecules, many are complex
and large molecules (called biopolymers), which are composed of similar repeating
subunits (called monomers). Each class of polymeric bio-molecule has a different set
of subunit types. For example, a protein is a polymer whose subunits are selected
from a set of 20 or more amino acids. Biochemistry studies the chemical properties of
important biological molecules, like proteins, and in particular the chemistry of
enzyme-catalyzed reactions.
The biochemistry of cell metabolism and the endocrine system has been extensively
described. Other areas of biochemistry include the genetic code (DNA, RNA), protein
synthesis, cell membrane transport and signal transduction.
Over the last 40 years biochemistry has become so successful at explaining living
processes that now almost all areas of the life sciences from botany to medicine are
engaged in biochemical research. Today the main focus of pure biochemistry is in
understanding how biological molecules give rise to the processes that occur within
living cells, which in turn relates greatly to the study and understanding of whole
organisms

12.2 RELATIONSHIP TO OTHER "MOLECULAR-SCALE" BIOLOGICAL

SCIENCES

Researchers in biochemistry use specific techniques native to biochemistry, but

increasingly combine these with techniques and ideas developed in the fields of
genetics, molecular biology and biophysics. There has never been a hard-line
between these disciplines in terms of content and technique. Today, the terms
molecular biology and biochemistry are nearly interchangeable. The following figure
is a schematic that depicts one possible view of the relationship between the fields:

 Biochemistry is the study of the chemical substances and vital processes

occurring in living organisms. Biochemists focus heavily on the role, function,
and structure of bio-molecules. The study of the chemistry behind biological
processes and the synthesis of biologically active molecules are examples of
biochemistry.
 Genetics is the study of the effect of genetic differences on organisms. Often
this can be inferred by the absence of a normal component (e.g., one gene).
The study of "mutants" – organisms with a changed gene that leads to the
organism being different with respect to the so-called "wild type" or normal

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phenotype. Genetic interactions (epistasis) can often confound simple

interpretations of such "knock-out" or "knock-in" studies.

Figure 12.1 Schematic relationships between biochemistry, genetics, and molecular biology

 Molecular biology is the study of molecular underpinnings of the process of

replication, transcription and translation of the genetic material. The central
dogma of molecular biology where genetic material is transcribed into RNA
and then translated into protein, despite being an oversimplified picture of
molecular biology, still provides a good starting point for understanding the
field. This picture, however, is undergoing revision in light of emerging novel
roles for RNA.

 Chemical Biology seeks to develop new tools based on small molecules that
allow minimal perturbation of biological systems while providing detailed
information about their function. Further, chemical biology employs biological
systems to create non-natural hybrids between bio-molecules and synthetic
devices (for example emptied viral capsids that can deliver gene therapy or
drug molecules).

The similarity in body chemistry suggests inheritance of genes from a common

ancestor. The degree of similarities between groups helps us determine the
closeness of the relationships. Body chemicals studies include blood proteins such
as haemoglobin.

Other evidences include population studies, domesticated animals and cultivated

plants shows the degree of similarities between their groups.

12.3 SIMILARITIES BETWEEN ORGANISMS

Biochemistry also reveals similarities between organisms of different species. For
example, the metabolism of vastly different organisms is based on the same complex
biochemical compounds. The protein cytochrome c, essential for aerobic respiration,
is one such universal compound. The universality of cytochrome c is evidence that all
aerobic organisms probably descended from a common ancestor that used this
compound for respiration. Certain blood proteins found in almost all organisms give
additional evidence that these organisms descended from a common ancestor. Such

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biochemical compounds, including cytochrome c and blood proteins, are so complex

it is unlikely that almost identical compounds would have evolved independently in
widely different organisms.
The similarities described below are not the only ones scientists have noticed among
organisms of different species. The image to the left shows that embryos of certain
species develop almost identically, especially in the early stages. Such physical
similarities indicate that there are genetic similarities between the organisms.
These similarities can be considered evidence that the organisms shown probably
descended from a common ancestor.
The similarities between living species-- in ancestry, in homologous and vestigial
structures, in embryological development, and in biochemical compounds-- all could
be explained as extremely remarkable coincidences. However, a far more probable
explanation of these similarities is that species have arisen by descent and
modification from more ancient forms.
Such biochemical compounds, including cytochrome c and blood proteins, are so
complex it is unlikely that almost identical compounds would have evolved
independently in widely different organisms. Further studies of cytochrome c in
different species reveal variations in the amino acid sequence of this molecule.

Figure 12.2 showing the homologous structures of different organisms

Scientists have similarly compared the biochemistry of universal blood proteins. Their
studies reveal evidence of degrees of relatedness between different species. This
evidence implies that some species share a more recent common ancestor than
other species do. From such evidence scientists have inferred the evolutionary
relationships between different species of organisms.

12.4 CHEMICAL COMPOSITION OF LIVING MATTER

Every living cell contains, in addition to water and salts or minerals, a large number of
organic compounds, substances composed of carbon combined with varying
amounts of hydrogen and usually also of oxygen. Nitrogen, phosphorus, and sulfur

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are likewise common constituents. In general, the bulk of the organic matter of a cell
may be classified as:
(1) protein,
(2) carbohydrate, and
(3) fat or lipid.
Nucleic acids and various other organic derivatives are also important constituents.
Each class contains a great diversity of individual compounds. Many substances that
cannot be classified in any of the above categories also occur, though usually not in
large amounts.
Proteins are fundamental to life, not only as structural elements (e.g., collagen) and
to provide defence (as antibodies) against invading destructive forces but also
because the essential biocatalysts are proteins. The chemistry of proteins is based
on the researches of the German chemist Emil Fischer, whose work from 1882
demonstrated that proteins are very large molecules, or polymers, built up of about
24 amino acids. Proteins may vary in size from small—insulin with a molecular weight
of 5,700 (based on the weight of a hydrogen atom as 1)—to very large—molecules
with molecular weights of more than 1,000,000. The first complete amino acid
sequence was determined for the insulin molecule in the 1950s. By 1963 the chain of
amino acids in the protein enzyme ribonuclease (molecular weight 12,700) had also
been determined, aided by the powerful physical techniques of X-ray-diffraction
analysis. In the 1960s, Nobel Prize winners J.C. Kendrew and M.F. Perutz, utilizing
X-ray studies, constructed detailed atomic models of the proteins haemoglobin and
myoglobin (the respiratory pigment in muscle), which were later confirmed by
sophisticated chemical studies. The abiding interest of biochemists in the structure of
proteins rests on the fact that the arrangement of chemical groups in space yields
important clues regarding the biological activity of molecules.
Carbohydrates include such substances as sugars, starch, and cellulose. The second
quarter of the 20th century witnessed a striking advance in the knowledge of how
living cells handle small molecules, including carbohydrates. The metabolism of
carbohydrates became clarified during this period, and elaborate pathways of
carbohydrate breakdown and subsequent storage and utilization were gradually
outlined in terms of cycles (e.g., the Embden–Meyerhof glycolytic cycle and the
Krebs cycle). The involvement of carbohydrates in respiration and muscle contraction
was well worked out by the 1950s.

Refinements of the schemes continue.

Fats, or lipids, constitute a heterogeneous group of organic chemicals that can be
extracted from biological material by non-polar solvents such as ethanol, ether, and
benzene. The classic work concerning the formation of body fat from carbohydrates
was accomplished during the early 1850s. Those studies, and later confirmatory
evidence, have shown that the conversion of carbohydrate to fat occurs continuously
in the body. The liver is the main site of fat metabolism. Fat absorption in the intestine,
studied as early as the 1930s, still is under investigation by biochemists. The control
of fat absorption is known to depend upon a combination action of secretions of the

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pancreas and bile salts. Abnormalities of fat metabolism, which result in disorders
such as obesity and rare clinical conditions, are the subject of much biochemical
research. Equally interesting to biochemists is the association between high levels of
fat in the blood and the occurrence of arteriosclerosis (―hardening‖ of the arteries).
Nucleic acids are large, complex compounds of very high molecular weight present in
the cells of all organisms and in viruses. They are of great importance in the
synthesis of proteins and in the transmission of hereditary information from one
generation to the next. Originally discovered as constituents of cell nuclei (hence their
name), it was assumed for many years after their isolation in 1869 that they were
found nowhere else. This assumption was not challenged seriously until the 1940s,
when it was determined that two kinds of nucleic acid exist: deoxyribonucleic acid
(DNA), in the nuclei of all cells and in some viruses; and ribonucleic acid (RNA), in
the cytoplasm of all cells and in most viruses.

12.5 GENETICS
Genetics is the study of heredity in general and of genes in particular. Since the
dawn of civilization, mankind has recognized the influence of heredity and has
applied its principles to the improvement of cultivated crops and domestic animals. A
Babylonian tablet more than 6,000 years old, for example, shows pedigrees of horses
and indicates possible inherited characteristics. Other old carvings show cross-
pollination of date palm trees. Most of the mechanisms of heredity, however,
remained a mystery until the 19th century, when genetics as a systematic science
began.

Figure 12.3 The initial proposal of the

structure of DNA by James Watson and
Francis Crick, which was accompanied by a
suggestion on the means of replication.

Genetics arose out of the identification of genes, the fundamental units responsible
for heredity. Genetics may be defined as the study of genes at all levels, including the
ways in which they act in the cell and the ways in which they are transmitted from
parents to offspring. Modern genetics focuses on the chemical substance that genes
are made of, called deoxyribonucleic acid, or DNA, and the ways in which it affects
the chemical reactions that constitute the living processes within the cell. Gene action

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depends on interaction with the environment. Green plants, for example, have genes
containing the information necessary to synthesize the photosynthetic pigment
chlorophyll that gives them their green colour. Chlorophyll is synthesized in an
environment containing light because the gene for chlorophyll is expressed only
when it interacts with light. If a plant is placed in a dark environment, chlorophyll
synthesis stops because the gene is no longer expressed.

Genetics as a scientific discipline stemmed from the work of Gregor Mendel in the
middle of the 19th century. Mendel suspected that traits were inherited as discrete
units, and, although he knew nothing of the physical or chemical nature of genes at
the time, his units became the basis for the development of the present
understanding of heredity. All present research in genetics can be traced back to
Mendel's discovery of the laws governing the inheritance of traits. The word gene,
coined in 1909 by Danish botanist Wilhelm Johannsen, has given genetics its name.

Genetics forms one of the central pillars of biology and overlaps with many other
areas such as agriculture, medicine, and biotechnology.

Chromosomes

The microscopic, threadlike part of the cell that carries hereditary information in the
form of genes

Figure 12.4 Showing DNA packing into chromatin and chromosome

Source: Encyclopaedia Britannica, Inc.

The structure and location of chromosomes is one of the chief differences between
the two basic types of cells: prokaryotic cells and eukaryotic cells. Among organisms
with prokaryotic cells (i.e., bacteria and blue-green algae), chromosomes consist
entirely of deoxyribonucleic acid (DNA). The single chromosome of a prokaryotic cell
is not enclosed within a nuclear membrane. Among all other organisms (i.e., the
eukaryotes), the chromosomes are contained in a membrane-bound cell nucleus.
The chromosomes of a eukaryotic cell consist primarily of DNA attached to a protein

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core. They also contain ribonucleic acid (RNA). Among both prokaryotes and
eukaryotes, the arrangement of components in the DNA molecules determines the
genetic information. The remainder of this article pertains to eukaryotic chromosomes.
Every species has a characteristic number of chromosomes (chromosome number).
In species that reproduce asexually, the chromosome number is the same in all the
cells of the organism. Among sexually reproducing organisms, the number of
chromosomes in the body (somatic) cells is diploid (2n; a pair of each chromosome),
twice the haploid (1n) number found in the sex cells, or gametes. The haploid number
is produced during meiosis (q.v.). During fertilization, two gametes combine to
produce a zygote, a single cell with a diploid set of chromosomes.
Somatic cells reproduce by dividing, a process called mitosis (q.v.). Between cell
divisions the genetic material (chromatin) is diffused throughout the nucleus in a
tangled network of filaments called chromonemata. These long filaments are formed
from the uncoiled chromosomes and probably provide a large surface area, thereby
facilitating DNA synthesis. During this phase, DNA duplicates itself in preparation for
cell division.
At the onset of cell division, the chromonemata coil up and are surrounded by a
protein sheath, forming a tiny rod, or chromosome. Each chromosome actually
consists of a set of duplicate chromatids that are held together by the centromere.
The centromere is the point of attachment to the spindle fibres (part of a structure
that pulls the chromatids to opposite ends of the cell). During the middle stage in cell
division, the centromere duplicates, and the chromatid pair separates; each
chromatid becomes a separate chromosome at this point. The cell divides, and both
of the daughter cells have a complete (diploid) set of chromosomes. The
chromosomes uncoil in the new cells, again forming the diffuse network of filaments.
Among many organisms that have separate sexes, there are two basic types of
chromosomes: sex chromosomes and autosomes. Autosomes control the inheritance
of all the characteristics except the sex-linked ones, which are controlled by the sex
chromosomes. Humans have 22 pairs of autosomes and one pair of sex
chromosomes. All act in the same way during cell division.
Chromosome breakage is the physical breakage of subunits of a chromosome. It is
usually followed by reunion (frequently at a foreign site, resulting in a chromosome
unlike the original). Breakage and reunion of homologous chromosomes during
meiosis is the basis for the classical model of crossing over, which results in
unexpected types of offspring of a mating.

Sex-linked characteristics
In genetics, all of the genes on a single chromosome are inherited as a group; that is,
during cell division they act and move as a unit rather than independently. The
existence of linkage groups is the reason some traits do not comply with Mendel's
law of independent assortment (recombination of genes and the traits they control);
i.e., the principle applies only if genes are located on different chromosomes.
Variation in the gene composition of a chromosome can occur when a chromosome
breaks, and the sections join with the partner chromosome if it has broken in the

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same places. This exchange of genes between chromosomes, called crossing over,
usually occurs during meiosis, when the total number of chromosomes is halved.
Sex linkage is the tendency of a characteristic to be linked to one sex. The X
chromosome in Drosophila flies and human beings, for example, carries a complete
set of genes; the Y chromosome has only a few genes. Eggs of females carry an X
chromosome; sperm of males may carry an X or a Y. An egg fertilized by a sperm
with an X chromosome results in a female; one fertilized by a sperm with a Y
chromosome results in a male. In offspring with the XY chromosome pair, any trait
carried by the X chromosome will appear unless there is a corresponding gene
(allele) on the Y chromosome. Examples of sex-linked traits in man are red–green
colour blindness and haemophilia. These traits are controlled by genes on the X
chromosome and thus occur much more frequently in men than in women because
there is no allele on the Y chromosome to offset them

Chromosomes Numbers
Precise number of chromosomes is typical for a given species. In any given asexually
reproducing species, the chromosome number is always the same. In sexually
reproducing organisms, the number of chromosomes in the body (somatic) cells is
diploid (2n; a pair of each chromosome), twice the haploid (1n) number found in the
sex cells, or gametes. The haploid number is produced during meiosis (q.v.). An
organism with any multiple of the diploid number of chromosomes is said to be
polyploid. Although it is a normal evolutionary strategy among many plant groups,
polyploidy is frequently linked to abnormalities in animals. Any change from the
typical chromosome number for a species may be accompanied by changes—
sometimes drastic—in the organism. The number of chromosomes does not correlate
with the apparent complexity of an animal or plant: in human beings, for example, the
diploid number is 2n = 46 (that is, 23 pairs), compared with 2n = 78, or 39 pairs, in
the dog and 2n = 36 (18) in the common earthworm. There is an equally great range
of numbers among plants.
In general, the karyotype is the characteristic chromosome complement of a
eukaryote species. The preparation and study of karyotypes is part of cytogenetics.
Although the replication and transcription of DNA is highly standardized in
eukaryotes, the same cannot be said for their karyotypes, which are often highly
variable. There may be variation between species in chromosome number and in
detailed organization. In some cases, there is significant variation within species.

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Figure 12.5 Karyotype; human chromosome number

Often there is:

1 variation between the two sexes
2 variation between the germ-line and soma (between gametes and the rest of
the body)
3 variation between members of a population, due to balanced genetic
polymorphism
4 geographical variation between races
5 mosaics or otherwise abnormal individuals
Also, variation in karyotype may occur during development from the fertilised egg.
The technique of determining the karyotype is usually called karyotyping. Cells can
be locked part-way through division (in metaphase) in vitro (in a reaction vial) with
colchicine. These cells are then stained, photographed, and arranged into a
karyogram, with the set of chromosomes arranged, autosomes in order of length, and
sex chromosomes (here X/Y) at the end; see Figure 12.5 above.
Like many sexually reproducing species, humans have special gonosomes (sex
chromosomes, in contrast to autosomes). These are XX in females and XY in males.

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SUMMARY

The study of the chemical substances and processes that occur in plants, animals,
and microorganisms and of the changes they undergo during development and life. It
deals with the chemistry of life, and as such it draws on the techniques of analytical,
organic, and physical chemistry, as well as those of physiologists concerned with the
molecular basis of vital processes. All chemical changes within the organism-either
the degradation of substances, generally to gain necessary energy, or the build-up of
complex molecules necessary for life processes-are collectively termed metabolism.
These chemical changes depend on the action of organic catalysts known as
enzymes, and enzymes, in turn, depend for their existence on the genetic apparatus
of the cell. It is not surprising, therefore, that biochemistry enters into the investigation
of chemical changes in disease, drug action, and other aspects of medicine, as well
as in nutrition, genetics, and agriculture.
The term biochemistry is synonymous with two somewhat older terms: physiological
chemistry and biological chemistry. Those aspects of biochemistry that deal with the
chemistry and function of very large molecules (e.g., proteins and nucleic acids) are
often grouped under the term molecular biology. Biochemistry is a young science,
having been known under that term only since about 1900. Its origins, however, can
be traced much further back; its early history is part of the early history of both
physiology and chemistry.
Every living cell contains, in addition to water and salts or minerals, a large number of
organic compounds, substances composed of carbon combined with varying
amounts of hydrogen and usually also of oxygen. Nitrogen, phosphorus, and sulfur
are likewise common constituents. In general, the bulk of the organic matter of a cell
may be classified as:
(1) protein,
(2) carbohydrate, and
(3) fat or lipid.
Nucleic acids and various other organic derivatives are also important constituents.
Each class contains a great diversity of individual compounds. Many substances that
cannot be classified in any of the above categories also occur, though usually not in
large amounts.
Genetic studies have shown that the hereditary characteristics of a species are
maintained and transmitted by the self-duplicating units known as genes, which are
composed of nucleic acids and located in the chromosomes of the nucleus. One of
the most fascinating chapters in the history of the biological sciences contains the
story of the elucidation, in the mid-20th century, of the chemical structure of the
genes, their mode of self-duplication, and the manner in which the deoxyribonucleic
acid (DNA) of the nucleus causes the synthesis of ribonucleic acid (RNA), which,
among its other activities, causes the synthesis of protein. Thus, the capacity of a
protein to behave as an enzyme is determined by the chemical constitution of the
gene (DNA) that directs the synthesis of the protein.

