16. The valves in the heart control the flow of blood within the heart.
17. The bicuspid or mitral valve guards the opening of the left auricle into the left ventricle. It
consists of two flaps or cusps.
18. The tricuspid valve is present at the point of origin of aorta from the left ventricle. It
consists of three flaps or cusps.
19. Aortic semilunar valve is present at the point of origin of aorta from the left ventricle.
20. Pulmonary semilunar valve is present at the base of pulmonary artery.
21. Circulation of blood in the human heart is double circulation.
22. Circulation of blood between the heart and body organs except lungs is called systemic
circulation.
23. Circulation of blood between the heart and lungs is called pulmonary circulation.
24. The heart beat occurs due to its contraction and relaxation.
25. Pressure of blood on the wall of blood vessel (artery) is the blood pressure.
26. A healthy human has his blood pressure 120/80 mm Hg.
27. Uric acid is the chemical which is produced from purine rich food like pulse, drinks, sea
food etc.
28. The disease that occurs when the body is unable to regulate the amount of glucose (sugar)
in the blood is called diabetes.
Project Work
1. Separating the Blood corpuscles.
(a) Bring some fresh blood from a butcher’s shop.
(b) Stir the blood for some time and let it settle in the glass.
(c) You will notice two different zones.
(i) What could be the thin clear layer?
(ii) What is the name of coagulated matter? What corpuscles are found in this part?
2. Finding heart beat by stethescope
3. This activity can be done in pairs. One student should act as a patient.
a. Put the bell of a stethoscope against the chest wall and listen the heart beat by
keeping the bell in different part of the chest.
b. Find out which is the best place to put the stethescope to get the loudest sound?
What do you think causes the heart sounds?
Blooming Science Book 10 251
Exercise
1. What is blood circulatory system?
2. What is blood? Write its composition.
3. Blood circulation in the body does three functions. Explain transport function and control
function.
4. Of the three types of living cells present in the blood, mention which
a.occurs in the greatest numbers
b. helps in the clotting process when injury occurs
c. transports oxygen to and carbon dioxide away from the body cells
5. Why is plasma important? Name two components present in it.
6. a. Where are the erythrocytes produced in the body?
b. For about what length do they function in blood circulation?
c. What gives them red colour?
d. How do they transport oxygen and carbon dioxide?
7. What is fibrinogen? How does red bone marrow relate with red blood cells?
8. What prevent the coagulation of blood in blood vessels during normal circulation?
9. What is haemoglobin? In which part of the blood is haemoglobin found and what is its
function?
10. What is the shape of red blood cells? What are the advantages of its shape?
11. What happens if the number of RBC decreases in the body?
12. What disadvantage is caused by the increase in the WBC?
13. Where does platelets form and mention its function.
14. Blood being carried by most arteries is bright red in colour while blood being carried by
most veins is a dark red. What is responsible for this colour difference?
15. a. What is the heart made of?
b. What are the upper parts of the heart called?
c. What are the coronary arteries and veins for?
d. What happens when auricles contract?
16. Which side of the heart contains oxygenated blood?
17. What are the blood vessels that take impure blood to right auricle and pure blood to left
auricle.
18. Draw a diagram of human heart and name any four parts of it.
19. Name the valves between auricles and ventricles. What happens if these valves were not
present?
20. Explain with reasons:
a. The wall of left ventricle is thicker than the wall of the right ventricle.
252 Blooming Science Book 10
b. An anaemic person feels tired in a short walk.
c. Blood is red in colour.
d. Right auricle is larger than the left auricle.
e. Arteries have no valves but veins have valves.
f. Arteries are deeply seated.
g. Arteries have more thick wall than veins.
h. It is difficult for the blood to clot in a wounded artery than in a wounded vein.
i. Capillaries are thin walled.
j. Heart beat increases during exercise.
21. The blood in an artery flows faster and at higher pressure than the blood in a vein. Can you
explain why?
22. How do arteries and veins differ in structure and function?
23. Where does aortic valve lie? Could blood circulation be interrupted if this valve were not
existed?
24. State one function of each of the following:
a. Fibrinogen b. Pulmonary vein c. Leucocytes
d. Aortic valve e. Pericardial fluid f. Lymphocytes
25. Mention two differences between:
a. RBC and WBC b. Auricle and ventricle
c. Artery and vein d. Pulmonary and systemic circulation
e. Pulmonary artery and pulmonary vein f. Tricuspid valve and the bicuspid valve
26. Give one effect of the following:
a. If the haemoglobin content becomes low in the red blood cell.
b. If white blood cells decrease in a person.
c. If artery is cut. 1 A
27. The diagrams given alongside are cross sections of blood vessels. B
a. Identify the blood vessels A, B, and C. C
b. Label the part 1 and mention its function.
c. Which category of blood vessels have valves in their inner
lining?
d. Which one carries pure and impure blood respectively?
28. What do you mean by heart beat? When does it increase? The systolic BP of a person is
120 mm of Hg. What does it mean?
29. What is blood pressure? If a person has blood pressure 140/100mm Hg, what does it
mean?
Blooming Science Book 10 253
30. The diagram represents a mammalian heart. Observe the diagram and answer the following
questions:
a. Name the parts A, B, C and D with one function
of each.
b. From where do structures labeled B and A receive F
blood respectively? B
c. Why is A larger than B? A G
d. Name the membrane covering the heart.
e. Write one function of E, F and G. E
31. What is uric acid? Write its symptoms and preventive C D
measures.
32. What is diabetes? Write its symptoms and ways to
control it.
33. What is high BP ?Write its causes and preventive measures.
34. Study the diagram of blood cells and answer these question: C
i. Label ‘A’ , ‘B’ and ‘C’ with a function of each.
ii. What happen if ‘C’ is increased and decreased? B
iii. Name a disease caused by decrease in ‘A’. A
35. Choose the correct alternatives from the following options.
i. The disease caused due to decrease in WBC in our body is:
a. Leukaemia b. Anaemia
c. Leukopenia d. All of the above
ii. Tricuspid valve is found in between:
a. Left and right auricle b. Left auricle and left ventricle
c. Pericardium d. None of them
iii. The range of normal blood pressure in adult healthy person is:
a. 120/80 mm of Hg b. 140/80 mm of Hg
c. 80/60 mm of Hg d. All of the above
iv. Which disease is caused due to lack of insulin in our body?
a. Uric acid b. Anaemia
c. Diabetes d. All of the above
v. Which blood vessel contains valve in it?
a. Artery b. Capillary
c. Venacava d. Vein
254 Blooming Science Book 10
Chapter Chromosome Heinrich Wilhelm Gottfried von
and Sex Waldeyer-Hartz
17
Determination 1836 – 1921
Learning Outcomes Estimated Periods: 5+1
On the completion of this unit, the students will be able to:
introduce chromosomes.
tell about the features of chromosomes.
list out the number of chromosomes of some common plants and animals.
differentiate between autosomes and sex-chromosomes.
explain the process of determination of sex.
describe chromosomal disorders.
Introduction
All living things are made up of cell or cells. Cells are the structural and functional units of
life as they give the structure of the body and perform all the life related functions. Unicellular
organisms have only one cell to make their body. The single cell in these unicellular organisms
gives the shape and size of the whole body and carries out all the life processes. Multicellular
organisms like men and roses are made up of trillions of cells. There are different types of cells
in the multicellular organisms. These varied types of cells give different various shapes and sizes
to the tissues and organs of the organisms. Different types of cells have different functions in
multicellular and advanced organisms. Cells are differentiated to do certain functions in well
developed organisms. Plants and animals are different from each other in shapes, structure and
functions. Animals of different species are different from each other in many respects. Even
the individuals of same species have a lot of variations. Offsprings from same parents are also
different to some extent in many features and abilities. How is this possible? What governs all
these things? Have you ever thought about it? The answer is: the chromosomes. We should know
the structure and functions of chromosomes. Let’s discuss about chromosomes and their features
and functions in this lesson.
Chromosome
The word ‘chromosome’ was first used by Heinrich Wilhelm Gottfried von Waldeyer-Hartz in
1888 AD. Waldeyer derived it from Greek root words: Chroma - colour and soma - body. They
were seen under light microscope by using staining colour to the cells. Each chromosome is made
up of long chain of DNA molecules and protein stabilizers known as histones. Chromosomes are
found inside the nucleus of the cell. They look like mass of entangled bundle of thread under
microscope. Chromosomes work as the physical agents to carry the hereditary characters from
parents to offspring. They carry all the information needed for an organism to develop into and
behave as it should. Chromosomes carry all the biological information obtained from its parents
about the physicals features: the structure of body, appearance and all the biological possibilities
like face cut, hair structure and colour, eye colour and some hereditary defects too. Chromosomes
instruct to produce specific proteins that are responsible for giving shape, size, behavior patterns,
Blooming Science Book 10 255
and life span of a cell. Chromosomes not only transfer the hereditay characters but also they
determine sex of an individual change in the number of chromosomes causes various disorder
in the body.
Structure of Chromosome
Chromosomes are found in the nucleus of nucleus chromosome
cells. Each nucleus has a network of fine telomere
threads also known as chromatin reticulum.
The chromatin threads are usually seen centromere
scattered and entangled with one another
but they arrange in certain pattern in the cell cell chromatids telomere
during cell division. During prophase of cell nucleosomes
division, each chromosome is seen with its
duplicate chromatin fibre that is produced
during interphase by DNA transcription.
Such two chromatin fibres are called bases pair histones
sister chromatids. In some of the stages
(metaphase and anaphase) of cell division,
the number of chromosomes can be counted
under microscope. Scientists study the
karyotypes of different cell taking pictures of
thickened chromosomes. When we observe DNA of double helix
chromosomes in detail, they look like two
sausages tied together at some constriction points known as centromeres or kinetochores. It is
called primary constriction. The narrow area in chromosome other than primary constriction is
called as secondary constriction. The spherical ball like structure at the end of chromosome is
called satellite where DNA contain is found very low.
