Science 10

1) Transportation

a. Blood carries oxygen from lungs to the various cells of the body
and carbon dioxide from cells and tissues to the lungs.

b. It transports the absorbed foods to the cells and tissues.
c. It collects the waste materials from cells and tissues and

transports to the excretory organs such as lungs, kidney,
intestine, liver, skin, etc.
d. It transports the hormones secreted by endocrine glands to the
different parts of our body.

2) Regulation

a. It maintains body temperature.
b. It controls the amount of water and various chemicals inside

the body.

3) Protection

a. It protects the human body from different diseases with the
help of WBCs.

b. Fibrinogen helps in blood clotting in wounds or cuts and helps
for recovery of the wound.

Blood Vessels

Blood vessels are network of tube like structures that carry
blood to various parts. They are of three types: arteries, veins and
capillaries.

Arteries Tunica Tunica
media
They carry blood pumped externa Tunica
by heart to different interna
parts. The arteries
Lumen

further divide into

smaller vessels called

arterioles. The blood

flowing through them Internal structure of artery

has high pressure. To withstand high blood pressure, the walls of

the arteries are thick and elastic. All arteries carry oxygenated

blood except pulmonary artery. They are deeply seated inside the

muscles. They can bear high pressure: The wall of arteries is made

of three layers. The outermost layer is called tunica adventitia, the

middle layer is called tunica media and the innermost layer is called

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tunica intima. Any damage or injury in the arteries may cause death
of a person.

Fact &Reason

Why is the rupture of artery dangerous?
The blood flows with great force and pressure in artery. If artery gets injured,
large amount of oxygenated blood is lost through bleeding. So, the rupture of
artery is dangerous.

Veins Tunica Tunica
externa interna
Veins are blue coloured

blood vessels. They

collect blood from Lumen
different organs and pour Valves
to the heart. They carry Tunica
blood with low pressure. media
They contain valves.

The valves prevent the Internal structure of vein

back flow of the blood. The opening of the valve is in the direction of

heart which causes the flow of blood towards the heart only. Veins are

formed by the joining of smaller blood vessels called venules. All veins

carry deoxygenated blood except pulmonary veins. The walls of veins

is also formed of three layers as that of capillaries.

Fact &Reason

Why are valves present in veins?
The blood flows with less pressure in veins, due to which there is chance of
backflow of the blood. When valves are present in the veins, they prevent the
backflow of the blood. Hence, valves are present in veins to prevent backflow of
the blood.

Capillaries

Capillaries are very thin hair like blood

vessels which supply blood to every cell.

They connect arterioles and venules in the

form of network. They help to exchange Capillaries

nutrients, gases, etc between blood and cells of the body.

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Differences between arteries and veins

Arteries Vein

1. They are blood vessels which 1. They are blood vessels which

carry blood from heart to carry blood from different

different organs. organs to the heart.

2. They are thick walled. 2. They are thin walled.

3. Blood flowing through them 3. Blood flowing through them

has high pressure. has low pressure.

4. Valves are absent. 4. Valves are present.

5. Generally arteries carry 5. Generally, veins carry de-

oxygenated blood except oxygenated blood except

pulmonary artery. pulmonary veins.

Heart

It is the main part of blood circulatory system. It is roughly conical in
shape and located in the middle of the chest cavity. It is made up of
thick cardiac muscles. It is covered by double walled membranous sac
called pericardium. In this sac, there is a liquid called pericardial
fluid which protects the heart from shock. Human heart consists of
four chambers. The upper two chambers are called auricles and lower
two chambers are called ventricles. The heart is divided into left and
right parts by a septum.
Two large veins called superior venacava and inferior venacava open
to right auricle. A valve named tricuspid valve is present between right
auricle and right ventricle. It lets the blood flow from right auricle to
right ventricle but not in opposite direction.

Pulmonary artery originates from right ventricle and grows
towards lungs. Pulmonic valve is present between pulmonary artery
and right ventricle. Left auricle is connected with four pulmonary
veins which carry blood from lungs to the heart. Left auricle opens
to left ventricle through bicuspid valve. A large blood vessel named
aorta originates from the left ventricle. It carries blood from the heart
to various parts of the body. Aortic valve is present between aorta and
left ventricle.

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Superior venacava Aorta
Right auricle Left auricle
Left ventricle
Inferior venacava
Right ventricle External Structure

Superior venacava Aorta

Pulmonary artery Pulmonary vein
Left auricle
Right auricle
Tricuspid valve Bicuspid valve
Left ventricle
Right ventricle Septum
Inferior venacava

Internal Structure

Blood circulation Head

Deoxygenated blood is Lungs
collected from upper parts of
body by superior venacava Right
and from lower parts by auricle Left
inferior venacava to the right auricle

auricle. From the right auricle, Right Left
blood flows to the right ventricle ventricle
ventricle through tricuspid

valve. The right ventricle Liver

pumps the blood to the lungs Kidney
through pulmonary artery.

The pulmonary artery divides Posterior pats of body
into left and right pulmonary Blood circulation
arteries. Left pulmonary

artery carries blood to the left lung and right artery carries blood to

the right lung. In the lungs, the blood is purified by taking oxygen and

throwing carbon dioxide.

The oxygenated blood is carried from each lung to the left auricle
by two pulmonary veins. The oxygenated blood passes from the left

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auricle to the left ventricle through bicuspid or mitral valve. From the
left ventricle, blood is carried by aorta to the various parts.
The aorta divides into small arteries then to the arterioles. The
arterioles further divide into capillaries inside the organs. The
capillaries supply oxygen to the organs. Capillaries also collect carbon
dioxide and supply to the veins. Veins combine together to form
venacava. From the venacava, blood comes to the right auricle. In the
same way, blood circulation continues.

Fact &Reason

Why is the wall of left ventricle thicker than that of right ventricle?
Left ventricle pumps the blood to different parts of the body through aorta and
arteries with great force and pressure whereas right ventricle pumps the blood
to lungs with less force and pressure. So, the the wall of left ventricle is thicker
than that of right ventricle.

Fact &Reason

Right auricle is larger than left auricle, why?
Right auricle receives large amount of blood coming from the different parts of
the body through superior and inferior venacava, whereas left auricle receives
less amount of blood coming from lungs through pulmonary vein. Hence, right
auricle is larger than left auricle.

Types of blood circulation

In human being, the blood circulates in two ways: They are (i)
pulmonary circulation (ii) systematic circulation.

Pulmonary circulation

The circulation of blood between heart and lungs is called pulmonary
circulation. In this circulation, the right ventricle pumps de-oxygenated
blood to the lungs through pulmonary artery. The blood is oxygenated
in the lungs. The oxygenated blood is carried to the left auricle through
pulmonary veins.

Left auricle Pulmonary veins

Lungs

Right Ventricle Pulmonary artery

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Systematic circulation

Circulation of the blood between the heart and different organs except
lungs is called systematic circulation. In this process, when left ventricle
contracts, the purified blood is pumped to different parts of the body
through aorta. The aorta is the largest artery which supplies blood to
the different parts. The aorta divides into branches called arteries.
The arteries supply the oxygenated blood to the different parts. The
cells and tissues of the body parts absorb the essential nutrients and
oxygen. Then, the blood returns to the right auricle through inferior
and superior venacava.

Right Auricle Venacava

Organs

Left Ventricle Aorta

Heart beat

The contraction and relaxation of heart muscles cause the pumping of
the blood. The continuous rhythemic beat produced due to contraction
and relaxation of heart muscles is called heart beat. The heart beat
per minute is called heart beat rate. The heart beat rate of a healthly
person is 70 - 80 with average of 72 times per minute. The heart
beat rate differs according to the age, sex and the nature of work of a
person. A child has faster heart beat whereas an oldman has slower
heart beat. The heart beat rate increases when a person is in tension,
in fever, or does exercise or gets excited.

Blood pressure

The pressure exerted by blood to the walls of the blood vessels is called
blood pressure. Blood pressure makes the blood flow in the blood
vessels. The blood pressure depends upon the force created by the
pumping of the heart, the volume of the circulating blood and the
size of the blood vessels. Blood pressure is of two types: systolic blood
pressure and diastolic blood pressure.

Systolic blood pressure

The pressure exerted by the blood on the wall of arteries when the
ventricles contract and push the blood to the aorta is systolic blood
pressure. It is the maximum pressure of blood exerted on the wall

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of arteries. It is also called the upper limit of arterial pressure. In a
healthy adult, it is about 90mm of Hg to 130 mm of Hg. In average its
value is 120mm of Hg.
Diastolic blood pressure
The pressure exerted by the blood on the wall of arteries when the
ventricle gets relaxed is called diastolic blood pressure.

It is the minimum pressure of the blood on the wall of the artery. It is
also called lower limit of arterial blood pressure. In a healthy adult,
it is about 60 to 90mm of Hg. The blood pressure is measured by
sphygmomanometer. The blood pressure varies with age, nature of the
work, sex, motion of the body, excitement, etc. If a person has a blood
pressure of 120/80mm of Hg, it means that person has systolic blood
pressure of 120mm of Hg and diastolic blood pressure of 80mm of Hg.
Rise in blood pressure is called high blood pressure and fall in the
blood pressure is called low blood pressure.