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Student Learning Activity 13

1 What evidence is available that shows similarities between relationships of

organisms?
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2 What is name of the universal compound responsible for aerobic respiration?

________________________________________________________________

3 What are fundamental to life?

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4 Substances such as sugars, starch, and cellulose are collectively known as

what?
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UNIT 13.0

EARLY VIEWS ON CREATION

Learning Outcomes

At the end of this unit, you can:

1 understand the different views of the doctrines of creation

2 explain the theological and philosophical doctrines of creation

3 identify relationships between religion and science

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INTRODUCTION

Everybody these days, it seems, has a different take on the Creation Account. The
scientific community once had Christendom running scared with what seemed to be
fairly conclusive evidence that the Bible's understanding of the origin of the universe
held no ground in reality. Not to be vanquished so easily, many Christians began
searching for answers – for ways they might accord Scripture with science.
Differing perspectives on the Creation have existed for ages, but recently, the fervour
seems to have raised a notch with people becoming increasingly dogmatic on the
side of their own perspective. Christians of one perspective are becoming skeptical of
the genuineness of the salvation of those who hold to another interpretation.
With all this in mind, it should be of benefit to summarize the differing views (while
supplying bibliographies of additional resources for further studies) and allow
Christians to make their own choices as to which view accords best with Scripture.

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13.1 MYTHS
The myth of creation is the symbolic narrative of the beginning of the world as
understood by a particular community. The later doctrines of creation are
interpretations of this myth in light of the subsequent history and needs of the
community. Thus, for example, all theology and speculation concerning creation in
the Christian community are based on the myth of creation in the biblical book of
Genesis and of the new creation in Jesus Christ. Doctrines of creation are based on
the myth of creation, which expresses and embodies all of the fertile possibilities for
thinking about this subject within a particular religious community.
Myths are narratives that express the basic valuations of a religious community.
Myths of creation refer to the process through which the world is centred and given a
definite form within the whole of reality. They also serve as a basis for the orientation
of man in the world. This centring and orientation specify man's place in the universe
and the regard he must have for other humans, nature, and the entire nonhuman
world; they set the stylistic tone that tends to determine all other gestures, actions,
and structures in the culture. The cosmogonic (origin of the world) myth is the myth
par excellence. In this sense, the myth is akin to philosophy, but, unlike philosophy, it
is constituted by a system of symbols; and because it is the basis for any subsequent
cultural thought, it contains rational and non-rational forms. There is an order and
structure to the myth, but this order and structure is not to be confused with rational,
philosophical order and structure. The myth possesses its own distinctive kind of
order.

13.2 CREATIONISM
Creationism is a broad range of beliefs involving an appeal to the miraculous
intervention of a God to explain the origin of the universe, of life, and of the different
kinds of plants and animals on Earth. Since the second half of the 20th century, the
most visible and politically active creationists have been from Christian tradition.
Their ideas are usually based on a literal reading of the Bible. The first was the so-
called Day-Age theory, according to which the six days of the Biblical creation
(Genesis 1:1-2:4) represented vast geological ages rather than 24-hour periods.
Many object to the theory of evolution by natural selection first proposed by Charles
Darwin in the 19th century and now forming the backbone of the biological sciences,
and specifically to the idea that human beings evolved from apes.
The Bible framework for earth history makes no statement about continental splitting,
so it is unnecessary and unwise to take a "Biblical" position on the question. When
God created the land and sea, the waters were "gathered together unto one place"
(Genesis 1:9), which may imply one large ocean and one large land mass. The
scripture which says "the earth was divided" in the days of Peleg (Genesis 10:25) is
generally thought to refer to the Tower of Babel division (Genesis 11:1-9) and some
suppose this included continental separation. To believe, however, that the
continents moved thousands of miles during the Tower of Babel incident without
causing another global flood requires a miracle. Similarly, it is doubtful whether the
long day of Joshua can be explained naturalistically by plate tectonics.

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The idea that sea-floor plates form slowly and continuously at a rate of a few
centimeters each year as the ocean crust is being rift apart, is not supported by
geologic data nor Biblical sound. The concept of destruction of sea-floor plates over
millions of years by slow under thrusting below ocean trenches is also doubtful.
Furthermore, the cause for the alleged gradual and uninterrupted motion of plates is
an unsolved mystery. Despite these failures in the modern theory of "plate tectonics,"
the notion that the earth's surface has been deformed at the margins of moving plate-
like slabs appears to be a valid one. The facts indicate that the separation of the
continents, rifting of the ocean floor, and under thrusting of ocean trenches, were
accomplished by rapid processes, not occurring today, initiated by a catastrophic
mechanism. Noah's Flood, as described in the Bible, was certainly associated with
tectonic processes and provides the time in the Biblical framework of earth history
when continental separation may have occurred.
Given the stark difference between evolution and six-day creation, many people
assume that Darwin‘s theory shook the foundations of the Christian faith. In truth, the
literal six-day interpretation of Genesis 1-2 was not the only perspective held by
Christians prior to modern science. St. Augustine (354-430), John Calvin (1509-1564),
John Wesley (1703-171), and others supported the idea of Accommodation. In the
Accommodation view, Genesis 1-2 was written in a simple allegorical fashion to
make it easy for people of that time to understand. In fact, Augustine suggested that
the 6 days of Genesis 1 describe a single day of creation. St. Thomas Aquinas
(1225-1274) argued that God did not create things in their final state, but created
them to have potential to develop as he intended. The views of these and other
Christian leaders are consistent with God creating life by means of evolution.

13.3 THEOLOGICAL AND PHILOSOPHICAL DOCTRINES

Myths and poetic renderings in legends, sagas, and poetry express the basic cultural
insights into some of the elements involved in the human consciousness about
creation. Theological, philosophical, and scientific theory are types of rationalizations
of these basic insights in terms of the particular culture and historical periods of the
cultures in question.
The attempt to integrate the meanings of primordiality, dualisms and antagonisms,
sacrifices, and ruptures and to meet demands of some kind of logical order and, at
the same time, keep alive the meaning of these structures as religious realities,
objects of worship, and a charter for the moral life, has led to the development of
doctrines.
In ―primitive‖ and archaic societies, the correct ritual enactment of mythical symbols
ensures the order of the world. These rituals usually take place at propitious
moments (e.g., at the birth of a child, marriage, the founding of a new habitation, the
erection of a house or temple, the beginning of a new year). In each case, the
seemingly practical activities imitate the mythic structure of the first beginning.
Theological and philosophical speculations and controversies centre within and
between religious communities over the issues of the primordial nature of reality,
dualisms, the process of creation, and the nature of time and space. A doctrine of
creation must contain or suggest the manner in which all cultural meanings, both

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empirical and abstract, constitute an integral totality. Speculations that are based on
the initial insights of a mythical theme explicate some principle in the myth as a basis
for generalization and logical form on which all elements and themes may be ordered.

Interpretative Methods
Facing the modern Christian are two distinct methods for interpreting the Creation
Account: by consulting the discoveries of science or by consulting Scripture's
testament to itself. Within both methods are several perspectives and so we will treat
each one briefly. Because the science-based methods focus more upon interpreting
God's Word through the light of empirical data rather than through the hermeneutical
demands of context, we will refer to all these methods as "theories," while
exegetically-based methods, being naturally more rigorous and adherent to the
discovery of the true meaning of Scripture, will be called "interpretations." We shall
also begin with the science-based method and then proceed to deal with those views
which are more thoroughly entrenched in Scripture in greater depth.

Science-Based Methods
Science-based views interpret Scripture through the filter of their experience of
general revelation. They see the sciences and their own observations of the world
around them saying something incontrovertible; and so, they interpret Scripture in
light of these things. Truly, the pressure of the scientific communities - both Christian
and secular - can seem overwhelming and nobody wants to feel they have their head
in the sand and are ignoring plain evidence. But never should the Christian allow
current scientific understanding to supersede the historical and literary intent of the
authors of Scripture. We will here discuss briefly several of these viewpoints, but
dismiss them in the end as being built upon eisegesis.

Theistic Evolution
Surrendering the historicity and honesty of Scripture beyond all other popular
viewpoints, theories of theistic evolution force interpreters to mythologize the Genesis
narrative. While maintaining that God did truly maintain control of all creative
processes, the view strips Scripture of its accuracy by positing that Adam was not
arrived at by fiat creation but through thousands of years of natural evolutionary
process aided and directed by a divine touch. The specifics of the view are beyond
the scope of this treatment as they question seriously traditional and conservative
methods for the interpretation of Scripture-as well as its ability to function as an
authority for the believer.

Gap Theory
When the scientific community began discovering evidence to support long
geological eras in the 18th century, a segment of Christendom felt compelled to
syncretize their interpretation of Scripture with this newfound empirical data. Motive
askew, they postulated that the universe was already in existence for an

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indeterminate duration before the Creation Week began (and hence allow for a very
old earth, but are able still to maintain God's recent fiat creation of mankind).
A once-popular revision of this theme is the Restoration Theory. Proponents of this
version of Gap Theory believed that the universe was created full-form and populated
only to be decimated by a cataclysmic war led between God and Satan. This war left
the earth a wasteland, "formless and void" (and explains why we find fossilized
dinosaur bones that seem to be millions of years old). So then, by theory, the recent
Creation Week would be a re-Creation or restoration of a world that was once
destroyed.
The hinge upon which Gap Theory turns is the interaction between verses 1, 2, and 3
of Genesis 1. But while the theory's suppositions are imaginative and interesting to
ponder, they really must be forced upon the text — and are forced upon the text for a
poor reason. A clear example of this eisegetical pattern of interpreting Scripture in
light of science can be found in the following quote from a Gap Theory supporter:
"Wherefore, as by one man sin entered into the world, and death by sin; and so
death passed upon all men, for that all have sinned:" (Rom 5:12).
But under Adam's feet, entombed in the sedimentary rocks of the planet, was God's
testimony to the reality of the existence of death long before Adam; the fossil record;
the evidence of a previous world that was destroyed and wiped off the face of the old
earth.
This is a distressing demonstration of the Gap Theory hermeneutic. It is as if the
author is saying, "Scripture says death came through Adam, but science says it came
earlier, so we ought to change our interpretation of Scripture because science is our
ultimate authority." This reliance upon science as a hermeneutic principle is why we
will not here give any real consideration to the view's interpretive accuracy.

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SUMMARY
Myths are narratives that express the basic valuations of a religious community. The
myth of creation is the symbolic narrative of the beginning of the world as understood
by a particular community. The later doctrines of creation are interpretations of this
myth in light of the subsequent history and needs of the community. Thus, all
theology and speculation concerning creation in the Christian community are based
on the myth of creation in the biblical book of Genesis and of the new creation in
Jesus Christ. Doctrines of creation are based on the myth of creation, which
expresses and embodies all of the fertile possibilities for thinking about this subject
within a particular religious community.
Myths of creation refer to the process through which the world is centred and given a
definite form within the whole of reality. They also serve as a basis for the orientation
of man in the world. This centring and orientation specify man's place in the universe
and the regard he must have for other humans, nature, and the entire nonhuman
world; they set the stylistic tone that tends to determine all other gestures, actions,
and structures in the culture. The cosmogonic (origin of the world) myth is the myth
par excellence. In this sense, the myth is akin to philosophy, but, unlike philosophy, it
is constituted by a system of symbols; and because it is the basis for any subsequent
cultural thought, it contains rational and non-rational forms. There is an order and
structure to the myth, but this order and structure is not to be confused with rational,
philosophical order and structure. The myth possesses its own distinctive kind of
order.
Myths of creation have another distinctive character in that they provide both the
model for non-mythic expression in the culture and the model for other cultural myths.
In this sense, one must distinguish between cosmogonic myths and myths of the
origin of cultural techniques and artefacts. Insofar as the cosmogonic myth tells the
story of the creation of the world, other myths that narrate the story of a specific
technique or the discovery of a particular area of cultural life take their models from
the stylistic structure of the cosmogonic myth. These latter myths may be etiological
(i.e., explaining origins); but the cosmogonic myth is never simply etiological, for it
deals with the ultimate origin of all things.
The cosmogonic myth thus has a pervasive structure; its expression in the form of
philosophical and theological thought is only one dimension of its function as a model
for cultural life. Though the cosmogonic myth does not necessarily lead to ritual
expression, ritual is often the dramatic presentation of the myth. Such dramatization
is performed to emphasize the permanence and efficacy of the central themes of the
myth, which integrates and undergirds the structure of meaning and value in the
culture. The ritual dramatization of the myth is the beginning of liturgy, for the
religious community in its central liturgy attempts to re-create the time of the
beginning.
From this ritual dramatization the notion of time is established within the religious
community. To be sure, in most communities there is the notion of a sacred and a
profane time. The prestige of the cosmogonic myth establishes sacred or real time. It
is this time that is most efficacious for the life of the community. Dramatization of

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sacred time enables the community to participate in a time that has a different quality
than ordinary time, which tends to be neutral. All significant temporal events are
spoken of in the language of the cosmogonic myth for only by referring them to this
primordial model will they have significance.

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Student Learning Activity 14

1 Which myth is said to be the myth par excellence? Why/

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

2 Where in the Bible does it mention the continental shift supposedly?

___________________________________________________________________
___________________________________________________________________
___________________________________________________________________

3 What are some of the moments that are seemingly practical activities that
imitate the mythical structure of the first beginning?
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___________________________________________________________________
___ _______________________________________________________________

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ANSWERS
TO

STUDENT
LEARNING
ACTIVITIES

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UNIT 1.0 ECOLOGY

Student Learning Activity One

1 State at least three different biomes of the world.

The major biomes are desert, tropical rainforest, savannah grassland, temperate deciduous
forest and coniferous forest. All biomes vary geographically from each other. Other minor
biomes includes the associated freshwater communities (streams, lakes, ponds, wetlands)
and marine environment (Open Ocean, littoral-shallow water regions, benthic-bottom regions,
rocky shores, sandy shores, estuaries, and associated tidal marshes.

There are twelve types of Biomes in the World: Tundra Biome, Desert Biome, Taiga Biome,
Tropical Rainforest Biome, Chaparral Biome, Coral Reef Biome, Freshwater Biome,
Grassland Biome, Ocean Biome, Savannah Biome, Temperate Deciduous Forest Biome and
Wetland Biome

2 Outline the main adaptations that plants in tundra posses in order to survive
the harsh cold and icy environment.

Plant adaptations of the tundra biome:

1. The Arctic Willow – is a tiny tree that grows very slowly due to the cold conditions.
Morphological adaptation: grows horizontally to the ground where it is warmest and protected
from the cold.
Physiological Adaptation: produces antifreeze chemicals in the sap to prevent the cells from
freezing in the winter.

2. The Arctic Poppy – a small annual plant with large yellow flowers growing close to the
ground.
Morphological Adaptation: large flower attract the few insects and trap weak sunshine to
raise the temperature slightly.
Physiological Adaptation: fast growing, pollinating and setting of seeds to beat the start of
winter.

3 Name the four types of consumers?

Animals cannot make their own food. They must eat other organisms to obtain their nutrients
and energy so they are called consumers. There are four different types of consumers:

 Herbivores – eat only plant material such as; leaves, nectar, and fruits. Herbivores
spend a lot of time eating because plants are not a concentrated source of protein
and also contain a large proportion of cellulose which is difficult to digest.
 Carnivores – eat other animals. Meat is a good source of protein and energy so
carnivores do not spend much time eating as herbivores.
 Omnivores – eat both plants and animals.
 Parasites – live and feed on or inside another living organism called its host.

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4 Why do forests, deserts, and types of life in each area differ from each other?

Forest types are distinguished from each other according to species composition (which
develops in part according to the age of the forest), the density of tree cover, type of soils
found there, and the geologic history of the forest region.

Desert environments are so dry that they support only extremely sparse vegetation; trees are
usually absent and, under normal climatic conditions, shrubs or herbaceous plants provide
only very incomplete ground cover. Extreme aridity renders some deserts virtually devoid of
plants; however, this barrenness is believed to be due in part to the effects of human
disturbance, such as heavy grazing of cattle, on an already stressed environment.

5 List the different types of deserts and their proprieties?

The deserts in the world are divided into three types.

1 Subtropical deserts - they are the hottest deserts with dry terrain and rapid
evaporation rate.
2 Cool coastal deserts - the average temperature in these deserts is much cooler
because of cold offshore oceanic currents.
3 Cold winter deserts - they are striking with harsh temperature differences ranging
from 38°C in summers to -12°C in winters.

Student Learning Activity Two

1 Outline the main adaptations that both plants and animals in the desert posses
in order to survive the harsh, hot and dry climate.

The adaptations for animals are:

Desert mammals such as bears, bobcats, coyotes, kit foxes, mule deer, raccoons, rabbits,
gophers and squirrels stay cool in the peak desert heat by hiding out in trees or digging
burrows underground.

Mountain lions and bobcats are the elusive carnivores of the desert, hunting deer, rabbits,
birds, snakes and rodents primarily at night. Coyotes, kit foxes and raccoons are omnivores
that survive in the desert by eating cacti, frogs, toads, fish, rabbits, squirrels and anything
else they can scavenge.

Animals that live in the hot desert have many adaptations. Some animals never drink, but get
their water from seeds and plants. Many animals are nocturnal, sleeping during the hot day
and only coming out at night to eat and hunt. Some animals rarely spend any time above
ground.

In order to survive, desert animals have developed a number of ways of adapting to their
habitat. The most common adaptation in behaviour is staying in the shade of plants or rocks
or by burrowing underground in the heat of the day. Many desert animals are nocturnal: they
stay inactive in shelter during the day and hunt at night when it is cool.

The adaptations for plants are:

Plants have adaptations to help them survive (live and grow) in different areas. Adaptations
are special features that allow a plant to live in a particular place or habitat. These

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adaptations might make it very difficult for the plant to survive in a different place. Plants
must cope with extensive water loss.

 Some plants, called succulents, store water in their stems or leaves;

 Some plants have no leaves or small seasonal leaves that only grow after it rains.
The lack of leaves helps reduce water loss during photosynthesis. Leafless plants
conduct photosynthesis in their green stems.
 Long root systems spread out wide or go deep into the ground to absorb water;
 Some plants have a short life cycle, germinating in response to rain, growing,
flowering, and dying within one year. These plants can evade drought.
 Leaves with hair help shade the plant, reducing water loss. Other plants have leaves
that turn throughout the day to expose a minimum surface area to the heat.
 Spines to discourage animals from eating plants for water;
 Waxy coating on stems and leaves help reduce water loss.
 Flowers that open at night lure pollinators who are more likely to be active during the
cooler night.
 Slower growing requires less energy. The plants don't have to make as much food
and therefore do not lose as much water.

2 What is an ecosystem?

Ecosystem is the complex of living organisms, their physical environment, and all their
interrelationships in a particular unit of space. An ecosystem can be categorized into its
abiotic constituents, including minerals, climate, soil, water, sunlight, and all other nonliving
elements, and its biotic constituents, consisting of all its living members. Linking these
constituents together are two major forces: the flow of energy through the ecosystem, and
the cycling of nutrients within the ecosystem.