Each chromosome carries hundreds and thousands of hereditary units called genes. Length of
chromosomes varies as they carry different number of genes. Genes are the molecular units of
hereditary characters. Genes are certain regions in the long DNA molecule. DNA molecules are
double helix structures like wound rope ladder.
They carry the genetic instructions to direct the
growth, development and reproduction of the
organisms. Genes are made up of nucleotides. phosphate group
Nucleotides are the base units of DNA pentose sugar
molecule. DNA molecules are composed up of
phosphates, deoxyribose sugars and four types
of nitrogen basses. The four types of nitrogen
bases are: Adenine, Thiamine, Cytosine and
Guanine. Adenine makes pair with thiamine
(A-T) and Cytosine makes pair with Guanine
(C-G) as these pairs well fit together like lock
and key. Sugar and phosphate group make the
rope like part of the helix and the nitrogen base
pairs lie inside as the rungs of the rope ladder.
Human genome has about three billion base DNA (double helix) nitrogenous base
pairs of DNA in 46 chromosomes.
256 Blooming Science Book 10
Chromosomes are found in certain sets in organisms. Most often, chromosomes are found in pairs
known as diploid sets. It is denoted by 2n. Each set of chromosomes are obtained from parents
during fertilization. One set comes from female parent through her ovum and next set comes from
male parent via sperm. Single set of chromosomes is called haploid set and it is indicted as (n). In
some plants and animals chromosomes are seen in single set or more than two sets as well. Having
more than two sets is called polyploidy. The two almost identical sets of chromosomes, one
obtained from maternal side and next from paternal side are called the homologous chromosomes.
Homologous chromosomes are almost same in length and shape and they carry genes for similar
characters along the length of the chromatin fibres.
Types of Chromosomes
Chromosomes are classified into four types as metacentric, submetacentric, acrocentric and
telocentric chromosomes according to the position of centromere along the chromosome.
Metacentric chromosome: If the chromosome has its centromere at the middle and the arms
on the both sides are equal in length, it is called metacentric chromosome. They look X-shaped
chromosomes during anaphase of cell division. Chromosome number 1, 3, 16, 19 and 20 of
human cells are of this type.
Submetacentric chromosome: centromere chromatids
When the centromere is lying
primary
slightly away from the centre constriction short satellite
towards one side and the arm arm secondary constriction
arms are unequal, it is called
submetacentric chromosome. long
These chromosomes take the arm
shape of ‘J’ during anaphase.
The 2nd, 4th to 12th, 17th, 18th metacentric sub- acrocentric telocentric
and the X-chromosomes are of metacentric
this kind.
Acrocentric chromosome: If the centromere is placed more away from the centre and one arm
is much longer on one side than the other side, it is called acrocentric chromosome. In these
chromosomes, the shorter arm (the p-arm) is so shorter than the longer arm (the q-arm) that it is
hard to observe under light microscope. The 13th, 14th,15th,21st, 22nd and the Y-chromosomes
of human cells are this type of chromosomes.
Telocentric chromosome: When the centromere is at the terminal end of the chromosome, it is
called telocentric chromosome. This kind of chromosome looks like ‘i’ during anaphase. This
kind of chromosomes are not found in our human cells. This kind of chromosomes are seen in
house mouse (Mus musculus).
Sometimes, a segment may detach from a chromosome and remain without any centromere.
Such piece of chromosome lacking centromere is called acentric chromosome. It does not take
part in cell division as centromere is essential for the attachment with spindle fibre. Similarly,
in some chromosomes, the entire length of the chromosome work as points of attachment due
to presence of multiple centromeres along the length. Such chromosomes are called holocentric
chromosomes.
Blooming Science Book 10 257
Activity
To observe the chromosomes under microscope.
Materials required:
compound microscope, permanent slide of metaphase stage of cell division.
Method:
1. Adjust a compound microscope to view the permanent slide under its high
magnification.
2. Keep a permanenet slide of metaphase stage of mitosis cell division of a cell.
3. Observe the chromosomes arranged at the equatorial region of the cell and try to
identity various parts.
Draw the diagram of chromosomes that you could observe and show to your teacher.
Autosomes and Sex chromosomes in human
Human Karyotype (Normal)
12 3 45 12 3 45
6 78 9 10 11 12 6 78 9 10 11 12
13 14 15 16 17 18 13 14 15 16 17 18
19 20 21 22 X/Y 19 20 21 22 X/X
Male (44+XY) Female (44+XX)
The chromosomes that regulate the body features but do not determine the sex are called
autosomes or somatic chromosomes. The chromosomes which are responsible to determine the
sex are called sex chromosomes or heterosomes. In diploid human cells there are 23 pairs of
chromosomes in each cell. Out of these 23 pairs of chromosomes, 22 pairs are only responsible
for the structure of body and other features but they do not determine the sex of human. These
chromosomes are called autosomes or somatic chromosomes. They are numbered 1 to 22 in
descending order of their length. The remaining 23rd pair of chromosomes are responsible for
the determination of sex as male or female. These particular chromosomes which determine the
sex of human are called sex chromosomes or heterosomes.
In human female, the sex chromosomes are equal in length and they are labeled as XX. Thus a
human female has 44 autosomes and XX sex chromosomes i.e. 44+XX. In human male, the sex
chromosomes are unequal. So, they are labeled as XY. The ‘Y’ chromosome is shorter than the
‘X’ chromosome. Thus, a human male has 44 autosomes and XY sex chromosomes i.e. 44+XY.
258 Blooming Science Book 10
When the number of sex chromosomes are in other sets than ‘XX’ or ‘XY’, the person has
some abnormality and the person become infertile due to inability to produce normal gametes by
meiosis. There may be abnormal combination of sex chromosomes like ‘X0”, ‘XXY’, ‘XXX’ etc.
The presence of abnormal number of chromosomes in cell other than normal 46 chromosomes
i.e. 44+XX or 44=XY, is called aneuploidy. The following arrangement of human chromosomes
(Karyotype) explains it clear.
Number of chromosomes
The number of chromosomes in plants and animals is a fixed number for a species. The somatic
cells of the organisms generally contain a diploid set (2n) of chromosomes. The gametes like (egg
and sperm) carry only the haploid (n) set of chromosomes in each. When a male gamete (sperm)
and a female gamete (ovum) combine during fertilization, the two sets of haploid chromosomes
make a diploid set of chromosomes (n + n = 2n). Thus, a diploid cell contains one haploid set of
chromosomes from it maternal parent (mother) and the next haploid set from its paternal parent
(father). The zygote undergoes mitotic cell divisions to produce diploid cells to produce the
embryo. The cells in the embryo further divide mitotically to produce body cells. These somatic
cells carry diploid set of chromosomes and thus have all the genetic information of the organism.
[After special process called differentiation, cells of different body parts carry out only
certain functions specific information required to particular tissue or organ and turn off other
information. Some cells of body still may be capable of manifesting all the characters of the
genetic information. Such cells are called stem cells. These stem cells can be used now to produce
the whole new organ to whole new organism by cloning.]
The diploid number of chromosomes present in some of the plants and animals are listed in the
table below:
Organism Chromosomes(2n)
Human (Homo sapiens) 46 (23 pairs)
Gorilla (Gorilla gorilla) 48 (24 pairs)
Rhesus monkey (Macaca mulatta) 42 (21 pairs)
Dog (Canislupus familiaris) 78 (39 pairs)
Tiger (Panthera tigris) 38 (19 pairs)
House mouse (Mus musculatus) 40 (20 pairs)
Frog (Rana tigrina) 26 (13 pairs)
House fly (Musa domestia) 12 (6 pairs)
Pigeon (Collumba sp.) 80 (40 pairs)
Fruit fly (Drosophila melanogaster) 08 (4 pairs)
Organism Number of chromosomes (2n)
Bread mould (mucor hiemalis) 2 (1 pair)
Onion (Allium cepa) 16 (8 pairs)
Pine (Pinus sp.) 24 (12 pairs)
Nightshed plant (Kaligedi)(Solanum nigrum) 16 (8 pairs)
Rice (Oryza sativa) 24 (12 pairs)
Blooming Science Book 10 259
Sugarcane (Saccharum officinarum) 80 (40 pairs)
Maize (Zea mays) 20 (10 pairs)
Wheat (Triticum aestium) 42 (21 pairs)
Potato (Solanum tuberosum) 28 (14 pairs)
Mango (Magnifera indica) 40 (20 pairs)
Sex determination
Male and female are the two distinct sexes of unisexual organisms. Sex in some animals like
human beings, is determined by sex chromosomes. Human cell has 46 chromosomes. Out of
these 23 pairs of chromosomes, 22 pairs of chromosomes (autosomes) are not, but one pair
(sex chromosomes) is responsible for the determination of sex in human population. These
chromosomes are called sex chromosomes. They are labeled and ‘X’ and ‘Y’.
Female human cells have 22 pairs of autosomes and XX chromosomes in each of them (44+XX).
Male human cells have 22 pairs of autosomes and XY chromosomes in each of them. During
meiotic cell division of the reproductive cells, female produce haploid gametes (ova or eggs)
each containing 22 autosomes and one ‘X’ chromosome i.e. 22+X. But male produce 50 %
gametes (sperms) consisting of 22 autosomes and one ‘X’ chromosome i.e. (22+X) and next
50 % gametes consisting of 22 autosomes and one ‘Y’ chromosome i.e. (22+Y). Thus, all the
ova from female are with only 22+X chromosomes whereas there are 50% sperms carrying
X-chromosome and next 50% sperms carrying Y-chromosome.
