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National Book Foundation

Federal Textbook Board
Islamabad
Based on National Curriculum of Pakistan 2022-23

Model Textbook of

Biology
Grade
9

National Curriculum Council

Ministry of Federal Education and Professional Training

National Book Foundation

as
Federal Textbook Board
Islamabad
 © 2024 National Book Foundation as Federal Textbook Board, Islamabad
All rights reserved. This volume may not be reproduced in whole
or in part in any form (abridged, photo copy, electronic etc.)
without prior written permission from National Book Foundation

Model Textbook of Bialagy

for Grade 9

Authors
Jawaid Mohsin Malik, Ruquaya Shaikh, Dr. Kashif Ali,
Abid Mughal, Sajid Ali Shah

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Ministry of Federal Education and Professional Training, Islamabad

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 Preface
This Model Textbook for Biology Grade 9 has been developed by NBF according to the
National Curriculum of Pakistan 2022-2023. The aim of this textbook is to enhance learning
abilities through inculcation of logical thinking in learners, and to develop higher order
thinking processes by systematically building the foundation of learning from the previous
grades. A key emphasis of the present textbook is creating real life linkage of the concepts
and methods introduced. This approach was devised with the intent of enabling students to
solve daily life problems as they grow up in the learning curve and also to fully grasp the
conceptual basis that will be built in subsequent grades.
After amalgamation of the efforts of experts and experienced authors, this book was
reviewed and finalized after extensive reviews by professional educationists. Efforts were
made to make the contents student friendly and to develop the concepts in interesting ways.
The National Book Foundation is always striving for improvement in the quality of its
textbooks. The present textbook features an improved design, better illustration and
interesting activities relating to real life to make it attractive for young learners. However,
there is always room for improvement, the suggestions and feedback of students, teachers
and the community are most welcome for further enriching the subsequent editions of this
textbook.
May Allah guide and help us (Ameen).

Dr. Raja Mazhar Hameed

Managing Director
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Contents
Chapter Description P. No.

The Science of Biology

Biodiversity

Cell

Cell Cycle

Tissues, Organ and Organ Systems

Molecular Biology

Metabolism

Plant Physiology 112

Plant Reproduction 129

10 Evolution 146

Glossary 1957
Chapter 1

THE SCIENCE OF BIOLOGY

SLOs: After completing this lesson, the student will be able to:
Define biology
State Quran instructs to reveal the study of life.
Ses

Define major fields of biology as Botany, Zoology and Microbiology

Define with examples that biology has many sub-fields: Morphology, Anatomy, Physiology, Histology,
Cytology, Genetics, Molecular biology, Embryclogy, Paleontology, Taxonomy, Ecology, Marine biology,
Pathology, Immunology, Pharmacology.
Relate that biology connects with other natural sciences. Students should be able to distinguish in
terms of the broad subject matter of the given fields: Biophysics, Biochemistry, Computational biology,
Biogeography, Biostatistics, Biotechnology, Bio-economics.
Identify the careers in biology and explain with examples how biology is a subset of the natural
Sciences.
Justify with examples that science is a collaborative field that requires interdisciplinary researchers
working together to share knowledge and critique ideas.
Describe the steps of the scientific method: Recognition, Observation, Hypothesis, Deduction,
Experiments, and Results.
Evaluate the terms ‘hypothesis’, ‘theory’ and ‘law’ in the context of research in natural sciences.
 [ Chapter 1: The Science of Biology |

Among all the living organisms human beings are the most intelligent ones. By using their
intelligence human beings started learning and this learning lead to development of
science.

1.1 INTRODUCTION TO BIOLOGY

What is science? When you look at the plants you observe leaves and flowers. You wonder
‘why are the leaves green? Why are the flowers of various colours? Asking this type of
question is the first step in doing science, Science is a process of collecting information
about the world around us. Much of the time, the first step in collecting information is
asking a question. Why do I feel pain when I touch a hot object? Making observations,
asking questions and trying to find the answers is what science all about. The study of
science helps us to answer the how, what, where and why of our surroundings.

1.1.1 Definition of Biology

The word biology consists of two Greek words bios meaning life and fogos meaning
thought, reasoning and study. Biology is the study of living organisms. It helps us to explain
how living things relate to one another and to their surroundings.

1.1.2 Quranic Instructions to Reveal the Study of Life

What science is discovering today, the Holy Quran has already hinted several hundred
years ago, The Holy Quran is a book for all times to come. It gives us spiritual, moral and
practical knowledge. There are many verses in Quran which tell us about the origin of life.
Some are quoted here;
1. Origin of Life in Water
b
Fd q ts ht we dl ed ald
F Pte slolgslilegs
“We made every living thing from water”
(Sura Ambia 21, Ayat-30}
As we know that living things consists of 60 to 90 percent of water. So all living things
have come out of water and thus they have a common origin.

2. Creation of Man

J5HE Jlalegeskiyhfa
“He made man from clay like the potter”
(Sura Rehman, Ayat 14)
Creation of man consisted of two steps. The first step was the creation from water. The
second step was to mix clay with water to create man. It can be said for all animals as
man shares all characteristics of life with other animals.
 [ Chapter 1: The Science of Biology |

3. Development
ai Se 2 93 wei ae 2? 9 Seiek ite neta Ee af vite ad
hc det GS AR Asdklasl GaSasle das Gals $3
oo t 7e ied
EZ sad 3253
“Then fashioned we the drop a clot, then fashioned we the
clot a little lump, then fashioned we the little lump bones,
then clotted the bones with flesh,”
{Sura Al-mominoon, Ayat 14)

The sequence of developmental stages is described in Quran many times.

Muslim Scientists have made great contribution to the field of biology. The knowledge
of Jabir Bin Hayyan, Adul Malik Asmai and Bu Ali Sina have contributed a lot in the
development of present-day knowledge of plants and animals.

1.2 MAJOR FIELDS OF BIOLOGY

Biology has three main divisions: Botany, Zoology and Biology
Microbiology. Botany is the study of plants. Zoology is the
study of animals. Microbiology is the study of micro-
organisms e.g., viruses, bacteria etc.
Botany Zootoy| microbotogy|

Sub-fields of Biology

Morphology Anatomy Physiology Histology Cytology

Genetics Molecular biology | Embryology Paleontology Taxonomy
Ecology Marine biology Pathology Immunology Pharmacology

By dividing biology into a number of sub-fields its study becomes convenient. Some of the sub-
fields of biology are:
1. Morphology: The study of the size, shape, and structure of animals, plants, and
microorganisms is called morphology. For example, the morphology of a flowering plant
includes the roots, stem, leaves, flowers, and fruits. Dental structure in humans is an
example of human morphology.
2. Anatomy: The study of the internal structure of the organisms is called anatomy. Anatomy
is also called internal morphology. The examples of anatomy include human body parts such
as muscles, heart, brain, and kidneys etc.
3. Physiology: The study of the functions of various organs of the organisms is called
physiology. The examples of physiology are digestion, respiration, excretion,
photosynthesis etc.
 | Chapter 1: The Science of Biology |

4.Histology: The microscopic study of tissues of organisms is called

histology. The example is epithelial tissue that form a
continuous layer covering the entire body surface.
Cytology: The study of the structure and functions of the cell is
called cytology. It is also called cell biology. For example, the
study of plant and animal cells.
. Genetics: The study of genes, and heredity in organisms is called Fig 1.1. Epithelial tissue
genetics. For example the plants having red flowers
produce red flowerers. The white cats produce white | Fossils are remains of the living things
kittens. preserved by natural process, Study of
fossils help us to understand the life of
Molecular biology: Molecular biology is the study of | past and satiate @f Geclition,
biology at molecular level.
Embryology: Embryology is the study of the
development of an organism from a fertilized egg.
Paleontology: It is the study of the history of life on |
Earth as based on fossils.
10. Taxonomy: The classification and naming of ©
organism is called taxonomy. For example humans
are mammals. Its scientific name is Homo sapiens.
11. Ecology: The study of the interrelationship of
organisms and their environment is called ecology. It is also known as environmental
biology. For example the study of ecology of pond, lake, forest, desert etc.
12. Marine biology: The study of organisms that live in sea is called marine biology. For example
the study of fish, whales, dolphins, and porpoises, sponges, crustaceans, and molluscs etc.
13. Pathology: Pathology: Pathology is a branch of science which deals with the study and
diagnosis of diseases.
14. Immunology: The ability of the body to protect itself from foreign substances and cells
including infectious microbes is called immunity and the study of immunity is called
immunology. For example, immunization is a process by which a person becomes protected
against a disease through vaccination. The example of vaccine for diseases are polio,
corona, dengue etc.
15. Pharmacology: The science that deals with the study ; :
of drugs is called pharmacology. In pharmacology, a il skopilay abe gti nr
drug is a chemical substance. For example, Aspirin is | accurate models of the human brain,
a pharm of drug often used to treat pain, fever, and | map the 3D structure of genomes and
inflammation. The other example of drugs is | modelof biological system.
morphine, insulin, penicillin etc.

The word pharmacology is derived from Greek word, pharmakon, meaning "drug" or "poison", together
with other Greek word logia with the meaning of "study of or "knowledge of"

{
SS8 }
 | Chapter 1: The Science of Biology |

1.3 RELATIONSHIP OF BIOLOGY WITH OTHER SCIENCES

Biology in one way or other is integrated with other disciplines
of science. The animals move, walk or run on the principles of
physics. There is a similarity between working principle of lever
in physics and human limbs. The behaviour of atoms and
molecules underline and explain the behaviour of living cell. The
physical structure of atoms and molecules determine their
chemical properties and the roles they play in cells. To
understand biology, basic knowledge of chemistry is necessary.
So, biology is not an isolated science and is associated with other
branches of science.
Fig. 1.3: Relationship of biology
with other sciences
Table 1.1 RELATIONSHIP OF BIOLOGY WITH OTHER SCIENCES
Biophysics Biological organisms work on the principles of physics e.g., movement of
muscles and bones. The study of biological phenomena according to the
principles and laws of physics is called biophysics.
Biochemistry The study of chemical constituents found in an organism and chemical
reactions taking place in the living organism is called biochemistry. Living
organisms consist of carbon, hydrogen, oxygen, nitrogen, etc., and chemical
reactions such as digestion of food, respiration, and photosynthesis takes place
in the organism.
Biostatistics Statistics is related to collecting and analysing various data or facts. The
collection of biological data or facts through observations, experiments and
analysing them according to statistical rules for biological study. It is also is
called biometry.
Computational The study of the use of data analysis, mathematical modeling, and
biology computational simulations to understand biological system is called
computational biology. The example of computational biology includes the
process of locating fragments of DNA on chromosomes.

Biogeography The study of distribution of plants and animals in different geographical regions
of the world is called biogeography.
Biotechnology The study of use of different techniques to manipulate the living organisms for
the benefit of mankind is called biotechnology.
Bio-economics The study of biology from economic point of view is called bio-economics.
Production of wheat, fish, rice and studying their export value etc., are the
examples of bio-economics.

1.4. CAREERS THAT REQUIRE A BACKGROUND IN BIOLOGY

After studying the basic courses in biology at secondary and higher secondary level a person has
to select a career or profession. Pursuing a career in biology can be immensely rewarding and
exciting. There are several applied fields in biology that you can select as a career e.g.,
medicine, surgery, fisheries, agriculture, animal husbandry, biotechnology, horticulture,
farming and forestry etc.

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 [ Chapter 1: The Science of Biology |
L )
Table 1.2 CAREERS THAT REQUIRE A BACKGROUND IN BIOLOGY
Medicine and MBBS stand for bachelor of medicine and bachelor of surgery. Medicine is the
surgery diagnosis and treatment of different diseases. Surgery is the branch which
treats diseases by removal, or replacement of the defective parts or organs.
After MBBS a student can specialize in various fields of medicine and surgery.
Fisheries The fisheries sector makes a significant contribution to the economy of
Pakistan. Careers associated with it are fish farming, fishery management and
related research.

Farming and Farming is the growth of crops and animals to provide food, wool and other
Agriculture products. The practice of agriculture is farming while agriculture is the science
of improving farming methods. Careers associated with agriculture are food
science, agricultural engineering, agricultural entomology (a person who
studies insects) etc.
Animal Husbandry | Animal husbandry is the care and breeding of domestic animals. The careers
associated with animal husbandry are veterinary science, animal breeding,
animal training etc.
Biotechnology Biotechnology is the use of living organisms or their components to make useful
products. The careers associated with biotechnology are bacteriology,
virology, molecular genetics etc.
Horticulture Horticulture means the art of gardening. The careers involved are plant
breeding, horticulture etc.
Forestry It is the science of planting, managing and caring for forests. The careers
related to forestry are forest ecology, environmental engineering etc.

1.5 SCIENCE IS A COLLABORATIVE FIELD

Scientists from all around the world team up to share
ideas and make progress in their research. Some are Bioinformatics is a combination of
biology and information technology.
studying similar things, while others have different It helps to understand complex
knowledge that can help. biological data. The new emerging
careers of biology are
When researchers from different fields work together to
bioinformaticians (apply their
create new scientific knowledge, it's called computer skills in solving problems
interdisciplinary research collaboration. This is important in life science), biomedical
because they can work on research, find solutions, and engineers (develop new devices and
use what they learn to solve problems and discover new equipment for improving human
health), Astrobiologists (study
things. effects of outer spaces on living
For example, Cognitive Science combines knowledge organisms), Cryobiologists (study of
effects of low temperature on living
from neurology, psychology, anthropology, linguistics,
organisms) etc.
environmental, engineering, pharmacology and statistics.
Women's Studies combines what we know about gender,
history, literature, and biology. Public health combines information from medicine, sociology,
and psychology.
 [ Chapter 1: The Science of Biology |
c
There was a special issue about research collaboration during the COVID era, showing how it
was good for both science and society, when we work together across borders, cultures, and
different fields of study.
One famous example of scientists working together is the International Space Station, where
space agencies from Europe, the USA, Russia, and Japan all team up.

Fig.1.4. Collaboration in science

STEAM ACTIVITY 1.1

Topic: CLIMATE CHANGE
The teacher will divide the students into three groups. Each group may comprise of 3-5 students. And
give each group different subtopics related to climate change. The students will investigate or
research on the topics given.
Group 1: Causes of climate change.
Group 2. Effects of climate change.
Group 3. To overcome the problem of climate change.
The students will be given five days to prepare their research work.
Each group will read their research paper in the classroom before the students.
Then the teacher will ask each group to work together and prepare a joint research paper on ‘Climate
change’ and submit.