3 What are the major parts of an ecosystem?

Ecosystems consist of life forms existing in a symbiotic relationship with their environment.
Life forms in ecosystems compete with one another to become the most successful at
reproducing and surviving in a given niche, or environment. Two main components exist in
an ecosystem: abiotic and biotic. The abiotic components of an ecosystem consist of the
nonorganic aspects of the environment that determine what life forms can thrive. The biotic
components of an ecosystem are the life forms that inhabit it. The life forms of an ecosystem
aid in the transfer and cycle of energy.

4 Name the types of deserts and their distinct characteristics.

The deserts in the world are divided into three types.

Subtropical deserts - they are the hottest deserts with dry terrain and rapid evaporation rate.
Cool coastal deserts - the average temperature in these deserts is much cooler because of
cold offshore oceanic currents.
Cold winter deserts - they are striking with harsh temperature differences ranging from 38°C
in summers to -12°C in winters.

5 What are the two main adaptations that desert animals must make?

Animals that live in the hot desert have many adaptations. Some animals never drink, but get
their water from seeds and plants. Many animals are nocturnal, sleeping during the hot day

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and only coming out at night to eat and hunt. Some animals rarely spend any time above
ground.

In order to survive, desert animals have developed a number of ways of adapting to their
habitat. The most common adaptation in behaviour is staying in the shade of plants or rocks
or by burrowing underground in the heat of the day. Many desert animals are nocturnal: they
stay inactive in shelter during the day and hunt at night when it is cool.

6 How do desert animals prevent water from leaving their bodies?

Desert animals are known to store water in the fatty tissues in their tails and other parts of
the body. Also, the hump of the camel has fatty tissue. When this fatty tissue is metabolized,
it produces both energy as well as water. Desert animals like reptiles have minimized loss of
water by excreting waste in the form of an insoluble white compound uric acid.

UNIT 2.0 TROPICAL RAINFOREST

Student Learning Activity Three

1 List at least 3 components of an ecosystem.

The rainforest are distinctive in their variety of plant and animal life and complex ecosystem
structure. Due to the high levels of water and solar energy available, they are among the
most productive ecosystems of the world.

2 Name the distinct layers of the rain forest.

Rainforest now make up about 6% of the Earth's surface. They are typically divided into four
distinct layers. These layers are: the forest floor, the understory (lower canopy), the upper
canopy, and the emergent.

3 List some of the abiotic factors that affect plants and animals?

Rainforests are home to half the plants and animals found of the planet, and the abiotic
factors of these rainforests play a crucial role in adding to their biodiversity.
Abiotic factors, i.e. the non-living elements such as sunlight and precipitation, play an
important role in determining the biodiversity of a region. For a species of plant or animal to
survive in any region, it has to adapt itself to the abiotic conditions which exist there.

The abiotic factors of this rainforest biome are-the amount of water and sunlight, climate,
weather and precipitation. These things affect the trees and animals that live there. These
are very important because without the right amount of water and sunlight the trees in the
rainforest would not be able to grow and would die.

4 What are three animal adaptations in the rainforest biome?

 Tropical rainforests are almost perfect for animal survival. It is always warm, and there
are no season changes bringing times when there is little food. There is shade from the
heat and shelter from the rain. There is no shortage of food and water.

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 Because there are so many creatures living in the rainforest, there is a great deal of
competition for food, sunlight and space. Animals have developed special features in
order to survive.

5 Refer to the picture of a destructive rainforest and answer the questions that
follow.

A Explain why deforestation can reduce soil fertility.

 Humus is not replaced.

 Nutrients are washed away downwards.
 Leaves do not fall to create humus.
 The vegetation creates most of the nutrients.

B How can deforestation affect people who live in these areas?

 Increased flooding/homes lost/moved to urban areas.

 Created jobs.
 Increased surface runoff due to deforestation can cause increased flooding, which
can lead to the destruction of infrastructure.
 Homes of native groups of people living in the forests can be lost.
 As the soil becomes less fertile farmers move to shanty towns, and or urban areas.
 The timber project creates jobs for the locals.

UNIT 3.0 THE SOIL

Student Learning Activity Four

1 Define soil.
Soil is one of the principal substrata of life on Earth, serving as a reservoir of water and
nutrients, as a medium for the filtration and breakdown of injurious wastes, and as a
participant in the cycling of carbon and other elements through the global ecosystem. It has
evolved through weathering processes driven by biological, climatic, geologic, and
topographic influences.

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2 What does Horizon A compose primarily of?

Soil horizons are defined by features that reflect soil-forming processes. For instance, the
uppermost soil layer (not including surface litter) is termed the A horizon. This is a weathered
layer that contains an accumulation of humus (decomposed, dark-coloured, carbon-rich
matter) and microbial biomass that is mixed with small-grained minerals to form aggregate
structures.

3 List the factors that influence soil degradation.

Soil degradation is a major consequence of ecosystem destruction and soil disturbance. It
can be physical, chemical and the anthropogenic causes. It refers to the decline in soil
productivity through adverse changes in nutrient states, organic matter, structural stability
and concentrations of electrolytes and toxic chemicals.
Soil degradation incorporates a number of environmental problems, some of which are
interrelated. The extent of soil degradation is influenced by a number of factors, namely soil
characteristics, relief, climate, land use and socio-economic and political controls.
4 On what is soil quality based?
Soil quality may be defined as the capacity of a soil to function for human survival and for the
related bio-geocycling. Many people have begun to support a native plant industry, selecting
these plants rather than non-native species for their landscaping. These native plants offer
natural habitats for many soil creatures. The increasing popularity of organic farming and
organic produce has begun to lessen the impact of pesticides and chemical fertilizers on the
soil. All of these efforts make a difference in keeping and protecting the soil habitats that soil
critters need.
Four basic soil functions contribute to such ecosystem maintenance:
1 Sustenance of biological activity, diversity, and productivity
2 Storage and cycling of nutrients
3 Water and solute partition and regulation
4 Filtration, buffering, decomposition, immobilization and detoxification of organic and
inorganic materials
These functions apply to any ecosystem that comprises soil as a component, whether
directly or indirectly altered by man. When any of these functions are hampered, soil quality
decreases.

5 Why are soils in the tropical rainforest region infertile?

Soils in tropical rainforests are typically deep but not very fertile, partly because large
proportions of some mineral nutrients are bound up at any one time within the vegetation
itself rather than free in the soil. The moist, hot climatic conditions lead to deep weathering of
rock and the development of deep, typically reddish soil profiles rich in insoluble
sesquioxides of iron and aluminium, commonly referred to as tropical red earths. Because
precipitation in tropical rainforest regions exceeds evapo-transpiration at almost all times, a
nearly permanent surplus of water exists in the soil and moves downward through the soil
into streams and rivers in valley floors. Through this process nutrients are leached out of the
soil, leaving it relatively infertile. Most roots, including those of trees, are concentrated in the
uppermost soil layers where nutrients become available from the decomposition of fallen
dead leaves and other organic litter. Sandy soils, particularly, become thoroughly leached of

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nutrients and support stunted rainforests of peculiar composition. A high proportion of plants
in this environment have small leaves that contain high levels of toxic or unpalatable
substances

6 Name the distinct profile or sequence of horizontal layers of soil.

Soils differ widely in their properties because of geologic and climatic variation over distance
and time. Even a simple property, such as the soil thickness, can range from a few
centimetres to many metres, depending on the intensity and duration of weathering,
episodes of soil deposition and erosion, and the patterns of landscape evolution.
A vertical sequence of layers is produced by the combined actions of percolating waters and
living organisms. These layers are called horizons, and the full vertical sequence of horizons
constitutes the soil profile. Soil horizons are defined by features that reflect soil-forming
processes. The uppermost soil layer (not including surface litter) is termed the A horizon.
This is a weathered layer that contains an accumulation of humus (decomposed, dark-
coloured, carbon-rich matter) and microbial biomass that is mixed with small-grained
minerals to form aggregate structures.
Below A lies the B horizon. In mature soils this layer is characterized by an accumulation of
clay (small particles less than 0.002 mm [0.00008 inch] in diameter) that has either been
deposited out of percolating waters or precipitated by chemical processes involving dissolved
products of weathering.
Below the A and B horizons is the C horizon, a zone of little or no humus accumulation or soil
structure development. The C horizon often is composed of unconsolidated parent material
from which the A and B horizons have formed. It lacks the characteristic features of the A
and B horizons and may be either relatively unweathered or deeply weathered. At some
depth below the A, B, and C horizons lies consolidated rock, which makes up the R horizon.
First, two additional horizons are defined. Litter and decomposed organic matter (for
example, plant and animal remains) that typically lie exposed on the land surface above the
A horizon are given the designation O horizon, whereas the layer immediately below an A
horizon that has been extensively leached (that is, slowly washed of certain contents by the
action of percolating water) is given the separate designation E horizon, or zone of eluviation.
The development of E horizons is favoured by high rainfall and sandy parent material, two
factors that help to ensure extensive water percolation.
The combined A, E, B horizon sequence is called the solum. The solum is the true seat of
soil-forming processes and is the principal habitat for soil organisms.
The second enhancement to soil horizon nomenclature is the use of lowercase suffixes to
designate special features that are important to soil development. The most common of
these suffixes are applied to B horizons: g to denote mottling caused by water logging, h to
denote the illuvial accumulation of humus, k to denote carbonate mineral precipitates, o to
denote residual metal oxides, s to denote the illuvial accumulation of metal oxides and
humus, and t to denote the accumulation of clay.

7 List the processes that result in the formation of horizons.

The uppermost soil layer (not including surface litter) is termed the A horizon. This is
a weathered layer that contains an accumulation of humus (decomposed, dark-coloured,
carbon-rich matter) and microbial biomass that is mixed with small-grained minerals to form
aggregate structures.

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Below A lies the B horizon. In mature soils this layer is characterized by an accumulation of
clay (small particles less than 0.002 mm [0.00008 inch] in diameter) that has either been
deposited out of percolating waters or precipitated by chemical processes involving dissolved
products of weathering.
Below the A and B horizons is the C horizon, a zone of little or no humus accumulation or soil
structure development. The C horizon often is composed of unconsolidated parent material
from which the A and B horizons have formed. It lacks the characteristic features of the A
and B horizons and may be either relatively unweathered or deeply weathered. At some
depth below the A, B, and C horizons lies consolidated rock, which makes up the R horizon.
First, two additional horizons are defined. Litter and decomposed organic matter (for
example, plant and animal remains) that typically lie exposed on the land surface above the
A horizon are given the designation O horizon, whereas the layer immediately below an A
horizon that has been extensively leached (that is, slowly washed of certain contents by the
action of percolating water) is given the separate designation E horizon, or zone of eluviation.
The development of E horizons is favoured by high rainfall and sandy parent material, two
factors that help to ensure extensive water percolation.
The combined A, E, B horizon sequence is called the solum. The solum is the true seat of
soil-forming processes and is the principal habitat for soil organisms.
The second enhancement to soil horizon nomenclature is the use of lowercase suffixes to
designate special features that are important to soil development. The most common of
these suffixes are applied to B horizons: g to denote mottling caused by water logging, h to
denote the illuvial accumulation of humus, k to denote carbonate mineral precipitates, o to
denote residual metal oxides, s to denote the illuvial accumulation of metal oxides and
humus, and t to denote the accumulation of clay.

8 What influences soil fertility?

In agriculture, the pH is probably the most important single property of the moisture
associated with a soil, since that indication reveals what crops will grow readily in the soil and
what adjustments must be made to adapt it for growing any other crops. Soil fertility is
directly influenced by pH through the solubility of many nutrients. Acidic soils are often
considered infertile, and so they are for most conventional agricultural crops, although
conifers and many species of shrub will not thrive in alkaline soil. At a pH lower than 5.5,
many nutrients become very soluble and are readily leached from the soil profile.
Acidic soil can be ―sweetened‖ or neutralized by treating it with lime. As soil acidity increases
so does the solubility of aluminium and manganese in the soil, and many plants (including
agricultural crops) will tolerate only slight quantities of those metals. At high pH, nutrients
become insoluble and plants cannot readily extract them. Maximum soil fertility occurs in the
range 6.0 to 7.2. Acid content of soil is heightened by the decomposition of organic material
by microbial action, by fertilizer salts that hydrolyze or nitrify, by oxidation of sulfur
compounds when salt marshes are drained for use as farmland, and by other causes.

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UNIT 4.0 MEASURING CLIMATE

Student Learning Activity Five

1 How is climate usually described?

Climate has been understood to mean the atmospheric conditions that prevail in a given
region or zone. In the older form, climate, it was sometimes taken to include all aspects of
the environment, including the natural vegetation. The best modern definitions of climate
regard it as constituting the total experience of weather and atmospheric behaviour over a
number of years in a given region. However, climate is not just the ―average weather‖ (an
obsolete, and always inadequate, definition). It should include not only the average values of
the climatic elements that prevail at different times but also their extreme ranges and
variability and the frequency of various occurrences. Climate is therefore time-dependent,
and climatic values or indexes should not be quoted without specifying what years they refer
to.
2 List the instruments that are used to measure climate.

How can it be What instruments can we

What is it?
measured? use to measure it?
This is a Degrees
measurement of Celsius or Thermometers
Temperature
heat. Fahrenheit
Wind sock,
This measures the
Knots Anemometer
Wind movement or air.
Ventimeters
This is the
Intensity of Campbell-Stokes sunshine
Sun measurement of light
sunlight recorder
and heat
This is the
Rain and snow
measurement of
(Precipitation) Millimetres Rain Gauge
moisture from the
clouds.
Humidity This is the moisture Psychrometer,
Percentages
in the air humidity gauge
This is the moisture
Cloud Oktas Cloud Mirror
built up in air.
This is the
measurement of Map, ruler
Visibility Kilometres
things being visible or binoculars
not
This is the
Barometer,
measurement of the Millibars and
Pressure aneroid barometer, mercury
force exerted on the hectopascals
barometer
earth

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3 Define the term Climate.

The best modern definitions of climate regard it as constituting the total experience of
weather and atmospheric behaviour over a number of years in a given region. However,
climate is not just the ―average weather‖ (an obsolete, and always inadequate, definition). It
should include not only the average values of the climatic elements that prevail at different
times but also their extreme ranges and variability and the frequency of various occurrences

4 What is climate change?

It is much easier to document the evidence of climate variability and past climate change
than it is to determine their underlying mechanisms. Climate is influenced by a multitude of
factors that operate at timescales ranging from hours to hundreds of millions of years. Many
of the causes of climate change are external to the Earth system. Others are part of the
Earth system but external to the atmosphere. Still others involve interactions between the
atmosphere and other components of the Earth system and are collectively described as
feedbacks within the Earth system. Feedbacks are among the most recently discovered and
challenging causal factors to study. Nevertheless, these factors are increasingly recognized
as playing fundamental roles in climate variation

UNIT 5.0 AQUATIC ECOSYSTEMS

Student Learning Activity Six

1 Explain what is meant by osmosis.

Osmosis is the spontaneous passage or diffusion of water or other solvents through a semi
permeable membrane (one that blocks the passage of dissolved substances—i.e., solutes).
This is a separation technique in which a semi permeable membrane is placed between two
solutions containing the same solvent. The membrane allows passage of small solution
components (usually the solvent) while preventing passage of larger molecules. The natural
tendency is for the solvent to flow from the side where its concentration is higher to the side
where its concentration is lower.

2 When does osmotic gradient become useful?

Usually the osmotic gradient is used while comparing solutions that have a semi permeable
membrane between them allowing water to diffuse between the two solutions, toward the
hypertonic solution (the solution with the higher concentration).

3 What is meant by Osmotic pressure?

The pressure produced by or associated with osmosis and dependent on molar
concentration and absolute temperature: such as (i): the maximum pressure that develops in
a solution separated from a solvent by a membrane permeable only to the solvent (ii): the
pressure that must be applied to a solution to just prevent osmosis

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4 In which way do animals depend on plants for their survival?

Some plants and animals live in more than one habitat. Some plants are good at growing
anywhere (we call many of these weeds!). Animals are able to move around so they can
graze or hunt in more than one habitat. The organisms in a habitat depend on each other.
Animals need plants for food, for shelter from the weather and as hiding places from
predators. Without plants there would be no animals for the carnivores to eat. Plants need
animals to pollinate their flowers, to spread (disperse) their seeds and to help keep the soil
fertile.

5 Name the three basic types of freshwater ecosystems and briefly describe their
composition.
Lentic: slow moving water, including pools, ponds, and lakes.
Lake ecosystems can be divided into zones. One common system divides lakes into three
zones (see figure). The first, the littoral zone, is the shallow zone near the shore. This is
where rooted wetland plants occur. The offshore is divided into two further zones, an open
water zone and a deep water zone. In the open water zone (or photic zone) sunlight supports
photosynthetic algae, and the species that feed upon them. In the deep water zone, sunlight
is not available and the food web is based on detritus entering from the littoral and photic
zones.
Ponds are small bodies of freshwater with shallow and still water, marsh, and aquatic plants.
They can be further divided into four zones: vegetation zone, open water, bottom mud and
surface film
Lotic: faster moving water, for example streams and rivers.
The major zones in river ecosystems are determined by the river bed's gradient or by the
velocity of the current. Faster moving turbulent water typically contains greater
concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving
water of pools. These distinctions forms the basis for the division of rivers into upland and
lowland rivers
Wetlands: areas where the soil is saturated or inundated for at least part of the time.
Wetlands are dominated by vascular plants that have adapted to saturated soil. There are
four main types of wetlands: swamp, marsh, fen and bog (both fens and bogs are types
of mire). Wetlands are the most productive natural ecosystems in the world because of the
proximity of water and soil. Hence they support large numbers of plant and animal species.
Due to their productivity, wetlands are often converted into dry land
with dykes and drains and used for agricultural purposes.

UNIT 6.0 FOOD CHAINS AND FOOD WEBS

Student Learning Activity Seven

1 Give three examples of food chains that exist in nature.

Food chain is the sequence of transfers of matter and energy from organism to organism in
the form of food. Food chains intertwine locally into a food web because most organisms
consume more than one type of animal or plant. Plants, which convert solar energy to food
by photosynthesis, are the primary food source. In a predator chain, a plant-eating animal is
eaten by a larger animal. In a parasite chain, a smaller organism consumes part of a larger

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host and may itself be parasitized by even smaller organisms. In a saprophytic chain,
microorganisms live on dead organic matter.
Because energy, in the form of heat, is lost at each step, or trophic level, chains do not
normally encompass more than four or five trophic levels. In overpopulated areas people
commonly increase the total food supply by cutting out one step in the food chain: instead of
consuming animals that eat cereal grains, the people themselves consume the grains.
Because the food chain is made shorter, the total amount of energy available to the final
consumers is increased.