When an ovum with 22+X is fertilized by a sperm with 22+X set, the zygote will have 44+XX
set and the child produced will be a baby girl. When an ovum with 22+X is fertilized by a sperm
with 22+Y set, the zygote will have 44+XY set and the child produced will be a baby boy.
Father Mother
Parents
Father Mother 44+XY 44+XX
44+XY 44+XX
22+X 22+Y Gyno Andro
Gynosperm Androsperm 22+X Eggs 22+X X Sperm Y Sperm X Eggs X Gametes
girl baby boy baby girl baby boy baby Offspring
sex determination in humans
Baby boy
Baby girl Baby boy Baby girl 44+XY
44+XX 44+XY 44+XX
Normally, there is only one egg with 22+X set chromosomes in female at the time of fertilization.
But there are millions of sperms in each ejaculation. Half of them (50%) are with ‘X’ and next
half (50%) are with ‘Y’. So, there are equal chances for both types of sperms (X-carrying or
Y-carrying) to fertilize the egg. Out of millions of sperms, only one fertilizes the egg. And it is
mere a matter of chance which one gets to fertilize. That is why the male and female population
of human is almost equal. Be getting son or daughter is matter of chance and not in the hand of
husband or wife.
260 Blooming Science Book 10
Genetic disorder
All living beings carry genetic information through DNA molecules. In eukaryotic cells, DNA
molecules are packed in chromosomes by proteins known as histones. Genes are the molecular
units of heredity in the long chain of DNA molecule. In 46 chromosomes of human cells, there
are about three billion base pairs that make thousands of genes. Each chromosome carries
thousands of genes in the form of certain segments of DNA molecules. Our physical and
biological characters are determined by these genes. When there are some changes in the genes,
they are manifested in form of variation or mutation in our bodily features. Some of the changes
are disadvantageous and cause defects to the body of an organism. These defects produced due
to abnormalities in genes are called genetic disorders. Haemophilia, muscular dystrophy, cyst
fibrosis, melanoma, sickle-cell anemia, colour-blindness, Turner syndrome, Down’s syndrome,
Klinefelter’s syndrome etc. are some examples of genetic disorders. Genetic disorders are of two
types:
1. Mendalian disorders
If the genetic disorders are due to one gene mutation and inheritable according to Mendel’s
laws of inheritance, they are also called Mendalian disorders. Haemophilia, sickle-cell anemia,
xeroderma pigmentosa, cystic fibrosis and thalassemia are some of the Mendalian disorders.
These disorders can be predicted by pedigree analysis of the family history.
Some genetic disorders are related to sex chromosomes (X or Y chromosome). These disorders
are inherited from the carrier parent to the child. Such genetic disorders linked with the sex
chromosomes are called sex-linked disorders. Haemophilia, colour-blindness and fragile
X-syndrome are some of sex-linked disorders. Colour-blindness makes person unable to
distinguish between red and green colours and fragile X-chromosome results into children low
intellectual ability.
Haemophilia is one of such sex-linked disorders. It is the X-chromosome linked disease that get
inherited from a carrier mother of defective X-chromosome to her son. As it is a recessive allele,
it rarely gets inherited to a girl child. The dominant next healthy X-chromosome suppresses its
effects in the girl. It is rare chance for girl child to have this disorder as it needs both defective X-
chromosomes to result such combination. Boy has X and Y chromosomes and thus does not have
next unaffected X-chromosome to suppress the defective gene. The affected boy suffers from
non-stop bleeding even from minor cuts, injuries and bruises. The person lacks blood clotting
factors and thus blood does not clot at the injury sites. Person is at risk of excess loss of blood in
injuries than normal person. This can be highly dangerous and even fatal too if the bleeding is in
the internal vital organs like brain.
2. Chromosomal disorders
The genetic disorders caused due to change in chromosome number or change in the structure
of chromosome are called chromosomal disorders. Normal human cell should have 46 (22 pair
of autosome and one pair of sex chromosomes) i.e. 44+XX or 44+XY. It is called normal set of
chromosomes or euploidy. But sometimes there are some errors during meiosis cell division and
either egg or sperm carries less or extra number of chromosomes. When such gametes carrying
abnormal number of chromosome happen to fuse to produce zygote, the resultant cell will have
unequal or abnormal number of chromosome than a normal human cell should have e.g. 45
or 47 chromosomes. This condition is called aneuploidy. Such abnormality in chromosome
number results into premature death of the fetus during gestation period or produce some
Blooming Science Book 10 261
defects in the child born. Down’s syndrome (21-trisomy), Edward’s syndrome (18 trisomy),
and Patau syndrome (13 trisomy) are some examples of aneuploidy due to presence of one
extra chromosome. Similarly, Klinefelter syndrome (XXY) and Jacob’s syndrome (XYY) are
also chromosomal disorders. They are due to presence of one extra sex-chromosome. Turner’s
syndrome (44+X0) is chromosomal disorder due to absence of one chromosome.
a. Down’s syndrome (47, xy, +21) or (47, xx, +21)
Down’s syndrome is one of the chromosomal disorders caused due to presence of one extra
chromosome (trisomy of 21). In this case the cell has 47 chromosomes instead of normal 46
chromosomes. Both the chromosomes of chromosome number 21 remain in the egg during
meiosis. Thus there are already 24 chromosomes in the egg nucleus. So, when it gets fertilized
by normal sperm there are three strands of chromosomes number 21. It is called 21-trisomy or
trisomy of 21. This was first described by John Langdon Down, a British doctor, in 1866 AD.
This case normally occurs in the eggs of women above 40 years of age.
The person with Down’s syndrome has delayed physical growth. They have some distinctive
physical features like: round face with large forehead, short neck, short and flat hands with small
stubby fingers, flattened nose, partially opened mouth with narrow roof, large and furrowed
tongue, abnormal teeth, widely separated first and second toes, and small eyelids. They have
creased thick palms. They have some other physical problems as well. They are more likely to
have heart defects from birth, thyroid disorders, mental disorder and eye and ear defects.
Their immune function is also poor. They have mild to moderate intellectual disability. Adults
may have intellectual capacity that of 8-9 year-old child. Male usually cannot become father and
females are also have very low fertility as their gonads are not well developed. Females may have
menopause at early age. Down’s syndrome is confirmed by examination of the chromosomes
from blood test. This disorder can be suspected from the physical appearance of the child too.
Upslanting Flattened
palpebral nasal bridge
fissures Brushfield
Low-set, small, spots
folded ears
Short neck
Epicanthal fold Small, typically white spots,
arranged in a ring
Fig: A child with Down’s syndrome
Upper eyelid skin fold
covers the inner corner of the eye
b. Klinefelter’s syndrome (47, xxy)
Klinefelter’s syndrome is a chromosomal disorder caused due to presence of at least one extra
X-chromosome in males. There are 47 chromosomes (44 autosomes +XXY) instead of normal
46 (44+XY) in males with this genetic disorder. So, it is also known as XXY or 47 XXY
disorder. This disorder was first described by Doctor Harry Klinefelter in 1942 AD in USA.
262 Blooming Science Book 10
This disorder may take place randomly but older women may have more risk. This may happen
due to abnormal separation of sex chromosomes during meiosis cell division in male or female
reproductive cells. Either the egg carries two X-chromosomes (22+XX) or the sperm carries both
X and Y chromosomes (22+XY). When such abnormal gametes undergo fertilization, the zygote
has 47 chromosomes with one extra X-chromosome: 44+XXY. This disorder can be diagnosed
by testing blood sample to look at the karyotype that reveals the extra X- chromosome.
The person having this disorder may not realize it until his puberty. Boys with this disorder have
weaker muscle and reduced strength than other boys of their age. They have small genitals.
Children may have poor coordination, difficulty in reading and speech problems and lower IQ than
their siblings but many have normal intelligence. They tend be quiet and sensitive. These problems
can be solved by speech and language therapy, counseling and adjustment teaching methods.
The female secondary sex-characters start to be more prominent during puberty. They start
developing breasts like that of females. They have less body and facial hair. They have less
production of testosterone hormone. They are usually infertile males. They are taller and have
longer arms and legs than normal boys.
frontal baldness
absent
tendency to poor beard
grow fewer growth
chest hairs
breast narrow
development shoulders
female-type 1 23 45
public hair wide hips
pattern
small
testicular
size 6 7 8 9 10 11 12
long legs 13 14 15 16 17 18
19 20 21 22
X Y
Fig: Klinefelter’s syndrome Fig: Karyotype of Klinefelter’s syndrome
c. Turner’s syndrome (45, xo)
Turner’s syndrome is a genetic disorder occurring due to absence of one sex chromosome. The
cell has only 45 chromosomes (44+X) instead of normal 46 chromosomes. Person having this
disorder is an infertile female missing one X-chromosome in her cells. This genetic disorder
was first discovered by Henry Turner in 1938 AD. This disorder may be caused due to missing
of X- chromosome during meiosis by an egg (22+0) or a sperm (22+0) and the fertilization
resulted in an abnormal zygote (44+X0). This genetic disorder is also known as monosomy
for sex chromosome (monosomy X), or 45,X, or TS. This chromosomal abnormality can be
diagnosed by special genetic test at the time of fetus development by extracting cells from the
Blooming Science Book 10 263
womb. Ultrasound diagnosis can also show some defects in heart and kidneys of the fetus.
The person with Turner’s syndrome is a female by body structure with some of masculine
characters like narrow hip and heavy neck. The girl child shows some abnormal features at the
birth: swollen hands and feet, short webbed neck, low set of ear. The girls with this disorder
have short stature, broad chest with widely spaced nipples. Some of them may be with normal
intelligence but many have problem with concentration, memory and attention needed for
learning mathematic skills and social skills. Their body and face have some specific features like
drooping eyelids, small lower jaw, forearms angle away, soft and upturned nails, short 4th finger,
low hairline on back of their neck etc.