1.6 BIOLOGICAL METHOD

There is nothing magical about science. You already have some of the qualities of a scientist
@.g., you are curious. You like to do new and different things. You like to explore new places.
These are the natural talents or skills of a scientist which he may use to solve different scientific
problems.
 | Chapter 1: The Science of Biology |

Scientists, including biologists, employ an approach for solving scientific problem that is known
as the scientific method. Biological problems are solved by a series of steps of biological
method.
Biological method: It has the following steps:
Recognition of a biological problem
oe

Observation and identification

eee

Building up hypothesis
Drawing deductions
Devising experiment
See

Inferring result
1. Recognition of the biological problem: Biological problem is a question related to living
organisms. This question is either asked by someone or comes in mind of a researcher.
2. Observations: Observations are very important step in solving a biological problem.
Observations are made by five senses of vision, hearing, smell, taste and touch. Observations
are of two types;
Qualitative observations; which are based on some quality or characteristic. Quantitative
observations; which are based on measurable value. Quantitative observations being
measurable are invariable and can be expressed in terms of numbers, so are more accurate.
3. Formulation of hypothesis: Hypothesis is a statement that may prove to be the answer of
the biological problem under study. Hypothesis is a tentative explanation of the observations
that might be true. A hypothesis should have following characteristics;
a. It should be a general statement.
b. It should be tentative idea.
c. It should agree with the available observations.
d. It should be testable and potentially falsifiable.
4. Deductions: Deductions are the logical consequences of the hypothesis. To draw deductions
hypothesis is taken as true. Deductions involve “if” and “then” logic.
5. Experimentation: It is the most important step of biological method. Experiments are performed
to prove if hypothesis is true or not. The deductions drawn from the hypothesis are subjected to
rigorous testing. Through experimentation, biologist learns which hypothesis is correct.
6. Summarization of the results: The biologist gathers actual quantitative data from
experiments. This data arranged to draw results.

1.7 HYPOTHESIS, THEORY AND LAW

Ahypothesis is a tentative answer to a question. It is based on past experience and the available
data. A scientific hypothesis makes prediction that can be tested by recording additional
observations. In deduction-based science, deduction usually takes the form of predictions about
what outcomes of experiments or observations. We should expect if a particular hypothesis is
correct. We then test the hypothesis by performing the experiment to see whether or not the
results are predicted. This deduction reasoning takes the form of ‘if...then’ logic.

{ a2 }
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 | Chapter 1: The Science of Biology |

Theory
What is a scientific theory and how it is different from a hypothesis? A scientific theory is much
broader in scope than a hypothesis. Compared to any one hypothesis, a theory is generally
supported by more evidence.
In spite of the body of evidence supporting a widely accepted theory, scientists must sometimes
modify or even reject theories when a new research method produce results that do not fit.
A theory that has been verified and appears to have wide application may become biological
law for example, Mendel’s law of inheritance.

The collection of facts or information is called data. First data is collected then data is organized by
using techniques such as tables and graphs. To predict on the basis of data is called analysis. Analysis
of data is done by means of ratio and proportion.

1.8 MALARIA AN EXAMPLE OF BIOLOGICAL METHOD OF STUDY

Malaria has killed more people than any other disease. The malaria is an example of a biological
problem and how such problems can be solved.

Symptoms of Malaria: The patient of malaria feels very chill and cold. His temperature rises above
normal value of 98.6°F. The patient suffers from headache and has feeling of nausea. After some time,
the person begins to sweat, feels better. The whole series of events are repeated after every 24, 48
or 72 hours depending upon the species of Plasmodfum.

1. Cause of malaria
By adopting the steps of biological method, it was proved that malaria is caused by Plasmodium.
Recognition of the problem: Malaria was a problem since ancient times, but its cause was not
known.
Observations: In 19" century, many different causes of malaria were being suggested. By that
time, there were four major observations about malaria.
a. Malaria and marshy areas have some relation.
b. Quinine is an effective drug for treating malaria.
c. Drinking the water of marshes does not cause malaria.
d. Plasmodium is seen in the blood of a malarial patient.
Hypothesis: Based on these observations and other information, following hypothesis was
formulated by a French physician Laveran in 1882.
“Plasmodium is the cause of malaria”.

Deduction: Although hypothesis is a tentative idea, to draw deductions it is accepted to be

true. One of the deductions from the above hypothesis was;
“If Plasmodium is the cause of malaria, then all persons ill with malaria should have
Plasmodium in their blood”
 | Chapter 1: The Science of Biology |

Experiments: This deduction was tested through experiment. Experiment was designed as;
Blood of 100 patients was examined under microscope. For the purpose of having control group,
the blood of 100 healthy persons was also examined under microscope.
Results: The results of experiments showed that almost all malarial patients had Plasmodium
in their blood. Only 07 out of 100 healthy persons had Plasmodium in their blood. Other 93
healthy persons were without any trace of Plasmodium in their blood.
In the 07 healthy persons with Plasmodium in their blood, Plasmodium was in incubation
period. The incubation period is time between the entry of parasite in the host and the
appearance of the symptoms of disease. After few days those 07 healthy persons became ill
with malaria.
Results were quite convincing to prove the hypothesis that “Plasmodium is the cause of
malaria”
Reporting the results: Results of these experiments were announced worldwide which helped
to control malaria.
2. Spread of malaria
Biological method helped to find that mosquitoes spread malaria.
Recognition of the problem: Malaria is a fatal disease since ancient times. After the
confirmation that malaria is caused by Plasmodium, it was important to find how Plasmodium
gets into the blood of man. This disease was more common in areas near stagnant water ponds
where mosquitoes breed. It was found that;
a. Malaria is associated with marshes.
b. Drinking water of marshes does not cause malaria.
From these points, it can be concluded that Plasmodium was not present in the marshy water.
So Plasmodium must be carried by something that comes to marshy water. Problem in this study
was to find that agent.
Observations: An American scientist A. F. A. King listed 20 observations in 1883 about spread
of malaria. Some important observations were;
a. People who slept outdoors were more likely to get malaria than those who slept indoors.
b. People who slept under fine nets were less likely to get malaria than those who did not
use such nets.
c. People who slept near smoky fire usually did not get malaria.
Hypothesis: On the basis of these observations King suggested a hypothesis;
“Mosquitoes transmit Plasmodium so are involved in the spread of malaria”
Deductions: Following deductions were made considering the hypothesis true.
Deduction |: “Plasmodium should be present in mosquito”.
Deduction Il: “A mosquito can get Plasmodium by biting a malarial patient”.
Experiments: In order to test the above deductions, many experiments were performed.
Experiments of Ronald Ross: Ross, a British army physician working in India performed an
important experiment in 1897.

{
Las 14 |
 [ Chapter 1: The Science of Biology |

He allowed a female Anopheles mosquito to bite a malarial patient. He killed the mosquito
some days later and found Plasmodium multiplying in mosquito’s stomach.
Next Ross used sparrows in his experiments. He allowed female Culex mosquitos to bite the
sparrows suffering from malaria. He then allowed these mosquitoes to bite healthy sparrows.
After few days these sparrows became ill with malaria.
In the end, the hypothesis was tested by direct experimentation on human beings. An Italian
biologist allowed an Anopheles mosquito to bite a malarial patient. The mosquito was kept for few
days and then it was allowed to bite a healthy man. The person later became ill with malaria.

Ww —
Healthy we
-%& x
Sparrow s Culex

Fig. 1.5: Malaria in man is transmitted by Anopheles and in birds by Culex

Results: All these experiments confirmed that mosquito transmit Plasmodium and spread malaria.

When a female mosquito pierces the skin with the The word vector means transmitter. Any
mouthparts, a small amount of saliva is injected into the || organism which carries a parasite and
wound before drawing blood. The saliva prevents the blood || transfers it from one organism to
from clotting in the food canal of the mosquito. another is called vector.

Dengue Fever
It is caused by a Dengue virus and is transmitted by mosquite Aedes
aegypti, which has zebra like white and black stripes on its body. Typical
case of Dengue haemorrhage fever is characterized by high grade fever,
bleeding from nose, blood in urine and enlarged liver etc. There is no
specific antiviral drug available for the treatment of patients suffering |
from Dengue fever. The second attack can be more serious and
dangerous. The best prevention is personal protection from mosquito bite and measures to prevent
mosquito breeding.
 [ Chapter 1: The Science of Biology |

| Recognition of Problem |

|
| Observation |
|
» | Develop hypothesis |

|
Make deduction

|
| Perform experiment |
|
4 4
Control group Experimental group
| |
¥
| Infer result |

i |
'_| Hypothesis not supported| | Hypothesis is supported |

|
Experiment or result may
suggest further research

|
Theory |

!
| Principle |

Fig 1.6: Scientific method of study

SUMMARY
Science is the study of world around us.
SS

Biology is the study of living organisms.

The Holy Quran instructs us to study life.
Biology has many divisions and subfields. Biology is related to physics, chemistry,
-

statistics, geography, technology and economics.

Medicine, surgery, fisheries, agriculture, animal husbandry, biotechnology,
horticulture and forestry are dependent directly or indirectly on the study of
biology.
Science is a collaborative field.
Scientific method is a system of observing and recognizing problem, developing
hypothesis, making a prediction that can be tested, performing experiments and
drawing conclusions from the result that support or testify the hypothesis.

{ 16 |
Los
 | Chapter 1: The Science of Biology |

8. Data is the collection of facts.

9, A hypothesis is a possible explanation for a group of related observations.
10. Deduction is the logical explanation of hypothesis.
11.A scientific hypothesis is a tentative, testable explanation for a phenomenon in the
natural world.
12.A scientific theory is an explanation of some aspect of the natural world. It is based
on the facts that have been repeatedly confirmed through observation and
experiments.
13.A scientific law is a statement that describes an observable occurrence in nature
that appears to always be true.
EXERCISE
Section |: Multiple Choice Questions
Select the correct answer:
1. The study of functions of various organs of an organism is:
A) morphology B) histology C) anatomy D) physiology
2. Histology is the microscopic study of:
A) tissues B) cells C) fossils D) plants
3. Paleontology is the study of:
A) environment B) development C) fossils D) animals
4. The other name of environmental biology is:
A) ecology B) biotechnology C) microbiology D) cell biology
5. Microbiology is the study of:
A) fungi B) animals C) plants D) microorganism
6. If a scientist is studying the methods of inserting human insulin gene in bacteria, which
branch of biology may this be?
A) anatomy B) physiology C) biotechnology D) pharmacy
7. The starting point of scientific investigation is:
A) hypothesis B) theory C) observation D) data
8. Information that is gathered as a result of an experiment is called:
A) hypothesis B) data C) theory D) Observation
9. Which of the following represents the correct sequence of different steps of scientific study?
A) observation, —» hypothesis —» experiment —* deduction —» theory
B) observation, —»* deduction —» hypothesis —» theory — experiment
C) hypothesis —* observation —* deduction —» experiment —> theory
D} observation —» hypothesis -—» deduction —* experiment —» Theory
 | Chapter 1: The Science of Biology |

10. Which of the following statements best distinguishes hypothesis from theories in science?
A) theories are hypothesis that have been proven true
B) theories are based on limited data while hypothesis are based on wide range of data
C) theories are uncertain while hypothesis are certain
D) theories are educated guess while hypothesis are widely accepted explanation of
natural phenomenon
11, Malaria is caused by:
A) mosquito B) stagnant water C) swamp D) Plasmodium
12, Malarial patient has plasmodium in his blood. What would be the possible explanation if a
healthy person whe is not having any malarial symptoms shows plasmodium in his blood?
A) Plasmodium are dead B) Plasmodium are in incubation period
C) Plasmodium are not mature D) Plasmodium are inactive
13. You are doing a control experiment which
A) proceeds slowly enough that a scientist can record the results
B) may include experimental groups and control groups tested in parallel
C) is repeated many times to make sure the results are accurate
D)} proceed slowly enough that a scientist can test predictions
14. Which option has correctly matched disease and vector mosquito?
Malaria in humans Malaria in birds Dengue fever
A_ | Anopheles Aedes Culex
B | Aedes Culex Anopheles
C | Anopheles Culex Aedes
D | Culex Anopheles Aedes

Section Il: Short Answer Questions

1. Define the following branches of biology and give at least one significance of studying these
branches
a) Molecular biology b) Physiology
c) Palaeontology d) Pharmacology
2. Can you distinguish between?
a) Anatomy and Morphology b) Cytology and Genetics
c) Biotechnology and Immunology d) Marine Biology and Ecology
3. Healthy life of a person depends on healthy life choices. How study of biology is going to
help you to live a healthy life.
4, What is the contribution of the following scientists?
a) A.F.A King b) Ronald Ross c) Laveran
5. Observations are mainly of two types i.e., qualitative and quantitative. Sort the following
observation according to these two types. Colour of cat, Height of giraffe, Weight of mango
fruits, Body temperature of birds, Volume of blood in humans, Shape of leaves, Climate of
desert, Speed of tiger, Song of a bird.

{ as }
Lise
 [ Chapter 1: The Science of Biology |

6. A Noble prize winner gave a hypothesis about effects of COVID-19 vaccine. Can it be
wrong? Why? Develop deduction from this hypothesis, “Vaccination of COVID-19 can
reduce the severity of complications in case of infection.”
7. Why it is impossible to eradicate malaria?
8. The diagram shows one insect. Answer the following questions related to it.

ii. What is name of organism which transmit malaria disease in man and birds?
iii.. What was the main purpose of experiment by Ronald Ross?
9. Why Ross did not allow the infected mosquitoes to bite a healthy person?
10. A student wants to investigate the effect of different factors on the activity of
salivary amylase. He will design an experiment in order to reach conclusion. What
would be the most appropriate first step to initiate?
11. Hepatitis B virus was found in blood of 10 persons. Only 6 of them were suffering
from Hepatitis B disease. Why?

Section Ill: Extensive Answer Questions

1. How biology is related with other sciences? Show and explain the link.
2. How biology can lead to career of medicine, surgery, fisheries, agriculture, animal
husbandry, biotechnology, horticulture, farming, forestry.
3. Explain that science is a collaborative field.
4, Why is biology important for the welfare of human beings? Give reasons.
5. Give at least ten examples of farming of animals which can improve economy of Pakistan.
Describe the products and benefits of each example as well.
6. Discuss biological method of study and its application.
7. How biological method is applied to find the cause of malaria?
8. Explain use of biological method to understand the spread of malaria.
 BIODIVERSITY
SLOs: After completing this lesson, the student will be able to:
Define biodiversity and classification.
Describe advantages of classification.
OL ass

Discuss the history of classification schemes.

List the three distinct domains into which living organisms are broadly classified into.
List the taxonomic ranks of classification.
Define species
Outline the binomial nomenclature system.
Describe the complications of classifying viruses.
fe
 ( Chapter 2: Biodiversity ]

In the previous chapter we have learned that biology is the study of living organisms. The living
organisms have been divided into major groups so that they can be studied easily.

2.1 DEFINITION AND INTRODUCTION TO BIODIVERSITY

The similarity among living organisms is that they share all the characteristics of life, i.e.,
movement, respiration, sensitivity, nutrition, excretion, reproduction and growth. At the same
time these living things differ from one another and their variety is enormous.