2 In a ecological pyramid, what happens to energy, biomass and the number of

species as you move up? Why?
A small amount of the energy stored in plants, between 5 and 25 percent, passes into
herbivores (plant eaters) as they feed, and a similarly small percentage of the energy in
herbivores then passes into carnivores (animal eaters). The result is a pyramid of energy,
with most energy concentrated in the photosynthetic organisms at the bottom of food chains
and less energy at each higher trophic level. Some of the remaining energy does not pass
directly into the plant-herbivore-carnivore food chain but instead is diverted into the detritus
food chain. Bacteria, fungi, scavengers, and carrion eaters that consume detritus (detritivores)
are all eventually consumed by other organisms.
The rate at which these consumers convert the chemical energy of their food into their own
biomass is called secondary productivity. The efficiency at which energy is transferred from
one trophic level to another is called ecological efficiency. On average it is estimated that
there is only a 10 percent transfer of energy.
Energy is lost in several ways as it flows along these pathways of consumption. Most plant
tissue is uneaten by herbivores, and this stored energy is therefore lost to the plant-
herbivore-carnivore food chain. In terrestrial communities less than 10 percent of plant tissue
is actually consumed by herbivores. The rest falls into the detritus pathway, although the
detritivores consume only some of this decaying tissue.

3 What is biomass?
Biomass is the weight or total quantity of living organisms of one animal or plant species
(species biomass) or of all the species in the community (community biomass), commonly
referred to a unit area or volume of habitat. The weight or quantity of organisms in an area at
a given moment is the standing crop. The total amount of organic material produced by living
organisms of a particular area within a set period of time, called the primary or secondary
productivity (the former for plants, the latter for animals), is usually measured in units of
energy, such as gram calories or kilojoules per square metre per year. In a different though
related sense, the term biomass refers to plant materials and animal waste used especially
as a source of fuel.

4 In an ecosystem, can there be more carnivores than herbivores?

Some organisms' position in the food chain can vary as their diet differs. For example, when
a bear eats berries, the bear is functioning as a primary consumer. When a bear eats a plant-
eating rodent, the bear is functioning as a secondary consumer. When the bear eats salmon,
the bear is functioning as a tertiary consumer (this is because salmon is a secondary
consumer, since salmon eat herring that eat zooplankton that eat phytoplankton, that make
their own energy from sunlight). Think about how people's place in the food chain varies -
often within a single meal.

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In any food web, energy is lost each time one organism eats another. Because of this, there
have to be many more plants than there are plant-eaters. There are more autotrophs than
heterotrophs, and more plant-eaters than meat-eaters. Although there is intense competition
between animals, there is also interdependence. When one species goes extinct, it can
affect an entire chain of other species and have unpredictable consequences.
As the number of carnivores in a community increases, they eat more and more of the
herbivores, decreasing the herbivore population. It then becomes harder and harder for the
carnivores to find herbivores to eat, and the population of carnivores decreases. In this way,
the carnivores and herbivores stay in a relatively stable equilibrium, each limiting the other's
population. A similar equilibrium exists between plants and plant-eaters.

5 What is the 10% rule? What is its significance? Why is energy lost?
A small amount of the energy stored in plants, between 5 and 25 percent, passes into
herbivores (plant eaters) as they feed, and a similarly small percentage of the energy in
herbivores then passes into carnivores (animal eaters). The result is a pyramid of energy,
with most energy concentrated in the photosynthetic organisms at the bottom of food chains
and less energy at each higher trophic level.
The rate at which these consumers convert the chemical energy of their food into their own
biomass is called secondary productivity. The efficiency at which energy is transferred from
one trophic level to another is called ecological efficiency. On average it is estimated that
there is only a 10 percent transfer of energy.
Energy is lost in several ways as it flows along these pathways of consumption. Most plant
tissue is uneaten by herbivores, and this stored energy is therefore lost to the plant-
herbivore-carnivore food chain. In terrestrial communities less than 10 percent of plant tissue
is actually consumed by herbivores. The rest falls into the detritus pathway, although the
detritivores consume only some of this decaying tissue.
The efficiency by which animals convert the food they ingest into energy for growth and
reproduction is called assimilation efficiency. Herbivores assimilate between 15 and 80
percent of the plant material they ingest, depending on their physiology and the part of the
plant that they eat. Herbivores eating seeds and young vegetation high in energy have the
highest assimilation efficiencies, those that eat older leaves have intermediate efficiencies,
and those that feed on decaying wood have very low efficiencies. Carnivores generally have
higher assimilation efficiencies than herbivores, often between 60 and 90 percent, because
their food is more easily digested.
The overall productivity of the biosphere is therefore limited by the rate at which plants
convert solar energy (about 1 percent) into chemical energy and the subsequent efficiencies
at which other organisms at higher trophic levels convert that stored energy into their own
biomass (approximately 10 percent). Human-induced changes in net primary productivity in
the parts of the biosphere that have the highest productivity, such as estuaries and tropical
moist forests, are likely to have large effects on the overall biological productivity of the
Earth.

6 What is the difference between food chain and a food web?

Food chains intertwine locally into a food web because most organisms consume more than
one type of animal or plant. Plants, which convert solar energy to food by photosynthesis, are
the primary food source. In a predator chain, a plant-eating animal is eaten by a larger
animal. In a parasite chain, a smaller organism consumes part of a larger host and may itself

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be parasitized by even smaller organisms. In a saprophytic chain, microorganisms live on

dead organic matter.
Because all species are specialized in their diets, each trophic pyramid is made up of a
series of interconnected feeding relationships called food chains. Most food chains consist of
three or four trophic levels. A typical sequence may be plant, herbivore, carnivore, top
carnivore; another sequence is plant, herbivore, parasite of the herbivore, and parasite of the
parasite. Many herbivores, detritivores, carnivores, and parasites, however, eat more than
one species, and a large number of animal species eat different foods at different stages of
their life histories. In addition, many species eat both plants and animals and therefore feed
at more than one trophic level. Consequently, food chains combine into highly complex food
webs. Even a simplified food web can show a complicated network of trophic relationships.

7 Who do the skunks depend on for survival?

Skunks are a black-and-white mammal, found primarily in the Western Hemisphere, that use
extremely well-developed scent glands to release a noxious odour in defence. The term
skunk, however, refers to more than just the well-known striped skunk (Mephitis mephitis).
The skunk family is composed of 11 species, 9 of which are found in the Western
Hemisphere. Primarily nocturnal, skunks are diverse carnivores that live in a wide variety of
habitats, including deserts, forests, and mountains. Most are about the size of a housecat,
but some are significantly smaller.
Hog-nosed skunks are capable diggers and have powerfully built upper bodies, which allow
them to climb in rough terrain. Spotted skunks are the most agile, able to climb squirrel-like
both up and down trees. Striped skunks spend most of their time on the ground and are less
agile than spotted skunks. Striped skunks are omnivorous, feasting on insects, small
vertebrates, and eggs, as well as vegetable matter. Hog-nosed skunks and stink badgers
have elongated snouts adapted to rooting for grubs and other insects in the soil; they too rely
on a variety of foods. Spotted skunks are the most carnivorous.

8 Refer to the food web below and answer the questions that follow.

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A Which organisms may not increase in population if all the lantern fish were
removed from this ecosystem?

copepods, pteropods

B Using the same food web, which organisms would be affected if the marlin
were to overproduce?

lancet fish, amphipods, copepods, diatoms (more from food web)

C From the food web, sketch out a food chain.

diatoms copepods amphipods lancet fish

UNIT 7.0 NUTRIENT CYCLES

Student Learning Activity Eight

1 List the major components of the

A Nutrient Cycle
The nutrient cycle describes how nutrients move from the physical environment into living
organisms, and subsequently is recycled back to the physical environment. This movement
of nutrients, essential for life, from the environment into plants and animals and back again,
is a vital function of the ecology of any region. These essential nutrients alternate between
inorganic and organic states as they rotate through their respective biogeochemical cycles.
These cycles can include all or part of the following: the atmosphere, which is made up
largely of gases including water vapour; the lithosphere, which encompasses the soil and the
entire solid crust of the Earth; and the hydrosphere, which includes lakes, rivers, and oceans.

B Nitrogen Cycle
1 Nitrogen, a component of proteins and nucleic acids, is essential to life on Earth.
Although 78 percent by volume of the atmosphere is nitrogen gas, this abundant
reservoir exists in a form unusable by most organisms. Through a series of microbial
transformations, however, nitrogen is made available to plants, which in turn
ultimately sustain all animal life. The steps, which are not altogether sequential, fall
into the following classifications: nitrogen fixation, nitrogen assimilation,
ammonification, nitrification, and denitrification.

2 More simplied version of components

Bacterial Oxidation (Nitrosomonas)
Bacterial Oxidation (Nitrobacter)
Fertilizer Uptake
Consumption of Food
Death/Waste Matter
Bacterial Decomposition (Oxidation)

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3 Carbon Cycle
Life is built on the conversion of carbon dioxide into the carbon-based organic compounds of
living organisms. The carbon cycle illustrates the central importance of carbon in the
biosphere. Different paths (decomposition, respiration, consumption, photosynthesis) of the
carbon cycle recycle the element at varying rates.

4 Water Cycle
A portion of the biogeochemical cycle of all elements involves time spent cycling through the
hydrosphere. Water itself cycles within the biosphere. Unlike the cycles of the other major
nutrients, however, the hydrologic (water) cycle would continue in some form even in the
absence of living organisms. Most of the Earth's water is in its core, in the sedimentary rocks
near its surface, and in the ocean. A minute percentage of the water, however, continually
cycles through the atmosphere, oceans, and terrestrial environments mainly by the
processes of evaporation and precipitation.
This cycle is made up of a few main parts:
 evaporation (and transpiration)
 condensation
 precipitation
 collection

5 What are the 3 processes of water cycle?

The water cycle (hydrologic cycle) consists of various complicated processes of precipitation,
evaporation, interception, transpiration, infiltration, percolation, retention, detention, overland
flow, through flow, and runoff.

6 Why are bacteria important components of the Nitrogen Cycle?

Nitrogen, a component of proteins and nucleic acids, is essential to life on Earth. Although 78
percent by volume of the atmosphere is nitrogen gas, this abundant reservoir exists in a form
unusable by most organisms. Through a series of microbial transformations, however,
nitrogen is made available to plants, which in turn ultimately sustain all animal life. The steps,
which are not altogether sequential, fall into the following classifications: nitrogen fixation,
nitrogen assimilation, ammonification, nitrification, and denitrification.
Nitrogen is fixed, or combined, in nature as nitric oxide by lightning and ultraviolet rays, but
more significant amounts of nitrogen are fixed as ammonia, nitrites, and nitrates by soil
microorganisms. More than 90 percent of all nitrogen fixation is affected by them. Two kinds
of nitrogen-fixing microorganisms are recognized: free-living (non-symbiotic) bacteria,
including the cyanobacteria (or blue-green algae) Anabaena and Nostoc and such genera as
Azotobacter, Beijerinckia, and Clostridium; and mutualistic (symbiotic) bacteria such as
Rhizobium, associated with leguminous plants, and Spirillum lipoferum, associated with
cereal grasses.

7 What are the main greenhouse gases causing global warming?

Many greenhouse gases occur naturally, such as water vapour, carbon dioxide, methane,
nitrous oxide, and ozone. Others such as hydrofluoro carbons (HFCs), perfluoro
carbons (PFCs), and sulfur hexafluoride (SF6) result exclusively from human industrial
processes.

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Human activities also add significantly to the level of naturally occurring greenhouse gases:
 Carbon dioxide is released into the atmosphere by the burning of solid waste, wood
and wood products, and fossil fuels (oil, natural gas, and coal).
 Nitrous oxide emissions occur during various agricultural and industrial processes,
and when solid waste or fossil fuels are burned.
 Methane is emitted when organic waste decomposes, whether in landfills or in
connection with livestock farming. Methane emissions also occur during the
production and transport of fossil fuels.
The Properties of Greenhouse Gases vary in their ability to absorb and hold heat in the
atmosphere, a phenomenon known as the "greenhouse effect." HFCs and PFCs are the
most heat-absorbent, but there are also wide differences between naturally occurring gases.
For example, nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide,
and methane absorbs 21 times more heat per molecule than carbon dioxide

8 What is Global Warming?

The gases in the atmosphere that absorb radiation are known as "greenhouse gases" (GHG)
because they are largely responsible for the greenhouse effect. The greenhouse effect, in
turn, is one of the leading causes of global warming.
Global warming is the gradual increase in the overall temperature of the earth's atmosphere
due to the greenhouse effect caused by increased levels of carbon dioxide,
Chlorofluorocarbons (CFCs), and other pollutants.
Global warming is related to the more general phenomenon of climate change, which refers
to changes in the totality of attributes that define climate. In addition to changes in air
temperature, climate change involves changes to precipitation patterns, winds, ocean
currents, and other measures of Earth's climate. Normally, climate change can be viewed as
the combination of various natural forces occurring over diverse timescales. Since the advent
of human civilization, climate change has involved an ―anthropogenic,‖ or exclusively human-
caused, element, and this anthropogenic element has become more important in the
industrial period of the past two centuries. The term global warming is used specifically to
refer to any warming of near-surface air during the past two centuries that can be traced to
anthropogenic causes.

9 What is air pollution?

Air pollution is the introduction into the atmosphere of chemicals, particulates, or biological
materials that cause discomfort, disease, or death to humans, damage other living organisms
such as food crops, or damage the natural environment or built environment. Dust storms in
desert areas and smoke from forest and grass fires contribute to particulate and chemical air
pollution. Volcanic activity is the major natural source of air pollution, pouring huge amounts
of ash and toxic fumes into the atmosphere. Air pollution may affect humans directly, causing
irritation of the eyes or coughing.
The atmosphere is a complex dynamic natural gaseous system that is essential to support
life on planet Earth. Stratospheric ozone depletion due to air pollution has long been
recognized as a threat to human health as well as to the Earth's ecosystems.

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UNIT 8.0 POPULATION

Student Learning Activity Nine

1 What is a population?

A A population is a summation of all the organisms of the same group or species, who
live in the same geographical area, and have the capability of interbreeding. In
ecology the population of a certain species in a certain area is estimated using
the Lincoln Index. In sociology, population refers to a collection
of human beings. Demography is a social science which entails the statistical study of
human populations.

B A population is a subset of individuals of one species that occupies a particular

geographic area and, in sexually reproducing species, interbreeds. The geographic
boundaries of a population are easy to establish for some species but more difficult
for others.

3 Why do you need to know who or what are in a population?

There are numerous merits of knowing about population. Target markets in more better ways
and increase the chances of success of business. Helps the Government to analyse how to
do the planning for the population because it the responsibility of the government, needed to
control the population growth and to improve the better quality of life.

4 When is a population identified?

The population is simply all the members of the group that you are interested in. A sample is
a sub-set of the population that is usually chosen because to access all members of the
population is prohibitive in time, money and other resources. A key issue in choosing the
sample relates to whether the members you have chosen are representative of the
population. Often the sample is chosen randomly from a list that contains all the members of
the population; such a list is called a sampling frame.

5 How can population be controlled and indicate some reasons to justify this
action?

Human population control is the practice of artificially altering the rate of growth of a human
population. Historically, human population control has been implemented by limiting the
population's birth rate, usually by government mandate, and has been undertaken as a
response to factors including high or increasing levels of poverty, environmental
concerns, religious reasons, and overpopulation. While population control can involve
measures that improve people's lives by giving them greater control of their reproduction,
many programs have exposed them to exploitation.

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6 Identify four characteristics of a population.

The organism size growth rate population density

7 Identify the characteristics that describe populations.

Population characteristics describe the diverse social, demographic, and economic features
of the habitat. Comparison of data by factors such as sex, age, and race and ethnicity can be
used to tailor the development and evaluation of programs and policies and service delivery.
Some of these characteristics include the age and racial and ethnic distribution of the
population, income, household composition, education, and occupation, and participation in
social compositions.

UNIT 9.0 EVOLUTION

Student Learning Activity Ten

1 Explain why the birds have different sized beaks.

A bird's beak is a tool adapted for survival. Darwin's finches provide a classic example of
divergence among closely related species. Each species has evolved its own beak design
variation. Some finches have adapted thick, heavy beaks for cracking big seeds; others have
tiny, pointy beaks for cracking small seeds or probing flowers and cacti. The woodpecker
finch even uses twigs to dig insects out of wood.

So-called cactus finches boast longer, more pointed beaks than their relatives the ground
finches. Beaks of warbler finches are thinner and more pointed than both.

These adaptations make them more fit to survive on available food.

In other words, beaks changed as the birds developed different tastes for fruits, seeds, or
insects picked from the ground or cacti. Long, pointed beaks made some of them more fit for
picking seeds out of cactus fruits. Shorter, stouter beaks served best for eating seeds found
on the ground. Eventually, the immigrants evolved into 14 separate species, each with its
own song, food preferences, and beak shapes.

2 List at least four evidence of evolution of the vertebrates from a common

ancestor.

Evolutionary theory predicts that, if all organisms have a shared ancestry, then all living
things should have certain characteristics in common. The genetic code is universal; all
plants, animals, fungi, bacteria and protists have the same genetic code. There is no
chemical reason for the specific code that we have; that is the genetic code is not chemically
constrained to be the way it is.

There are two patterns of similarity in traits among species. The first type is an analogous
similarity, which is when a trait in two different species is similar and they have the same

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function. The other type of similarity is homologous similarity, which is when two traits are
similar, regardless of the function of the trait. In this case, two traits are similar even when it
is not functionally necessary for them to be similar. The best explanation for this pattern of
homologous similarity is that the traits are similar because of a common history of the two
species. In other words, two species have the same trait because the common ancestor of
the two species had the trait. The best explanation for this similarity in embryos is a shared
history of vertebrates-all vertebrates share a common ancestor that had a tailed embryo with
gill pouches.

3 Darwin’s Theory of Evolution by Natural Selection has four main points.

Describe any two.

The theory of evolution is one of the great intellectual revolutions of human history,
drastically changing our perception of the world and of our place in it. Charles Darwin put
forth a coherent theory of evolution and amassed a great body of evidence in support of this
theory. Darwin‘s process of natural selection has four components.

1 Variation

Organisms within populations exhibit individual variation in appearance and

behaviour. These variations may involve body size, hair colour, facial markings, voice
properties, or number of offspring. On the other hand, some traits show little to no variation
among individuals—for example, number of eyes in vertebrates.

2 Inheritance

Some traits are consistently passed on from parent to offspring. Such traits are heritable,
whereas other traits are strongly influenced by environmental conditions and show weak
heritability.

3 High rate of population growth

Most populations have more offspring each year than local resources can support leading to
a struggle for resources. Each generation experiences substantial mortality.

4 Differential survival and reproduction

Individuals possessing traits well suited for the struggle for local resources will contribute
more offspring to the next generation.

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From one generation to the next, the struggle for resources (―struggle for existence‖) will
favour individuals with some variations over others and thereby change the frequency of
traits within the population. This process is natural selection.

In order for natural selection to operate on a trait, the trait must possess heritable variation
and must confer an advantage in the competition for resources. If one of these requirements
does not occur, then the trait does not experience natural selection.

Natural selection operates by comparative advantage, not an absolute standard of design.

―…as natural selection acts by competition for resources, it adapts the inhabitants of each
country only in relation to the degree of perfection of their associates‖ (Charles Darwin, On
the Origin of Species, 1859).

5 Define natural selection.

Natural selection is the gradual natural process by which biological traits become either more
or less common in a population as a function of the effect of inherited traits on the differential
reproductive success of organisms interacting with their environment. It is a key mechanism
of evolution

From one generation to the next, the struggle for resources (―struggle for existence‖) will
favour individuals with some variations over others and thereby change the frequency of
traits within the population. This process is natural selection.