Internally, they have less developed ovaries, weak bones, some kind of heart defects, low thyroid
and estrogen hormone production, kidney problems, eye and ear defects etc. The girls with
Turner syndrome do not have normal menstruation periods and secondary sex characters that
should develop in puberty. Thus, they are infertile.
short stature characteristic
facial features
low hairline
fold of skin
shield-shaped constriction of aorta
thorax poor breast
development
widely spaced
nipples elbow deformity
shortened rudimentary ovaries
metacarpal iv gonadal streak
small finger nails (underdeveloped
gonadal structures)
brown spots (nevi)
no menstruation
Fig: Turner’s syndrome
Fig: Karyotype of Turner’s syndrome Fig: A girl with TS
264 Blooming Science Book 10
Let's Learn
1. Human genome has about three billion base pairs of DNA in 46 chromosomes.
2. The chromosomes that regulate the body features but do not determine the sex are
called autosomes or somatic chromosomes. The chromosomes which are responsible to
determine the sex or maleness or femaleness are called sex chromosomes.
3. Sex in some animals like human beings, is determined by sex chromosomes labeled as X
and Y chromosomes; 44+XX make female and 44+XY make male.
4. Haemophilia, muscular dystrophy, cystic fibrosis, melanoma, sickle-cell anemia, colour-
blindness, Turner syndrome, Down’s syndrome, Klinefelter’s syndrome etc. are some
examples of genetic disorders.
Points to Remember
1. Cells are the structural and functional units of life as they give the structure of the body
and perform all the life related functions.
2. Chromosomes are made up of microscopic thread like structures called chromatin fibres
made from long chain of DNA molecules.
3. DNA molecules are composed up of phosphates, deoxyribose sugars and four types of
nitrogen basses: Adenine, Thiamine, Cytosine and Guanine.
4. Each chromosome carries hundreds and thousands of hereditary units called genes.
5. Chromosomes are usually found in pairs known as diploidsets (2n ) in organisms.
6. The two almost identical sets of chromosomes, one obtained from maternal side and next
from paternal side are called the homologous chromosomes and they carry genes for
similar characters.
7. Chromosomes are classified into four types as metacentric, submetacentric, acrocentric and
telocentric chromosomes according to the position of centromere along the chromosome.
8. The chromosomes that regulate the body features but do not determine the sex are called
autosomes or somatic chromosomes and the chromosomes which are responsible to
determine the sex are called sex chromosomes.
9. Any defect, deletion or addition of genes, imbalanced in chromosome number or
juxtaposition of one chromosome in place of another results into abnormality known as
genetic disorders or chromosomal defects.
10. Down’s syndrome is one of the chromosomal disorders caused due to presence of one
extra chromosome (trisomy of 21).
11. Klinefelter’s syndrome is a chromosomal disorder caused due to presence of at least one
extra X-chromosome in males. There are 47 chromosomes (44+XXY) instead of normal
46 (44+XY).
12. Turner’s syndrome is a genetic disorder occurring due to absence of one sex chromosome
in female. The cell has only 45 chromosomes (44+X0) instead of normal 46+XX
chromosomes.
Blooming Science Book 10 265
Project Work
To prepare the model of chromosomes
Material required:
Chart paper, woolen thread of different colours, scissors , glue stick etc.
Method:
1. Cut the woolen thread of different colours into different sizes.
2. Give the shapes of a chromosome to by combing two pieces of thread of same colour.
3. Stick the thread pieces with the help of gluestick in chart paper so that you can form
chromosomes of threads connecting at cnetromere.
Show the chart paper with chromosomes to your teacher and mange to keep in the wall of
your classroom.
Exercise
A. Multiple choice questions: Choose the correct answer from the alternatives.
1. How many chromosomes are there in pine cells?
a) 23 pairs b) 12 pairs c) 24pairs d) 20 pairs
2. What is the basic unit of heredity called?
a) Mitochondria b) Chromosomes c) Gene d) RNA
3. What is the name of sex determining factor?
a) Centromeres b) Sex-chromosomes c) Autosomes
d) Nucleotides
4. What do we call a cell if it has two sets of chromosomes?
a) Haploid b) Triploid c) Diploid d) Polyploid
5. Which chromosomal disorder is caused by 44+XXY condition?
a) Down’s syndrome b) Klinefelter’s syndrome
c) Turner’s syndrome d) Edward’s syndrome
6. What is the normal karyotype for a human male ?
a) 44+XX b) 44+XY c) 44+XXY d) 44+X0
7. Which cell division produces gametes?
a) Amitosis b) Mitosis c) Meiosis d) Multiple fission
266 Blooming Science Book 10
B. Define the following terms:
a) Genes b) Somatic cells c) Haploid cell
d) Diploid cell e) Euploidy f) Aneuploidy
g) Ploypoidy h) Sister chromatids i) Homologous chromosomes
C. Differentiate between:
a. Autosomes and sex-chromosomes
b. Homologous chromosomes and sister chromatids
c. Diploid cell and haploid cell
d. Metacentric and submetacentric chromosomes
e. Acrocentric and telocentric chromosomes
f. Chromosome and chromatid
D. Answer the following questions:
1. What are the units of heredity? Where are they found?
2. What are chromosomes? What are they made up of?
3. What are the four types of chromosomes according to the position of centromeres?
4. Write short note on DNA molecule.
5. How is sex determined in human? Explain in brief with appropriate diagrams.
6. What do you understand by diploid cell? How many pair of chromosomes are
found in the following organisms: human, rice, onion, frog, dog, potato, sugar cane
and mould?
7. What do you understand by karyotype?
8. What do you understand by aneuploidys? Explain in brief with example.
9. What do you understand by chromosomal disorders? Explain inn brief with example.
10. What is Down’s syndrome? Give some features of person with this disorder.
11. What is Klinefelter syndrome? Why does the person with this syndrome normally
show feminine features despite his male sex?
12. What is Turner’s syndrome? Give the features of this syndrome.
13. What is gene? Where is it located? Write its function.
Blooming Science Book 10 267
Chapter
18 Reproduction
Oscar Hertwig
1849 – 1922
(German embryologist
and cytologist)
Learning Outcomes Estimated Periods: 8+3
On the completion of this unit, the students will be able to:
describe asexual reproduction in animals and plants.
tell about sexual reproduction in animals and plants.
write examples of asexual and sexual reproduction in animals and plants.
explain the artificial vegetative propagation in plants.
Living organisms have different fundamental characters, out of which reproduction is the most
important characteristics. Reproduction is not benificial to an individual but is essential for the
continuity of life from one generation to the next. The continuity of life has been possible from
the time of its origin about millions of years ago because of reproduction. Living things tend to
produce offspring that resemble them. All organisms reproduce again and again in their lifetime
to continue their generation. In this process, one generation of living organisms produces the next
generation of similar living organisms. Reproduction is the outstanding characteristic of living
organisms by which every kind of living organism multiplies to form new individuals of its own
kind. In living organisms, reproduction is carried out by two methods. They are:
A. Asexual reproduction
B. Sexual reproduction
A. Asexual Reproduction
Asexual reproduction represents the primitive form of reproduction, which produces identical
offsprings. This type of reproduction has the following characters.
1. There is involvement of a single individual.
2. It produces new offspring genetically similar to its parents.
3. Asexual reproduction is performed by involvement of mitosis.
4. It completes in short period.
5. It does not involve production or fusion of sex-cell (gametes) by two sexes, thus it is
called asexual reproduction. In short, it can be said that asexual reproduction is that type
of reproduction in which fertilization does not occur.
Asexual reproduction in organisms takes place by the following methods:
a. Fission b. Budding
c. Fragmentation and regeneration d. Sporulation
e. Vegetative propagation
Out of them, plants have fission, budding, sporulation, fragmentation and vegetative
268 Blooming Science Book 10
propagation. Similarly animals reproduce asexually by fission, budding, fragmentation and
regeneration.
1. Fission
This is a simple method of division in which an organism divides into two approximately equal
parts. This type of reproduction mainly takes place in unicellular organisms. When the individual
cell is fully matured, it is divided into two during favourable condition. This is called binary
fission. During this process, the nucleus divides simultaneously. Binary fission is very common
in amoeba, euglena, paramecium like animals and bacteria, diatom like plants.
Development Scan for practical experiment
of groove
Nucleus Elongation of
nucleus
Two
daughter
cells
Division of visit: csp.codes/c10e18
nucleus and
cytoplasm
Fig: Binary fission in Amoeba
When several new individuals are formed from a single parent under unfavourable condition, it
is called multiple fission. In this method, a thick covering or cyst is formed around the cell under
unfavourable condition. Then the nucleus is divided into many nuclei. On return of favourable
conditions, the cyst bursts and the entire nucleus come out in the form of new organisms. It is
common in animals like plasmodium and plants like chlamydomonas.
many daughter cells daughter cells
nucleus produced by multiple fission release
ccyyttooppllaassmm
schizont cell
Fig: multiple fission
2. Budding
Budding is a common asexual reproduction in which an organism forms a small outgrowth at its
one side. It is called bud. The nucleus of parent divides and one of them migrates to the bud. The
bud enlarges its size and later detaches from the parent body. Then it grows into new daughter
organism. This is very common in animals like hydra and plants like yeast.
New hydra
Mother hydra Bud Fully grown bud
Fig: Budding in hydra
Blooming Science Book 10 269
Mother yeast Forming bud Growing bud Chain of buds
Fig: Budding in yeast
3. Fragmentation and Regeneration
It is a process in which elongated body of an organism breaks into two or more fragments due to
various agencies like heat, wind etc. The activity of living organisms in each fragment grows to
form a new individual. This method is very common in plants like spirogyra, riccia, marchantia
etc.
