COURSE

GUIDE

BIO101
GENERAL BIOLOGY I

Course Team: Prof. Mohammed Bello Abdullahi (Course

Reviewer)–Federal University, Kashere - Gombe
Dr. Maureen N. Chukwu (Reviewed Content
Editor)
NOUN
Dr. Maureen N. Chukwu (Course Coordinator)
NOUN

NATIONAL OPEN UNIƁERSITY OF NIGERIA

BIO 101 GENERAL BIOLOGY I

@ 2023 by NOUN Press

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All rights reserved. No part of this book may be reproduced, in any

form or by any means, without permission in writing from the publisher.

Published by:
National Open University of Nigeria

Reviewed: 2023

Printed: 2023

ISBN: 978-978-058-993-6

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BIO 101 GENERAL BIOLOGY I

INTRODUCTION

GENERAL BIOLOGY I is a one semester, 16 Units course. It will be

suitable to all students to take towards the core module of B.Sc. (Hons)
Biological Sciences. It will also be suitable as an elective course for any
student in Faculty of Sciences who does not want to complete an NOU
qualification but want to learn about Biology. The course involves the
study of Cell structure and organization, functions of cellular organelles,
characteristics and classification of living things, chromosomes, genes
their relationships and importance, general reproduction,
interrelationships of organisms (competitions, parasitism, predation,
symbiosis, commensalisms, mutualism, saprophytism); heredity and
evolution (introduction to Darwinism and Lamarkism, Mendelian laws,
explanation of key genetic terms), elements of ecology and types of
habitat.

Course Competencies
This course aims to enable you to know/understand the basic concepts of
ecology, life support and ecosystem. It will guide your understanding of
various natural phenomena in the planet earth.

Course Objectives

The Comprehensive Objectives of the Course as a whole are to;

1. Explain cell structure and organizations,
2. Summarize functions of cellular organelles
3. Characterize living organisms and state their general reproduction
4. Describe the interrelationship that exists between organisms
5. Discuss the concept of heredity and evolution
6. Describe the basic elements of ecology and enumerate habitat
types and their characteristics.

Working Through this Course

To successfully complete this course, you are required to read each

study unit, read the textbooks and other materials provided.
Reading the reference materials can also be of great assistance. Each
unit has self –assessment exercise which you are advised to do.
There will be a final examination at the end of the course. The course
should take you about 8 weeks to complete.

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BIO 101 GENERAL BIOLOGY I

This course guide provides you with all the components of the course,
how to go about studying and how you should allocate your time to each
unit so as to finish on time and successfully
Study Units

The study units in this course are given below:

BIO 101 GENERAL BIOLOGY I (2 UNITS)

MODULE 1 INTRODUCTION TO BIOLOGY

Unit 1 Properties of Life

Unit 2 The Diversity of life and its organization
Unit 3 Introduction to Biological Inquiry
Unit 4 Scientific Inquiry method
Unit 5 Microscopy and the Cell Theory

MODULE 2 STRUCTURE AND FUNCTIONS OF THE CELL

Unit 1 Cell and Cell Components

Unit 2 Cells Communication
Unit 3 Tissues, Organs and Organ Systems
Unit 4 Characteristics and Classification of Living Things
Unit 5 The Study of Genes and Chromosomes
Unit 6 Reproduction Process and Life cycles

MODULE 3 INTERRELATIONSHIP BETWEEN ORGANISMS

Unit 1 Interrelationship between organisms

Unit 2 Heredity and Variation
Unit 3 Introduction to Evolution
Unit 4 Natural selection
Unit 5 Elements of Ecology

References and Further Readings

You would be required to read the recommended references and

textbooks as provided in each unit of the course.

Presentation Schedule

There is a time-table prepared for the early and timely completion and
submissions of your TMAs as well as attending the tutorial classes. You
are required to submit all your assignments by the stipulated date and
time. Avoid falling behind the schedule time.

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Assessment

There are three aspects to the assessment of this course. The first one is
the in-text questions and the second is self-assessment exercises, while
the third is the written examination or the examination to be taken at the
end of the course. Review the exercises or activities in the unit by
applying the information and knowledge you acquired during the course.
The work submitted to your tutor for assessment will account for 30% of
your total work. At the end of this course, you will have to sit for a final
or end of course examination of about a two-hour duration and this will
account for 70% of your total course mark.

How to get the Most from the Course

In this course, you have the course units and a course guide. The course
guide will tell you briefly what the course is all about. It is a general
overview of the course materials you will be using and how to use those
materials. It also helps you to allocate the appropriate time to each unit
so that you can successfully complete the course within the stipulated
time limit.

The course guide also helps you to know how to go about your in-text
questions and Self-assessment questions which will form part of your
overall assessment at the end of the course. Also, there will be tutorial
classes that are related to this course, where you can interact with your
facilitators and other students. Please I encourage you to attend these
tutorial classes.

This course exposes you to Introductory Ecology, a sub-discipline and

very interesting field of Biological Sciences.

Online Facilitation

Eight weeks are provided for tutorials for this course. You will be
notified of the dates, times and location for these tutorial classes.
As soon as you are allocated a tutorial group, the name and phone
number of your facilitator will be given to you.

The duties of your facilitator is to monitor your progress and provide

any necessary assistance you need.
Do not delay to contact your facilitator by telephone or e-mail for
necessary assistance if

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BIO 101 GENERAL BIOLOGY I

• You do not understand any part of the study in the course

material.
• You have difficulty with the self-assessment activities.
• You have a problem or question with an assignment or with the
grading of the assignment.

It is important and necessary you attend the tutorial classes because this
is the only chance to have face to face contact with your facilitator and
to ask questions which will be answered instantly. It is also a period
where you can point out any problem encountered in the course of your
study.

Course Information
Course Code: BIO 101
Course Title: GENERAL BIOLOGY I
Credit Unit: 2
Course Status: COMPULSORY
Course Blub: This course is designed to enable the students to
understand the basic concepts of ecology, life support and ecosystem. It
will also guide their understanding of various natural phenomena in the
planet earth.

Semester: 2 SEMESTERS
Course Duration: 13 WEEKS
Required Hours for Study: 65 hours

Ice Breaker
Prof. Mohammed Bello Abdullahi is a Professor of Biology
(Biodiversity and Environmental Management) in the Department of
Biological Sciences, Federal University, Kashere-Gombe. He has been
briefly in the Department of Biological Sciences, National Open
University of Nigeria from 2017-2021 participating in all academic
activities in the Department; examining, moderating and facilitating
courses such as; BIO101;

BIO202; BIO204; BIO304 and BIO412, and seminars and practicals.

Prof. Abdullahi's research interest covers phytosociology, climate
change, ecological economics, ethnobotany, plant physiology,
biodiversity and environmental management, and environmental
toxicology.

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BIO 101 GENERAL BIOLOGY I

MODULE 1 INTRODUCTION TO BIOLOGY

Module Structure
In this module we will discuss about the properties, diversity and
organization of life and the scientific method of inquiry:

Unit 1 Properties of Life

Unit 2 The Diversity of life and its organization
Unit 3 Introduction to Biological Inquiry
Unit 4 Scientific Inquiry method
Unit 5 Microscopy and the Cell Theory
Glossary
End of the module Questions

MODULE 1 INTRODUCTION TO BIOLOGY

Unit 1 Properties of Life

Unit Structure
1.1 Introduction
1.2 Intended Learning Outcomes (ILOs)
1.3 The Study of Biology
1.4 The origin and nature of life
1.5 Properties of Life
1.6 Summary
1.7 References/Further Readings/Web Sources
1.8 Possible Answers to Self-Assessment Exercises

1.1 Introduction

Biology is the science of life. All living organisms share several key
properties such as order, sensitivity or response to stimuli, reproduction,
adaptation, growth and development, regulation, homeostasis, and
energy processing. Living things are highly organized following a
hierarchy that includes atoms, molecules, organelles, cells, tissues,
organs, and organ systems. Organisms, in turn, are grouped as
populations, communities, ecosystems, and the biosphere.

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1.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Define Biology
• Trace the origin of life
• Identify and describe the properties of life
1.3 The Study of Biology

Earth provides few hints about the variety of life forms that inhabit it
when viewed from space. Microorganisms are assumed to have been the
first life forms on Earth, existing for billions of years before the
emergence of plants and animals. Our familiar mammals, birds, and
flowers are all quite recent, having evolved 130 to 200 million years
ago. Only in the last 300,000 years have humans begun to resemble the
creatures we are today, despite the fact that humans have only been on
this planet for the past 2.5 million years. The science that examines life
is called Biology. What is life, exactly? Although it may seem like a
frivolous question with a simple solution, it is difficult to define life. For
instance, the study of viruses, which share some traits with living things
but not all of them, is one area of Biology called virology. Viruses do
not fit the criteria that scientists use to define life, despite the fact that
they may assault living things, spread diseases, and even reproduce. In
the past, the study of living things was limited to fields of pure science,
such as botany and zoology, which together make up Biology. However,
as time went on, other branches emerged. New technologies emerged in
both applied and pure domains, giving rise to a highly expansive
concept of science known as biological sciences. The field of biological
sciences spans a wide range of topics, from the intricate interactions of
chemical elements within living cells to the expansive ideas of
ecosystems and planetary environmental changes. Additionally, it is
interested in the physical traits and actions of both modern and extinct
species. How did they come into being, and what relationships do they
have with one another and their surroundings? The biological sciences
deal with a close examination of the inner workings of the human brain,
the make-up of our genes, and even how our reproductive system
functions. Four problems have plagued biology from its earliest days:
What characteristics unify things to be considered "alive"? How do the
different living things work? How do we organise the various types of
organisms so that we can better understand them in the face of the
astounding diversity of life? And finally, how did this diversity develop
and how is it maintaining itself is what biologists eventually aim to
understand. Biologists are constantly looking for solutions to these and
other issues as new creatures are found every day. Biology is the study
of living things as a result. Because of this, biology is sometimes
referred to as "life science." The term "systematic study of living beings
or study of nature" refers to the biological sciences. The main focus of

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teaching life science is to enlighten students on the most recent

advancements being made worldwide in the biological sciences. What
are the four problems that plagued biology from its earliest days?

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Self-Assessment Exercises 1

1. What are the first forms of life that appeared on planet earth?
2. How many years ago did humans starts to inhibit the earth?

1.4 The Origin and Nature of Life

The origin or emergence of life is one of the biggest and most significant
emergent phenomena. Science is still divided on the enigma of life's
beginning. It is difficult to give a definitive response to the question
"what is life?" since we truly want to know why it exists. To put it
another way, "we are really asking, in physical terms, why a given
material system is an organism and not anything else." In order to
respond to this why question, we must comprehend the potential origins
of life. There are numerous hypotheses on the beginning of life. These
various theories regarding the origin of life are highlighted in the
following few sections. The following series of occurrences have
occurred during the evolution of life on Earth. Single-celled organisms
were the most basic species to first exhibit signs of life. These gave rise
to more advanced, multicellular creatures. More cells exhibited cellular
specialisation, meaning that some cells within the multicellular organism
carried out certain activities, which meant that becoming more complex
meant more than just an increase in cell quantity. The evolution of
organisms through millions or perhaps billions of years gave rise to the
living entities we now refer to as plants and animals. Since most
geologists, paleontologists, biologists, and even theologians agree on
this basic timeline of events, one would infer that Moses, Aristotle, and
Darwin were all sharp observers and naturalists who were capable of
logically determining the most likely creation story. Most Scientists
agree that our solar system formed around 4.5 billion years ago, and that
time has passed since then. People who hold the six-day creationism
theory are frequently referred to as creationists. Their approach to
research is predicated on the idea that the Bible should be taken as a
perfectly accurate account of everything it discusses. On the other side,
Scientists apply what they refer to as the scientific method, which
enables them to test theories and hypotheses and to create concepts and
ideas. The origin of life on earth has been the subject of numerous
explanations over the years. As a result, these theories each propose a
different explanation for how life might have originated. Here are a few
of them:
1. Idea of Special Creation: According to this theory, God, the All-
Powerful, created all the many forms of life that exist today on
planet Earth. Hypothesis of Spontaneous Generation: According
to this theory, any type of non-living material could unexpectedly

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BIO 101 GENERAL BIOLOGY I

and spontaneously give rise to a living organism. Aristotle, a Greek

philosopher, was one of the ardent supporters of spontaneous
creation (384-322 BC).
2. The notion of catastrophe is merely a special case of the theory of
special creation. It claims that God has created life on earth in
several ways, each of which was preceded by a disaster brought
on by a geological disturbance of some kind. This hypothesis holds
that since every catastrophe wiped out all existing life, every new
life form that was created was distinct from the preceding ones.
3. Cosmozoic Theory (Theory of Panspermia): In accordance with
this theory, some organisms' highly resistant spores travelled to
Earth from other heavenly bodies like meteorites. This idea was
proposed by Richter in 1865 and supported by Arrhenius (1908)
and other contemporary Scientists. The theory did not gain any
support. This theory lacks evidence, hence it was discarded.
4. Theory of Chemical Evolution: This theory is also known as the
physical-chemical hypothesis or the materialistic theory.

According to this view, the chemical evolution that led to the origin of
life on Earth probably took place over the course of 3.8 billion years.
Two Scientists separately proposed this theory: A.I. Oparin, a Russian
Scientist, in 1923 and J.B.S. Haldane, an English Scientist, in 1928.
How do we best refer to the theory of physical-chemical hypothesis or
the materialistic theory in Biology?

Self-Assessment Exercises 2
1. What are the four prominent theories on the origin of life?
2. What is the thrust of the theory of Chemical Evolution?

1.5 Properties of Life

All groups of living organisms share several key characteristics or

functions: order, sensitivity or response to stimuli, reproduction,
adaptation, growth and development, regulation/homeostasis, and
energy processing. When viewed together, these eight characteristics
serve to define life.

Order
Cells make up organisms, which are highly organised structures. It is
amazing how intricate even extremely basic, single-celled organisms
are. Molecules are made up of atoms inside each cell. Organelles or cell
components are created from these. Multicellular creatures, which can
have millions of individual cells, have an advantage over single-celled
organisms in that they can specialise their cells to carry out particular

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BIO 101 GENERAL BIOLOGY I

tasks and even sacrifice them in some circumstances for the benefit of
the organism as a whole. How these specialised cells in creatures like
toads combine to generate organs like the heart, lung, or skin.

Sensitivity or Response to Stimuli

Organisms react to a variety of stimuli. For instance, plants might sway
in the direction of a light source or react to touch. Even very little
bacteria can move in response to chemicals or light (a process known as
chemotaxis) (phototaxis). Moving away from a stimulus is regarded as a
negative response, but moving toward it is regarded as a good response.
The plant returns to normal after a short while.

Reproduction
The genetic material, or DNA, of single-celled organisms is first
duplicated, and then it is divided equally when the cell gets ready to
divide into two new cells. Numerous species with more than one cell, or
multicellular organisms, create specialised reproductive cells that give
rise to new individuals. DNA containing genes is transferred to an
organism's progeny during reproduction. Because of these genes, the
progeny will be of the same species as the parents and will share traits
like fur colour and blood type with them.

Adaptation
Every living thing displays a "fit" to its surroundings. This adaptability,
as described by Biologists, is the result of evolution by natural selection,
which affects every lineage of reproducing creatures. Examples of
adaptations range from heat-resistant Archaea that can survive in
steaming hot springs to a nectar-eating moth whose tongue length
matches that of the flower it feeds on. The ability to survive and
reproduce is improved by adaptations in the individual who is displaying
them. Adaptations change with time. Natural selection drives the traits
of individuals in a population to follow environmental changes.

Growth and Development

Genes encode specific instructions on how organisms should grow and
develop. These genes give instructions for cellular growth and
development, ensuring that the offspring of a species will develop into
adults who share many traits with their parents.

Regulation/Homeostasis
Living organisms are complex and need various regulatory mechanisms
to regulate internal processes like nutrition, transport, stimulus response,
and stress management.

Homeostasis, which is defined as a "steady state," is a generally stable

internal environment needed to support life. For instance, organ systems

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BIO 101 GENERAL BIOLOGY I

like the digestive or circulatory systems convey oxygen throughout the

body, remove waste, give nutrients to every cell, and cool the body,
among other specific tasks.

Cells need the right circumstances to function effectively, including the

right temperature, pH, and chemical concentrations. These
circumstances could, however, change at any time. By turning on
regulatory systems, organisms are able to nearly constantly maintain
homeostatic internal conditions within a small range, despite changes in
their environment. For instance, many species use a mechanism called
thermoregulation to control their body temperatures. Cold-adapted
organisms, like the polar bear, have physical characteristics that enable
them to survive extreme cold and retain body heat. In hot regions,
species have mechanisms to assist them release extra body heat, such as
perspiration in humans or panting in canines. By producing heat and
preventing heat loss through their thick fur and a layer of dense fat under
their skin, polar bears and other mammals that live in ice-covered areas
keep their body temperatures stable.

Energy Processing
All living things require a source of energy for their metabolic
processes. Some species use chemical energy from molecules they
consume, whereas others use chemical energy that is captured from the
Sun and transformed into chemical energy in food.

Evolution
Mutations, or chance changes in hereditary material over time, are the
cause of the diversity of life on Earth. These mutations give organisms
the chance to adapt to a shifting environment. According to the laws of
natural selection, an organism with traits adapted to its surroundings will
reproduce more successfully. Why do living things require energy?

Self-Assessment Exercises 3
1. How does the process of reproduction in single celled organisms
begins?
2. How does organisms respond to environmental changes?

1.6 Summary

You have learned about the concept of Biology as the study of living
things. You have studied about the characteristics of living things such
as order, sensitivity or response to stimuli, reproduction, adaptation,
growth and development, regulation, homeostasis, and energy
processing and the organization of life itself into hierarchy that includes
atoms, molecules, organelles, cells, tissues, organs, and organ systems.

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BIO 101 GENERAL BIOLOGY I

Organisms, in turn, are grouped as populations, communities,

ecosystems, and the biosphere.
1.7 References/Further Readings/Web Sources

Mader, S. (2017). Essentials of Biology. Published by McGraw-Hill

Education. ISBN 10: 1259660265 ISBN 13: 9781259660269
Putman, R.J. and S.D. Wratten (1984). Principles of Ecology,
Publisher Springer Dordrecht, eBook PackagesSpringer Book
Archive, DOIhttps://doi.org/10.1007, /978-94-011-6948-6, eBook
ISBN978-94-011-6948-6. 388pp
https://opentextbc.ca/biology/chapter/1-1-themes-and-concepts-of-
biology/

https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biolog
y/Book%3A_General_Biology_(Boundless)/04%3A_Cell_Structure/4.0
3%3A_Studying_Cells_-_Cell_Theory#title
https://www.youtube.com/watch?v=cQPVXrV0GNA
https://www.youtube.com/watch?v=juxLuo-sH6M
https://www.youtube.com/watch?v=juxLuo-sH6M
https://www.youtube.com/watch?v=ltRApt0IpCE

1.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. The first forms of life that appeared on Earth are thought to have
been microorganisms
2. Humans have inhabited this planet for only the last 2.5 million
years

Answers to SAE 2
1. Several theories attempts to offer explanation on the possible
mechanism of origin of life and prominent of these are:
1. Theory of Special Creation
2. Theory of Catastrophism
3. Cosmozoic Theory
4. Theory of Chemical Evolution
2. According this theory, Origin of life on earth is the result of a
slow and gradual process of chemical evolution that probably occurred
about 3.8 billion years ago.

Answers to SAE 3
1. Single-celled organisms reproduce by first duplicating their
DNA, which is the genetic material, and then dividing it equally as the
cell prepares to divide to form two new cells

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2. As an environment change, natural selection causes the

characteristics of the individuals in a population to track those
changes.

Unit 2 The Diversity of life and its organization

Unit Structure

2.1 Introduction
2.2 Intended Learning Outcomes (ILOs)
2.3 The Diversity of Life
2.4 Levels of Organization of Living Things
2.5 Evolutionary Relationships of Life Forms
2.6 Summary
2.7 References/Further Readings/Web Sources
2.8 Possible Answers to Self-Assessment Exercises

2.1 Introduction

You will learn about the diversity of life on planet earth today. You will
study about evolutionary relationships of life forms and the levels of
organization of living things

2.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• Explain the diversity of life on planet earth.

• Describe the levels of organization of living things and
• Explain the evolutionary relationships of life forms

2.3 The Diversity of Life

Biology is a science with a relatively broad field of study because there

is a wide variety of life on Earth. Evolution, the process of progressive
change in which new species develop from more established ones is the
cause of this diversity. The development of living beings in all spheres
of existence, from the microscopic to ecosystems, is studied by
evolutionary Biologists. The idea of classifying all known species of
creatures into a hierarchical taxonomy was first put forth in the 18th
century by a Scientist by name Carl Linnaeus. In this concept, a genus is
a collection of the species that are most similar to one another.
Additionally, within a family, comparable genera (plural of genus) are
grouped together. The level at which all creatures are gathered together

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into groups is reached at the end of this grouping. From lowest to

highest, the eight levels of the present taxonomic hierarchy are: species,
genus, family, order, class, phylum, kingdom, and domain. As a result,
species are grouped inside genera, families and orders are grouped
within classes, and so on.
The system's highest level, domain, has only recently been added since
the 1990s. There are currently three recognised domains of life:
Eukarya, Archaea, and Bacteria. Eukaryotic creatures are those that have
cells with nuclei. It comprises various protist kingdoms as well as the
kingdoms of fungi, plants, and animals. Numerous extremophiles,
single-celled organisms without nuclei that can survive in extreme
conditions like hot springs, are members of the Archaea. Another
distinct category of single-celled organisms without nuclei is the
bacteria. Bacteria and Archaea are both prokaryotes, a colloquial term
for cells devoid of nuclei. The suggestion to categorise life into three
domains was inspired by the 1990s realisation that some "bacteria," now
known as the Archaea, were different genetically and biochemically
from other bacterial cells as they were from eukaryotes. This abrupt shift
in our understanding of the tree of life shows that classifications are
subject to change when new data becomes available.

Linnaeus was the first to name creatures using two distinct names,
commonly known as the binomial naming system, in addition to the
hierarchical taxonomic system. Because there were regional variations
in these popular names prior to Linnaeus, using them to refer to species
caused confusion. The capitalised genus name and the species name
make up binomial names (all lower-case). When printed, both names are
put in italics. Every species is given a distinct binomial that is known
around the world, allowing any Scientist to identify the species being
discussed. As an illustration, the North American blue jay has its own
scientific name, Cyanocitta cristata. Homo sapiens is our own species.
Who was the first to come up with the idea of classifying all known
species of creatures into a hierarchical taxonomy in the 18th century?

Self-Assessment Exercises 2
1. What is the source of biological diversity?
2. Who was the first scientist to name organisms using two unique
names, now called the binomial naming system.

2.4 Levels of Organization of Living Things

Living things follow a hierarchy from little to large and are highly
structured and organised. The atom is the lowest and most basic unit of
matter that yet has elemental characteristics. It consists of an electron-

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surrounded nucleus. Moles are made of atoms. A molecule is an organic

compound made up of at least two atoms joined by a chemical bond.
Numerous biologically significant molecules are macromolecules, which
are huge molecules created typically by joining monomers, or smaller
building blocks. Deoxyribonucleic acid (DNA), which carries the
blueprints for an organism's operation, is an illustration of a
macromolecule. Organelles are collections of macromolecules seen in
some cells that are encased in membranes, and they carry out specific
tasks within cells. The smallest essential unit of structure and function in
living beings, the cell, makes up all living things. Some organisms only
have one cell, whereas others have several cells. There are two types of
cells; eukaryotic or prokaryotic cells. Prokaryotes are single-celled
organisms that lack nuclei and organelles that are encased in nuclear
membranes. In contrast, eukaryotic cells do include nuclei and
organelles that are encased in membranes.

The majority of multicellular organisms combine cells to form tissues,

which are collections of comparable cells performing the same function.
Organs are assemblages of tissues arranged according to a shared
purpose. Organs can be found in both plants and animals. An organ
system is a more advanced level of organisation made up of organs with
similar functions. Vertebrate animals, for instance, have a variety of
organ systems, such as the circulatory system, which carries blood to
and from the lungs as well as throughout the body. This system is made
up of the heart and blood arteries. Organisms are unique forms of life.
For instance, every tree in a forest is a living thing. Even though they are
commonly referred to as microbes, single-celled prokaryotes and
eukaryotes are also regarded as organisms.

A population is the aggregate term for all members of a species that are
present in a given location. For instance, a forest can have a lot of white
pine trees. The population of white pine trees in this woodland is
represented by all of these trees. Various populations may coexist in the
same region. For instance, there are communities of flowering plants,
insects, and microbiological colonies in the forest of pine trees. A
community is made up of all the people who live in a certain location.
For instance, the community of a forest is made up of all the populations
of trees, flowers, insects, and other living things. An ecology exists in
the forest itself. Abiotic, or non-living, elements of the environment,
such as nitrogen in the soil or precipitation, coexist with all the living
things in a certain area to form an ecosystem. At the highest level of
organization, the biosphere is the collection of all ecosystems, and it
represents the zones of life on Earth. It includes land, water, and
portions of the atmosphere.

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Figure 2.1. Biological Levels of Organization: The biological levels of

organization of living things follow a hierarchy, from a single organelle
to the entire biosphere, living organisms are part of a highly structured
hierarchy, such as the one shown above. What does the biosphere
represent at the highest level of organization of living things?

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Self-Assessment Exercises 1

Explain the meaning of each of the following

1. molecule
2. macromolecule
3. polymerization

2.5 Evolutionary Relationships of Life Forms

A phylogenetic tree can summarise the relationships between different

types of life on Earth in terms of evolution. A phylogenetic tree is a
diagram that depicts the relationships between biological species in
terms of their shared and unique genetic, physical, or both features. A
phylogenetic tree is made up of branches and branch points, or nodes.
The internal nodes indicate ancestors and are instances in evolution
when two new species are believed to have sprung from a common
ancestor, according to scientific data. Each branch's length can be
viewed as a relative time estimate. Animals, plants, fungus, protists, and
bacteria were the five kingdoms that Biologists previously divided
living things into. However, the groundbreaking research of American
microbiologist Carl Woese in the early 1970s has demonstrated that the
three lineages of life on Earth—Bacteria, Archaea, and Eukarya—have
developed over time. To represent the new evolutionary tree, Woese
proposed the domain as a new taxonomic level and Archaea as a new
domain. Extremophiles are creatures from the Archaea domain that
thrive in harsh environments. Woese built his tree using genetic linkages
rather than morphological similarities (shape). In phylogenetic analyses,
various genes were employed. Woese's tree was created using
comparative sequencing of genes that are widely distributed, conserved
(meaning that they have undergone only minor changes during
evolution), of an appropriate length, and can be found in some form in
every organism.

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BIO 101 GENERAL BIOLOGY I

Figure 2.2. The Phylogenetic tree of life

How was Woese's tree built using genetic linkages?

Self-Assessment Exercises 3
1. List the past grouping of living organisms into the five kingdoms
2. Who is the 18th century scientists that first proposed the grouping
of organisms into a hierarchical taxonomy?

2.6 Summary

You have studied about evolution as the source of biological diversity

on Earth. A diagram called a phylogenetic tree was also used to show
evolutionary relationships among organisms. You have also learned
about the many branches and sub disciplines of Biology such as
molecular biology, microbiology, neurobiology, zoology, and botany,
among others.

14
BIO 101 GENERAL BIOLOGY I

2.7 References/Further Readings/Web Sources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive Belmont,
CA 94002-3098 USA, ISBN-13: 978-0-495-55795-1, 383pp

Putman, R.J. and S.D. Wratten (1984). Principles of Ecology,

Publisher Springer Dordrecht, eBook PackagesSpringer Book
Archive, DOIhttps://doi.org/10.1007, /978-94-011-6948-6, eBook
ISBN978-94-011-6948-6. 388pp

https://opentextbc.ca/biology/chapter/1-1-themes-and-concepts-of-
biology/
https://www.youtube.com/watch?v=xSIrobQxuzI
https://www.youtube.com/watch?v=wxjSx9wluAQ
https://www.youtube.com/watch?v=fV2aaV-Hp2U
https://www.youtube.com/watch?v=P3lsApPq-OQ

2.8 Possible Answers to Self-Assessment Exercises

Answers to SAEs 1
1. The source of the diversity is evolution, the process of gradual
change during which new species arise from older species.
2. Carl Linnaeus

Answers to SAEs 2
The meaning of the following terms:
1. molecule: The smallest particle of a specific compound that
retains the chemical properties of that compound; two or more
atoms held together by chemical bonds.
2. macromolecule: a very large molecule, especially used in
reference to large biological polymers (e.g. nucleic acids and
proteins)
3. polymerization: The chemical process, normally with the aid of
a catalyst, to form a polymer by bonding together multiple identical
units (monomers).

Answers to SAEs 3
1. In the past, biologists grouped living organisms into five
kingdoms: animals, plants, fungi, protists, and bacteria.
2. In the 18th century, a scientist named Carl Linnaeus first
proposed organizing the known species of organisms into a
hierarchical taxonomy.

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BIO 101 GENERAL BIOLOGY I

Unit 3 Introduction to Biological Inquiry

Unit Structure

3.1 Introduction
3.2 Intended Learning Outcomes (ILOs)
3.3 Scope of Biology
3.4 The Study of Life
3.5 The Nature of Science
3.6 Summary
3.7 References/Further Readings/Web Sources
3.8 Possible Answers to Self-Assessment Exercises

3.1 Introduction

You will learn that the scope of biology is broad and therefore contains
many branches and sub disciplines. You will study about the shared
characteristics of the natural sciences and understand the process of
scientific inquiry. You will also be able understand the application of
forensic science in law and describe the basic scientific ethics in
research. Science is knowing. Scientists search for knowledge through
inquiry, which is a way of questioning and explaining phenomena that
occur in nature. Let's begin by exploring how biologists and researchers
use the scientific method in the scientific inquiry of life

3.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Appreciate the various branches of biology

• Identify the shared characteristics of the natural sciences
• Describe the application of forensic Scientist to answer law
matters
• Understand the basic Scientific ethics in research

3.3 The Scope of Biology

Since biology has a wide range of applications, there are numerous

branches and subfields within it. It is possible for biologists to specialise
in one of such subdisciplines. For instance, the study of biological
processes at the molecular level, including interactions between
molecules like DNA, RNA, and proteins as well as how they are
controlled, is known as molecular biology. The study of the composition
and operation of microbes is known as microbiology.

16
BIO 101 GENERAL BIOLOGY I

It is a somewhat diverse field in and of itself, with additional specialists

including geneticists, ecologists, and microbial physiologists depending
on the area of research. Neurobiology is a different area of biological
study that focuses on the biology of the nervous system. It is
acknowledged as a branch of biology as well as an interdisciplinary
subject of study. This sub-discipline, which is interdisciplinary in nature,
uses molecular, cellular, developmental, medicinal, and computational
approaches to study many aspects of the nervous system.

Another area of biology called palaeontology examines the evolution of

life using fossils. The study of animals and plants is known as zoology
and botany, respectively. Biotechnologists, ecologists, and physiologists
are just a few of the areas in which biologists can specialise.
Biotechnologists employ their understanding of biology to develop
practical products. Ecologists investigate how creatures interact with
their surroundings. Physiologists research how cells, tissues, and organs
function. These are just a few of the numerous careers that biologists
might choose from. Biology-related discoveries can have a very
significant and immediate impact on us, on everything from our bodies
to the environment we live in. We rely on these findings for our food
security, our health, and the advantages our ecosystem offers. Because
of this, having a basic understanding of biology might help us make
better judgments in our daily lives. Biology has been altered by the
technological advancements of the 20th century, notably those related to
the description and manipulation of DNA. This change will make it
possible for scientists to continue learning more about the evolution of
life, the human body, our ancestry, and how we can continue to exist as
a species on this planet despite the pressures brought on by our
expanding population. The fact that biologists are still solving complex
questions concerning life suggests that we are only at the beginning of
our understanding of the planet's history, the origins of life, and our
place within it. For these and other reasons, the biology information you
acquire from this textbook and other printed and electronic materials
should be useful in whichever line of work you choose.
Which area of biology examines the evolution of life using fossils?

Self-Assessment Exercises 1
1. What is the scope of molecular biology?
2. What is the interest of Forensic Science?

3.4 Forensic Science and Scientific Ethics

Forensic science is the application of science to answer questions related

to the law. Forensic scientists can be biologists, chemists, or

17
BIO 101 GENERAL BIOLOGY I

biochemists. The work of forensic scientists involves looking at

evidence linked to crimes and providing scientific testimony for use in
court. In recent years, interest in forensic science has grown, probably as
a result of well-liked television programmes that showcase forensic
scientists in action. Additionally, the types of work that forensic
scientists can perform have been updated thanks to the advancement of
molecular techniques and the creation of DNA databases. The majority
of their work is focused on crimes against humans like murder, rape, and
assault. Their work entails processing DNA from a variety of locations
and materials in addition to evaluating samples including hair, blood,
and other bodily fluids. Other biological evidence, such bug fragments
or pollen grains, that has been left at crime sites is also examined by
forensic specialists. Most likely, students who want to major in forensic
science will need to complete chemistry, biology, and some challenging
math courses.

Scientists have a responsibility to protect people, animals, and the

environment from unwarranted harm. Additionally, they must make sure
that their research and communications are impartial and that all
relevant factors—including financial, legal, safety, and replicability—
are correctly balanced. In the significant and ever-evolving discipline of
bioethics, scholars cooperate with other organisations and individuals.
They try to establish standards for current practise and are constantly
thinking about new innovations and upcoming technology to come up
with solutions for the coming years and decades. Unfortunately, a
number of patently unethical activities, where biologists failed to treat
research subjects with dignity and, in some cases, actually harmed them,
preceded the development of the area of bioethics. 399 African
American men were diagnosed with syphilis in the Tuskegee Syphilis
Study of 1932, but they were never told they had the infection, so they
continued to live with it and spread it to others. Because the aim of the
study was to comprehend the effects of untreated syphilis on Black
males, doctors even withheld proven medicines. While the choices made
in the Tuskegee research cannot be justified, certain choices are really
challenging. Bioethicists, for instance, may investigate the ethical
implications of gene editing technologies, such as the potential for
creating species that could supplant others in the ecosystem and the
potential for "designing" human beings. Ethicists will probably attempt
to strike a balance between the positive and negative effects of their
work, such as bettering medicines or preventing specific diseases.
Because bioethics is seldom straightforward, scientists frequently must
weigh benefits and risks. You will learn about medical advancements
that, at their root, have what many people view as an ethical failing in
this literature and course. Henrietta Lacks, an African American woman
in her 30s, received a cervical cancer diagnosis at Johns Hopkins
Hospital in 1951.

18
BIO 101 GENERAL BIOLOGY I

Her illness-specific traits allowed her cells to divide continuously,

effectively rendering them "immortal." Researchers obtained samples of
her cells without her knowledge or consent and used them to make the
immortal HeLa cell line. Major medical advancements made possible by
these cells include the development of the polio vaccine, as well as
studies into cancer, AIDS, cell ageing, and, most recently, COVID-19.
Lacks' contributions to those discoveries have largely gone
unrecognised, and neither she nor her family have reaped the millions of
dollars in pharmaceutical revenues made possible in part by the use of
her cells. Even if it could save the lives of other patients, taking tissue or
organs without the patient's permission nowadays is not just regarded as
unethical but also unlawful. Examining related concerns before, during,
and after research or practise is conducted, adhering to accepted
professional standards, and taking into account the safety and dignity of
all organisms participating or impacted by the work are all part of the
function of ethics in scientific research. What is forensic science?

Self-Assessment Exercises 1
1. What is the scope of molecular biology?
2. What is the interest of Forensic Science?