2.1.1 Biodiversity
If you look around you will find variety of various kinds of organisms. The term biodiversity
comes from ‘biological diversity’. Biodiversity has ecological and economic importance. It
provides us with nourishment, housing, fuel, clothing etc. Biodiversity is defined as “the variety
of living organism on earth”.

2.1 Biodiversity
STEAM ACTIVITY 2.1
Take a chart paper. Cut pictures of various plants and animals from old newspapers or
magazines and paste on the chart paper. You have placed all the organisms together at one
place. What is it? This is biodiversity.

The natural biodiversity provides us oxygen, clean water and air. They help carbon cycle and fix
nutrients. They enable the plants to grow. Pests are controlled by organisms such as by insects, birds
and fungi. They help protect against flooding and regulate climate. They help in pollination and crop
production. Biodiversity provides our food stuff and medicines derived mainly from plants. The
industrial materials such as building materials, fibres, dyes, resins, gums, adhesives, rubber and oil
etc., are derived directly from plants.
 ( Chapter 2: Biodiversity ]

2.2 CLASSIFICATION
Classification is the grouping of related facts into classes. It is a process which brings together
like things and separates unlike things.
STEAM ACTIVITY 2.2
Write the names of the organisms in their respective groups on the basis of having similar
characteristics.
Rose, guava, fowl, pigeon, mango, sparrow, snake, crocodile, sunflower, lizard, cat, tiger,
cow, tortoise, goat, dove. For example, rose, fowl, snake and goat have been placed in
separate groups.

Why did you put rose and mango in one group whereas, fowl and pigeon in another group?
You placed the organisms of similar characteristics in groups. For example, you made a group
of flowering plants with Rose, mango, guava and sunflower. You made another group of fowl,
pigeon, dove, and sparrow. All of them have the similar characteristics in each group.
You have separated the organisms into groups on the basis of similarities and differences.
Thus, you have classified the organisms.
To put organisms into separate groups on the basis of similarities and differences is called
classification.

2.2.1 Advantages of Classification

Biologists have devised ways of grouping organisms. The grouping of organisms is called
classification. Taxonomy is the branch of biology concerned with identification, naming and
classification of organisms. Suppose you were asked to classify the living organisms of your
surroundings. What criteria would you use to classify the organisms? The scientific study of
diversity of organisms and their evolutionary relationship is called systematics.
The main aims and objectives of classification are: (1) To determine similarities and differences
between organisms. (2) To arrange organisms on the basis of similarities and differences.
(3) Identify the organisms to study them systematically. {4} To find out evolutionary
relationships among organisms.

2.3 HISTORY OF CLASSIFICATION

The Greek philosopher Aristotle was the first person who classified the living organisms. In 700s,
Abu Usama Aljahiz described 350 species of animals. In the end of 15“ century many biologists
have worked on classification method.
 ( Chapter 2: Biodiversity ]

Andrea Caesalpino (1519-1603): He divided plants into fifteen groups and called them genera.
John Ray (1627-1705): He published important works on the classification of plants.
Tournefort (1656-1708): He introduced the taxa of class and species
Carolus Linnaeus (1707-1778): He grouped species according to similar physical characteristics.
According to earlier classification system, organisms were classified into two kingdoms, then
three-kingdom and then five-kingdom system.
[Classification System]

Two kingdom System] [Three kingdom System] Five kingdom System

1. Two-kingdom classification system: It is the oldest system and classifies organisms into two
kingdoms, the Plantae and Animalia. The kingdom Plantae includes the autotrophs. Bacteria,
fungi and algae were also included in the kingdom. The organisms which depend on autotrophs
or other heterotrophs are included in the kingdom Animalia.
Many unicellular organisms like Euglena have both plant like (presence of chlorophyll) and
animal like (heterotrophic mode of nutrition in darkness and lack of cell wall) characteristics.
So separate kingdom was introduced for such organisms.
2.Three-kingdom classification system: The German Scientist Ernst Haeckel proposed a third
kingdom, Protista to accommodate Euglena like organisms and to separate unicellular
microscopic organisms from multicellular ones.
3.Five-kingdom classification system: In 1937 E-Chatton Tie auenieie wien bck niceus
suggested the terms ‘Procariotique’ to describe bacteria | i, their cells are called
‘Eucariotique’ to describe plant and animal cells. In 1967 | prokaryotes while the organisms
Robert Whittekar introduced five-kingdom classification | which have nucleus in their cells
system. The five kingdoms are: Monera, Protista, Fungi, Bie called eumaryetas:
Plantae and Animalia. In the five kingdom system bacteria and archaea were combined in a
single kingdom Monera, because they shared the prokaryotic form of cell structure.

2.4 CLASSIFICATION- THE THREE DOMAINS SYSTEM

In biology, a domain means the largest of all groups in
the classification of life. Domain is group of kingdoms or
taxonomic category above the kingdom.in 1990 Cart
Woese introduced a three domains system of
classification. The three domains of life are Archaea,
Bacteria and Eukarya.
Classification into three domains is based on difference
in the sequence of nucleotides in the rRNA (ribosomal
Ribonucleic acid) of the cell, the cell’s membrane lipid
structure and its sensitivity to antibiotics.
Fig. 2.2 The three domains of life
 Chapter 2: Biodiversity ]
)

a
1. The Domain Archaea Peptidoglycan or murein is a
polysaccharide, consisting of
The domain Archaea have the following characteristics: sugar and amino acids that form a
a. Archaea are prokaryotic cells. layer outside the rig Animalia id
cell wall.
b. The cell walls of Archaea contain no peptidoglycan.
Cc. The rRNA (ribosomal RNA) are not found in Bacteria
and Eukarya.
Archaea are not sensitive to some antibiotics that
affect bacteria. They are sensitive to some
antibiotics that affect the Eukarya.
Archaea often live in extreme environmnet.
Archae membrane can withstand higher
temperature and stronger acid concentration. S= Sugar
Archaeal creatures include : AA= Amino Acid

Methanogens, Halophiles, Thermoacidophiles.

2. The Domain Bacteria

The domain bacteria have the following characteristics:
1. Microorganisms that produce
Bacteria are prokaryotic cells. methane as a metabolic
The cell walls of bacteria contain peptidoglycan. byproduct is called
ao

They contain rRNA that is unique to bacteria. methanogens.

Bacteria are sensitive to traditional antibacterial 2. Microorganisms that live in
antibiotics but are resistant to most antibiotics high salt concentration are
that affect eukarya. called halophiles.
3. The microorganisms that can
3. The Domain Eukarya live in high temperature and
high acidity are called
The domain Eukarya (also spelled Eucarya) have the thermoacidophiles.
following characteristics:
Eukarya have eukaryotic cells.
aoa oe

Not all Eukarya have cells with a cell wall. Their cell wall contains no peptidoglycan.
Eukarya contains rRNA that is unique to Eukarya.
Eukarya are resistant to traditional antibacterial antibiotics but are sensitive to most
antibiotics that affect eukaryotic cells.
Domain Eukary |

The domain Eukarya are divided into four kingdoms: Protista, Fungi, Plantae and Animalia.
1. Protista: Protists include eukaryotic organisms with unicellular or colonial organization.
These are mostly aquatic. It is a diverse group of organisms. It includes: Animal like protists
called protozoa e.g., Amoeba. Plant like protists called algae e.g., Euglena. Fungi like
protists e.g., slime molds.

{ 24 |
Coe
 ( Chapter 2: Biodiversity ]
J
2, Fungi: Fungi are eukaryotic organisms which have The organisms that are capable of
chitin in their cell wall. Fungi are saprotrophic producing their own food are called
decomposers. Mostly fungi are multicellular. Some autotrophs (photosynthetic mode
fungi are unicellular. The examples of fungi are black of nutrition) @.g., green plants,
autotrophic bacteria, and algae.
bread mold, yeast, mushroom, etc. These are producers.
. Plantae: The members of kingdom plantae are Organisms which eat other things
eukaryotic multicellular and autotrophic with as food are called heterotrophs
chloroplasts containing chlorophyll. Their cell wall is (ingestive mode of nutrition) ¢.g.,
made up of cellulose e.g., moss, mustard. animals, animal like protists, etc.
These are consumers
Animalia: Animals are multicellular heterotrophic
The organisms that depend on
eukaryotes. Animals lack cell wall and chlorophyll.
dead, decaying matter are called
They can generally move from place to place. This saprotrophs (absorptive mode of
kingdom includes invertebrates e.g., insects, starfish nutrition) 9.g., fungi, bacteria.
and vertebrates e.g., fish, frogs and man. Thess are decomposers.

2.5 TAXONOMIC RANKS OF CLASSIFICATION

The group into which organisms are classified are known as taxonomic
categories or taxa (singular ‘taxon’). The taxa form a ladder, called y :
Domain
taxonomic hierarchy. There are eight main taxonomic ranks: (= 2S
kingdom, phylum or division, class, order, family, genus and species.
In addition domain is now usually used as a fundamental rank.
The kingdom is the largest taxon or rank, Each kingdom is further
divided into smaller taxa in the following way:
Phylum (Division: for plants and fungi): A phylum is a group of
related classes.
Class: A class is a group of related orders.
Order: An order is group of related families.

Family: A family is a group of related genera.

Genus: A genus is a group of related species.

Species: A species is a group of similar organisms.

Fig2.3: Taxonomic ranks

of classification
 ( Chapter 2: Biodiversity ]

Table 2.1: Simple classification of human and pea

Taxa Human Taxa Pea
Kingdom Animalia Kingdom Plantae
Phylum Chordata Division Magnoliophyta
Class Mammalia Class Magniopsida
Order Primate Order Fabales
Family Homonidae Family Fabaceae
Genus Homo Genus Pisum
Species Homo sapiens Species Pisum sativum

2.6 SPECIES
Species is a group of similar organisms individuals capable of
interbreeding or exchanging genes among themselves and
producing fertile offspring.
Cross between a male donkey and a female horse produces mule.
It is infertile, because of the odd number of chromosomes, they
can't reproduce. So, it is not a species. Species is the most basic
unit of classification, as well as a taxonomic rank. of
age e >

Fig 2.4: Infe rtile alles

2.7 BINOMIAL NOMENCLATURE
Carolus Linnaeus introduced a naming system to give each organism a name consisting of two
Latin names. The first name is genus name and the second name represents the particular
species. The genus name begins with a capital letter but the species name begins with a small
letter. Since each name has two parts so it is called binomial nomenclature, e.g., biological
name of human beings is Homo sapiens. Our genus name is Homo and specie name is sapiens.
A genus may have many species e.g., all cats belong to genus Felis including lion.

Importance of Binomial Nomenclature

Why do organisms need to be given a scientific name in Latin? Why can’t we just use common
names for organisms? A common name will vary from country to country just because different
countries use different languages. Hence there was a need for a universal language such as
Latin. Even those who speak the same language sometime use different common name for the
same organisms. Example: Brinjal is Baigun in Urdu, Bataoon in Punjabi, Vagton in Sindhi. Is it
not confusing? Its biological name is Solanum metangena. Find out the Punjabi, Sindhi, Pushto
or other local names or German, French, Spanish, Arabic, Russian, Chinese names of the
following organisms which will show the importance of biological name.
1. Potato - Solanum tuberosum
2. Rice - Oryza sativa
 ( Chapter 2: Biodiversity ]
)
A scientific name has the advantage of standing for a single kind of animal, plant or
microorganism all over the world.

2.8 COMPLICATIONS OF CLASSIFYING VIRUSES

Viruses show characteristics of both living and nonliving things. The living characteristics of
viruses are:
1. They occur in different varieties. Prions are composed of proteins
2. They have their own genetic material in the form of only. Viroids are composed of
either RNA or DNA. circular RNA only. Both causes
3. They reproduce using the material of the host cell they infectious diseases in certain
infect. plants. Both are acellular
particles. They are not included in
4. They enter the cells of living organisms and cause
any kingdom of classification
diseases. system.
The non-living characteristics of viruses are:
1. They lack cellular structure and enzyme system.
2. They can be crystallized and store in bottle.
3. They do not respire.
4. Viruses behave as non-living, inert infectious particles outside the host.
Viruses are at the borderline of living and non-living. So, they are not included in any domain
and kingdom under modern classification.

SUMMARY
Biodiversity is the variety of organisms on Earth.
The grouping of organisms is called classification.
Taxonomy is concerned with identification, naming and classification of organisms.
The scientific study of diversity of organisms and their evolutionary relationship is
called systematics.
Aristotle was the first person who classified the living organisms.
According to earlier classification systems organisms were classified into two
kingdoms, three kingdoms and then five kingdom system.
Two-kingdom classification system classifies organisms into two kingdoms the Plantae
and Animalia.
Three system classification system introduced the third kingdom Protista to separate
unicellular microorganisms from multicellular ones.
Five-kingdom classification system includes the kingdoms Monera, Protista, Fungi,
Plantae and Animalia.
. Domain is a group of kingdoms or taxonomic category above the kingdom.
. The three domains of life are domain Archaea, domain Bacteria and domain Eukarya.
. Classification into three domains is based on sequence of nucleotides in the rRNA of
the cell.
. The four kingdoms of domain Eukaya are Protista, Fungi, Plantae and Animalia.
. The group into which organisms are classified are known as taxonomic categories or
taxa.

{a
27 }
 [ Chapter 2: Biodiversity ]
L )
15. The kingdom is largest taxon or rank. Each kingdom is further divided into smaller taxa
which are: Phylum, Class, Order, Family, Genus and Species.
16. Species is a group of organisms that consist of similar individuals capable of
interbreeding.
17. Binomial nomenclature is the biological system of naming the organisms. In it the
name is composed of two terms. The first term indicates the genus and the second
term indicates the species of the organism.
18. Viruses are at the borderline of living and nonliving. There are not included in any
domain or kingdom under modern classification

EXERCISE
Section |: Multiple Choice Questions
Select the correct answer:
1. Inte which kingdom you place a multicellular land organism that performs
photosynthesis:
A) monera B) protista C) plantae D) animalia
2. Which kingdom is mismatched with the characteristics?
A) fungi - usually saprotrophic B) animalia - rarely ingestive
C)} protista - various modes of nutrition D) plantae - photosynthetic
3. The kingdom to which the algae belongs is:
A) animalia B) protista C) plantae D) fungi
4. Scientific name has advantages of:
A) same name applied to different organisms.
B) same organisms have different name in different areas
C) has no scientific basis.
D) has scientific basis and is universally accepted.
5. Binomial nomenclature was introduced by:
A) Aristotle B) Carolus Linnaeus
C) Ernest Haeckel D) R.H Whittaker
8. The organisms that feed on dead, decaying matter are called:
A) saprotrophs B) autotrophs C) heterotrophs D) parasites
10. Viruses are assigned to the kingdom:
A) Plantae B) Protista
C) Fungi D) Not included in any kingdom
 ( Chapter 2: Biodiversity |

11. The common characteristic of viruses, prions and viroids is:

A) Respiration B) Movement C) Infectious nature D) Excretion
12. Colonial organization is the unique feature of kingdom:
A) Animalia B) Protista C) Fungi D) Plantae
13. Which option is correct regarding the mode of nutrition of following organism?
Animal Prokaryote Fungi Plant
A) heterotrophic heterotrophic ingestive autotrophic
B) ingestive absorptive autotrophic heterotrophic
C) ingestive heterotrophic absorptive photosynthetic
D) absorptive autotrophic ingestive autotrophic
14. Viruses are not included in any domain or classification as:
A) they are poorly understood.
B) they are too large.
C) they are of various colours.
D) they are not considered as organism.
15. A related groups of genera consists of:
A) a phylum B) a class C) an order D) a family
16. In which of the following the first letter is capitalized in binomial nomenclature?
A) genus B) class C) species D) family
17. If humans and cats belong to the same class, they must belong to the same:
A) phylum B) order C) family D) genus
Section Il; Short Answer Questions
1. Why are the following scientists famous for?
(a) Aristotle (b) Carolus Linnaeus (c} Carl Woese
Define:
(a) Biodiversity (b) Classification (c) Taxonomy (d) Systematics
(e) Domain (f) Taxa (g) Species.
3. What is domain? Name the three domains of life.