Mother spirogyra
Fragmenting spirogyra
Fig: Fragmentation in spirogyra Daughter spirogyra
Mother planarion Cuts at planarion Regeneration in
planarion
Scan for practical experiment
visit: csp.codes/c10e19
Fig: Regeneration in planarion
Accidentally when some organism divide into two parts, each part can regenerate into the
complete organism. It is very common in hydra, tapeworm, planaria, starfish etc like animals. In
this way sometimes regeneration is also considered as a method of asexual reproduction.
4. Sporulation Sporangium
Most of the non-flowering plants like mucor, Spores being shed
mushroom, bacteria, moss, ferns etc. like plants produce
spores inside the sporangium. The spores are small, Stalk
light unicellular reproductive structure. The spores Hypha
are released out by bursting of matured sporangium.
Such spores germinate into their corresponding new
plants under favourable conditions.
Protozoan like amoeba sometimes reproduces by sporulation. In which number of spores are
formed in side of them which come out from their body in the form of new amoebae.
270 Blooming Science Book 10
5. Vegetative Propagation
The process in which the vegetative parts of plants such as roots, stem and leaves take part in the
formation of new plants is called vegetative propagation. For example, when the piece of stem
of a rose plant sown, under favourable conditions it grows into a new rose plant such vegetative
propagation is very common in higher plants. It is of two types:
a. Natural method of vegetative propagation.
b. Artificial method of vegetative propagation.
a. Natural Vegtetative Propagation
This type of vegetative propagation is not done by human beings but it occurs naturally. It
takes place by following vegetative parts: Leaves
i. By roots: The adventitious roots of some Aerial shoot
plants become thick, swollen and tuberous
due to the storage of food. They bear
adventitious buds. When such adventitious
roots are planted, new plants are produced.
This method is common in sweet potato,
dahlia etc. Adventitious
roots
Scale leaf
ii. By stem: The stems of a large number of Young plant
plants are modified for vegetative propagation.
In some plants, the stem develops lateral Potato tuber
branches from the mother plant. Then it
breaks from the parent plant and develops into Potato
a new individual plants. Such stems are called
subaerial stems. e.g. mint, potato, cynodon,
etc.
The stems of some plants like potato, canna, turmeric, ginger, onion, garlic, etc. grow
in different forms below the soil. The stems of such plants are modified for food. They
are called underground stems. They are like root in appearance but are different from
the roots by nodes, internodes and buds. When the stems with nodes are planted in the
soil, they develop into new plants.
iii. By leaves: In Bryophyllum, the leaves are Leaf
thick and fleshy. Their leaves bear buds in New plants
the marginal notches. When leaves fall and
come in contact with moist soil, new plants Leaf of bryophyllum
develop on it. They grow into new small
plants. Begonia also reproduces by this
method.
Blooming Science Book 10 271
Activity-1
To observe vegetative propagation in some plants
Material required:
sweet potato root, potato tuber, rhizome of ginger, bryophyllum leaf, cotton, etc.
Method:
1. Take some roots ( swollen parts of sweet potato), potato, tuber with sufficient eyes,
rhizome of ginger with buds and a bryophyllum leaf with buds in the notches.
2. Put these plant parts in wet cotton placed on a tray and water it once in a day for few
days.
3. Observe the changes take place in all the planted parts after 7-8 days.
Draw the conclusion and show to your teacher.
b. Artificial Vegetative Propagation in Plants
There are many plants which do not produce viable seeds. It is almost impossible to grow them
by their seeds. We can grow those plants by using vegetative parts like stem, root, leaves in
artificial way as well. We can produce large number of saplings of good yielding crop plants or
fruits by tissue culture. This ensures the same quality of the plant products and it is easy to grow
in short time as we do not have wait for all the processes needed seeds. Farmers have been
availing of this technology to grow better plants in horticulture, floriculture and general agriculture
for greater yields, better products and advanced crops. Some of the artificial methods of vegetative
propagation are discussed here.
i) Cutting: In this method, plants are propagated by cutting of
small pieces of stem. This cutting piece must contain nodes and
internodes. When the pieces are placed in soil, roots emerge
from the nodes and to new plants grow from the piece. This
method is very common in rose, sugarcane, orange etc.
ii) Layering: The process of growing new plants by producing roots from the branches of a
parent plant is called layering. This process is used in the plants of horticulture (fruits
farming) and floriculture (flower farming). We can produce many new plants from one
parent plant. Layering ensures the qualities of parent plant in the new plants. There are
various types of layering techniques. Some of them are:
a) Simple layering: In simple layering, branches of at least
one year old age are chosen. The branches from the parent
plant are bent and buried under soil leaving about 20cm above
the ground level. The buried part of the branches give out roots
are in about two to three months. The stem continue to get
supply of water and nutrients from the parent plant. After the
roots developed, these branches are cut off from the parent
plant and transferred to nursery bed for further growth by
the end of rainy season. This method is used for citrus fruits like lemon, and lime in
horticulture.
272 Blooming Science Book 10
b) Compound layering: This type of layering is similar to
simple layering but in this method, whole part of the stem
is buried under the ground leaving only the tips above the
soil. Roots are given out from each of the nodes in the
stem. After roots are formed, the stem is cut out from the
parent plant and each piece of stem with roots are
transferred to nursery for further growth. This method of layering is used in plants like
apple, pear, walnut.
c) Tip layering: In tip layering method, the tips of
the branches from the parent plant are buried under
the soil up to 5-8 cm. Each tip develops new stem
and roots after 3-4 months. After the roots are
developed, the new plants are cut off the parent
plant and transferred to new bed for further growth.
Plants like black berry and rasp berry are propagated in this way.
d) Mound or Stool layering: In this type of
layering the stem of the plant 5-10 cm above the
ground is cut in the spring season. Numerous new
leaf buds are produced from the part below the cut
part. When these buds grow 8-15 cm, they are
covered with mound of soil or saw-dust up to 20-
25 cm height. The new buds produce roots inside
the mound. The plants are separated from the parent plant after about a year. Horticulture
plants like apple, plum, pear, mango and guava are propagated by this method.
e) Air layering: In this method of plant propagation stems of at least
two years of age are selected for layering. The bark from the aerial
stem is peeled about 2-3 cm in a circular ring form. Bark and wood
part are carefully removed from the scar so that the food and hormones
prepared in leaves do not go down to lower part of the stem. Thus the
callus can develop at the cut part. The cut part is treated with oxygen
or IBA (Indol-3-butaric acid) hormone for better callus formation. The
scar part is covered with moss and wet soil with help of cloth or plastic
tape. Roots develop from the callus region of the peeled part in 4-5
weeks depending on the condition of the stem. One month after the development of roots,
the stem is detached from the parent plant and transferred to nursery bed. This method is
popular among farmers for its ease and popularity. Lots of plants species like mango are
propagated in this method in horticulture and floriculture.
Blooming Science Book 10 273
iii) Grafting: The horticultural technique of attaching one variety of plant part on another
variety of plant by stacking one part on next is called grafting. Different but closely related
varieties of plants are joined one or many on top of another plant species. The plant part
which is joining on top is called scion and the plant part that is at bottom is called the
stock. The plant species used as scion and stock should be of close relation for successful
grafting. The vascular tissues and the cambium part of the scion and stock must match
perfectly with each other. Some of the grafting are as follow:
a) Whip grafting: This is a simple way of grafting. prepared scion
Both the scion and stock are taken with similar size so
that they fit well. After selection of scion and stock,
they are cut about 3.5 cm in oblique way. The obliquely graft in position
cut parts are attached tightly with each other not letting with stock and
any air pockets between them. The joint is covered scion matched
with plastic tape not to allow air or any movement.
When the joint is formed well in about 2-3 months, the
covering cloth or plastic tape should be removed. By
then, the joint is well formed between the scion and prepared stock
stock. This kind of grafting in extensively used for many horticulture plants and floriculture
varieties.
b) Tongue grafting : This is one of the popular techniques in prepared scion
grafting. It is easier and reliable method of grafting in
horticulture and floriculture. In this grafting both the scion
and stock are cut in oblique fashion with tongue like structures graft in position
that fit well with each other and secure the joint. For this, the with stock and
lower part of scion and the upper part of stock are cut about scion matched
3cm – 5cm obliquely. Then a tongue like structure is produced
on scion and stock by making groove of 2cm in the stem.
These two stems are fixed tightly with each other and covered
with plastic sheet or tape not letting air to pass inside. A knot prepared stock
is developed at the joint of scion and stock in about 2-3
months. This kind of grafting in used in fruit varieties like pear and grapes.
c) Cleft grafting: In cleft grafting, the stock stem is cut
smoothly and a groove of 5-8 cm is made in the middle.
Scion stems are relatively smaller than the stock stem. The
scion stem are cut with wedge like structures (v shape) that
fit in the groove of stock stem. The wedge part of scion are
inserted into the groove of stock with the help of wax or
grease and the joint is covered with tape or plastic sheet.
This is usually done when both the scion and stock are
in dormant condition in winter. The joints get fixed and
develop into healthy new stems.
274 Blooming Science Book 10
Activity-2
To study method of grafting.
Material needed :
two small plants for stock and scion, knife, plastic piece.
Method:
1. Select a suitable stock and scion for your experiment.
2. Cut the lower part of scion and upper part of stock in required shape.
3. Fix the scion and stock with each other and make it air tight by wrapping
the joint portion with plastic.
4. Observe it after three months.
Draw your conclusion and share it in your class with your friends and teacher.
Technique of tissue culture
Tissue culture of plants is done in special laboratories where the apparatus are made sterile to
avoid any contamination or adulteration. Special culture media containing plant growth regulators
(PGRs = plant hormones) like auxin and cytokinin, and nutrients are used for the growth of plant
tissues in test tubes or petri dish.
Excess of auxin results in growth of root tissue and excess of cytokinin results in growth of
stem tissue. Balanced amount of auxin and cytokinin develops tissues mass known as callus.