Fact &Reason

The blood pressure of a man is 120 / 80 mm of Hg. What does this statement
means?
It means that the systolic pressure exerted by the blood to the wall of arteries
during contraction is 120 mm of Hg and the diastolic pressure exerted by the
blood to the wall of arteries during relaxation is 80 mm of Hg.

High blood pressure (Hypertension)

The blood pressure of people may increase beyond the limits due to
some causes. If the systolic pressure crosses 140 mm of Hg and the
diastolic crosses 90 mm of Hg (i.e. the blood pressure is 140/90 mm
of Hg or more), such blood pressure is taken as high blood pressure.
The high blood pressure is very risky for the health of people; it can
damage heart, kidneys, brain, etc.

Causes

The major causes of high blood are as follows:
i) Regular intake of oily, fatty and salty food.
ii) Bad habits like smoking, drinking alcohol etc.
iii) Health problems like kidney disorders, mental tensions, adrenal

and thyroid disorders etc.
iv) Lack of physical exercise, genetic history, age factor ( above 40

years ) and so on.

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Symptoms

The major symptoms of high blood pressure are as follows:

i) Feelings of dizziness , light headache or fainting
ii) Blurred vision
iii) Short breathes and irregular heartbeat
iv) Chest pain, vision problems, fatigue or confusion etc.

Preventive measures

The major preventive measures that can be taken to control high blood
pressure are as follows:

i) Balanced diet should be taken.
ii) Oily and spicy food should be avoided.
iii) Unnecessary quarrels, arguments, worries, and tension should be

avoided.
iv) People should have a habit of doing regular exercise, walking,

jogging, etc. to keep the blood pressure in normal level.

Activity20 .1 To hear heartbeat.

Materials required :
A stethoscope.

Procedure
i) Take a stethoscope and place the diaphragm (funnel shaped

end) of the stethoscope on the chest of your friend and put ear
piece in your ears.
ii) Shift the diaphragm on the different parts of the chest. Can
the heartbeat be heard?
iii) Find the location at which the heart beat is the loudest.
Observation:
The heart beat is the loudest at the left side of the chest.

Blood sugar (Diabetes)
Blood sugar or blood glucose is the main sugar found in our blood. It
comes from the food we eat, and is our body's main source of energy.
Our blood carries glucose to all of our body's cells to use for energy.

Diabetes is a disease in which our blood sugar level is too high. Having
too much glucose in our blood can cause serious problems. Diabetes
is also called sugar disease because the patient of diabetes excretes
urine mixed with sugar. This disease is common in those people who

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consume much nutritious food but perform very less physical activities
or exercises. It usually develops in the people at the age of 40 to 45
years.

Causes

Diabetes is a non-communicable disease. It is supposed to be caused
by the following factors:

1. It develops in those people who take too much carbohydrate in their
food and do not perform physical labour or exercise.

2. Tensions, worries and much idleness may also result in diabetes.
3. It is also a hereditary disease and is more likely to be found in

those people whose parents are diabetic.

Symptoms

The main symptoms of diabetes are as follows:

1. Frequent urination.
2. Appearance of white or faint yellow concentrated liquid after

urination.
3. Frequent thirst for water.
4. Gradual decrease in the body weight.
5. Weak, lazy and sleepy feeling in the patient.
6. Since the urine of the patient contains sugar, ants and flies

gather in urine if urinated in the open field.
7. If the treatment measures are not taken on time, the vital

organs such as heart, kidneys, eyes, and nerves are impaired.

Prevention
1. The intake of carbohydrate should be balanced according to the
body size and the nature of work.
2. People should have a habit of doing regular exercise, walking, jogging, etc.
3. Unnecessary quarrels, arguments, worries, and tension should be
avoided.
4. Consumption of sweets, chocolates and white sugar should be
discouraged.
5. Consumption of fats and oily foods should be minimized to keep a fit
body weight.

Uric acid

Uric acid is a waste product created during the normal breakdown of
purines, naturally occurring substances found in foods such as liver,
mushrooms, anchovies, mackerel and dried beans. Normal uric acid

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levels are 3.4 to 7.0 milligram per deciliter (3.4-7.0 mg/dL) in men and
2.4-6.0 mg/dL in women. However, these values may differ slightly.

Uric acid is normally cleaned out of the blood
by the kidneys and passes out of the body along
with urine. However, high levels of uric acid can
accumulate in the body, either when the kidneys
excrete too little uric acid or when the body
produces too much uric acid. This condition is
known as hyperuricemia.

The high concentration of uric acid in the blood will eventually convert
the acid into urate crystals, which can then accumulate around the
joints and soft tissues. Deposits of the needle-like urate crystals are
responsible for the inflammation and the pain in the joints. This
condition is called gout. The gout is a painful form of arthritis caused
by too much uric acid in the body. People with gout suffer from joint
pain, most often in their toes, but in other joints as well.

There are several factors that can make a person more susceptible to
gout. Some of them are:

1. Having a family history of gout
2. Being overweight
3. Having kidney problems
4. Lead exposure
5. Drinking too much alcohol
6. Taking certain medications like diuretics or niacin

Symptoms

The common symptoms of gout are as follows:

1. Intense joint pain that is most severe in the first 12 to 24 hours
2. Joint pain that lasts a few days to a few weeks and spreads to

more joints over time.
3. Redness, tenderness and swelling of the joints.

Prevention and control
1. Consumption of lemon juice helps to control uric acid level in the blood.
2. Cherries and dark berries contain chemicals that help reduce
uric acid levels.
3. Baking soda, also called bicarbonate of soda, is highly beneficial
for lowering uric acid levels and reducing gout pain.
4. Drinking plenty of water helps optimize uric acid filtering.

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It helps dilute the uric acid and stimulates the kidneys to
eliminate excess amounts from the body through urine.
5. The consumption of foods such as liver, mushrooms, anchovies,
mackerel and dried beans should be minimized

Learn and Write

1. Artery has thicker wall than the veins. Why?

Artery has to carry the blood pumped by the heart. Therefore,
the blood flowing through the artery has high blood pressure. To
withstand the high pressure of the blood, the artery must have
thick wall. But the vein has to carry the blood of low pressure
from the organs to the heart. Therefore, vein has thin wall.

2. The wall of ventricle is thicker than that of auricle. Why?

The ventricle has to pump the blood to different parts through
arteries. To withstand the high pressure created due to pumping,
the ventricle must have thick wall.

3. Colour of the blood in the pulmonary artery is purple. Why?

Colour of the oxygenated blood is scarlet and that of deoxygenated
blood is purple. The pulmonary artery carries the deoxygenated
blood from heart to the lungs. Therefore, the colour of the blood
in pulmonary artery is purple.

4. A person suffering from anaemia feels tired even in a short walk. Why?

Haemoglobin carries oxygen from lungs to the organs. The oxygen
is required for the production of energy from the food. A person
suffering from anaemia lacks haemoglobin. Therefore, a person
suffering from anaemia feels tired even in the short walk due to
lack of sufficient oxygen.

Main points to remember

1. Circulatory system consists of blood, blood vessels and heart.
2. Blood is a liquid connective tissue which keeps on circulating

throughout the body.
3. Plasma is a liquid portion of blood which transports digested

food, excretory products, hormones, etc throughout the body.
4. Red blood cells are disc shaped cells which contain haemoglobin.
5. Leucocytes are larger cells which fight with disease germs.
6. Platelets are fragments of larger cells which help for blood cloting.
7. Arteries are blood vessels that carry blood to different parts from heart.
8. Veins are blue coloured blood vessels that collect blood from

various parts to the heart.

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9. Heart is a conical shaped organ which pumps blood to the various
parts of the body.

10. The pressure exerted by the blood to the wall of blood vessels is
called blood pressure.

11. The continuous rhythemic beat produced due to contraction and

relaxation of the heart muscle is called heart beat.

Exercise

A. Very short answer questions (1 mark )

1. What is blood ?

2. Write the main function of fibrinogen in plasma.

3. What is vein?

4. Write down the function of platelets or thrombocytes.

5. Write down two functions of erythrocytes or RBCs.

6. Write the name of non-granular leucocytes.

7. What happens if there is shortage of WBCs in blood ?

8. What happens when the number of platelets increases or

decreases ?

9. Write any two parts of the body in which white blood cells are

produced.

10. Write any two functions of leucocytes or WBCs.

11. What is normal blood pressure of a healthy young person?

12. What is heart beat?

13. Write one function of right and left ventricle of human heart.

14. Give one function of fibrinogen.

15. Where are bicuspid and tricuspid valve located?

16. What is haemophilia?

17. Write down the use of sphygmomanometer.

18. What is uric acid?

19. Where are red blood cells formed and destroyed?

20. What is diastolic blood pressure ? Write down the diastolic

pressure of a healthy young person.

21. What is systolic pressure ? Write down the systolic pressure of

a healthy young person.

22. What is blood pressure?

23. What are blood vessels ?

24. Write the name of blood vessels which carry pure blood from

lungs to the heart.

25. What is the function of pericardium?

26. What happens if the pericardial fluid decreases?

27. Write the name of valves that are found in human heart.

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28. What is anemia? How does it occur?