3.5 The Nature of Science

However, what exactly is science? Biology is a science. What

connections exist between the study of biology and other scientific
fields? The definition of science is "knowledge of the natural world"
(from the Latin scientia, "knowledge"). A particularly precise method of
learning about or knowing the world is science. The previous 500 years
have shown that science is a highly potent way of understanding about
the world, and that it has played a significant role in the technological
revolutions that have occurred during this time. The tools of science,
however, cannot be used to study all fields of knowledge and human
experience. These include things like providing answers to only moral
questions, questions about aesthetics, or questions that can be broadly
characterised as spiritual concerns. These topics are not within the
purview of material phenomena, the phenomena of matter and energy,
and hence cannot be witnessed or quantified.

The scientific method is a structured approach to research that includes

meticulous observation and experimentation. The testing of hypotheses
is one of the most crucial parts of this strategy. A testable hypothesis is a
theory put out to explain an occurrence. Typically, tentative
explanations, or hypotheses, are developed within the framework of a

19
BIO 101 GENERAL BIOLOGY I

scientific theory. A widely accepted, rigorously investigated, and

verified explanation for a collection of observations or a phenomenon is
what is known as a scientific theory. The basis of all scientific
knowledge is scientific theory. Additionally, there are scientific laws
that describe how parts of nature will act under specific circumstances in
many scientific disciplines (less so in biology). These laws are succinct
descriptions of areas of the world that can be expressed using formulas
or mathematics. There is no progression from hypotheses to theories to
laws, as though these concepts signified a rise in worldly certainty.

The value of various branches of science has been a topic of discussion

within the scientific community for the last few decades. Is it
worthwhile to pursue science for the sake of merely learning something,
or does scientific information only have value if we can use it to solve a
particular issue or improve our quality of life? The distinctions between
basic science and applied science are the main subject of this query.
• Basic science or Regardless of how such knowledge might be
used in the near future, "pure" science aims to further knowledge. It is
not concentrated on creating something with immediate
commercial or public benefit. Although knowing for knowledge's
sake is the immediate aim of basic research, this does not
preclude the possibility of an application in the long run.
• In contrast, The goal of applied science, sometimes known as
"technology," is to apply scientific knowledge to solve practical
issues. For instance, it could be possible to identify a treatment
for a specific disease, increase crop yields, or save animals in danger
from a natural disaster. In applied science, the researcher
typically has the problem defined for them.

Some people could view basic science as "useless" while viewing

applied science as "helpful." These people might ask, "What for?" to a
scientist who promotes knowledge acquisition. However, a close
examination of the history of science indicates that many outstanding
applications of enormous value have been made possible by
fundamental knowledge. Since many scientists believe that a
fundamental understanding of science is required before an application
can be produced, applied science is dependent on the findings of basic
science. Others believe it is time to move beyond fundamental research
and focus on developing answers for real-world issues. Both strategies
are appropriate. It is true that there are problems that demand immediate
attention; however, few solutions would be found without the help of the
knowledge generated through basic science. The understanding of the
molecular mechanisms driving DNA replication that resulted from the
discovery of DNA structure is one instance of how basic and applied
science can cooperate to solve practical challenges. Our cells contain
DNA strands that are particular to each individual and which carry the

20
BIO 101 GENERAL BIOLOGY I

instructions for life. Before a cell divides to create new cells, DNA
replication creates new copies of the DNA. In order to identify genetic
illnesses, locate people who were present at a crime scene, and establish
paternity, scientists had to first understand the principles of DNA
replication. It seems doubtful that applied science would exist without
foundational science.

The Human Genome Project, a study in which each human chromosome

was examined and mapped to ascertain the specific sequence of DNA
subunits and the precise position of each gene, serves as another
illustration of the relationship between basic and applied research. (The
genome is a person's entire collection of genes; the gene is the
fundamental unit of heredity.) As part of this project, research on other
organisms has also been done in order to better understand human
chromosomes. Basic research using non-human organisms and later the
human genome was crucial to the Human Genome Project. Utilizing the
data for applied research to find treatments for genetically based
diseases eventually became a significant end goal. It is crucial to
remember that while research projects in both basic and applied science
are typically meticulously planned, some discoveries are made by
serendipity, that is, by way of a fortunate accident or a happy surprise.
When biologist Alexander Fleming unintentionally left a petri dish of
Staphylococcus bacteria uncovered, penicillin was accidently
discovered. The microorganisms were killed by an unwelcome mould
growth. Penicillium was found to be the mould, and a new antibiotic
was found. Even in the highly structured field of science, serendipity can
produce surprising discoveries when combined with an attentive,
inquisitive mind. What is a genome?

Self-Assessment Exercises 3
1. What is the scientific method?
2. Which is the one of the most important aspects of the scientific method?

3.6 Summary

You must have learned about the scope of biology as containing many
branches and sub disciplines. You have also studied the shared
characteristics of the natural sciences and the process of scientific
inquiry. The nature of science as a critical component of scientific
literacy that enhances students' understandings of science concepts and
enables them to make informed decisions about scientifically-based
personal and societal issues have been highlighted in the unit.

21
BIO 101 GENERAL BIOLOGY I

3.7 References/Further Readings/Web Sources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive Belmont,
CA 94002-3098 USA, ISBN-13: 978-0-495-55795-1, 383pp

Putman, R.J. and S.D. Wratten (1984). Principles of Ecology,

Publisher Springer Dordrecht, eBook PackagesSpringer Book
Archive, DOIhttps://doi.org/10.1007, /978-94-011-6948-6, eBook
ISBN978-94-011-6948-6. 388pp

https://www.cambridge.org/core/books/nature-of-life/what-is-the-
meaning-of-life/77B3F144E9C039AEB1CC06FCE39D470A
https://study.com/academy/lesson/the-basic-nature-of-life.html
https://pubmed.ncbi.nlm.nih.gov/6679625/
https://people.reed.edu/~mab/papers/life.OXFORD.html
https://www.youtube.com/watch?v=IadAzzx7EHc
https://www.youtube.com/watch?v=HaVmHJzBrMg
https://www.youtube.com/watch?v=hBBEOgD_bwY
https://www.youtube.com/watch?v=oIMUPPIoqPY

3.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Life of the body (physical), life of the mind and life of the spirit.
2. The methods of science include careful observation, record
keeping, logical and mathematical reasoning, experimentation,
and submitting conclusions to the scrutiny of others.

Answers to SAE 2
1. Molecular biology studies biological processes at the molecular
level, including interactions among molecules such as DNA,
RNA, and proteins, as well as the way they are regulated.
2. Forensic science is the application of science to answer questions
related to the law. Biologists as well as chemists and biochemists
can be forensic scientists. Forensic scientists provide scientific
evidence for use in courts, and their job involves examining
trace material associated with crimes.

Answers to SAE 3
1. The scientific method is a method of research with defined steps
that include experiments and careful observation.
2. One of the most important aspects of this method is the testing of
hypotheses

22
BIO 101 GENERAL BIOLOGY I

Unit 4 Scientific Inquiry method

Unit Structure

4.1 Introduction
4.2 Intended Learning Outcomes (ILOs)
4.3 Scientific Inquiry
4.4 Hypothesis in Science
4.5 Basic and Applied Science
4.6 Summary
4.7 References/Further Readings/Web Sources
4.8 Possible Answers to Self-Assessment Exercises

4.1 Introduction

You will learn the meaning and method of the scientific inquiry in this
unit. You will study the meaning of hypothesis and how to test and
apply it in science research. You will also learn about basic and applied
research in science.

4.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• Understand the meaning and method of the scientific inquiry.

• Explain the meaning of hypothesis
• Describe how to test and apply hypothesis in science research.
• Explain the meaning of basic and applied research in science.

4.3 Scientific Inquiry

All branches of science share the same ultimate objective, which is "to
know." The advancement of science is fueled by curiosity and enquiry.
The goal of science is to comprehend the world and how it works.
Inductive reasoning and deductive reasoning are the two types of logical
thinking that are employed. Inductive reasoning is a type of logical
reasoning that draws a generalisation from a set of related observations.
In descriptive science, this kind of thinking is typical. A biologist or
other life scientist will make observations and note them. These data
may be quantitative (containing of statistics) or qualitative (descriptive),
and the raw data may be supplemented with illustrations, photographs,
films, or other visual media. The scientist can draw conclusions

23
BIO 101 GENERAL BIOLOGY I

(inductions) based on evidence from several observations. Formulating

generalisations via inductive reasoning requires close observation and
in-depth data investigation. This is how many brain studies operate.
While people are performing a task, several brains are being watched. It
is then shown that the area of the brain controlling the reaction to that
task is the part that lights up, signifying activity. Science that is
hypothesis-based employs a sort of logic known as deductive reasoning
or deduction. In contrast to inductive reasoning, deductive reasoning
follows a different pattern of thought. Deductive reasoning is a type of
logical reasoning where specific outcomes are predicted using a general
principle or law. A scientist can infer and forecast specific conclusions
from those broad principles, provided that the general principles are
true. For instance, it is expected that as a region's climate warms, the
distribution of plants and animals will alter. Distributions in the past and
the present have been compared, and numerous alterations have been
discovered that are compatible with a warming climate. The discovery
of the distributional change serves as support for the validity of the
climate change conclusion.

The two primary avenues of scientific inquiry, descriptive science and

hypothesis-based research, are connected to both types of logical
thinking. While hypothesis-based science begins with a specific issue or
problem and a potential response or solution that can be investigated,
descriptive (or discovery) science attempts to observe, explore, and
discover. Because most scientific activities use both methodologies, the
line separating these two fields of study is frequently blurred.
Observations spark questions, those questions prompt the creation of a
hypothesis as a potential response, and finally the hypothesis is put to
the test. As a result, descriptive science and science based on hypotheses
are constantly conversing. What are the two primary avenues of
scientific inquiry?

Self-Assessment Exercises 1
1. What are the two methods of logical reasoning in science?
2. What are the two main pathways of scientific study?

4.4 Hypothesis in Science

By asking questions about the living world and looking for logical
answers, biologists investigate it. Other sciences also use this process,
which is frequently referred to as the scientific method. Although Sir
Francis Bacon (1561–1626), an Englishman, established inductive
methods for scientific investigation, the scientific method was employed
already in antiquity. The scientific method can be used to solve

24
BIO 101 GENERAL BIOLOGY I

practically any logical problem; hence it is not just used by biologists.

The scientific method often begins with an observation that prompts a
query (often a problem to be solved). Let's consider a straightforward
issue that begins with an observation and use the scientific process to
find a solution. A student walks into class on a Monday morning and
immediately notices that the room is too warm. The classroom is
excessively warm, which is an observation that also indicates a problem.
The youngster then inquires as to why the classroom is so warm.
Remember that a hypothesis is an explanation that has been proposed
and may be tested. There may be various hypotheses put out to address a
problem. One possible explanation, for instance, could be that "No one
switched on the air conditioner, thus the classroom is heated." However,
there might be other answers to the query, and as a result, different
hypotheses might be put out. Another possibility is that the air
conditioner isn't working because there is a power outage, which is why
the classroom is heated. A prediction can be made after a hypothesis has
been chosen. Similar to a hypothesis, a prediction usually follows the
structure "If... then..." For instance, if the student turns on the air
conditioning, the classroom won't be overly warm any longer, according
to the prediction for the first hypothesis. For a theory to be proven
correct, it must be testable. A hypothesis that depends on what a bear
thinks, for instance, cannot be tested because it is impossible to know
what a bear thinks. Additionally, it must be able to be refuted by the
outcomes of experiments, or be falsifiable. The statement "Botticelli's
Birth of Venus is beautiful" is an example of an unprovable hypothesis.
There is no experiment that might disprove this claim. A researcher will
carry out one or more experiments meant to rule out one or more of the
hypotheses in order to test a hypothesis. This is crucial. Although a
theory can be refuted or rejected, it can never be proven. Like
mathematics, science does not deal with proofs. We find evidence in
favour of an explanation when an experiment fails to refute a
hypothesis, but this does not preclude the discovery of a more
convincing explanation or the use of a more meticulously planned
experiment in the future. There will be one or more controls and one or
more variables in every experiment. Any element of the experiment that
is subject to modification or variation is referred to as a variable. A
control is a variable that stays the same throughout the experiment. The
next example asks you to look for the variables and controls. As a
straightforward illustration, a test may be done to see whether
phosphorus limits the growth of algae in freshwater ponds. Half of a
series of man-made ponds that contain water are treated each week by
adding phosphate, while the other half are treated by adding a salt that is
known not to be consumed by algae. The phosphate (or lack thereof) is
the variable in this situation; the experimental or treatment instances are
the ponds with added phosphate, while the control ponds are those with
inert additives like salt added. Another safeguard against the likelihood

25
BIO 101 GENERAL BIOLOGY I

that adding more matter to the pond has an impact is to just add
something. If the treated ponds exhibit decreased algal growth, then our
hypothesis is supported. If they don't, we'll have to abandon our
hypothesis. Be mindful that rejecting one hypothesis merely eliminates
the one that is invalid, not whether the other hypotheses can be accepted
or not. The scientific method is used to disprove assumptions that don't
match up with the results of experiments. Due to the exponential growth
of data deposited in various databases in recent years, a new method of
testing hypotheses has emerged. A new discipline known as "data
research" (also known as "in silico" research) offers new techniques for
data analysis and its interpretation using computer algorithms and
statistical analyses of data in databases. The demand for experts in both
biology and computer science will rise as a result, creating an exciting
employment opportunity.
What does "in silico" research step to offer?

Self-Assessment Exercises 2
1. What is the new approach of testing hypotheses?
2. What happens to the hypotheses that are inconsistent with
experimental data using the scientific method?

4.5 Basic and Applied Science

The value of various branches of science has been a topic of discussion

within the scientific community for the last few decades. Is it
worthwhile to pursue science for the sake of merely learning something,
or does scientific information only have value if we can use it to solve a
particular issue or improve our quality of life? The distinctions between
basic science and applied science are the main subject of this query.
Regardless of how such knowledge might be used in the near future,
basic or "pure" science aims to advance understanding. It is not
concentrated on creating something with immediate commercial or
public value. Although knowing for knowledge's sake is the immediate
aim of basic research, this does not preclude the possibility of an
application in the long run.

In contrast, applied science, also known as "technology," tries to apply

research to solve real-world issues. For instance, it may be able to
increase crop yields, discover a treatment for a specific illness, or save
animals in danger from a natural disaster. In applied science, the
researcher typically has the problem defined for them. Some people
could view basic science as "useless" while viewing applied science as
"helpful." These people might ask, "What for?" to a scientist who
promotes knowledge acquisition. However, a close examination of the

26
BIO 101 GENERAL BIOLOGY I

history of science indicates that many amazing applications of

fundamental knowledge have been made. Since many scientists believe
that a fundamental understanding of science is required before an
application can be produced, applied science is dependent on the
findings of basic science. Others believe it is time to move beyond
fundamental research and focus on developing answers for real-world
issues. Both strategies are appropriate. While it is true that some issues
require immediate attention, few would be resolved without the aid of
the information produced by basic research. The understanding of the
molecular mechanisms driving DNA replication that resulted from the
discovery of DNA structure is one instance of how basic and applied
science can cooperate to solve practical challenges. Our cells contain
DNA strands that are particular to each individual and which carry the
instructions for life. Before a cell divides to create new cells, DNA
replication creates new copies of the DNA. In order to identify genetic
illnesses, locate people who were present at a crime scene, and establish
paternity, scientists had to first understand the principles of DNA
replication. Applied science is unlikely to exist without foundational
science. The Human Genome Project, a study in which each human
chromosome was examined and mapped to ascertain the specific
sequence of DNA subunits and the precise position of each gene, serves
as another illustration of the relationship between basic and applied
research. (The gene is the basic unit of heredity represented by a specific
DNA segment that codes for a functional molecule.) As part of this
initiative, research on other organisms has also been done in order to
better understand human chromosomes. Basic research with non-human
species and later the human genome was crucial to the Human Genome
Project. Utilizing the data for applied research to find treatments for
genetically based disorders subsequently became a significant end aim.
It is crucial to remember that while research projects in both basic and
applied science are typically meticulously planned, some discoveries are
made by serendipity, that is, by way of a fortunate accident or a happy
surprise. When biologist Alexander Fleming unintentionally left a petri
dish of Staphylococcus bacteria uncovered, penicillin was accidently
discovered. The microorganisms were killed by an unwelcome mould
growth. Penicillium was identified as the mould, and a brand-new, very
important antibiotic was found. Similar to this, Percy Lavon Julian was
a renowned medicinal chemist who was working on a method to mass
synthesise chemicals used in the production of significant medications.
It wasn't until water inadvertently leaked into a sizable soybean oil
storage tank that he discovered his strategy for using soybean oil to
produce progesterone, a hormone crucial to the menstrual cycle and
pregnancy. He started the process of reproducing and industrialising the
procedure after immediately identifying the produced molecule as
stigmasterol, a key component in progesterone and comparable
medications. This has benefitted millions of individuals. Even in the

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BIO 101 GENERAL BIOLOGY I

highly organized world of science, luck—when combined with an

observant, curious mind focused on the types of reasoning discussed
above—can lead to unexpected breakthroughs. What is the main aim of
applied science research?

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BIO 101 GENERAL BIOLOGY I

Self-Assessment Exercises 3
1. What value of different types of science was the scientific community
debating for the last few decades?
2. What can lead to unexpected breakthroughs even in the highly organized
world of science?

4.6 Summary

You must have learned about the meaning and method of the scientific
inquiry in this unit. You have studied about the meaning of hypothesis
and how to test and apply it in science research. You must have also
learned about basic and applied research in science.

4.7 References/Further Readings/Web Sources

Allchin, D., H.M. Andersen and K. Nielsen, (2014). “Complementary

Approaches to Teaching Nature of Science: Integrating Student
Inquiry, Historical Cases, and Contemporary Cases in Classroom
Practice”, Science Education, 98: 461–486.

Anderson, C. (2008). “The end of theory: The data deluge makes the
scientific method obsolete”, Wired magazine, 16(7): 16–07

Fox, K., E. (2003). “Models, Simulation, and ‘computer experiments’”,

in The Philosophy of Scientific Experimentation, H. Radder (ed.),
Pittsburgh: Pittsburgh University Press, 198–215.

Gimbel, S. (2011). Exploring the Scientific Method, Chicago: University

of Chicago Press.
https://plato.stanford.edu/entries/scientific-method/
https://thescienceteacher.co.uk/the-scientific-method/
https://www.teachstarter.com/au/teaching-resource-collection/scientific-
method/
https://openbooks.lib.msu.edu/isb202/chapter/nature-of-science-draft/
https://www.youtube.com/watch?v=16Q6NMCsLq8
https://www.youtube.com/watch?v=lN7yd23hCbE
https://www.youtube.com/watch?v=Fu2TS0DjBxE

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BIO 101 GENERAL BIOLOGY I

4.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. The two methods of logical thinking are inductive reasoning and
deductive reasoning.
2. The two main pathways of scientific study are descriptive science
and hypothesis-based science

Answers to SAE 2
1. In recent years a new approach of testing hypotheses has
developed using computer algorithms and statistical analyses of
data in databases, known as "data research" which provides new
methods of data analyses and their interpretation.
2. Using the scientific method, the hypotheses that are inconsistent
with experimental data are rejected.

Answers to SAE 3
1. The scientific community has been debating for the last few
decades about whether it is valuable to pursue science for the
sake of simply gaining knowledge, or does scientific knowledge only
have worth if we can apply it to solving a specific problem or
bettering our lives?
2. Luck—when combined with an observant, curious mind focused
on the types of reasoning discussed above— can lead to
unexpected breakthroughs even in the highly organized world of
science

30
BIO 101 GENERAL BIOLOGY I

Unit 5 Microscopy and the Cell Theory

Unit Structure

5.1 Introduction
5.2 Intended Learning Outcomes (ILOs)
5.3 The Cell and Cell Theory
5.4 How Cells Are Studied
5.5 Role of Cell Technologist in the Study of the Cell
5.6 Summary
5.7 References/Further Readings/Web Sources
5.8 Possible Answers to Self-Assessment Exercises

5.1 Introduction

You will study the meaning of cell, structure, and functioning in this
unit. The various essential characteristics of cells will also be
highlighted. You will also learn about the different types of cells. You
will study the differences between Prokaryotic and Eukaryotic Cells.
You will also learn how cells are being studied with the use of
microscopes. Electron microscopes provide higher magnification, higher
resolution, and more detail than light microscopes.

5.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Justify that cell is the basic structural and functional unit of all
organisms
• List the components of the cell and state cell theory
• Differentiate between prokaryotic and eukaryotic cells
• Describe the roles of cells in organisms
• Compare and contrast light microscopy and electron microscopy

5.3 The Cell and Cell Theory

In biology, the cell is the fundamental building block of all living things.
It is the smallest structural unit of living matter capable of functioning
on its own. A cell is a collection of cytoplasm that is held together on
the outside by a cell membrane. Cells are the smallest structural units of
living matter and make up all living things. They are typically tiny in
size. Numerous organelles, including one or more nuclei, are present in
most cells and perform a range of functions. Like a bacterium or yeast,
some single cells are entire organisms. Others serve as specialised
components of multicellular organisms like plants and animals. As in

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BIO 101 GENERAL BIOLOGY I

the case of bacteria and protozoans, a single cell can be an entire

organism in and of itself. In multicellular organisms like higher plants
and animals, specialised cell groups are arranged into tissues and organs.
Prokaryotic cells and eukaryotic cells are two different types of
cells.Eukaryotic cells include those found in animals, plants, fungi, and
protists, whereas prokaryotic cells include those found in bacteria and
archaea. Prokaryotic and eukaryotic cells have different shapes, yet they
have a lot of similarities in their molecular make-up and functions.
Proteins, polysaccharides, and nucleic acids make up the majority of the
molecules in cells. A membrane that surrounds a cell allows it to
exchange specific materials with its environment. This membrane is
contained within the rigid cell wall of plant cells.

By the late 1830s, zoologist Theodor Schwann and botanist Matthias

Schleiden were researching tissues and putting forth the unified cell
hypothesis. According to the unified cell theory, each living entity is
made up of one or more cells, each cell is the building block of life, and
new cells develop from existing cells. Later, this idea benefited greatly
from the contributions of Rudolf Virchow.

Schleiden and Schwann advocated spontaneous generation (also known

as abiogenesis) as the mechanism for cell origination, but spontaneous
generation was later demonstrated to be false. "Omnis cellula e
cellula"—"All cells only come from pre-existing cells"—was a famous
phrase used by Rudolf Virchow. "However, the portions of the
hypothesis that did not concern the genesis of cells withstood scientific
investigation and are now generally accepted by the scientific
community. The following are the elements of contemporary cell theory
that are commonly acknowledged:
1. The basic unit of structure and functionality in living things is the
cell.
2. One or more cells make up every living thing.
3. Cellular division creates new cells from existing ones.

The cell theory can be broadened to cover the following as well: 1). All
cells have roughly the same chemical makeup; 2). All cells carry genetic
material that is passed on to daughter cells during cellular division. and
3). Energy flow (metabolism and biochemistry) takes place inside of
cells. The following are the essential characteristics of cells:
• Cells provide structure and support to the body of an organism.
• The cell interior is organised into different individual organelles
surrounded by a separate membrane.
• The nucleus (major organelle) holds genetic information
necessary for reproduction and cell growth. Every cell has one
nucleus and membrane-bound organelles in the cytoplasm.

32
BIO 101 GENERAL BIOLOGY I

• Mitochondria, a double membrane-bound organelle is mainly

responsible for the energy transactions vital for the survival of the
cell.
• Lysosomes digest unwanted materials in the cell.
• Endoplasmic reticulum plays a significant role in the internal
organisation of the cell by synthesising selective molecules and
processing, directing and sorting them to their appropriate
locations.

What does specialized cells in multicellular creatures like higher plants

and animals, come to form as the next level of organization of life?

Self-Assessment Exercises 1
1. How is the unified cell theory stated?

2. What are the components of the expanded version of the cell theory?

5.4 How Cells Are Studied

The majority of cells are too tiny to be seen with the human eye,
therefore, in order to study cells, scientists must utilise microscopes.
Electron microscopes offer greater magnification, resolution, and details
compared to optical microscopes. All organisms are made up of one or
more cells. In multicellular organisms, a number of cells of the same
kind interact with one another and carry out shared functions to form
tissues (eg. muscle tissue, connective tissue, and nervous tissue), a
number of tissues come together to form an organ (eg. stomach, heart, or
brain), and a number of organs make up an organ system (such as the
digestive system, circulatory system, or nervous system). Together,
various systems compose an organism (such as an elephant, for
example). Now let's examine how biologists study cells.
• Light Microscopes
Sizes of cells differ. Individual cells are typically too small to be
observed with the human eye, therefore researchers employ microscopes
to investigate them. An instrument that magnifies a thing is a
microscope. Micrographs are photographs of individual cells that are
typically taken under a microscope. A typical human red blood cell
measures eight millionths of a metre, or eight micrometres (abbreviated
as m), in diameter. In comparison, the head of a pin measures
approximately two thousandths of a metre (millimetres, or mm). Thus,
250 red blood cells or so may fit on the head of a pin. A light
microscope's optics adjust how the lenses are oriented. When examined
using a microscope, a specimen that is upside-down and facing right on
the microscope slide will seem upside-down and facing left, and vice

33
BIO 101 GENERAL BIOLOGY I

versa. Similar to how the slide would appear to move right and left when
viewed through a microscope, moving the slide down will make it
appear to move up. This happens as a result of the two sets of lenses that
microscopes use to enlarge the image. The way light passes through the
lenses in this lens system causes an inverted image to be created
(binoculars and a dissecting microscope work in a similar manner, but
include an additional magnification system that makes the final image
appear to be upright). Light microscopes are the most common type of
student microscope. The lens mechanism allows the user to see the
specimen by allowing visible light to flow through while also deflecting
it. Light microscopes are useful for observing live things, but since
individual cells are typically transparent, it is difficult to tell which parts
of an organism are which without the use of specific stains. However,
staining typically results in cell death. Light microscopes, which are
frequently used in lab settings in undergraduate colleges, may magnify
up to 400 times. Magnification and resolving power are two factors that
are significant in microscopy. The degree of an object's enlargement is
known as its magnification. The ability of a microscope to differentiate
two nearby structures as separate is known as its resolving power; the
greater the resolution, the closer those two items can be and the clearer
and more detailed the image would be. Magnification is typically
increased to 1,000 times when oil immersion lenses are used to
investigate smaller cells, such as the majority of prokaryotic cells. Light
microscopy can be used to view a specimen because light entering a
specimen from below is directed into the observer's eye. For this reason,
a sample must be thin or translucent in order for light to travel through
it.

The dissecting microscope is a second kind of microscope utilised in

labs. These microscopes can give a three-dimensional image of the
specimen and have a lesser magnification (20 to 80 times the object
size) than light microscopes. Thick objects allow for the simultaneous
examination of numerous components in focus. These microscopes are
made to provide a clear, enlarged image of both the anatomy of the
entire organism and the tissue structure inside it. The majority of
contemporary dissecting microscopes are binocular, meaning that they
contain two different lens systems, one for each eye, just like light
microscopes. As a result of the distance between the lens systems, the
subject appears to have depth, which facilitates manual manipulations.
Dissecting microscopes also have optics that correct the image so that it
appears as if being seen by the naked eye and not as an inverted image.
The light illuminating a sample under a dissecting microscope typically
comes from above the sample, but may also be directed from below.

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BIO 101 GENERAL BIOLOGY I

• Electron Microscopes
Electron microscopes, as opposed to light microscopes, employ an
electron beam as opposed to a light beam. This offers higher resolving
power in addition to increased magnification and, thus, more detail. Live
cells cannot be examined using an electron microscope since the
preparation of a specimen for viewing under one will kill it.
Furthermore, because the electron beam moves best in a vacuum, it is
not possible to observe live things.

A scanning electron microscope reveals the specifics of a cell's surface

properties by reflection when an electron beam travels back and forth
across it. The typical coating on cells and other structures is made of a
metal like gold. In a transmission electron microscope, the electron
beam is transmitted through the cell and provides details of a cell’s
internal structures. As you might imagine, electron microscopes are
significantly more bulky and expensive than are light microscopes. How
is the electron beam transmitted in a transmission electron microscope?

Self-Assessment Exercises 2
1. What is a microscope?
2. What is the contrasting feature between the light and an electron microscope?

5.5 Role of Cell Technologist in the Study of the Cell

Cytotechnologists (cyto- = cell) are professionals who study cells

through microscopic examinations and other laboratory tests. They are
trained to determine which cellular changes are within normal limits or
are abnormal. Their focus is not limited to cervical cells; they study
cellular specimens that come from all organs. When they notice
abnormalities, they consult a pathologist, who is a medical doctor who
can make a clinical diagnosis. Cytotechnologists play vital roles in
saving people’s lives. When abnormalities are discovered early, a
patient’s treatment can begin on time, thus increasing the chances of
survival. Have you ever heard of a medical test called a Pap smear? In
this test, a doctor takes a small sample of cells from the uterine cervix of
a patient and sends it to a medical lab where a cytotechnologist stains
the cells and examines them for any changes that could indicate cervical
cancer or a microbial infection. The microscopes we use today are far
more complex than those used in the 1600s by Antony van
Leeuwenhoek, a Dutch shopkeeper who had great skill in crafting
lenses. Despite the limitations of his now-ancient lenses, van
Leeuwenhoek observed the movements of protists (a type of single-
celled organism) and sperm, which he collectively termed
“animalcules.” In a 1665, a scientist Robert Hooke coined the term

35
BIO 101 GENERAL BIOLOGY I

“cell” (from the Latin cella, meaning “small room”) for the box-like
structures he observed when viewing cork tissue through a lens. In the
1670s, Van Leeuwenhoek discovered bacteria and protozoa. Later
advances in lenses and microscope construction enabled other scientists
to see different components inside cells. By the late 1830s, botanist
Matthias Schleiden and zoologist Theodor Schwann were studying
tissues and proposed the unified cell theory, which states that all living
things are composed of one or more cells, that the
cell is the basic unit of life, and that all new cells arise from existing
cells. These principles still stand today. Who is a Cytotechnologist?

Self-Assessment Exercises 3
1. Who is a Cytotechnologist?
2. When did van Leeuwenhoek discovered bacteria and protozoa?

5.6 Summary

You have studied about the smallest unit that can live on its own and
that makes up all living organisms and the tissues of the body. You
have also learned about the different types of cell and the three main
parts of the cell: the cell membrane, the nucleus, and the cytoplasm. The
cell membrane surrounds the cell and controls the substances that go
into and out of the cell.

5.7 References/Further Readings/Web Sources

Anderson, C., (2008). “The end of theory: The data deluge makes the
scientific method obsolete”, Wired magazine, 16(7): 16–07

https://www.britannica.com/science/cell-biology/Secretory-vesicles
https://nios.ac.in/media/documents/SrSec314NewE/Lesson-04.pdf
https://ncert.nic.in/pdf/publication/exemplarproblem/classVIII/science/h
eep108.pdf

https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book
%3A_Human_Anatomy_and_Physiology_Preparatory_Course_(Liacho
vitzky)/04%3A_Smallest_Level_of_Complexity_Alive-
_Cells_Their_Structures_and_Functions/4.01%3A_Cell_Structure_and_
Function
https://www.youtube.com/watch?v=URUJD5NEXC8
https://encrypted-
vtbn0.gstatic.com/video?q=tbn:ANd9GcRvB4Sn3kiummaGCLdnWMb
pRu8faf_dNOAMzQ
https://www.youtube.com/watch?v=kcG1F88KQA0

36
BIO 101 GENERAL BIOLOGY I

https://www.youtube.com/watch?v=V6s0xOTNmT4

5.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. The unified cell theory states that: all living things are composed
of one or more cells; the cell is the basic unit of life; and new
cells arise from existing cells.
2. The expanded version of the cell theory is made up of:
• Cells carry genetic material passed to daughter cells during
cellular division
• All cells are essentially the same in chemical composition
• Energy flow (metabolism and biochemistry) occurs within cells

Answers to SAE 2
1. A microscope is an instrument that magnifies an object
2. In contrast to light microscopes, electron microscopes use a beam
of electrons instead of a beam of light.

Answers to SAE 3
1. Cytotechnologist (cyto- = cell) is a professionals who study cells
through microscopic examinations and other laboratory tests.
2. 1670s

Glossary
Applied science: a form of science that solves real-world problems

Basic science: science that seeks to expand knowledge regardless of the

short-term application of that knowledge

Control: a part of an experiment that does not change during the

experiment

Deductive reasoning: a form of logical thinking that uses a general

statement to forecast specific results

Descriptive science: a form of science that aims to observe, explore, and

find things out

Falsifiable: able to be disproven by experimental results

Hypothesis: a suggested explanation for an event, which can be tested

Inductive reasoning: a form of logical thinking that uses related
observations to arrive at a general conclusion

37
BIO 101 GENERAL BIOLOGY I

Life science: a field of science, such as biology, that studies living

things

Natural science: a field of science that studies the physical world, its
phenomena, and processes

Physical science: a field of science, such as astronomy, physics, and

chemistry, that studies nonliving matter

Science: knowledge that covers general truths or the operation of

general laws, especially when acquired and tested by the scientific
method

Scientific law: a description, often in the form of a mathematical

formula, for the behavior of some aspect of nature under certain specific
conditions

Scientific method: a method of research with defined steps that include

experiments and careful observation

Scientific theory: a thoroughly tested and confirmed explanation for

observations or phenomena

End of the module Questions

1. What process causes the diversity of life?

2. How do we organize diversity of life?
3. How does evolution lead to both the diversity and unity of life?
4. Why is organization of life important?
5. List the levels of organization, ranging from simplest to most
complex.
6. Describe what it means to "Construct a Hypothesis."
7. What does a scientist do if the hypothesis is not supported?
8. Outline the steps of a scientific investigation.
9. Give an example of a scientific question that could be
investigated with an experiment.

38
BIO 101 GENERAL BIOLOGY I

MODULE 2 STRUCTURE AND FUNCTIONS OF THE

CELL

Module Structure

In this module we will discuss about the cellular organization, structure

and functions

Unit 1 Cell and Cell Components

Unit 2 Cells Communication
Unit 3 Tissues, Organs and Organ Systems
Unit 4 Characteristics and Classification of Living Things
Unit 5 The Study of Genes and Chromosomes
Unit 6 Reproduction Process and Life cycles
Glossary
End of note questions

Unit 1 Cell and Cell Components

Unit Structure

1.1 Introduction
1.2 Intended Learning Outcomes (ILOs)
1.3 Cellular Organization
1.3.1 Prokaryotic Cell
1.3.2 Eukaryotic Cell
1.4 Cell Organelles
1.5 Other Organelles
1.6 Summary
1.7 References/Further Readings/Web Sources
1.8 Possible Answers to Self-Assessment Exercises

1.1 Introduction

You will learn in this unit that the cell falls into one of two broad
categories: prokaryotic and eukaryotic. You will study that the
predominantly single-celled organisms of the domains Bacteria and
Archaea are classified as prokaryotes (pro- = before; -karyon- =
nucleus), and all other animal cells, plant cells, fungi, and protists are
eukaryotes (eu- = true). You will also learn how to draw and describe
the structure of the various cell organelles

39
BIO 101 GENERAL BIOLOGY I

1.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Illustrate the structure of a prokaryote and eukaryote cells

• Describe the structure of plant and animal cells by drawing
labelled diagrams;
• Differentiate between a Unicellular and Multicellular organisms
• describe the structure and function of the various cell organelles

1.3 The Cell and its Components

Although all cells share certain features (for example, every cell has a
plasma membrane), biologists recognize two fundamentally different
categories of cells: prokaryotic and eukaryotic. We compartmentalize
cells into several structures, organelles with specific functions.
Organelles are subunits in the anatomy of the cell. The
compartmentalization inside the cell allows many different functions to
be localized in specific places. This brings about a high level of
organization and efficiency in the cell. In this unit we will discuss the
structures and functions of the different parts of the cell.