This callus is divided into tiny parts and again grown in separate culture media. When the tissue
develops into shoot parts, they are segregated and kept in for development of root parts. After
roots are developed, the plant saplings are developed in greenhouse for further growth before
they are distributed for farming. Horticulturist, floriculturists and farmers can then grow them as
normal plant saplings.
Tissue culture is extensively used in forestry, horticulture, floriculture and botany studies. Many
rare and indigenous plant species which are at verge of extinction due to over collection, overgrazing
or deforestation can be preserved and multiplied by using the technique of tissue culture.
Scan for practical experiment
Adantages of Tissue culture
1. A large number of genetically identical plant species can be
produced by using tissue culture.
2. It helps to preserve the rare and endangered plants.
3. We get definite variety of flowers leaves, fruits, stems or visit: csp.codes/c10e20
desired plant product
4. Hydrid plants that have some sterile or do not produce viable seeds can be multiplied
in number for the commercial use.
5. Plants with medicinal value can be grown in large number by this method.
Blooming Science Book 10 275
Advantages of Vegetative Propagation
1. The plants which do not produce viable seeds can be easily propagated by this method;
e.g. banana, rose, sugarcane, potato, etc.
2. The plants produced by vegetative propagation bear flowers and fruit earlier than those
produced from seeds. e.g. orange, lemon, mango etc.
3. It is a cheap and rapid method relative to long period of seed dormancy.
4. It gives rise to genetically uniform population, the clone.
Advantages of Asexual Reproduction
1. It does not need any particular environments as a single individual involves in it. Thus it
is a rapid and cheap method of reproduction.
2. It helps to produce quality organisms groups.
3. Offspring produced by this method get ready for further reproduction fast.
B. Sexual Reproduction
Sexual reproduction is a process in which a new organism is formed by the fusion of male and
female gametes. The process of fusing gametes is called fertilization.
When male and female reproductive organs are found in separate individual, they are called
unisexual or dioecious. But, when male and female reproductive organs are found in the
same individual, they are called bisexual, hermaphrodite or monoecious Hydra, earthworm,
tapeworm, etc., are some examples of such animals. In lower organisms like paramecium, the
sexual reproduction takes place by conjugation. Conjugation is the simplest method of sexual
reproduction.
Characteristics of Sexual Reproduction
1. Male and female gametes participate in it through fertilization.
2. Offspring show the mixed characters of father and mother both i.e. they show variation.
3. In it, gametes are formed by meiosis cell division which is followed by mitosis cell
division after the formation of zygotes.
4. It takes long time to complete.
1. Sexual Reproduction in Plants Petal
In angiosperms, gametes are formed in Stigma Anther
specialized organs called flowers. Usually a
flower is borne on a stalk called pedicel. It has Style Filament
a upper swollen region known as thalamus or Sepal
receptacle. A typical flower has four floral Ovary Receptale
whorls, which are borne on the thalamus.
The four whorls, of flower are calyx, corolla,
androecium and gynoecium. Calyx is the
outermost whorl of the flower. It is formed by
a group of leaf like or scale like green structure
276 Blooming Science Book 10
called sepals. Sepals enclose the bud and protect it. Corolla is the second whorl of the flowers
and consists of a number of petals. Petals attract insects for pollination. Androecium is the third
whorl of the flower. It consists of varying number of stamens. Each stamen consists of filament
and anther. Anther forms pollen grains and the pollen grains form male gametes. Gynoecium is
the inner most part of the flower. It constitutes the female reproductive organ of the flower. It is
composed of ovary, style and stigma. Ovary encloses the ovules. Ovules form female gametes.
Activity-3
To observe various parts of a complete flower.
Materials required:
mustard flower, forceps, handlens etc.
Methods:
Take some mustard flower. Study the different parts using handlens. Separate the
various parts by using forceps. Observe these carefully and find out various facts about
the parts of a mustard flower. Make a table to show the colour, number and nature of
different parts.
Draw the diagrams of each part and show to your teacher.
Development of pollen grains and male gamete
An anther of a stamen is bilobed structure, connected by a connective. Each lobe contain pollen
sacs. There are four pollen sacs or microsporangia in an anther. Each pollen sac is filled with many
microspore mother cells which are diploid. Each microspore mother cell undergoes reduction
division (meiosis) and produces four haploid microspores in the form of tetrad structure. Each
microspore develops into pollen grains. The pollen grain form male gametes inside pollen tube
formed after pollination.
Development of ovules or female gamete
A pistil consists of basal swollen ovary, long slender style and stigma. An ovule develops from the
inner wall of ovary. As the ovule develops, it gets raised up from ovarian wall by a short funicle.
The main body of ovule is oval in shape. It is composed of many cells and is known as nucellus. It
is covered by one or two protective layers called integuments. The basal part of nucellus is known
as chalaza while the small opening at the apex of the integument is called micropyle.
Centrally, an ovule consists of a megaspore mother cell. Each megaspore mother cell is diploid
which undergoes meiotic division and gives four haploid cells. Out of four cells, three are
degenerated and only one is functional which is known as megaspore. Megaspore develops into
embryo sac. Embryo sac consists of eight cells. Among these eight cells, three are antipodal cells,
two are polar nucleus (secondary nucleus), two are synergids and one is egg cell. The egg cell
functions as the female gamete.
Blooming Science Book 10 277
Pollination
The transfer of pollen grains from the anther to stigma is called pollination. In some plants,
pollen transfers from the anther to the stigma within the same flower without any agent. This is
known as self pollination. Self pollination occurs in closed bisexual flowers.
If the pollen grains from the anther of one flower go to the stigma of another flower, it is called
cross-pollination. For cross-pollination, the pollen must be carried by external agents like insects,
birds, wind, water, etc. They are called agents of pollination. It is common in open flowers,
which may be unisexual and bisexual.
Fertilization
Fertilization is defined as a process in which Pollen grain
Pollen-tube
male and female gametes fuse together. When Stigma
a pollen grain comes on stigma, a pollen tube
grows, in which two male gametes are formed.
As the tube gets longer, it grows through the Style
style. Finally it reaches the microphyle of the
ovule.
The tip of tube breaks when it enters inside
the embryo sac and the two male gametes are Ovule
released into it. One gamete of them unites Ovary Antipodal cells
with the egg and other with secondary nucleus. Secondary nucleus
Egg cell
The process is called fertilization. It produces Synergids
the fertilized egg called zygote. The other Micropyle
male gamete which unites with the secondary
nucleus forms the endosperm. In higher
angiosperms, there is fusion of two pairs of
nuclei during fertilization, that’s why it is called
double fertilization.
Formation of seed and fruit
Fertilization brings a sudden end to the work of flower. The sepals, petals and stamens wither.
The ovule as a whole develops into seed while the ovary develops into fruit. When the seeds get
matured, they come out from the fruit and form seedlings in suitable conditions.
2. Sexual Reproduction in Animals
In animals, the sexual reproduction takes place by various methods. In multicellular animals
testes produce sperms and ovaries produce ova. The male and the female gametes unite to form
a diploid cell called zygote. The process of fusion of sperm with an ovum is called fertilization.
Fertilization is of two types. They are external and internal.
When fertilization takes place outside the body is called external fertilization. The external
fertilization generally occurs in water. The male releases the sperm into the water at about the
same time that the female releases ova. Some sperms come in contact with eggs and fertilize
them. Fish and frog do this type of fertilization. This type of fertilization takes place in fishes
and amphibian.
278 Blooming Science Book 10
When the fusion of the sperm and the ovum takes place inside the body it is called internal
fertilization. Insects, birds, mammals, etc do this type of fertilization.
The zygote resulting from fusion of two haploid gametes becomes diploid. For example, there
are 23 chromosomes in each of sperm and ovum of human. When a sperm and an ovum fuse, the
chromosomes combine to form 46 and a diploid zygote is formed.
Male reproductive By Male Fertilization
organs meiosis gamete Zygote Mitosis Embryo
(2n)
Female reproductive By (n)
organs meiosis
Female
gamete (n)
Comparison of External Fertilization and Internal Fertilization
External Fertilization Internal Fertilization
1. Male gametes fused with female gametes 1. Male gametes fused with female gametes
outside the female body usually in water. inside the female body.
2. The male gamete is shed into a large 2. The male gametes are shed into a confined
space, there is less chance of fertilization. space, there is a greater chance of fertilization.
3. Zygote develops outside the body. 3. Zygote develops inside the body.
4. Most common in fish, amphibians and 4. Most common in land plants, reptiles, birds
algae. and mammals.
Significance of Sexual Reproduction
1. Due to sexual reproduction, the race of a species is continued but daughter organisms
genetically differ from the parents.
2. Since there are variations, it contributes to the evolution of the species.
3. Offspring formed by this method are of more resistant type.
Let's Learn
1. Asexual reproduction is advantageous to farmers because, it is a rapid method of
reproduction and the plants formed by this reproduction bear flowers and fruit after a short
duration.
2. Gametes are haploid and zygotes are diploid, because gametes are formed by meiosis cell
division and zygote is formed by the fusion of nuclei of male and female gametes.
3. Sexual reproduction plays a very important role in making the number of chromosomes
diploid in offspring. It is because in the reproduction fertilization takes place in which two
haploid gametes fuse for the formation of zygote.
4. Double fertilization occurs in higher angiosperms, because two pairs of nuclei fuse in
them. Out of the two nuclei of pollen grain one of them fuses with egg nucleus to form
embryo and other fuses with secondary nucleus to form endosperm.
Blooming Science Book 10 279
5. Cross pollination does not occur in closed flowers, because in such flowers the pollen
grains transfer from the anther to stigma of the same flower without any agent. In such
flowers the reproductive organs are covered by their petals and, pollen grain cannot
transfer from one flower to another flower in them.
6. The fertilization in amphibians is called external fertilization, because in them the nuclei
of male and female gametes fuse in water, not inside their body.