B. Short answer questions (2 marks)

1. Rupturing of an artery is dangerous, why?

2. Write any two differences between pulmonary artery and

pulmonary vein.

3. Write any two causes of increasing uric acid.

4. Write any two symptoms of hemophilia disease.

5. The person suffering from anemia feels tired after walking

short period. Why?

6. Differentiate between white blood cells and red blood cells

(erythrocytes).

7. Differentiate between auricles and ventricles..

8. Write any two differences between bicuspid valve and

tricuspid valve.

9. The wall of left ventricle is thicker than that of right ventricle,

why?

10. Write any two differences between arteries and veins.

11. Write any two differences between systemic and pulmonary

circulation.

12. Veins have valves at intervals in their inner lining whereas

the arteries do not have valves,why?

13. The blood pressure of a healthy person is 120/80 mm of Hg,

what does it mean?

14. Differentiate between:

i) RBC and WBC

ii) Artery and Vein

iii) Auricle and Ventricle

iv) Pulmonary artery and Pulmonary vein

C. Long answer questions (3 marks)

1. Write down the preventive measures of diabetes.

2. Suggest any three precautions to be taken to reduce the

amount of uric acid in the blood.

3. Write any six causes of high blood pressure.

4. Draw a neat labelled diagram showing internal structure of

heart.

5. Write down the major symptoms of diabetes.

6. Write any three functions of the plasma.

7. Draw a neat and labelled diagram showing blood film.

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D. Very Long answer questions
1. Write down the measures to control high blood pressure.
2. Explain blood circulation in human being in detail.
3. Study the following diagram and answer the following
questions:
i) Label A, B, C and D
ii) Write the function of A, B, C and D

AC

DB

Project Work

Bring a heart of goat from a butcher shop nearby your school or home. Observe
its external structure. Then cut its outer walls carefully and observe its internal
parts. Draw the diagram and label its all parts.

Glossary

• Erythrocytes : red blood cells

• Corpuscles : blood cells

• Pathogen : something that can cause disease, e.g. a
bacterium or a virus

• Withstand : to bear something without suffering damage

• blurred vision : lack of sharpness of vision.

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Chapter

17 Chromosomes And Sex
Determination

Robert Hooke

He coined the term cell and is also famous for

microEscsotpiym. ated Periods: 5 (4T+1P)

Objectives

At the end of the lesson, students will be able to:
• introduce chromosome and explain different types of chromosomes;
• describe the mechanism of sex determination of organism during embryonic
stage.

Body of all living things is composed of cells. A cell performs all the
functions of life such as respiration, growth, reproduction, etc. Therefore,
a cell is defined as the functional and structural unit of life. It is capable
of self reproduction.

A cell is capable of independent existence. All living things start their
life from a single cell. This single cell undergoes process of cell division
and many cells are produced from a single cell.

Nucleus is one of the important parts of a cell. It contains nucleoplasm,
chromosomes and nucleolus remained inside the nuclear membrane.
Chromosomes become distinct during the time of cell division. The
number of chromosomes in a cell varies from organisms to organisms.
Some examples are as follows.

Organisms Number of Organisms Number of
chromosome in chromosome in
Human Pine
Frog each cell Mucor each cell
Rat 46 (23 pairs) Housefly 24 (12 pairs)
Onion 26 (13 pairs) Horse
Rice 40 (20 pairs) Monkey 2 (1 pair)
16 (8 pairs) 12 (6 pairs)
Sugarcane 24 (12 pairs) Pea 64 (32 pairs)
Gorilla 80 (40 pairs) Potato 54 (27 pairs)
Solanum 48 (24 pairs) 14 (7 pairs)
16 (8 Pairs) Dog 48 (24 pairs)
78 (39 pairs)

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Chromosomes are made up of nucleic acid and proteins. They contain
genes. Genes are responsible for determining characters of an organism.
The genes also transmits the hereditary characters to the offspring.
Each chromosome consists of two identical strands called chromatids.
These two strands are attached to each other at a constricted part
called centromere.

Chromosomes are responsible for the transfer of hereditary characters from
parents to offspring. Sometimes, they also transfer the sex linked diseases
such as hemophilia.
Each organism has particular sets of chromosomes. The change in the
number of chromosomes on the body leads to chromosomal disorders.

Shape, size and structure of chromosomes

The shape of chromosomes changes continously during cell divison.
Generally, its shape is determined by the position of centromere. The
size of chromosome varies from species to species in organisms.

The filament like structure of chromosome is called chromatid.
In some stages, the chromosome forms alternate thick regions in a
chromosome giving the appearance of beads in a string. The thick
bead-like structure of chromonema are known as chromomeres.

The chromosomes may occur in pairs. The two chromosomes of a pair
which are similar in shape, size, appearance and function are called
homologous chromosomes. Each chromosome of a homologous pair
contains genes for the same characteristics at the same place.

Structure of chromosomes

Secondary Two
chromonemate
constriction

Satellite Satellite Chromosome structure
A. External structure
B. Helically coiled chromonemate

A Primary Centromere
constriction B

or centromere

Chromosomes are the microscopic threadlike structures present in the nucleus
of a cell which contain genes. A gene is a sub-microscopic unit present in
chromosome which carries hereditary characters. The chromosomes are made
of deoxyribonucleic acid (DNA), protein and small amount of ribonucleic acid

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(RNA). Each chromosome consists of two identical strands called chromatids.
The chromatids are connected to each other by centromere. The centromere is
a constriction point in a chromosome which divides the chromosome into two
sections or arms. The centromere is also known as kinetochore. The location of
the centromere on each chromosome gives the chromosome its characteristic
shape and can be used to determine the location of specific genes.
The chromosomes are divided into four types on the basis of location of
centromere. They are as follows:
1. Metacentric chromosome
The chromosome which contains centromere at its middle with the equal
lengths of arms is called metacentric chromosome.

Centromere

Metacentric Sub-metacentric Acrocentric Telocentric

2. Sub-metacentric chromosomes
The chromosome which contains centromere slightly away from its middle
resulting in the unequal length of arms is called sub-metacentric chromosome.
3. Acrocentric chromosome
The chromosome which contains centromere near an end is called acrocentric
chromosome. In such chromosome, one arm of chromatid is long and the
other is very short.
4. Telocentric chromosome
The chromosome which contains centromere at its one end is called telocentric
chromosome.
Importance of chromosomes

a. Chromosomes conain genes which carry hereditary characters.
b. Chromosomes have an important role in cell division cell growth

and cell repair.

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Diploid and haploid cells

A cell which contains pairs of chromosomes is called diploid cell. One
chromosome of each pair is inherited from each parent. For example, a
somatic (body) cell of a human contains 23 pairs of chromosomes. One
chromosome of each pair comes from father and another from mother.
The number of chromosomes in diploid cell is represented by 2n.

A cell which contains only one chromosome of each pair is called haploid cell.

For example, gamete (sperm or ovum) of human has 23 chromosomes.

The number of chromosomes in haploid cell is represented by 'n'.

Somatic and germ cells
Somatic cells are any cells forming the body of an organism. They are the
diploid cells and divide only by mitosis. Every other cell except sperm and
ovum in the mammalian body is the somatic cell. Hence, it is also known as
body cell. Even the gametocytes (the cells which produce gametes, i.e. sperm
and ovum) are the somatic cells. Internal organs, muscles, skin, bones, blood
and connective tissue are all made of somatic cells.
Germ cells are the specialized haploid cells which are involved in reproduction.
The gametes, i.e. sperm and ovum combine together to form a zygote ( a
diploid cell) which can develop into a foetus.
The germ cells carry the germline, the genetic material which an organism
can pass on to its offspring. In humans, the germ cells are haploid, i.e. they
carry only half the number of chromosomes necessary to create an organism.

Sex determination

There are two types of chromosomes in the cells of all organisms. They
are autosomes and sex chromosomes. The autosomes determine body
characters of an organism whereas the sex chromosomes determine
the sex of an individual.
A human cell contains 23 pairs of chromosomes. Among them,
22 pairs are autosomes and the remaining one pair is called sex
chromosomes. In males, there are 22 pairs of autosomes, and X and
Y sex chromosomes in the remaining pair. i.e. (44 + XY). In males, 50
percent sex chromosomes carry X chromosome and 50 percent carry
Y chromosome during gamete formation. It means that 50 percent
sperms carry X chromosomes i.e. (22 + X) and 50 percent sperms carry
Y chromosomes i.e.(22 + Y). In females, there are 22 pairs of autosomes,
and XX sex chromosomes in the remaining pair i.e. (44 + XX).
Hence, all female gametes (ova) carry X chromosomes only i.e. (22 + X)
because all female sex chromosomes have XX pair.

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If the sperm having X chromosomes fertilizes the ovum (always having
X chromosome), the zygote develops into the foetus of female sex. Then
the mother will give birth to a daughter. On the other hand, if the
sperm having Y chromosomes fertilizes the ovum (always having X
chromosome), the zygote develops into the foetus of male sex. Then the
mother will give birth to a son. This shows that the mother has no role
to give birth to the son or daughter. There is 50 percent probability of
giving birth to a daughter or a son at a time.