In order for natural selection to operate on a trait, the trait must possess heritable variation
and must confer an advantage in the competition for resources. If one of these requirements
does not occur, then the trait does not experience natural selection.

6. What is Darwin's Theory of Evolution as presented in 'The Origin of Species'

mainly concerns with?

Until the publication in 1859 of Charles Darwin's On the Origin of Species by Means of
Natural Selection or the Preservation of Favoured Races in the Struggle for Life. Darwin
stated that all living creatures multiply so rapidly that, if left unchecked, they would soon
overpopulate the world. According to Darwin, the checks on population size are maintained
by competition for the means of life. Hence, if any member of a species differs in some way
that makes it better fitted to survive, then it will have an advantage that its offspring would be
likely to perpetuate.

7 Why are Darwin's Finches important?

Distinctive group of birds whose radiation into several ecological niches in the competition-
free isolation of the Galapagos Islands and on Cocos Island gave the English naturalist
Charles Darwin evidence for his thesis that ―species are not immutable.‖

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Darwin is the English naturalist whose theory of evolution by natural selection became the
foundation of modern evolutionary studies.

8 What is meant by Geological Timescale?

The geologic time scale (GTS) is a system of chronological measurement that

relates stratigraphy to time, and is used by geologists, paleontologists, and other earth
scientists to describe the timing and relationships between events that have occurred
throughout Earth's history.
Evidence from radiometric dating indicates that the Earth is about 4.54 billion years old. The
geology or deep time of Earth's past has been organized into various units according to
events which took place in each period. Different spans of time on the GTS are usually
delimited by changes in the composition of strata which correspond to them, indicating major
geological or paleontological events, such as mass extinctions.

9 What was the significance of the carboniferous period?

The Carboniferous is a geologic period and system that extends from the end of the
Devonian Period, about 359.2 million years ago, to the beginning of the Permian Period. The
name Carboniferous means "coal-bearing" and derives from the Latin words carbo (coal)
and ferre (to carry).

The Carboniferous period, part of the late Palaeozoic era, takes its name from large
underground coal deposits that date to it. Formed from prehistoric vegetation, the majority of
these deposits are found in parts of Europe, North America, and Asia that were lush,
tropically located regions during the Carboniferous.

The Upper Carboniferous was a period of marked disturbances caused by collisions of

crustal plates. In the Lower Carboniferous, or Mississippian, period, the submersion-on
several occasions-of the interior of North America under shallow seas resulted in the
formation of limestone, shale, and sandstone.

9 Explain what relationship has Embryology with evolution.

One of the most important distinctions made by the evolutionary embryologists was the
difference between analogy and homology. Both terms refer to structures that appear to be
similar. Homologous structures are those organs whose underlying similarity arises from their
being derived from a common ancestral structure. For example, the wing of a bird and the
forelimb of a human are homologous. Moreover, their respective parts are homologous.
Analogous structures are those whose similarity comes from their performing a similar
function, rather than their arising from a common ancestor. Therefore, for example, the wing
of a butterfly and the wing of a bird are analogous. The two types of wings share a common
function, but the bird wing and insect wing did not arise from an original ancestral structure
that became modified through evolution into bird wings and butterfly wings.

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10 Explain how Evolutionary relationships are worked out.

If two organisms share an evolutionary relationship means that they have a common
ancestor on the evolutionary tree. The more recently the shared common ancestor lived, the
more closely related the two present organisms are, evolutionarily.

Change in the genetic composition of a population during successive generations, as a result

of natural selection acting on the genetic variation among individuals, and resulting in the
development of new species.

It means how two things are related with respect to their evolutionary descent. For example
when talking about genes, orthology is a property of genes where two genes separated from
their last common ancestor by a speciation event. In the context of whole organisms, it just
means how close the organisms are in the evolutionary tree.

The same is for evolutionary relationships, pretty much what familial relationships mean for
humans. You are more closely related to your siblings than your cousins. And you are more
closely related to your cousins than to complete strangers. More, we are more closely related
to other apes than to monkeys. But we are much more closely related to monkeys than to
crocodiles or bananas.

UNIT 10.0 GEOLOGICAL CONTINENTAL DRIFT

Student Learning Activity Eleven

1 Name the major plates.

There are 15 major tectonic plates which cover the majority of planet Earth's landmass, and
oceanic surface. They all move gradually – between 21mm & 75mm per year – and will all
disappear completely at some point, but by then we will hopefully have some new continents
to inhabit, with new plates having appeared. The World's tectonic plates can have a depth of
up to an estimated 100 km, and are comprised of the entire planets crust, most of a
mysterious layer called the 'moho', and a small bit of the upper mantle. This collective area of
rocky planets is generally called the 'lithosphere'.

There are 8 primary plates on the planet (or 7 if you count the Indo-Australian Plate as a
single plate), and they comprise of the majority of the World's continents' landmass, along
with most of the surface area of the World's Ocean's. The secondary plates are smaller in
size than the primary plates, and they do not cover any substantial landmass, apart from the
Arabian Plate

There are a further group of smaller plates, often called tertiary plates, which are the
disappearing remains of much larger ancient plates that are now on the edges of our major
plates, plus some micro-plates, many of whom will be widely-considered as a part of a
primary or secondary plate on maps and in scientific publications.

Primary Tectonic Plates

African Plate

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Antarctic Plate
Australian Plate
Eurasian Plate
Indian Plate
North American Plate
Pacific Plate
South American Plate

2 Name the Minor plates (Secondary Tectonic Plates).

Arabian Plate
Caribbean Plate
Cocos Plate
Juan de Fuca Plate
Nazca Plate
Philippine Sea Plate
Scotia Plate

Other (minor) plates

Aegean Sea Plate Altiplano Plate Amurian Plate Anatolian Plate

Balmoral Reef Plate Banda Sea Plate Bird's Head Plate Burma Plate
Caroline Plate Conway Reef Plate Easter Plate Futuna Plate
Galapagos Plate Hellenic Plate IranianPlate Fernandez Plate
Kermadec Plate Manus Plate Maoke Plate Mariana Plate
Molucca Sea Plate New Hebrides Plate Niuafo'ou Plate N.Andes Plate
North Bismarck Plate Okhotsk Plate Okinawa Plate Panama Plate
Rivera Plate Sandwich Plate Shetland Plate Solomon Sea Plate
Somali Plate South Bismarck Plate Sunda Plate Timor Plate
Tonga Plate Woodlark Plate Yangtze Plate

3 What happens when two oceanic plates converge?

The size of the Earth has not changed significantly during the past 600 million years, and
very likely not since shortly after its formation 4.6 billion years ago. The Earth's unchanging
size implies that the crust must be destroyed at about the same rate as it is being created.
Such destruction (recycling) of crust takes place along convergent boundaries where plates
are moving toward each other, and sometimes one plate sinks (is subducted) under another.
The location where the sinking of a plate occurs is called a sub-duction zone.

The type of convergence - called by some a very slow "collision" - that takes place between
plates depends on the kind of lithosphere involved. Convergence can occur between an
oceanic and a largely continental plate, or between two largely oceanic plates, or between
two largely continental plates.
Scientists now have a fairly good understanding of how the plates move and how such
movements relate to earthquake activity. Most movement occurs along narrow zones
between plates where the results of plate-tectonic forces are most evident.

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There are four types of plate boundaries:

Divergent boundaries - where new crust is generated as the plates pull away from each
other.
Convergent boundaries - where crust is destroyed as one plate dives under another.
Transform boundaries - where crust is neither produced nor destroyed as the plates slide
horizontally past each other.
Plate boundary zones - broad belts in which boundaries are not well defined and the effects
of plate interaction are unclear.

4 What are the three types of plate boundaries as characterized by the way the
plates move relative to each other?

Divergent boundaries - where new crust is generated as the plates pull away from each
other.
Convergent boundaries - where crust is destroyed as one plate dives under another.
Transform boundaries - where crust is neither produced nor destroyed as the plates slide

5 What are the names of the two outermost part of the Earth's interior?
The structure of Earth can be defined in two ways: by mechanical properties such as
rheology, or chemically. Mechanically, it can be divided into lithosphere,
asthenosphere, mesospheric mantle, outer core, and the inner core. The interior of Earth is
divided into 5 important layers. Chemically, Earth can be divided into the crust, upper mantle,
lower mantle, outer core, and inner core.

The geologic component layers of Earth are at the following depths below the surface:

Depth
Kilometres Miles Layer

0–60 0–37 Lithosphere (locally varies between 5 and 200 km)

0–35 0–22 … Crust (locally varies between 5 and 70 km)

35–60 22–37 … Uppermost part of mantle
35–2,890 22–1,790 Mantle
100–200 62–125 … Asthenosphere
35–660 22–410 … Upper mesosphere (upper mantle)
660–2,890 410–1,790 … Lower mesosphere (lower mantle)
2,890–5,150 1,790–3,160 Outer core
5,150–6,360 3,160–3,954 Inner core

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The layering of Earth has been inferred indirectly using the time of travel of refracted and
reflected seismic waves created by earthquakes. The core does not allow shear waves to
pass through it, while the speed of travel (seismic velocity) is different in other layers

6 Name the oceanic and continental plates.

The current continental and oceanic plates include the:

Eurasian plate Australian-Indian plate

Philippine plate Pacific plate
Juan de Fuca plate Nazca plate
Cocos plate North American plate
Caribbean plate South American plate
African plate Arabian plate
Antarctic plate Scotia plat.

These plates consist of smaller sub-plates.

7 What was Alfred Wegener's proposal on the continental drifts based on was it
accepted?

In 1915, the German geologist and meteorologist, Alfred Wegener (1880-1930) first
proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift
atop a liquid core. The fossil record supports and gives credence to the theories of
continental drift and plate tectonics. Wegener hypothesized that there was an original,
gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth".
Pangaea was a supercontinent consisting of all of Earth's land masses. It existed from the
Permian through Jurassic Periods. It began breaking up during the Jurassic period, forming
continents Gondwanaland and Laurasia, separated by the Tethys Sea.

Pangaea started to break up into two smaller supercontinents, called Laurasia and
Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, the
continents were separating into land masses that look like our modern-day continents.

Eduard Suess was an Austrian geologist who first realized that there had once been a land
bridge between South America, Africa, India, Australia, and Antarctica. He named this large
land mass Gondwanaland. This was the southern supercontinent formed after Pangaea
broke up during the Jurassic period. He based his deductions on the plant Glossopteris,
which is found throughout India, South America, southern Africa, Australia, and Antarctica.

Fossils of one of the first marine reptiles, the Mesosaurus, (even older than the dinosaurs)
were found in both South America and South Africa. These finds, plus the study of
sedimentation and the fossil plant Glossopteris in these southern continents led Alexander
duToit, a South African scientist, to bolster the idea of the past existence of a supercontinent
in the southern hemisphere, Eduard Suess's Gondwanaland. This lent further support to
Alfred Wegener's Continental Drift Theory.

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8 What does the theory of evolution suggests of life on earth?

1.
Evolution is the change in the inherited characteristics of biological populations over
successive generations. Evolutionary processes give rise to diversity at every level of
biological organisation, including species, individual organisms and molecules such
as DNA and proteins.
All life on Earth is descended from a last universal ancestor that lived approximately 3.8
billion years ago. Repeated speciation and the divergence of life can be inferred from shared
sets of biochemical and morphological traits, or by shared DNA
sequences. These homologous traits and sequences are more similar among species that
share a more recent common ancestor, and can be used to reconstruct evolutionary histories,
using both existing species and the fossil record. Existing patterns of biodiversity have been
shaped both by speciation and by extinction.
According to the evolutionary theory, life began billions of years ago, when a group of
chemicals inadvertently organized themselves into a self-replicating molecule. This tiny
molecule gave rise to everything that has ever lived on the planet. Different and more
complex organisms grew from this simple beginning through mutation of DNA and natural
selection.
The theory of evolution seeks to explain the origin of life on Earth and the origin of different
species. Despite the fact that most of the scientific community has regarded it as fact for
more than a century, a large number of people still dispute the theory of evolution, and
various public controversies have resulted from this disagreement.
2.
Evolution by means of natural selection is the process by which genetic mutations that
enhance reproduction become and remain more common in successive generations of a
population. It has often been called a "self-evident" mechanism because it necessarily
follows from three simple facts:
 Heritable variation exists within populations of organisms.
 Organisms produce more progeny than can survive.
 These offspring vary in their ability to survive and reproduce.
These conditions produce competition between organisms for survival and reproduction.
Consequently, organisms with traits that give them an advantage over their competitors pass
these advantageous traits on, while traits that do not confer an advantage are not passed on
to the next generation.
The central concept of natural selection is the evolutionary fitness of an organism. Fitness is
measured by an organism's ability to survive and reproduce, which determines the size of its
genetic contribution to the next generation. However, fitness is not the same as the total
number of offspring: instead fitness is indicated by the proportion of subsequent generations
that carry an organism's genes. For example, if an organism could survive well and
reproduce rapidly, but its offspring were all too small and weak to survive, this organism
would make little genetic contribution to future generations and would thus have low fitness.

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UNIT 11.0 CLASSIFICATION

Student Learning Activity Twelve

1 Why do we classify things?

There are a lot of things in our universe. To be able to study them, we need some ways to
group or classify them together. Initially, scientists divided all things into living vs. non-living,
then subdivided those (i.e. animal kingdom and plant kingdom), then continued dividing them
on how the items were similar or dissimilar (phlyum, genus, species). While this worked for
centuries, genetic testing is causing some divisions to be reconsidered.
 It makes the study of such a wide variety of organisms easy.
 It projects before us a good picture of all life forms at a glance.
 It helps us understand the interrelationship among different groups of organisms.
 It serves as a base for the development of other biological sciences such as
biogeography etc.
 Various fields of applied biology such as agriculture, public health and environmental
biology depend on classification of pests, disease vectors, pathogens and
components of an ecosystem.
Classification provides scientists and students a way to sort and group organisms for easier
study. There are millions of organisms on the earth! (Approximately 1.5 million have been
already named)
Organisms are classified by their:
 physical structure (how they look)
 evolutionary relationships
 embryonic similarities (embryos)
 genetic similarities (DNA)
 biochemical similarities
All living things carry out the life functions. There are many different types of organisms.
In one classification system, there are 2 main groups. In others, there are 3. In the one used
by most of the world's scientists, which we will also use, there are 5 main groups. All living
things are placed in one of the five KINGDOMS which are the most general group. They are
then broken down into smaller groups, then smaller groups, then smaller and so on until
there is just one. SPECIES is the most specific group.

2 How many organisms have been already named of the millions of organisms
found on earth?

There are millions of organisms on the earth! (Approximately 1.5 million have been already
named.)

3 How are organisms classified?

Organisms are basic unit of living things and there are five main kingdoms of living things.
These are animal, plant, fungi, moneran and protist. Organisms are classified first according
to kingdom, then phylum, class, order, family, genus and the species. Humans primarily

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emphasize traits that can be seen with their eyes since they mostly rely on their sense of
vision.
The members of each group of living things share a set of special features unique to that
group.
For example, plants contain a chemical called chlorophyll that they use to make their own
food (it also makes them green). Every member of the plant kingdom shares this
characteristic. Other characteristics of plants may be how it feeds, how it reproduces, its
uses, where can it be found etc forms the bases for their class or group.
Scientists are always looking for these characteristics or 'observable features' which allow
them to group different species together and see how they are related to each other.
By comparing the features of different animals they have been able to classify them further,
dividing each of the kingdoms into smaller groups.
To understand the whole thing a bit more it is good to look at an example.
The squirrel belongs to the Kingdom Animalia. Each kingdom is divided into groups, and
these groups are divided into smaller groups. Each level of group has a special name:
 Phylum
 Order
 Class
 Family
 Genus
 Species
By examining its observable features scientists have determined that the squirrel belongs to
the phylum Chordata, phylum Chordata, class Mammalia and so on.

4 Which branch of science is responsible for the naming and classification of

organisms?

The branch of science that is responsible for naming and classification of organisms is
Biology. The branch of biology that deals with naming and classification of organisms is
taxonomy.
The branch of biology that is concerned with tissue is histology, while the branch of biology
that is concerned about forms of organisms is morphology.

5 How many living things only currently known species are there on the planet?

About 1.8 million have been given scientific names. Thousands more are added to the list
every year. Over the last half century, scientific estimates of the total number of
living species have ranged from 3 to 100 million. The most recent methodical survey
indicates that it is likely to be close to 9 million, with 6.5 million of them living on the land and
2.2 million in the oceans. Tropical forests and deep ocean areas very likely hold the highest
number of still unknown species. However, we may never know how many there are
because it is probable that most will become extinct before being discovered and described.
The tremendous diversity in life today is not new to our planet. The noted paleontologist
Stephen Jay Gould estimated that 99% of all plant and animal species that have existed
have already become extinct with most leaving no fossils. It is also humbling to realize that
humans and other large animals are freakishly rare life forms, given that 99% of all known
animal species are smaller than bumble bees

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6 What are kingdoms?

To help us understand the number of living things on the planet, scientists organise them into
groups, like 'the animals' or 'the plants'. This is called classification.
To start with, all living things are divided into large groups called 'kingdoms'. Scientists
haven't quite agreed how many kingdoms there are, but many think that there are five: the
monera, the protoctista, the plants, the fungi and the animals.
You probably know about the plants, animals and fungi (like mushrooms and yeast), but the
monera and the protoctista may be new to you.
A realm or sphere in which one thing is dominant: the kingdom of the imagination.
The three main divisions (animal, vegetable, and mineral) are into which natural organisms
and objects are classified.
In the Linnaean taxonomic system, the highest taxonomic classification into which organisms
are grouped is based on fundamental similarities and common ancestry. The Linnaean
system designates five such classifications: animals, plants, fungi, prokaryotes, and
protoctists.

From most general to most specific:

Kingdom
(only 5 kingdoms for everything: Bacteria, Plants, Animals, Fungi, and Single-celled
organisms)
Phylum
(A subdivision of one kingdom, our phylum is chordata, meaning we have a spinal cord)

Order

Family

Genus

Species (one for every distinct organism)

There's talk of adding a sixth kingdom, archaea, which is for ancient bacteria that don't share
some characteristics with modern bacteria.

7 How do scientists classify living things?

The members of each group of living things share a set of special features unique to that
group.
For example, plants contain a chemical called chlorophyll that they use to make their own
food (it also makes them green). Every member of the plant kingdom shares this
characteristic. Other characteristics of plants may be how it feeds, how it reproduces, its
uses, where can it be found etc forms the bases for their class or group.
Scientists are always looking for these characteristics or 'observable features' which allow
them to group different species together and see how they are related to each other.

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By comparing the features of different animals they have been able to classify them further,
dividing each of the kingdoms into smaller groups.
To understand the whole thing a bit more it is good to look at an example.
The squirrel belongs to the Kingdom Animalia. Each kingdom is divided into groups, and
these groups are divided into smaller groups. Each level of group has a special name:
 Phylum
 Order
 Class
 Family
 Genus
 Species
By examining its observable features, scientists have determined that the squirrel belongs to
the phylum Chordata, phylum Chordata, class Mammalia and so on.