Points to Remember
1. Reproduction is an outstanding characteristic of living beings, by which organisms
reproduce to continue their generation.
2. Asexual reproduction takes place without fertilization. It takes place by fission, budding,
sporulation and vegetative propagation.
3. Sexual reproduction takes place by fertilization.
4. Flower is a reproductive organ of plants. The calyx, corolla, androecium and gynoecium
are four whorls in flowers.
5. Androecium are male reproductive organs, which form pollen grains in their anther and
the pollen grains form male gametes in the pollen tube.
6. Gynoecium are female reproductive organs which form ovules. An ovules forms female
gametes in it.
7. The process of transformation of pollen grains from anther to stigma is called pollination.
8. Pollination is of two types. They are self-pollination and cross-pollination.
9. Any external agent is not required for self-pollination, in which pollen grains transfer
from anther to stigma of same flower.
10. An external agent is required for cross-pollination in which pollen grains transfer from
anther to stigma of different flower.
11. Pollen grain germinates and form pollen tube. Male gametes are formed in it.
12. Male and female gametes fuse to form zygote. The process is called fertilization.
It is of two types, they are internal and external.
13. Internal fertilization takes place inside the body.
14. External fertilization takes place outside the body.
15. The process of growing new plants by producing roots from the branches of a parent
plant is called layering.
16. The horticultural technique of attaching one variety of plant part on another variety of
plant by stacking one part on next is called grafting.
17. Tissue culture is an artificial method of growing plant saplings from cell, tissue or part of
organs with help of some culture medium.
Project Work
Visit a Horticulture center or a floriculture center or an agriculture farm near your
community. Observe the different methods of artificial vegetative propagation of
different plants adopted in that center. Prepare a report about artificial vegetative propagation
and show to your teacher.
280 Blooming Science Book 10
Exercise
1. What is reproduction? What are its advantages?
2. Mention the types of reproduction. List the types of asexual reproduction.
3. Define the following with two examples of each.
a. Binary fission b. Budding c. Fragmentation
d. Sporulation e. Simple layering f. Compound layering
g.Tip layering h. Mound layering i. Whip grafting
j. Tongue grafting k. Cleft grafting l. Tissue culture
4. What is vegetative propagation? List any four significance of vegetative propagation.
5. List any three methods of natural vegetative propagation with their short description.
6. List any three methods of artificial vegetative propagation with their short description.
7. What is layering? What is its importance
8. What is grafting? Why is grafting done?
9. What do you understand by tissue culture? Give the importance of tissue culture.
10. Define sexual reproduction. Write differences between asexual and sexual reproduction.
11. Name the floral parts, which help in sexual reproduction of plants. Also write their function.
12. Differentiate between:
a. Male and female gametes b. Spores and gametes
c. Pollination and fertilization d. Self and cross pollination
e. Internal and external fertilization f. Spores and zygote
g. Layering and grafting h. Whip grafting and tongue grafting
i. Simple layering and compound layering j. Tip layering and air layering
13. Write in short about sexual reproduction in plants with a diagram.
14. Write in short about sexual reproduction in animals.
15. List the significance of sexual reproduction.
16. Study the given diagram and answer the questions asked.
x
y
z
(a) (b) (c) (d)
a. Which one of them shows vegetative propagation? Which part of the plant is
participating in the reproduction?
b. What is the name of animal shown in b? What is the method of reproduction in it?
c. What type of reproduction is shown by ‘c’? Write in short about this method.
d. Which one of them is the simplest method of reproduction? Write in short about it.
e. Name the plants shown in the diagram (d) and label x, y and z in it.
Blooming Science Book 10 281
15. Give reasons
a. Reproduction is important for the living things.
b. Vegetative propagation is advantageous to farmers.
c. Gamete is simpler than zygote.
d. Fusion of gametes in angiosperms is called double fertilization.
e. An earthworm is called hermaphrodite animal.
16. How do zygotes form?
17. Answer the following questions on the basis of given illustration.
Male reproductive A Male
organs gamete D
Zygote C Embryo
Female reproductive B Female
organs gamete
(a) What is shown in the chart?
(b) What are the processes ‘A’ and ‘C’ called?
(c) What is ‘D’? How many types of ‘D’ are found?
(d) What are the animals called which can form male and female gametes in the same
individual?
18. Answer the following questions on the basis of the diagram. e
a. Label ‘a’, ‘b’ and ‘c’.
b. Write the function of ‘d’ and ‘e’
c. What is the process called when ‘e’ comes from one flower to a
another by any agent? b
d. Which parts of them form seed and fruit?
c
19. Choose the correct alternatives from the following options. d
i. In which organism does binary fission take place?
a. Amoeba b. Fern c. Hydra d. Tapeworm
ii. The fertilization which takes place inside female body is:
b. External b. Internal c. Asexual d. None of the above
iii. The plant that produces through leaf is:
a. Begonia b. Cauliflower c. Rose d. Potato
iv. Which type of reproduction is found in starfish?
a. Fission b. Budding
c. Sporulation d. Fragmentation and regeneration
v. The term stock and scion is related to:
a. Layering b. Tissue culture
c. Fertilization d. Grafting
282 Blooming Science Book 10
Chapter Heredity
19 Gregor Johann Mendel
(1822 - 1884 AD)
(Father of Genetics)
Lesson Objectives Estimated Periods: 5
On the completion of this unit, the students will be able to:
explain Mendel’s law with experiment and diagrams.
identify dominant and recessive characters.
describe the process of variation and mutation.
interpret the process of transformation of hereditary characters.
introduce gene as a factor of heredity.
define phenotype and genotype ratio in F1 and F2 generation.
Reproduction is a fundamental characteristics of living organisms, by which they reproduce
young ones of same type. The offspring of organisms resemble with their parents. Some
characteristics may differ. The characters which pass from parents to their offspring are called
hereditary characters. The new characters which are different from the parents of any individual
offspring are called acquired characters. The difference between characters of parents and their
offspring is called variation. It is observed that the characters like colour of hair, skin, appearance,
facial shape, nose, colour of eyes resemble somehow with their parents.
Genetics is the word derived from ancient Greek language which means origin. Genetics deals
with the molecular structure and function of genes and gene behavior in context of cell or
organism. Genes are universal to living organisms, genetics can be applied to the study of all
living systems, from viruses and bacteria, through plants and domestic animals, to humans (as
in medical genetics). Genetics is the branch of biology which deals with the study of genes and
hereditary characters. Although genetics plays a large role in the appearance and behavior of
organisms, it is the combination of genetics with what an organism experiences and determines
the ultimate outcome.
It is believed that the earth was originated about 4600 million years ago. The first life on the earth
was seen nearly 3200 million years ago. The first organism was unicellular and very simple. But
many well-developed and complex organisms are now in distinct existence on the earth. It is not
possible to find any two exactly alike organisms in the world. Such a condition that develops clear
and definite differences between organisms is called variation. Variation is the result determined
by the factors like environment and heredity. Environment can affect the outward expression of
an organism but not the genetic constitution of it. Genetic constitution is affected by heredity
and variation. Different forms of life have come on the earth through the process of organic
evolution. In this unit we will understand about heredity, variation and organic evolution through
the study of experiments done by the scientists of this field and the theories propounded by them.
Blooming Science Book 10 283
Heredity
You must have observed that in a family, the children are generally similar to their parents. The
children resemble the parents in skin colour, pattern of hair, colour of eyes, etc. It is because the
parental characters transfer into the offspring. The process through which the parental characters pass
from generation to generation is called heredity or inheritance. Due to heredity, duck’s chick cannot
be hatched from hen’s egg. Though similarity is found among the members of a family, they are not
exactly alike i.e., there are some dissimilarities called variation.
The branch of biology which deals with the mechanism of heredity and variation is called
Genetics. Gregor Johann Mendel is known as Father of Genetics. Because he was the first person
to study the mechanism of heredity and propounded the roles of heredity.
Gregor Johann Mendel was born on 2nd July 1822 A.D in a village of Germany. His father was a
poor gardener. After finishing his schooling, he was sent to Brunn of Austria by a Christian
missionary. He worked in a church of Brunn. Then he joined Vienna University for his higher
education and learnt the methods of crossing in plants. He got inspiration from this study and did
various kinds of crosses in sweet pea (Pisum sativum) in the garden of the church of Brunn. His
work was published in the Annual Proceedings of the Natural History Society of Brunn in 1866
AD. It was a Local Journal, so scientists of other countries could not know about the discovery
of Mendel. Mendel died in 1884 AD. In 1900 A.D. three biologists working independently in
three different countries got the same result, which was already published by Mendel some forty
years ago. The biologists were Correns of Germany, Tschermark of Austria and De Vries of
Holland. They supported the Mendel’s law strongly and then only it was accepted by the scientists.
Nowadays his work is known as Mendelism or Law of Inheritance or Law of Genetics and
he is known as the Father of Genetics.
Some main terms concerned with Mendelism are explained below:
Unit Character
Definite external character of an individual of a cross is called its unit character. Each organism
consists of its own type of unit character, for example a rose plant has its own type of leaf, flower,
stem etc. which act as unit character for it.
Monohybrid and Dihybrid cross
When only one unit character is involved in a cross, it is called monohybrid cross. For example,
a cross is made between tall and dwarf pea plants. Height of plant is involved in this cross. When
two unit characters are involved in a cross, it is called dihybrid cross. For example, a cross is made
between round yellow seed and a wrinkled green seed of pea plants. In shape and colour of seed,
two characters are involved in this cross. When more than two unit characters are involved in a
cross, it is called polyhybrid. For example, a cross is made between tall, red-flowered, smooth-
seeded and dwarf white-flowered, wrinkled-seeded of pea plant. Height of plant, colour of flower
and shape of seed are also involved in this cross.