Figure 1. An image illustrating the difference between Prokaryotic and

Eukaryotic Cells. Note that the prokaryotic cell is a complete individual
organism. Source: www.byjus.com

40
BIO 101 GENERAL BIOLOGY I

Advancements in science and technology shed more light into the cell,
with new findings and discoveries about its structure and cellular
components. In 1950s, scientists postulated the concept
of prokaryotic and eukaryotic cells, with earlier groundwork laid
by Edouard Chatton, a French biologist in 1925. Anatomically, cells
vary in respect to their classification, thus, prokaryotic cells and
eukaryotic cells differ from each other drastically. Read on to explore
how they differ from each other.

1.3.1 Prokaryotic Cell

The term “prokaryote” is derived from the Greek word “pro”

(meaning: before) and “karyon” (meaning: kernel). It translates to
“before nuclei”. Prokaryotes are one of the most ancient groups of
living organisms on earth, with fossil records dating back to almost 3.5
billion years ago.

These prokaryotes thrived in the earth’s ancient environment, some

using up chemical energy and others using the sun’s energy. These
extremophiles thrived for millions of years, evolving and adapting.
Scientists speculated that these organisms gave rise to the eukaryotes.
Prokaryotic cells are comparatively smaller and much simpler than
eukaryotic cells. The other defining characteristic of prokaryotic cells is
that they do not possess membrane-bound cell organelles such as a
nucleus, and reproduction is by binary fission.

Structurally, each prokaryote has a capsule enveloping its entire body

which functions as a protective coat. This is crucial for preventing the
process of phagocytosis (where the bacteria gets engulfed by other
eukaryotic cells, such as macrophages). A hair-like appendage found on
the external surface of most prokaryotes is called pilus, and it helps the
organism to attach itself to various environments. The pilus is
commonly observed in bacteria and essentially resists being flushed,
hence, it is also called attachment pili.

Right below the protective coating lies the cell wall, which provides
strength and rigidity to the cell. Further down lies the cytoplasm that
helps in cellular growth, and is contained within the plasma membrane.
This separates the inner contents of the cell from the outside
environment. Ribosomes exist within the cytoplasm; it is also one of the
smallest components within the cell and plays an important role in
protein synthesis. Some prokaryotic cells contain special structures
called mesosomes which assist in cellular respiration. Most
prokaryotes also contain plasmids, which contain small, circular pieces
of DNA. To help with locomotion, flagella are present, though, pilus can

41
BIO 101 GENERAL BIOLOGY I

also serve as an aid for locomotion. Common examples of Prokaryotic

organisms are bacteria, archaea and all members of Kingdom Monera.
1.3.2 Eukaryotic Cell

The term “Eukaryotes” is derived from the Greek word “eu“, (meaning:
good) and “karyon” (meaning: kernel), being translated to “good or true
nuclei.” Eukaryotes are more complex and much larger than
prokaryotes. They include almost all the major kingdoms except
kingdom monera. Structurally, eukaryotes possess a cell wall, which
supports and protects the plasma membrane. The cell is surrounded by
the plasma membrane which controls the entry and exit of some
substances. The nucleus is surrounded by the nuclear membrane and
contains DNA, which is responsible for storing all genetic information.
Within the nucleus is the nucleolus, and it plays a crucial role in proteins
synthesis. Eukaryotic cells also contain mitochondria, which are
responsible for the production of energy utilized by the cell.

Chloroplasts are the subcellular sites of photosynthesis present in only

plant cells. The endoplasmic reticulum helps in the transportation of
materials. Besides these, there are also other cell organelles that
perform various other functions, these include ribosomes, lysosomes,
Golgi bodies, cytoplasm, chromosomes, vacuoles and centrosomes.
Examples of eukaryotes include almost every unicellular organism with
a nucleus and all multicellular organisms.

1.3.3 Difference between Prokaryotic and Eukaryotic Cells

Though these two classes of cells are quite different, they do possess
some common characteristics. For example, both possess cell
membranes and ribosomes. The complete list of differences between
prokaryotic and eukaryotic cells is summarized as follows:

Feature Prokaryotes Eukaryotes

Organisms Bacteria Protists, fungi, plants and
animals
Cell size Average diameter 0.5 - Diameter commonly
10µm 1000 – 10000 times the
volume of prokaryotes
Form Mainly unicellular Mainly multicellular
Evolution 3.5 thousand million 1.2 thousand million
origin years ago years ago, evolve from
prokaryotes
Cell division Mostly binary fission, no Mitosis, meiosis or both,
spindle spindle formed
Genetic DNA is circular and lies DNA linear and
material freely in the cytoplasm contained in a nucleus.

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BIO 101 GENERAL BIOLOGY I

(no true nucleus). DNA is DNA is also associated

also naked; not associated with RNA to form
with RNA to form chromosomes
chromosomes.
Protein 70s ribosomes, no 80s ribosomes, and may
synthesis endoplasmic reticulum be attached to
endoplasmic reticulum
Organelles Few organelles, none Many organelles and
surrounded by envelope envelope-bound
(two membranes) organelles present eg.
nucleus, mitochondria,
chloroplast. There are
also some organelles
bounded by single
membrane eg. golgi
apparatus, lysosomes,
endoplasmic reticulum.
Cell wall Rigid and contain Cell walls of green plants
polysaccharides with and fungi are rigid and
amino acids; murein contain polysaccharides;
strengthening cellulose is the main
compounds. strengthening compounds
of plant cell walls. Chitin
for fungal cell wall while
there is no cell wall in
animal cells.
Flagella Simple, lacking Complex with
microtubules; microtubules;
extracellular, 20nm intracellular, 200nm
diameter diameter
Respiration Membranes in blue green Mitochondria for aerobic
bacteria respiration
Photosynthesis No chloroplasts; takes Chloroplasts containing
place in membranes membranes which are
which show no stacking usually stacked into
lamellae or grana
Nitrogen Some have the ability to None can fix nitrogen
fixation fix nitrogen

What is the main difference between the ribosomes of prokaryotic and

eukaryotic cells?

Self-Assessment Exercises 1
1. Give the general example of a eukaryote.
2. Differentiate between prokaryotes and eukaryotes.

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BIO 101 GENERAL BIOLOGY I

1.4 The Nature and Function of Cells

The plasma membrane that encloses a cell creates a selective barrier that
allows nutrients to enter and waste products to exit. Each of the
numerous specialised compartments, or organelles, that make up a cell's
inside is encircled by a different membrane. The nucleus is one
important organelle that houses the genetic materials required for cell
division and growth. each cell only has one nucleus, while other
organelles are found in many copies in the cytoplasm. These organelles
include mitochondria, which carry out the energy exchanges required for
cell viability, and lysosomes, which break down waste products inside
the cell, the endoplasmic reticulum and the Golgi apparatus, which play
important roles in the internal organization of the cell by synthesizing
selected molecules and then processing, sorting, and directing them to
their proper locations. In addition, chloroplasts, parts of plant cells, are
involved in photosynthesis, the process by which carbon dioxide (CO2)
and water molecules are changed into carbohydrates using the energy of
sunlight. The region of the cytoplasm known as the cytosol is located
between all these organelles. The cytoskeleton, gives a cell its shape,
allows organelles to move inside the cell, and provides a mechanism by
which the cell itself can move, is an organised framework of fibrous
molecules found in the cytosol. The process of producing large
biological molecules from smaller ones, known as cellular biosynthesis,
involves more than 10,000 different types of molecules, all of which can
be found in the cytosol. Specialized organelles are a characteristic of
eukaryotic cells. In contrast, prokaryotic cells do not contain organelles
and are generally smaller than eukaryotic cells. However, all cells share
strong similarities in biochemical functions.

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BIO 101 GENERAL BIOLOGY I

Figure 1.2 Typical example of a cell containing the primary organelles

and internal structures.
1.4.1 The Cell Organelles

Cell organelles are the cellular constituents and they differ in their
structures and functions. They include both membrane-bound and non-
membrane-bound organelles. For the cell to function properly, they
coordinate and work effectively. Some of them giving shape and support
to a cell, while others are involved in a cell's movement and
reproduction. The cells are divided into three groups based on whether
they have a membrane or not. However, as we will see in a moment, a
semi-permeable plasma membrane protects the cytoplasm that is home
to these organelles will be treated as component part of the cell.

1. The Plasma Membrane

Eukaryotic cells, like prokaryotes, have a plasma membrane (Figure 3),
a phospholipid bilayer with proteins embedded that seperates the inside
of the cell from its external environment. A phospholipid is a lipid
molecule that has a phosphate-containing group and two fatty acid
chains. The flow of organic molecules, ions, water, and oxygen into and
out of the cell is regulated by the plasma membrane. Wastes such as
including ammonia and carbon dioxide also exit the cell through the
plasma membrane.

Figure 1.3: The eukaryotic plasma membrane

The eukaryotic plasma membrane is a phospholipid bilayer with proteins
and cholesterol embedded in it.

2. Microvilli, the plasma membranes of cells that specialise in

absorbing substances are folded into fingerlike projections
(Figure 4.).
3. The small intestine, being the organ that absorbs nutrients from
digested food, is normally lined by these cells. This is a superb
illustration of structure adhering to function. Gluten, a protein
included in wheat, barley, and rye, causes an immunological
reaction in people with celiac disease. The immune response

45
BIO 101 GENERAL BIOLOGY I

harms microvilli, making it impossible for those with the condition to

absorb nutrition. Malnutrition, cramps, and diarrhoea result from
this. Gluten-free diets are required for celiac disease patients.

Figure 1.4 Microvilli, shown here as they appear on cells lining the
small intestine, increase the surface area available for absorption.

These microvilli are only found on the area of the plasma membrane that
faces the cavity from which substances will be absorbed.

2. The Cytoplasm
The total area of a cell between the nuclear envelope and the plasma
membrane is known as the cytoplasm. The Cytoplasm is made up of the
cytoskeleton, numerous molecules, and organelles suspended in the gel-
like cytosol. The proteins in the cytoplasm give it a semi-solid solidity,
despite the fact that it contains between 70 and 80 percent water.
However, organic compounds other than proteins can also be present in
the cytoplasm. In addition, polysaccharides, amino acids, nucleic acids,
fatty acids, and glycerol derivatives are present there along with glucose
and other simple carbohydrates. The cytoplasm also contains dissolved
sodium, potassium, calcium, and many other elemental ions. The
cytoplasm is where many metabolic processes, including as protein
synthesis, take place.

1.4.2 Organelles without membrane

The Cell wall, Ribosomes, Cytoskeleton (actin filaments, intermediate

filaments, centrioles) and microtubules are non-membrane-bound cell
organelles. They are present both in the prokaryotic land the eukaryotic
cells.

1. The Cell wall

Outside of the plasma membrane is a structure known as cell wall. The
cell wall is a thick layer that serves as the cell's defense, structural
support, and form. Cell walls are also present in fungus and protozoan
cells. While peptidoglycan is the main organic molecule in the cell walls
of prokaryotic organisms, cellulose, a polysaccharide comprising of
glucose units, is the main organic molecule in the cell walls of plants

46
BIO 101 GENERAL BIOLOGY I

(figure 1.5). Have you ever noticed how a raw vegetable, like celery,
crunches as you chew it? This is due to the fact that you are shredding
the celery cells' stiff cell walls with your teeth. The dashed lines at each
end of the figure indicate a series of many more glucose units. The size
of the page makes it impossible to portray an entire cellulose molecule.

Figure 1.5. Cellulose is a long chain of β-glucose molecules connected

by a 1-4 linkage.

2. Ribosomes
Ribosomes are biological elements in charge of producing proteins.
Under an electron microscope, ribosomes can be observed as either
solitary, tiny specks floating freely in the cytoplasm or as polyribosome
clusters. They might be connected to the plasma membrane, the
cytoplasmic side of the endoplasmic reticulum, or the nuclear envelope
(Figure 6.). Since ribosomes are large complexes of protein and RNA,
electron microscopy has shown that they are composed of two subunits
known as large and small subunits. The ribosomes receive their "orders"
for protein synthesis from the nucleus, where DNA is transformed into
messenger RNA (mRNA). The mRNA travels to the ribosomes, which
translate the code provided by the sequence of the nitrogenous bases in
the mRNA into a specific order of amino acids in a protein. Amino acids
are the building blocks of proteins.

Figure 1.6 Ribosomes are made up of a large subunit (top) and a small
subunit (bottom).

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BIO 101 GENERAL BIOLOGY I

Ribosomes put together amino acids into proteins during the process of
protein synthesis. All cells including enzymes, hormones, antibodies,
pigments, structural elements, and surface receptors must be able to
synthesise proteins, hence ribosomes are present in almost all cells. In
cells that produce a lot of protein, ribosomes are very prevalent, as seen
in the pancreas that is in charge of producing a number of digestive
enzymes. We observe another instance of form following function as a
result.

3. Cytoskeleton
Would the plasma membrane and the cytoplasm be the only elements
left in a cell if all the organelles were taken out? No. Ions and organic
molecules would still be present in the cytoplasm, along with a network
of protein fibres that support some organelles in particular places, permit
movement of cytoplasm and vesicles inside the cell, and allow
movement of cells within multicellular animals. The term "cytoskeleton"
refers to this web of protein fibres as a whole. The cytoskeleton is made
up of three different types of fibres: microfilaments, intermediate
filaments, and microtubules (Figure 7.). Here, we'll look at each. Inside
the cell, microtubules prevent compressive forces from changing the
shape of the cell. Intermediate filaments are found throughout the cell
and hold organelles in place.

Figure 1.7 Microfilaments thicken the cortex around the inner edge of a
cell; like rubber bands, they resist tension.

4. Microfilaments
Of the three types of protein fibers in the
cytoskeleton, microfilaments are the narrowest. They function in
cellular movement, have a diameter of about 7 nm, and are made of
two intertwined strands of a globular protein called actin (Figure 7.). For
this reason, microfilaments are also known as actin filaments.

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BIO 101 GENERAL BIOLOGY I

Figure 1.8 Microfilaments made of two intertwined strands of actin.

The filamentous form of actin, which serves as a conduit for the motion
of the myosin motor protein, is created using ATP. Actin can now take
part in cellular activities that require movement, such as cell division in
animal cells and cytoplasmic streaming, the circular movement of the
cell cytoplasm in plant cells. Actin and myosin are both abundantly
dispersed in muscle cells. As actin and myosin filaments pass by one
another, your muscles tighten. Microfilaments also give the cell some
form and stiffness. A cell can change and migrate because it has the
capacity to depolymerize (disassemble) and reconstruct quickly. The
cells in your body that fight infections, called white blood cells, are
quite good at using this ability.

5. Intermediate Filaments
Intermediate filaments are made of several strands of fibrous proteins
that are wound together (Figure 9.). These elements of the cytoskeleton
get their name from the fact that their diameter, 8 to 10 nm, is between
those of microfilaments and microtubules.

Figure 1.9 Intermediate filaments consist of several intertwined strands

of fibrous proteins.

In the migration of cells, intermediate filaments play no part. Their sole

purpose is structural. They support tension, preserving the cell's
structure, and serve as anchors for the nucleus and other organelles.
Figure 9 demonstrates how internal scaffolding is built by intermediate
filaments. The cytoskeletal elements with the highest variety are the
intermediate filaments. The intermediate filaments contain several kinds
49
BIO 101 GENERAL BIOLOGY I

of fibrous proteins known as keratin, which supports your hair, nails,

and skin's epidermis, is perhaps the one you know best.

6. Microtubules
Microtubules are little, hollow tubes, as their name suggests. Two
globular proteins, α-tubulin and β -tubulin, are polymerized dimers that
make up the walls of the microtubule (Figure 10). The largest
cytoskeleton elements are microtubules, which have a diameter of
roughly 25 nm. They enable vesicles to flow across the cell along a track
and draw replicated chromosomes to the opposite ends of a dividing
cell. They also aid in the cell's resistance to compression. Microtubules
can dissolve and swiftly regenerate, just like microfilaments.

Figure 1.10 Microtubules are hollow. Their walls consist of 13

polymerized dimers of α-tubulin and β-tubulin (right image). The left
image shows the molecular structure of the tube.

Microtubules are also the structural elements of flagella, cilia, and

centrioles (the latter are the two perpendicular bodies of the
centrosome). In fact, in animal cells, the centrosome is the microtubule-
organizing center. In eukaryotic cells, flagella and cilia are quite
different structurally from their counterparts in prokaryotes, as discussed
below.

7. Flagella and Cilia

Recall that flagella are long, hairlike projections that emerge from the
plasma membrane and are used to propel an entire cell (for example,
sperm, Euglena). The cell may have one or more flagellums when they
are present. However, a sizable number of cilia (singular: cilium) cover
the whole surface of the plasma membrane when they are present. They
are microscopic, hair-like structures that transfer materials or whole
cells, like paramecia, along the surface of the cell (for example, the cilia
of cells lining the Fallopian tubes that move the ovum toward the uterus,
and cilia lining the cells of the respiratory tract that trap particulate
matter and move it toward your nostrils.) Despite their differences in
length and number, flagella and cilia share a common structural

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BIO 101 GENERAL BIOLOGY I

arrangement of microtubules called a "9 + 2 array". This is an

appropriate name because a single flagellum or cilium is made of a ring
of nine microtubule doublets, surrounding a single microtubule doublet
in the center (Figure 10.).

Figure 1.11 This transmission electron micrograph of two flagella shows

the 9 + 2 array of microtubules: nine microtubule doublets surround a
single microtubule doublet.

1.4.3 Single membrane-bound organelles

Vacuole, Vesicles, Lysosome, Golgi Apparatus, Endoplasmic

Reticulum, mitochondria, peroxisomes, and transport vesicles are single
membrane-bound organelles present only in a eukaryotic cell.

1. Vesicles and Vacuoles

Vacuoles and vesicles are single membrane-bound sacs with storage and
transport capabilities. There is a little or no difference between vacuoles
and vesicles save the fact that the former are slightly larger: Vesicle
membranes are capable of joining with the cell's plasma membrane or
other membrane systems. Furthermore, some substances, like the
enzymes found in plant vacuoles, degrade macromolecules. A vacuole's
membrane does not meld with the membranes of other cellular parts. In
response to shifting external conditions, the central vacuole is crucial in
controlling the water content within the cell. Have you ever observed
that plants wilt if they go without water for a few days? This is due to
water moving out of the central vacuoles and cytoplasm as the water
concentration in the soil drops below the water concentration in the
plants, the cell wall is left unsupported while the central vacuole
contracts. The plant appears wilted as a result of the loss of support to
the cell walls of the plant cells. The expansion of the cell is also
supported by the central vacuole which can store more water, thus
allowing the cell to grow without expending a lot of energy on
producing new cytoplasm.

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BIO 101 GENERAL BIOLOGY I

2. Lysosome
Lysosomes are thought to be a member of the endomembrane system in
addition to serving as the animal cell's organelle recycling facility of
digestive system. Lysosomes also use their hydrolytic enzymes to
eliminate any pathogens (organisms that cause disease) that might enter
the cell. The immune system of your body's macrophages, a class of
white blood cells, serves as a good illustration of this. A portion of the
macrophage's plasma membrane invaginates (folds in) and engulfs a
pathogen during phagocytosis or endocytosis. The pathogen-filled
invaginated area subsequently pinches itself off from the plasma
membrane and transforms into a vesicle. The pathogen is then
eliminated by the lysosome's hydrolytic enzymes (Figure 12.).

Figure 1.12 A macrophage has engulfed (phagocytized) a potentially

pathogenic bacterium and then fuses with lysosomes within the cell to
destroy the pathogen. Other organelles are present in the cell but for
simplicity are not shown.

3. Golgi Apparatus
The Golgi apparatus, also known as the Golgi body, is a collection of
flattened membranes that is responsible for the classification, labelling,
packaging, and distribution of lipids and proteins (Figure 13). We have
already mentioned that vesicles can form in the emergency room and
travel elsewhere with their contents, but where do the vesicles
themselves go? The transport vesicles' lipids or proteins still need to be
processed, packaged, and labelled before they go to their final location
to ensure they end up there.

52
BIO 101 GENERAL BIOLOGY I

Figure 1.13 The Golgi apparatus in this white blood cell is visible as a
stack of semicircular, flattened rings in the lower portion of the image.

The cis face refers to the receiving side of the Golgi apparatus. The trans
face is the side that faces the other way. When the transport vesicles
from the endoplasmic reticulum (ER) fuse with the cis face, they release
their contents into the lumen of the Golgi apparatus. The proteins and
lipids go through additional changes in the Golgi apparatus that enable
sorting as they move through it. The most common alteration is the
insertion of sugar molecules in short chains. Then, in order to direct
these newly altered proteins and lipids to their correct locations, they are
marked with phosphate groups or other tiny molecules. Finally,
secretory vesicles that bud from the trans face of the Golgi are used to
package the changed and tagged proteins. Other secretory vesicles fuse
with the plasma membrane and release their contents outside the cell,
while some of these vesicles deposit their contents into other areas of the
cell where they will be utilised. Another example of shape following
function is the profusion of Golgi in cells that release a lot of materials,
such as salivary gland cells that secrete digestive enzymes or immune
system cells that secrete antibodies. The Golgi apparatus in plant cells
also plays the additional task of synthesising polysaccharides, some of
which are utilised to build the cell wall and others in other regions of the
cell.

4. The Endoplasmic Reticulum

The endoplasmic reticulum (ER) (Figure 14.) is a collection of mesh
worked sacs and tubules that work together to manufacture lipids and
modify proteins. The rough ER and the smooth ER, respectively, are
where these two tasks are carried out in the ER. The lumen or cisternal
space refers to the hollow area of the ER tubules. The nuclear envelope
and the phospholipid bilayer that makes up the ER's membrane are one
continuous structure. The two are as follows: I Rough ER: i). The rough
endoplasmic reticulum (RER) is named as such because, when studied
under an electron microscope, the ribosomes clinging to its cytoplasmic
surface give it a studded look. (Figure 5).

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BIO 101 GENERAL BIOLOGY I

Figure 1.14 This transmission electron micrograph shows the rough

endoplasmic reticulum and other organelles in a pancreatic cell.

The freshly synthesised proteins are transferred by ribosomes into the

lumen of the RER, where they go through structural changes such
folding or side chain acquisition. These altered proteins will either be
released from the cell or integrated into cellular membranes, such as the
ER membrane or those of other organelles (such as protein hormones,
enzymes). Phospholipids for cellular membranes are also produced by
the RER. If the phospholipids or altered proteins are not meant to remain
in the RER, transport vesicles that sprout from the RER's membrane will
carry them to their intended locations (Figure 14) You would be right in
believing that the RER is prevalent in cells that produce proteins
because it is involved in altering proteins such as enzymes, that will be
released from the cell such as liver cells.

ii). The smooth endoplasmic reticulum (SER), which is continuous with

the RER, has few or no ribosomes on the surface of its cytoplasm
(Figure 4.18). The SER performs several functions, such as calcium ion
storage, drug detoxification, and the production of carbohydrates, lipids,
and steroid hormones. The sarcoplasmic reticulum, a specific type of
SER, is in charge of storing the calcium ions required to start the
coordinated contractions of muscle cells.

5. Peroxisomes
Small, spherical organelles called peroxisomes are surrounded by a
single membrane. In their oxidation reactions, fatty acids and amino
acids are broken down. They also cleanse the body of numerous toxins
that might be ingested. (Many of these oxidation events produce
hydrogen peroxide, H2O2, which can harm cells; however, when these
reactions take place inside of peroxisomes, enzymes safely break down
the H2O2 into oxygen and water.) For example, peroxisomes in liver

54
BIO 101 GENERAL BIOLOGY I

cells detoxify alcohol. Plants' specialised peroxisomes called

glyoxysomes are in charge of converting stored fats into sugars.

Self-Assessment Exercises 2
1. What is a flagellum?

2. Which form of peroxisomes are responsible for the conversion of

stored fat into sugars?

1. Flagella are long, hair-like structures that extend from the plasma
membrane and are utilised to move a complete cell such as sperm
and Euglena cells.
2. Glyoxysomes

1.5 Double membrane-bound organelles

Nucleus, mitochondria and chloroplast are double membrane-bound

organelles present only in a eukaryotic cell.
1. Nucleus
Typically, the nucleus is the most prominent organelle in a cell (Figure
1.15). The nucleus (plural nuclei) houses the cell's DNA and directs the
synthesis of ribosomes and proteins. Let's look at it in more detail
(Figure 1.15).

Figure 1.15 The nucleus stores chromatin (DNA plus proteins) in a gel-
like substance called the nucleoplasm.

55
BIO 101 GENERAL BIOLOGY I

Ribosome synthesis takes place in the nucleolus, a compressed area of

chromatin. The nuclear envelope is the term used to describe the
nucleus' outside. It is made up of an outer membrane and an inner
membrane which are both phospholipid bilayers. The endoplasmic
reticulum and the nuclear membrane are one unit. Nuclear pores allow
substances to enter and exit the nucleus.

The Nuclear Envelope

The nuclear envelope is a double-membrane structure that constitutes
the outermost portion of the nucleus (Figure 14). Both the inner and
outer membranes of the nuclear envelope are phospholipid bilayers. The
nuclear envelope is punctuated with pores that control the passage of
ions, molecules, and RNA between the nucleoplasm and cytoplasm.

The nucleoplasm is the semi-solid fluid inside the nucleus, where we

find the chromatin and the nucleolus.

Chromatin and Chromosomes

It is useful to start with chromosomes in order to comprehend
chromatin. Chromosomes are nucleus-located components consisting of
DNA, the genetic material. In prokaryotes, DNA is arranged into a
single circular chromosome, as you may recall. Chromosomes are
organised in a linear fashion in eukaryotes. In the cell nuclei of its body,
each eukaryotic species has a certain number of chromosomes.

For instance, the number of chromosomes in humans is 46, whereas it is

just eight in fruit flies. Only when the cell is about to divide can the
chromosomes be seen and distinguished from one another. Proteins are
connected to chromosomes during the growth and maintenance phases
of the cell's life cycle, and they take on the appearance of an unravelled,
disorganised collection of threads.

These unwound protein-chromosome complexes are

called chromatin (Figure 15); chromatin describes the material that
makes up the chromosomes both when condensed and decondensed.

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BIO 101 GENERAL BIOLOGY I

Figure 1.16. (a) This image shows various levels of the organization of
chromatin (DNA and protein). (b) This image shows paired
chromosomes.

The Nucleolus
We already know that the nucleus directs the synthesis of ribosomes, but
how does it do this? Some chromosomes have sections of DNA that
encode ribosomal RNA. A darkly staining area within the nucleus called
the nucleolus (plural = nucleoli) aggregates the ribosomal RNA with
associated proteins to assemble the ribosomal subunits that are then
transported out through the pores in the nuclear envelope to the
cytoplasm.

The Centrosome
The centrosome is a microtubule-organizing center found near the
nuclei of animal cells. It contains a pair of centrioles, two structures that
lie perpendicular to each other. Each centriole is a cylinder of nine
triplets of microtubules.

Figure 1.17. The centrosome consists of two centrioles that lie at right
angles to each other.

Nine triplets of microtubules make up each centriole, which is shaped

like a cylinder. The microtubule triplets are held together by nontubulin
proteins, which are represented by the green lines. Before a cell divides,
57
BIO 101 GENERAL BIOLOGY I

the centrosome (the organelle from which all microtubules originate)

copies itself, and centrioles seem to play a part in directing the
duplicated chromosomes to the opposing ends of the dividing cell. The
precise role of centrioles in cell division, however, is unclear because
plant cells, which lack centrosomes, can divide even after having their
centrosomes removed from them.

2. Mitochondria
Mitochondria (singular mitochondrion) are often called the
"powerhouses" or "energy factories" of a cell because they are
responsible for making adenosine triphosphate (ATP), the cell's main
energy-carrying molecule. ATP represents the short-term stored energy
of the cell. Nine triplets of microtubules make up each centriole, which
is shaped like a cylinder. The microtubule triplets are held together by
nontubulin proteins, which are represented by the green lines. Before a
cell divides, the centrosome (the organelle from which all microtubules
originate) copies itself, and centrioles seem to play a part in directing the
duplicated chromosomes to the opposing ends of the dividing cell. The
precise role of centrioles in cell division, however, is unclear because
plant cells, which lack centrosomes, can divide even after having their
centrosomes removed from them.

Figure 1.18. This electron micrograph shows a mitochondrion as viewed

with a transmission electron microscope.

This organelle has an outer membrane and an inner membrane. The

inner membrane contains folds, called cristae, which increase its surface
area. The space between the two membranes is called the intermembrane
space, and the space inside the inner membrane is called the
mitochondrial matrix. ATP synthesis takes place on the inner membrane.
3. Chloroplast
Chloroplasts have their own DNA and ribosomes, just like
mitochondria, but they serve a completely different purpose. Organelles
in plant cells called chloroplasts are responsible for photosynthesis. The
set of chemical processes known as photosynthesis convert carbon
dioxide, water, and light energy into glucose and oxygen. This is a key

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BIO 101 GENERAL BIOLOGY I

distinction between plants and animals; although animals (heterotrophs)

must consume their food, plants (autotrophs) may produce food like
sugars on their own. Chloroplasts, like mitochondria, have an inner and
an outer membrane. However, the inner membrane of a chloroplast
encloses a collection of interconnected and stacked fluid-filled
membrane sacs known as thylakoids (Figure 19). A granum (plural:
grana) is the name given to each stack of thylakoids. the liquid that fills
the space between the inner membrane and the grana

Figure 1.19. The chloroplast has an outer membrane, an inner

membrane, and membrane structures called thylakoids that are stacked
into grana.

The space inside the thylakoid membranes is called the thylakoid space.
The light harvesting reactions take place in the thylakoid membranes,
and the synthesis of sugar takes place in the fluid inside the inner
membrane, which is called the stroma. Chloroplasts also have their own
genome, which is contained on a single circular chromosome.

The chloroplasts contain a green pigment called chlorophyll, which

captures the light energy that drives the reactions of photosynthesis.
Like plant cells, photosynthetic protists also have chloroplasts. Some
bacteria perform photosynthesis, but their chlorophyll is not relegated to
an organelle.

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BIO 101 GENERAL BIOLOGY I

Comparing the Components of Prokaryotic and Eukaryotic Cells

Components of Prokaryotic and Eukaryotic Cells

Prese
Prese Prese
nt in
Cell nt in nt in
Anim
Compone Function Proka Plant
al
nt ryotes Cells
Cells
? ?
?

Separates cell from external

Plasma environment; controls passage of organic
Yes Yes Yes
membrane molecules, ions, water, oxygen, and
wastes into and out of cell

Provides turgor pressure to plant cells as

Cytoplas fluid inside the central vacuole; site of
Yes Yes Yes
m many metabolic reactions; medium in
which organelles are found

Darkened area within the nucleus where

Nucleolus No Yes Yes
ribosomal subunits are synthesized.

Cell organelle that houses DNA and

Nucleus directs synthesis of ribosomes and No Yes Yes
proteins

Ribosome
Protein synthesis Yes Yes Yes
s

Mitochon
ATP production/cellular respiration No Yes Yes
dria

Oxidizes and thus breaks down fatty

Peroxiso
acids and amino acids, and detoxifies No Yes Yes
mes
poisons

Vesicles
Storage and transport; digestive function
and No Yes Yes
in plant cells
vacuoles

Unspecified role in cell division in

Centroso
animal cells; source of microtubules in No Yes No
me
animal cells

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BIO 101 GENERAL BIOLOGY I

Components of Prokaryotic and Eukaryotic Cells

Prese
Prese Prese
nt in
Cell nt in nt in
Anim
Compone Function Proka Plant
al
nt ryotes Cells
Cells
? ?
?

Lysosome Digestion of macromolecules; recycling

No Yes No
s of worn-out organelles

Yes,
Yes,
prima
prim
Protection, structural support and rily
Cell wall No arily
maintenance of cell shape peptid
cellul
oglyc
ose
an

Chloropla
Photosynthesis No No Yes
sts

Endoplas
mic Modifies proteins and synthesizes lipids No Yes Yes
reticulum

Golgi Modifies, sorts, tags, packages, and

No Yes Yes
apparatus distributes lipids and proteins

Maintains cell's shape, secures

organelles in specific positions, allows
Cytoskele
cytoplasm and vesicles to move within Yes Yes Yes
ton
cell, and enables unicellular organisms
to move independently

No,
exce
pt for
some
Flagella Cellular locomotion Some Some
plant
sper
m
cells.

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BIO 101 GENERAL BIOLOGY I

Components of Prokaryotic and Eukaryotic Cells

Prese
Prese Prese
nt in
Cell nt in nt in
Anim
Compone Function Proka Plant
al
nt ryotes Cells
Cells
? ?
?

Cellular locomotion, movement of

Cilia particles along extracellular surface of Some Some No
plasma membrane, and filtration

What is the set of chemical processes that converts carbon dioxide,

water, and light energy into glucose and oxygen known?

Self-Assessment Exercises 3
1. Which cell organelle is referred to as the Powerhouse of the cell?
2. What do you refer to as the double-membrane structure that
constitutes the outermost portion of the nucleus?

1.6 Summary

You have learnt in this unit that the cell falls into one of two broad
categories: prokaryotic and eukaryotic. You have also learnt that the
predominantly single-celled organisms of the domains Bacteria and
Archaea are classified as prokaryotes, and all other animal cells, plant
cells, fungi, and protists are eukaryotes, and how to draw and describe
the structure of the various cell organelles

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BIO 101 GENERAL BIOLOGY I

1.7 References/Further Readings/Web Sources

Ahern, K. (2019). Biochemistry and Molecular Biology, The Great

Courses, The Teaching Company.

Russel, P. J. (2010). iGenetics: A Molecular Approach, 3rd edition,

Benjamin Cummings (2010), p. 111-117

Holt, R. I. G. and Hanley, N. A. (2012). Essential Endocrinology and

Diabetes, 6th edition, Wiley-Blackwell (2012), p. 18-23

https://byjus.com/biology/cell-organelles/
https://www.ncbi.nlm.nih.gov/books/NBK9941/
https://hsc.one/courses/biology-preliminary/module-1/
https://untamedscience.com/biology/cells/basic-types-of-cells/
https://www.youtube.com/watch?v=UHJGy1ZW7kE
https://www.youtube.com/watch?v=8IlzKri08kk&vl=en
https://www.youtube.com/watch?v=t5DvF5OVr1Y
https://www.youtube.com/watch?v=JL19uv7NT7s
https://www.youtube.com/watch?v=8v4HE8dCfgI

1.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Examples of eukaryotes include almost every unicellular
organism with a nucleus and all multicellular organisms.
2. Prokaryotes are always unicellular, unlike eukaryotes which are
both unicellular and multi-cellular

Answers to SAE 2
1. Flagella are long, hair-like structures that extend from the plasma
membrane and are utilised to move a complete cell (for example,
sperm, Euglena)
2. Glyoxysomes

Answers to SAE 3
1. Mitochondria
2. Nuclear envelope

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BIO 101 GENERAL BIOLOGY I

Unit 2 Cells Communication

Unit structure

2.1 Introduction
2.2 Intended Learning Outcomes (ILOs)
2.3 Cells Communication
2.4 Transport in Cells
2.5 Active transport
2.6 Summary
2.7 References/Further Readings/Web Sources
2.8 Possible Answers to Self-Assessment Exercises

2.1 Introduction

You already know that a group of similar cells working together is

called a tissue. As you may expect, if cells are to work together, they
must communicate with each other, just as you need to communicate
with others if you work on a group project. Let's take a look at how cells
communicate with each other.