8 How do we divide the animal kingdom?

Option 1

Classification is all about organising living things into groups. The members of any group all
possess a shared characteristic - it is this characteristic or feature that defines the group.
Taking the animal kingdom as an example, we can see that it is split into two clear groups:
Invertebrates - animals without a backbone.
Vertebrates - animals with a backbone.
The animals have been divided into two groups based on the presence or absence of a
backbone. The backbone is the observable feature that defines whether the animal is a
vertebrate or an invertebrate.
These groups are divided into smaller 'sub-groups'.
Sponges, corals, worms, insects, spiders and crabs are all sub-groups of the invertebrate
group - they do not have a backbone.
Fish, reptiles, birds, amphibians and mammals are different sub-groups of vertebrates - they
all have internal skeletons and backbones.
The animals that belong to these sub-groups all share the observable features of that group.
Just as all the vertebrates have backbones, all birds have feathers and lay eggs, and all
mammals have fur and suckle their young

Option 2
In order for us to understand how all living organisms are related, they are arranged into
different groups. The more features that a group of animals share, the more specific the
group is. Animals are given scientific names so that people all around the world can
communicate about animals, no matter what language they speak. Animals belong to a
number of different groups, starting with the animal kingdom.
 Kingdom
All living organisms are first placed into different kingdoms. There are five different kingdoms
to classify life on Earth, which are Animals, Plants, Fungi, Bacteria, and Protists (single-
celled organisms).

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 Phylum
The animal kingdom is divided into 40 smaller groups, known as phylum. Here, animals are
grouped by their main features. Animals usually fall into one of five different phylum which
are Cnidaria (invertebrates), Chordata (vertebrates), Arthropods, Molluscs and Echinoderms.
 Class
The phylum group is then divided into even smaller groups, known as classes. The Chordata
(vertebrates) phylum splits up into Mammalia (Mammals), Actinopterygii (Bony Fish),
Chondrichthyes (Cartilaginous Fish), Aves (Birds), Amphibia (Amphibians) and Reptilia
(Reptiles).
 Order
Each class is divided into small groups again, known as orders. The class Mammalia
(Mammals), splits into different groups including Carnivora, Primate, Artiodactyla and
Rodentia.
 Family
In every order, there are different families of animals which all have very similar features. The
Carnivora order breaks into families that include Felidae (Cats), Canidae (Dogs), Ursidae
(Bears), and Mustelidae (Weasels).
 Genus
Every animal family is then divided into small groups known as genus. Each genus
containsanimals that have very similar features and are closely related. For example, the
Felidae (Cat) family contains genus including Felis (small Cats and domestic Cats), Panthera
(Tigers, Leopards, Jaguars and Lions) and Puma (Panthers and Cougars).
 Species
Each individual species within the genus is named after its individual features and
characteristics. The names of animals are in Latin so that they can be understood worldwide,
and consist of two words. The first word in the name of an animal will be the genus, and the
second name indicates the specific species.

UNIT 12.0 BIOCHEMISTRY

Student Learning Activity Thirteen

1 What evidence is available that shows similarities between relationships of

organisms?

Evidences include population studies, domesticated animals and cultivated plants shows the
degree of similarities between their groups.

2 What is name of a universal compound responsible for aerobic respiration?

The protein cytochrome c, essential for aerobic respiration

3 What are fundamentals to life?

A cell is capable of independent existence and can carry out all the functions which are
necessary for a living being. A cell carries out nutrition, respiration, excretion, transportation
and reproduction; the way an individual organism does. Unicellular organisms are capable of

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independent existence which shows a cell‘s capability to exist independently. Due to this, a
cell is called the fundamental and structural unit of life. All living beings are composed of the
basic unit of life, i.e. cell.

 All living organisms are composed of one or more cells.

 The cell is the basic unit of structure, function, and organization in all organisms.
 All cells come from pre-existing, living cells.

Every living cell contains, in addition to water and salts or minerals, a large number of
organic compounds, substances composed of carbon combined with varying amounts of
hydrogen and usually also of oxygen. Nitrogen, phosphorus, and sulfur are likewise common
constituents. In general, the bulk of the organic matter of a cell may be classified as:

1 protein,
2 carbohydrate, and
3 fat, or lipid.

Nucleic acids and various other organic derivatives are also important constituents. Each
class contains a great diversity of individual compounds. Many substances that cannot be
classified in any of the above categories also occur, though usually not in large amounts.
Proteins are fundamental to life, not only as structural elements (e.g., collagen) and to
provide defence (as antibodies) against invading destructive forces but also because the
essential biocatalysts are proteins. Carbohydrates include such substances as sugars, starch,
and cellulose. Fats, or lipids, constitute a heterogeneous group of organic chemicals that can
be extracted from biological material by non-polar solvents such as ethanol, ether, and
benzene.
Substances as sugars, starch, and cellulose are collectively known as

What‘s most important is the type of carbohydrate you chose to eat because some sources
are healthier than others. The amount of carbohydrate in the diet – high or low – is less
important than the type of carbohydrate in the diet. For example, healthy, whole grains such
as whole wheat bread, rye, barley and quinoa are better choices than highly refined white
bread or Big Rooster fries/chips.

4 What are carbohydrates?

Carbohydrates are found in a wide array of both healthy and unhealthy foods-bread, beans,
milk, popcorn, potatoes, cookies, spaghetti, soft drinks, corn, and cherry pie. They also come
in a variety of forms. The most common and abundant forms are sugars, fibers, and starches.

Foods high in carbohydrates are an important part of a healthy diet. Carbohydrates provide
the body with glucose, which is converted to energy used to support bodily functions and
physical activity. But carbohydrate quality is important; some types of carbohydrate-rich
foods are better than others:

 The healthiest sources of carbohydrates-unprocessed or minimally processed whole

grains, vegetables, fruits and beans-promote good health by delivering vitamins,
minerals, fiber, and a host of important phytonutrients.

 Unhealthier sources of carbohydrates include white bread, pastries, sodas, and other
highly processed or refined foods. These items contain easily digested

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carbohydrates that may contribute to weight gain, interfere with weight loss, and
promote diabetes and heart disease.

In most cases plants elaborate much more food than can be used immediately for plant
growth, or as a source of energy. Identify the three main types of food materials that are
manufactured by plants and give a brief account of each.

Carbohydrates - These are the simplest of plant foods. They consist of carbon, hydrogen
and oxygen in the proportion of two parts of hydrogen to one of oxygen. The main
carbohydrates are sugar, starch and cellulose.

Starch come in the form of grains such as wheat, rice and maize; sugars in the form of
sugars in fruits and sugarcane, beetroot and fats in the form of oils from oil seeds like
safflower, groundnut, sesame.

Proteins come from Soybean, Gram and a lot more.

Sugar - Grape sugar that is manufactured by the plant in photosynthesis is most often
present in plant cells. This basic material of metabolism, known as Glucose, has the formula
C6H12O6. It is at times stored in large amounts such as is found in the stems of maize. Fruit
sugar, or Fructose, another product of photosynthesis, has the same formula, but it
possesses slightly different properties. It is most commonly found only in fruits.

Starch - Starches are insoluble compounds with a complex nature and formula
(C6H10O6)n. They are derived from grape sugar and constitute the first visible product of
photosynthesis. Starch is the most common type of reserve food in green plants and is of
the highest importance in their metabolism. However, due to its insoluble nature starch must
be digested, i.e., made soluble, before it can be used. This is done through the aid of
enzymes that are present in the cells. Starch is stored in large thin-walled cells in the form of
distinctive grains. Humans are very dependent on starch that constitutes a most important
plant food and is vital in the industrial world as well.

UNIT 13.0 EARLY VIEWS ON CREATION

Student Learning Activity Fourteen

1 Which myth is said to be the myth par excellence?

It is the philosophical and theological elaboration of the primal myth of creation within a
religious community. The term myth here refers to the imaginative expression in narrative
form of what is experienced or apprehended as basic reality. The term creation refers to the
beginning of things, whether by the will and act of a transcendent being, by emanation from
some ultimate source, or in any other way.

Nature and significance

The myth of creation is the symbolic narrative of the beginning of the world as understood by
a particular community. The later doctrines of creation are interpretations of this myth in light
of the subsequent history and needs of the community. Thus, all theology and speculation
concerning creation in the Christian community are based on the myth of creation in the
biblical book of Genesis and of the new creation in Jesus Christ. Doctrines of creation are

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based on the myth of creation, which expresses and embodies all of the fertile possibilities
for thinking about this subject within a particular religious community.

The world as a structure of meaning and value has not appeared in the same manner to all
human civilizations. There are, therefore, almost as many cosmogonic myths as there are
human cultures. Until quite recently, the classification of these myths on an evolutionary
scale, from the most archaic cultures to contemporary Western cultures (i.e., from the
assumedly simplest to the most complex) was the most dominant mode of ordering these
myths. Recent 20th-century scholars, however, have begun to look at the various types of
myths in terms of the structures that they reveal rather than considering them on an
evolutionary scale that extends from the so-called simple to the complex, for, in a sense,
there are no simple myths regarding the beginning of the world. The beginning of the world is
simultaneously the beginning of the human condition, and it is impossible to speak of this
beginning as if it were simple.

2 Where in the Bible does it mention the continental shift supposedly?

The Bible framework for earth history makes no statement about continental splitting, so it is
unnecessary and unwise to take a "Biblical" position on the question. When God created the
land and sea, the waters were "gathered together unto one place" (Genesis 1:9), which may
imply one large ocean and one large land mass. The scripture which says "the earth was
divided" in the days of Peleg (Genesis 10:25) is generally thought to refer to the Tower of
Babel division (Genesis 11:1-9) and some suppose this included continental separation. To
believe, however, that the continents moved thousands of miles during the Tower of Babel
incident without causing another global flood requires a miracle. Similarly, it is doubtful
whether the long day of Joshua can be explained naturalistically by plate tectonics.

If continental separation did occur, the only place within the Bible framework where it could fit
would be during Noah's Flood. The cause of Noah's Flood is described in tectonic terms: "all
the fountains of the great deep broken up" (Genesis 7:11). The Hebrew word for "broken up"
is baga and is used in other Old Testament passages (Zechariah 14:4; Numbers 16:31) to
refer to the geologic phenomena of faulting. The mechanism for retreat of the Flood waters is
also associated with tectonics. Psalm 104:6,7 describes the abating of the waters which
stood above the mountains; the eighth verse properly translated says, "The mountains rose
up; the valleys sank down." It is interesting to note that the "mountains of Ararat" (Genesis
8:4), the resting place of the Ark after the 150th day of the Flood, are in a tectonically active
region at the junction of three lithospheric plates.

If continental separation occurred during Noah's Flood, a host of problems in the tectonic
dilemma can be solved. Rapid mid-ocean rifting can explain the large quantity of volcanic
rocks on the sea floor. The presence of low density crustal rock down to a depth of 700
kilometers within the mantle below trenches can be attributed to rapid under thrusting. The
cause for the ancient breaking up of continents can be explained easily by the enormous
catastrophic forces of Noah's Flood which broke the lithosphere into moving plates which for
a short time overcame the viscous drag of the earth's mantle. The amazing similarity of
sedimentary Flood layers in the northeastern United States to those of Britain (i.e.,
Carboniferous coal strata and Devonian red sandstones) and the absence of these in the
North Atlantic Ocean basin suggests that continental separation occurred toward the end of
the Flood.

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3 What are some of the moments that are seemingly practical activities that
imitate the mythical structure of the first beginning?

Myths of creation have distinctive character in that they provide both the model for nonmythic
expression in the culture and the model for other cultural myths. In this sense, one must
distinguish between cosmogonic myths and myths of the origin of cultural techniques and
artifacts. Insofar as the cosmogonic myth tells the story of the creation of the world, other
myths that narrate the story of a specific technique or the discovery of a particular area of
cultural life take their models from the stylistic structure of the cosmogonic myth. These latter
myths may be etiological (i.e., explaining origins); but the cosmogonic myth is never simply
etiological, for it deals with the ultimate origin of all things.

The cosmogonic myth thus has a pervasive structure; its expression in the form of
philosophical and theological thought is only one dimension of its function as a model for
cultural life. Though the cosmogonic myth does not necessarily lead to ritual expression,
ritual is often the dramatic presentation of the myth. Such dramatization is performed to
emphasize the permanence and efficacy of the central themes of the myth, which integrates
and undergirds the structure of meaning and value in the culture. The ritual dramatization of
the myth is the beginning of liturgy, for the religious community in its central liturgy attempts
to re-create the time of the beginning.

4 Provide a comparative account of Biblical Creationist and Scientific Creationist.

Biblical creationists believe that the story told in Genesis of God's six-day creation of all
things is literally correct.

Scientific creationists believe that a creator made all that exists, but they may not hold that
the Genesis story is a literal history of that creation.

Both types of creationists, however, believe that changes in organisms may involve changes
within a species or downward changes (negative mutations), but they do not believe that any
of these changes can lead to the evolution of a lower or simpler species into a higher or
more-complex species.

5 Define or explain what is meant by Natural selection.

It can be defined as the differential reproduction of alternative hereditary variants, determined

by the fact that some variants increase the likelihood that the organisms having them will
survive and reproduce more successfully than will organisms carrying alternative variants.
Selection may occur as a result of differences in survival, in fertility, in rate of development, in
mating success, or in any other aspect of the life cycle. All of these differences can be
incorporated under the term differential reproduction because all result in natural selection to
the extent that they affect the number of progeny an organism leaves.

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SAMPLE ASSIGNMENTS
Assignment 1

1 In your own words describe the difference between a community and an

ecosystem.
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2 Define the following terms.

a. species
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b. population
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c. ecosystem
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d. biosphere
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e. biome
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f. habitat
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g. niche
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3 Explain the three components that make up a biosphere.

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4 The world is split up into several biomes but scientists just can‘t agree on how
many, so we are going to look at six major types described below. Your task is
to name the type of biome described below.
A This biome is the driest; it only receives 50cm of rainfall a year (about 10%
of the rainfall in the rainforest). Its plants and animals have to survive in an
environment with little water and dramatic temperature changes from day
to night. Some animals and plants may find it difficult to adapt, but reptiles
and cacti thrive in these conditions.
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B This biome covers about 1/3 of the Earth‘s land surface. They are
dominated by trees and contain many different plants and animals. It takes
in the carbon dioxide that we exhale and give off the oxygen we breathe in,
making them really important to our survival.
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C This biome is water that has a salt level of less than 1%. Most species
living in it cannot live in salt water, although there are some exceptions.
This biome also plays an important role for life on Earth. It provides
drinking water for humans and other animals, it is also vital for plant
growth.
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D It may not surprise you to hear that these biomes are filled with grasses.
However, the length of the grass and the number of trees within these
biomes vary depending on the amount of rainfall. Since rainfall in this
biome is lower than rainforest but higher than desert, trees exist, but they
are limited to growing near streams and other water sources.
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E This biome covers more of the Earth‘s surface than any other – about 70%.
Some areas are so deep that they can contain entire mountains and even
volcanoes. Like many of the other biomes on the planet, they play an
important role. This biome provides most of the rainwater that comes
down from the sky and it is home to some of the planet‘s most diverse
species.
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F This is the coldest of all the biomes and species diversity is limited as a
result. In fact, its name comes from the Finnish word tunturi, meaning
treeless plain. It receives even less rainfall than most deserts, although it
remains wet because the cold temperatures delay water from being
evaporated. Plants, such as mosses and lichens, adapt to these frigid
conditions by having a shorter growing season.
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Assignment 2

1 Describe the term ‗biome.‘

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2 Give two examples of each to show the difference between the term niche and
habitat.
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3 Using the geographical descriptions of the location of Papua New Guinea,

describe the types of biome for Papua New Guinea.
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4 Explain the differences between the following types of ecosystems.

a. desert – savannah grassland

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b. tundra – tropical rain forest

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c. Lower-montane and mid-montane

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d. lowlands and Pre-montane

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e. coniferous forest - deciduous forest

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5 Explain the kind of climatic zones for Port Moresby and Lae and state what
factor influences such climate.
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6 Name the main land biomes.

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7 Briefly describe the kind of vegetation found in the following places of PNG.

a) Markham valley of Morobe Province

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b) National Capital District in Port Moresby

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c) Tambul in Western Highlands Province

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Assignment 3

1 What are the components of the ecosystem?

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2. Briefly explain the following terms.

a) biotic factors
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b) abiotic factors
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3 List 5 biotic and 5 abiotic factors in an ecosystem.

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4 What are the main abiotic components of an ecosystem, and how do they
affect the animal life that lives there?

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5 Biotic components are the living things that shape an ecosystem. A biotic
factor is any living component that affects another organism,
including animals that consume the organism in question, and the
living food that the organism consumes. Each biotic factor needs energy to do
work and food for proper growth. Biotic factors include human influence.
List the 3 biotic components and their function in the ecosystem.
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Assignment 4

1 What is the difference between weather and climate?

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2 State the factors that can cause climate changes.

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3 What methods do scientists use to study past climates?

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4 Name the four major climatic zones around the world.

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5 List two important types of symbiosis. Define and provide an example of each.
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6 Why are scavengers very important in an ecosystem?

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Assignment 5

1 What do you understand about the following?

a) Primary producers
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b) Primary consumers
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c) Secondary consumers
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2 Explain why autotrophs always occupy the lowest level of ecological pyramids.

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3 Draw a food web of an ecosystem with at least 8 organisms.

4 Name the two essential kinds of commodities contain in an ecosystem and

explain the significant role the two commodities play in an ecosystem.
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5 Differentiate between autotrophs and heterotrophs.

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6 Distinguish between food chain and food web.

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Assignment 6

1 Explain briefly the concept of energy flow through ecosystems.

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2 Explain what happens when going from one trophic level to the next higher
level.
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3 Explain what a trophic pyramid is.

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4 The diagram below shows an ecological pyramid.

According to the ecological pyramid above, at each trophic level, what percent of
energy is stored in the organisms at that level?

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5 Read the following passage very carefully and draw a food/energy pyramid
and identify each level correctly.

A small amount of the energy stored in plants, between 5 and 25 percent, passes
into herbivores (plant eaters) as they feed, and a similarly small percentage of the
energy in herbivores then passes into carnivores (animal eaters). The result is a
pyramid of energy, with most energy concentrated in the photosynthetic organisms at
the bottom of food chains and less energy at each higher trophic level. Some of the
remaining energy does not pass directly into the plant-herbivore-carnivore food chain
but instead is diverted into the detritus food chain. Bacteria, fungi, scavengers, and
carrion eaters that consume detritus (detritivores) are all eventually consumed by
other organisms.

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Assignment 7

1 Explain the term biogeochemical cycle.

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2 Use a diagram to explain how carbon is cycled through the environment from
carbon dioxide in the air into plants, animals, fuel, and then is returned to the
atmosphere.

3 Name the organisms that are responsible for releasing the carbon dioxide in
dead organisms into the environment.
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4 How do humans affect the carbon cycle?