4. What are basis of classification of life into domains?

5. Can you differentiate between? :

(a) Bacteria and Protists (b) Fungi and Plants (c) Plants and Animals.
 ( Chapter 2: Biodiversity |

6. Answer the following with supportive reasons.

(a) Which the simplest domain?
(b) Which is the complex domain?
(c) Are most bacteria harmful?
(d) Which domain/s can flourish or survive in most adverse conditions?
7. Compare the two-kingdom, three kingdom and five-kingdom system of classification.
8. Compare the three-domain system of classification.
9. Why mule is not regarded as a species.
10. Complete the following chart:

Unicellular f
Able to perform photosynthesis

Prokaryotes ¢
With Cell Wall ™=® Unable to perform photosynthesis
Organisms =
t '
Eukaryotes =m (ulticellular
: t
Unicellular Without Cell Wall =>

Section Ill: Extensive Answer Questions

What is biodiversity? Write the importance of biodiversity in the natural ecosystem.
>

Describe classification. How are the organisms classified?

es Sh

What are the main aims and objectives of classification?

Give an account of history of classification.
What are the characteristics of the domain Archaea?
eS

What are the characteristics of the domain (a) Bacteria (b) Eukarya ?
What are the diagnostic characteristics of the four kingdoms of domain Eukarya?
PRPS

Describe the taxonomic ranks of classification.

Write a brief note on species.
. What is Binomial nomenclature? Describe aims, principles and importance of Binomial
ge
i=]

nomenclature using local examples.

11. State the complications of classifying viruses.
 The Cell
SLOs; After completing this lesson, the student will be able to:
Describe cell as the basic unit of life
Compare with diagram the structure of animal and plant cell.
SN

Sketch different subcellular organelles nucleus, mitechondria, cell membrane etc. and outline their
roles.
Outline structural advantages of plant and animal cells.
Identify different types of cells mesophyll, epidermal cells, neurons, muscles, red blood cells, liver
2

cells and sketch their structures

6. Describe the concept of division of labour and how it applies to
7. Within cell across subcellular organelles
8. Multicellular organisms across cell
9. Describe cell specialization
10. Define stem cells as unspecialized cells
 ——,
Unit 3: The Cell

—
3.1 CELL
Earth is a living planet. It is home of a huge variety of life from microscopic organisms to
magnificent blue whales and giant redwood trees. Irrespective of their size and shape all life
forms are made up of units called cells. The functions performed by the living organisms are
also performed at the cell level. So cell is the basic unit of structure and function of all living
organisms.

3.1.1 Structure of cell

In 1665, Robert Hooke discovered cell when he examined a thin slice of cork tissue under a
compound microscope. He observed cells as empty chambers with thick outer coverings.
However, the quality of microscope lenses improved greatly in the nineteenth century which
lead to the discovery of cell nucleus in 1831 and many cytoplasmic organelles in coming years.

Cell membrane

Golgi
apparatus Groplacm

Centrosome Rough
Vacuole endoplasmic
reticulum
Mitochondrion Ribosome

Nucleus S ——TSF Nucleolus

Nuclear
endoplasmic membrane
reticulum

Intermediate Cytoplasm
filaments
Smooth endoplasmic: Nucleus
reticulum Nucleolus
Vacuole Rough endoplasmic
reticulum
Vacuole membrane Ribosome

Cell wall Golgi bodies

Cell membrane
Golgi vesicles
Mitochondria
Chloroplast
Microtubles

Fig 3.2: Plant cell

 ————_
Unit 3: The Cell

a
Cell wall
The cell wall surrounds the plasma membrane of Middle lamella Primary call wall
plant cells. It is rigid, inert covering secreted and oman
deposited outside the cell membrane. It consists of cola
three layers namely middle lamella, primary wall === Nucleus
and secondary wall. neo <==
Middle lamella is a made up of magnesium and K
calcium salts of pectin. It is sticky in nature that
holds the neighbouring cell walls together. Primary |
wall contains cellulose fibres arranged in a criss-
cross fashion. It is thin and flexible. Some plant cells |
like xylem vessels form secondary wall inside the a = Plasma membrane
primary wall. It is very thick and rigid structure due
to presence of lignin which cements the cellulose Fig 3.3: Plant cell wall
fibres together. Cell wall bears tiny pores through
which neighbouring cells form cytoplasmic connections called plasmodesmata.
Algae have cellulose in their cell wall. Fungal cell wall is made up of chitin. Prokaryotes also
possess cell wall made up of peptidoglycan. Cell wall is absent in animals and animal like
protists (protozoa).
Cell wall supports the structure of individual cells and the plant as a whole. It protects and
gives shape to the cell. Plant cells can develop turgor pressure due to presence of cell wall.

Cell membrane
Cell membrane is a thin sheet like covering of
Outside of cell
the cell. Chemically it is composed of proteins
60-80 %, phospholipids 20-40 % and traces of i
Carbohydrate
carbohydrates. The structure of cell membrane re preieine chains

&
is explained according to fluid mosaic model. It _Lipig | teed wis
Np
postulates that cell membrane consists of a_ bilayer, | sang 2 te a
double layer of phospholipids in which proteins ~" ‘ er
iy,
Bie»

are incorporated in a mosaic fashion. In fact, Trasnspor™ :

Phospholipids
protein molecules float like icebergs in a sea like protein
fluid of phospholipids. Cell membranes of
eukaryotes also contain cholesterol. It prevents Inside of cell (cytoplasm)
stiffening of cell membrane. Cholesterol is
required for the fusion of secretory vesicles with
Fig 3.4. Fluid mosaic model of cell membrane
membrane. Carbohydrates are either linked
with proteins or lipids.
Cell membrane acts as barrier and gatekeeper for the cell. It is semipermeable so some
molecules can move across the lipid bilayer but others are blocked. It maintains fixed
environment inside the cell. Cell membrane acts as a barrier between the cell and its
environment. It regulates the exchange of materials between cell and its environment.

{cP
LS 33 | )
 ————_
Unit 3: The Cell

a
Cytoplasm
Between the cell membrane and nucleus of the cell is an aqueous substance called cytoplasm.
It is about 90% water having many dissolved and suspended materials. It is the site for many
biochemical processes. It stores food granules and waste materials. It is home for a variety of
cell organelles which are discussed below.
Endoplasmic reticulum
It is a system of membranes present Rough Smooth endoplasmic
throughout the cytoplasm of eukaryotic endoplasmic reticulum (SER)
cells. Flattened sacs of the endoplasmic ER).
reticulum are called cisternae which form
a network of interconnected channels.
There are two forms of endoplasmic Vesicle
reticulum. Rough Endoplasmic Reticulum
(RER}) are covered with ribosomes. If Golgi
ribosomes are absent it is Smooth —
Endoplasmic Reticulum (SER). ial Lysosome
A complex network of endoplasmic
reticulum provides mechanical support to
the cell. They are also involved in
transport of substances within the cell. Fig 3.5: Structure of Rough and Smooth Endoplasmic
Due to attached ribosomes RER have role Reticulum
in the synthesis of some proteins. SER
synthesize lipids including steroids. SER also detoxify harmful substances. In muscle cells SER
have important role in contraction process.
Ribosomes
Proteins make up to about 55 % dry weight of a cell. A cell thus needs protein synthesis at high
rate. This role is performed by the ribosomes. Ribosomes are tiny granular structures found
both in prokaryotic and eukaryotic cells. They are not bound by any membrane. They are
composed of roughly equal amount of proteins and ribosomal RNA (rRNA). The prokaryotic
ribosomes, however, are smaller in size. A large number of ribosomes are scattered in the
cytoplasm. In eukaryotes many ribosomes are also attached on the surface of RER.

Amino acid chain ©

(protein}

strove Small tl
subnit Small 1
subunit VY
nad bab mRNA
——]
Ribosome

Fig 3.6: Function of ribosome Fig 3.7: Subunits of ribosomes

 ( Unit 3: The Cell ]
L )
Each ribosome consists of two subunits, one small and one large. These two subunits join when
ribosome has to perform its function.

Golgi apparatus Incoming transport

vesicles Cis face
Golgi apparatus was discovered by Camillo
Golgi. It is present in all eukaryotic cells. Like
Lumen,
endoplasmic reticulum, Golgi apparatus is % Cisterae
also collection of flattened sacs called
cisternae. However, in Golgi apparatus many
cisternae are stacked over each other. They
are constantly formed at one end and breakup
Newly
forming —_
vesicle aan
into vesicles at the other end. vesicle
Trans face
Golgi apparatus store and modify materials
Fig 3.8: Structure of Golgi apparatus
into finished form before packing into
vesicles. Some of these vesicles settle in
cytoplasm as organelles like lysosomes.
Others fuse with the cell membrane to release out packed material as cell secretion. Products
of glands like enzymes, hormones, mucus etc. are secreted ij
cellulose fibres which arrange themselves to
form cell wall. Membrane

Lysosomes Lumen

They are single membrane bound small sac Digestive enzyme

like structures. They contain a variety of Proteins.
digestive enzymes. The enzymes contained
in lysosomes are synthesized on RER and then Enzyme substrate
complex
transported to Golgi apparatus. Lysosomes
then bud off from Golgi apparatus with their
processed enzymes.
One important role of lysosome is
intracellular digestion. In this process
lysosomes digest materials taken up by the cell
from outside as food vacuole. When lysosome
fuses with the food vacuole, the lysosomal
enzymes act on complex food substances and
convert them into simple form. They also
engulf and digest unwanted cell organelles.
This process is termed as autophagy.
=
Transport vesicle Sa
—
_\ (containing in-
; active hydrolytic ——s of :
Mitochondria
Energy is an important theme is biology. All
systems, from cells to ecosystems require
energy to work. Cells get energy by the
breakdown of organic food in a process called
respiration. If it requires oxygen, it is called Fig 3.10: Formation and function of lysosome

{ 35 |
 ( Unit 3: The Cell ]
L )
aerobic respiration. It takes place in Matrix
mitochondria. Mitochondria are found in all | = Onerimenuiane
aerobic eukaryotic cells. Mitochondria are y oghtien
double membrane bound structures. The py~a—_#=* \*y |). ‘ 7 Ribsomoe
outer membrane is smooth and inner ef ils ft ON
membrane forms finger like projections called See es oF 8 cristae
cristae. They increase the surface area for =
the respiration. The fluid inside the Inner membrane
mitochondrion is called matrix. Mitochondria Fig 3.11: Structure of mitochondria
have their own DNA and ribosomes. They can
multiply within the cell at their own. They produce energy in the form of ATP that is why they
are called power house of cell.

PLASTIDS
Plastids are double membrane bound organelles. They are found in plants and algae. There are
three types of plastids i.e., chloroplast, chromoplast and leucoplast.

Chloroplast
Chloroplasts are usually oval in structure. Outer Grnum
Two membranes of the chloroplasts form Membrane
chloroplast envelope. They have their own
DNA and ribosomes. They can multiply within
the cell at their own. They have a system of
membranes containing chlorophylls and other

|yy sey
photosynthetic pigments. This system
Wy

consists of hollow coin like membranous

structures called thylakoids. Many thylakoids
a
stack to form granum. Some thylakoids of

\
Membrane Stroma Thylakoids
adjacent grana fuse to from intergrana. The
fluid part of chloroplast is called stroma.
Chloroplasts synthesize food by Fig 3.12: Structure of chloroplast
photosynthesis process. It takes place in two
phases;
a. Light-dependent phase which takes place in thylakoid membranes.
b. Light-independent phase which takes place in stroma.

Chromoplast
Chromoplasts are coloured other than green. They may be red, pink, yellow, blue, purple etc.
They are found in flower petals to attract insects. Insects help in pollination. They are also
present in the wall of ripened fruits where they attract birds and other animals which help in
seed dispersal.

Leucoplasts
Leucoplasts are non-pigmented plastids. They are food storing organelles usually found in roots,
bulbs and stem tubers. They store carbohydrates, proteins or lipids.

{Loe
36 |
 ( Unit 3: The Cell ]

Vacuole tt
A vacuole is a membrane bound fluid filled sac. we Contractile
Animal cell may have many small vacuoles = ~~~ MACHO f ) %
which exist temporarily. They contain water | Nueisas Nei \
and food substances. Some freshwater
organisms like amoeba and sponges have \ @ Food
contractile vacuoles which collect and pump \ Cytoplasm ®& vaeoulwa
out extra water and other wastes. Some cells Sr
ingest food by forming food vacuoles which is acai ‘Membrane
then digested into simple molecules. Food
vacuoles also store food. Fig 3.13: Structure and types of vacuole in animal
cell
Plants cells have a large central vacuole as
shown in figure 4.1. It is formed by joining
small vacuoles. The membrane of plant vacuole is called tonoplast. It contains liquid called
cell sap. Cell sap has dissolved materials like mineral salts, sugars, and amino acids. It also
provides support and helps in growth. The primary role of the central vacuole in a plant cell is
to maintain turgor pressure within the plant cell. Turgor pressure occurs when the fluid
content of a cell pushes the cell membrane against the cell wall in order to provide shape to
the plant cell.