44+XY 44+XX

22 22 22 22
X YX X

44+XX 44+XX 44+XY 44+XY

XX female and XY male mechanism of
sex determination in human

Each chromosome is formed of a large number of hereditary units called

genes. Each gene present in a chromosome represents a particular

character. The gene is formed of DNA. The change in the number of

chromosomes or the sequence of genes in the germ cells can result in

different disorders in our body. Hemophilia is one of such disorders. It

is known as a sex linked disease. The peculiar feature of a sex linked

disease is that it is seen in a particular sex. For example, if there is

defect in the Y chromosome, the sex linked disorder will be seen in the

sons only. Hemophilia is a disorder in which bleeding does not stop

from wound or cut parts of the body. Such diseases are transmitted to

the offspring from their parents.

Fact &Reason

What are the sex chromosomes found in male and female?

The sex chromosomes found in male are XY and female are XX.

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Chromosomal disorders

The disorder that arises in the body due to the change in the number
of chromosomes is called chromosomal disorder. It results due to
the absence of one or more chromosomes, addition of one or more
chromosomes or the improper arrangement of chromosomes. If the
chromatids do not separate properly during cell division, the number
of chromosomes in the cell does not remain constant. This condition is
called aneuploidy. The other examples of chromosomal disorders are
Down's syndrome, Klinefelter's syndrome, Turner's syndrome, etc.

Down's syndrome (47, XY, +21) or (47, XX, +21)

Down's syndrome is autosomal chromosomal
disorder. The people with Down's syndrome has
an extra chromosome in 21st pair of chromosomes
which is also known as trisomy of 21st chromosome..
This syndrome was explained for the first time by
Langdon Down.

Following are the symptom of people having Down’s syndrome:

1) The people born with Down's syndrome are dwarf with a small and
round head.

2) They have an open mouth and a furrowed tongue.
3) Their palm is thick with a crease.
4) People with such disorder have retarded physical, mental and

psychological development.
5) They have upward slanting eyes.
6) They have risk of respiratory infection, leukemia and heart

diseases.

Fact &Reason

What is the cause of Down’s syndrome?
The main cause of Down’s syndrome is the development of extra number of 21st
autosome. (45+XY) or (45+XX)

Fact &Reason

Why is Down’s syndrome called trisomy 21?
Down’s syndrome is caused by the development of extra number of 21st
chromosome. So, it is called trisomy 21.

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Klinefelter's syndrome (44+XXY)
The Klinefelter's syndrome arises due to the increase
in number of sex chromosomes. In such case, the
number of X chromosomes is two and number of
Y chromosome is one which results in 44 + XXY
karyotype.

People with Klinefelter’s syndrome have following symptoms:

1) People with this syndrome are sterile male with mental retardation.
2) The people with such syndrome have longer arms and legs.
3) They have wider hips and underdeveloped testes.
4) They are abnormally tall.
5) They have learning disability.

Fact &Reason

What is the cause of Klinefelter’s syndrome?
Klinefelter’s syndrome is the genetic disorder caused when a person gets two
X-chromosomes and one Y-chromosome.

Turner's syndrome ( 44+X0)
The Turner's syndrome arises due to the deficiency
of an X chromosome in female. Hence, the number
of chromosomes is 45 + X0. It was first described by
Henry Turner.

The people with this syndrome have following
symptoms:

1) They are sterile females with poorly developed
ovaries.

2) They have shorter body structure with short neck.
3) They possess many male characteristics like heavy neck muscle

and narrow hip.

Fact &Reason

What is the cause of Turner’s syndrome?
Turner’s syndrome is caused due to lack of one X-chromosomes in female.

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Learn and Write

1. What are somatic cells ? Where are they found?

Somatic cells are any cells forming the body of an organism. They
are the diploid cells and divide only by mitosis. Internal organs,
muscles, skin, bones, blood and connective tissue are all made of
somatic cells.

2. What is the importance of chromosomes?

The importance of chromosomes is as follows:

a. The chromosomes transmit parental characters to the offspring
with the help of genes.

b. Sex chromosomes determine the sex of an organism.

c. They form a link between parents and their offspring.

d. Chromosomes play an important role in cell division , cell
growth and cell repair.

3. How is sex determined in human beings?

In human beings, a baby’s genetic sex is determined at the time
of conception. When the baby is conceived, a chromosome from
the sperm cell, either X or Y, fuses with the X chromosome in the
egg cell, determining whether the baby will be genetically female
(XX) or male (XY). To be genetically female, one needs to be (XX),
whereas to be a genetic male, (XY) is needed.

4. What do you mean by homologous chromosomes?

A pair of chromosomes which are similar in shape, size and
apearance are called homologous chromosomes.

Main points to remember

1. Nucleus is one of the important parts of a cell which contains
nucleoplasm, chromosomes and nucleolus.

2. There is a fixed number of chromosomes in an organism.
3. Cell division is a process of dividing a cell into two or more cells.
4. There are two types of chromosomes. They are : autosomes and sex

chromosomes.
5. Autosomes determine the overall characters of an organism whereas

sex chromosomes determine the sex of an individual.
6. The coiled filament like structure of chromosome is called chromosoma.
7. The two chromosomes of a pair which are similar in shape, size,

appearance and function are called homologous chromosomes.
8. A cell which contains pairs of chromosomes is called diploid cell.
9. A cell which contains only one chromosome of each pair is called haploid cell.

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10. Somatic cells are any cells forming the body of an organism. They
are the diploid cells and divide only by mitosis.

11. Germ cells are the specialized haploid cells which are involved in
reproduction.

12. In human beings, a baby’s genetic sex is determined at the time of
conception.

Exercise

A. Very short answer questions (1 mark)

1. What are genes?

2. What is kinetochore?

3. What is a sex-linked disease?

4. What is sex chromosome?

5. What is metacentric chromosome?

6. How many types of chromosomes are there on the basis of

position of centromere?

7. What are the sex chromosomes that are found in male and

female?

8. What are chromosomes?

9. What is centromere?

10. Define somatic cell.

11. Define reproductive cell.

12. What is chromosomal disorder? Write with examples.

13. Write down the major functions of chromosome.

14. What is the cause of Turner's syndrome?

15. Write down the major cause of Klinefelter's syndrome.

16. What is Klinefelter's syndrome?

17. Write down the major cause of Down's syndrome.

B. Short question (2 marks)

1. Which process is represented by given chart? According to

that process, write down two differences between (44, XX)

and (44, XY).

Male / Female ( 22, X ) ( 22, X )

( 22, X ) ( 44, XX ) ( 44, XX )

(22, Y ) ( 44, XY ) ( 44, XY )

2. Write any two effects of Down's Syndrome.
3. A cell of girl contains only 45, XO chromosomes, which types

of chromosome disorder is present in her body? Write any one
symptom of it.
4. Write down the major symptoms of Down's syndrome.

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5. Write down the major symptoms of Klinefelter's syndrome.

6. What is meant by sex determination? Write in brief.

7. Write any two differences between Down's syndrome and

Turner's syndrome.

C. Long question (3 marks)

1. Draw diagrams for each Metacentric, Sub-metacentric and

Telocentric chromosomes.

2. Differentiate between chromosomes and chromatids.

3. Differentiate between autosome and sex chromosomes.

4. Differentiate between somatic cell and reproductive cell.

5. Differentiate between haploid cell and diploid cell.

D. Very long answer questions (4 marks)

1. Justify with suitable chart that women is not responsible to

give birth to daughters or son.

2. Explain various types of chromosomes on the basis of position

of centromere.

Project Work

Take a white sheet of paper, adhesive tape, scissors, glue,etc.
Cut the paper in different shapes to make the models of different
types of chromosomes.

Glossary

• Autosome : chromosome that determines body characters

• Sex chromosome : chromosome that determines the sex (male
or female) of an individual

• Centromere : place where the arms of a chromosome are
joined

• Chromomere : thick bead-like structures of chromonema

• Syndrome : a set of symptoms

• Homologous : similar

• Bone marrow : a fluid found inside bone

• Bicuspid : tow lobed

• Tricuspid : three lobed

• Arterioles : branch of arteries

• Venules : branch of veins.

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Chapter

18.a Asexual and sexual
Reproduction
Alfred Russel Wallace

Alfred Russel Wallace was a British naturalist,
explorer, geographer, anthropologist, and biologist

Estimated Periods: 7 (5T+2P)

Objectives

At the end of the lesson, students will be able to:

• define sexual and asexual reproduction;
• explain various types of asexual and sexual reproduction in plants and animals.

The number of a certain species does not decrease even they die due
to various reasons. This is possible due to reproduction. All organisms
reproduce again and again to continue their generations.

Reproduction is the process by which all living things produce new
offspring of their own kind.

It is needed to carry out the continuity of race. It is one of the important
characteristics of organisms. It is of two types. They are:

i) Asexual reproduction
ii) Sexual reproduction

Asexual reproduction

The reproduction which takes place without fusion of male and female
gamete is called asexual reproduction. In this reproduction, there is
no involvement of both male and female parents. Only one individual
is able to produce new individuals. Certain parts of the parent body
give rise to new individuals. The offspring produced by this method
are genetically similar with parents. Bacteria, yeast, chlamydomonas,
amoeba, hydra, tapeworm, hookworm, etc reproduce by this method.