2.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Explain why and how passive transport occurs

• Understand the processes of osmosis and diffusion
• Define tonicity and describe its relevance to passive transport
• Understand how electrochemical gradients affect ions
• Describe endocytosis, including phagocytosis, pinocytosis, and
receptor-mediated endocytosis
• Understand the process of exocytosis

3.3 Cells Communication

We have devoted a lot of time to study the components of a cell. Now

what exactly is outside? What kind of cell you are looking at makes a
big difference. Animal cells have the ability to secrete substances into
their environment to create the extracellular matrix, a meshwork of
macromolecules that provides support and protection for plants, fungi,
and other living things. Here, we'll delve deeper into these extracellular
elements and the functions they serve in various cell types.

1. Extracellular Matrix of Animal Cells

Extracellular space is where the majority of animal cells releases stuff;
proteins being the main building blocks of these materials, and collagen

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BIO 101 GENERAL BIOLOGY I

the most prevalent protein. Proteoglycans, which are protein molecules

with carbohydrates, are woven into collagen fibres. These substances are
referred to as the extracellular matrix collectively (Figure 1.). The
extracellular matrix not only holds the cells together to form a tissue, but
also enables intercellular communication between
The cells. How is this possible?

Figure 2.1 The extracellular matrix consists of a network of proteins and

carbohydrates.

On the extracellular surfaces of their plasma membranes, cells have

protein receptors. The receptor's chemical structure is altered when a
molecule from the matrix attaches to it. The microfilaments located
immediately inside the plasma membrane are modified by the receptors,
which in turn modify their shapes. These conformational changes cause
chemical signals to be released inside the cell, which travel to the
nucleus and modify the transcription of particular DNA segments. This
in turn affects the creation of linked proteins, which alters the activities
carried out by the cell. A case study of the extracellular matrix's function
in cell communication is blood coagulation. When blood vessel lining
cells are harmed, they exhibit a protein receptor known as tissue factor.
When tissue factor binds with another factor in the extracellular matrix,
it causes platelets to adhere to the wall of the damaged blood vessel,
stimulates the adjacent smooth muscle cells in the blood vessel to
contract thus, constricting the blood vessel, and initiates a series of steps
that stimulate the platelets to produce clotting factors.

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2. Intercellular Junctions
Intercellular junctions, which allow cells to communicate directly with
one another, are another method of cell communication. Animal and
plant cells function in this fashion somehow differently. In contrast to
animal cell interactions like tight junctions, gap junctions, and
desmosomes, plant cell junctions are called plasmodesmata.

3. Plasmodesmata
In general, the cell wall that encloses each plant cell prevents the lengthy
stretches of plasma membranes from nearby plant cells from touching
one another. So how does a plant get water and other nutrients from the
soil from its roots to its stems and finally to its leaves? Vascular tissues
(xylem and phloem) are predominantly used in this transport.
Additionally, there are structural alterations known as plasmodesmata
(plural: plasmodesma), which are numerous channels that pass through
the cell walls of neighbouring plant cells, connect their cytoplasm, and
allow materials to be transported from one cell to the next and thus
throughout the entire plant.

Figure 2.2. A plasmodesma is a channel between the cell walls of two

adjacent plant cells. Plasmodesmata allow materials to pass from the
cytoplasm of one plant cell to the cytoplasm of an adjacent cell.

4. Tight Junctions
A tight junction is a watertight seal between two adjacent animal cells
(Figure 2.3). The cells are held tightly against each other by proteins
(predominantly two proteins called claudins and occludins).

Figure 2.3. Tight junctions form watertight connections between

adjacent animal cells. Proteins create tight junction adherence.

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This tight adherence prevents materials from leaking between the cells;
tight junctions are typically found in epithelial tissues that line internal
organs and cavities, and comprise most of the skin. For example, the
tight junctions of the epithelial cells lining your urinary bladder prevent
urine from leaking out into the extracellular space.

5. Desmosomes
These are found only in animal cells and act like spot welds between
adjacent epithelial cells (Figure 2.4.). Short proteins called cadherins in
the plasma membrane connect to intermediate filaments to create
desmosomes. The cadherins join two adjacent cells together and
maintain the cells in a sheet-like formation in organs and tissues that
stretch, like the skin, heart, and muscles.

Figure 2.4. A desmosome forms a very strong spot weld between cells.
It is created by the linkage of cadherins and intermediate filaments.
(credit: modification of work by Mariana Ruiz Villareal)

6. Gap Junctions
Gap junctions in animal cells are like plasmodesmata in plant cells in
that they are channels between adjacent cells that allow for the transport
of ions, nutrients, and other substances that enable cells to
communicate (Figure 6). However, gap junctions and plasmodesmata
differ.

Figure 2.5. A gap junction is a protein-lined pore that allows water and
small molecules to pass between adjacent animal cells. (credit:
modification of work by Mariana Ruiz Villareal)

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Gap junctions develop when a set of six proteins (called connexins) in

the plasma membrane arrange themselves in an elongated donut-like
configuration called a connexon. When the pores ("doughnut holes") of
connexons in adjacent animal cells align, a channel between the two
cells forms. Gap junctions are particularly important in cardiac muscle:
The electrical signal for the muscle to contract is passed efficiently
through gap junctions, allowing the heart muscle cells to contract in
tandem. What is the watertight seal between two adjacent animal cells
called?

Self-Assessment Exercises 1
1. Gap Junctions
2. What is the role of intercellular Junctions in cells

2.4 Transport in Cells

Transport is the movement of substances across the cell membrane

either into or out of the cell. Sometimes things just move through the
phospholipid bilayer. Other times, substances need the assistance of a
protein, like a channel protein or some other transmembrane protein, to
cross the cell membrane. Several types could be noticed:

1. Passive transport
Plasma membranes must permit some compounds to enter and exit a cell
while blocking the entry of hazardous molecules and the exit of
necessary ones. Plasma membranes are selectively permeable
(semipermeable); chemicals pass through them while others do not. The
cell would be destroyed if it were to lose its selectivity, which would
prevent it from continuing to function. Some cells need certain
compounds in greater concentrations than others. These cells must have
a method of acquiring these substances from the extracellular fluids. The
movement of specific materials back and forth may cause this to occur
passively, or the cell may have unique processes to ensure movement.
Adenosine triphosphate (ATP), primarily used by cells, is used to
establish and maintain an unbalanced distribution of ions on the
opposing sides of their membranes. These tasks are aided by the plasma
membrane's structure, but it has significant drawbacks. Passive
membrane transport methods are the most direct. Passive transport is a
phenomenon that occurs naturally and doesn't require energy. Diffusion
is the process by which chemicals travel passively from a region of
higher concentration to a region of lower concentration. A concentration
gradient is a difference in the concentration of one substance throughout
a physical region.

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2. Selective Permeability
Plasma membranes are asymmetric, which means that despite the
phospholipids' creation of a mirror image, the interior and exterior of the
membrane are not the same. Integral proteins that function as pumps or
channels only move one way. Outside the plasma membrane are also
found carbohydrates that are linked to proteins or lipids. These
carbohydrate complexes assist the cell in binding components from the
extracellular fluid that the cell need. This greatly enhances the
selectiveness of plasma membranes. Keep in mind that the hydrophilic
and hydrophobic sections of plasma membranes exist. This property
facilitates the passage of some elements through the membrane while
impeding the passage of others. Lipid-soluble material scan easily pass
through the hydrophobic lipid core of the membrane. The plasma
membranes in the gastrointestinal system and other tissues are easily
permeable to substances like the fat-soluble vitamins A, D, E, and K.
Drugs that are soluble in fat are also easily absorbed by cells and are
quickly absorbed by tissues and organs of the body. Carbon dioxide and
oxygen molecules have no charge and go through via simple diffusion.
The membrane has trouble with polar chemicals. While some polar
molecules can easily connect with a cell's exterior, they cannot easily
travel through the plasma membrane's lipid core. Small ions could also
easily pass through the cracks in the mosaic of the membrane, but they
can't because of their charge ions.

3. Diffusion
Transport that is done passively is called diffusion. Until the
concentration is the same throughout the space, a single substance has a
tendency to travel from an area of high concentration to an area of low
concentration. You are aware of how compounds diffuse through the air.
Consider the scenario of someone opening a perfume bottle in a
crowded space. The perfume is most concentrated in the bottle and least
concentrated at the room's perimeter. As the perfume vapour diffuses, or
spreads from the bottle, more and more individuals will eventually be
able to smell it. Diffusion is the process by which certain substances
pass through the plasma membrane and others diffuse within the
cytoplasm of the cell (Figure 2.6).

Rather the different concentrations of materials in different areas are a

form of potential energy, and diffusion is the dissipation of that potential
energy as materials move down their concentration gradients, from high
to low.

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Figure 2.6. Diffusion through a permeable membrane follows the

concentration gradient of a substance, moving the substance from an
area of high concentration to one of low concentration.
Each separate substance in a medium, such as the extracellular fluid, has
its own concentration gradient, independent of the concentration
gradients of other materials. In addition, each substance will diffuse
according to that gradient. The rate of diffusion is affected by several
factors. These include:
• Extent of the concentration gradient: The greater the difference in
concentration, the more rapid the diffusion. The closer the
distribution of the material gets to equilibrium, the slower the rate
of diffusion becomes.
• Mass of the molecules diffusing: More massive molecules move
more slowly, because it is more difficult for them to move
between the molecules of the substance they are moving through;
therefore, they diffuse more slowly.
• Temperature: Higher temperatures increase the energy and
therefore the movement of the molecules, increasing the rate of
diffusion.
• Solvent density: As the density of the solvent increases, the rate
of diffusion decreases. The molecules slow down because they
have a more difficult time getting through the denser medium
(facilitated transport).

Material flows across the plasma membrane with the help of

transmembrane proteins along a concentration gradient (from high to
low concentration) in assisted transport, also known as facilitated
diffusion, without using up any cellular energy. The compounds that are
transported more easily and quickly would not otherwise diffuse over
the plasma membrane. The proteins that cover the plasma membrane's
surface hold the key to transporting polar chemicals and other
compounds across it. The substance being transported is initially
anchored to protein or glycoprotein receptors on the plasma membrane's
outer surface. This enables the substance that the cell requires to be
taken out of the extracellular fluid. The substances are then transferred
to particular integral proteins that help them pass through the membrane
by forming channels or pores that allow specific substances to do so.
Transport proteins are the collective name for the integral proteins that

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play a role in facilitated transport and serve as either carriers or material

channels.
4. Osmosis
The process of osmosis involves the passage of free water molecules
across a semipermeable membrane in response to the gradient of water
concentration across the membrane, which is inversely proportional to
the concentration of the solutes. Osmosis moves just water across a
membrane, and the barrier restricts the diffusion of solutes in the water,
whereas diffusion transports material across membranes and within
cells. A specific example of diffusion is osmosis. Water flows from a
region with a high concentration of free water molecules to one with a
low concentration of free water molecules, just like other things do.
Imagine a beaker with two sides or halves separated by a semipermeable
membrane (Figure 2.7). The water level is the same on both sides of the
membrane, but the concentration of a dissolved material, or solute, that
cannot cross the barrier varies on each side. Water, the solvent, will have
different concentrations on either side of the membrane if the volume of
water is the same but the solute concentrations are different.

Figure 2.7. In osmosis, water always moves from an area of higher

concentration (of water) to one of lower concentration (of water).

The selectively permeable membrane in this system is impermeable to

the solute. The molecules travel and, if possible, distribute uniformly
throughout the medium, according to a diffusion principle. Only
substances that can pass through the membrane, however, will diffuse
across it. In this case, the water can permeate through the barrier even
though the solute cannot. In this system, water exhibits a gradient in
concentration. Water will therefore diffuse along its gradient of
concentration and cross the membrane to the side where it is less
concentrated. Osmosis, the process of water diffusing through a
membrane, will continue until the water's concentration gradient is zero.
Living systems continually undergo osmosis, the classic example used
to demonstrate osmosis and osmotic pressure is to immerse cells
into sugar solutions of various concentrations. There are three possible
relationships that cells can encounter when placed into a sugar solution.

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A B C

Figure 2.8. Shows what happens in osmosis through the semi-permeable

membrane of the cells.

A= Hypertonic solution. A solution that has a higher solute

concentration than another solution. Water particles will move out of
the cell, causing crenation.

B= Isotonic solution. A solution that has the same solute concentration

as another solution. There is no net movement of water particles, and the
overall concentration on both sides of the cell membrane remains
constant.

C= Hypotonic solution. A solution that has a lower solute concentration

than another solution. Water particles will move into the cell, causing
the cell to expand and eventually lyse.

The concentration of solute in the solution can be greater than the

concentration of solute in the cells. This cell is described as being in
a hypertonic solution (hyper = greater than normal). The net flow or
water will be out of the cell

The concentration of solute in the solution can be equal to the

concentration of solute in cells. In this situation, the cell is in
an isotonic solution (iso = equal or the same as normal). The amount of
water entering the cell is the same as the amount leaving the cell

The concentration of solute in the solution can be less than the

concentration of solute in the cells. This cell is in a hypotonic

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solution (hypo = less than normal). The net flow of water will be into
the cell

5. Tonicity
The quantity of solute in a solution is referred to as tonicity. The
osmolarity of a solution is a measurement of its tonicity, or the total
number of solutes dissolved in a given volume of solution. The
relationship between the osmolarity of a cell and the osmolarity of the
extracellular fluid in which the cell is contained is termed hypotonic,
isotonic, and hypertonic. Water enters the cell in a hypotonic solution,
eg. tap water, since the extracellular fluid has a lower solute
concentration than the fluid inside the cell. The prefix hypo- denotes that
the extracellular fluid has a lower concentration of solutes or a lower
osmolarity than the cell cytoplasm. Also, it implies that the extracellular
fluid contains more water than the cell does. In this case, water will
enter the cell by following its gradient of concentration. An animal cell
may lyse or burst as a result of this. The extracellular fluid, such as
saltwater, has less water than the cell does in a hypertonic solution (the
prefix hyper- alludes to the extracellular fluid having a higher
concentration of solutes than the cell's cytoplasm). The water will leave
the cell since the solute concentration is lower there. The solute is
actually sucking water out of the cell. An animal cell may shrink or
crenate as a result of this. The extracellular fluid and the cell have the
same osmolarity in an isotonic solution. There won't be any net flow of
water into or out of the cell if the solute content of the cell and the
extracellular fluid are equal. Blood cells have distinctive appearances in
hypertonic, isotonic, and hypotonic solutions. Certain species have cell
walls that enclose the plasma membrane and inhibit cell lysis, including
some plants, fungi, bacteria, and protists. The plasma membrane can
only stretch as far as the cell wall allows, preventing the cell from
lysing. In fact, water always enters a cell if water is available, and the
cytoplasm in plants is always slightly hypertonic in comparison to the
cellular environment. This increase in water pressure creates turgor
pressure, which stiffens the plant's cell walls (Figure 2.9). Turgor
pressure provides support for non woody plants. Water will leak out of
the cell if the plant cells become hypertonic, which happens during
droughts or if a plant is not given enough water. In this situation, plants
wilt as they lose turgor pressure.

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When is a solution said to be isotonic?

Figure 2.9. The turgor pressure within a plant cell depends on the
tonicity of the solution that it is bathed in.

Self-Assessment Exercises 2
1. How is the relationship between the osmolarity of a cell and the
osmolarity of the extracellular fluid in which the cell is contained
described?
2. Outline factors affecting rate of diffusion.

2.5 Active transport

The usage of the cell's energy, often in the form of adenosine

triphosphate (ATP), is necessary for active transport processes. The cell
must expend energy to transfer a material into the cell when it must
move against its concentration gradient, or when the concentration of the
substance inside the cell must be higher than its concentration in the
extracellular fluid. Small-molecular weight substances, such as ions, are
transported through the membrane via several active transport processes.
Cells must expel and take in bigger molecules and particles in addition
to transporting tiny ions and molecules via the membrane. Some cells
have the capacity to completely engulf unicellular creatures. You may
have guessed properly when you said that the cell needs energy to take
in and release big particles. A large particle, however, cannot pass
through the membrane, even with energy supplied by the cell.

1. Electrochemical Gradient
While simple concentration gradients—differential concentrations of a
chemical across a region or a membrane—have been covered, gradients
in living systems are more intricate. There is an electrical gradient, or
difference in charge, across the plasma membrane because cells contain
proteins, the majority of which are negatively charged, and because ions
migrate into and out of cells. Living cells have an electrically negative
interior compared to the extracellular fluid in which they are bathed.
Cells also have higher potassium (K+) and lower sodium (Na+)
concentrations than the extracellular fluid does. Therefore, in a live cell,
the electrical gradient of Na+ (a positive ion) tends to pull it inward to

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the negatively charged interior, while the concentration gradient of Na+

favours diffusion of the ion into the cell. However, the situation is more
complicated for some elements, including potassium; while the
concentration gradient of K+ promotes diffusion out of the cell, the
electrical gradient of K+ favours diffusion of the ion into the cell (Figure
2.10). Its electrochemical gradient, which refers to the combined
gradient that influences an ion, is crucial for muscle and nerve cells in
particular.

Figure 2.10. Electrochemical gradients arise from the combined effects

of concentration gradients and electrical gradients. (credit: modification
of work by “Synaptitude”/Wikimedia Commons)

2. Moving Against a Gradient

The cell must use energy to transfer materials against a concentration or
electrochemical gradient. ATP is used to generate this energy, which is
produced by cellular metabolism. Pumps or carrier proteins collectively
refer to active transport systems that operate against electrochemical
gradients. Small compounds continuously move through plasma
membranes, with the exception of ions. In the face of these passive
variations, active transport keeps concentrations of ions and other
chemicals needed by live cells constant. A significant portion of a cell's
metabolic energy supply might go into supporting these processes.
Active transport mechanisms are vulnerable to several metabolic toxins
that disrupt the flow of ATP since they rely on cellular metabolism for
energy. There are two methods for moving macromolecules and
materials with modest molecular weights. Primary active transport
generates a difference in charge across a membrane while moving ions
across it. A material, such as an ion, is transported into the cell via the
major active transport system using ATP, and frequently at the same
time, a different substance is transported out of the cell. An essential
pump in animal cells called the sodium-potassium pump uses energy to
transfer potassium ions into the cell and a different number of sodium
ions out of the cell (Figure 2.11). This pump's operation causes a
concentration and charge differential to exist across the membrane.

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Figure 2.11. The sodium-potassium pump moves potassium and sodium

ions across the plasma membrane.

The movement of material utilising the primary active transport-created

electrochemical gradient is referred to as secondary active transport.
Other molecules, including amino acids and glucose, can enter the cell
through membrane channels by utilising the energy of the
electrochemical gradient produced by the major active transport
mechanism through secondary active transport utilising a hydrogen ion
gradient in the mitochondrion, ATP being created.

3. Endocytosis
Active transport, such as endocytosis, transports particles into a cell,
including big molecules, fragments of cells, and even complete cells.
Endocytosis comes in a variety of forms, but they all have one thing in
common: Invasion of the cell's plasma membrane creates a pocket
around the target particle. The particle is held in a freshly generated
vacuole made of the plasma membrane after the pocket pinches off.

Figure 2.12. Three variations of endocytosis are shown. (a) In one form
of endocytosis, phagocytosis, the cell membrane surrounds the particle
and pinches off to form an intracellular vacuole. (b) In another type of
endocytosis, pinocytosis, the cell membrane surrounds a small volume
of fluid and pinches off, forming a vesicle. (c) In receptor-mediated
endocytosis, uptake of substances by the cell is targeted to a single type
of substance that binds at the receptor on the external cell membrane.

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A cell takes in huge objects like cells through a process called

phagocytosis. For example, a kind of white blood cell known as a
neutrophil removes the intruder when bacteria enter the human body
through this mechanism, encircling and engulfing the bacterium, which
is subsequently destroyed by the neutrophil (Figure 2.12). Pinocytosis is
an alternative to endocytosis. This term, which literally translates to
"cell drinking," was given to a cell when it was thought that the cell was
actively ingesting extracellular fluid at the time it was named. Actually,
this process draws the necessary solutes from the extracellular fluid that
the cell needs. Utilizing binding proteins in the plasma membrane that
are specific for particular compounds, a targeted version of endocytosis
is carried out (Figure 2.12.). The substance and the proteins enter the
cell after the particles bind to the proteins and the plasma membrane
protrudes. It won't be eliminated from the tissue fluids or blood if
passage across the membrane of the target of receptor-mediated
endocytosis is unsuccessful. Instead, it will persist and become more
concentrated in those fluids. Failure of receptor-mediated endocytosis is
a contributing factor in some human illnesses. For example, receptor-
mediated endocytosis is used to remove low-density lipoprotein, or
LDL, generally known as "bad" cholesterol, from the blood. LDL
receptors are damaged in the human hereditary condition familial
hypercholesterolemia or missing entirely. People with this condition
have life-threatening levels of cholesterol in their blood, because their
cells cannot clear the chemical from their blood.

4. Exocytosis
This process stands in contrast to these mechanisms for introducing
material into a cell. Exocytosis serves to expel material from the cell
into the extracellular fluid, which is the polar opposite of the activities
outlined above. Membrane-encased particles combine with the inside of
the plasma membrane. The particle is released into the extracellular
space as a result of this fusion, which makes the membranous envelope
of the cell accessible to the outside (Figure 10.)

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Figure 2.13. In exocytosis, a vesicle migrates to the plasma membrane,

binds, and releases its contents to the outside of the cell. What is
Pinocytosis?

Self-Assessment Exercises 3
Differentiate between the following type of solutions:
1. Hypertonic solution
2. Isotonic solution
3. Hypotonic solution

2.6 Summary

You must have learned why and how passive transport occurs within the
cells of multicellular organisms. You have also studied the processes of
osmosis, diffusion, tonicity and describe its relevance to passive
transport. You have also learned about how electrochemical gradients
affect ions.

You have also studied the processes;

• Describe endocytosis, including phagocytosis, pinocytosis, and
receptor-mediated endocytosis
• Understand the process of exocytosis

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2.7 References/Further Readings/Web Sources

Reece, B. , L. A. Urry, M. L. Cain, S. A. Wasserman, P. V. Minorsky, R.

B. Jackson.Biology, 9th edition, Benjamin Cummings p. 104-
118

Ross, M. H. (2011): Histology: A Text and Atlas, 6th edition, Lippincott

Williams & Wilkins, p. 22-29; 35-39; 45-67

https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Hum
an_Biology_(Wakim_and_Grewal)/05%3A_Cells/5.07%3A_Cell_Trans
port
https://byjus.com/biology/cell-organelles/
https://www.kenhub.com/en/library/anatomy/cellular-organelles
(nucleus https://youtu.be/VJhYCYxBbys
https://youtu.be/5dSCNDqH-Gk
https://youtu.be/zVqYOnwpKDo types
https://youtu.be/Q1IHL8TytMY
organelles https://youtu.be/tgMZcHpL_ts
cyto https://youtu.be/9kb_JJwapRg
membrane https://youtu.be/gh4ciqmXLsU)

2.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Gap junctions in animal cells are like plasmodesmata in plant
cells in that they are channels between adjacent cells that allow for the
transport of ions, nutrients, and other substances that enable cells
to communicate
2. Intercellular junctions, allow cells to communicate directly with
one another, are another method of cell communication.

Answers to SAE 2
1. It is described by the following terms: terms hypotonic, isotonic,
and hypertonic.
2. Factors affecting rate of diffusion

• Extent of the concentration gradient

• Mass of the molecules diffusing
• Temperature
• Solvent density

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Answers to SAE 3
1= Hypertonic solution. A solution A solution that has a higher solute
concentration than another solution. Water particles will move out of
the cell, causing crenation.
2= Isotonic solution. A solution that has the same solute concentration
as another solution. There is no net movement of water particles, and the
overall concentration on both sides of the cell membrane remains
constant.
3= Hypotonic solution. A solution that has a lower solute concentration
than another solution. Water particles will move into the cell, causing
the cell to expand and eventually lyse.

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Unit 3 Tissues, Organs and Organ Systems

Unit Structure

3.1 Introduction
3.2 Intended Learning Outcomes (ILOs)
3.3 Tissues, Organs and Organ Systems
1.3.1 Types of Animal Tissues
1.3.2 Types of Plant Tissues
3.4 The Organs and Organ System
1.4.1 The Organ Systems in Animals
1.4.2 The Organ Systems in Plants
3.5 Organs in a system work together.
3.6 Summary
3.7 References/Further Readings/Web Sources
3.8 Possible Answers to Self-Assessment Exercises

3.1 Introduction
You will Learn about the various tissue types of both plants and animals
and organ and organ systems of plants and animals. You will also learn
how the organs in a system work together.

3.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Define tissues, organs and organ system as part of the level of

organization of living things
• Describe the organ in both animals and plants
• Describe the major organ systems of the animal and plant bodies
• Explain how organs in a system work together and
• Explain the workings of organ systems in animals and plants.

3.3 Tissues, Organs and Organ Systems

In physiology, a group of physically and functionally related cells and

their intercellular materials make up a tissue, which is a level of
organisation in multicellular organisms. Tissues are by definition absent
in unicellular organisms. Even the most basic multicellular animals, like
sponges, lack or have poorly differentiated tissues. However, highly
developed multicellular animals and plants have specialised tissues that
can plan and control an organism's response to its environment. Life
would be simple if you were a single-celled organism and you were in a
nutrient-rich environment. If you were an amoeba living in a pond, for
example, you could directly take in nutrients from the water. Through
your cell membrane, the oxygen you need for metabolism could enter,

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and carbon dioxide and other waste products could exit. You could
simply divide yourself in half when the time comes to reproduce!

3.3.1 Types of Animal Tissues

There are four different types of tissues in animals: connective, muscle,

nervous, and epithelial. Groups of tissues make up organs in the body
such as the brain and heart.
1. Connective
Groups of various tissues are connected or divided by connective tissue.
It can be found between every other tissue and organ in the body. Cells
and ground material, a gel that surrounds cells, make up connective
tissue. Except for lymph and blood, the majority of connective tissues
comprises fibres, which are long, slender proteins. Collagenous fibres
attach bones to tissues, elastic fibres enable the movement of organs
such as the lungs, and reticular fibres give cells structural support. In
addition, connective tissue enables the diffusion of oxygen from blood
vessels into the cells. About 1 in every 10 people have a disorder
involving connective tissues. Some connective tissue disorders include
sarcomas, Marfan syndrome, lupus, and scurvy; is a Vitamin C
deficiency that leads to fragile connective tissues.

2. Muscle
All the muscles in the body are made of muscular tissue, and the ability
to contract is due to the tissue's specific makeup. Skeletal muscle,
cardiac muscle, and smooth muscle are the three different forms of
muscle tissue. Skeletal muscle holds tendons to bones and permits
movement of the body. The heart contains cardiac muscle, which
contracts to pump blood. In addition to the intestines, where it aids in
the passage of food through the digestive tract, smooth muscle is also
present in blood arteries, the uterus, and the bladder. The sarcomeres (a
unit of muscle tissue) in skeletal and cardiac muscles are striated, which
means they are arranged in a predictable pattern. Sarcomeres are absent
in the smooth muscle. One condition of the muscle tissue is Duchenne
muscular dystrophy. Muscle atrophy is brought on by this genetic
condition over time. As the muscles deteriorate, they shorten, which can
result in scoliosis and stiff joints. Due to the disorder's X chromosome-
associated gene, those who have it are often male (of which males have
only one).

3. Nervous
The brain, spinal cord, and peripheral nerves are all components of the
nervous system and contain nervous tissue. Neurons, which are nerve
cells, and neuroglia, which support the transmission of nerve impulses,
make up this structure. Gray matter and white matter in the brain, as
well as nerves and ganglia in the peripheral nervous system, are two of

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the four categories of nervous tissue. The primary distinction between

grey and white matter is that although white matter's axons are
myelinated, grey matter's are not. A white, fatty material called myelin
protects neurons and is essential for the proper operation of the
neurological system. Memory loss, irritability, and confusion are some
of the signs of Alzheimer's disease that are brought about by the
degeneration of nerve tissue. Another condition that involves the
degeneration of neural tissue and, over time, the loss of higher brain
functions is Amyotrophic Lateral Sclerosis (ALS). Other conditions
affecting the nervous system include multiple sclerosis, in which the
immune system attacks and damages the nervous system, Huntington's
disease, in which an abnormal protein results in the death of neurons,
and Parkinson's disease, in which the dopamine-producing region of the
brain is compromised.

4. Epithelial
The skin, trachea, reproductive system, and inner lining of the digestive
tract are only a few of the organ surfaces covered in epithelial tissue, or
epithelium. It functions to absorb water and nutrients, get rid of waste,
and secrete enzymes or hormones in addition to forming a barrier that
aids in protecting organs. All of the glands in the body are created by
epithelial ingrowths. Skin conditions like eczema and psoriasis, which
can result in rashes, are examples of prevalent epithelial tissue illnesses.
A carcinoma is a form of cancer that arises from epithelial tissue.
Asthma is characterised by airway inflammation that causes shortness of
breath and is caused by epithelial cells in the airways.

Figure 3.1. The different types of Tissues: Source:

https://byjus.com/biology/structural-organization-animals/

3.3.2 Types of Plant Tissues

Plants are multicellular eukaryotes, and their tissue systems are made up
of many cell types that serve distinct purposes. Meristematic tissue and
permanent (or non-meristematic) tissue are the two main forms of plant

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tissue systems. Meristems, which are areas of plants that experience

continuous cell division and expansion, are where the meristematic
tissue's cells may be located. Meristematic tissue cells continue to divide
and support plant growth despite being either undifferentiated or
incompletely differentiated. The meristematic tissue in a plant's apical
meristems, which are found at the tips of its stems and roots, allows it to
grow longer. A mature plant's lateral meristems enable increase in
thickness or girth. Only monocots have intercalary meristems, which are
found at the bases of leaf blades and at nodes (the areas where leaves
attach to a stem). The monocot leaf blade can lengthen from the leaf
base because of this tissue; for example, it permits lawn grass leaves to
lengthen even after frequent mowing.

Meristems generate cells that swiftly specialise or differentiate into

permanent tissue, dormant plant cells, which are no longer actively
dividing. Such cells acquire particular functions and stop proliferating.
Based on where they are located in the plant, meristematic tissues are
divided into three categories; Dermal, vascular, and ground tissues.
Vascular tissue carries water, minerals, and sugars to various areas of
the plant, while dermal tissue covers and protects the plant. In addition
to acting as a photosynthetic site and vascular tissue support matrix,
ground tissue also helps to store water and sugars. Secondary tissues can
be straightforward (made up of similar cell types) or complex
(composed of different cell types). For instance, dermal tissue is a
straightforward tissue that covers the plant's exterior and regulates gas
exchange. One example of a complex tissue is vascular tissue, which is
composed of the specialised conducting tissues; xylem and phloem.
Xylem tissue conducts water and nutrients from the roots to various
sections of the plant and are made up of three main cell types; xylem
parenchyma, vessel elements, and tracheids (two of which conduct
water). The phloem tissue transports organic compounds from the centre
of photosynthesis to other sections of the plant are made up of four
distinct cell types; companion cells, sieve cells (which conduct
photosynthates), phloem parenchyma, and phloem fibres. Phloem
conducting cells are alive at maturity, in contrast to xylem conducting
cells. Phloem and xylem are constantly next to one another (Figure 3.2).
The xylem and phloem combine to produce a structure in stems known
as a vascular bundle; in roots, this structure is known as a vascular stele
or vascular cylinder.

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Figure 3.2. Plant Organs and Tissues (Each plant organ contains all three
tissue types).
Source: http://plantphys.info/plant_physiology/plantbasics1.shtml.

Assessment Exercises 1
1. What are different types of animal tissues?
2. What is the function of an epithelial tissue?

3.4 The Organs and Organ System

The organ is the next level of animal organisation. An organ is a group

of tissues that structurally constitute a functional unit that is specialised
to carry out a specific function. The word organ comes from the Latin
word "organum," which means an instrument or tool. Tissues with a
similar structure and function make up each organ. The heart, skin (the
biggest human organ), lungs, stomach, kidneys, and heart are a few
examples of organs. Organs are composed of two or more types of tissue
that are arranged to perform specific functions. For example, the heart
pumps blood, the lungs bring in oxygen and eliminate carbon dioxide,
and the skin provides a barrier to protect internal structures from the
external environment. The small intestine's stratified walls serve as a
good illustration of how tissues combine to form an organ. Epithelial
cells line the interior of the colon; some of these cells release hormones
or digesting enzymes, while others absorb nutrition. There are layers of
smooth muscle and connective tissue surrounding the epithelium layer,
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as well as glands, blood arteries, and neurons. Under the direction of the
accompanying neuronal networks, the smooth muscle contracts to
convey food through the intestine.

Plants have four main organs:

i). The primary organs for absorbing sunlight for photosynthesis are
leaves;
ii. The primary organs that draw water and nutrients from the soil
are the roots;
iii). The primary organs for moving materials between leaves and
roots are stems; and
iv). Similarly, flowers, reproductive organs release seeds that develop
into new plants.

Typically, flowers have vibrant petals that entice bees, butterflies, and
other pollinators. The next level of organisation are the organ systems.
An organ system is made up of two or more organs that cooperate to
carry out a certain task for the organism. The circulatory, neurological,
skeletal, muscular, integumentary, endocrine, digestive, immunological,
reproductive, excretory, and respiratory systems are the main organ
systems that make up the human body. The integumentary system, for
instance, consists of the skin, hair, nails, and glands. The deeper tissues
and organs of the body are safeguarded by this system, which receives
impulses from the outside world. There are several organs that make up
the digestive system. The stomach aids in digestion and stores food.
Intestines break down food and take in nutrients. The liver contributes to
the function of the digestive system by secreting bile, a lipid-degrading
agent that aids in the digestion of fats. Multiple organ systems can
cooperate with a single organ. For example, the liver and circulatory
system collaborate to filter wastes from the blood. Although we
frequently refer to the various organ systems as though they were
separate, components of one system may have an impact on another.
The various systems also have a lot of functional overlap. For example,
although we frequently associate the circulatory system with the
delivery of oxygen and nutrients to cells, it also contributes to the
regulation of body temperature. White blood cells are an essential part
of the immune system, and the blood also carries hormones produced by
the endocrine system's glands.

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1.4.1 The Organ Systems in Animals

S/ Organs and tissues
NO Organ system/Function involved
Cardiovascular:
Transports oxygen, nutrients, and other
substances to the cells and transports
wastes, carbon dioxide, and other
substances away from the cells; it can
also help stabilize body temperature and Heart, blood, and blood
1. pH vessels
Lymphatic:
Defends against infection and disease
and transfers lymph between tissues and Lymph, lymph nodes, and
2. the blood stream lymph vessels
Mouth, salivary glands,
esophagus, stomach, liver,
Digestive: gallbladder, exocrine
Processes foods and absorbs nutrients, pancreas, small intestine,
3. minerals, vitamins, and water and large intestine
Endocrine:
Provides communication within the Pituitary, pineal, thyroid,
body via hormones and directs long- parathyroids, endocrine
term change in other organ systems to pancreas, adrenals, testes,
4. maintain homeostasis and ovaries.
Integumentary:
Provides protection from injury and
fluid loss and provides physical defense
against infection by microorganisms;
5. involved in temperature control Skin, hair, and nails
Muscular:
Provides movement, support, and heat Skeletal, cardiac, and
6. production smooth muscles
Nervous: Brain, spinal cord, nerves,
Collects, transfers, and processes and sensory organs; eyes,
information and directs short-term ears, tongue, skin, and
7. change in other organ systems nose
Fallopian tubes, uterus,
Reproductive: vagina, ovaries, mammary
Produces gametes—sex cells—and sex glands (female), testes, vas
hormones; ultimately produces deferens, seminal vesicles,
8. offspring prostate, and penis (male)

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S/ Organs and tissues

NO Organ system/Function involved
Mouth, nose,
Respiratory: pharynx, larynx,
Delivers air to sites where gas exchange trachea, bronchi,
9. can occur lungs, and diaphragm
Skeletal:
Supports and protects soft tissues of the
body; provides movement at joints;
produces blood cells; and stores Bones, cartilage, joints,
10. minerals tendons, and ligaments
Urinary:
Removes excess water, salts, and waste
products from the blood and body and Kidneys, ureters, urinary
11. controls pH bladder, and urethra
Immune: Leukocytes, tonsils,
Defends against microbial pathogens— adenoids, thymus, and
disease-causing agents—and other spleen
diseases

Although we frequently refer to the various organ systems as if they

were separate, components of one system may have an impact on
another. For example, the mouth is a part of both the digestive and
respiratory systems. The various systems also have a lot of functional
overlap. For example, although we frequently associate the circulatory
system with the delivery of oxygen and nutrients to cells, it also
contributes to the regulation of body temperature. White blood cells are
an essential part of the immune system, and the blood also carries
hormones produced by the endocrine system's glands.