Centrioles
Centrioles are hollow open ended cylinder like
structures. They are found in animal cell. They
exist in pairs near the nuclear envelope. Each
centriole consists of nine triplets of
microtubules, At the start of cell division
centrioles duplicate and two pairs move to the
opposite poles, thus help in the formation of
spindle apparatus. They are also involved in Centrioles
the formation of cilia and flagella.
RD
Cytoskeleton
Fig 3.14: Pair of centrioles
Cell has a system of a variety of fibrous proteins
throughout the cytoplasm. These proteins collectively form cytoskeleton. Three types of
cytoskeletal fibres are identified in the cell. These include; microtubules, microfilaments and
intermediate filaments.
Microtubules are made up of tubulin protein. They are unbranched hollow tube like structures.
Microtubules give rise to spindle fibres, cilia and flagella. Microfilaments are very thin protein
fibres. They consist of contractile proteins mainly actin. They are responsible for the streaming
movements of the cytoplasm. The overall cell movement is also regulated by the
microfilaments. Intermediate filaments are composed of a variety of proteins including keratin
and vimentin. They form a branching network in the cell. They maintain the cell structure. In
tissues, they fix cells with each other.
 ————_
Unit 3: The Cell

as
Cell membrane —_—_ &
The cytoskeleton =

Rough
endoplasmic
reticulum
Microtubules
Ribosome (Tubulin)

Intermediate
filaments

Mitochondrion Microfilaments
e (Actin) y

Fig 3.15: Structure and types of cytoskeleton

Cilia and Flagella

Some eukaryotic cells have extensions that look somewhat like hair. These structures are called
cilia, Some cells have whip like extensions called flagella. Cilia and flagella consist of nine pairs
of microtubules which surround a single central pair of microtubules. Cilia and flagella are
connected to the basal body. The basal body serves to anchor a cilium or flagellum to the cell.
The function of cilia and flagella is movement.

(a} Flagella

Fig. 3.15: Cilia and Flagella

Nucleus
Cell activities like metabolism, growth and reproduction need to be well regulated. In eukaryotic
cell this role is served by the nucleus. Nucleus acts as control centre of the cell because it contains
hereditary material DNA.
Nucleus is surrounded by two membranes which collectively form the nuclear envelope. Nuclear
envelope bears nuclear pores at points where both membranes fuse with each other. Through
nuclear pore nucleus communicates with the cytoplasm. Some nutrients and proteins enter the
nucleus through these pores and ribosomes and mRNA leave the nucleus. Nucleus contains a fluid
called nucleoplasm.

{C=
38 |
 ( Unit 3: The Cell ]

Nucleolus is a round darkly stained area in the nucleus. — Nuclear Nuclear envelope
Ribosomes are assembled at this point. Here ribosomal pore?
RNA (rRNA) is formed which combines with proteins to Nasiealus
form ribosomes. It disappears for some time during cell
division. _- Chromatin
- Nucleoplasm
Hereditary material in the nucleus is actually in the form
of chromatin. Chromatin consists of DNA fibres coiled on Endoplasmic
histone proteins. During cell division chromatin fibres reticulum
condense into more tightly coiled threads known as ~ Ribosomes
chromosomes. Each species has its own unique
chromosomal set different from other species.
Fig 3.16: Structure of nucleus
3.1.2 Structural advantages of animal and
plant cell
The cells of living organisms have basic similarities in structure due to common origin, however,
they differ in many respects. Cell wall makes a major difference in plant and animal cell. The
presence of cell wall in plant cell and absence in animal cell is reflected in their life styles.
Plant cell advantages/ disadvantages Animal cell advantages/ disadvantages
Due to cell wall adjoining plant cells are The supportive structure of an animal as a
cemented with each other. Supportive whole is not dependent on a cell wall but
structure of plant as a whole is thus formed rather on the collective arrangement and
by cell wall. organization of tissues, organs, and skeletal
systems present in the animal's body.
Transport channels in plants, xylem and In animal cells, since they lack a cell wall,
phloem, are also formed because of the transport of fluids, nutrients, and gases
presence of cell walls. occurs through different structures and
mechanisms.
The rigid wall helps plant cell to withstand Animal cells cannot withstand high osmotic
high osmotic stress and store water. pressure and cannot store larger volumes of
water.
Plant cell can become turgid which allows Animal cell cannot become turgid to provide
plant parts to maintain structure and stay support to the body
upright.
Plants cannot move from place to place Lack cell walls which makes then very
because of rigidness provided by the cell flexible. Animal cells can move. Animal
wall. cells/ animals can move to suitable
environmental conditions, find shelter and
better feeding fields and opportunities for
reproduction.
Due to rigid structure plant cell cannot It also helps animal cell to divide and
reproduce at a faster rate. reproduce at faster rate.

3.2 CELL SPECIALIZATION

In multicellular organisms, cells are specialized to perform their specific roles. Daughter cells
formed by mitosis process undergo changes in a process called differentiation. They alter in
size, stricture, metabolic activities and physiological responses. As a result, they become
specialized in their role in the body. Some examples of the specialized cells are given below.

{Css
39 |
 ( Unit 3: The Cell ]

Epidermal cells of plants form protective covering of root, stem and leaves. They are flattened
cells which pack tightly to form a continuous outer layer of plant body. Epidermal cells having some
additional role are modified accordingly. For example, root hair cells which absorb water and
minerals from the soil and guard cells of leaves which regulate the opening and closing of stomata.
ea ested:
Tee LIV LAY
Epidermal cell
NA MAA bigs

PS AML AY, FI 6 ||
Chloroplast
a An
Stomatal pore
fi '
Guard cells

fh W
Many mitochondna
Protective Epidermis Root hair cell Guard cells

Fig 3.17: Epidermal cells

Cuticle
Mesophyll cells are photosynthetic cells of
Upper Epidermis
plants. They are present in plant leaves. They Palisade Mesophy Il
contain a large number of chloroplasts.
Chlorophyll and other photosynthetic pigments
Spongy Mesophyll
are anchored in the thylakoid membranes of
chloroplasts. These pigments absorb light Lower Epidermis
energy and use it to produce food in
photosynthesis process.

Red blood cells (RBCs) are haemoglobin filled

cells to transport oxygen in the body. They are
biconcave disk shaped cells. This shape
provides more surface area to absorb and
release oxygen. Nucleus, mitochondria,
endoplasmic reticulum etc. are absent. It helps
to accommodate more haemoglobin. These
cells are very flexible so they can easily pass
through blood capillaries. The average age of §
RBCs is 120 days.
Fig 3.19: Red Blood cells
Neurons are the cells of nervous system. They
are responsible for coordination in the animal
bodies. To accomplish this job their structure is -_ Dendrites
very unique. A neuron cell has a cell body and
two types of cytoplasmic fibres. One of them are
dendrites which conduct nerve impulses to the
cell body. Others are axons which conduct
messages away from the cell body. The
dendrites and axons make it possible for neurons Axon
Cell body .
to communicate with far away cells of the body.
Fig 3.20: Neuron

{CT
ao |
 ( Unit 3: The Cell ]

Muscles cells have ability to contract and relax. Locomotion, breathing movements, blood pumping
by the heart, change in size of eye pupil, peristaltic contraction of the gut, speech movements of
tongue, lips etc. are result of the muscle contraction. To produce contractions muscle cells have
elongated shape and are filled with actin and its associated contractile proteins.

Smooth Striated Cardiac

muscle cells muscle cells muscle cells

Fig 3.21: Types of muscles

Liver cells are almost round in shape and have
prominent nucleus and abundance of cytoplasmic
organelles. They are metabolically most active cells of
the body. Their few important roles are;
a. Storage of glycogen, iron and some vitamins.
b. Detoxification of toxic substances.
c. Production of clotting proteins of blood.
d. Recycling of old red blood cells.

3.3 DIVISION OF LABOUR

Within a cell different organelles perform their Fig 3.22: Liver and liver cells
assigned roles. Mitochondria act as powerhouse of the
cell as they produce energy for the cell. Ribosomes remain engaged in protein synthesis.
Chloroplasts harvest light energy to manufacture organic food. For the normal survival and
functioning of a cell its organelles must do their specified jobs. The performance of given
function by different organelles is the division of labour.
Cell is the unit of life, so a cell can perform all basic function of life. A cell can respire, take
and utilize nutrients, grow in size, reproduce, show movements etc. In unicellular organisms,
a single cell lives as an organism and performs all these life processes independently.
A huge number of cells assemble a body of multicellular organism. In multicellular organism it
is not possible for billions or trillions cells to perform all life tasks independently. So cells
arrange in groups to perform some given role. A group of cells performing same function is
called tissue.
The cell originating from same zygote change their cell lines and differentiate into unique
structures suitable for their roles. Muscles cells are elongated to make the body parts move by
their contractions. Neurons form thin cytoplasmic fibres to conduct messages in the body.
Muscles cells and neurons cannot exchange their function. Similarly, RBCs transport oxygen and

{Co
41 |
 ( Unit 3: The Cell ]

bone tissue provides mechanical support. In plants mesophyll cells prepare food by
photosynthesis process and phloem cells transport this food to all parts of the plant body.

3.4 Stem cells

Around 220 types of cells are identified in human body. These cells vary in their size, shape and
role. However, all these types of cells have a common origin. They all develop from a single
cell the zygote. A cell which gives rise to cells of other types is called the stem cell. The zygote
is very basic stem cell which has ability to produce all kinds of cell an organism.
In sexually reproducing organisms, life starts from zygote. As the development progresses,
different cell lines are formed. Each cell line has its own stem cell. Brain, liver, and other body
tissues are products of stem cells.
Stem cells by themselves are not differentiated and are un-specialized. Each daughter cell
produced by division of a stem cell has capacity to remain un-specialized stem cell or
differentiate into mature cell of some tissue. So stem cells divide, renew themselves and
daughter cells differentiate into distinct cell type.
Stem Cells

‘ean
xy
a » Other
Hamatopoietic stem cells

/|
stem cells

% —— 4 | . a

Red blood cells White blood cells Platelets Muscle cells Nerve cells Liver cells

Fig 3.23: Stem cells and formation of specialized cells

{Co
42 |
 Unit 3: The Cell

=
STEAM ACTIVITY 3.1
Study of a plant cell
Place a small piece of onion skin in a drop of water on a slide and cover it with a cover
slip.
b. Observe it under the microscope first under low power objective then under the high
power objective.
Cc. Draw diagrams of onion skin cells in following table.

Diagram under low power Diagram under high power

objective lens objective lens

Steam Activity 3.2

Study of an animal cell
a. Gently pass the broad end of tooth pick on the inner side of your cheek.
b. Place the material o tooth pick in a drop of methylene blue solution on a slide and
cover it with a cover slip.
¢; Observe it under the microscope first under low power objective then under the high
power objective.
Draw diagrams of human cheek cells in following table.

Diagram under low power Diagram under high power

objective lens objective lens

SUMMARY
. The cell is considered as the basic unit of life because it is the smallest unit of living
material.
Every cell is surrounded by cell membrane. The cell membrane is a highly fluid mixture of
phospholipids and proteins.
A nucleus is a double membrane system with pores that communicates with the cytoplasm.
It contains genetic information, which is carried by the DNA, Nucleolus is a region in the
nucleus that is the site for ribosomal RNA synthesis and ribosome assembly.

{
LS a3 |
 ( Unit 3: The Cell ]

Mitochondria are double membrane organelles in which the inner membrane is folded to
form cristae. Mitochondrion is the site of aerobic respiration.
Golgi bodies are a series of flattened membrane sacs that process, sort, and modify proteins
synthesized on the ER, and transport proteins to the plasma membrane, to the outside the
cell and the lysosomes.
The endoplasmic reticulum is a series of internal membranes with many functions, i-.e.,
protein synthesis lipid synthesis and transport.
7. Ribosomes are the site of protein synthesis.
8. Lysosomes breakdown organic molecules like proteins into simpler compounds that can be
used by the cells.
9. Plant cell has cell wall, plastids and large vacuole.
10. Mesophyll cells, epidermal cells, neurons, muscles, red blood cells and liver cells are
adapted to their particular functions.
11. Within a cell different organelles perform their assigned roles as there is division of labour.
AZ. A cell which gives rise to cells of other types is called the stem cell.

EXERCISE
Section |: Multiple Choice Questions
Select the correct answer:
1. A network of channels extending from cell membrane to nuclear membrane is called:
A) centriole B) endoplasmic reticulum
C) ribosomes D) centrosome
2. The site of enzyme synthesis in cells is:
A) lysosome B) smooth endoplasmic reticulum
C) Golgi bodies D) ribosome
3. What are the functions of mitochondria?
A) lipid synthesis B) protein synthesis
C) photosynthesis D) cellular respiration
4. Ared blood cell and a plant root hair cell both have:
A) Cellulose cell wall B) haemoglobin

C) Large surface area D) nucleus

{aa }
 Unit 3: The Cell ]

as
5. The diagrams show cells from different types of
tissues (not drawn on scale}. Which type of cell
contracts when it is stimulated?

6. Which of the following cell organelles does not

contain DNA?
A) Nucleus B) Lysosomes
C) Chloroplast D) Mitochondria
7. Phospholipids are required for cell membrane formation are synthesized in:
A) Mitochondria D) Cytoplasm
C) Endoplasmic Reticulum D) Smooth Endoplasmic Reticulum
8. Cytoskeleton is an important component of eukaryotic cells. Which of the following
statement correctly describes cytoskeleton?
A) All the cytoskeletal structures are made up of same protein
B) There is no contractile protein in any cytoskeletal component.
C) Cytoskeleton provides mechanical support and has role in cell division.
D) The entire cytoskeleton is present around the cell membrane.
9. The shape of normal red blood cells is:
A) Oval B) Crescent
C) Biconvex D) Biconcave
10. Plastids of different types are correctly represented by:
Photosynthetic | Pigmented Food storage Colour variety
A) Chloroplasts Leucoplasts Chromoplasts Chloroplasts
B) Chromoplasts | Chloroplasts and | Chromoplasts and | Chromoplasts
chromoplasts leucoplasts
C) Leucoplasts Chromoplasts and | Leucoplasts Chloroplasts
and leucoplasts
chloroplasts
D) Chloroplasts Chloroplasts and | Leucoplasts Chromoplasts
chromoplasts

{ 45 |
 ( Unit 3: The Cell ]
L J
11. Which of the following statement correctly represents ribosomes?
A) They are present only in eukaryotic cell.
B) They are produced in the nucleus then migrate to the cytoplasm where they
synthesize proteins.
C) They are covered by single membrane.
D) All ribosomes are attached to the inner surface of RER.
Section Il; Short Answer Questions
1. Why mitochondria are known as powerhouse of the cell?
2. What makes red bload cells more suitable for the transport of oxygen?
3. Give the modifications of epidermal cells for;
a. Exchange of gases
b. Absorption of water and minerals.
4. Following diagram shows a plant cell;

Keeping in view the parts labeled 1 to 4, answer the following questions:

a. Give the number indicating the structure which controls the cell activities?
b. Name a biochemical process taking place in part 2.
c. What will happen to cell if part 1 is removed and part 3 is overfilled with water?
5. The diagram below represents a nucleus.

Name the structure labeled E and F.

Give the function of F.
Which cytoplasmic organelles are formed by E?
ano

What happens to E during cell division?