Features of asexual reproduction

i) There is involvement of single individual.
ii) The offsprings are genetically similar to their parents.
iii) It occurs by mitosis cell division.
iv) It completes in short period.
v) It does not involve the fusion of male and female gametes.

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Sexual reproduction

The reproduction which takes place with the fusion of male and female
gametes is called sexual reproduction. Male gametes (sperms) are
produced inside the body of male organisms whereas female gametes
(ova) are produced inside the body of female organisms by meiosis cell
division. Organisms that have male and female sex organs in different
individuals are called unisexual organisms. Human being, cow, fish,
frog, etc are examples of unisexual organisms. Some organisms
produce both male and female sex organs in an individual. They are
called bisexual organisms or hermaphrodites.

Fact &Reason

Animals like hydra and earthworm are called hermaphrodite, why?
Animals like hydra and earthworms have both male and female parts that produce
male and female gametes in the same individual . So, they are called hermaphrodite.

Features of sexual reproduction
i) It involves both male and female parents.
ii) The offspring are not genetically similar to parents. They show
the mixed characters of both father and mother.
iii) In this process, meiosis produces gametes. After the fertilization
of the gametes, development of the zygote occurs by mitosis.
iv) It completes in long period.

Sexual reproduction occurs mostly in higher organisms. Generally,
male gametes are small and active whereas female gametes are
large and less active. Gametes are haploid and are formed from a
diploid cell through meiosis in their reproductive organs. Two haploid
gametes (i.e. sperm and ovum) fuse together to form diploid zygote.
Zygote grows into new individual through mitosis.

Male cell Meiosis Male gamete Fertilization

(2n) (n) Zygote mitosis Embryo
Female cell Meiosis Female gamete (2n) (2n)

(2n) (n)

During the formation of gametes, crossing over takes place between
the chromosomes of a homologous pair. Due to this, the offspring will
be different from the parents, i.e. variation occurs.

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Differences between asexual and sexual reproduction

Asexual reproduction Sexual reproduction

1) A single parent produces 1) Male and female individuals

offspring. participate to produce offspring.

2) There is no production and 2) There is production and fusion

fusion of male and female of male and female gametes.

gametes.

3) The offsprings produced are 3) The offsprings produced are

genetically similar to their not genetically similar to their

parents. parents.

4) It is common in primitive 4) It is common in advanced

organisms. organisms.

5) It occurs by mitosis cell 5) It occurs by first meiosis then

division. by mitosis.

Asexual reproduction in plants
Plants reproduce asexually by the following methods:

1. Fission 2. Budding 5. Vegetative propagation

3. Fragmentation 4. Sporulation

Fission

The method of reproduction in which an organism divides into two or
more daughter organisms is called fission. This process mostly occurs
in unicellular plants like bacteria, euglena, etc. It is of two types :
binary fission and multiple fission.

Binary fission Nucleus and cytoplasm

In this method, a fully mature individual divided. Genetically similar
cell divides into two daughter cells. During
this process, nucleus and cytoplasm euglena
divide together and finally a cell splits
into two daughter cells. Binary fission Binary fission in euglena
occurs during favourable conditions.

Multiple fission Multiple fission in euglena

In this method, a fully matured individual 323 Times' Crucial Science Book - 10
divides into many daughter individuals.

This process occurs during unfavourable conditions.

During multiple fission, a thick covering called cyst is formed around
the cell. Then, the nucleus divides repeatedly to produce many
daughter nuclei. Each nucleus is surrounded by the cytoplasm and
cell membrane. As a result, many daughter cells are formed inside
the cyst. Under favourable condition, the cyst breaks releasing many
daughter cells. The daughter cells become new individuals.

Budding

It is a process of reproduction in which an outgrowth is developed
from the parent body in the form of bud. The bud enlarges and later
gets detached from the parent body. The detached bud grows into new
individual. This method is common in unicellular plants like yeast,
volvox, etc.

Bud Chain

Mother yeast

Budding in yeast

In some cases, the process of formation of buds is so fast that it cannot
separate from the parent body. Then it looks like chain.

Fragmentation Fragmented part
It is a method of reproduction in

which body of an organism breaks into

fragments and each fragment develops Fragmentation in spirogyra

into a new individual.

Filamentous algae like spirogyra and riccia reproduce by this method.
Sporulation

In some non-flowering plants like ferns, Sporangium

bryophytes, mushroom, mucor, etc; spores are

produced inside sporangia. The sporangia burst Spores

when spores become matured. Then the spores

are disseminated. These spores germinate into

new individuals during favorable conditions. Sporulation in mucor

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Vegetative propagation

Flower is the reproductive part of a plant. The parts rather than the
flower are called vegetative parts. Root, stem, leaf, etc are vegetative
parts.

The process of production of new plants by cutting, sowing or grafting
any vegetative parts of a plant like root, shoot, leaf, etc is called
vegetative propagation.

It is of two types: natural method of vegetative propagation and
artificial method of vegetative propagation.

Natural method of vegetative propagation

i. By roots

Some flowering plants like dahlia, sweet Vegetative
potato, etc reproduce naturally by roots. Roots propagation by roots

of these plants bear adventitious buds which grow into new plants.

ii) By stem

The stem of some plants like ginger, potato, mint, onion, garlic, etc are
modified to carry out vegetative propagation.

Underground stem of potato, turmeric, ginger, onion, garlic, etc look
like roots but they are different from roots due to the presence of nodes
and internodes. When the stems with nodes are planted in the soil,
they grow into new plants.

iii) By leaf

Leaves of plants like bryophyllum,
begonia, etc produce adventitious
buds. When these buds become
mature, they get detached from the
leaf and grow into new plants.

Advantages of vegetative propagation Vegetative propagation by leaf

1. It is a faster, cheaper and easier method of propagation.
Farmers, gardeners, botanists, etc propagate large number of
plants from a single plant in short period of time.

2. Plants like sugarcane, potato, rose, grapes, banana, etc do not
produce seeds of good quality. Vegetative propagation is the
only method of reproduction in such plants.

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3. The plants produced by vegetative propagation produce flowers
and fruits in earlier period.

4. The species of rare and endangered plants can be conserved.
5. The offspring produced by vegetative propagation are similar

to their parents.
Asexual reproduction in animals
Generally animals reproduce asexually by fission, budding and
regeneration.
Fission
This is a method of reproduction in which an organism divides into two
or more daughter organisms. This process mostly occurs in unicellular
animals like Amoeba, Paramecium, etc. It is of two types : binary
fission and multiple fission.
Binary fission
In this method, a fully mature individual cell divides into two daughter
cells. During this process, nucleus and cytoplasm divide together and
finally a cell splits into two daughter cells.

Binary fission occurs during favourable conditions.

Multiple fission
In this method, a fully
matured individual divides
into many daughter
individuals. This process
occurs during unfavourable
conditions. Eg: Plasmodium,
Amoeba.

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During multiple fission, a thick covering called cyst is formed around
the cell. Then, the nucleus divides repeatedly to produce many
daughter nuclei. Each nucleus is surrounded by the cytoplasm and
cell membrane. As a result, many daughter cells are formed inside
the cyst. Under favourable conditions, the cyst breaks releasing many
daughter cells. The daughter cells become new individuals.

Budding

In this process, a finger like projection called bud grows at the side
of the parent body. When the bud grows and becomes fully matured,
it detaches from the parent body. The detached bud grows into new
individual.

Bud New hydra

Parent hydra Growing Bud

Budding in hydra

This method is common in hydra. The animals like sponges, tunicates,
etc also reproduce by this method.

Regeneration Anterior Grows
half with new head
In some animals, their
body gets divided into no tail
many parts and each
part grows into new Flatworm Posterior Grows
individual. This process divides in two half with new tail
is called regeneration. no head
Hydra, tapeworm,
Planaria, etc can Regeneration in Planaria

develop into new individuals from their divided parts.

Fact &Reason

Planarians reproduce by regeneration. What does it mean?

It means when planarians are divided into two or more parts, new planarians are

generated from each part.

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Advantages of asexual reproduction

i) Asexual reproduction produces offspring exactly similar to the parents.
ii) It is an easier, faster and cheaper method of reproduction.
iii) The plants produced by vegetative propagation bear flowers

and fruits in earlier period.
iv) The plants like sugarcane, banana, rose, grapes, etc which do not

produce good quality of fruits, can be produced by this method.
v) There is no need of involvement of two parents.

Sexual reproduction in plants

In flowering plants, sexual reproduction Stigma
is the common method of reproduction. Anther
Flower is the reproductive organ in Stamen
flowering plants. A bisexual flower has
following parts. Petal
Ovary

Calyx: It is the outermost whorl of Sepal

a flower. It consists of green leaf like

structures called sepals. Calyx protects Flower
the flowers in bud stage.

Corolla: It is the second whorl of a flower. It consists of colourful petals.

Petals attract insects for pollination and also protect the reproductive

parts of a flower.

Androecium: It is the male reproductive organ of a flower. It consists

of a group of stamens. Each stamen consists of a swollen part called

anther and a long stalk called filament. Anther contains fine powder

like pollen grains. Pollen grains contain male gametes.

Gynoecium : It is the female reproductive organ of a flower. It may

contain one or more carpels or pistils. Each carpel consists of ovary,

style and stigma.