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5 Using a diagram, explain how nitrogen is cycled through the environment from
nitrogen in the air into soil, bacteria, and then is returned to the atmosphere.

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6 Explain how water cycles between the atmosphere and Earth.

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Assignment 8

1 Explain briefly how soil plays an important function in ecosystems.

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2 State the most important benefits humus provides soil with.

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3 List all the physical properties of soil.

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4 List the common chemical properties of soil.

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5 Explain why biotic component of soils are important.

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Assignment 9

1 Define succession, and explain why it occurs.

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2 Succession that occurs in an area where existing community has been

partially destroyed is called

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3 The transformation over time as shown in the diagram below is known as

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5 Explain what Greenhouse Effect is and what causes the green house effect?
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6 Differentiate between greenhouse effect and global warming.

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7 What are some implications of climate change?

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8 What must be done to reduce human contributions to the greenhouse effect?

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Assignment 10

1 Explain what is Genetics?

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2 Explain what is Molecular biology?

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3 What is Chemical Biology?

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4 Explain briefly what similarities Biochemistry reveals between organisms of

different species.
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5 Give a detailed explanation of biochemistry.

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BIBLIOGRAPHY

ALLOT, Andrew, Biology for the IB Diploma, Oxford, 2007

Beckett Biology, OUP, 1986

CADOGAN, Green, Biology, Heinemann, 1985

HILL, Coben, NEW Care Biology, Practical Manual. McDonnell Heinemann, 1983

JOENSSON, H.; RICHERT, A.; VINNERAAS, B.; SALOMON, E. (2004): Guidelines

on the Use of Urine and Faeces in Crop Production . Stockholm: EcoSanRes.

JONES, JONES, Biology, GCSE Edition, CUP, 1984

MACKEAN, D.G. (1986) GSCE Biology, John Murray Publisher, UK

MAHENDRAPPA, T. (2007): The Nutrient Cycle “Soil is the basis of life.” Canadian
Forest Service.

MARDIE, K. and BROTHERTON J. (2000) Heinemann Biology, Malcolm Parson,

Singapore.

MARTIN, C. (2010): What is the nutrient cycle?

MURRAY, John, Introduction to Biology, Tropical Edition, Mackean, 1984

MURRAY John, Life Study, Mackean, 1981

MURRAY, John, GCSE Biology, Mackean, , 1986

NELSON T., M.B.V. Roberts (1981), Biology for Life, Publisher, Melbourne, Australia

PARKINS, Terry, SIMPKINS, John Biology, Longman, 1999

ROBERTS, M.B.V., Biology, A Functional Approach, 1993

USDA NRCS Conserving Soils (Editor); NSTA (Editor) (2010): Soil Ecosystem.

USDA NRCS Conserving Soils & NSTA

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APPENDIX 1

GLOSSARY

Abiogenesis, Origin of life through self duplicating of biochemical complexity

Abiotic, adj: Nonliving or not containing any living organisms.
Abiotic factors, n: Environmental influences produced other than by living organisms; for
example, temperature, wind patterns, humidity, pH, substrate rock type, and other physical
and chemical influences.
Absolute poverty, n: The lack of sufficient income in cash or exchange items for meeting
the most basic needs of food, clothing, and shelter.
Acid fallout, n: Molecules of acid formed from reactions high in the atmosphere involving
nitrogen, sulfur oxides, and water vapor that settle out of the atmosphere without any
additional water.
Acid precipitation, n: Includes acid rain, acid fog, acid snow, and any other form of
precipitation that is more acidic that normal (i.e., less that pH 5.6). Excess acidity is derived
from certain air pollutants, namely sulfur dioxide and oxides of nitrogen. The effects can
include: fish kills and eutrophication of lakes; tree kills, leading to soil erosion; and physical
corrosive damage to vehicles and buildings. Many historic buildings in Europe and the NE
United States are suffering damage from severe corrosion due to acid precipitation.
Aerobe, n: An organism that utilizes atmospheric oxygen (0 2) in its metabolic pathways. An
organism that must have oxygen in order to survive is an obligate aerobe.
Aerobic, adj: Living or occurring only in the presence of oxygen: aerobic bacteria. 2. Of or
relating to aerobes, organisms that require and utilize oxygen. 3. Involving or improving
oxygen consumption by the body: aerobic exercise.
Age-Sex Pyramid (Population Pyramid) A series of horizontal bars that illustrate the
structure of a population; the horizontal bars represent different age categories, which are
placed on either side of a central vertical axis. Males are to the left of the axis, females to
the right.
Ageing Population In the population structure of many MEDCs there is often a high
proportion of elderly people who have survived due to advances in nutrition and medical
care. This creates problems since these people do not work and have to be provided with
pensions, medical care, social support, sheltered housing etc. from the taxes paid by a
proportionally smaller number of workers. In addition, an increasing number of young
people are employed as care workers for the elderly. This removes them from more
productive jobs within the economy and harms a country's competitiveness.
Agroforestry, n: Production of tree crops in a manner similar to agriculture; also production
of trees along with regular crops.
Anaerobe, n.: 1: An organism capable of living in the absence of free oxygen (O2). 2:
Obligate anaerobe: An organism that must live without oxygen, for which oxygen (O2) is
toxic.
Anaerobic, adj.: 1: Lacking or seriously depleted of oxygen; opposite of aerobic. 2: Of or
relating to organisms, such as certain bacteria, that can live in the absence of atmospheric
oxygen (indeed, for most anaerobic bacteria, oxygen is toxic).
Autotrophs, n: Literally, "self eater." Organisms capable of producing their own food through
photosynthesis

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Background extinction rate, n: Normal rate of extinction -- as a natural part of the

evolutionary process -- of various species as a result of changes in local environmental
conditions and the actions of natural evolutionary forces. Extinctions not caused or
contributed to by the actions of humans.
Bioaccumulation, n: An increase in the concentration of a chemical in specific organs or
tissues at a level higher than would normally be expected.
Biodegradable, adj: Able to be broken down into simpler substances (elements and
compounds) by naturally occurring decomposers. Essentially, anything that can be ingested
by an organism without causing that organism harm. 2. Nontoxic and able to be decomposed
in relatively short period even on a human time scale.
Biodiversity, n: The variety of biotic factors found within a specified geographic region. 2.
The combined differences of living things, generally classified in four broad categories:
 Genetic Diversity: Variety among individuals within a species -- or, more specifically,
the variety in the DNA of a species. See also "alleles."
 Species Diversity: Variety of different organisms at the species taxonomic level. See
also species and taxonomy.
 Cultural Diversity: Variety of learned behaviours among individuals of a species.
 Ecosystem Diversity: Variety of biomes and habitats occurring in the biosphere.
Binomial nomenclature, n: The two-name system, developed by Carolus Linnaeus (the
founder of modern taxonomy), used to assign scientific names to all living things. Homo
sapiens, for example, is the scientific name for humans. The first name is the genus name
and is always capitalized. This is sort of like your last name... it belongs to several of your
close relatives, too, and it shows that you are all closely related. The second name is the
species name is always lower case. This is like your first name, which no one else in your
circle of relatives possesses and so it uniquely identifies you. Memory tool: you probably
know the meanings of the terms generic (i.e. general, broad) and specific (i.e. precise,
exact). These terms come from the same origins as genus and species, so recalling their
meaning will help you recall the relationship between the two portions of a scientific name.
Biome, n: A specific type of terrestrial region inhabited by well-defined types of life,
especially zones of vegetation that generally cannot live outside that specific region.
Examples include types of deserts ("high desert" like the Mojave or "low desert" like the
Chihuahua), grasslands (prairies, coastal dunes), and forests (lodge pole pine vs. taiga;
temperate rain forest; bamboo forest, tropical rain forest, cloud forest, etc.).
Biosphere, n: The portion of the earth and its atmosphere in which living organisms exist or
that is capable of supporting life. 2. All of earth's ecosystems combined into one inclusive
unit; also called the "ecosphere." 3. The living organisms and their environment composing
the biosphere. "...all life on earth and the realms that support it, from the outermost reaches
of the atmosphere to the deepest trenches of the seas." (National Geographic Atlas of the
World, 6th Edition)
Birth Rate The number of individuals produced during a certain amount of time; The
number of live births per 1000 people per year.
Bulge of Young Male Migrants: On a population pyramid; young males move to urban
areas due to push-pull factors.
Carrying capacity, n: The amount of animal or plant life (or industry) that can be supported
indefinitely on available resources; the number of individuals that the resources of a habitat
can support; also called biological carrying capacity.

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Census A counting of people by the government every ten years to gather data for
planning of schools, hospitals, etc; This is unreliable for a number of reasons.
Child Dependency ratio The number of children in relation to the number of working
(economically active) population, usually expressed as a ratio.
Chromosome comes from the Greek χρῶμα (chroma, colour) and σῶμα (soma, body) due
to their property of being very strongly stained by particular dyes.
colligative depending on the number of particles (as molecules) and not on the nature of
the particles
Concentrated Population Distribution Where people are grouped densely in an
urbanised area (see Port, Bridging-Point, Route Centre, Wet Point Site, Market Town,
Mining Town, Resort).
Conservation biology, n: Multidisciplinary science created to deal with the crisis of
maintaining the genes, species, communities, and ecosystems that make up earth's
biological diversity. Its goals are to investigate human impacts on biodiversity and to develop
practical approaches to preserving biodiversity and ecological integrity.
Conservation-tillage farming, n: Crop cultivation in which the soil is disturbed little
(minimum-tillage farming) or not at all (no-till farming) to reduce soil erosion, lower labor
costs, and save energy.
Consumers Organisms that eat/consume other organisms for food
Contraception Using birth control to stop pregnancy.
Counter-urbanisation Movement of people in MEDCs away from urban areas to live in
smaller towns and villages (see de-urbanisation and urban-rural shift)
Coral bleaching, n: The loss of color from a coral as it expels its zooxanthellae-usually a
stress response.
Cost-benefit analysis, n: Estimates and comparison of short-term and long-term costs
(losses) and benefits (gains) from an economic decision. If the estimated benefits exceed the
estimated costs, the decision to buy an economic good or provide a public good is
considered worthwhile.
cytochrome any of several intracellular hemoprotein respiratory pigments that are enzymes
functioning in electron transport as carriers of electrons
Death rate The number of deaths per 1000 people per year.
Decomposers Organisms that break down the remains of plants and animals
Deforestation, n: Removal of trees from a forested area without adequate replanting.
Demographic transition, The change from high birth rates and death rates to low birth rates
and death rates; n: Hypothesis that countries, as they become industrialized, have declines
in death rates followed by declines in birth rates.
Demographic Transition Model Diagram which shows the relationship between birth
and death rates and how changes in these affect the total population
Demography The study of the vital statistics affecting a population size.
Desertification, n: Conversion of rangeland, rain-fed cropland to desert-like land, with a drop
in agricultural productivity of 10% or more. It is usually caused by a combination of
overgrazing, soil erosion, prolonged drought, and climate change.

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Dioxin, n: A synthetic, organic chemical of the chlorinated hydrocarbon class. It is one of the
most toxic compounds known to humans, having many harmful effects, including induction of
cancer and birth defects, even in extremely minute concentrations. It has become a
widespread environmental pollutant because of the use of certain herbicides that contain
dioxin as a contaminant
Distribution (of a population) Where people are found and where they are not found
Ecological efficiency, n: The percentage of energy in biomass produced by one trophic
level that is incorporated into biomass by the next highest trophic level.
Ecological fitness, n: The number of a parent's young that live to reproduce; divided by two
if sexual reproduction is involved.
Ecological succession, n: Process in which communities of plant and animal species in a
particular area are replaced over time by a series of different and often more complex
communities.
Ecologically sustainable development, n: Development in which the total human
population size and resource use in the world (or in a region) is limited to a level that does
not exceed the carrying capacity or the existing natural capital and is therefore sustainable.
Ecologist, n: A scientist who studies ecology.
Ecology, n: The study of the relationships between organisms and their environments,
including: the interactions of living organisms with one another and with their non-living
surroundings, the flow of matter and energy in an environment, and the structure and
functions of nature; also called bionomics. 2. The relationship between organisms and their
environment. 3. The branch of sociology that is concerned with studying the relationships
between human groups and their physical and social environments; also called human
ecology. 4. The study of the detrimental effects of modern civilization on the environment,
with a view toward prevention or reversal through conservation; a component of the field of
human ecology.
Economic Migrant Person leaving her/his native country to seek better economic
opportunities (jobs) and so settle temporarily in another country
Ecosystem, n: An ecological community of various plants, animals, and other organisms,
interacting with each other and with the nonliving resources in their environment, all
functioning as a unit.
Ecosystem services, n: Services, vital to the support of human life, provided by intact
natural ecosystems. These include the purification of air and water, detoxification and
decomposition of wastes, regulation of climate, regeneration of soil fertility, and production
and maintenance of biodiversity, from which key ingredients of our agricultural,
pharmaceutical, and industrial enterprises are derived. Historically, the nature and value of
Earth‘s life support systems have largely been ignored until their disruption or loss
highlighted their importance.
Ecotourism, n: The enterprises involved in promoting tourism of unusual or interesting
ecological sites. Environmentally, culturally, and scientifically responsible tourism that takes
great efforts to ensure tourism revenues benefit the local communities where tourism occurs,
the local inhabitants benefit the most economically (revenues are not returned to the
traveler's country of origin) and native culture is not diluted with imported tourist cultures.
Ecotourism safeguards the nature of the attraction that instigated the tourism and serves to
strengthen conservation and scientific research efforts in the area. Very few large
corporations who claim to engage in ecotourism actually do so. The most notorious and
damaging of tourism industries -- the cruise line industry -- is an excellent example of a

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branch of travel that claims to be environmentally-friendly but is in fact extremely damaging,

both culturally and ecologically.
El Nino Southern Oscillation (ENSO), n: Flip-flopping pressure systems in the South
Pacific that trigger short-lived global changes in climate. Warm waters from the western
Pacific move across the ocean, just below the equator, and significantly warm the eastern
tropical Pacific.
Emergent, n: A tree with a canopy that forms about the general upper most continuous
canopy.
Emerging disease, n: The Institute for Medicine defines emerging and re-emerging
diseases as: "New, re-emerging, or drug-resistant infections whose incidence in humans has
increased in the last two decades or whose incidence threatens to increase in the near
future."
Emigrant Someone who leaves an area to live elsewhere.
Energy - Flow The movement of energy from the producer through various consumers
Estivate also aestivate
1: to spend the summer usually at one place
2 : to pass the summer in a state of torpor compare hibernate
Estivation also aestivation the state of one that estivates
Ethnic Group The group of people a person belongs to categorized by race, nationality,
language, religion or culture.
Endangered species, n: Wild species with so few individual survivors that the species could
soon become extinct in all or most of its natural range.
Endangered Species Act, n: The United States federal legislation that mandates protection
of species and their habitats that are determined by scientific consensus to be in danger of
extinction.
Environment, n: All external conditions and factors, living and nonliving (chemicals and
energy), that affect an organism or other specified system during its lifetime; the earth's life-
support systems for us and for all other forms of life - in effect another term for describing
solar capital and earth capital.
Environmental degradation, n: A reduction of an ecosystem's or habitat's ability to support
its natural biota. 2. Depletion or destruction of a potentially renewable resource such as soil,
grassland, forest, or wildlife by using it at a faster rate than it is naturally replenished. If such
use is continued, the resource can become nonrenewable (on a human timescale) or
nonexistent. 3. Pollution, toxification, or other alteration of an environment that makes it less
productive, hospitable, usable, or enjoyable.
Environmental worldview, n: How individuals think the world works, what they think their
role in the world should be, and what they believe is right and wrong environmental behavior
(i.e. ethics).
Epidemiology, n: Study of the patterns of disease or other harmful effects from toxic
exposure within defined groups of people to find out why some people get sick and some do
not.
ERID, acronym: Emerging and Re-emerging Infectious Diseases. See emerging disease
Ethnobotany, n: The study of indigenous knowledge bases regarding plants and their uses.

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Ethnopharmacology, n: The study of indigenous knowledge bases regarding medicines and

how they are produced, as well as the medical practices, treatment protocols, etc. that utilize
these medicines.
Exponential growth, n: Growth in which some quantity, such as population size or
economic output, increases by a fixed percentage of the whole in a given time; when the
increase in quantity over a long enough time is plotted, this type of growth typically yields a
curve shaped like the letter J.
Extant, adj: A species that is still alive and reproducing. All species that currently live on
earth are extant.
Extinct, adj: A species that is no longer living on earth. All representatives of the species are
dead. All the species that once occupied the earth but are no longer living are extinct. We
know of their existence through studying the fossil record. Compare to extant.
Extinction, n: Complete disappearance of a species from the earth. This happens when a
species cannot adapt and successfully reproduce under new environmental conditions, when
it evolves (through a process called radiation) into one or more new species, or when every
member of the species is killed by over predation, pollution, or other man-made causes.
Family Planning Using contraception to control the size of your family.
Family Ties The lack of family ties (no wife or children) encourages young males to
migrate from LEDCs to MEDCs or from rural to urban areas to seek a better life. The young
(20-35) are also best-suited physically to heavy unskilled/semi-skilled work.
Fertile Age Group The child-bearing years of women, normally 18-45 years of age
First law of human ecology, n: We can never do merely one thing. Any intrusion into nature
has numerous effects, many of which are unpredictable. For example, one classic dilemma is
the case of behavioral biologists who observe their study subjects at close range: Are the
observed behaviors truly natural or are they influenced by the researcher's presence?
Food chain, n: Figure of speech describing the dependence of heterotrophy on other
organisms for food, progressing in a series beginning with primary producers (plants) and
ending with the largest carnivores. The food chain is used as a figurative image for
educational purposes only... real trophic systems resemble webs rather than chains. See
food web .
Food web, n: The combination of all the feeding relationships that exist in an ecosystem.
Most prey species are eaten by many different predators, and most predators eat more than
one prey item. As a result, a picture of a trophic system with lines (representing ecological
relationships) drawn between predators and prey soon resembles an intricate web.
Fossil, n: A remnant, impression, mineralized mold, amber encasement, or other trace of a
once-living organism. Technically, anything that once lived and has been permanently
preserved is a fossil, but the most common usage implies great age. This common usage of
fossil generally refers to the mineralized remains or impressions, preserved in stone (almost
always sedimentary rock), of extinct organisms from past geologic ages.
Fossil fuel, n: Products of partial of complete decomposition of plants and animals that
occur as crude oil, coal, natural gas, or heavy oils as a result of exposure to heat and
pressure in earth's crust over millions of years.
Fossil record, n: The cumulative taxonomic information and historical perspective provided
by the wealth and diversity of fossils and related geologic data stored in the earth's crust.
Gene pool, n: The sum total of all the genes that exist among all the individuals of a species.