{Lose
a6 |
 ( Unit 3: The Cell ]

Cell shape is related to cell function. Give three examples to support your answer.
Plasma membrane has two main components according to fluid mosaic model. Which
component represents fluid and which component represents mosaic?
Select the structures which are present in all cells of all kingdoms. Write one function of
each selected structure.
Cell membrane; Nucleus; Chromosomes; Cytoplasm; Ribosome; RER; SER; Golgi
apparatus; Lysosome; Mitochondria; Centriole; Cilia; Flagella; Cell wall; Cytoskeleton;
Vacuole; Plastids
9. Which cells in animals and plants do not have a nucleus? How do these cells perform their
functions without nucleus?

10. Unripe oranges are green in colour. After ripening their colour changes. Suggest which
organelles’ number changed in them during ripening.
Tt. Which organelles are abundant in the salivary gland cell? Explain.

Section Ill: Extensive Answer Questions

Explain the structural model of cell membrane and give the roles of cell membrane.
ee Bees

How cell wall is important in the lifestyle of plants?

If a cell is rich in SER, list the roles in which this cell will be more efficient.
Give the significance of muscles in the life of animals.
Give the types of plastids and enlist the roles of each type.
PY Sr

Describe the structure and functions of animal cell. How it is different from plant cell?
Justify how the cells of leaf have a variety of specialized structure and function.
State the relationship between structure and function of mesophyll cells, epidermal
Se

cells, neurons, muscles, red blood cells and liver cells

Describe the role of the cell membrane in maintaining equilibrium while exchanging
matter?
 G1 Phase

Cell Cycle
SLOs; After completing this lesson, the student will be able to:
Describe cell cycle
Explain mitosis mefosis and stages of mitosis and mefosis, by use of sketch and diagrams
ON

Compare the process of mitosis and meiosis.

Outline the significance of mitosis and meiosis.
 ( Unit4 : Cell Cycle |

According to the cell theory, new cells originate by division in the pre-existing cell. The cell
which divides is called parent cell and the new cell formed as a result of division are called
daughter cell. The process of cell division is needed of development, growth, healing and for
sexual and asexual reproduction. Cell not only increase in number but also manage to transfer
genetic characteristics to the next generations. During cell cycle, cells grow in size, form new
molecules and organelles, replicate their chromosomes and divide by equally distributing
genetic material in the daughter cell.

4.1 CELL CYCLE

The cell cycle is the sequence of events which involves growth of newly formed cell, replicates
its genome and divides into two daughter cell ultimately. It consists of two main phases;
interphase and mitotic phase.
Interphase is the period in cell cycle between two consecutive divisions. It is divided into G,
(Gap 1), S (Synthesis), and G2 (Gap 2).
G, phase: It starts with the production of new cell. Cell grows in size, increases the number of
its organelles, forms needed proteins and other substances. During this phase cell prepares
itself for the next phase of cell cycle (S phase}. It forms enzymes and nucleotides of DNA
required for replication process.
S phase: It is the synthesis phase of DNA. The cell replicates its entire genetic material to form
its two copies. That is why each chromosome has two chromatids during cell division, one for
each of the daughter cell. These chromatids are attached with one centromere and are called
sister chromatids.
G» phase: During this phase cell prepares for
mitotic phase. Cell forms proteins especially
those required for the formation of spindle
fibres. Also cell accumulates energy to
complete the division process. More
mitochondria are formed.
G, phase: During G;, cell may exit the cell cycle
and enter in Go phase. In Go cell stops to divide.
Some cells e.g., neurons, once mature never
divide again. They remain in G, forever. Cell of
liver, kidneys etc. enter Gp temporarily. When
needed they re-enter the cell cycle and start to
divide again. Many epithelial cells divide Synthesis Phase
continuously. They never enter in G, phase. Fig 4.1: Cell cycle
Mitotic phase (M phase): During this phase cell
divides into daughter cell.
Cancer is a disease of cell cycle. Unlike normal cells of the body, cancer cells do not have a
proper functioning cell cycle control system and therefore divide excessively. This excessive
growth can result in an abnormal mass of cells called tumour. Not all tumours are cancerous
however, a benign tumour is an abnormal mass of essential normal cells. They always remain

{eS
a9 }
 ( Unit4 : Cell Cycle |

at their original site in the body. A malignant tumour is cancerous. It is capable of spreading
into neighbouring tissues and often to other distant parts of the body. The spread of cancer
cells beyond their original site is called metastasis.

4.2 SPINDLE APPARATUS

Cytoskeleton of the eukaryotic cell forms spindle
apparatus during the cell division. Major component of the
cytoskeleton are microtubules. The spindle apparatus
separates chromatid or chromosomes during cell division
and move them to opposite poles. In this way hereditary
material of the parent cell is equally distributed into
daughter cell.
A pair of centrioles is situated near the nucleus of animal
cell. They duplicate and another pair is formed. Both pairs
migrate to opposite poles. They also give rise to spindle
fibres. Spindle apparatus is formed around the nucleus,
but as soon as nuclear envelop disintegrates, spindle fibres Fig 4.2: Spindle apparatus
penetrate in to the region of nucleus, They later on attach
to the centromere of chromosome and pull them to their poles.
There are no centrioles in plant cell, the spindle apparatus of plant cell is formed without
centrioles.

4.3 MITOSIS
The cell division in which parent cell produces two daughter
cell with the same number of chromosomes as in the parent cell. Mitosis is a continuous and
very fast process which takes less than an hour, but to study easily it is divided into karyokinesis
and cytokinesis.

Karyokinesis
It is division of the nucleus, which form two nuclei in a dividing cell. It is further divided into;
prophase, metaphase, anaphase and telophase.

Prophase
During interphase hereditary material is found in the form of very thin threads called chromatin.
If a cell is going to divide, all of its chromatin fibres duplicate during S$ phase of interphase.
Prophase is the longest phase of cell division. At the start of prophase chromatin fibres coil up
and condense into chromosomes. Due to duplication all chromosome consists of two chromatids.
The chromatids of each chromosome are attached to each other at centromere.
Nucleolus disappears as its DNA is packed into chromosomes. At the end of prophase nuclear
membrane splits into vesicles which disperse in the cytoplasm.
Spindle apparatus is formed.
 [ Unité : Cell Cycle ]
K )

r ?
ye

F eg ~V~

aaetie:
Chromosomes. —_-__ — =) ‘

q ~.>s a Metaphase Anaphase- '

*
\ a i
Le

Early mitotic /
spindles Pe Telophase (R
AON
\ Prophase
‘= m9
by
\ CY °

Centrosome a \

Interphase
Duplicated
chromatin > G
46 chromosomes 2 daughter
46 chromosome each

Fig 4.3: Mitosis

Metaphase
Chromosomes are aligned at the equator of spindles. Two spindle fibres, one from each pole,
are attached at the centromere of chromosomes.

Anaphase
Spindle fibres pull the centromeres which split and chromatids are separated from each other.
Individual chromatids are pulled until they reach their respective poles.

Telophase
Chromatids reach at their poles. They uncoil and lengthen to form chromatin fibres again. The
spindle apparatus disintegrates. Nuclear
membrane is formed around chromatin at each
pole. Nucleoli reappear in both nuclei.
Cytokinesis
It is division of the cytoplasm which results in
the formation of two daughter cells. It starts
while telophase is in progress. The pattern of
cytokinesis is different in animal and plant
cell.
 L
[
ty
Unité : Cell Cycle
J]
Cell membrane in animal cell begins to invaginate in Daughter nucle!
the equator region. As a result, a cleavage furrow is
formed which continues to grow inward. Cell
membranes in the furrow finally join up and separate
the two daughter cells.
In plant cell spindle fibres in the equator region form
a structure called phragmoplast. Golgi apparatus
forms vesicles which appear in the centre of
phragmoplast initially and then grow at equatorial Se |i
plane. The content in these vesicles form middle ramen en likes
lamella and primary walls of daughter cells. Later on Fig 415: Cytokinesis.in Blarit cell
some cells form secondary walls.

4.3.1 Significance of Mitosis

The main function of mitosis is to maintain the number of chromosomes and genetic material
in all cells of an organism. Following is the significance of the mitosis.
Genetic stability: Mitosis produces two daughter cells with the same number of chromosomes
as in parent cell. Before the start of cell division, DNA of the parental chromosomes replicates
to form two exact copies. Daughter cells thus will have same genetic information.
Development and growth: Life of sexually reproducing multicellular organisms start from a
single cell, the zygote. The continuous cell division process leads to the development of adult
form. The organisms also grow in size by increasing cell number. Thus the development and
growth of multicellular organisms depends on mitosis.
Cell replacement and wound healing: The replacement of worn out cells involves mitosis. The
epithelial cells of skin, digestive tract and respiratory tract die off regularly. They are replaced
by identical cells produced by mitosis. Damage repair and wound healing depends on the
process of mitosis.
Regeneration: Some animals have ability to form whole part of the body if it is removed
accidentally. This is called regeneration. For example; sea star can regenerate arm,
earthworms can regenerate head, and salamander can regenerate its limb. The production of
new cells to form missing parts involves mitosis.
 ( Unit4 : Cell Cycle |

Asexual reproduction: Mitosis is the basis of asexual reproduction. This reproduction involves
only one parent. All asexually produced offspring are genetically identical to their parent
organism. The vegetative propagation is very common in plants. It involves new generations
from root, stem or leaf of parent plant. Potato, onion, garlic, ginger, grasses etc. reproduce
asexually. Many animal species like sponges, planaria and hydra undergo asexual reproduction.

Parent Hydra Developing New bud New hydra

bud

Fig 4.7: Budding in Hydra

Cloning and tissue culture; Mitosis has made it possible for scientists to produce a very large
number of identical copies of the living organisms in artificial environment. This process is
called cloning or tissue culture if small mass of tissue cells is used.

Shoots ~
Tissue sample scraped Tissue sample place in
from parent plant agar growth medium containing
nurtrients and auxins

Plantlets planted into compost Samples develop into ‘a> vie j

tiny plantlets » Roots

Fig 4.8: Cloning by (a) Tissue culture (b) Vegetative propagation in potato

4.5 MEIOSIS
It is a type of cell division which give rise to four daughter cells each having half the number
of chromosome of the parent cell. It takes place only in cells involved in sexual reproduction.
Such parent cells are usually diploid which by this reduction division produce haploid daughter
cells. Cells which have two sets of chromosomes are called diploid (2n) and cells with half the
number of chromosomes are called haploid (n). Chromosomes in a diploid cell are in homologous
pairs. Haploid cells carry one member of each homologous pair.

{S_
53 |
 ( Unit4 : Cell Cycle |

Meiosis is a continuous process but for convenience is divided into interphase |, meiosis I,
interphase Il and meiosis II.

Interphase |
Before the onset of division process, cell forms a copy of its genome by replication process.
That is why chromosomes appear with two chromatids during division process.

Meiosis |
It is the reduction division which for daughter cells reduces the number of chromosomes to
half. Firstly, karyokinesis forms two haploid nuclei which is followed by cytokinesis.

Karyokinesis in meiosis |
It is further divided into prophase |, metaphase |, anaphase | and telophase I.

“Ky
Prophase |
It is the longest phase of meiosis. Chromosomes begin to appear as thicker fibres due to coiling
of chromatin. Homologous chromosomes line up point to point against each other and form
pairs. Their centromeres are in the same position. This pairing process of homologous
chromosomes is called synapsis. Each pair is called bivalent.

Aomologous
chromosomes

Crossing over between

non-sister chromatids

Bis

Non-sister
chromatids

Fig 4.9: Crossing over in non-sister chromatids

The non-sister chromatids of homologous chromosomes | sister chromatids are two exactly
join each other at some points along their length. Such | similar copies attached by a
points are called chiasmata. Each chiasma is a site for | centromere while The chromatids
the exchange some genetic material between | of two homologous chromosomes
chromatids. The exchange of segments of non-sister | are non-sister chromatids.
chromatids during prophase | is called crossing over.
To the end of prophase I, chromosomes are fully condensed and paired chromosomes repel each
other. However, they are still attached at chiasmata.
Nucleoli and nuclear envelop disappear. Spindle apparatus is formed.

{EE
5a |
 Unité : Cell Cycle

po,
fo
Metaphase |
Bivalents are arranged at the equatorial plate. Spindle fibres are attached to the centromere
of chromosome. One member of a homologous pair receives a spindle fibre from one pole and
other member from the opposite pole.

Anaphase |
Spindle fibres pull on the homologous chromosomes. Separated chromosomes of each pair move
to the opposite poles. Each pole receives haploid set of chromosomes.

Telophase |
Once at their pole, chromosomes uncoil into chromatin. A nuclear envelop is formed at each
pole around the haploid set.

Meiasis |

Interphase |Prophase! Metaphase | Anaphase | Telophase | Cytokinesis|

Synapsis and : Sister
Centrosomes ._ Nucleolus crossing over Spindle fifiber chromatids Sale (on)
Cell membrance, Sax, ae (a {-

chromosome eam \>¢ We —> |”)+29>@a- a &,

Nuclear membrane“ |” in ~
Tetrad Centromere y
Cytoplasm Nucleus <
1 Diploid
Cells (2n)} Meiosis Il

Prophase ll Metaphase ll Anaphase Il Telophase Il Cytokinesis Il

Sister
: 4 Haploid

eo a~ 2 ar
chromatids calls (im)

\ fz ti) ( ii) (aa Se53 (eS)a) (a |

Haploid §/ ‘ , = ,
cells et > oS 7 = = —— 2
Meiosis | \ fi "4 Pe aS f \ na , fa
Le . \ (i we) (SD) (SD)i) ae!) Cp)
le ne \ uf] " } Lo a / \ J \ " i \ i y

Fig 4.10: Meiosis

Cytokinesis
Cytokinesis occurs by cleavage in animal cell of by forming cell wall in plant cell. Although each
daughter cell is haploid with half the number of chromosomes, their chromosomes are
composed of two chromatids. Due to crossing over, these chromatids are not genetically
identical. They must be separated in second meiosis.
Two haploid daughter cells thus formed enter in interphase II.