The ovary is swollen part a of carpel which contains ovules. Ovary

extends upwards as style and ends at stigma.

Pollination

Pollen grains are formed in anther of stamen. Each anther is bilobed
structure connected by a connective. Each lobe contains pollen sacs
which are filled with microspore mother cell. Each microspore mother
cell undergoes meiosis cell division and haploid male gametes are
produced. These male gametes are contained inside pollen grains.

The pollen grains produced in an anther are transferred to the stigma of
carpel by various agents. This process is called pollination. Pollination
is of two types: self pollination and cross pollination.

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The process of transfer of pollen grains from anther of a flower to the
stigma of the same flower is called self pollination. This process occurs
in bisexual flowers. The transfer of pollen grains from anther of one
flower to the stigma of another flower of same plant or different plants
is called cross pollination. It needs external agents like insects, birds,
wind, water, etc. It is common in open flowers which may be unisexual
or bisexual.

Differences between self pollination and cross pollination

Self pollination Cross pollination

1. It is the transfer of pollen 1. It is the process of transfer of
grains from anther of a pollen grains from anther of a
flower to the stigma of the flower to the stigma of another
same flower. flower of same or different
plant.

2. It does not need external 2. It needs external pollinating

pollinating agent. agents.

3. It occurs in closed bisexual 3. It occurs in open flowers which

flowers. may be bisexual or unisexual.

4. Origin of new species is not 4. Origin of new species takes

possible. place.

5. Harmful characters 5. Harmful characters can be
cannot be eliminated. eliminated.

Fertilization Stigma Pollen grain

Fertilization is defined as the fusion Pollen tube
Ovule
of male and female gamete to form Style
Egg-cell
a zygote. Micropyle
Fertilization in a plant
Stigma of a carpel is either hairy

or sticky to catch pollen grains.

When pollen grain is deposited to

the stigma, it produces a pollen

tube. The pollen tube grows
towards the ovary through style. Ovary

The ovary contains ovules. Each

ovule contains an egg cell (female

gamete), secondary nucleus and

some other cells.

When the pollen tube reaches the ovule, its tip gets ruptured and two

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male gametes are released. One male gamete fuses with egg cell to
form zygote and another with secondary nucleus to form endosperm.
The zygote develops into embryo and endosperm provides nutritive
foods to the embryo.

In angiosperms, the fertilization involves fusion of male gamete with
female gamete (egg cell) and fusion of male gamete with secondary
nucleus. Therefore, it is called double fertilization. Petals, sepals and
stamen dry up and fall down after fertilization, . Then the ovules will
grow into seeds and ovary into fruit. The seeds germinate into new
plants under suitable conditions.

Fact &Reason

Cross fertilization is more superior to self fertilization, why?
Hybrids are formed as an offspring through cross fertilization which are more
healthy and vigorous with more adaptive characteristics. So, cross fertilization is
more superior to self fertilization.

Sexual reproduction in animals

All vertebrates carry out their reproduction process through sexual means.

They produce sperms as male gametes and ova as female gametes.
Sperm is produced inside testes and ovum is produced inside ovaries
by meiosis cell division of diploid reproductive cell. Due to this, sperms
and ova are haploid cells. The male gamete and female gamete fuse
together to form diploid zygote. The zygote develops into embryo which
later grows into new individual.

The process by which male gamete fuses with female gamete is called
fertilization. The fertilization may be external or internal.

When fertilization takes place outside the body of female, it is called
external fertilization. For example, female frog lays eggs on the surface
of water. Then the male frog leaves sperms near the eggs and these
sperms fuse with the eggs. Thus, external fertilization occurs in frogs.
All fishes and amphibians carry out external fertilization.

When fertilization takes place inside the body of female, it is called
internal fertilization. Reptiles, birds and mammals carry out internal
fertilization.

Male animals deposit sperms to the body of female. Then, the sperm fuses
with the egg to form zygote. The zygote grows into new individual. Each

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zygote contains diploid set of chromosomes. For example, zygote of human
being contains 46 chromosomes. Out of 46 chromosomes, 23 chromosomes
come from sperm and other 23 chromosomes come from ovum.

Differences between external and internal fertilization

External fertilization Internal fertilization

1. The male and female 1. The male and female gametes

gamete fuse outside the fuse inside the body of female.

body of female.

2. There is no copulation 2. There is copulation of male and

of male and female female organisms.

organisms.

3. Many female gametes are 3. One or few female gametes are

produced. produced.

4. It is common in fishes and 4. It is common in reptiles, birds

amphibians. and mammals.

Significance of sexual reproduction
1. New characters appear in the offspring which causes the
evolution of new organisms.
2. Offspring produced by sexual reproduction are more resistant
to the diseases.
3. Sexual reproduction is the only means of reproduction in
vertebrates. Thus, race of species is continued and balance of
organisms is established.

Fact &Reason

Justify the statement that “there wouldn’t be many species of organisms if there
was no sexual reproduction”.
Sexual reproduction causes variation which is responsible for the evolution of
new organisms. So it can be assumed that there wouldn’t be many species of
organisms if there was no sexual reproduction.

Learn and Write

1. Gametes are haploid but zygotes are diploid. Why?

Gametes are formed by meiosis cell division of reproductive
cell. Due to which, haploid gametes are produced. But, zygote is
formed by the fusion of haploid male and female gametes. Thus,
diploid zygote is formed.

2. Double fertilization occurs in higher angiosperms. Why?

In higher angiosperms, two male gametes are released to the ovules.

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One male gamete fuses with egg cell (female gamete) to form zygote
and another male gamete fuses with secondary nucleus to form
endosperm. Thus, double fertilization occurs in angiosperms.

3. Asexual reproduction is advantageous to farmers. Why?

Asexual reproduction is cheaper and faster method of
reproduction. The offspring produced by asexual reproduction
bear flowers and fruits in short period. Asexual reproduction is
the only way of reproduction for the plants which do not bear
flowers. Thus, asexual reproduction is advantageous to farmers.

4. Differentiate between sperm and ovum.

Sperm Ovum

1. It is produced by male 1. It is produced by female sex

sex organs. organs.

2. It is motile and smaller in 2. It is non-motile and larger in
size. size.

3. Generally, sperms are 3. Generally, ova are produced in

produced in large small number.

number.

4. Itisproducedbytheprocess 4. It is produced by the process of

of spermatogenesis. oogenesis.

Main points to remember

1. Reproduction is the process by which all living things reproduce
new offspring of their own kind.

2. The reproduction which takes place without fusion of male and
female gamete is called asexual reproduction.

3. The reproduction which takes place with the fusion of male and

female gamete is called sexual reproduction.

4. Fission is a method of reproduction in which an organism divides into
two or more daughter organisms.

5. Budding is the process of reproduction in which an outgrowth is
developed from the parent body in the form of bud.

6. The process of production of new offspring by cutting, sowing or
grafting any vegetative parts of a plant like root, shoot, leaf, etc is
called vegetative propagation.

7. Flower is a reproductive part of a plant which consists of calyx,
corolla, androecium and gynoecium.

8. Androecium is a male sex organ which produces pollen grains
inside which male gametes are produced.

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9. Gynoeciumisafemalesexorganwhichproducesfemalegametesinsideovary.
10. Pollination is the process of transfer of pollen grains from the

anther of a stamen to the stigma of carpel.
11. Fertilization is the process of fusion of male and female gamete.

Exercise

A. Short answer questions (2 marks)

1. Define reproduction.

2. Define asexual reproduction.

3. Define sexual reproduction.

4. Give examples of external fertilization.

5. Define binary fission .

6. Define budding.

7. Define sporulation.

8. Define regeneration.

9. Write the name of two plants that reproduced by sporulation

process of reproduction.

10. Name any two organisms which reproduce by multiple fission.

11. State two basic features of asexual reproduction.

12. Name any two organisms which reproduce through budding.

13. What is external fertilization?

14. How is zygote formed ?

15. What is vegetative propagation?

16. Define hermaphrodite animals with examples.

17. Name any two plants that reproduce by sporulation.

18. What is multiple fission?

19. Name one plant that reproduces through root.

20. What is self pollination?

21. Write the name of parts of a flower that change into seed and

fruit after fertilization.

22. How many chromosomes are there in human sperm and zygote?

B. Short answer questions (2 marks)

1. Mention any two differences between asexual reproduction

and sexual reproduction.

2. Mention any two differences between sperm and ovum.

3. "Offspring produced by asexual and sexual reproduction

process are dissimilar." Why?

4. Write any two differences external fertilization and internal

fertilization.

5. Write any two differences between binary fission in amoeba

and budding in yeast.

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6. Write any two differences between self pollination and cross
pollination.

7. Write any two differences between binary fission and multiple
fission.

8. Differentiate between pollination and fertilization. Write any
two advantages of vegetative propagation.

9. What is the significance of sexual reproduction in the
evolution of organisms?

10. Write any two differences between ovum and zygote.
11. Write down any two major causes of applying tissue culture

for asexual reproduction.

C. Long Answers (3 marks)

1. Describe sexual reproduction in flowering plant with diagram.

2. Draw neat and clean diagram of reproductive part of plant

and label its four major parts.