1.4.2 The Organ Systems in Plants

A tissue is created by comparable cells coming together, exactly like in

animals and plants. An organ is created when many tissue types
collaborate to carry out a certain function; organ systems are created
when multiple organs act as a unit. A shoot system and a root system are
the two separate organ systems found in vascular plants. The root and
any accompanying fibres that branch off the main root are included in
the root system, which is normally underground. This structure holds the
plant in place and draws moisture and nutrients from the soil. The stem,
leaves, and reproductive organs, such as flowers, are all parts of the
shoot system, which is normally above ground. Photosynthesis and
reproduction are just two of the many tasks performed by this system.

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As with animals, the organ systems of plants work together to make up

the structure and function of the entire organism.

Figure 3.3 The organ system in plants. Source:

http://plantphys.info/plant_physiology/plantbasics1.shtml.

Self-Assessment Exercises 2
1. Name the main organs in the digestive system.
2. Which plant organ is most important?
3. What are the organ system of plants working together?

3.5 Organs in a system work together

The organs in an organ system must cooperate with one another in order
for the system to function as a whole, just like employees on an
assembly line. For example, the digestive system relies on each
succeeding organ performing its particular task in order to function—
that is, to take in food, break it down into molecules small enough to be
absorbed, absorb it, and eliminate undigested waste items. Food is
broken down during digestion so that its nutrients can be absorbed. It
consists of both chemical and mechanical digestion. Smaller particles of
food are broken down into larger ones during mechanical digestion.
Large molecules like proteins and carbohydrates are broken down into
smaller, more easily absorbed pieces during chemical digestion. In the
mouth and stomach, mechanical digestion takes place in addition to
some initial chemical digestion. Food is broken down into tiny bits
through chewing, and is then mixed with fluid in the stomach. In

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addition, the stomach serves as a storage space, allowing for the

controlled release of partially digested food into the small intestine.

Chemical digestion takes place mostly in the small intestine and is

accomplished by pancreatic and liver-derived enzymes. Majority of
nutrient absorption occurs in the small intestine, where cells pick up
substances like carbohydrates and amino acids and transfer them into
circulation for usage. Efficiency in food digestion and nutrient
absorption depends on the cooperation of the mouth, stomach, small
intestine, and other digestive system organs. If your stomach stopped
turning or if one of your glands that makes enzymes, like the pancreas,
take a day off, digestion wouldn't function as well. Plants have two
organ systems; the shoot and the root systems. The leaves, stems, and
flowers are all a part of the shoot system. The soil's nutrients and water
are absorbed by the roots. These two systems supply the entire plant
with water and nutrients. The various organ systems collaborate to keep
the body functioning, just as the organs in an organ system work
together to accomplish their mission. For example, the respiratory
system and the circulatory system work closely together to deliver
oxygen to cells and to get rid of carbon dioxide from the cells. The
circulatory system transfers carbon dioxide from the tissues into the
lungs, where it is ultimately reconverted to oxygen by the lungs. The
carbon dioxide is expelled by the lungs, and fresh air containing oxygen
is breathed in. Oxygen and carbon dioxide can only be successfully
exchanged between cells and the environment when both systems are
functioning properly. Similarly, without the kidneys' filtration and the
nutrients from your digestive system, the blood in your circulatory
system would not be able to support your body's cells and flush out the
wastes they create. Chemical messengers are used by these two
regulatory systems to influence the operation of other organ systems and
to synchronise activity across the body.

How are the nerve and endocrine systems different? Hormones are
secreted into the blood serve as the chemical messengers in the
endocrine system. Neurotransmitters are chemical messengers that are
delivered directly from one cell to another across a very small gap in the
nervous system.

The endocrine system often coordinates operations on a slower time

scale than the neurological system because hormones must travel
through the bloodstream to reach their targets. In contrast, the neural
system delivers messages immediately to the target cell. For example,
during the fight-or-flight reaction to a serious threat, the neurological
and endocrine systems collaborate to create a physiological response.

Self-Assessment Exercise 3

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1. What are the two main organ systems of a plant?

2. Give examples of organ systems working together?
3.6 Summary

You must have learned how to draw and describe the various cell
organelles. You have also studied the main tissue types and organ
systems of both plants and animals. How the various organ systems
work in tandem was also highlighted. In this unit you have learned about
the organs and organ systems of organisms. In animals there are about
twelve major organs, while plants consists of four organs and two organ
systems. The shoot system includes the aboveground vegetative portions
(stems and leaves) and reproductive parts (flowers and fruits).
You have also studied how the organs in a system work together, and
the workings of organ systems in both animals and plants.

3.7 References/Further Readings/Web Sources

Gurevitch, J., Scheiner, S. M. and Fox, G.A. (2020). The Ecology of

Plants, 3rd Edition,

Matthew, R. Fisher (2018). Environmental Biology, Publisher: Open

Oregon Educational Resources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp

Putman, R.J. and S.D. Wratten (1984). Principles of Ecology, Publisher

Springer Dordrecht, eBook Packages Springer Book Archive,
DOIhttps://doi.org/10.1007, /978-94-011- 6948-6, eBook
ISBN978-94- 011-6948-6. 388pp
https://www.britannica.com/science/cell-biology/Secretory-vesicles
https://www.labxchange.org/library/items/lb:LabXchange:aedf2fbb-
0aa0-3751-88f4-bcaad6454864:html:1
http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/Organization-in-
plants-and-animals.pdf
https://byjus.com/biology/what-is-tissue/
https://courses.lumenlearning.com/wm-biology2/chapter/plant-tissues-
and-organs/
https://www.britannica.com/science/organ-biology
https://biologydictionary.net/organ/
https://www.youtube.com/watch?v=UHJGy1ZW7kE
https://www.youtube.com/watch?v=RKmaq7jPnYM
https://www.youtube.com/watch?v=LReJG7PrXFY

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https://www.youtube.com/watch?v=gEUu-A2wfSE
https://www.youtube.com/watch?v=8Nb9E62p2c0

3.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. An organ system consists of two or more organs working
together to perform a specific function for the organism.
2. Yes, there is a functional overlap among the different systems,
for example, while we tend to think of the cardiovascular system as
delivering oxygen and nutrients to cells, it also plays a role in
maintaining temperature.

Answers to SAE 2

1. The main organs of the human digestive system participate in the

following order in process of digestion:
Mouth, esophagus, stomach, small intestine, large intestine, rectum, and
anus.

2. Leaves: Leaves are the most important part of a plant. They

contain chlorophyll that helps the plants to prepare their food
using sunlight, carbon dioxide and water. A leaf consists of three main
parts- petiole, leaf base and lamina.

3. Plant organs are organized into two organ systems. The shoot
system includes the leaves, stems, and flowers. The root system
takes up water and nutrients from the soil. These two systems
work together to deliver water and nutrients to the entire plant.

Answers to SAE 3

1. Each plant has two main organ systems. They are;

Root system and Shoot system

2. Some body systems work together to complete a job. For

example, the respiratory and circulatory systems work
together to provide the body with oxygen and to rid the body of
carbon dioxide. The lungs provide a place where oxygen can
reach the blood and carbon dioxide can be removed from it.

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Unit 4 Characteristics and Classification of Living Things

Unit Structure

4.1 Introduction
4.2 Intended Learning Outcomes (ILOs)
4.3 Characteristics of Living Things
4.3.1 Non-living things
4.3.2 Difference between living and non-living things
4.4 The use of the hierarchical classification system
4.4.1 The hierarchical classification system
4.4.2 Properties of the Five Kingdoms
4.5 Systems of Classification
4.5.1 Evolutionary relationships
4.5.2 Artificial classification and the binomial system
4.6 Summary
4.7 References/Further Readings/Web Sources
4.8 Possible Answers to Self-Assessment Exercises

4.1 Introduction

In this Unit, you will learn the main characteristics and developments in
the classification of organisms, and the scientific method of naming of
organisms using the binomial nomenclature. All organisms have
only one scientific name but many common names. The division of
organisms into prokaryotes and eukaryotes, and the major differences
between the two. The classification of living organisms into five major
kingdoms: Monera, Protista, Fungi, Plantae and Animalia and the
unique characteristics of each kingdom.

4.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• Understand and describe the characteristics of living and non

living things.
• Know the definition of the biological classification system.
• Explain the hierarchical manner of grouping of living organisms
based on similarities and differences.
• Describe living organisms into five major kingdoms.

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4.3 Characteristics of Living Things

We can find many things around us, from mountains and oceans to
plants and animals. The earth in which we live is made up of several
things. These “things” can be categorized into Living and Non-living
Things.
• All living things breathe, eat, grow, move, reproduce and have
senses.
• Non-living things do not eat, grow, breathe, move and reproduce.

Even though some living organisms may not display obvious symptoms,
they all have "life". For example, a tree definitely wouldn't respond the
same way a person would when we struck it, but it is not be able to
move. The fact that they don't exhibit many observable indicators of life
does not imply that they are not alive. Cells are the building blocks of all
living organisms, and they develop and show signs of motility. They go
through metabolism, which involves both catabolic and anabolic
processes. Through the process of reproduction, living beings are able to
create brand-new lives that are of their own types. Everything that is
alive has a finite lifespan and is not eternal.

Cellular Respiration enables living organisms to acquire energy used

by cells to perform their functions. They digest food for energy and also
excrete waste from their bodies. Their life cycle can be summarised as
follows – birth, growth, reproduction and death. Examples of living
things are animals, birds, insects, and human beings.

Fig. 4.1. Characteristics of Living Things. Source: www.byjus.com

The important characteristics of living things include:
1. Living things move and display locomotory motion. Animals can
move because they have specific locomotory organs. For
example, earthworms use their circular and longitudinal muscles to

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move across the soil surface. Movement helps plants capture sunlight for
photosynthesis.
2. Life forms breathe. A chemical mechanism called respiration
takes place inside of cells to extract energy from food. Through the
process of digestion, food is broken down to release energy
which is used by the body to create the byproducts of water and carbon
dioxide.
3. Living things are capable of detecting changes in their
surroundings and are sensitive to touch (as well as other stimuli).
4. They grow: Living things grow and mature through different
stages of development.
5. One of the remarkable characteristics is that through the process
of reproduction, in which genetic information is conveyed from the
parents to the offspring, living beings are able to produce
offspring of their own type.
6. Through the process of nutrition and digestion, which involves
ingesting and digesting the food, they obtain and fulfil their
nutritional needs. Autotrophs can produce food using sunlight or
chemical energy.
7. The body expels the food that has been digested through the
excretion process.

4.3.1 Non-Living Things

Non-living things don't have life in them. They do not develop, have
cells, or exhibit motility or movement. They don't go through anabolic
and catabolic responses throughout metabolism, neither do they
procreate nor have a lifespan. Since they do not need food for energy,
they do not breathe or excrete. They are not subject to any cycle of birth,
development, or demise. External influences both build and destroy
them. Examples of non-living things are stones, pencils, books, bikes,
and bottles. Following are some of the crucial traits of non-living things:
1. Non-living things are lifeless. They do not have cells, and there is
no protoplasm which forms the basis for life to exist.
2. Lack of protoplasm leads means no metabolic activities.
3. They do not have a definite and certain size of their own. They
take the shape of the substance they are contained in, for example, a
liquid takes the shape of its container. Stones, rocks and boulders
are mould by the changing environment and landscape. The
change in the state of a non-living thing is due to an external
influence.
4. Non-living things “grow” by accretion which occurs through
adding materials externally. For example, A snowball may
increase in size due to the accumulation of smaller units of its
own on its outer surface.

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5. Non-living things never die as they do not have cells with a

definite lifespan. Immortality is a distinguishing factor.
6. Fundamental life processes such as reproduction, nutrition,
excretion, etc. are absent in non-living things.

4.3.2 Difference Between Living and Non-Living Things

Scientists have developed qualities or characteristics exclusive to living

things in order to distinguish them from non-living things. The
classification standard is required to prevent erroneous grouping. As a
result, science created a framework for classification. A live thing is
defined as anything that has life. Examples include people, pets, and
trees. Non-living things are those that do not have any form of life. For
example, a watch, a stone, or a mountain. The following are some key
distinctions between living and non-living things:
Living Things Non-Living Things

They possess life. They do not possess life.

They are capable of giving birth to

They do not reproduce.
their young ones.

They depend on water, air and food They have no such

for survival. requirements

They are sensitive and responsive to They are not sensitive and do
stimuli. not respond to stimuli.

Metabolic reactions constantly occur There are no metabolic

in all living things. reactions in Non-living things.

They undergo growth and

They do not grow or develop.
development.

They have a lifespan and are not They have no lifespan and are
immortal. immortal.

They move from one place to They cannot move by

another. themselves.

They respire and the exchange of

They do not respire.
gases takes place in their cells.

Example: Humans, animals, plants, Example: Rock, pen, buildings,

insects. gadgets.

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What are non-living things?

Self-Assessment Exercises 1

1. What is the one characteristic that enables living organisms to

acquire energy used by cells to perform their functions?
2. What is the process that is lacking in non-living things which
distinguishes them from living things?

4.4 The Use of Hierarchical Classification System

We can impose order and a broad scheme on the diversity of living

things by classifying them. Scientists have always attempted to
categorise and organise the surrounding items, including biological
things. Classification means grouping organisms based on structural
similarity. This implies that species with comparable traits are grouped
together. These groups are arranged from the group to the smallest.
Kingdom, phylum (plural phyla), class, order, family, genus (plural
genera), and species are the groups as listed in order of largest to
smallest. The smallest class of organisms is the species. As you move up
the classification hierarchy, you will notice that scientists classified
organisms into kingdoms, which are the largest groups of organisms,
using broader features. The characteristics become more specialised as
you get closer to the species, which are the smallest groups of
organisms. In other woeds, two organisms from the same species have
more traits in common than two organisms from the same kingdom but
different species. A group of organisms with comparable characteristics
that are able to reproduce and give birth to healthy offspring are referred
to as species. You are undoubtedly already aware that although horses
and donkeys come from separate species, they are members of the same
kingdom, phylum, class, order, family, and genus. As a result, if a
donkey and a horse were to breed, the result would be a creature known
as a mule. The mule cannot produce children because it is a hybrid of
various species of organisms, making it sterile. Hierarchical
classification has various applications. First, it aids scientists in the
classification of organisms. Secondly, it helps in finding out which
category a new organism belongs helping them recognise it. Thirdly,
grouping organisms makes it simpler to research with them.

4.4.1 The Hierarchical Classification System

Based on very fundamental, common traits, groups of all living things

are identified. The organisms within each category are subsequently
sorted into even more compact groups. These more specific similarities
within each bigger group form the basis for these smaller groups. It is

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simpler for scientists to investigate particular groupings of species;

thanks to this classification scheme. The kingdom is the biggest group.
Prokaryotes, which comprises bacteria, protoctista, fungus, plants, and
animals make up the five kingdoms. Based on a few traits that certain
organisms share, phyla are smaller groups that are further subdivision of
each kingdom. For example, the arthropod phylum, which includes
insects, crustaceans, and spiders, includes all organisms without a
backbone who also have jointed legs and a hard covering over their
bodies. The subdivisions within a phylum are classes, orders, families,
genera, and finally species. The various categories in this classification
scheme are referred to as taxa (singular: taxon). The classification
hierarchy is depicted in figure 4.2 below. The taxonomy of living things
refers to all of these specific divisions, and seven categories that make
up the taxonomy of living things are kingdom, phylum, classes, order,
families, genus, and species.

Figure 4.2. The Hierarchical Classification System. Source:

www.byjus.com

The most basic classification of living things is kingdoms. Currently

there are five kingdoms. Living things are placed into certain kingdoms
based on how they obtain their food, the types of cells that make up their
body, and the number of cells they contain.

Phylum
The phylum is the next level following kingdom in the classification of
living things. It is an attempt to find some kind of physical similarities
among organisms within a kingdom. These physical similarities suggest
that there is a common ancestry among those organisms in a particular
phylum.

Classes
Classes are way to further divide organisms of a phylum. As you could

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probably guess, organisms of a class have even more in common than

those in an entire phylum. Humans belong to the Mammal Class because
we drink milk as a baby.

Order
Organisms in each class are further broken down into orders. A
taxonomy key is used to determine to which order an organism belongs.
A taxonomy key is a checklist of characteristics that determines how
organisms are grouped together.

Families
Orders are divided into families. Organisms within a family have more
in common than with organisms in any classification level above it.
Because they share so much in common, organisms of a family are said
to be related to each other. Humans are in the Hominidae Family.

Genus
Genus is a way to describe the generic name for an organism. The genus
classification is very specific so there are fewer organisms within each
one. For this reason, there are a lot of different genera among both
animals and plants. When using taxonomy to name an organism, the
genus is used to determine the first part of its two-part name.

Species
Species are as specific as you can get. It is the lowest and most strict
level of classification of living things. The main criterion for an
organism to be placed in a particular species is the ability to breed with
other organisms of that same species. The species of an organism
determines the second part of its two-part name.

4.4.2 Properties of the Five Kingdoms

The properties of the five kingdoms are as follows:

Monera
The cell type is prokaryotic. The cell wall is present and it is non-
cellulosic. The nuclear membrane is absent. It is a unicellular organism
and the mode of nutrition is autotrophic and heterotrophic. Bacteria are
an example of an organism in the monera kingdom.

Protista
The cell type is eukaryotic. The cell wall is present. The nuclear
membrane is also present. It is a unicellular organism and the mode of
nutrition is autotrophic.

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Fungi
The cell type is eukaryotic. The cell wall is present. The nuclear
membrane is also present and it is a multicellular organism and the
mode of nutrition is heterotrophic. Example mushroom is a fungus.
They cannot make their own food.

Plantae
The cell type is eukaryotic. The cell wall is non-cellulosic. The nuclear
membrane is present. The organism is tissue or organ. The mode of
nutrition is autotrophic. Examples are plants, trees, and a bush.

Animalia
The cell type is eukaryotic. The cell wall is absent. The nuclear
membrane is present. The organism is a tissue, organ or organ system.
The mode of nutrition is heterotrophic.
Which kingdom has a prokaryotic cell type?

Self-Assessment Exercises 2

1. What are the levels of classification of organisms?

2. What does genus represent in the classification scheme?

4.5 Systems of Classification

There are two different systems that can be used for classification:
natural and artificial. First, let's examine natural classification. Natural
categorization The aforementioned hierarchical categorization method is
based on a natural classification scheme that makes use of traits that all
living things have in common. Two concepts serve as the foundation for
natural classification: 1) homologous structures, and 2) evolutionary
links. Homologous structures are characteristics of organisms that share
a similar structure, but can have extremely distinct appearances and
serve various functions. Homologous features are frequently seen in the
forelimbs of vertebrates, where the forelegs of four-legged vertebrates
like dogs and crocodiles, as well as the arms of primates, whales' front
flippers, and bats' and birds' wings, are all descended from the same
ancestral tetrapod. Their identical bone count and arrangement indicates
that they most likely descended from a single type of structure that
existed in a common ancestor millions of years ago. The wing of a fly
and the wing of a bat are not analogous. Despite having a similar
appearance and performing the same function, it has a totally different
beginning. The wing of the fly is not covered with feathers and has no
bones. It is said that a fly's wing and a bat's wing are comparable. You
wouldn't mix a fly and a bat together! Relationships formed through the

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worldwide process of evolution between two separate creatures are

known as evolutionary relationships. They are, in other words, the
connections between two species that shared an ancestor. Evolutionary
relationships are crucial to research because they provide insight into the
timing and processes by which particular traits were developed in
particular species. Phylogenetics is the study of evolutionary
relationships and their effects. There is frequently remarkable physical
resemblance between persons who have a shared ancestry, like a
grandmother or great grandparent. The individuals in the pictures are
undoubtedly linked to one another and have traits that they got from
their ancestors. Biologists classify species according to their common
ancestry and structural similarities in a natural classification system. A
branching collection of associations is produced via natural
classification. This demonstrates how the key plant subgroups, including
mosses, ferns, conifers, and flowering plants, are separated out. It is
possible to divide each of these groupings; humans, Homo sapiens, and
cockroach Periplaneta americanus are in the animal kingdom. Humans
and cockroaches share a common ancestor more than 500 million years
ago! You can see many structural differences between humans and
cockroaches and so there is no natural relationship, thus we classify
Homo sapiens and Periplaneta americanus into very different groups.

4.5.1 Artificial classification and Binomial system

You are free to use whichever grouping you like while using artificial
classification. You could classify all flying animals together. Birds, bats,
and a variety of insects would then be included in this group. All aquatic
creatures with bodies that are streamlined and resemble those of fish
could be grouped together. Fish and whales would then be included in
this group. Biologists employ dichotomous keys to distinguish different
types of organisms, and these dichotomous keys are based on artificial
classification systems species naming using the binomial system. The
hierarchical classification scheme that we have so far examined was first
proposed by the Swedish naturalist Carl Linnaeus, who lived from 1707
to 1778. He also assigned a Latin scientific name to each and every
species giving each living thing two Latin names known as the
"binomial" system of species naming (scientific names). Binomial
literally translates to "two names" because "bi" stands for "two" and
"nomial" stands for "name." Scientific names for organisms were
derived by Linnaeus from their genus and species. The genus name is
written first and begins with a capital letter when writing a scientific
name, and the species name is written second and begins with a small
letter. When typing or handwriting the scientific name, it should be
printed in italics or underlined individually. The tiger is a member of the
Panthera genus and the tigris species, hence its scientific name will be
written as Panthera tigris or typed as Panthera tigris. Scientific names

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are universal because, for example, every biologist will understand that
Felis catus means ‘house cat’ without resorting to the dictionary, no
matter what language they speak. Can you think of the scientific names
for some other organisms?

4.5.2 History and the Study of Evolutionary Relationships

The evolution of interactions between species dates back to the dawn of

time. Small microorganisms in water were the first organisms to be
produced on land. Amphibians started to evolve over time, old World
monkeys were the first to diverge from the primary root of the primate
family tree approximately 25–30 million years ago. The earliest relatives
of modern humans diverged from their forebears about 6 million years
ago, starting the evolutionary tree that produced many humanoid and
ape species, including the Ardipithecus family, Australopithecus
afarensis, Homo habilis, and many others. Homo erectus eventually
evolved between 1.5 and 2 million years ago. Numerous variations of
Homo sapiens have descended from this species. Homo sapiens, the
current species, is a combination of all of these previous versions.
Understanding the relationships between numerous non-human species
as well as those between humans and similar species can be aided by an
understanding of evolutionary relationships. For instance, it is possible
to determine who descended from whom and how by comparing two
species of birds that are similar to one another. The comprehensive field
of phylogenetics focuses on scientifically classifying and analysing the
traits of various species to ascertain their evolutionary ties, which is why
people investigate evolutionary relationships. The following are
characteristics of phylogenetic research:
• Systematics- the method through which species are placed into
particular families and how their connections to one another are
established. In other words, this is the system that establishes
taxonomy.
• Taxonomy - Taxonomy is the labelling of certain species in order
to highlight the connections between various species and
investigate their interconnections. A taxon is the name for a
certain group or family's designation. Classes, orders, families,
and species, for instance, each have their own distinct taxa. A taxa is
a group of taxons.
• Evolution- Without the basis of evolution to build on,
phylogenetics would be functionally meaningless. The study of
phylogenetics was founded on the theory of evolution. To
understand how evolution works, systematic research is
conducted at all taxonomic levels.

What is Systematics in taxonomy?

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Self-Assessment Exercises 3

1. The tiger belongs to the genus called Panthera and the species
called tigris, therefore what is its scientific name?
2. Describe the binomial classification.

4.6 Summary

You have learned the main characteristics and developments in the

classification of organisms.

You have studied the scientific method of naming of organisms using

the binomial nomenclature. The division of organisms into prokaryotes
(simple, unicellular) and eukaryotes (mostly multicellular) and the major
differences between the two has been highlighted. You have also learned
about the classification of living organisms into five major kingdoms

4.7 References/Further Readings/Web Sources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp

https://assets.cambridge.org/97805216/80547/excerpt/9780521680547_e
xcerpt.pdf https://byjus.com/biology/living-and-non-living-things/
https://www.youtube.com/watch?v=wt5ZE5Qcr0Y
https://www.youtube.com/watch?v=UjOz-My9gEI
https://www.youtube.com/watch?v=z8znhBuIwr4
https://www.youtube.com/watch?v=-jFIjA8YHfE

4.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Cellular respiration
2. Life processes

Answers to SAE 2
1. The classification of living things include 7
levels: kingdom, phylum, classes, order, families, genus,
and species .
2. The genus classification is very specific so there are fewer

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organisms within each one. Genus is a way to describe the

generic name of an organism.

Answers to SAE 3
1. Panthera tigris
2. The binomial system of naming species means giving organisms
two names in Latin (scientific names)

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Unit 5 The Study of Genes and Chromosomes

Unit Structure

5.1 Introduction
5.2 Intended Learning Outcomes (ILOs)
4.3 Study of Genes and Chromosomes
5.3.1 Proteins and DNA
5.3.2 Structure of DNA
5.4 Synthesizing Proteins
5.5 Gene replication and Mutations
5.6 Summary
5.7 References/Further Readings/Web Sources
5.8 Possible Answers to Self-Assessment Exercises

5.1 Introduction

In this unit we shall highlight the occurrence and significance of genes

and chromosomes. The contribution of proteins and DNA in heredity
will be explained. You will learn about the structure of DNA and be able
to explain the process of synthesizing proteins. You will also learn the
process of gene replication and mutations, coding, transcription and
translation, and the control of gene expression

5.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• Describe the occurrence and significance of genes and

chromosomes
• Describe proteins and the structure of DNA
• Explain the synthesizing proteins
• Describe the process of gene replication and mutations
• Explain the meaning of coding, transcription and translation, and
the control of gene expression

5.3 The Study of Genes and Chromosomes

Deoxyribonucleic acid (DNA) segments called genes are responsible for

carrying out specified protein functions in one or more types of bodily
cells. The sizes of the proteins that genes code for determine the size of
the genes. Chromosomes, found in the cell nucleus, are where genes are
found. Any characteristic that is influenced by more than one gene is
called a trait. Some features are brought about by mutated genes, either
ones that are passed down from parents or ones that arise from new gene
mutations. A person's genotype (or genome) is their particular set of

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genes or genetic make-up. As a result, the genotype has a

comprehensive set of instructions for how that person's body should
synthesise proteins, and consequently, how their body should be
constructed and operate. The physical makeup and capabilities of an
individual make up their phenotype. Not all the instructions in the
genotype may be followed out, and the phenotype is how the genotype
manifests in an individual (or expressed). The environment (including
sicknesses and diet) and other factors, some of which are unknown, as
well as the genotype affect how a gene is expressed. The structures
called chromosomes found in cells house a person's genes. Each cell in
the human body normally contains 46 chromosomes; two sex
chromosomes and twenty-two pairs of autosomes.

There are between 20,000 and 25,000 genes on these chromosomes, new
genes being discovered on daily basis. According to size, the paired
chromosomes are numbered from 1 to 22. (The largest chromosome is
number one.) Autosomes are the name for these non-sex chromosomes,
each chromosome typically has two copies in an individual. Their
mother passes one copy on to them through the egg, while their father
passes the other one along (via the sperm). Each egg and sperm have a
single set of 23 chromosomes. Two copies of each chromosome and two
copies of each gene are present when the sperm fertilises the egg,
resulting in the formation of an embryo. Sex chromosomes are the X and
Y chromosomes, which are responsible for a baby's sex. An X
chromosome is typically contributed by the mother's egg, and either an
X or a Y chromosome is contributed by the father's sperm. The
biological gender of a person with a XX pairing of sex chromosomes is
female, while the biological gender of a person with an XY pairing is
male. The sex chromosomes contain genes that regulate numerous
bodily activities in addition to determining sex. Fewer genes are found
on the Y chromosome than there are on the X chromosome. The term
"X-linked" refers to genes that are located on the X chromosome. Y-
linked genes are those that reside on the Y chromosome. A karyotype is
a representation of a person's entire chromosomal set as seen in their
cells.

5.3.1 Proteins and DNA

The most significant class of substance in the body is likely proteins.

Proteins serve as more than only the building blocks for skin, connective
tissue, muscles, and other organs. The production of enzymes also
requires them. Nearly all chemical reactions and functions in the body
are controlled and carried out by sophisticated proteins called enzymes.
There are thousands of distinct enzymes that the body makes. As a
result, the kinds and quantities of proteins the body synthesises control
the overall structure and operation of the body. Genes, which are found

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on chromosomes, regulate the production of proteins. There is

deoxyribonucleic acid in genes (DNA). The instructions, or blueprint,
needed to synthesise a protein are found in DNA. Each DNA molecule
is a lengthy double helix with millions of steps, resembling a spiral
staircase. The steps of the staircase consist of pairs of four types of
molecules called bases (nucleotides). In each step, the base adenine (A)
is paired with the base thymine (T), or the base guanine (G) is paired
with the base cytosine (C). Each extremely long DNA molecule is coiled
up inside one of the chromosomes.

5.3.2 Structure of DNA

The genetic substance of the cell is DNA (deoxyribonucleic acid), which

is found in chromosomes within the cell nucleus and mitochondria. The
nucleus of every cell includes 23 pairs of chromosomes, with the
exception of some cells (such as sperm and egg cells and red blood
cells). Many genes are found on one chromosome. A gene is a section of
DNA that contains the instructions needed to build a protein. The DNA
molecule is a lengthy, double-helix structure that coils around itself like
a spiral staircase. In it, bases—pairs of four molecules that make up the
staircase's steps—connect two strands of sugar (deoxyribose) and
phosphate molecules. In the process, guanine and cytosine are coupled
with adenine and thymine, respectively. A hydrogen bond holds each
pair of bases together. A gene consists of a sequence of bases.
Sequences of three bases code for an amino acid (building blocks of
proteins) or other information.

Fig. 1. The structure of DNA Source: www.byjus.com

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Self-Assessment Exercises 1
1. What are Genes?
2. What is deoxyribonucleic acid?

5.4 Protein Synthesis

A lengthy chain of consecutively linked amino acids makes up proteins.

There are 20 different amino acids that can be used to make proteins;
some must be obtained through diet (essential amino acids), while others
are produced by the body's own enzymes. A chain of amino acids forms
a complicated three-di5.mensional shape when it folds in on itself during
synthesis. The function of the folded structure in the body is determined
by its shape. Every individual sequence produces a different protein
because the specific sequence of amino acids controls how the protein
folds. Some proteins, such as haemoglobin, have many folded chains in
them. DNA contains codes that specify how to make proteins.

5.4.1 Coding, Transcription and Translation

The order of the bases (A, T, G, and C) in DNA serves as a code for
information. Triplets are used to write the programme. In other words,
the bases are placed in three-base groups. DNA codes for precise
instructions, such as the insertion of one amino acid to a chain, using
specific three-base sequences. For example, the addition of the amino
acid, alanine is coded for by GCT (guanine, cytosine, thymine), and the
addition of the amino acid, valine is coded for by GTT (guanine,
thymine, thymine). As a result, the arrangement of triplet base pairs in
the gene for a protein on the DNA molecule determines the order of
amino acids in that protein. Transcription and translation are required for
the conversion of genetic information encoded in a protein.

The process of transcription involves transferring (transcription) data

encoded in DNA to ribonucleic acid (RNA). Similar to a strand of DNA
is RNA, a lengthy chain of bases, except that the base uracil (U) is used
instead of the base thymine (T). So, like DNA, RNA carries triplet-
coded information too.

A portion of the DNA double helix opens and unwinds when

transcription starts. A complementary strand of RNA is created using
one of the unwound DNA strands as a template. The name of the RNA's
complementary strand being messenger RNA (mRNA). The mRNA
dissociates from the DNA, leaves the nucleus, and enters the cytoplasm
of the cell, and connect to the ribosome, a small cell structure where
protein synthesis takes place. The mRNA coding (from the DNA)

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instructs the ribosome how and what kind of amino acids to bind with
during translation. An RNA subtype known as transfer RNA (tRNA),
which is much smaller, transports the amino acids to the ribosome. One
amino acid is added by each tRNA molecule to the expanding protein
chain, which is folded into a complicated three-dimensional structure by
the action of neighbouring molecules known as chaperone molecules.

5.4.2 Control of Gene Expression

A person's body contains a variety of cells which cells have varied

appearances, behaviours, and chemical outputs. However, because each
cell is descended from a single fertilised egg cell, they all have the same
DNA. However, since different genes are expressed in different cells,
cells have extremely distinct looks and activities. DNA also contains
codes that specify when a gene should be expressed. The kind of tissue,
the individual's age, the availability of particular chemical signals, and a
variety of other factors and methods all affect how genes are expressed.
Although our understanding of these additional factors and mechanisms
that regulate gene expression is rapidly expanding, many of them remain
poorly understood. The processes by which genes regulate one another
are extremely intricate. Chemical markers in genes serve as start and
stop signals for transcription. Numerous chemicals in and around the
DNA including histones either prevent or allow transcription. In
addition, translation can be stopped by pairing with a complementary
strand of mRNA known as antisense RNA.

Cells divide into two to reproduce. When a cell divides, the DNA
molecules in the original cell must replicate themselves because each
new cell needs a full set of DNA molecules. Replication also involves
the double-stranded DNA molecule unwinding and splitting in two.
Following the splitting, bases on each strand bind to floating
complementary bases (A with T and G with C). Two identical double-
strand DNA molecules result from this procedure.

5.3.3 Gene replication and Mutations

Cells feature a "proofreading" mechanism helps to make sure that bases

are matched correctly in order to prevent errors during replication.
Chemical processes are also available to fix improperly duplicated
DNA. However, errors could occur due to the complexity of the protein
synthesis process and the billions of base pairs that are involved. Such
errors may happen from a variety of causes such as exposure to
radiation, medications, or infections, or seemingly for no reason at all.
Majority of people have extremely little variances in their DNA.
Mutations are errors that appear twice in successive copies. Mutations
that are passed on to offspring are referred to as inherited mutations.

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Majority of mutations have little impact on the gene's subsequent copies.

The majority of mutations have little impact on the gene's subsequent
copies. The mutation could modify the amino acid sequence in a protein
or reduce the amount of protein generated, depending on its size and
position. A protein may operate differently or not at all if it has a
different amino acid sequence. Proteins that are missing or dysfunctional
are frequently damaging or lethal. For example, phenylalanine
hydroxylase is deficient or absent in phenylketonuria due to a mutation.
This defect enables the body to accumulate the amino acid
phenylalanine, which is consumed through food, leading to severe
intellectual impairment. Rarely does a mutation bring about a beneficial
alteration. For example, if a person receives two copies of the defective
sickle cell genes, he would experience sickle cell disease. However, a
person who has only one copy of the sickle cell gene (a carrier) obtains
some immunity against malaria. Sickle cell disease generates symptoms
and problems that may limit life span, even though the immunity against
malaria can help a carrier survive.

According to the theory of natural selection, mutations that reduce

survival in a particular environment are less likely to be passed on to
children (and thus reduce in frequency in the population), but mutations
that increase survival gradually increase the frequency. Thus, beneficial
mutations, although initially rare, eventually become common. The slow
changes that occur over time caused by mutations and natural selection
in an interbreeding population collectively are called evolution.