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Genetics A discipline of biology, is the science of genes, heredity, and variation in living
organisms.
Genetic engineering, n: The artificial transfer of specific genes from one organism to
another.
Geologic time scale, n: Occurring at such a slow pace, or at such infrequent intervals, as to
be imperceptible to humans. 2. Occurring in a pre-human era. 3. The whole of earth's history,
as opposed to the very recent period when humans have walked the earth. One common
and effective means of conceptualizing the disparity between the geologic time scale and the
human time scale is the "calendar year history model," wherein the entire history of the
planet is condensed into a single calendar year. In this model, human ancestors do not
appear until late December and Homo sapiens do not arise until the last second before
midnight on December 31st.
Geology, n: The branch of science that deals with the earth's history, particularly its physical
history, as recorded in the substrate and the fossil record
Geopolitics, n: The study of the influence of such factors as geography, natural resources,
economics, and demography on the politics (especially the foreign policy) of nations.
Ghetto An urban district containing a high proportion of one particular ethnic group; the
term ghetto comes from the district of Geto in medieval Venice which was reserved for
Jews.
Global warming, n: The term given to the possibility that Earth's atmosphere is gradually
warming because of the greenhouse effect of carbon dioxide and other gases. Global
warming is thought by many to be the most serious global environmental issue facing our
society.
Greenhouse effect, n: A natural effect that traps heat in the atmosphere (troposphere) near
the earth's surface. Some of the heat flowing back toward space from the earth's surface is
absorbed by water vapor, carbon dioxide, ozone, and several other gases in the lower
atmosphere (troposphere) and then radiated back toward the earth's surface. If the
atmospheric concentrations of these greenhouse gases rise and are not removed by other
natural processes, the average temperature of the lower atmosphere will gradually increase.
Greenhouse gases, n: Gases in the earth's lower atmosphere (troposphere) that cause the
greenhouse effect. Examples are carbon dioxide, chlorofluorocarbons, ozone, methane,
water vapor, and nitrous oxide.
Green Revolution, n: Refers to the development and introduction of new varieties of wheat
and rice (mainly) that increased yields per acre dramatically in some countries.
Gross primary productivity, n: The rate at which an ecosystem's producers capture and
store a given amount of chemical energy as biomass in a given length of time.
Gross National Product (GNP) per capita: the total value of goods produced and services
provided by a country in a year, divided by the total number of people living in that country.
Habitat, n: Place or type of place where an organism, population, or community lives.
Hazardous waste, n: Any solid, liquid, or containerized gas that can catch fire easily, is
corrosive to skin tissue or metals, is unstable and can explode or release toxic fumes, or has
harmful concentrations of one or more toxic materials that can leach out.
Heterotroph, Organisms the eat/consume autotrophs or other heterotrophs for food and use
their energy. n: Literally, "eats others‖; an organism that must consume other organisms to
fuel its metabolism. Animals, including humans, are heterotrophy; heterotrophic, adj.

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homozygosity the state of being homozygous

homozygous having the two genes at corresponding loci on homologous chromosomes
identical for one or more loci
Human capital, Physical and mental talents of people used to produce, distribute, and sell
an economic good.
Human Development Index: a social welfare index, adopted by the United Nations as a
measure of development, based upon life expectancy (health), adult literacy (education),
and real GNP per capita (economic).
Human time scale, n: Occurring within a short enough timeframe that the event can be
perceived, remembered, and recounted by humans through oral traditions, written histories,
or other mechanisms of human memory. Compare to geologic time scale
Hybrid, n: The offspring of two parents from separate (though closely related) species;
usually sterile, though occasionally able to breed back into one of the parent lines. A hybrid
can almost never produce viable offspring when mated with another hybrid. A common
example is a mule, which is produced by breeding a horse with a donkey (note that the horse
must be the mother, due to the large size of the foal). Hybridization is fairly common among
wind-pollinated plants, while hybridization is quite uncommon among higher animals.
Hydrologic cycle, n: Biogeochemical cycle that collects, purifies, and distributes the earth's
fixed supply of water, from the environment to living organisms and then back to the
environment.
Hydrosphere, n: The earth's liquid water (oceans, lakes other bodies of surface water, and
underground water), the earth's frozen water (polar ice caps, floating ice caps, and ice in soil
known as permafrost), and small amounts of water vapor in the atmosphere.
Immigrant: someone who moves into an area from elsewhere.
Indicator species, n: Species that serve as early warnings that a community or an
ecosystem is being degraded. Fish and amphibians make particularly excellent indicator
species. Large predators (those generally at the apex of the food pyramid) are also good
indicators in many habitats.
Integrated pest management (IPM), n: Combined use of biological, chemical, and
cultivation methods in proper sequence and timing to keep the size of a pest population
below the size that causes economically unacceptable loss of a crop or livestock animal.
Interspecific competition, n: Members of two or more species trying to use the same
limited resources in an ecosystem.
Intraspecific competition, n: Two or individual organisms of a single species trying to use
the same limited resources in an ecosystem.
Infant Mortality The number of babies dying before their first birthday per 1000 live
births.
Land-use planning, n: Process for deciding the best present and future use of each parcel
of land in an area.
Late successional plant species, n: Mostly trees that can tolerate shade and that form a
relatively stable complex forest community.
Laterite: n. Product of rock decomposition with high iron and aluminum hydroxide content;
generally bright red to deep orange in color. 2. Land, usually in the tropics, baked by the sun
after deforestation removes the protective and restorative forest layer above the soil. Abiotic
hardpack ground, red in color. Normal soil microbiotic community, as well as macrobiotic

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flora and fauna, are absent; prone to extensive erosion due to lack of plant cover. Lateralized
hillsides have contributed to several devastating and deadly landslides in tropical countries.
Laterization, n: The process of turning formerly healthy soils into laterite. What becomes of
tropical forest lands when deforested and left exposed to the elements. The ground becomes
extremely hard and cannot be penetrated by germinating forest seeds, so recolonization is
slow or absent.
Lichen, n: A symbiotic relationship between a fungus and a moss. The moss does most of
the work, producing sugars for the lichen's collective metabolic pathways. Lichen are
generally low-growing, vary in color from bright orange or yellow to gray or black, and are
often found growing on rocks and tree bark. An easy mnemonic to assist recall of the nature
of a lichen's symbiosis is: "A fungus took a likin' to a moss, and now they live together."
Life Expectancy The average number of years a person born in a particular country
might be expected to live.
mafic relating to, or being a group of usually dark-colored minerals rich in magnesium and
iron
Mass extinction, n: A catastrophic, widespread -- often global -- event in which major
groups of species are wiped out over a relatively short period when compared to normal
(background) extinction rates. There have been five major mass extinctions, of natural
causes (in at least one case due to an asteroid impacting the earth), in the earth's history.
We are now entering a sixth great mass extinction, this time of unnatural causes... human
activities.
Median lethal dose (LD50), n: Amount of a toxic material per unit body weight of test
animals that kills half the test population in a certain time.
Migrant Someone who moves from one place to another to live.
Migration Movement of people
Monoculture, n: Cultivation of a single crop, usually on a large area of land. This unnatural
agricultural system generally requires the use of large quantities of artificial fertilizers,
herbicides, pesticides, nematocides, and other pest control efforts. Even with these chemical
aids, monocultures are prone to disease outbreaks and pest infestations, largely due to the
genetic homogeneity of such systems.
Mutualism, n: One category of symbiosis in which both participating species generally
benefit.
natality birth-rate
Natural resources, n: Nutrients and minerals in the soil and deeper layers of the earth's
crust; water; wild and domestic plants and animals; air; and other resources produced by the
earth's natural processes.
Natural selection, n: One of several gradual mechanisms through which evolution occurs.
Process by which a particular beneficial gene (or set of genes) is reproduced more than
other genes in succeeding generations due to selective pressures in the environment that
favor the beneficial gene. The result of natural selection is a population that contains a
greater proportion of organisms better adapted to certain environmental conditions.
Nitrogen cycle, n: Cyclic movement of nitrogen in different chemical forms from the
environment to organisms and then back to the environment.

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Nitrogen fixation, n: The process of chemically converting nitrogen gas (N 2 ) from the air
into compounds, such as nitrates (NO 3 ), nitrites (NO 2 ), or ammonia (NH 3), that can be
used by plants in building amino acids and other nitrogen-containing organic molecules.
Nonbiodegradable, adj: Not able to be consumed and/or broken down by biological
organisms. Nonbiodegradable substances include plastics, aluminum, and many chemicals
used in industry and agriculture. Particularly dangerous are nonbiodegradable chemicals that
are also toxic and tend to accumulate in organisms.
Non-renewable resource, n: Resource that exists in a fixed amount (stock) in various
places in the earth's crust and has the potential for renewal only by geological, physical, and
chemical processes taking place over hundreds of millions to billions of years. Examples are
copper, aluminum, coal, and oil. We classify these resources as exhaustible because we are
extracting and using them at a much faster rate than they were formed.
Nutrient, n: Any food or element an organism must take in to live, grow, or reproduce. Plant:
An essential element in a particular ion or molecule that can be absorbed and used by the
plant. For example, carbon, hydrogen, nitrogen, and phosphorus are essential elements;
carbon dioxide, water, nitrate (NO 3 ), and phosphate (PO 4 ) are respective nutrients.
Animal: Materials such as protein, vitamins, and minerals that are required for growth,
maintenance, and repair of the body and also materials such as carbohydrates that are
required for energy.
Organic, adj: All living things, and products that are uniquely produced by living things, such
as wood, leather, and sugar. 2. All chemical compounds or molecules, natural or synthetic
that contain carbon atoms as an integral part of their structure.
Overburden, n: Layer of soil and rock overlying a mineral deposit, removed during surface
mining.
Overconsumption, n: Situation in which some people consume much more than they need
at the expense of those who cannot meet their basic needs- and at the expense of earth's
present and future life-support systems for humans and other forms of life.
Overgrazing, n: Destruction of vegetation when too many grazing animals feed too long and
exceed the carrying capacity of a rangeland area.
Overnutrition, n: Diet so high in calories, saturated (animal) fats, salt, sugar, and processed
foods, and so low in vegetables and fruits that the consumer runs high risks of diabetes,
hypertension, heart disease, and other health hazards.
Overpopulation Where there are too many people and not enough resources to support
a satisfactory quality of life.
Population A group of one species of organisms occupying the same general area, using
the same resources, and acted upon by the same environmental factors
Population Change Births - Deaths + In-Migration -Out-Migration = Population Change.
Population Density Number of people per square kilometre.
Population genetics Studies the distribution of genetic differences within populations
and how these distributions change over time.
Population Pyramid A graph which shows the age and sex structure of a place.
Pyramid A diagram illustrating the flow of a commodity through the ecosystem.
solum the altered layer of soil above the parent material that includes the A and B horizons
Speciation A population that splits into two or more population in which it cannot interbreed
with each other because they are physically separated.

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Structure (of a population) The relative percentages of people of different age groups,
usually shown on a population pyramid.
Paleoecology, n: The study of ancient ecosystems. Paleoecologists use data from such
sources as tree rings, geologic deposits, fossils (pollen is a particularly popular tool), and
coral bores to reconstruct the climate and ecology or ancient ecosystems.
Phosphorus cycle, n: Cyclic movement of phosphorus, in varying chemical forms, from the
environment to organisms and then back to the environment.
Pioneer species, n: First hardy, often xerophytic , species (often microbes, mosses, and
lichens) that begin colonizing a site as the first stage of ecological succession.
Pollutant, n: A particular chemical or form of energy that can adversely affect the health,
survival, or activities of humans or other living organisms.
Population, n: A group within a single species, the individuals of which can and do freely
interbreed. Breeding between populations of the same species is less common because of
differences in location, culture, nationality, and so on.
Population change, n: An increase or decrease in the size of a population. It is equal to
(births + immigration) - (deaths + emigration).
Population density, n: Number of organisms in a particular population found in a specified
area.
Population dispersion, n: General pattern in which the members of a population are
arranged throughout its habitat.
Population distribution, n: Variation of population density over a particular geographical
area. For example, a country has a high population density in its urban areas and a much
lower population density in rural areas.
Positive feedback loop, n: Situation in which a change in a certain direction provides
information that causes a system to change further in the same direction. This can lead to a
runaway or vicious cycle.
Potentially renewable resource, n: Resource that theoretically can last indefinitely without
reducing the available supply, either because it is replaced more rapidly through natural
processes than are nonrenewable resources or because it is potentially inexhaustible (solar
energy). Examples are trees in forests, grasses in grasslands, wild animals, fresh surface
water in lakes and streams, most groundwater, fresh air, and fertile soil. If such a resource is
used faster than it is replenished, it can be depleted and converted into a nonrenewable
resource.
Poverty, n: Inability to meet basic needs for food, clothing, and shelter.
Primary producer, n: An organism, such as a plant or microbe that makes its own food and
forms the bottom-most tier in a trophic system. Primary producers are the basis of the food
web in most ecosystems (the exceptions are open system communities based entirely on
scavenging nutrients flushed into the system from elsewhere, such as some deep sea
communities -- though even in these cases, the food flushed into the system comes from
another system where primary producers are the basis of the trophic pyramid). Primary
producers are able to convert abiotic raw materials into biotic tissue, either by capturing the
sun's energy through photosynthesis (plants) or by harnessing the energy in chemical bonds
through chemosynthesis (some microbes).
Pyramid of biomass, n: Diagram representing the biomass (total dry weight of living
organisms) that can be supported at each trophic level in a food web. The bottom of the
pyramid is comprised of primary producers, while the peak of the pyramid is topped by one

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(or at most a small handful) apex predator. Humans are abnormal in that we cross all
ecosystems and biomass pyramids, and in almost every one (excepting the polar caps and
deepest of oceanic environments) we are the dominant apex predator.
Pyramid of energy flow, n: Also called a trophic pyramid; Diagram representing the flow of
energy through each trophic level in a food chain or food web. With each energy transfer,
only a small part (typically 10%) of the usable energy entering one trophic level is transferred
to the organisms at the next trophic level, with the remaining 90% lost as heat or expended in
metabolic processes.
Resource economics, n: The study of natural ecosystem services and the economic values,
in terms real-world currencies and capital valuations, of those services. One of the goals of
resource economics is to assist policy makers in performing the cost-benefit analysis of
various plans of action or inaction with regard to the natural world. The value of an
ecosystem service is determined by calculating what it would cost to perform the same
service artificially if the naturally-occurring service were disrupted or destroyed.
Resource partitioning, n: Process of dividing up resources in a ecosystem so that species
with similar requirements (overlapping ecological niches) use the same scarce resources at
different times, in different ways, or in different places.
Runoff, n: Surface water effluent (usually from precipitation but may be from human
activities such as irrigation) that moves too quickly to be absorbed into the ground. It flows
down contour gradients to enter stream and river systems, carrying with it anything light
enough to be borne in the volume of water, which may be light after a small rain or
tremendous in the wake of a storm, when even large boulders and trees get swept up in the
runoff. When runoff travels over deforested or unplanted agricultural lands, it carries away
large quantities of topsoil. Runoff from agricultural areas often carries heavy doses of
biocides, fertilizers, and other nutrients, which can lead to eutrophication when introduced
into aquatic systems.
Salinization, n: Accumulation of salts in soil that can eventually make the soil unable to
support plant growth.
Second law of thermodynamics, n: In any conversion of heat energy to useful work, some
of the initial energy input is always degraded to lower quality, more dispersed, less useful
energy -- usually low-temperature heat that flows into the environment; every energy system
has "leaks" and looses energy or heat to attenuation.
Soil Erosion, n: The loss of topsoil through silt-laden runoff, strong winds, or other forces
that transport soil away from its natural location.
Specialist species, n: Species with a narrow ecological niche. They may be able to live in
only one type of habitat, tolerate only a narrow range of climatic or other environmental
conditions, or they may use only one or a few types of food.
Speciation, n: Formation of two species from one species as a result of divergent natural
selection in response to changes in environmental conditions; usually takes thousands or
tens of thousands of years.
Species, n: The boundaries of this taxonomic level (the most precise in the hierarchical
system of binomial nomenclature) are hotly debated among scientists and there is little real
consensus about where to draw the lines between species, subspecies, morphs, races,
variants, etc. In general, a species is a group of organisms that resemble one another in
appearance, general behavior, ecological niche, chemical makeup and processes, and
genetic structure. Organisms that reproduce sexually are classified as members of the same
species only if they can actually or potentially interbreed with one another and produce fertile
offspring. It should be noted that some (though quite few) taxonomists believe the species

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level of classification is frequently invalid and these scientists only recognize classifications
down to the level of genus (again, these taxonomists represent a very small minority view).
Sulfur cycle, n: Cyclic movement of sulfur in different chemical forms, from the environment
to organisms and then back to the environment.
Sustainability, n: Ability of a system to survive for some specified (finite) time.
Sustainable agriculture, n: Method of growing crops and raising livestock based on organic
fertilizers, soil conservation, water conservation, biological control of pests, and minimal use
of non-renewable fossil-fuel energy.
Sustainable development, n: Forms of economic development and activities that do not
deplete or degrade the natural resources upon which present and future economic growth
and life depend.
Sustainable living, n: Taking no more potentially renewable resources from the natural
world than can be replenished naturally and not overloading the capacity of the environment
to cleanse and renew itself by natural processes.
Sustainable society, n: A society that manages its economy and population size without
doing irreparable environmental harm by overloading the planet's ability to absorb
environmental insults, replenish its resources, and sustain human and other forms of life over
a specified period-usually hundreds to thousands of years. During this period it satisfies the
needs of its people without depleting earth capital and thereby jeopardizing the prospects of
current and future generations of humans and other species.
Sustainable system, n: A system that survives and functions over some specified (finite)
time; a system that attains its full expected lifetime.
Sustainable yield (sustained yield), n: Highest rate at which a potentially renewable
resource can be used without reducing its available supply throughout the world or in a
particular area.
symbiont an organism living in symbiosis; esp: the smaller member of a symbiotic pair
Symbiosis, n: Literally means "living together" in Latin. Any intimate relationship or
association between members of two or more species; The members of the relationship are
symbionts. Obligate symbionts rely so heavily on the relationship that they cannot feed,
reproduce, or perform some other crucial life function in the absence of their symbiotic
partner(s). There are three main categories of symbiosis: commensalism, mutualism, and
parasitism with some degree of blending at the edges of these definitions in many cases.
Symbiotic, adj: Refers to a component or member of a system of symbiosis. "These
organisms have a symbiotic relationship."
Taxonomy, n: The classification of living organisms according to the hierarchy of
relationships.
Threatened species, n: Wild species that is still abundant in its natural range but is likely to
become endangered because of a decline in numbers.
Total fertility rate (TFR), n: Estimate of the average number of children that will be born
alive to a woman during her lifetime if she passes through all her childbearing years (ages
15-44) conforming to age-specific fertility rates of a given year. In simpler terms, it is an
estimate of the average number of children a woman will have during her childbearing years.
Transmissible disease, n: A disease that is caused by living organisms (such as bacteria,
viruses, and parasitic worms) and that can spread from one person to another by air, water,
food, body fluids (or in some cases by insects or other organisms).

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Urban heat island, n: Buildup of heat in the atmosphere above an urban area. This is
produced by the large concentration of cars, buildings, factories, and other heat-producing
activities.
Zero population growth (ZPG), n: State in which the birth rate (plus immigration) equals the
death rate (plus emigration) so that the population of a geographical area is no longer
increasing.
Zoonosis, n: A disease of animals, such as rabies or psittacosis that can be transmitted to
humans; zoonotic, adj.

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