3. Write any three significance of asexual reproduction.

4. Write any three significance of sexual reproduction.

D. Very long answer questions (4 marks)

1. Draw the labeled diagram of stamen and pistil.

2. Explain fertilization in detail with diagram.

3. What is sexual reproduction? Explain sexual reproduction in

animals.

Project Work

Visit your locality and find various methods of reproduction used
in plants for increasing their number.

Glossary

• Significance : importance
• Pollination : reaching of pollen grains into stigma
• Fertilization : union of male and female gametes
• Regeneration : growth of a complete organism from a part of

a body or growth of lost organ of an organism.
• Germ cell : gamete
• Mutation : a sudden chromosomal change which leads to

new or different offsprings.

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Chapter

18.b Artificial Vegetative
Propagation in Plants
Richard Dawkins
Richard Dawkins is an English ethologist,
evolutionary biologist and author.
Estimated Periods: 5 (5T+0P)

ObAjetctthieveesnd of the lesson, students will be able to:

• define artificial method of reproduction.
• explain various methods of artificial vegetative propagation.

The method of asexual reproduction in which new plants are produced
from the vegetative parts of plants like root, stem or leaf by the human
assistance is called artificial vegetative propagation. Such type of
vegetative propagation is common in higher plants.

The artificial methods of plant reproduction are very useful for farmers,
gardeners, horticulturists, etc. Various methods like cutting, grafting,
layering, tissue culture, etc are used to reproduce useful varieties of
plants in short time.

1. Cutting

It is a common artificial method of
vegetative propagation in which new
plants are grown by planting a cut piece
of stem or root of plants during favourable
condition. The cutting piece must contain
nodes and internodes for the growth of
new plant.

Orange, sugarcane, rose, potato, etc are propagated by stem cutting.

2. Layering

It is an artificial method of vegetative reproduction in which roots
are developed on stem or branch while the branch is still attached to
the parent plant. Layering is commonly used in jasmine, lemon, rose,
strawberry, raspberry, etc.

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In layering, one of the lower branches of the plant is bent and covered
partially with moist soil. Then the covered part develops roots. When
the branch is separated from the parent plant, the new plant grows
independently and bears flowers and fruits.

a. Simple layering

It is the method of developing new

plants from the lower branches of

parent plant that are more than one

year old. In this method, the part of

branch about 20 cm far from its tip is

bent and dipped inside moist soil. Then Fig: Simple layering

the roots develop in the dipped part within 2 – 3 months. Such plant

is then removed from the parent plant during last quarter of the rainy

season and is planted in a nursery. Such method is suitable for lemon,

rose, lime, etc.

b. Compound layering

If a long branch of a parent plant is dipped Fig: Compound layering
inside moist soil by keeping its tip above
the soil, roots and shoot grow from each
node of the dipped part. The new plants
are separated by cutting the stem and
planted in a nursery bed. Such method
of layering is called compound layering.
This method is useful for apple, pear, etc.

c. Tip layering

Tip layering is a method of growing new

plants by dipping the tips of selected

branches of plant in moist soil. About 5 – 8

cm of the tip of the branch is dipped into

the soil. Then roots and a shoot develop

from the dipped tips. The new plants are

separated and their roots are buried in a Fig: Tip layering

new place after 3 – 4 months. This method is useful in black berry,

raspberry, etc.

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d. Mound or stool layering

In mound layering, the whole plant

is cut at a distance of about 6 – 10

cm from the soil surface. A number

of new branches grow below the cut

part after some months. When the

new branches grow 10 – 15 cm tall,

they are covered with a mixture of

wood dust and soil by making a heap

of 20 – 25 cm tall. This enhances the

origin and development of roots. Such Fig: Mound layering

plants can be separated from the

parent support after one year. This method is useful for mango, apple,

plum, pear, etc.

e. Air layering

It is a cheap and popular method of layering. In
this method, a branch of about two metres is used.
Some leaves are removed from the branch and bark
is removed marking the area of 2 – 3 cm length in a
ring shape. The fibres or tubes of the bark and wood
are removed completely. This helps to prevent the
transport of food and hormones prepared in the leaves
toward the roots. The cut part is wrapped with plastic
containing moist soil making it airtight.

Roots develop inside the wrapped part after 4 – 8
weeks. The branch is cut carefully after one month of
development of roots and is planted in a new place.

3. Grafting Fig: Air layering

It is a technique of artificial vegetative propagation in which new
plant is grown by inserting a branch or stem of a plant into the root
system of another plant. It is a method in which a plant of superior
quality is obtained by combining root system of one plant and shoot
system of another plant.

The lower rooted plant used in grafting is called stock whereas the
upper stem or branch of another plant used in grafting is called scion.
The scion contains branches or bud for the growth of the plant.

The cut surfaces of the grafted plants should be held tightly by
wrapping or tying. This technique is used in rose, lemon, mango,
apple, pear etc.

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Methods of grafting

The process of grafting can be carried out in the following ways:
a. Whip grafting

In whip grafting the scion and the stock

are cut by making slanting surface and

then joined. For it about 3.5 cm long

slanted cut is made in scion and stock.

The grafted point is then bound with Whip grafting

tape and covered with soft wax to prevent dehydration and germs.

After 2 - 3 months, the parts join and grow as a single plant.

b. Tongue grafting

In this method, the lower part of
scion and the upper part of stock are
cut slanted by 3 – 5 cm. A tongue
shaped cleft of depth of about 2
cm is made in each part. Then the
tongues of both the parts are fitted
with each other and are wrapped
with plastic to make air tight. They Tongue grafting
are tied together firmly. The scion and stock are firmly held together
after 2 – 3 months. It is also an easy and effective method of grafting.
This method is popular for grafting mountain fruits.

c. Cleft grafting

The most common form of grafting is cleft

grafting. This is best done in the spring.

In cleft grafting, a small cut is made in the

stalk and then the pointed end of the scion

is inserted in the stalk. The branch or stock

should be split carefully down the middle to

form a cleft about 3 cm deep. The end of the Cleft grafting
scion should be cut cleanly to a long shallow

wedge, preferably with a single cut for each wedge surface.

Advantages of grafting

1. It is useful to get benefit from fruit trees in short time. No time is
required as that needed by saplings for full growth and maturity.

2. It is an easy method for the propagation of plants.

3. It helps to reduce the height of the fruit trees and make them
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dwarf. Most apple trees in modern orchards are grafted on to dwarf
or semi-dwarf trees planted at high density. They provide more
fruit per unit of land and higher quality fruit.
4. It helps to speed maturity of hybrids in fruit tree breeding programs.
Hybrid seedlings may take ten or more years to flower and fruit
on their own roots. Grafting can reduce the time to flowering and
shorten the breeding program.
5. It helps to produce diseases or germs resistant varieties of fruit plants.

4. Tissue Culture

Tissue culture is a modern technique of producing new plants from
isolated plant cells or small piece of plant tissue in an artificial culture
medium.

The artificial culture medium contains plant hormones and nutrients.
When isolated plant cell or piece of plant tissue is kept in the medium,
it grows into an unorganized mass of cells called callus. As the callus
grows, pieces are sliced off and transferred into new media.

In this new media, roots and shoot are developed in each slice and
it develops into new plantlet. The plantlets thus produced are then
planted into the soil and they grow as new plants. Various types
of plant hormones are used in tissue culture. Auxin and Cytokinin
are two main hormones which help for the balanced development of
plants. Auxin helps for the growth of roots whereas cytokinin helps for
the growth of shoot. By putting balanced amount of hormones, plants
parts are grown in controlled environment.

Application of plant tissue culture

The main applications of plant tissue culture can be summarized as follows:

1. It can be used in the production of desirable and rare plants.
2. It is used to produce genetically variable plants.
3. It is used to produce pathogen free or disease resistant plants.
4. It is used for the production of novel hybrid plants from somatic

hybridization.
5. It is used for the production of haploid plants.

Advantages of vegetative propagation

1. It is cheaper, easier and faster method of propagation.
2. Seedless fruits like seedless grapes, seedless oranges, etc can be

produced by this method.
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3. Plants that do not produce viable seeds are propagated by this
method, e.g. rose, potato, banana, sugarcane, etc.

4. The fruit trees or flowers produced by this method start to bear
flowers and fruits much earlier than those obtained from their seeds.

5. People can grow desirable plants by vegetative propagation.

Disadvantages of vegetative propagation

1. Plants produced by vegetative propagation are genetically identical
to their parents. This restricts their adaptability to changing
environment.

2. Plants produced by this method are often overcrowded. Therefore,
they gradually become prone to diseases.

3. It hampers the process of evolution of an organism as there is no
variation.

Learn and Write

1. What is callus? Write its one use.

Callus is the mass of highly vacuolated, unorganized and
undifferentiated cells. As the callus grows, pieces are sliced off
and transferred to new media to induce the growth of plantlets.
The plantlets thus produced are then planted into the soil.

2. What do you mean by stock and scion?

The lower rooted plant used in grafting is called stock whereas the
upper stem or branch of the plant used in grafting is called scion.
The scion contains branches or bud for the growth of the plant.

3. Write any two differences between simple layering and
compound layering.

Differences between simple layering and compound layering are below.