Self-Assessment Exercises 2

1. What is Transcription?
2. What are the factors controlling gene expression?

5.5 General Reproduction

In general, reproduction is one of the most

important concepts in biology: it means making a copy, a likeness, and
thereby providing for the continued existence of species. Although
reproduction is often considered solely in terms of the production of
offspring in animals and plants, the more general meaning has far
greater significance to living organisms. To appreciate this fact, the
origin of life and the evolution of organisms must be considered. One of
the first characteristics of life that emerged in primeval times must have
been the ability of some primitive chemical systems to make copies of
themselves, thus its lowest level, reproduction is chemical replication.
As evolution progressed, cells of successively higher levels
of complexity must have arisen, and it was absolutely essential that they

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had the ability to make likenesses of themselves. In unicellular

organisms, the ability of one cell to reproduce itself means the
reproduction of a new individual; in multicellular organisms, however, it
means growth and regeneration. Multicellular organisms also reproduce
in the strict sense of the term—that is, they make copies of themselves
in the form of offspring—but they do so in a variety of ways, many
involving complex organs and elaborate hormonal mechanisms. There
are several levels of reproduction: Molecular replication and
reproduction, Cell Reproduction, Reproduction of organisms, Life cycle
Reproduction.

5.3.1 Molecular replication and reproduction

The characteristics that an organism inherits are largely stored in cells as

genetic information in very long molecules of deoxyribonucleic acid
(DNA). In 1953 it was established that DNA molecules consist of
two complementary strands, each of which can make copies of the other.
The strands are like two sides of a ladder that has been twisted along its
length in the shape of a double helix (spring). The rungs, which join the
two sides of the ladder, are made up of two terminal bases. There are
four bases in DNA: thymine, cytosine, adenine, and guanine. In the
middle of each rung a base from one strand of DNA is linked by
a hydrogen bond to a base of the other strand. However, they can pair
only in certain ways: adenine always pairs with thymine, and guanine
with cytosine. This is why one strand of DNA is considered
complementary to the other.

The double helices duplicate themselves by separating at one place

between the two strands and becoming progressively unattached. As one
strand separates from the other, each acquires new complementary bases
until eventually each strand becomes a new double helix with a new
complementary strand to replace the original one. Because adenine
always falls in place opposite thymine and guanine opposite cytosine,
the process is called a template replication—one strand serves as the
mold for the other. The steps involving the duplication of DNA thus do
not occur spontaneously; they require catalysts in the form of enzymes
that promote the replication process.

In Molecular reproduction, the sequence of bases in a

DNA molecule serves as a code by which genetic information is stored.
Using this code, the DNA synthesizes one strand of ribonucleic acid
(RNA), a substance that is so similar structurally to DNA that it is also
formed by template replication of DNA. mRNA serves as
a messenger for carrying the genetic code to those places in the cell
where proteins are synthesized. The way by which the mRNA is
translated into specific proteins is a remarkable and complex process.

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For more detailed information concerning DNA, RNA, and the genetic
code, see the articles nucleic acid and heredity: Chromosomes and
genes. The ability to synthesize enzymes and other proteins enables the
organism to make any substance that existed in a previous generation.
Proteins are reproduced directly; however, other substances such as
carbohydrates, fats, and other organic molecules found in cells are
produced by a series of enzyme-controlled chemical reactions, each
enzyme being derived originally from DNA through mRNA. It is
because all the organic constituents made by organisms are derived
ultimately from DNA that molecules in organisms are reproduced
exactly by each successive generation.

5.3.2 Cell Reproduction

The chemical constituents of the cytoplasm are not resynthesized from

DNA every time a cell divides. This is because each of the two daughter
cells formed during cell division usually inherits about half of the
cellular material from the mother cell, and is important because the
presence of essential enzymes enables DNA to replicate even before it
has made the enzymes necessary to do so. Cells of higher organisms
contain complex structures, and each time a cell divides the structures
must be duplicated. The method of duplication varies for each structure,
and in some cases the mechanism is still uncertain. One striking and
important phenomenon is the formation of a new membrane. Cell
membranes, although they are very thin and appear to have a simple
form and structure, contain many enzymes and are sites of great
metabolic activity. This applies not only to the membrane that surrounds
the cell but to all the membranes within the cell. New membranes,
which seem to form rapidly, are indistinguishable from old ones. Thus,
the formation of a new cell involves the further synthesis of many
constituents that were present in the parent cell. This means that all of
the information and materials necessary for a cell to reproduce itself
must be supplied by the cellular constituents and the DNA inherited
from the parent cell.

Binary fission
Of the various kinds of cell division, the most common mode is binary
fission, the division of a cell into two separate and similar parts.
In bacteria (prokaryotes) the chromosome (the body that contains
the DNA and associated proteins) replicates and then divides in two,
after which a cell wall forms across the elongated parent cell. In higher
organisms (eukaryotes) there is first an elaborate duplication and then a
separation of the chromosomes (mitosis), after which
the cytoplasm divides in two. In the hard-walled cells of higher plants, a
median plate forms and divides the mother cell into two compartments;
in animal cells, which do not have a hard wall, a delicate membrane

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pinches the cell in two, much like the separation of two liquid
drops. Budding yeast cells provide an interesting exception. In these
fungi the cell wall forms a bubble that becomes engorged with
cytoplasm until it is ultimately the size of the original cell. The nucleus
then divides, one of the daughter nuclei passes into the bud, and
ultimately the two cells separate.
In some cases of binary fission, there may be an unequal cytoplasmic
division with an equal division of the chromosomes. This occurs in a
large number of higher organisms during meiosis—the process by
which sex cells (gametes) are formed: originally, each chromosome of
the cell is in a pair (diploid); during meiosis these diploid pairs of
chromosomes are separated so that each sex cell has only one of each
pair of chromosomes (haploid). During the two successive meiotic
divisions involved in the production of eggs,
a primordial diploid egg cell is converted into a haploid egg and three
small haploid polar bodies (minute cells). In this instance the egg
receives far more cytoplasm than the polar bodies.

Multiple fission
Some algae, protozoans, and true slime molds (Myxomycetes) regularly
divide by multiple fission. In such cases the nucleus undergoes several
mitotic divisions, producing a number of nuclei. When the nuclear
divisions are complete, the cytoplasm separates, and each nucleus
becomes encased in its own membrane to form an individual cell. In the
Myxomycetes, the fusion of two haploid gametes or the fusion of two or
more diploid zygotes (the structures that result from the union of two
sex cells) results in the formation of a plasmodium—a motile,
multinucleate mass of cytoplasm. The nuclei are in a syncytium, that is,
there are no cell boundaries, and the nuclei flow freely in the motile
plasmodium. As it feeds, the plasmodium enlarges, and the nuclei divide
synchronously about once every 24 hours. The plasmodium may
become very large, with millions of nuclei, but, ultimately, when
conditions are right, it forms a series of small bumps, each of which
becomes a small, fruiting body (a structure that bears the spores). During
this process the nuclei undergo meiosis, and the final haploid nuclei are
then isolated into uninucleate spores (reproductive bodies).

Many algae (eg. the Siphonales and related groups) are multinucleate. In
most cases, the nuclei are in one common cytoplasm within a large and
elaborate organism surrounded by a hard cell wall. As the wall becomes
extended, the nuclei, which wander freely in the central cavity, undergo
repeated mitoses. Again, either during the formation
of zoospores (asexual reproductive cells) or after meiosis
(gamete formation), a massive progressive division occurs. The most
unusual of such organisms is the marine alga, Acetabularia; many nuclei
stay clumped together in one compound nucleus in the rootlike base,

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which often is as much as two inches (five centimetres) away from the
tip of the plant. The compound nucleus breaks up just before gamete
formation, and the minute individual nuclei undergo meiosis and wander
to the elaborate tip structures, where they are released as uninucleate
gametes.
Syncytial organisms raise the question of whether or not cells, in the
strict sense, are necessary for the development of large organisms.
Syncytia are also found in animals—e.g., in the early stages of
development of fishes and insects, and in the voluntary muscles of man.
The proposal of the 19th-century botanist Julius von Sachs is generally
considered a satisfactory answer to this question; he suggested that the
important matter was the existence not of a cell membrane but of a
certain amount of cytoplasm surrounding a nucleus and acting as a unit
of metabolism, which he called an energid. Cell reproduction, therefore,
might be considered a special case of energid reproduction. What is the
role of the sequence of bases in a DNA molecule?

Self-Assessment Exercises 3
1. What is Binary fission?
2. Why is it that the chemical constituents of cytoplasm are not
resynthesized from DNA every time a cell divides?

5.6 Summary

You must have learned about the meaning and significance of genes and
chromosomes in the body of organisms. The contribution of proteins
and DNA in heredity, and process of synthesizing proteins was
explained. You have also learned about the structure of DNA, the
process of gene replication and mutations, coding, transcription and
translation, and the control of gene expression in organisms.

5.7 References/Further Readings/Web Sources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp

Putman, R.J. and S.D. Wratten (1984). Principles of Ecology,

Publisher Springer Dordrecht, eBook PackagesSpringer Book
Archive, DOIhttps://doi.org/10.1007, /978-94-011- 6948-6,
eBook ISBN978-94- 011-6948-6. 388pp
https://www.britannica.com/science/taxonomy/A-classification-of-
living-organisms

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https://www.nust.na/sites/default/files/documents/classification%20of%
20living%20things.pdf
https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/gen
es-and-genetics
https://www.youtube.com/watch?v=R61GoO8j048
https://www.youtube.com/watch?v=sFMv7Gdryc0
https://www.youtube.com/watch?v=z8znhBuIwr4

5.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Genes are segments of deoxyribonucleic acid (DNA) that contain
the code for a specific protein that functions in one or more types
of cells in the body hormosomes
2. DNA (deoxyribonucleic acid) is the cell’s genetic material,
contained in chromosomes within the cell nucleus and
mitochondria.

Answers to SAE 2
1. Transcription is the process in which information coded in DNA
is transferred (transcribed) to ribonucleic acid (RNA)
2. Gene expression depends on the type of tissue, the age of the
person, the presence of specific chemical signals, and numerous
other factors and mechanisms.

Answers to SAE 3
1. Of the various kinds of cell division, the most common mode is
binary fission, the division of a cell into two separate and similar
parts.
2. This is because each of the two daughter cells formed during cell
division usually inherits about half of the cellular material from
the mother cell, and is important because the presence of essential
enzymes enables DNA to replicate even before it has made the
enzymes necessary to do so.

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Unit 6 Reproduction Process and Life cycles

Unit Structure

6.1 Introduction
6.2 Intended Learning Outcomes (ILOs)
6.3 Reproduction Process and Molecular Replication
6.4 Cell reproduction
6.5 Life cycles
6.6 Summary
6.7 References/Further Readings/Web Sources
6.8 Possible Answers to Self-Assessment Exercises

6.1 Introduction

In this unit you will learn about reproduction, a process by which

organisms replicate themselves in both unicellular and multicellular
organisms, study about the differences in reproduction between
organisms. You will learn about cell reproduction and life cycles

You will also learn about the number of cells in our bodies in this unit,
and the two ways in which cells divide—mitosis and meiosis, and cell
cycles. In addition, you will learn how cells regulate their division by
communicating.

6.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you will be able to:

• Explain and describe the meaning and process of reproduction in

both unicellular and multicellular organisms.
• Differentiate between Binary fission and Multiple fission
• Describe the cell reproduction and life cycles
• Describe animal and plant life cycles
• Explain the meaning of natural selection
• Illustrate and describe the Mitosis and Meiosis divisions and Cell
Cycles
• Recognize the function and products of mitosis and meiosis
• Compare and contrast the behaviors of chromosomes in mitosis
and meiosis
• Recognize when cells are diploid vs. haploid
• Predict DNA content of cells in different phases of mitosis and
meiosis
• Recall and describe the phases of the cell cycle

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6.3 Reproduction of organisms

In single-celled organisms (e.g., bacteria, protozoans, many algae, and

some fungi), organismic and cell reproduction are synonymous, for
the cell is the whole organism. Details of the process differ greatly from
one form to another and, if the higher ciliate protozoans are included,
can be extraordinarily complex. It is possible for reproduction to
be asexual, by simple division, or sexual. In sexual unicellular
organisms the gametes can be produced by division (often multiple
fission, as in numerous algae) or, as in yeasts, by the organism turning
itself into a gamete and fusing its nucleus with that of a neighbour of the
opposite sex, a process that is called conjugation. In ciliate protozoans
(eg., Paramecium), the conjugation process involves the exchange of
haploid nuclei; each partner acquires a new nuclear apparatus, half of
which is genetically derived from its mate. The parent cells separate and
subsequently reproduce by binary fission. Sexuality is present even in
primitive bacteria, in which parts of the chromosome of one cell can be
transferred to another during mating.

Multicellular organisms also reproduce asexually and sexually; asexual,

or vegetative, reproduction can take a great variety of forms. Many
multicellular lower plants give off asexual spores, either aerial, motile or
aquatic (zoospores), which may be uninucleate or multinucleate. In
some cases, the reproductive body is multicellular, as in the soredia of
lichens and the gemmae of liverworts. Frequently, whole fragments of
the vegetative part of the organism can bud off and form a new
individual, a phenomenon found in most plant groups. In many cases a
spreading rhizoid (rootlike filament) or, in higher plants,
a rhizome (underground stem) gives off new sprouts. Sometimes, other
parts of the plant have the capacity to form new individuals; for
example, buds of potentially new plants may form in the leaves; even
some shoots that bend over and touch the ground can give rise to new
plants at the point of contact.

Among animals, many invertebrates are equally well endowed with

means of asexual reproduction. Numerous species of sponges produce
gemmules, masses of cells enclosed in resistant cases, that can become
new sponges. There are many examples of budding among
coelenterates, the best known of which occurs in freshwater Hydra. In
some species of flatworms, the individual worm can duplicate by
pinching in two, each half then regenerating the missing half; this is a
large task for the posterior portion, which lacks most of the major
organs; brain, eyes, and pharynx. The largest animals that
exhibit vegetative reproduction are the colonial tunicates (e.g., sea
squirts), which, just like plants, send out runners in the form of stolons,
small parts of which form buds that develop into new

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individuals. Vertebrates have lost the ability to reproduce vegetatively;

their only form of organismic reproduction is sexual. In the sexual
reproduction of all organisms except bacteria, there is one common
feature: haploid, uninucleate gametes are produced that join
in fertilization to form a diploid, uninucleate zygote. At some later stage
in the life cycle of the organism, the chromosome number is again
reduced by meiosis to form the next generation of gametes. The gametes
may be equal in size (isogamy), or one may be slightly larger than the
other (anisogamy); the majority of forms have a large egg and a
minute sperm (oogamy). The sperm are usually motile and the egg
passive, except in higher plants, in which the sperm nuclei are carried in
pollen grains that attach to the stigma (a female structure) of the flower
and send out germ tubes that grow down to the egg nucleus in the ovary.
Some organisms, like most flowering plants, earthworms, and tunicates,
are bisexual (hermaphroditic, or monoecious)—i.e., both male and
female gametes are produced by the same individual. All other
organisms, including some plants (eg., holly and the ginkgo tree) and all
vertebrates, are unisexual (dioecious): the male and female gametes are
produced by separate individuals. Some sexual organisms partially
revert to the asexual mode by a periodic degeneration of the sexual
process. For example, in aphids and in many higher plants the egg
nucleus can develop into a new individual without fertilization, a kind of
asexual reproduction that is called parthenogenesis.

Self-Assessment Exercises 1
1. How is sexuality in primitive bacteria?
2. Give example of a condition where some sexual organisms
partially revert to the asexual mode by a periodic degeneration of
the sexual process.

6.4 Life Cycle of Organisms

A series of changes that members of a species undergo as they pass from

the beginning of a given developmental stage to the inception of that
same developmental stage in a subsequent generation is called life cycle.

1. Animals Life Cycle

Invertebrate animals have a rich variety of life cycles, especially among
those forms that undergo metamorphosis, a radical physical
change. Butterflies, for eg. have a caterpillar stage (larva), a dormant
chrysalis stage (pupa), and an adult stage (imago). One remarkable
aspect of this development is that, during the transition from caterpillar
to adult, most of the caterpillar tissues disintegrate and are used as food,
thereby providing energy for the next stage of development, which
begins when certain small structures (imaginal disks) in the larva start

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growing into the adult form. Thus, the butterfly undergoes essentially
two periods of growth and development (larva and pupa–adult) and two
periods of small size (fertilized egg and imaginal disks). A somewhat
similar phenomenon is found in sea urchins; the larva, which is called
a pluteus, has a small, wartlike bud that grows into the adult while the
pluteus tissue disintegrates. In both examples it is as if the organism has
two life histories, one built on the ruins of another.

Another life-cycle pattern found among certain invertebrates illustrates

the principle that major differences between organisms are not always
found in the physical appearance of the adult but in the differences of
the whole life cycle. In the coelenterate Obelia, for example, the egg
develops into a colonial hydroid consisting of a series of
branching Hydra-like organisms called polyps. Certain of these polyps
become specialized (reproductive polyps) and bud off from the colony
as free-swimming jellyfish (medusae) that bear eggs and sperm. As with
caterpillars and sea urchins, two distinct phases occur in the life
cycle of Obelia: the sessile (anchored), branched polyps and the motile
medusae. In some related coelenterates the medusa form has been totally
lost, leaving only the polyp stage to bear eggs and sperm directly. In still
other coelenterates the polyp stage has been lost, and the medusae
produce other medusae directly, without the sessile stage. There are
furthermore, intermediate forms between the extremes.

2. Plants Life Cycle

Most life cycles, except perhaps for the simplest and smallest organisms,
consist of different epochs. A large tree has a period of seed formation
that involves many cell divisions after fertilization and the laying down
of a small embryo in a hard resistant shell, or seed coat. There then
follows a period of dormancy, sometimes prolonged, after which the
seed germinates, and the adult form slowly emerges as the shoots and
roots grow at the tips and the stem thickens. In some trees, the leaves of
the juvenile plant have a shape that is quite different from that of the
taller, more mature individuals. Thus, even the growth phase may be
subdivided into epochs, the final one being the flowering or gamete
bearing period. Some of the parasitic fungi have much more complex
life cycles. The wheat rust parasite, for example, has alternate hosts.
While living on wheat, it produces two kinds of spores; it produces a
third kind of spore when it invades its other host, the barberry, on which
it winters and undergoes the sexual part of its life cycle.

In plants, variations in the epochs of the life cycle are often centred
around the times of fertilization and meiosis. After fertilization, the
organism has the diploid number of chromosomes (diplophase); after
meiosis it is haploid (haplophase). The two events vary in time with
respect to each other. In some simple algae eg. Chlamydomonas, most

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of the cycle is haploid; meiosis occurs immediately after fertilization.

Yet in other algae, such as the sea lettuce (Ulva), two equal haploid and
diploid cycles alternate. The outward morphological structures of
mature Ulva are indistinguishable; the two cycles can
be differentiated only by the size of the cell or nucleus, those of the
haploid stage being half the size of those of the diploid stage.

In many of the higher algae, there is a progressive diminution of the

haplophase and an increase in the importance of the diplophase, a trend
that is especially noticeable in the evolution of the vascular plants
(e.g., ferns, conifers, and flowering plants). In mosses, the haplophase,
or gametophyte, is the main part of the green plant; the diplophase, or
sporophyte, usually is a sporebearing spike that grows from the top of
the plant. In ferns, the haplophase is reduced to a small, inconspicuous
structure (prothallus) that grows in the damp soil; the large spore-
bearing fern itself is entirely diploid. Finally, in higher plants the
haploid tissue is confined to the ovary of the large diploid organism, a
condition that is also prevalent in most animals.

3. Natural selection and reproduction

The significance of biological reproduction can be explained entirely by
natural selection. In formulating his theory of natural selection, Charles
Darwin realized that, in order for evolution to occur, not only must
living organisms be able to reproduce themselves but the copies must
not all be identical; that is, they must show some variation. In this way
the more successful variants would make a greater contribution to
subsequent generations in the number of offspring. For such selection to
act continuously in successive generations, Darwin also recognized that
the variations had to be inherited, although he failed to fathom the
mechanism of heredity. Moreover, the amount of variation is
particularly important. According to what has been called the principle
of compromise, which itself has been shaped by natural selection, there
must not be too little or too much variation: too little produces no
change; too much scrambles the benefit of any particular combination of
inherited traits.

Of the numerous mechanisms for controlling variation, all of which

involve a combination of checks and balances that work together, the
most successful is that found in the large majority of all plants and
animals—ie., sexual reproduction. During the evolution of reproduction
and variation, which are the two basic properties of organisms that not
only are required for natural selection but are also subject to it, sexual
reproduction has become ideally adapted to produce the right amount of
variation and to allow new combinations of traits to be rapidly
incorporated into an individual.

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4. The Evolution of Reproduction

An examination of the way in which organisms have changed since their
initial unicellular condition in primeval times shows an increase in
multicellularity and therefore an increase in the size of both plants and
animals. After cell reproduction evolved into multicellular growth,
the multicellular organism evolved a means of reproducing itself that is
best described as life-cycle reproduction. Size increase has been
accompanied by many mechanical requirements that have necessitated a
selection for increased efficiency; the result has been a great increase in
the complexity of organisms. This means a great increase in the
permutations of cell reproduction during the process of evolutionary
development.

Size increase also means a longer life cycle, and with it a

great diversity of patterns at different stages of the cycle. This is because
each part of the life cycle is adaptive in that, through natural selection,
certain characteristics have evolved for each stage that enable the
organism to survive. The most extreme examples are those forms with
two or more separate phases of their life cycle separated by
a metamorphosis, as in caterpillars and butterflies; these phases may be
shortened or extended by natural selection, as has occurred in
different species of coelenterates.

To reproduce efficiently in order to contribute effectively to subsequent

generations is another factor that has evolved through natural selection.
For example, an organism can produce vast quantities of eggs of which,
possibly by neglect, only a small percent will survive. On the other
hand, an organism can produce very few or perhaps one egg, which, as it
develops, will be cared for, thereby greatly increasing its chances for
survival. These are two strategies of reproduction; each has its
advantages and disadvantages. Many other considerations of the natural
history and structure of the organism determine, through natural
selection, the strategy that is best for a particular species; one of these is
that any species must not produce too few offspring (for it will become
extinct) or too many (for it may also become extinct
by overpopulation and disease). The numbers of some organisms
fluctuate cyclically but always remain between upper and lower limits.
The question of how, through natural selection, numbers of individuals
are controlled is a matter of great interest; clearly, it involves factors that
influence the rate of reproduction.

Self-Assessment Exercises 2
1. What is an organism’s life cycle?
2. What are the main stages of the life cycle of a typical plant?

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6.5 Body Cells

You and I began as a single cell, or what you would call an egg. By the
time you are an adult, you will have trillions of cells. That number
depends on the size of the person, but biologists put that number around
37 trillion cells. Yes, that is trillion with a "T." In cell division, the cell
that is dividing is called the "parent" cell. The parent cell divides into
two "daughter" cells. The process then repeats in what is called the cell
cycle.

Figure 6.1 Cell division of cancerous lung cell

Source: https://askabiologist.asu.edu/cell-division

Cells regulate their division by communicating with each other using

chemical signals from special proteins called cyclins. These signals act
like switches to tell cells when to start dividing and later when to stop
dividing. It is important for cells to divide so you can grow and your
cuts heal. It is also important for cells to stop dividing at the right
time. If a cell cannot stop dividing when it is supposed to stop, this can
lead to a disease called cancer. Some cells, like skin cells, are constantly
dividing. We need to continuously make new skin cells to replace the
skin cells we lose. Did you know we lose 30,000 to 40,000 dead skin
cells every minute? That means we lose around 50 million cells every
day. This is a lot of skin cells to replace, making cell division in skin
cells so important. Other cells, like nerve and brain cells, divide much
less often.

Depending on the type of cell, there are two ways cells divide—mitosis
and meiosis. Each of these methods of cell division has special
characteristics. One of the key differences in mitosis is a single cell
divides into two cells that are replicas of each other and have the same
number of chromosomes. This type of cell division is good for basic

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growth, repair, and maintenance. In meiosis a cell divides into four cells
that have half the number of chromosomes. Reducing the number of
chromosomes by half is important for sexual reproduction and provides
for genetic diversity.

6.5.1 Mitosis Cell Division

Mitosis is how somatic—or non-reproductive cells—divide. Somatic

cells make up most of your body's tissues and organs, including skin,
muscles, lungs, gut, and hair cells. Reproductive cells (like eggs) are not
somatic cells. In mitosis, the important thing to remember is that the
daughter cells each have the same chromosomes and DNA as the parent
cell. The daughter cells from mitosis are called diploid cells. Diploid
cells have two complete sets of chromosomes. Since the daughter cells
have exact copies of their parent cell's DNA, no genetic diversity is
created through mitosis in normal healthy cells.

Figure 6.2. Mitosis cell division creates two genetically identical

daughter diploid cells. The major steps of mitosis are shown here.
Source: https://askabiologist.asu.edu/cell-division

The Mitosis Cell Cycle

Interphase is the period when a cell is getting ready to divide and start
the cell cycle. During this time, cells are gathering nutrients and energy.
The parent cell is also making a copy of its DNA to share equally
between the two daughter cells. The mitosis division process has several
steps or phases of the cell cycle—interphase, prophase, prometaphase,
metaphase, anaphase, telophase, and cytokinesis—to successfully make
the new diploid cells.

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Figure 6.3 The mitosis cell cycle includes several phases that result in
two new diploid daughter cells. Each phase is highlighted here and
shown by light microscopy with fluorescence. Click on the image to
learn more about each phase.
Source: https://askabiologist.asu.edu/cell-division

When a cell divides during mitosis, some organelles are divided between
the two daughter cells. For example, mitochondria are capable of
growing and dividing during the interphase, so the daughter cells each
have enough mitochondria. The Golgi apparatus, however, breaks down
before mitosis and reassembles in each of the new daughter cells. Many
of the specifics about what happens to organelles before, during and
after cell division are currently being researched.

6.5.2 Meiosis Cell Division

Meiosis is the other main way cells divide. Meiosis is cell division that
creates sex cells, like female egg cells or male sperm cells. What is
important to remember about meiosis? In meiosis, each new cell
contains a unique set of genetic information. After meiosis, the sperm
and egg cells can join to create a new organism. Meiosis is why we
have genetic diversity in all sexually reproducing organisms. During
meiosis, a small portion of each chromosome breaks off and reattaches
to another chromosome. This process is called "crossing over" or
"genetic recombination." Genetic recombination is the reason full
siblings made from egg and sperm cells from the same two parents can
look very different from one another.

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Figure 6.4 The meiosis cell cycle has two main stages of division --
Meiosis I and Meiosis II. The end result of meiosis is four haploid
daughter cells that each contain different genetic information from each
other and the parent cell.
Source: https://askabiologist.asu.edu/cell-division

The Meiosis Cell Cycle

Meiosis has two cycles of cell division, conveniently called Meiosis I
and Meiosis II. Meiosis I halves the number of chromosomes and is also
when crossing over happens. Meiosis II halves the amount of genetic
information in each chromosome of each cell. The end result is four
haploid daughter cells. Haploid cells only have one set of chromosomes
- half the number of chromosomes as the parent cell. Before meiosis I
starts, the cell goes through interphase. Just like in mitosis, the parent
cell uses this time to prepare for cell division by gathering nutrients and
energy and making a copy of its DNA. During the next stages of
meiosis, this DNA will be switched around during genetic
recombination and then divided between four haploid cells. So
remember, Mitosis is what helps us grow and Meiosis is why we are all
unique!

Self-Assessment Exercises 3
1. Depending on the type of cell, what are the two ways cells
divides?
2. How do cells regulate their division?

6.6 Summary

You have learned about the meaning and process of reproduction in both
unicellular and multicellular organisms, which at the lowest level, is a
chemical replication and in multicellular organisms, however, means
growth and regeneration. You have studied about the differences
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between Binary fission and Multiple fission. The life cycles of animals
and plants has also been highlighted as invertebrate animals have a rich
variety of life cycles, especially among those forms that
undergo metamorphosis, a radical physical change and in vascular plants
, they have a period of seed formation that involves many cell divisions
after fertilization and the laying down of a small embryo in a hard
resistant shell or seed coat. You have also learned about the
chromosomal makeup of a cell using the terms chromosome, sister
chromatid, homologous chromosome, diploid, haploid, and tetrad. The
unit also highlighted the function and products of mitosis and meiosis,
this has enabled for the comparison of the behaviors of chromosomes.

6.7 References/Further Readings/Web Sources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp

Thomas, S. and Robert, S. (2018). Elements of Ecology 9th Edition,

Pearson

https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/gen
es-and-genetics
https://www.genome.gov/genetics-
glossary/Mutation#:~:text=A%20mutation%20is%20a%20change,muta
gens%20or%20a%20viral%20infection.
https://www.nationalgeographic.org/encyclopedia/natural-selection/
https://bioprinciples.biosci.gatech.edu/module-4-genes-and-genomes/4-
1-cell-division-mitosis-and-meiosis/
Wikimedia. https://commons.wikimedia.org/wiki/File:Movie_4._Cell_di
vision.ogv(link is external)
https://www.youtube.com/watch?v=BBI7GoIyoog
https://www.youtube.com/watch?v=k-4nrrMmNfI
https://www.youtube.com/watch?v=yRLQKZzFb68
https://www.youtube.com/watch?v=w7vp_uRA8kw
https://www.khanacademy.org/science/ap-biology/heredity/meiosis-and-
genetic-diversity/v/phases-of-meiosis-ii

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6.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Sexuality is present even in primitive bacteria, in which parts of
the chromosome of one cell can be transferred to another during
mating.
2. Some sexual organisms such as in aphids and in many higher
plants partially revert to the asexual mode by a periodic
degeneration of the sexual process where the egg nucleus
develops into a new individual without fertilization, a kind of
asexual reproduction that is called parthenogenesis.

Answers to SAE 2

1. Organisms Life cycle is the series of changes that the members of

a species undergo as they pass from the beginning of a given
developmental stage to the inception of that same developmental
stage in a subsequent generation.
2. A large tree has a period of seed formation that involves many
cell divisions after fertilization and the laying down of a
small embryo in a hard resistant shell, or seed coat. There then
follows a period of dormancy, sometimes prolonged, after which
the seed germinates, and the adult form slowly emerges as the
shoots and roots grow at the tips and the stem thickens.

Answers to SAE 3
1. mitosis and meiosis
2. Cells regulate their division by communicating with each other
using chemical signals from special proteins called cyclins.

Glossary
Anaphase - a stage in mitosis where chromosomes begin moving to
opposite ends (poles) of the cell.

Animal Cells - eukaryotic cells that contain various membrane-bound

organelles.

Allele - an alternative form of a gene (one member of a pair) that is

located at a specific position on a specific chromosome.

Biology - the study of living organisms.

Cell - the fundamental unit of life.

Cell Biology - the subdiscipline of biology that focuses on the study of

the basic unit of life, the cell.

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Cell Cycle - the life cycle of a dividing cell, including Interphase and
the M phase or Mitotic phase (mitosis and cytokinesis).
Cell Membrane - a thin semi-permeable membrane that surrounds the
cytoplasm of a cell.

Cell Theory - one of the five basic principles of biology, stating that the
cell is the basic unit of life.

Centrioles - cylindrical structures that are composed of groupings of

microtubules arranged in a 9 + 3 pattern.

Centromere - a region on a chromosome that joins two sister chromatids.

Chromatid - one of two identical copies of a replicated chromosome.

Chromatin - the mass of genetic material composed

of DNA and proteins that condense to form chromosomes during
eukaryotic cell division.

Chromosome - a long, stringy aggregate of genes that carries heredity

information (DNA) and is formed from condensed chromatin.
Cilia and Flagella - protrusions from some cells that aid in cellular
locomotion.

Cytokinesis - the division of the cytoplasm that produces distinct

daughter cells.

Cytoplasm - all of the contents outside of the nucleus and

enclosed within the cell membrane of a cell.

Cytoskeleton - a network of fibers throughout the cell's cytoplasm that

helps the cell maintain its shape and gives support to the cell.

Cytosol - semi-fluid component of a cell's cytoplasm.

Daughter Cell - a cell resulting from the replication and division of a

single parent cell.

Diploid Cell - a cell that contains two sets of chromosomes—one set of

chromosomes is donated from each parent.

Endoplasmic Reticulum - a network of tubules and flattened sacs that

serve a variety of functions in the cell.

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Gametes - reproductive cells that unite during sexual reproduction to

form a new cell called a zygote.

Genes - segments of DNA located on chromosomes that exist in

alternative forms called alleles.

Golgi Complex - the cell organelle that is responsible for manufacturing,

warehousing, and shipping certain cellular products.

Haploid Cell - a cell that contains one complete set of chromosomes.

Interphase - the stage in the cell cycle where a cell doubles in size and
synthesizes DNA in preparation for cell division.

Lysosomes - the membranous sacs of enzymes that can digest

cellular macromolecules.

Meiosis - a two-part cell division process in organisms that sexually

reproduce, resulting in gametes with one-half the number of
chromosomes of the parent cell.

Metaphase - the stage in cell division where chromosomes align along

the metaphase plate in the center of the cell.

Microtubules - fibrous, hollow rods that function primarily to help

support and shape the cell.

Mitochondria - cell organelles that convert energy into forms that are
usable by the cell.

Mitosis - a phase of the cell cycle that involves the separation of nuclear
chromosomes followed by cytokinesis.

Nucleus - a membrane-bound structure that contains the cell's hereditary

information and controls the cell's growth and reproduction.

Organelles - tiny cellular structures, that carry out specific functions

necessary for normal cellular operation.

Peroxisomes - cell structures that contain enzymes that produce

hydrogen peroxide as a by-product.

Plant Cells - eukaryotic cells that contain various membrane-bound

organelles. They are distinct from animal cells, containing various
structures not found in animal cells.

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Polar Fibers - spindle fibers that extend from the two poles of a dividing
cell.

Prokaryotes - single-celled organisms that are the earliest and most

primitive forms of life on earth.

Prophase - the stage in cell division where chromatin condenses into

discrete chromosomes.

Ribosomes - cell organelles that are responsible for assembling proteins.

Sister Chromatids - two identical copies of a single chromosome that are
connected by a centromere.

Spindle Fibers - aggregates of microtubules that

move chromosomes during cell division.

Telophase - the stage in cell division when the nucleus of one cell is
divided equally into two nuclei.

End of Module Questions

1. Define a cell.
2. What are tissues? What are the basic tissues in humans?
3. Describe organ systems.
4. How many organ systems are in the human body?
5. Organisms can carry out all basic life processes. Explain this
sentence.
6. Describe the levels of organization of a complex, multicellular
organism
7. What is the cell structure and organization?
8. Outline some examples of cellular organization.
9. What are the types of cell organization?

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MODULE 3 INTERRELATIONSHIP BETWEEN

ORGANISMS

Module Structure

In this module we will discuss about the interrelationship between

organisms and the theories of evolution and natural selection. We shall
also study some basic elements of ecology

Unit 1 Interrelationship between organisms

Unit 2 Heredity and Variation
Unit 3 Introduction to Evolution
Unit 4 Natural selection
Unit 5 Elements of Ecology
Glossary
End of Module Questions

Unit 1 Interrelationship between organisms

Unit Structure

1.1 Introduction
1.2 Learning Outcomes
1.3 Concept of Interrelationship
1.4 Interactions Between Organisms
1.5 The Environment and the Organisms
1.6 Summary
1.7 References/Further Readings/Web Sources
1.8 Possible Answers to Self-Assessment Exercises

1.1 Introduction

You will learn in this unit that every organism is shaped by, and in turn
shapes its environment in its life and reproduction. You will also learn
that ecological scientists study organism-environment interactions
across ecosystems of all sizes, ranging from microbial communities to
the Earth as a whole.