{Ss
55 |
 [———
Unit4 : Cell Cycle

yy
Interphase Il
This phase varies in length but there is no further DNA replication during this phase.
Meiosis II
It is similar to mitosis and is divided into prophase Il, metaphase Il, anaphase Il and telophase Il.
Prophase Il
Chromatin coils again so chromosomes appear as thick fibres. Spindle apparatus is organized.
Nucleoli disappear and nuclear envelop disintegrates.
Metaphase II
Chromosomes line up separately around the equator of the spindles. Spindle fibres are attached
to the centromere of chromosome. Like mitosis here each chromosome is attached by a fibre
from both poles.
Anaphase Il
Centromeres divide and spindle fibres pull the chromatids to the opposite poles.
Telophase II
Chromatids reach at their poles and uncoil. The spindle
apparatus disappears. Nuclear envelops are formed | Germ cell are diploid which undergo
* meiosis to from haploid gametes.
around chromatin at each pole. All other diploid cells of body
Cytokinesis undergo mitosis and are called
somatic cells,
Cleavage furrow is animal cells and cell wall formation in
plant cells gives four daughter cell at the end of meiosis
process. All cells formed by meiosis process are haploid as they have half the number of parental
chromosomes. Also they have changed genetic makeup because of crossing over between
homologous chromosomes during meiosis |.
4.4.1 Significance of meiosis
Maintenance of chromosomes in sexual reproduction
Maintenance of chromosomes:
During the life cycle of sexually
reproducing organisms, diploid germ _ Haploid sperm
cells undergo meiosis to produce ‘
haploid daughter cell which act as
gametes. Fusion of such haploid
gametes thus maintains chromosome
number specific for each species.
Human have 46 chromosomes in their
somatic cells. The haploid gametes Diploid zygote
(eggs and sperms) formed by meiosis Haploid egg
have 23 chromosomes. In fertilization
process a 23 chromosome sperm fuses Fig 4.11: Fertilization of sperm and egg cell to form zygote
with an egg also having 23
chromosomes. The original chromosome number of 46 is restored in the zygote.
In plants meiosis takes place during spore formation.

{os
56 |
 Unit4 : Cell Cycle

as
Genetic variations
Variations are the differences
among the members of same
species. They are necessary for the
survival of species in always
changing environment. It is because
of meiosis that new combinations of
genes appear in gametes and then
in zygote. Crossing over and
independently formed
combinations of chromosomes in
gametes are two important events
of meiosis. Both crossing over and
chromosomal combination provide Fig 4.12: Variation in Butterfly patterns
basis of variations.
Table 5.7 Comparison of mitosis and meiosis
Mitosis Meiosis
It occurs in somatic cells It occurs in germ line cells

Cell divides only once Cell divides twice

It produces two daughter cells Four daughter cells are produced
Daughter cells produced are diploid All daughter cells are haploid
Daughter cells become part of somatic body Daughter cells form gametes
All chromosomes remain independent of each Homologous chromosomes pair with each
other other
No chiasmata formation Chiasmata are formed
There is no crossing over during mitosis Crossing over takes place during meiosis |
process
Daughter cells are genetically alike. Daughter cells are genetically different from
each other and parent cell
In most cases daughter cells can divide again. Gametes produced by meiosis cannot divide
any more.

STEAM ACTIVITY 4.1

Study of Mitosis in onion root tip
Materials Required
Compound microscope, Acetocarmine stain, Water, Burner, N/10 Hydrochloric acid, Filter
paper, Coverslip, Aceto alcohol (Glacial acetic acid and Ethanol in the ratio 1:3), Glass Slide,
Onion root peel, Forceps, Blade, Watch glass, Dropper, Needle, Vial.
 Unit4 : Cell Cycle

——y

Procedure
1. Place an onion on a tile
With the help of a sharp blade, carefully snip the dry roots of the onion
YP

Place the bulbs in a beaker containing water to grow the root tips
It may take around 4 to 6 days for the new roots to grow and appear
Ser

Trim around 3 cm of the newly grown roots and place them in a watch glass
With the help of forceps, shift it to a vial holding freshly prepared aceto-alcohol i.e., a
mixture of glacial acetic acid and ethanol in the ratio 1:3
Allow the root tips to remain in the vial for one complete day
a

. With the help of forceps, pick one root and set in on a new glass slide
. With the help of a dropper, allow one drop of N/10 HCl to come in contact with the tip
of the root. Additionally, add around 2 to 3 drops of the acetocarmine stain
. Heat it lightly on the burner in such a way that the stain does not dry up
. Excessive stain can be carefully treated using filter paper
. The more stained part of the root tip can be trimmed with the help of a blade.
. Discard the lesser stained part while retaining the more stained section
. Add a droplet of water to it
. With the help of a needle, a coverslip can be mounted on it

{ ss |
aS
 ( Unit4 : Cell Cycle

SS
16. Gently tap the coverslip with an unsharpened end of a needle in order for the
meristematic tissue of the root tip present under the coverslip to be squashed properly
and to be straightened out as a fine cell layer
17. The onion root tip cells’ slide is now prepared and ready to be examined for different
stages of mitosis
18. Observe and study mitosis by placing the slide under the compound microscope. Focus
as desired to obtain a distinct and clear image

Observations and Conclusion

1. The slide containing the stained root tip cells is placed on the stage of the compound
microscope, changes taking place are noted and sketched.
2. The different phases of mitosis, such as prophase, metaphase, anaphase and telophase
can be observed.
SUMMARY
1. The cell cycle is the period from beginning of one division to the beginning of the next
division.
2. Interphase can be divided into the first gap phase (G;), the chromosomal synthesis (5),
and the second gap phase (G2).
3. During G; phase the cell grows and prepares itself for the S phase. DNA and the
chromosomes are replicated during the S phase. During G2 phase, protein synthesis
increases for cell division.
4. Spindle apparatus separates chromatid or chromosomes during cell division.
5. During mitosis, identical chromosomes are distributed to each daughter cell.
Chormosomal number remains after mitosis.
6. Mitosis is divided into two ph
7. Karyokinesis divides nucleus in four phases i.e., Prophase, Metaphase, Anaphase and
Telophase.
8. Cytokinesis divides cytoplasm to form two individual cells.
9. Mitosis is important for genetic stability, development, growth, cell replacement,
wound healing, regenration, asexual reproduction, tissue culture and cloning.
10. A diploid cell undergoing meiosis completes two successive cell divisions (Meiosis | and
Meiosis Il) to give rise to four haploid cells which later form gametes.
11. During meiotic prophase I, the members of a homologous pair of chromosomes undergo
synapses and crossing over, during which segments of DNA strands are exchanged
between homologous (non-sister) chromatids.
12. During meiosis Il the two chromatids of each chromosome separate and one is distributed
to each daughter cell. Each former chromatid is now referred to as chromosomes.
13. In sexual reproduction, two haploid gametes fuse to form a single diploid zygote.
14. Meiosis is important for mainrenance of chromosomal number in sexual reproduction
and genetic variations.

{eS
59 }
 Unit4 : Cell Cycle

——
a
EXERCISE
Section |; Multiple Choice Questions
Select the correct answer:
1. A bivalent consists of:
A) Two chromatids and one centromere
B) Four chromatids and two centromeres
C) Four chromatids and four centromeres
D) Two chromatids and two centromeres
During cell division spindle fibres attach a chromosome at:
A) Centromere B) Telomere
C) upper arm of chromosome D) lower arm of chromosome
Some student of SSC observed a thin cross section from root tip of onion plant under the
microscope. They found dividing cells at different stages of their life cycle. One of the
students found a cell at late prophase and counted 28 chromosomes in it. The number of
chromosomes in daughter cells should be:
A) 14 B) 28 C) 56 D) 07
Crossing over results in genetic recombination. It occurs between:
A) Two chromatids of the same chromosome.
B) Two chromatids of any two non-homologous chromosomes
C) Two chromatids of opposite gametes
D} Two chromatids of homologous chromosomes
The spindle apparatus of plants differs from that of animals in not having:
A) microtubules B) equator of spindle
C) centrioles D) centromere
Substance and energy required for the replication of DNA is accumulated in the cell during:
A) Gi B) G2 C) S phase D) M phase
All of the following events takes place both in mitosis and meiosis except:
A) Condensation of chromatin to form chromosomes
B) Formation of spindle apparatus
C) Nuclear envelop and nucleolus disappear
D) Chromosomes pair for crossing over
The cell shown in this diagram is passing through:

A) Prophase | of meiosis B) prophase of mitosis

C) telophase of meiosis | D) anaphase of meiosis II

{Sls)
60 |
 ( Unité : Cell Cycle

——y
9. The longest phase of meiosis is:
A) Interphase | B) Prophase |
C) interphase Il D) prophase I!
10. What causes the number of chromosomes to reduce to half when a cell divides by meiosis?
A) replication of DNA during interphase |
B) separation of homologous chromosomes during meiosis |
C) separation of sister chromatids of all the chromosomes during meiosis |.
D) crossing over during meiosis |

11. Which of the following cell is at Metaphase | stage?

12. This diagram is showing different stages of crossing over. Which stage contains chiasma?

13. Which processes involve meiosis?

Gamete Crossing over

formation

Ads
7 Regenration

{SSS
61 }
 f Unité : Cell Cycle

a,
L
14. diagram shows replication of chromosomes.

Centromere Rep iGatien ig

What is the total number of chromosomes in this diagram?

A. 2 B. 3 C.4 D. 6
15. Chromosomal number of Fruit fly is 8. The gametes of fruit fly contain:
A. 2 chromosomes B. 4 chromosomes
C. 8 chromosomes D. 16 chromosomes
Section Il: Short Answer Questions
1. Explain spindle apparatus in detail
2. What is the significance of crossing over?
3. Enlist the events taking place during G; phase.
4. Cell cycle below shows the formation of two daughter cells, cell A and cell B. Cell A
continues in the cell cycle while cell B exits in Go.

RDO
Cytokinesis

Mitosis -” SL /

DO
3 G, (growth}
CELL
: S life cycle 2

G, (growth)

(quiescence}

> @)
$ (synthesis}

What will be the difference in materials they synthesize after the production of cell A and
cell B?

{SSS
62 |
 ( Unit4 : Cell Cycle

SS
5. Why do epithelial cells of skin divide continuously?
6. Give differences between meiosis | and meiosis Il.
7. In rapidly dividing cells which phase of cell cycle is reduced? Explain.
8. What is the difference between cytokinesis of a plant cell and an animal cell?
9. Both skin cells and cancerous cells divide rapidly. Why cancerous cells are harmful but skin
cells are not?
10. How haploid organisms produce gametes?
11. Downs syndrome is due to extra copy of chromosome number 21. That is why Down syndrome
people have 47 chromosomes. Why their chromosome number is high?

Section Ill: Extensive Answer Questions

1. If acell completes meiosis | but meiosis II fails to occur, what type of anomalies will appear
in the two daughter cell thus formed?
2. Acell is shown in this diagram. Answer following questions after observing it.

a. Give at least one finding on the basis of which you can identify it animal or plant cell.
b. Identify the stage of cell division the given cell is passing through?
c. Enlist the reasons of your identification.
3. Meiosis ll is identical to mitosis, explain.
Chapter 5 :

TISSUES, ORGANS AND ORGAN

SYSTEMS
SLOs: After completing this lesson, the student will be able to:
1. Describe the concept of emergent properties as gain in functionalities and how it applies to the
following:
a. going from sub cellular organelles to cells
b. going from cells to tissues
c. going from tissues to organs
d. going from organ to systems
é, going from organ systems to living organisms
Distinguish between tissues, organs and systems, with examples fram animals and plants.
Gon Sty be

Enlist the different types of tissues come together to form the stomach organ in the human body.
Sol

Discuss the organ systems come together to form the human body.
Describe the advantages of homeostasis.
Discuss the various organs and systems of the human bady work to maintain homeostasis.
Discuss the different types of tissues come together to form the leaf.
Explain plant physiology in terms of structure and roles of various plant organs.
 Chapter 5: Tissues, Organs and Organs systems

5.1 THE LEVELS OF ORGANIZATION

Whether we study an individual organism or the world as whole, we can identify a pattern of
increasing complexity. Cell organelles are the parts that make up a cell, like the nucleus,
ribosomes and the mitochondria. Each individual organelle has a specific role to play, and when
combined, multiple organelles will form a single cell.
The cells in complex
multicellular organisms like
Muscle Tissue
=
MiesF — he Se
Nerve Tissue

human beings are organized

S = - »

> ~— ;
Cardiac musiceS= ™ _9 = ~ Brain Ve
into tissues i.e., groups of P ee 7

similar cells that work together Skeletal muscle _

ine
“~~ Spinal cord
on a specific task. Organs are pas
————
——
S
“SS
ey
;
=.
:
4 1
ah ie ~~ y ¢ .
Smooth nusch = f ™~_Netves | * fe
structures made up of two or
Muscle cells ee { — Narva cells
more tissues organized to carry ™~

\
out a particular function, and
groups of organs with related Epithelial Tissue (
[es
ik |
functions make up Lining of gastrointestinal
hia Tendon
tract and other hollow or
different organ systems.
— ~~ Bone a% )
At each level of organization— iy, W
a ha> iy Se
’ "

cells, tissues, organs, and organ Ciliated Simple Simple Simple a4 Fat and other
systems—structure is closely colummar colummar cuboidal squernoul _—&
Sa soft padding
( I
~~__tissue <p
related to function. For Skin Surface
oy »?
oo — A

instance, the cells in the small Basement >. « Fat cells

membrane
intestine that absorb nutrients
Figure 5.1: Types of tissues in humans
look very different from the
muscle cells needed for body movement. The structure of the heart reflects its job of pumping
blood throughout the body, while the structure of the lungs maximizes the efficiency with which
they can exchange gases.
Table 5.1; The Levels of Organization and their explanation
Level of Organization Explanation Example
Ke) Atoms are defined as the
smallest unit of an element
Carbon, Hydrogen, Oxygen
te that still maintains the
Atomic Level property of that element.

Atoms combine to form

molecules which can have
Water, DNA, Carbohydrates
entirely different properties
than the atoms they contain.

Biomolecules assemble in a
specific way to form
Nucleus, ribosomes
organelle. Organelles are
sub-cellular structure.
Organelle Level
 Chapter 5: Tissues, Organs and Organs systems ]
y
Cells are the smallest unit of

URSA) life. Cells are enclosed by a

membrane or cell wall and in
multicellular organisms often
Muscle cell, Skin cell,
Neuron
Cellular Level
perform specific functions

EE ‘ Tissues are groups of cells Muscle, Epithelial,

with similar functions Connective

Tissue Level
oN
Organs are two or more
types of tissues that work
Heart, Liver, Stomach
together to complete a
specific task.
Organ Level

An organ system is group of

Digestive System,
organs that perform related
Circulatory System
ii functions.

Organ System Level

y An organism has several

organ systems that function Human
together.
Organism Level

5.1.1. Organs Epithelial

tissue
Organs, such as the heart, the
lungs, the stomach, the kidneys,
the skin, and the liver, are made up
of two or more types of tissues “242 Connective
tissue
organized to serve a_ particular
function. 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.
Most organs contain all four tissue
types. The layered walls of the
Figure 5.2 Stomach as an organ

|66 }
 ( Chapter 5: Tissues, Organs and Organs systems
l
stomach provide a good example of how tissues form an organ. The inside of the stomach is
lined by epithelial cells which secretes mucus, hydrochloric acid and pepsin enzyme. Around
the epithelial layer are layers of connective tissue and smooth muscle, along with glands, blood
vessels, and neurons. The smooth muscle contracts to move food through the gut. Connective
tissues support the tissues of the mucosa and connect it to the muscular layer. The blood supply
of the submucosa provides nutrients to the wall of the stomach. Nervous tissue in the submucosa
controls smooth muscle contraction and secretion of digestive substances.