Simple layering Compound layering

1. In this, bending of branch 1. In this, bending of branch

occurs at a single spot. occurs at multiple spots.

2. It gives rise to a new single 2. It gives rise to many new plants at

plant. once.

Main points to remember

1. Vegetative propagation is a method of asexual reproduction in
which new plants are produced from the vegetative parts of plants
like root, stem or leaves.

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2. Grafting is a technique of vegetative propagation in which new
plant is grown by inserting a branch or stem of a plant into the
root system of another plant.

3. The lower rooted plant used in grafting is called stock whereas the
upper stem or branch of the plant used in grafting is called scion.

4. Tissue culture is a modern technique of producing new plants
from isolated plant cells or small piece of plant tissue in an
artificial culture medium.

5. The isolated plant cells grow into an unorganized mass of cells
with the help of plant hormones and nutrients. This mass is
known as callus.

6. The main steps involved in the process of tissue culture are
isolation of plant material, sterilization and preparation of
nutrient media.

Exercise

A. Very short answer questions (1 mark )

1. Write the name of upper part and lower part used in grafting

2. Name any two plant hormones.

3. Define scion.

4. Define stock.

5. What is layering?

6. What do you mean by explants?

7. Name the method of vegetative propagation in the following

plants.

a. Bryophyllum b. Begonia c. Onion d. Moss

e. Rose f. Potato g. Sugarcane h. Planaria

B. Short answer questions (2 marks)

1. Write two importance of tissue culture.

2. Write down any two major causes of applying tissue culture

for asexual reproduction.

3. A mango plant grown from grafting is better than that grown

from seed, why?

4. A potato is planted by cutting its tuber. Why?

C. Long answer questions (3 marks)

1. Write the step wise process to grow the maize plant in the

laboratory by tissue culture method.

2. Write any three uses of tissue culture.

3. How is air layering done? Explain with figure.

4. "Tissue culture method of an artificial vegetative propagation

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in plants plays a great role in forestry, horticulture and
agriculture fields." Justify the statement.
5. How can we grow new lemon plant from simple layering
process? Explain briefly with diagram.
6. Differentiate between layering and grafting .
7. Differentiate between micronutrients and macronutrients.
8. Differentiate between stock and scion.

D. Very long answer questions (4 marks)

1. Study the given diagram and answer the following

questions.

i) Name the method of vegetative propagation.

ii) How is this vegetative propagation applied

commercially?

iii) Write any two importance of this type of

reproduction.

Project Work

Select a proper plant to propagate it through layering. Collect
the materials necessary for layering and produce new plants
by this method. Plant the new plants at a fertile place in the
garden and observe their growth. Prepare a brief report of your
activities and observation.

Glossary

• Propagation : to reproduce a plant or animal, or cause one to
reproduce

• Scion : a living shoot or twig of a plant used for grafting
to a stock

• Stock : rooted part used in grafting

• Grafting : Grafting is a process of artificial vegetative
propagation in which shoot system of one plant is
attached to root system of another plant.

• Apex : Top or highest part of stem or root.

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Chapter

19 Heredity
Gregor Mendel

Gregor Mendel was an Austrian monk who discovered the

basic principles of heredity through experiments in his

garden. He is known as the Father of Modern Genetics.

Estimated Periods: 5 (5T+0P)

Objectives

At the end of the lesson, students will be able to:

• explain Mendel's experiment and laws;
• identify dominant and recessive characters;
• explain causes of variation and mutation.

Introduction

There are various types of organisms in our surroundings. These
organisms seem different from each other. Some organisms resemble
with each other in some aspects. But, they are not exactly similar.
The similarities or differences between the organisms depend upon
the presence of genes in the nucleus of cells of these organisms. Genes
are the chemicals which determine characters or traits of an organism.

Offspring are somehow similar to their parents. The parents give
birth to the offspring of the same species. For example, a dog always
gives birth to puppies not kittens, chicken are hatched out from hen's
eggs but not from crow's eggs. Similarly, a human child is born from
human, not from cow and maize seeds grow into maize plants, not
wheat plants and so on. These all are due to transfer of genes from
parents to the offspring. The process by which characters or genes
transfer from parents to the offspring is called heredity. The characters
which get transferred to the offspring are called hereditary characters.
Some of the characters are gained by an organism in its own life time
due to own effort or environmental influence. Such characters are
called acquired characters.

The branch of science which deals with the study of the heredity is
called genetics.

Gregor Mendel (1822-1884) was the first person to study the process of
heredity. Therefore, he is known as the father of genetics. He was the
priest of a church in Brunn of Austria. He performed many experiments

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on the crosses in the sweet pea (Pisum sativum) in the garden of the
Church. His work was published in the Annual Proceeding of the
Natural History Society of Brunn in 1866. AD. It was local magazine.
So, scientists of other countries could not know about the discovery
of Mendel. Mendel died in 1884 A.D. Later three scientists working
independently in three different countries got the same result which
was already published by Mendel forty years ago.

The characters or traits selected by Mendel

Mendel selected the seven pairs of contrasting characters of pea plant
(Pisum sativum) for his experiment. The characters are given below:

Trait or character Dominant character Recessive character

1) Shape of seed Round (R) Wrinkled (r)

2) Colour of cotyledon Yellow (Y) Green (y)

3) Height of plant Tall (T) Dwarf (t)

4) Colour of pod Green (G) Yellow (g)

5) Shape of the pod Inflated (I) Constricted (i)

6) Colour of flower Red (R) White (r)

7) Position of flower Axial (A) Terminal (a)

Why did Mendel select pea plants for his experiments ?

Mendel selected pea plant for his experiment due to the following
reasons.

i) Pea plant has bisexual flowers. Therefore, it is naturally
self pollinated and can be artificially cross pollinated.

ii) It has a number of distinguishable contrasting characters
like tall and a dwarf, red and white flowers, round and
wrinkled seeds, etc.

iii) Its life cycle is short. So, the results can be obtained in short period.
iv) It produces a large number of offspring after fertilization.
v) The plants can be handled conveniently. So, they can be

grown anywhere.
vi) The hybrid plants obtained as a result of cross-pollination

are also fertile.

Mendels experiment

Mendel selected 7 pairs of contrasting characters of pea for the study
of heredity. But, he concentrated his attention on only one pair
of character at a time. He controlled his experimental conditions

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carefully ensuring that the pea plants are pollinated by the selected
pollen grains only.

He selected pure tall plants and pure dwarf plants. He made artificial
crossing between them by transferring pollen grains from one plant
to another. He prevented self-pollination by removing the stamens of
the pollen grain receiving plants. The new plants were grown from the
seeds obtained from the cross-pollination. The new generation thus
obtained was called first filial generation or F1 in short. It was found
that all plants of F1 generation were tall, not intermediate between
tall and dwarf.

In the same way, he observed the results obtained after the cross-
pollination of six pairs of contrasting characters. He found that only one
type of character was expressed from the pair and the another remained
unexpressed. He called the character that expressed in F1 generation
as dominant character and the other that remained unexpressed as
recessive character. In the above experiment, tallness is dominant and
dwarfness is recessive character.

The plants obtained in F1 generation were allowed for self-pollination
among themselves. The plants obtained from the seeds of the plants
of F1 generation were observed. It was found that 75% of the plants
were tall and 25% the plants were dwarf. The ratio of tallness to
dwarfness was 3:1. The new plants thus obtained were called second
filial generation or F2 in short. The result of F2 generation were
allowed for self-pollination. In the next generation, the seeds of dwarf
plants gave only dwarf plants. Out of the seeds of tall plants, one-third
grew into pure tall and remaining two-thirds grew into tall and dwarf
plants in the ratio of 3:1. The plants hence obtained were called third
filial generation or F3 in short. The results obtained in the third filial
generation were as follows:

i) Pure tall plants developed only into tall plants.
ii) Hybrid tall plants developed into tall and dwarf plants in the

ratio of 3:1.
iii) Pure dwarf plants developed only into dwarf plants.

Explanation of Mendel's experiment

One pair of genes determine a single character. One of the each pair
inherits from each parent. Capitals letter is used to represent dominant
character and small letter is used to represent recessive character. For

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example, gene for tallness is represented by T and gene for dwarfness
is represented by t. The organism which contains both similar genes
for a character is called pure. The organism which contains dissimilar
genes for a particular character is called hybrid. For example, the
organism having genes TT is pure tall and the organism having genes
Tt is hybrid tall.

Results of Mendel's experiment can be shown as follows:

Phenotype of parents Pure tall (male) Pure dwarf (female)

Genotype of parents TT tt
Crossing

Gamete formation TT tt

Fertilization

F1 generation Tt Tt Tt Tt

All hybrid tall

All plants of F1 generation are hybrid tall (Tt).

Result of self pollination among the plants of F1 generation.

Hybrid tall (male) Hybrid tall (female)
Tt Tt
Phenotype of parents
Genotype of parents Selfing

Gamete formation Tt Tt

Fertilization

F2 generation TT Tt Tt tt
Pure tall Hybrid tall Pure dwarf

Phenotypic ratio = 75% tall : 25% dwarf or 3:1

Genotypic ratio = 25% pure tall: 50% hybrid tall: 25% pure dwarf
or (1:2:1)

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