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1.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• Recognize that every organism is shaped by, and in turn shapes

its environment in its life and reproduction.
• Explain the Concept of Interrelationship
• Describe how ecological scientists study organism-environment
interactions across ecosystems of all sizes, ranging from
microbial communities to the Earth as a whole.
• Describe the various interactions between organisms

1.3 Concept of Interrelationship

The diversity and scope of life on Earth is astounding, ranging from

microscopic viruses and bacteria that have gone unnoticed for millennia
to 200-ton blue whales and fungus that cover hundreds of hectares
underground. Inside a certain geographic area, within an ecological
community, entities reside in an assemblage of populations with at least
two different species that are constantly interacting with one another,
either directly or indirectly. Numerous biological processes in
ecosystems, such as the food chain and the nutrient cycle, are based on
interactions between species. These interactions take in many forms
depending on their surroundings and evolutionary history. These
interactions, which can be found in various ecosystems, can be
categorised in a number of ways. These interactions can be used as a
framework for ecological community analysis to characterise naturally
occurring processes, which can then be used to forecast human
adjustments that may affect the characteristics and processes of
ecosystems. These interactions might be intra-specific or inter-specific
(involving distinct species) (interactions between same species). The
environment is in a whirlwind with all living things. The organism
develops a certain kind of relationship with respect to resources; some
organisms compete with one another while others depend on one
another for survival. These traits are broken down into four categories:
parasitism, commensalism, predation, and mutualism. Both organisms
profit from a symbiotic connection. With commensalism, one organism
gains and the other is, in a sense, neutrally affected—neither aided nor
damaged. There are two forms of parasitic relationships: ectoparasites
and endoparasites, where one organism gains while the other suffers.
Predation occurs when one organism kills and consumes another. Some
species have extremely close symbiotic interactions with one another,
meaning that both of them depend on the other to survive.

Inside a certain geological region in a natural network, animals coexist

in a variety of populations that at least have two separate species that are

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constantly interacting with one another, either directly or indirectly.

Some organic processes in biological systems, such as the cycle of
nutrients and evolved forms of life, are shaped by interactions between
species. The concept behind these interactions depends on the
environmental factors and evolutionary perspectives that have led to
their existence. Different contexts have different ways of characterising
these interactions. These interactions can be used as a foundation for
breaking down the environmental network to show patterns that
naturally occur, which can then be used to predict changes made by
humans that might affect the characteristics and workings of biological
systems. These interactions might be intraspecific or specific (involving
different species) (interactions between same species). We will acquire
in-depth information on the various kinds of partnerships and
interactions between species in this unit. As an illustration, the cat
represents the predator and the bird is the prey. The predator is the cat,
one who kills and eats; the target is the bird, one who gets killed and
eaten. Any animal that hunts other organisms down, kills, and eats them
for survival is known as a predator. This process is called
predation. What do we refer the interactions between and within species
as?

Self-Assessment Exercises 1
1. What is a predator?
2. Upon what does the idea of species interactions rely on an
ecosystem?

1.4 Interactions Between Organisms

In a symbiotic connection known as parasitism, one organism gains

while the other suffers, and in certain cases, even perishes. Consider a
few instances: mosquitoes frequently attend picnics and consume food at
your cost. Some of the deadliest diseases that affect humans are spread
by mosquitoes. Thus, the mosquito eats, and you run the risk of being
ill. Ticks will behave similarly toward you, dogs, and even livestock.
When they begin to eat, they latch on to their hosts and spread a variety
of infections, including Lyme disease, to them. Leech, a segmented
worm that attaches to a host like you and feeds on your blood, is one of
many parasitic worms; They really release a chemical that stops the
blood from clotting. In addition to being crippling, if present in large
enough numbers, it may also be fatal.

Animals live in spaces known as niches. A niche is the area where an

organism lives, how it uses the resources in that area, and how it
interacts with other organisms there. Five different types of connections
can be used to describe how organisms interact inside or between

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overlapping niches: parasitism, commensalism, competition, predation,

and commensalism. Symbiotic connections are traditionally classified as
the last three kinds, but predation and competition are also examples of
symbiotic relationships. A close relationship in which one or both
organisms profit is referred to as symbiosis.

Competition and Predation

When one organism feeds on another to get nutrients, this is called
predation. The prey is the living thing that is consumed. Predators
include owls that consume mice and lions that consume gazelles.
Individuals or communities engaging in competition for the same
resource can be between or within species. Consumptive or exploitative
competition occurs when organisms compete for a resource (such food
or building materials). They engage in interference competition when
vying for territory. Preemptive competition is when two parties compete
for new territory by showing up first. The conflict between lions and
hyenas over prey is one example.

Commensalism
A relationship known as commensalism occurs when one organism
gains while the other is neither aided nor hurt. Examples are the
barnacles that develop on whales and other aquatic creatures. The
barnacle serves no purpose for the whale, but it gives the barnacles
greater movement, which enables them to avoid predators and exposes
them to a wider variety of eating options. Commensal relationships
come in four different fundamental varieties. When one bacterium
generates a chemical that supports another bacterium, this is known as
chemical commensalism. When one organism occupies a nest, burrow,
or place of residence of another species, this is known as inquilinism.
Commensalism that depends on another species for survival is known as
metabiosis. Phoresy is the temporary attachment of one organism to
another for the purpose of transportation.

Parasitism
In a connection known as parasitism, one organism gains and the other
is sometimes injured but not always killed. The parasite is the organism
that gains, and the host is the organism that suffers. When an organism
lays its egg inside of another organism, which is later consumed by the
hatchlings, this is known as parasitoidism, which is distinct from
parasitism because the host is always destroyed. Ectoparasites reside on
the host's surface eg. ticks, fleas, and leeches. Endoparasites, such as
intestinal worms, are another type of parasite that lives inside the host.
Endoparasites can also be divided into intracellular (which live inside
cells) and intercellular (which dwell between cells) parasites. There is
also something called hyperparasitism, a situation where a parasite is
infected by another parasite, such as a microorganism living in a flea,

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which lives on a dog. Lastly, a relationship called social parasitism is

exemplified by an ant species that does not have worker ants, living
among another ant species that do, by using the host species’ workers.

Mutualism
A partnership in which both species profit is known as mutualism. Three
types of mutualistic interaction patterns exist. When one organism
cannot thrive without the other, there is obligatory mutualism. When an
organism coexists with multiple partners, this is referred to as diffuse
mutualism. When one species can live on its own in specific
circumstances, this is known as facultative mutualism. Mutualistic
interactions also provide three other general goals. Lichens, which are
made up of either algae or cyanobacteria and fungi, are an excellent
example of trophic mutualism. The partners of the fungi produce sugar
through photosynthesis, while the fungi themselves provide nutrition by
breaking down rock. Ants and aphids are an example of a defensive
mutualism where one organism provides protection from predators
while the other provides food or refuge. Dispersive mutualism is when
one species receives food in return for transporting the pollen of the
other organism, which occurs between bees and flowers.

Self-Assessment Exercises 2
1. What is parasitism?
2. List the two types of parasites.

1.5 The Environment and the Organisms

The environment is dynamic because physical processes drive change in

Earth's attributes over time. However, research demonstrates that life
itself drives equally important environmental changes. Other organisms
being part of each individual’s environment, changes in species
distributions can profoundly alter ecological interactions within
communities. In some cases, the loss of a native species, or introduction
of a non-native one, can threaten the survival of other organisms. For
this reason, conservation of endangered organisms and control of
invasive species are of broad concern. Organisms inhabit nearly every
environment on Earth, from hot vents deep in the ocean floor to the icy
reaches of the Arctic. Each environment offers both resources and
constraints that shape the appearance of the species that inhabit it, and
the strategies these species use to survive and reproduce. Some of the
broadest patterns of environmental difference arise from the way our
planet orbits the Sun and the resulting global distribution of sunlight. In
the tropics, where solar radiation is plentiful year-round, temperatures
are warm, and plants may photosynthesize continuously as long as water
and nutrients are available. In polar regions, where solar radiation is

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seasonally limited, mean temperatures are much lower, and organisms

must cope with extended periods when photosynthesis ceases.

Across ecosystems, environmental resources and constraints shape the

structure and physiology of organisms. One of Earth’s oldest
environmental legacies is the array of chemical elements it contains. At
its birth, Earth inherited carbon atoms produced by stars that burned out
long before our sun was formed. These carbon atoms, with their unique
capacity to build chains and four-way links with other elements, provide
the backbone of all the organic molecules that make up life today.
Nitrogen and phosphorus are also essential elements in living organisms,
where they play central roles in the makeup of proteins, nucleic acids,
and energetic compounds. These elements are not always readily
available to organisms, so nutrient limitations can powerfully constrain
biological strategies. For example, inert nitrogen gas makes up 78% of
Earth’s atmosphere, but nitrogen forms readily useable by organisms are
typically much scarcer in terrestrial ecosystems. Over evolutionary time,
symbioses that developed between nitrogen-fixing bacteria and plants
helped increase the availability of nitrogen in many ecosystems.
Nonetheless, given strong competition for nitrogen and other elements,
ecologists find that nutrient limitations constrain life in many
environments. Organisms are shaped further by the physical properties
of the media in which they live, including the media’s densities and
temperatures. For example, marine mammals like Stellar sea lions
(Eumetopias jubatus) have developed streamlined bodies that move
efficiently through water, which is more than 700 times denser than air,
but that slow them down on land. As a result, sea lions sleep on shore,
but hunt for food primarily in the water, where their speed is optimized.

Ecologists have found that interactions among organisms come in

several different forms. In antagonistic relationships, organisms compete
for resources, spread disease to their neighbors, or consume each other.
In more mutualistic associations, one organism shelters another, two
organisms exchange resources, or tighter dependencies evolve, such as
coevolved relationships between specialized pollinators and flowers. In
some cases, species even cultivate others. For example, ecologists
recently found that coral reef damselfish tend underwater algal gardens,
where they remove less desirable algae species and chase away
predators. In other cases, species with large structures become habitat
for smaller organisms. For example, the human digestive tract harbors
so many bacteria that they outnumber the cells in the human body by
tenfold. Investigating how digestive tract microbes influence their hosts
is now a promising area of microbial ecology and medicine. At a bigger
scale, the evolutionary rise of flowering plants (angiosperms) and the
development of extensive rainforest canopies produced novel
environments in which animals tested new ecological strategies.

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Scientists suggest that evolution of the open branch structure of

rainforest trees helped drive the evolution of forelimb structure in apes,
permitting tree-to-tree swinging, and bequeathing manual dexterity to
humans.

Self-Assessment Exercises 3
1. Over evolutionary time, what helped increase the availability of
nitrogen in ecosystems?
2. Why may plants photosynthesize continuously as long as water and
nutrients are available in the tropics?

1.6 Summary
The species interactions discussed above are only some of the known
interactions that occur in nature and can be difficult to identify because
they can directly or indirectly influence other intra-specific and inter-
specific interactions. In addition, the role of abiotic factors adds
complexity to species interactions and how we understand them. That is
to say, species interactions are part of the framework that forms the
complexity of ecological communities.

1.7 References/Further Readings/Web Sources

Putman, R.J. and S.D. Wratten (1984). Principles of Ecology,

Publisher Springer Dordrecht, eBook Packages Springer Book
Archive, DOIhttps://doi.org/10.1007, /978-94-011- 6948-6,
eBook ISBN978-94- 011-6948-6. 388pp

Sharma, P. D. (2017). Ecology and Environment Thirteenth Edition,

Rastogi Publications, ISBN: 9789350781227, 9350781220.
776pgs

Yousaf, Z. (2017). Plant Ecology - Traditional Approaches to Recent

Trends. ISBN 978-953-51- 3340-7. pp200

https://www.nature.com/scitable/knowledge/library/ecologists-study-
the-interactions-of-organisms-and-13235586/
https://encrypted-
vtbn0.gstatic.com/video?q=tbn:ANd9GcTA24j6jJzeGHurKRJtdNwDsre
YnPqpoRkqDg
Video Link
https://www.youtube.com/watch?v=dKGNsye4HV8
https://www.youtube.com/watch?v=4n03ImI5_T8
https://www.youtube.com/watch?v=YFW55_diHzU
https://www.youtube.com/watch?v=q2zdiLn3gSE&vl=en

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1.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Any animal that hunts other organisms down, kills, and eats them
for survival is known as a predator.
2. Species interactions relied on the environmental conditions and
evolutionary angles wherein they exist
1. Any animal that hunts other organisms down, kills, and eats them
for survival is known as a predator.
2. Species interactions relied on the environmental conditions and
evolutionary angles wherein they exist

Answers to SAE 2
1. Parasitism is a relationship in which one organism benefits and
the other organism is harmed, but not always killed.
2. Parasites can be ectoparasites -- such as ticks, fleas, and leeches -
- that live on the surface of the host. Parasites can also be
endoparasites -- such as intestinal worms – that live inside the
host.

Answers to SAE 3
1. Over evolutionary time, symbioses that developed between
nitrogen-fixing bacteria and plants helped increase the
availability of nitrogen in many ecosystems.
2. Solar radiation is plentiful year-round, temperatures are warm

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UNIT 2 GENETICS AND EVOLUTION

Unit Structure

2.1 Introduction
2.2 Intended Learning Outcomes (ILOs)
2.3 Heredity
2.3.1 Contribution of Gregor Johann Mendel to the Study of
Genetics
2.3.2 Principle of segregation and independent assortment
2.4 Variation and its importance
2.5 How characteristics are inherited
2.5.1 Dominant and recessive genes
2.5.2 Gene changes and Co-dominant genes
2.6 Summary
2.7 References/Further Readings/Web Sources
2.8 Possible Answers to Self-Assessment Exercises

2.1 Introduction

In this unit you shall learn some fundamental aspects of genetics such as
Mendel’s laws, chromosomes, genes, how DNA duplicates, what makes
a fertilized egg male or female and about dominant and recessive genes,
and gene changes and co-dominant genes

2.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• define the term heredity and variation;
• state pattern of Mendelian inheritance;
• describe the location, structure and function of chromosomes and
genes
• give an account of the four blood groups in humans and the
manner of their inheritance;
• explain the chromosomal basis of sex determination in humans;

2.3 Heredity

Why does a baby who looks like a human also resemble its parents,
grandparents, or even distant cousins, uncles, or aunts? Why does a
kitten look like a tiny cat to you? Why do a seedling's leaves, stems, or
flowers develop similarly to those of its parents' plants? Why, in
addition, do all organisms share their parents' structural characteristics?
Heredity is the scientific term for the transmission of traits from one

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generation to the next. The phenomenon of passing on characteristics or

qualities from one set of parents to another is known as heredity. Any
quality that is passed down from parent to child is referred to as a trait.
The fertilised egg or zygote has characteristics that carry over from one
generation to the next. That zygote grows into a certain kind of
organism. Genes are in charge of heredity. Even among members of the
same family, variances or differences result from different gene
combinations. Genetics is the study of heredity and genetic variation.
Many scientists in the past were fascinated by the topic of heredity. A
monk from Austria named Gregor Johann Mendel (1822–1884)
undertook the arduous process of doing so. He chose a few pea plants,
raised them year after year, gathered a lot of data, examined it, and for
the first time theorised a few inheritance laws. His remarkable work,
however, got recognized years after his death when
Correns, Tschermak and Hugo de Vries came to the same conclusions as
Mendel did, after independently carrying out experiments in their own
countries.

2.3.1 Contribution of Gregor Johann Mendel to the Study of

Genetics

Mendel established that certain qualities appear in offspring without any

mixing of parent characteristics through the selective cross-breeding of
common pea plants (Pisum sativum) over many generations. For
example, the pea bloom is either purple or white; cross-pollinated pea
plants do not produce offspring with intermediate colours. Mendel
identified seven features that are instantly recognisable and seem to only
exist in two forms:
1. Flower color is purple or white
2. Flower position is axil or terminal
3. Stem length is long or short
4. Seed shape is round or wrinkled
5. Seed color is yellow or green
6. Pod shape is inflated or constricted
7. Pod color is yellow or green

Mendel picked common garden pea plants for the focus of his research
because they can be grown easily in large numbers and their
reproduction can be manipulated. Pea plants have both male and female
reproductive organs. As a result, they can either self-pollinate
themselves or cross-pollinate with another plant. In his experiments,
Mendel was able to selectively cross-pollinate purebred plants with
particular traits and observe the outcome over many generations. This
was the basis for his conclusions about the nature of genetic inheritance.

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Reproductive structures of flowers

Figure 1.1 Reproductive structures of flowers. Source:www.byjus.om

In cross-pollinating plants that either produce yellow or green pea seeds

exclusively, Mendel found that the first offspring generation (f1) always
has yellow seeds. However, the following generation (f2) consistently
has a 3:1 ratio of yellow to green.

This 3:1 ratio occurs in later generations as well. Mendel realized that
this underlying regularity was the key to understanding the basic
mechanisms of inheritance.

He came to three important conclusions from these experimental results:

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1. that the inheritance of each trait is determined by "units" or

"factors" that are passed on to descendents unchanged (these
units are now called genes )
2. That an individual inherits one such unit from each parent for
each trait
3. That a trait may not show up in an individual but can still be
passed on to the next generation.

It is important to realize that, in this experiment, the starting parent

plants were homozygous for pea seed color. That is to say, they each
had two identical forms (or alleles) of the gene for this trait--2 yellows
or 2 greens. The plants in the f1 generation were all heterozygous. In
other words, they each had inherited two different alleles--one from each
parent plant. It becomes clearer when we look at the actual genetic
makeup, or genotype of the pea plants instead of only the phenotype, or
observable physical characteristics.

Note that each of the f1 generation plants (shown above) inherited a Y

allele from one parent and a G allele from the other. When the f1 plants
breed, each has an equal chance of passing on either Y or G alleles to
each offspring.

With all of the seven pea plant traits that Mendel examined, one form
appeared dominant over the other, which is to say it masked the
presence of the other allele. For example, when the genotype for pea
seed color is YG (heterozygous), the phenotype is yellow. However, the
dominant yellow allele does not alter the recessive green one in any
way. Both alleles can be passed on to the next generation unchanged.

2.3.2 Principle of Segregation and Independent Assortment

Mendel's observations from his pea plant experiments lead to the

principles of segregation and principle of independent assortment.
According to the principle of segregation, for any particular trait, the
pair of alleles of each parent separate and only one allele passes from
each parent on to an offspring. Which allele in a parent's pair of alleles

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is inherited is a matter of chance. We now know that this segregation of

alleles occurs during the process of sex cell formation (i.e., meiosis ).

Figure 1.2. Segregation of alleles in the production of sex cells

According to the principle of independent assortment, different pairs
of alleles are passed to offspring independently of each other. The result
is that new combinations of genes present in neither parent are
possible. For example, a pea plant's inheritance of the ability to produce
purple flowers instead of white ones does not make it more likely that it
will also inherit the ability to produce yellow pea seeds in contrast to
green ones. Likewise, the principle of independent assortment explains
why the human inheritance of a particular eye color does not increase or
decrease the likelihood of having 6 fingers on each hand. Today, we
know this is due to the fact that the genes for independently assorted
traits are located on different chromosomes .

Five parts of Mendel's discoveries were an important divergence from

the common theories at the time and were the prerequisite for the
establishment of his rules.
1. Characters are unitary. That is, they are discrete (purple vs. white,
tall vs. dwarf).
2. Genetic characteristics have alternate forms, each inherited from
one of two parents. Today, we call these alleles.
3. One allele is dominant over the other. The phenotype reflects the
dominant allele.
4. Gametes are created by random segregation. Heterozygotic
individuals produce gametes with an equal frequency of the two
alleles.
5. Different traits have independent assortment. In modern terms,
genes are unlinked

What are the alternate forms of Genetic characteristic inherited from one
of two parents referred?

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Self-Assessment Exercises 1
1. What is heredity?
2. What were the prerequisite for the establishment of Mendel's rules
from his discoveries?

2.4 Genetic Variation and its Importance

Genetic variety describes variations in the genomes of individuals within

the same species. All an organism's genes and genetic material are
contained in its genome. For example, there are around 20.000–25000
genes in the human genome. Genes are inherited informational units that
contain the blueprints for making proteins. Cells can operate because of
the genes that are encoded in these proteins. Because each parent cell or
organism gives one copy of its genes to its offspring, most sexually
reproducing organisms have two copies of each gene. Genetic variation
can also be further increased by the existence of alleles, which are
slightly different versions of genes. The genotype for a given attribute,
such as hair texture, is determined by the mixture of alleles of a gene
that an individual receives from both parents. The phenotype—the
observable characteristics—that an individual has for a trait, such as
whether they truly have straight, wavy, or curly hair, is determined by
the genotype that person carries for that feature.

Multiple factors can cause genetic variation within a species. Genetic

diversity can come from various sources, one of which being mutations,
or alterations in the DNA's gene sequences. Gene flow, or the transfer of
genes between several groups of organisms, is another source. The
development of new gene combinations through sexual reproduction can
also result in genetic variety. Some animals in a group can survive in
their environment more successfully than others thanks to genetic
variety. Even among members of a small population, the degree to
which an organism is adapted to a given environment might vary
noticeably. Moths of the same species with variously coloured wings
serve as an illustration. Moths of a different hue are less effective at
concealing themselves than those with wings that resemble tree bark.
The tree-colored moths have a higher chance of surviving, procreating,
and passing on their genes as a result, a process known as natural
selection, and it is the primary driver behind evolution. The importance
of variation can be outlined as follows:
1. They enable the organism to adapt in a changing environment.
2. Variation forms the basis of heredity
3. They form raw material for evolution and development of new
species.

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Variations may or may not help organisms to survive:

a) Some variations help organisms to survive: Green bushes are
homes to several beetles. They multiply, which increases their
population. The red beetles are easily spotted by crows, who then
consume them. Due to some fluctuation, some green beetles
rather than red beetles are produced during reproduction. Crows cannot
see the green bugs and do not consume them. The population of
red beetles then progressively declines while the population of
green beetles gradually rises. The organisms' ability to live is due
to this variation.
b) Some variations do not help organisms to survive: Red beetles
undergo a colour change during sexual reproduction, and some
blue beetles are produced in place of red beetles. Crows can see
the red and blue insects, and they consume them both. The
population of red and blue beetles then starts to decline. The
organisms have not fared better as a result of this modification.
c) Acquired traits cannot be passed from one generation to the next:
Beetle population growth and plant disease both result in a reduction in
the amount of food accessible to them, which also affects their body
weight. The body weight of the beetles will also increase if, after a few
years, there is more food available. Since their genetic makeup has not
changed, this acquired trait cannot be passed from one generation to
another.

Self-Assessment Exercises 2
1. What is genetic variation?
2. Outline the importance of variation?
2.5 How Characteristics are Inherited

Parents pass on traits or characteristics, such as eye colour and blood

type, to their children through their genes. Some health conditions and
diseases can be passed on genetically too. Sometimes, one characteristic
has many different forms. For example, blood type can be A, B, AB or
O. Changes (or variations) in the gene for that characteristic cause these
different forms. Each variation of a gene is called an allele (pronounced
‘AL-eel’). These two copies of the gene contained in your chromosomes
influence the way your cells work. The two alleles in a gene pair are
inherited, one from each parent. Alleles interact with each other in
different ways called inheritance patterns. Examples of inheritance
patterns include:
• autosomal dominant – where the gene for a trait or condition is
dominant, and is on a non-sex chromosome
• autosomal recessive – where the gene for a trait or condition is
recessive, and is on a non-sex chromosome

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• X-linked dominant – where the gene for a trait or condition is

dominant, and is on the X-chromosome
• X-linked recessive – where the gene for a trait or condition is
recessive, and is on the X-chromosome
• Y-linked – where the gene for a trait or condition is on the Y-
chromosome
• co-dominant – where each allele in a gene pair carries equal
weight and produces a combined physical characteristic
• mitochondrial – where the gene for a trait or condition is in your
mitochondrial DNA, which sits in the mitochondria (powerhouse)
of your cells.

2.5.1 Dominant and recessive genes

The most common interaction between alleles is a dominant/recessive

relationship. An allele of a gene is said to be dominant when it
effectively overrules the other (recessive) allele. Eye colour and blood
groups are both examples of dominant/recessive gene relationships.
1. Eye colour
The allele for brown eyes (B) is dominant over the allele for blue eyes
(b). So, if you have one allele for brown eyes and one allele for blue
eyes (Bb), your eyes will be brown. (This is also the case if you have
two alleles for brown eyes, (BB). However, if both alleles are for the
recessive trait (bb) you will inherit blue eyes.
2. Blood groups
For blood groups, the alleles are A, B and O. The A allele is dominant
over the O allele. So, a person with one A allele and one O allele (AO)
has blood group A. Blood group A is said to have a dominant
inheritance pattern over blood group O. If a mother has the alleles A and
O (AO), her blood group will be A because the A allele is dominant. If
the father has two O alleles (OO), he has the blood group O. For each
child that couple has, each parent will pass on one or the other of those
two alleles. This is shown in figure 2.1. This means that each one of
their children has a 50 per cent chance of having blood group A (AO)
and a 50 per cent chance of having blood group O (OO), depending on
which alleles they inherit.
O O
Mother’s blood group A AO AO
(group A) (group A)
(AO, group A) O OO OO
(group O) (group O)
Figure 2.1: Father’s blood group (OO, group O)

The combination of alleles that you have is called your genotype (eg.
AO). The observable trait that you have – in this case blood group A – is
your phenotype.

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Recessive genetic conditions

If a person has one changed (q) and one unchanged (Q) copy of a gene,
and they do not have the condition associated with that gene change,
they are said to be a carrier of that condition. The condition is said to
have a recessive inheritance pattern – it is not expressed if there is a
functioning copy of the gene present. If two people are carriers (Qq) of
the same recessive genetic condition, there is a 25 per cent (or one in
four) chance that they may both pass the changed copy of the gene on to
their child (qq, see figure 2.2). As the child then do not have an
unchanged, fully functioning copy of the gene, they will develop the
condition. There is also a 25 per cent chance that each child of the same
parents may be unaffected, and a 50 per cent chance that they may be
carriers of the condition.
Q P
Mother (carrier) Q QQ Qq
(unaffected) (carrier)
q Qq qq
(carrier) (affected)
Figure 2.2: Father (carrier)
Recessive genetic conditions are more likely to arise if two parents are
related, although they are still quite rare. Examples of autosomal
recessive genetic conditions include cystic
fibrosis and phenylketonuria (PKU).

2.5.2 Gene changes and Co-dominant genes

A cell reproduces by copying its genetic information then splitting in

half, forming two individual cells. Occasionally, an alteration occurs in
this process, causing a genetic change. When this happens, chemical
messages sent to the cell may also change. This spontaneous genetic
change can cause issues in the way the person’s body functions. Sperm
and egg cells are known as ‘germ’ cells. Every other cell in the body is
called ‘somatic’ (meaning ‘relating to the body’).

If a change in a gene happens spontaneously in a person’s somatic cells,

they may develop the condition related to that gene change, but won’t
pass it on to their children. For example, skin cancer can be caused by a
build-up of spontaneous changes in genes in the skin cells caused by
damage from UV radiation. Other causes of spontaneous gene changes
in somatic cells include exposure to chemicals and cigarette smoke.
However, if the gene change occurs in a person’s germ cells, that
person’s children have a chance of inheriting the altered gene.

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Not all genes are either dominant or recessive. Sometimes, each allele in
the gene pair carries equal weight and will show up as a combined
physical characteristic. For example, with blood groups, the A allele is
as ‘strong’ as the B allele. The A and B alleles are said to be co-
dominant. Someone with one copy of A and one copy of B has the
blood group AB. The inheritance pattern of children from parents with
blood groups B (BO) and A (AO) is given in figure 2.3. Each one of
their children has a 25 per cent chance of having blood group AB (AB),
A (AO), B (BO) or O (OO), depending on which alleles they inherit.

B O
Mother’s blood group A AB AO
(group AB) (group A)
(group A) O OB OO
(group B) (group O)

Figure 2.3: Father’s blood group - (group B)

Differentiate between X-linked dominant and X-linked recessive
characters.

Self-Assessment Exercises 3
1. When is an allele of a gene is said to be dominant?
2. Distinguish between autosomal dominant and autosomal recessive

2.6 Summary

In this unit you have learned some fundamental aspects of genetics such
as Mendel’s laws, chromosomes, genes, how DNA duplicates, what
makes a fertilized egg male or female and about dominant and recessive
genes, and gene changes and co-dominant genes.

2.7 References/Further Readings/Web Sources

Matthew, R. Fisher (2018). Environmental Biology, Publisher: Open

Oregon Educational Resources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp
https://www.toppr.com/guides/biology/heredity-and-evolution/heredity/
https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/gen
es-and-genetics
https://byjus.com/biology/heredity-and-evolution/

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https://ncert.nic.in/textbook/pdf/jesc109.pdf
https://www.youtube.com/watch?v=Vj1k3fya0zw
https://www.youtube.com/watch?v=cBOlcV0EuOk
https://www.youtube.com/watch?v=AsDMi3-k6gI
https://www.youtube.com/watch?v=NSgT01BPnoo
1.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Heredity is known as the phenomena of inheritance of traits or
features of parents to offspring or progeny. A trait is any
characteristic that is transferred from parent to offspring.
2. Five parts of Mendel's discoveries were an important divergence
from the common theories at the time and were the prerequisite
for the establishment of his rules.
i. Characters are unitary. That is, they are discrete (purple vs. white,
tall vs. dwarf).
ii. Genetic characteristics have alternate forms, each inherited from
one of two parents. Today, we call these alleles.
iii. One allele is dominant over the other. The phenotype reflects the
dominant allele.
iv. Gametes are created by random segregation. Heterozygotic
individuals produce gametes with an equal frequency of the two
alleles.
v. Different traits have independent assortment. In modern terms,
genes are unlinked

Answers to SAE 2
1. The differences in the DNA sequences among every organism
leading to the diverse gene pool are called genetic variations.
2. The importance of variation can be outlined:
i. They enable the organism to adapt them in changing
environment.
ii. Variation forms the basis of heredity
iii. They form raw material for evolution and development of
new species

Answers to SAE 3
1. An allele of a gene is said to be dominant when it effectively
overrules the other (recessive) allele.
2. Autosomal dominant – where the gene for a trait or condition is
dominant, and is on a non-sex chromosome and Autosomal
recessive – where the gene for a trait or condition is recessive,
and is on a non-sex chromosome

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UNIT 3 INTRODUCTION TO EVOLUTION

Unit Structure

3.1 Introduction
3.2 Intended Learning Outcomes (ILOs)
3.3 Introduction to Evolution
3.4 Theories of Evolution
3.5 Encapsulating the concepts of Heredity and Evolution
3.6 Summary
3.7 References/Further Readings/Web Sources
3.8 Possible Answers to Self-Assessment Exercise

3.1 Introduction

You will learn about evolution as the gradual change of organisms on

the earth over long periods, with new forms replacing old ones. The unit
will explain the various theories of evolution, namely the theories of
Special creationism, evolutionary creationism, spontaneous generation,
eternity of life, Cosmozoan, and Biochemical theory

3.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you should be able to:

• Explain the meaning of evolution as the gradual change of

organisms on the earth over long periods, with new forms
replacing old ones.
• Explain the various theories of evolution, namely the theories of
Special creationism, evolutionary creationism, spontaneous
generation, eternity of life, Cosmozoan, and Biochemical theory
• You will also study how evidences of evolutionist theory support
the process of evolution

3.3 Introduction to Evolution

Evolution is the long-term, gradual replacement of previous forms by

new ones in all living things on Earth. Larger, more complex animals
have replaced smaller ones as evolution has proceeded, expanding the
diversity of the earth. Some species have also gone extinct. Another
definition of evolution is the shift in a population's genetic make-up
through time, which can be brought about by meiosis, hybridization,
natural selection, or mutation. As a result, the population begins to
diverge from other populations of the same species, which may result in
the emergence of a new species. theories concerning how life came to be
on Earth. The theory of evolution describes how the various forms of

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life on earth (including humans) emerged and developed. There are five
main theories of the origin of life on Earth:
• special creationism
• spontaneous generation
• eternity of life
• cosmozoan theory
• biochemical origin

a) Special creationism
According to the special creation idea, a Supreme Being/God created all
of the different types of life on Earth simultaneously over the course of
six days. Special creativity is always associated with religion and mostly
concentrated on spiritual issues that cannot be adequately felt, touched,
or quantified. There are two perspectives on how life came to be various
creationist theories

Gap creation – talks about the significant time lag between the earth's
origin and the emergence of all the creatures and vegetation. The
difference could amount to billions or millions of years. Progressive
creation acknowledges the Big Bangs as the universe's point of
beginning. It acknowledges that all living things have a history of
creation as evidenced by their fossil records, but it rejects the idea that
this process is ongoing (each is seen as unique creation).

Evolutionary creationism (Theistic evolution)

This view of evolution maintains that God ‘invented‟ evolution and
takes some form of an active part in the ongoing process of evolution.

Intelligent design – states that life developed (formed) from a

combination of natural forces and the intervention of a supernatural
being.
b) Spontaneous generation theory
Suggests that life can evolve 'spontaneously' from non-living objects.
Eg. people believed that rotting meat turned into flies.

c) Eternity of life
The theory of eternity of life states that the universe has always existed
and that there has always been life in the universe. There is no beginning
and no end to life on earth and so life is neither created nor generated
from non-living matters.

d) Cosmozoan Theory
According to this, life on Earth first evolved elsewhere in the universe
(possibly from another planet). For example, meteorites introduced
bacteria and other pathogens to the earth. However, because it lacks

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proof and is closely related to the "eternity of life" explanation of the

genesis of life, this theory did not get much favour.
e) Biochemical theory
This suggests that life on earth originated as a result of a number of
biochemical reactions producing organic molecules, which combined
(associated) to form cells. This theory is also called abiogenesis; states
that life originated from chemical inanimate (abiotic substances). The
two scientists (biologists) who developed the theory of abiogenesis
(origin of life from chemicals) were- Aleksander Oparin (1924) and
John Haldane (1929).
What does the Cosmozoan Theory postulates?

Self-Assessment Exercises 1
1. State the theory of Special creationism in evolution
2.Who are the two scientist that develop the theory of abiogenesis?

3.4 Theories of Evolution

There have been many theories of evolution that have explained how
does evolution occur, and what drives the population to become a new
species?
A. Lamarck Theory of evolution: In the 19th century (1809), Lamarck
published a paper entitled Philosophic ‘Zoologique‟ in which he
described the two-part mechanism by which change was gradually
introduced into the species and passed down through the generations.
This theory is also called ‘theory of transformation‟ or Lamarckism. The
two parts of Lamarck theory are:

i). Use and disuse: Lamarck suggested that a structure or process in

organism that can be used continuously will become enlarged or
more developed than any structure that is not. Example,
According Lamarck, giraffe had short neck but they stretched their
neck to reach high branches, an elongated neck use theory. The
wings of penguins would have become smaller than those of other
birds because penguins do not use their wings to fly, disuse theory.
ii). Inheritance acquired traits: Lamarck believed that traits changed
(acquired) during an organism’s lifetime could be passed on to its
offspring. Example: - Giraffes that had acquired long necks
would have offspring with long necks.

However, nowadays, Lamarck’s theories are not accepted because the

environmental changes that were believed by Lamarck have brought
about the changes in the phenotypes (Physical appearance) of the
organisms have no effect on their gametes and hence their heredity.

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B. Charles Darwin and Natural Selection: In 1858, both Charles

Darwin and Alfred Wallace jointly published a scientific paper
that proposed species were modified by natural selection. Darwin
visited five of the Galapagos Islands, made drawings, and
collected species. In particular, Darwin studied the finches found on
the different islands and noted there were many similarities between
them but they have some obvious differences. Darwin concluded
that an “ancestral finch” had colonized the Islands from mainland
and been able to adapt to the different conditions on the islands
and evolve into different species. Eg. He suggested that some finches
had evolved into insect eaters (pointed peak), others into
seedeaters (crushing peak). Darwin summarized his observations
in two main ideas:

• all species tend to produce more offspring than can possibly

survive (Fecundity)
• there is a variation among the offspring.