5.1.2. Organ systems

Organs are grouped into organ systems; in which they work together to carry out a particular
function for the organism.
For example, the heart and the blood vessels make up the cardiovascular system. They work
together to circulate the blood, bringing oxygen and nutrients to cells throughout the body
and carrying away carbon dioxide and metabolic wastes. Another example is the respiratory
system, which brings oxygen into the body and gets rid of carbon dioxide. It includes the
nose, mouth, pharynx, larynx, trachea, and lungs.

Trachea

Lung
Blood
vessels

Figure 5.3 Respiratory system Figure 5.4 Circularity system

5.1.3. Organ systems work together

Just as the organs in an organ system work together to accomplish their task, the different
organ systems also cooperate to keep the body running.
For example, the respiratory system and the circulatory system work closely together to deliver
oxygen to cells and get rid of the carbon dioxide that these cells produce. The circulatory
system picks up oxygen in the lungs and drops it off in the tissues, then performs the reverse
function for carbon dioxide. The lungs expel the carbon dioxide and bring in new oxygen-
containing air. Only when both systems are working together can oxygen and carbon dioxide be
successfully exchanged between cells and environment.

5.2 HOMEOSTASIS
The tendency to maintain a stable, relatively constant internal environment is
called homeostasis. The body maintains homeostasis for many factors for example,
temperature, the concentration of various ions, pH and the concentration of glucose. If these
values get too high or low, you can end up getting very sick.

| 67 }
 Chapter 5: Tissues, Organs and Organs systems

Homeostasis is maintained at many levels, not just the level of the whole body as it is for
temperature. For instance, the stomach maintains a pH that’s different from that of
surrounding organs, and each individual cell maintains ion concentrations different from those
of the surrounding tissue fluid. Maintaining homeostasis at each level is key to maintaining the
body’s overall function. $0, how is homeostasis maintained?

5.2.1. Maintaining homeostasis

Biological systems like those of your body are constantly being pushed away from their balance
points. For instance, when you exercise, your muscles increase heat production, pushing your
body temperature upward. Similarly, when you drink a glass of fruit juice, your blood glucose
goes up. Homeostasis is the ability of your body to detect and oppose these changes and work
to maintain balance points.

5.2.2. Homeostatic responses in temperature regulation

If you get either too hot or too cold, sensors in the periphery and the brain tell the temperature
regulation centre of your brain—in a region called the hypothalamus—that your temperature
has strayed from its set point.
For instance, if you’ve been exercising hard, your body temperature can rise above its set
point, and you'll need to activate mechanisms that cool you down. Blood flow to your skin
increases to speed up heat loss into your surroundings, and you might also start sweating so the
evaporation of sweat from your skin can help you cool off. Heavy breathing can also increase
heat loss.
How does this work? First, high temperature will be detected by sensors—primarily nerve cells
with endings in your skin and brain—and relayed to a temperature-regulatory control centre in
your brain. The control centre will process the information and activate effectors—such as the
sweat glands—whose job is to oppose the stimulus by bringing body temperature down.

Body temperature
exceeds 37'c

Sensors like nerve cells with

endings in the skin and brain

v
Temperature regulatory
center in brain

v
Sweat glands
Effector throughout body

Negative feedback loop Body temperature regulation

Figure 5.5: Homeostatic response in temperature regulation

 Chapter 5: Tissues, Organs and Organs systems

Table 5,2; Major organ systems of the human body and homeostasis

Organ system Function Organs, tissues, Role in

and structures Homeostasis
involved

Cardiovascular | Transports oxygen, nutrients, Heart, blood, and | help stabilize levels
and other substances to the blood vessels of gases and
cells and transports wastes, wastes, body
carbon dioxide, and other temperature and
substances away from the cells pH

Lymphatic Defends against infection and Lymph, lymph Maintain tissue

disease and transfers lymph nodes, and lymph | fluid homeostasis
between tissues and the blood | vessels
stream

Digestive Processes foods and absorbs Mouth, salivary Maintains levels of

nutrients, minerals, vitamins, glands, nutrients in blood
and water oesophagus,
stomach, liver,
gallbladder,
exocrine
pancreas, small
intestine, and
large intestine

Endocrine Provides communication within | Pituitary, pineal, | Maintains balance

the body via hormones and thyroid, of many blood
directs long-term change in parathyroid, components like
other organ systems to endocrine glucose, water,
maintain homeostasis pancreas, calcium etc.
adrenals, testes,
and ovaries.

Integumentary | Provides protection from injury | Skin, hair, and Involved in

and fluid loss and provides nails temperature
physical defence against regulation
infection by microorganisms;

Muscular Provides movement and Skeletal, cardiac, | Helps in

support and smooth temperature
muscles regulation by heat
production

{ 69 |
 Chapter 5: Tissues, Organs and Organs systems

Table 5,2; Major organ systems of the human body and homeostasis

Organ system Function Organs, tissues, Role in

and structures Homeostasis
involved

Nervous Collects, transfers, and Brain, spinal Maintains

processes information and cord, nerves, and | homeostasis
directs short-term change in sensory organs— by rapidly
other organ systems eyes, ears, controlling body
tongue, skin, and | functions
nose

Respiratory Delivers air to sites where gas Mouth, nose, Controlling the
exchange can occur pharynx, larynx, balance of oxygen
trachea, bronchi, | and carbon dioxide
lungs, and in the body
diaphragm

Skeletal Supports and protects soft Bones, cartilage, By regulating the

tissues of the body; provides joints, tendons, level of calcium
movement at joints; produces and ligaments and other minerals
blood cells; and stores in the blood
minerals (storing or
releasing them
from bones)

Urinary Removes excess water, salts, Kidneys, ureters, | By regulating levels

and waste products from the urinary bladder, of water, salts, H+
blood and body and controls and urethra and wastes in blood
pH

Immune Defends against microbial Leukocytes, By removing

pathogens—disease-causing tonsils, adenoids, | pathogens, fighting
agents—and other diseases thymus, and infections and
spleen helping in healing

9.3 PLANT TISSUES

Plants are multicellular eukaryotes with tissue systems. Plant tissues are composed of cells that
are similar and perform a specific function. Different tissues combine to form organs. Each
organ itself is also specific for a particular function together making up the tissue systems.
Plant tissues differentiate into three main types: dermal, ground, and vascular tissue. Dermal
tissue covers and protects the plant. The ground tissue serves as a site for photosynthesis,
 Chapter 5: Tissues, Organs and Organs systems

provide support, and helps to store water and sugars. The vascular tissue transports water,
minerals, and sugars to different parts of the plant.

5.3.1. Plant organs and organ systems Reoroluctive

relation with plant physiology Se Vegetative
Plant tissues form organs (such as leaves, stems, or roots), =
each of which perform a specific set of functions. Leaves Shoot
perform photosynthesis. Stems support the plant and | *’S°™
transport substances.
Together, organs often work to form organ systems.
Vascular plants have two distinct organ systems: a shoot Be
system, and a root system. The shoot system consists of y
Root
two portions: the vegetative (non-reproductive) parts of system
the plant, such as the leaves and the stems, and the
reproductive parts of the plant, which include flowers and
fruits. The shoot system generally grows above ground, Figure5.6 Plant organ systems
where it absorbs the light needed for photosynthesis. The root system, which is usually
underground anchors the plant into the ground, absorbs water and minerals, and serves as a
storage site for food.

5.3.2. Structure and Functions of Cells of a Leaf

Leaves are thin, flat organs responsible for photosynthesis in the plants. It develops laterally
at the node. It is an important part of the shoot system as it performs photosynthesis and
transpiration. Leaf cells need water, carbon dioxide and light for photosynthesis and oxygen
for respiration. Leaves transfer the synthesized food to other parts of the plant. So, there are
varieties of functions and accordingly there are varieties of cells, in the leaf. Each type of cell
performs a special function.
Xylem Intercellular

epidermis
Palisade
mesophyll

s
rriseontnl

—- Lower
epidermis

Fig 5.7 : Transverse section of a leaf

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 Chapter 5: Tissues, Organs and Organs systems

Epidermis is the outermost layer. It is a single layer of cells, covering the leaf surface. A
waxy substance called cutin, which forms the cuticle, covers the upper epidermis. The
function of the epidermis is to protect the tissues and to prevent loss of water. On the lower
epidermis tiny pores are present called stomata. Each stoma is enclosed by two guard cells,
having chloroplasts. The guard cells control the opening and closing of stoma. Exchange of
oxygen and carbon dioxide with the environment and evaporation of water vapour takes
place through stomata. Between the two-epidermal layers lies the group of cells called
mesophyll. These are of two types i.e., palisade mesophyll and the spongy mesophyll. The
palisade mesophyll consists of two or three layers of cylindrical cells. These cells contain
many chloroplasts. The spongy mesophyll consists of loosely arranged irregular shaped cells
having chloroplast. Large intercellular spaces are present among these cells. This
arrangement facilitates diffusion of gases. Xylem vessels present in the leaves are long and
dead cells. Through xylem cells transportation of water from root to leaves takes place.
The phloem cells carry the prepared food from the leaf to other parts of the plant.
Activity 4: Study of animal tissues
Materials required Main skills practised
Compound microscope Following instructions
Prepared slides of sections of animal’s Using microscope
epithelial, connective, muscle and nervous
: Observing slides
tissue
Making drawings
Charts of animal’s epithelial, connective, 8 8
muscle and nervous tissue Interpreting results
Making conclusions

Introduction
In this activity you will have an opportunity to observe animal tissues. You will identify shape
of cells and relate it with function of tissue.
Points for pre-lab discussion
Q.1. What is a tissue?

Q.2. How do animals support their body parts, absorb materials or move?
Q.3. Do you except any “photosynthetic tissue” in animals?
Q.4. What is the location of different tissues in animals?

Procedure
a. You are provided with charts and slides of four types of tissues.
b. Study the features of these tissues from charts.
c. Examine each tissue type one by one under the microscope using the low power
lens first and then the high power lens to see greater details.
d. Fill in the following table using the results of your observations.
 Chapter 5: Tissues, Organs and Organs systems

TISSUE DIAGRAM: LABEL MAJOR PARTS

Epithelial tissue

Connective tissue

Muscle tissue

Nervous tissue

SUMMARY
. Cell organelles are sub cellular structures which work together to form cells.
—

. Group of cells with similar functions make tissues.

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3. Organs are structures made up of two or more tissues organized to carry out a
particular function.
4. Groups of organs with related functions make up different organ systems.
5. All organ system work in a coordinated way to keep the organism living and working.
6. The tendency to maintain a stable, relatively constant internal environment is
called homeostasis.
Different organ systems of an organism work together to maintain homeostasis.
2 9 N

Plant tissues differentiate into three main types: dermal, ground, and vascular tissue.
. Animal tissues differentiate into four main types: epithelial, connective, muscular and
nervous tissue.

EXERCISE
Section |: Multiple Choice Questions
Select the correct answer:
1. The diagram shows cells in part of the leaf of a green plant. Which region contains cells
which are responsible for the process of transport?
 Chapter 5: Tissues, Organs and Organs systems

2. The table shows three functions of cells which row is correct?

absorption support transport

A red blood cell muscle cells root hair cell
B root hair cell xylem vessel red blood cell
muscle cell red blood cell xylem vessel
D xylem vessel root hair cell muscle cell

3. What are the functions of xylem and phloem in green plants?

xylem phloem
A. | support and transport of sugars transport of water
B_ | transport of sugars support and transport of water
C_ | support and transport of water transport of sugar
D | transport of water support and transport of sugars

4, If tissue level is not developed in the level of organization, which next level will not
form?
A) Molecular level = B) atomic level C) organ level D) organelle level
5. Following diagram shows level of organization in a rat. Which one is the organ level?

\ A

6. Which of the following lists the levels of body organization from smallest to largest?
A) organism, organ system, organ, tissue, cell
B) tissue, cell, organ, organ system, organism
C) organ, organ system, organism, tissue, cell
D) cell, tissue, organ, organ system, organism
7. This statement about Homeostasis is incorrect:
A) because of this, the fluctuations of the internal environment are of extremely
narrow range as compared to that of the external environment
B) there is one system regulating the homeostatic activities
 Chapter 5: Tissues, Organs and Organs systems ]
J
C) homeostatic mechanisms keep the internal environment constant despite wide
changes in the external environment
D) homeostasis is necessary for the survival of cells
8. Which of the following statements best describes homeostasis?
A) keeping the body in a fixed and unaltered state
B) dynamic equilibrium
C) maintaining a near-constant internal environment
D) altering the external environment to accommodate the body's needs
9. Organisms have the ability to change and modify their internal conditions according to
the environment through:
A) osmoregulation B) excretion
C} thermoregulation D) all of the above
10. You can observe spongy mesophyll and xylem in the section of leaf. These are part of
the same:
A) cell and organism B) organ and organism
C) cell and tissue D) tissue and organ
11. The diagram shows a sample of material taken from an organism.
Nucleus

Cell body

Which level o organization does the sample show?

A) cell B) organ
C) organ system D) tissue
12. Which structure is not an organ?
A) artery B) flower
C) spinal cord D) xylem
13. Which description of xylem is correct?
A) a cell used for absorption B) an organ system used for conduction
C) a tissue used for transport D) an organ used for transport

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 Chapter 5: Tissues, Organs and Organs systems ]
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14. Which structure is at a different level of organization from the other three?
A) kidney B) liver
C) neuron D) lung
15. The diagram shows tissues from section of leaf. Which
type of cells will perform photosynthesis?
A) 1 and 4 B) 2 and 5
C) 2 and 3 D) 3 and é

Section Il: Short Answer Questions

1. Can you differentiate between:
(a) Organ and organelle (b) Animal and plant tissues
(c) Xylem and phloem (d) Epithelial and muscular tissue
(e) Nervous and connective tissue (f} Epidermal and ground tissue
(g) Root and shoot system (h) Vegetative and reproductive part
2. How different tissues form stomach?

3. Why respiratory and cardiovascular systems work together?

4. How temperature is regulated in our body?

Section Ill: Extensive Answer Questions

. Justify how the cells of leaf have a variety of specialized structure and function.
State the relationship between structure and function of root hairs, xylem vessels and red
blood cell.
Write a detailed note on animal tissues.
Give an account of levels of biological organization.
oe

Explain the functions of different organ system of humans.

How different organ systems o humans work together to maintain homeostasis?
oP

Cells and tissues are adapted to perform their function in the best way. Explain this
statement by using example of leaf.
 Approved by National Curriculum Council, Secretariat
Ministry of Federal Education & Professional Training
vide letter No. F.1-1 (2024)-NCC/DEA/Dir/English, Dated: 04th March 2024

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