From these observation Darwin deduced (concluded) that:

• There will be a “struggle for existence” between members of a
species because they are over – reproduced and resources are
limited.
• Some members of a species will be better adapted than others to
the environment because there is a variation in the offspring.

Darwin proposed that hose members of a species, which are best

adapted to their environment, will survive and reproduce in greater
number than other less adapted (died out).

C. Neo – Darwinism Theory Charles Darwin knew very little about

genetics and did not propose how variations in the population was
passed to the next generation. Nowadays, genes and gene action are the
driving force of evolution in the theory of Natural selection. A Gene
pool is all the alleles in the population. It might be evolving a population
into a new species. Suppose an allele determines a feature that gives an
organism an advantage in its environment. The following will happen:
• Those individuals with the advantageous allele of a gene will
survive to reproduce in greater number than other types
• Advantageous allele pass to their offspring in greater numbers
than other genes (alleles).
• The frequency of the advantageous allele will be higher in the
next generation of a population. Mutations are important in
introducing variation into population. Any mutation could produce an
allele which:
• Increase in frequency if they are beneficial in their effect, may
increase slowly, stable or decrease if they are neutral and

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decrease and could disappear if they are harmful (disadvantages) in

their effects. Neo-Darwinism is a modification of Darwin’s original
theory that takes into account:- genetics and ethology
(behavioural pattens can also be advantageous or not). Eg. Young geese
‘imprint‟ upon the first moving object after they are hatched. State the
Lamarck’s theory of Use and disuse.

Self-Assessment Exercises 2
1. State the theory of Inheritance acquired traits.
2. Why is Lamarck’s theories are not accepted nowadays?

3.5 Encapsulating the concepts of Heredity and Evolution

Figure 3.1 Encapsulating the concepts of Heredity and Evolution

What are the features of acquired traits in Heredity?

Self-Assessment Exercises 3

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1. What are the key factors in modern concept of evolution?

2. What are inherited traits?

3.6 Summary

You must have learned the meaning of evolution as the gradual change
of organisms on the earth over long periods, with new forms replacing
old ones. The unit also highlighted the various theories of evolution,
namely the theories of Special creationism, evolutionary creationism,
spontaneous generation, eternity of life, Cosmozoan, and Biochemical
theory. The evidences of evolutionist theory that supports the process of
evolution was also explained.

3.7 References/Further Readings/Web Sources

Matthew, R. Fisher (2018). Environmental Biology, Publisher: Open

Oregon Educational Resources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp
https://cdn.kastatic.org/ka-youtube-
converted/GcjgWov7mTM.mp4/GcjgWov7mTM.mp4#t=0
https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/gen
es-and-genetics
https://www.britannica.com/science/natural-selection
https://education.nationalgeographic.org/resource/natural-selection
https://www.youtube.com/watch?v=EG3FuQ6xL3I
https://www.youtube.com/watch?v=rF8nhLJ0iV8
https://www.youtube.com/watch?v=Vj1k3fya0zw

3.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Special creation theory states that the different forms of life on
earth were created by a Supreme Being/ God/ at once with six
days.
2. The scientists who developed the theory of abiogenesis were:-
Aleksander Oparin (1924) and John Haldane (1929).

Answers to SAE 2
1. Lamarck believed that traits changed, acquired during an
organism’s lifetime could be passed on to its offspring's.

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2. Lamarck’s theories are not accepted because the environmental

changes that were believed by Lamarck have brought about the
changes in the phenotypes (Physical appearance) of the
organisms have no effect on their gametes and hence their heredity.

Answers to SAE 3
1. Factors in modern concept of evolution
i. Genetic variation
ii. Natural selections and
iii. Reproductive isolation

2. They are traits controlled by specific genes passed on from one

generation to another

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Unit 4 Natural selection

Unit Structure

4.1 Introduction
4.2 Intended Learning Outcomes (ILOs)
4.3 Natural Selection
4.3.1 The Process of Natural Selection
4.3.2 Natural Selection and the Evolution of Populations
4.4 Evolutionary Adaptation
4.5 The Concept of the Survival of the Fittest
4.6 Summary
4.7 References/Further Readings/Web Sources
4.8 Possible Answers to Self-Assessment Exercises

4.1 Introduction

You will learn about the Natural Selection as a mechanism of

evolution. You will equally study about the concept of the 'survival of
the fittest' and the process of natural selection.

4.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you shall be able to:

• Explain the meaning of natural selection as a mechanism of

evolution.
• Describe the process of natural selection
• Explain the concept of the 'survival of the fittest'

4.3 Natural Selection

English naturalist Charles Darwin developed the idea of natural

selection after a five-year voyage to study plants, animals, and fossils in
South America and on islands in the Pacific. In 1859, he brought the
idea of natural selection to the attention of the world in his best-selling
book, On the Origin of Species. Natural selection is the process through
which populations of living organisms adapt and change. Individuals in
a population are naturally variable, meaning that they are all different in
some ways. This variation means that some individuals have traits better
suited to the environment than others. Individuals with adaptive traits—
traits that give them some advantage—are more likely to survive and
reproduce. These individuals then pass the adaptive traits on to their
offspring. Over time, these advantageous traits become more common in

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the population. Through this process of natural selection,

favorable traits are transmitted through generations. Natural
selection can lead to speciation, where one species gives rise to a new
and distinctly different species. It is one of the processes that
drives evolution and helps to explain the diversity of life on Earth.

Darwin chose the name natural selection to contrast with “artificial

selection,” or selective breeding that is controlled by humans. He
pointed to the pastime of pigeon breeding, a popular hobby in his day, as
an example of artificial selection. By choosing which pigeons mated
with others, hobbyists created distinct pigeon breeds, with fancy feathers
or acrobatic flight, that were different from wild pigeons. Darwin and
other scientists of his days argued that a process much like artificial
selection happened in nature, without any human intervention. He
argued that natural selection explained how a wide variety of life forms
developed over time from a single common ancestor. Darwin did not
know that genes existed, but he could see that many traits are
heritable—passed from parents to offspring.

Mutations are changes in the structure of the molecules called DNA that
make up genes. The mutation of genes is an important source
of genetic variation within a population. Mutations can be random (for
example, when replicating cells make an error while copying DNA), or
happen as a result of exposure to something in the environment, like
harmful chemicals or radiation. Mutations can be harmful, neutral, or
sometimes helpful, resulting in a new, advantageous trait. When
mutations occur in germ cells (eggs and sperm), they can be passed on
to offspring. If the environment changes rapidly, some species may not
be able to adapt fast enough through natural selection. Through studying
the fossil record, we know that many of the organisms that once lived on
Earth are now extinct eg. Dinosaurs. An invasive species, a disease
organism, a catastrophic environmental change, or a highly
successful predator can all contribute to the extinction of species.

Today, human actions such as overhunting and the destruction of

habitats are the main cause of extinctions. Extinctions seem to be
occurring at a much faster rate today than they did in the past, as shown
in the fossil record.

4.3.1 The Process of Natural Selection

Darwin’s process of natural selection has four components.

1. Variation: Organisms (within populations) exhibit individual
variation in appearance and behavior. These variations may
involve body size, hair color, facial markings, voice properties, or
number of offspring. On the other hand, some traits show little to

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no variation among individuals—for example, number of eyes in

vertebrates.
2. Inheritance: Some traits are consistently passed on from parents
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.

From one generation to the next, the struggle for resources (what
Darwin called the “struggle for existence”) will favor individuals with
some variations over others and thereby change the frequency of traits
within the population. This process is natural selection. The traits that
confer an advantage to those individuals who leave more offspring are
called adaptations.

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. (We now know that such traits
may change by other evolutionary mechanisms that have been
discovered since Darwin’s time.)

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).

During the twentieth century, genetics was integrated with Darwin’s

mechanism, allowing us to evaluate natural selection as the differential
survival and reproduction of genotypes, corresponding to particular
phenotypes. Natural selection can only work on existing variation
within a population. Such variations arise by mutation, a change in
some part of the genetic code for a trait. Mutations arise by chance and
without foresight for the potential advantage or disadvantage of the
mutation. In other words, variations do not arise because they are
needed.

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4.3.2 Natural Selection and the Evolution of Populations

Though each has been tested and shown to be accurate, none of the
observations and inferences that underlies natural selection is sufficient
individually to provide a mechanism for evolutionary change.
Overproduction alone will have no evolutionary consequences if all
individuals are identical. Differences among organisms are not relevant
unless they can be inherited. Genetic variation by itself will not result in
natural selection unless it exerts some impact on organisms’ survival
and reproduction. However, any time all of Darwin's postulates hold
simultaneously—as they do in most populations—natural selection will
occur. The net result in this case is that certain traits (or, more precisely,
genetic variants that specify those traits) will, on average, be passed on
from one generation to the next at a higher rate than existing alternatives
in the population. In other words, when one considers who the parents of
the current generation were, it will be seen that a disproportionate
number of them possessed traits beneficial for survival and reproduction
in the particular environment in which they lived.

The important points are that this uneven reproductive success among
individuals represents a process that occurs in each generation and that
its effects are cumulative over the span of many generations. Over time,
beneficial traits will become increasingly prevalent in descendant
populations by virtue of the fact that parents with those traits
consistently leave more offspring than individuals lacking those traits. If
this process happens to occur in a consistent direction—say, the largest
individuals in each generation tend to leave more offspring than smaller
individuals—then there can be a gradual, generation-by-generation
change in the proportion of traits in the population. This change in
proportion and not the modification of organisms themselves is what
leads to changes in the average value of a particular trait in the
population. Organisms do not evolve; populations evolve. How would
Genetic variation results in natural selection?

Self-Assessment Exercises 1
1. What is meant by natural selection?
2. Outline the four Darwin’s process of natural selection components.

4.4 Evolutionary Adaptation

The term “adaptation” derives from ad + aptus, literally meaning

“toward + fit”. As the name implies, this is the process by which
populations of organisms evolve in such a way as to become better
suited to their environments as advantageous traits become predominant.

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The definition of evolutionary adaptation is the mechanism by which

an animal or plant alters itself to accommodate its changing
environment. Organisms can display three types of adaptation, each of
which increase the organism's chance of survival and reproduction,
thereby maximizing its number of descendants across time:
1. Behavioral adaptation: The organism changes how it interacts
with its environmental surroundings as well as other animals and
plants.
2. Physiological adaptation: The organism changes how its body
functions internally.
3. Structural adaptation: The organism changes at least one of its
physical features.

Consider the natural history of emperor penguins in Antarctica. To

survive in a frigid environment, emperor penguins mate in the winter.
This breeding schedule lets the chicks have enough time to mature into
independent juveniles before prey become abundant enough for them to
feed on their own. In addition, the males huddle together in tight circles
to share body heat throughout the winter. To accommodate the shortage
of prey during the winter season, only female emperor penguins voyage
to the ocean to feed. All three adaptations are the penguin's behavioral
responses to its extremely harsh living environment.

Physiologically, male emperor penguins can live for 100 consecutive

days without eating any food during the winter time. Emperor penguins
also can significantly reduce their heart rate so that they can stay
underwater for long periods of time when feeding before resurfacing to
breathe.

In terms of structural adaptations, the emperor penguins have tails that

are short and stiff enough to serve as a prop while they balance on their
heels. This standing position minimizes how much heat is lost from their
feet while standing on the snow and ice. In additionally, the bicolor
pattern of penguins serves as a camouflage while swimming in the
ocean. The penguins' black back blends in with the sea when predators,
such as leopard seals, look down upon them. Their white underside
blends in with the sky when predators are positioned far below them.

Evolutionary adaptation does not mean that only the best specimens
survive or that only the best genetic traits are passed from one
generation to the next. Instead, it means that the organisms better
suited for their environment survive; and that the genetic traits most
likely to confer success will be inherited among their offspring. What do
you understand by Evolutionary adaptation?

Self-Assessment Exercises 2

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Outline and define the three types of adaptation that Organisms can
display from evolutionary point of view?
4.5 The Concept of the Survival of the Fittest

In terms of evolution, an animal that is 'fit' is one that is adapted to its

environment. This concept is at the core of natural selection, although
the term 'survival of the fittest' has often been misunderstood and may
be best avoided. There is also a degree of randomness to evolution, so
the best-adapted animal won't always be the one to survive. Adrian
explains, 'If you're going to get hit by a rock or something, it's just bad
luck. But on average and over time, the ones that survive are the ones
that are fittest - the ones that have the best adaptations.' Some important
theories of evolution are as follows:
1. Darwin’s theory: Charles Robert Darwin was a British naturalist
who formulated his hypothesis that evolution took place due to
natural selection. Darwin’s theory of evolution tells us how life
evolved from simple to more complex forms.
• Over production.
• Almost constant population.
• Struggle for existence- Intraspecific, Interspecific, Environmental
Struggle.
• Variation: Appearance of variation in organisms during struggle
for existence.
• Natural selection / Survival of the fittest
• Inheritance of useful variation

2. Lamarckism
Lamarckism is a theory named after French naturalist Jean-Baptiste
Lamarck (1744-1829). It proposes that animals acquire characteristics
based on use or disuse during their lives, rather than through hard-coded
genetic changes. In Lamarckian theory, giraffes stretch their necks to
make them longer. These animal's offspring would inherit longer necks
as a result of their parents' efforts. Adrian says, 'If you tried to stretch
your neck for 10 minutes each morning, then you would probably end
up with your neck being a few millimetres longer for a few years.
However, your children would not inherit it. That's where this theory
fails.'
Lamarck’s theory:
• Organisms and their organs tend to increase their size
continuously due to some unknown forces of life.
• New organs in the organisms are found due to new needs which
occur due to change in the environment.
• Theory of use and disuse of organs.
• Theory of inheritance of acquired character.

3. Mutation Theory: by Hugo de Vries

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“A new species is originating from pre-existing species slowly in single

step due to genetic variation called ‘mutation’’. Mutation is sudden
inheritable change. It occurs commonly in naturally breading
population. Mutation is directional, less occurring in any direction. It is
a subject for natural selection and most of the mutation is lethal or fatal.
Changes in the genetic material, i.e., mutation, could introduce a wide
range of variability in a natural population. With a complex or shifting
environment, a particular variation may give an individual or its
offspring a slight edge. Most mutations are considered deleterious, as
they interfere with a genotype that works. However, occasionally, a
mutation arises that increases success. Mutation introduces variability
and the environment determines its value for survival and success. What
is the genetic variation that causes a new species to originate from pre-
existing species slowly in a single step?

Self-Assessment Exercises 3
1.From evolutionary point of view, which organism is being described as
'fit'?
2. What is the thrust of Lamarckism theory in evolution?

4.6 Summary

You have learned about natural selection as a mechanism of evolution in

this unit. Darwin's theory of evolution fundamentally changed the
direction of future scientific thought, though it was built on a growing
body of thought that began to question prior ideas about the natural
world. The core of Darwin's theory is natural selection, a process that
occurs over successive generations and is defined as the differential
reproduction of genotypes. Natural selection requires heritable variation
in a given trait, and differential survival and reproduction associated
with possession of that trait.

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4.7 References/Further Readings/Web Sources

Matthew, R. Fisher (2018). Environmental Biology, Publisher: Open

Oregon Educational Resources

Miller, G. Tyler Jr. and Scott E. Spoolman (2009). Essentials of

Ecology, 5e, Brooks/Cole, Cengage Learning, 10 Davis Drive
Belmont, CA 94002-3098 USA, ISBN-13: 978-0- 495-55795-1,
383pp

https://education.nationalgeographic.org/resource/natural-selection
https://www.globalchange.umich.edu/globalchange1/current/lectures/sel
ection/selection.html
https://www.khanacademy.org/science/ap-biology/natural-
selection/natural-selection-ap/a/darwin-evolution-natural-selection
https://evolution.berkeley.edu/evolution-101/mechanisms-the-processes-
of-evolution/natural-selection/
https://www.nhm.ac.uk/discover/what-is-natural-
selection.html#:~:text=Natural%20selection%20is%20a%20mechanism,
change%20and%20diverge%20over%20time.
https://www.youtube.com/watch?v=0SCjhI86grU
https://www.youtube.com/watch?v=7VM9YxmULuo&vl=en
https://www.youtube.com/watch?v=WmTlwD2Zd7E&vl=en
https://www.khanacademy.org/science/ap-biology/natural-
selection/natural-selection-ap/v/biodiversity-and-natural-selection-two

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4.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. The process through which organisms adapt and change
themselves in huge populations is known as natural selection.
2. Darwin’s process of natural selection has four components.
a) Variation.
b) Inheritance.
c) High rate of population growth.
d) Differential survival and reproduction.

Answers to SAE 2
1. Behavioral adaptation: The organism changes how it interacts
with its environmental surroundings as well as other animals and
plants.
2. Physiological adaptation: The organism changes how its body
functions internally.
3. Structural adaptation: The organism changes at least one of its
physical features.

Answers to SAE 3
1. In terms of evolution, an organism that is 'fit' is one that is
adapted to its environment
2. It proposes that animals acquire characteristics based on use or
disuse during their lives, rather than through hard-coded genetic
changes.

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Unit 5 Elements of Ecology

Unit Structure

5.1 Introduction
5.2 Intended Learning Outcomes (ILOs)
5.3 Defining of Ecology
5.4 Definitions of Ecological Terminologies
5.5 The meaning of Habitat in Ecology
5.5.1 Ecological Niche
5.5.2 Niche Formation and Partitioning
5.6 Summary
5.7 References/Further Readings/Web Sources
5.8 Possible Answers to Self-Assessment Exercises

5.1 Introduction

You will learn the meaning and elements of ecology in this unit. You
will appreciate the importance of the study of Ecology and understand
some basic ecological terms. The various branches of ecology and the
criteria employed for the classification of the various branches will be
highlighted.

5.2 Intended Learning Outcomes (ILOs)

By the end of this unit, you shall be able to:

• Define ecology
• Appreciate the importance of the study Ecology
• Understand some basic ecological terms.
• Describe the various branches of ecology
• Explain the criteria employed for the classification of the various
branches
• Explain the meaning of habitat and describe the various types

5.3 Defining Ecology

The word ‘Ecology‟ was coined from Greek word 'oikos' meaning
'house' or 'a place to live' and 'logos' meaning study. Ecology is the study
of the households of the planet earth. Living things depend on each other
and on the non-living components of the environment for survival.
Based on this, it is possible to say ecology is the study of the
relationship of living organisms among themselves and with the non-
living components of the environment. Different Authors defined
ecology differently. Some of them are:

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• Ecology is the scientific study of the interactions between

organisms and their environments
• The study of the relationships, distribution, and abundance of
organisms, or groups of organisms, in an environment

Ecology studies the interactions of living things with their physical

environments, with other organisms of the same species, different
species, and with the movement of matter and energy within biological
systems (Environment includes not only the physical but also the
biological conditions under which an organism lives). Ecologists
research these relationships to comprehend the variety and richness of
life throughout the ecosystems on Earth. In other words, why are there
so many different kinds of plants and animals? They may utilise
laboratory trials that examine processes like predation rates in controlled
settings, field measures like species counts and observations of
behaviour in their habitats, and other methods to try and find answers to
these problems; or field experiments, such as testing how plants grow in
their natural setting but with different levels of light, water, and other
inputs. Information about these interactions is used in applied ecology to
tackle problems like building land and marine conservation areas for
threatened species, managing fisheries without overharvesting, and
simulating how natural ecosystems may react to climate change.
Ecosystems are constantly changing due to natural phenomenoa such
climate change, species extinction, and ecological succession. We can
better forecast how ecosystems will react to environmental changes by
understanding how they work. However, because living things in
ecosystems are interconnected in complicated ways, it is sometimes
difficult to predict how a decision like introducing a new species would
impact the ecosystem as a whole.

Branches of Ecology
Ecology can be divided depending on the following concepts:
• Hierarchical organization –according to level of organization
• Taxonomic –according to organisms studied
• Time/Place -According to time/place

Many other ways to subdivide ecology:

A) Hierarchic: organism, population, community, ecosystem,
biosphere
B) Taxonomic: plant ecology, animal ecology, microbial ecology,
avian ecology, etc.
C) Time/Place: marine ecology, tropical ecology, freshwater ecology
Hierarchical structure of ecological systems
1. Organism: fundamental unit of ecology. No smaller unit in
biology has an independent life in the environment.

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2. Population: A group of organisms consisting of a number of

different populations that live in defined area and interact with
each other.
3. Community: A group of organisms consisting of a number of
different species that live in an area and interact with each other
4. Ecosystem: a biological community plus all of the abiotic factors
influencing that community.
5. Biome: A distinct ecological community of plants and animals
living together in a particular climate.
6. Biosphere: the aggregation of all ecosystems (the sum of all of
the organisms of the earth and their environment). Biome is the
living zone of the planet.

Self-Assessment Exercises 1
1. Outline the concepts upon which Ecology can be divided
2. What is the Hierarchical level of organization of ecology?

5.4 Definitions of Ecological Terminologies

You are expected to understand the meaning of the following

terminologies since they are important throughout the course to grasp its
concept.
1. Abiotic: all non-living components in the biosphere, e.g., air,
water, soil, climate.
2. Autotrophic: when an organism is able to produce its own food
using abiotic components.
3. Biotic: all the living components in the biosphere: animals,
plants, microorganisms, etc.
5. Biomass is the total dry weight of living organisms at a particular
tropic level or per unit area eg. total weight of maize crop per
hectare.
6. Carrying Capacity is the maximum number of organisms an area
can comfortably support without depletion of the available
resources.
7. Endemic species are found only in a particular area, eg.
kangaroos found in Australia
8. Key-stone species is mostly a predator species, which is not
present in large number but has a major influence on the
characteristics of a community, eg. lion in the forest.
9. Critical Link species; help other species in the vital activities, e.g.
pollinators for plants, parasitic and symbiotic relationships.
10. Habitat: It is a natural environment of an organism where it
grows, lives and reproduces. It is an ecological area best-suited

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for an organism. Habitats vary in the physical and chemical

composition. It includes abiotic components like water, temperature,
light and soil and biotic components too, eg. parasites, competitors,
pathogens and predators interacting with them constantly. Life exists not
only in the most favourable habitat but also in the most extreme and
harsh environment. Ecology at an organism level tries to understand
how different species adapt to their environments for their survival and
reproduction.
11. Niche: includes all the interaction of a species with the biotic and
abiotic factors of its environment. Each species has a defined
range of various abiotic factors that it can tolerate, a number of
resources it utilises for survival and performs a specific functional
role in an ecosystem, all these together form a niche, which is unique
to a species.
12. Carnivores: animals that eat only meat. They are generally
predators, eg. lions, cheetahs etc., in a specific environment.
13. Ecosystem: the combined physical and biological components of
a specific habitat where animals and plants are interdependent on
each other for survival.
14. Herbivores: animals that only eat plants, eg., buck, cows, goats,
sheep, rabbits etc.
15. Heterotrophic: Organisms that are unable to produce their own
food, and must eat other organisms
16. Omnivores: animals that eat both plant and animal matter, eg.,
humans, pigs, baboons.
17. Saprophytic organisms: organisms that live on dead organic
matter because they are able to decompose (break down) dead
plant and animal matter.
18. Scavengers: animals that eat what is left over by predators.
Examples are hyenas, crayfish and vultures.
19. Photosynthesis: a process where plants use sunlight energy,
water and CO2 from the air, to produce organic compounds like glucose
and inorganic compounds like O2.
20. Vegetation: the plant life that is found in a biome.

Self-Assessment Exercises 2

Explain what is the meaning of the following ecological terminologies:

1. Autotrophic
2. Biosphere

5.5 The meaning of Habitat in Ecology

Habitat ecology is a fascinating branch of natural science that deepens

our comprehension of the processes that influence the distribution and
abundance of species. It can also be described as a particular natural

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setting with both physical and biological characteristics where only a

few species of an organism can coexist. A plant, animal, or other
organism's natural environment or home is known as its habitat. It gives
the creatures that inhabit the area food, water, shelter, and a place to
live. There are many distinct sorts of habitats, such as those for wildlife,
aquatic life, grazing land, and coastal life, and each one supports a
unique ecosystem. Which wildlife species can be found there depends
on the habitat type. Each and every animal has a unique natural habitat
in which it can dwell. Different animals can be found in various habitats.
"Habitat" refers to a variety of things. Ecology refers to either an
assembly of living things along with their abiotic environment or the
space and resources utilised by a certain species (the habitat of a
species). This introduction's main concern is the latter. There are various
habitat types which include:

1. Aquatic Habitats
The world's lakes, rivers, wetlands, lagoons, and swamps are all
considered to be parts of the aquatic biome. There are mangroves, salt
marshes, and mud flats where freshwater and saltwater mix. These
aquatic habitats support aquatic plant and animal lives, where they are
safeguarded, provided with shelter, and provided with a steady supply of
food and water. These environments may house a variety of aquatic
ecosystems, including the coral reef ecosystem, which is a mechanism
for producing reefs made up of coral polyps linked together by calcium
carbonate. A wide variety of wildlife species call each of these habitats
home. Almost every animal group, including mammals, bird species,
amphibians, reptiles, and invertebrates, can be found in aquatic settings.
The intertidal zone, for example, is a mesmerizing place that is wet
during high tide and dries up as the tide goes out. The organisms that
exist in these parts must endure thrashing waves and survive in both
water and air. This is where you will be able to locate mussels and snails
as well as kelp and algae.

2. Desert Habitats
Scrublands and deserts are examples of areas with little rainfall. They
are known to be the driest places on Earth, which makes life there
extremely difficult. Desert animals dwell in arid areas and have unique
adaptations that allow them to survive there. Due to their ability to
tolerate the intense heat and inconsistent water supplies, desert animals
stand out from other species that inhabit different ecosystems thanks to
their richness. The same idea also applies to desert flora. It is possible
for human activities to push a drier region of land into the classification
of the desert biome. This phenomenon is termed desertification, and
typically results from agricultural mismanagement and deforestation.

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3. Forest Habitats
Trees cover the forests and woods biomes. There are forests in many
places around the world, covering around one-third of the planet's land
area. There is a huge genetic diversity seen in forests. More bird species
are reportedly found there than in any other natural area. There are many
different types of forests, such as temperate, tropical, cloud, coniferous,
and boreal types. Each one of them has a unique range of climatic
characteristics, species compositions, and wildlife groups. For example,
the Amazon rain forest is a varied bionetwork and is home to a tenth of
all animal species in the world. It encompasses a substantial section of
the Earth's forest biome, at around three million square miles.

4. Grassland Habitats
Grasslands are environments with a lot of large trees or shrubs but
predominantly grasses. Tropical grassland eg. Savannas, and temperate
grassland are the two types of grasslands. The world is covered in the
wild grass biome, which includes the American Midwest grasslands as
well as the African Savanna. There are organisms there that are specific
to that type of grassland, but you'll normally find a lot of hoofed animals
and some predators to hunt them. Grasslands have both dry and rainy
seasons. They are susceptible to cyclical flames because of these
extremes, and these fires can quickly spread across the landscape.

5. Tundra Habitats
It's frigid in the tundra. Low temperatures, minimal vegetation, long
winters, short growing seasons, and limited drainage are its defining
characteristics. Despite being a severe area, a variety of species call it
home. For example, the Arctic National Wildlife Refuge in Alaska is
home to 45 different species, including hardy rodents and bears and
whales. Close to the North Pole, Arctic tundra extends southward to
where coniferous trees are found. Alpine tundra can be found on
mountains all over the world, above the tree line. Permafrost is typically
located in the tundra biome. This is known as any rock or soil that
remains frozen throughout the year and it can be unstable ground when
it does defrost.

6. Microhabitats
The minimal physical requirements of a particular organism or
population are referred to as a microhabitat. Numerous microhabitats
with subtly different exposure to light, moisture, temperature, air
movement, and other factors make up every habitat. The lichens that
grow on the north face of a rock are different from those that grow on
the south face, the flat top, and the neighbouring soil; those that grow in
ruts and on elevated surfaces are also distinct from those that grow on

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quartz veins. The micro-fauna, various invertebrate species, is present

among these tiny "forests," each of which has specific environmental
requirements.
7. Extreme Habitats
Despite the fact that the bulk of life on Earth occurs in mesophyllic
(moderate) environments, a small number of organisms, primarily
bacteria, have been able to tolerate hazardous environments that are
inhospitable to more complex life forms. For example, microorganisms
can be found in Lake Whillans in Antarctica, which is half a mile below
the ice. Because of the lack of sunlight, these organisms must obtain
their organic material from other sources, such as decomposing matter
from glacier melt water or minerals from the underlying rock.

5.5.1 Ecological Niche

An ecological niche refers to the interrelationship of a species with all
the biotic and abiotic factors affecting it. This definition of niche though
has changed over time. Joseph Grinnell in 1917 coined the term niche,
which he used as mostly equivalent to a species habitat. George Evelyn
Hutchinson used the term niche to describe the multi-dimensional space
of resources available to and used by a species. In niche biology, a niche
pertains to any of the following: i). The specific area where
an organism inhabits; ii). The role or function of an organism or species
in an ecosystem; iii). The interrelationship of a species with all the biotic
and abiotic factors affecting it. Despite the fact that niches have been
defined differently, it is now generally accepted that it has to do with
how an organism or a population adapts to competition and the
distribution of resources. It specifically indicates the position of a
population or an organism in an ecosystem. An ecosystem's biotic and
abiotic variables may have an impact on a niche. However, a species'
ecological niche will influence the characteristics of its surroundings
because these characteristics are essential to its existence. The different
ecological niches.
• A fundamental niche is defined as the niche of a species in the
absence of competition. Conversely, a realized niche is the niche
that a species occupies due to pressures, eg. the arrival of a
competing species to its habitat.
• Niche overlap is defined as that when two organisms use the
same resources or other environmental variables. Often, niches overlap
only partially as the resources are shared.
• A vacant niche is a niche that is yet to be occupied in an
environment. However, the existence of a vacant niche is still a
matter of debate. Nevertheless, possible causes of vacant niches
are presumed to be habitat disturbances (eg. forest fires and
droughts) and evolutionary eventualities (ie. when species failed
to evolve).

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5.5.2 Niche Formation and Partitioning

Both abiotic and biotic factors help shape the niche of an ecosystem.
Abiotic factors, such as temperature, climate, and soil type, of an
ecosystem will help form the niches while natural selection works to set
which niches would be favored and not. Through time, the species
eventually develop special features that help them adapt to their
environment. If they fit in, they could thrive and survive in surroundings
that match their features. Nevertheless, the extent of their population
may be controlled by biological constraints, such as predation,
competition, and parasitism.
• Competition in a habitat could limit the population of a species as
co-habitats could compete for available nutrients, space, light,
and other vital resources.
• Predation could also restrain the species’ population depending
on the number of predators and the extent of predation.
• In parasitism, the presence of parasites that take the species as
their host and the vulnerability to pathogens causing diseases are
also factors that can restrain the species population. The niches in
an ecosystem form and evolve as these factors change.

As each niche is occupied by a single species, natural selection will

divide up the market for that species, a process known as niche
partitioning. Different species cannot share the same niche. However,
coexistence can enable rival species to carve out distinct ecological
niches. To prevent competing for scarce resources, they must be able to
cohabit, perhaps through resource differentiation (or niche partitioning).
If not, natural selection will favour one of the two competing species
while eventually eradicating the other.

Self-Assessment Exercises 3
1. Why Does an Organism Need Habitat?
2. Outline the major types of habitats in ecology

1.6 Summary

You have learned the meaning and elements of ecology in this unit.
The importance of the study Ecology and basic ecological terms were
also highlighted. The various branches of ecology and the criteria
employed for the classification of the various branches was also studied.
The unit explained the concept and types of habitats in ecology.

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1.7 References/Further Readings/Web Sources

Beerling, D. The Emerald Planet: How Plants Changed Earth's History.

Oxford, UK: Oxford University Press, 2007.

Biro, P. A., Beckmann, C. et al. Small within-day increases in

temperature affects boldness and alters personality in coral reef
fish. Proceedings of the Royal Society B: Biological
Sciences 277, 71-77 (2010).

Gurevitch, J., Scheiner, S. M. and Fox, G.A. (2020). The Ecology of

Plants, 3rd Edition,
https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biolog
y/ https://byjus.com/neet/ecology-and-environment/
https://byjus.com/biology/ecology/
https://www.cartercenter.org/resources/pdfs/health/ephti/library/lecture_
notes/env_health_science_students/ln_ecology_final.pdf
http://unaab.edu.ng/wp-
content/uploads/2009/12/472_BIO%20201%20NOTES.pdf
https://www.youtube.com/watch?v=GlnFylwdYH4
https://www.youtube.com/watch?v=OfV3VNgjpvw
https://www.youtube.com/watch?v=_NEIq-uoBb8
https://www.youtube.com/watch?v=EdKhQVHc3Ao

1.8 Possible Answers to Self-Assessment Exercises

Answers to SAE 1
1. Ecology can be divided depending on the following concepts:

• Hierarchical organization –according to level of organization

• Taxonomic –according to organisms studied
• Time/Place -According to time/place
2. A way to divide ecology could be Hierarchic:
organism, population, community, ecosystem, biosphere

Answers to SAE 2
1. Autotrophic: when an organism is able to produce its own food
using abiotic components.
2. Biosphere: it is the global sum of all ecosystems, and is the zone
where all living organisms live on earth.

Answers to SAE 3
1. As a good habitat is a good combination of food, water, cover,
and space to survive and reproduce. All these things are necessary for
good habitat and species cannot survive without them.

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2. There are different types of Habitats as follows:

a. Aquatic Habitats
b. Desert Habitats
c. Forest Habitats
d. Grassland Habitats
e. Tundra Habitats
f. Microhabitats
g. Extreme Habitats

Glossary
Applied ecology -A branch of ecology which uses ecological
principles and insights to solve environment.

Amensalism -An interaction between two organisms, where one suffers

a reduction in resources, or an increase in costs imposed by conditions,
due to the presence of another organism.

Biodiversity -An accepted shortening of the phrase ‘biological diversity’

commonly used to describe species richness.

Climate Change -Long-term changes in the climatic variables

experienced in a defined spatial area

Commensalism -This refers to the interaction between two species

where one organism gains resources or shelter from conditions, due to
the presence of the other species.

Community-This refers to all species in a defined spatial area or

ecosystem, which interact via trophic, competitive, commensal, amensal
or mutualistic interactions.

Competition -Competition is the process where organisms gain a

greater or lesser share of a limited resource.

Ecological niche -The sum total of all the resources used by, and the
biotic and abiotic conditions suffered by, a species.

Ecology -The scientific study of the distribution, abundance and

dynamics of organisms, their interactions with other organisms and
with their physical environment.

Ecosystem -All organisms and the abiotic environment found in a

defined spatial area, generally assumed to be the collective description
of a community and its physical environment.

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Evolution -Change in the relative frequencies of heritable genetic

information across generations of organisms.

Mutualism -A biotic interaction between two organisms, where they

gain an increase in resources, or a reduction in stressful conditions, from
the presence of the other organism.

Parasitism -A trophic interaction in which individuals of one species,

called the parasite, feeds upon the tissues of living individuals of another
species called the host.

Predation -A trophic interaction in which individuals of one species (the

predator) kills and eats individuals of the other species (the prey).

climax community -A community of biological species that has

reached a stable state, occurring when the different species are
best adapted to average conditions in a given area.

End of Module Questions

1. List any five (5) interactions between or within species.
2. Discuss the interrelationships of organisms.
3. Give examples of mutualistic versus antagonistic interactions
discuss some ecological and evolutionary consequences of
these interactions.
4. Discuss scenarios where predation plays an important ecological
role and others where it appears to be less important.
5. To what extent are the outcomes of species interactions context-
dependent?
6. Which factors drive the variable outcomes of interactions?
7. In which type of interactions, one entity hunts another animal to
suffice its nutritional requirement?

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