Dominant and Recessive Characters
In a cross, those characters, which express themselves by covering the other characters, are
called dominant characters. Dominant characters are represented by the first letter of the word
of the dominant character in capital form. For example, ‘tall’ is dominant character which is
represented by the letter ‘T’.
284 Blooming Science Book 10
In a cross, those characters, which are present but cannot express themselves due to the presence
of dominant characters, are called recessive characters. Recessive character is represented by the
first letter of the word of contrasting dominant character in small form. For example, dwarf is
represented by ‘t’.
Allele or Allelomorphs
A pair of genes controlling a pair of contrasting characters is usually known as an allelic pair. The
members of an allelic pair are said to represent alleles of each other. For example, in the allelic
pair Tt, ‘T’ is allele of ‘t’ and vice versa. Allele is the short form of allelomorphs.
Homozygous organism (Pure organism) :
An organism having two identical alleles that determine a particular characteristic for example;
Tall plant having TT.
Hetrozygous organism( Hybrid organism) :
An organism having two different alleles. For example; Hybrid tall pea plant with Tt.
Hybrid and Pure organisms
Pure organisms are those which have same phenotype and genotype. Hybrid are those organisms
which have different phenotype and genotype. For example, pure tall father has the genotypic
composition as TT in which ‘T’ stands for tallness. Similarly, pure dwarf mother is shown by tt
in which ‘t’ stands for dwarfness. The offspring formed, by the couple will have the characters of
father and mother both but it will be appeared tall, which is hybrid tall.
Phenotype of P1 Pure tall father Pure dwarf mother
Genotype of P1 TT tt
Gametes of P1 T t
Fertilization
F1 generation Tt (Hybrid tall)
Phenotype and Genotype
The morphological appearance of an organism is called phenotype of that organism and genetic
make-up of an organism is called genotype of that organism. For example, a pea plant having
traits TT is both phenotypically and genotypically tall but another tall pea plant having traits Tt
is phenotypically tall but genotypically tall and dwarf both.
Differences between Phenotype and Genotype
Phenotype Genotype
1. Phenotype is expression of the characters 1. Genotype is the gene composition
of an individual. It is the external (genetic make up) of an individual, which
manifestation of a genotype. determines the individual’s form, size,
colour, behaviour, etc
Blooming Science Book 10 285
2. Individuals having identical phenotype 2. Individuals having identical genotype
may or may not have the same genotype. usually have the same phenotype provided
they are present in the same environment.
3. Phenotype of an individual varies with 3. Genotype of an individual always remains
environment and with times eg. child, constant. It is not affected by environment.
adult, old age, etc.
Mendel’s Experiment
Mendel used seven pairs of contrasting characters for his experiment. To understand Mendel’s
experiment, tall and dwarf traits are taken as one example.
The Characters (Traits) of Pea Plant Selected by Mendel for his Experiment
Mendel selected the seven pairs of contrasting characters of pea plant (Pisum Sativum) for his
experiment. The characters are given below:
S.N. Characters Dominant Characters Recessive Characters
1. Position of flower Axial (A) Terminal (a)
2. Height of plant Tall (T) Dwarf (t)
3. Shape of seed Round (R) Wrinkled (r)
4. Colour of seed Yellow (Y) Green (y)
5. Colour of seed coat Brown (B) White (b)
6. Shape of pod Inflated (I) Constricted (i)
7. Colour of pod Green (G) Yellow (g)
Why did Mendel select Pea Plant for his experiments?
Mendel selected pea plant for his experiment because of the following reasons:
1. A pea plant is naturally self-pollinated and artificially cross-pollination also can be made in it.
2. It has a number of distinguishable contrasting characters like tall and dwarf pea plants, red
and white flowers, round and wrinkled seeds, etc.
3. The hybrid plants obtained as a result of cross-pollination in pea plants are also fertile. In
many cases it is found that such offsprings are sterile.
4. A larger number of progeny (offspring) can be obtained from a single plant.
5. The life cycle is of short duration, so result of experiment can be obtained in short period.
6. The plants are convenient to handle. So they can be grown anywhere.
Some Words Concerning Mendelism
Note: The knowledge of following terms is also helpful in order to understanding Mendelism:
P = Parents of any cross P1 = Immediate parent
P2 = Grand parents P3 = Great grand parents
F = Offspring F1 = First filial generation
F2 = Second filial generation F3 = Third filial generation
(The word filial refers to offspring)
286 Blooming Science Book 10
In a monohybrid cross, Mendel selected pure tall and dwarf pea plants. He made artificial
crossing between them by the help of a brush. In F1 (First filial) generation all the pea plants were
found tall. When plants of F1 generation were allowed to self-pollinate, in the F2 generation 75%
of the pea plants were found tall and 25% were found short (3:1). These 75% tall plants were
further examined in F3 generation, it was found that 25% of the pea plants were pure tall and
50% were hybrid tall. Therefore, the net result of this monohybrid cross was 25% pure tall, 50%
hybrid tall and 25% pure dwarf (1:2:1).
GENETICS
Parents Pure tall Pure dwarf
Crossing
F1 generation ...... Hybrid tall
Selfing
F2 generation .... Pure tall Hybrid tall Hybrid tall Pure short
F3 generation .... Pure Pure Hybrid Pure Pure Hybrid Pure Pure
tall tall tall dwarf tall tall dwarf dwarf
When Mendel studied F3 generation, he noticed the following points:
1. Pure tall pea plants form tall plants only.
2. Hybrid tall pea plants form both tall and short plants in the phenotype ratio of 3:1 and the
genotype ratio of pure tall, hybrid tall and pure dwarf is 1:2:1.
3. Pure dwarf pea plants form dwarf plants only.
Mendel tested the result of his experiment by taking the seven pairs of contrasting characters of
pea plants and he found the same result in each case.
Mendel’s Laws or Mendelism
On the basis of the result obtained from the Mendel’s experiment, he proposed the following
three laws:
1. Law of dominance
2. Law of segregation or law of purity of gametes
3. Law of independent assortment (It is not included in our syllabus.)
1. Law of Dominance (First Law of Mendel):
Law of dominance states that, "when a cross is made between a pair of pure contrasting characters,
only one of them is able to express itself phenotypically while the other remains hidden in the first
generation". The character which is expressed is dominant and the other one is recessive.
For example, when a cross is made in between pure tall (TT) and pure dwarf (tt) pea plants, in F1
generation all the pea plants are seen tall (Tt). In these tall pea plants, traits T and t both are found
but only tall (T) can express itself as it is dominant and the dwarf (t) remains hidden.
Blooming Science Book 10 287
Phenotype of parents Pure tall Crossing Pure dwarf
Genotype of parents TT tt
Gamete formation TT tt
Fertilization
F1 generation Tt Tt Tt Tt
[100% Hybrid tall]
2. Law of Segregation or Law of Purity of Gametes (Second Law of Mendel):
Law of segregation states that, "the two characters of a pair of factors separate during the
formation of gametes". They remain together for a long time without blending with other but
segregate or separate out into different gametes at the time of gamete formation. So this law is
also called as law of purity of gametes.
For example, in Mendel’s experiment when selfing occurred in two hybrid pea plants obtained
in F1 generation, the tall and dwarf pea plants were found in the ratio of 3:1 in F2 generation, i.e.,
phenotypic ratio was 3:1 (three tall and one dwarf). The genotypic ratio in this generation was
1:2:1 (one pure tall, two hybrid tall and one pure dwarf). The main reason of this result is that tall
and dwarf characters of hybrid pea plants get separated during formation of gametes.
Phenotype of parents Hybrid tall Selfing Hybrid tall
Genotype of parents Tt Tt
Gamete formation T t Tt
Fertilization
F2 generation TT Tt Tt tt
(Pure tall) (Hybrid tall) (Pure dwarf)
Some monohybrid crosses done in animals by different scientists in different times are given
below with result.
a Monohybrid cross in drosophila LL ll
Female (long winged) Male (short winged)
In America, Thomas Hunt Morgan tested
Mendel’s law in fruit-fly called drosophila. Ll Ll
He selected long-winged and short-winged
drosophillas for his experiment. When pure long- Female (long winged) Male (long winged)
winged and pure short-winged drosophillas were
crossed, in F1 generation all the drosophillas were LL Ll Ll ll
found long-winged. Again the drosophillas of F1
generation when crossed in F2 generation, 75% of
the drosophillas were found long-winged and the
rest 25% of them were found short-winged. Long winged Short winged
288 Blooming Science Book 10
b. Monohybrid cross in guinea pigs
When pure black guinea pig is crossed with pure white guinea pig, in F1 generation all
the guinea pigs are found black as it is dominant character. When the guinea pigs of F1
generation are crossed together, in F2 generation 75% guinea pigs are found black and
25% guinea pigs are found white. It also follows the Mendel’s law of dominance and law
of segregation or law of purity of gametes.
bb BB
sperm b
B Ovum
X
F1 generation All hybrid black
Sperm Bb b Bb Ova
or or
B Bb
X
B B b Black and white
BB Bb
F2 generation 3:1
b Bb bb
Some genetic characteristics in human beings
Like other organisms, human beings are also formed of their own different types of characters.
Each character of them acts as unit character. Some of the characters are dominant and some are
recessive. Some human hereditary characters are as mentioned below.
1. Curly hair (dominant), straight hair (recessive)
2. Isolated ear lobule (dominant), joint ear lobule (recessive)
3. Presence of dimple mark on cheeks (dominant), absence of dimple mark (recessive)
4. Straight thumb (dominant), back turned thumb (recessive)
5. Folding/Rolling of tongue (dominant), not rolling not folding of tongue (recessive).
6. Fore bending of tongue (dominant), not fore bending of tongue (recessive).
7. Desne body hair (dominant), less body hair (recessive)
Blooming Science Book 10 289
In human, some hereditary characters are found in male or female only. There are some diseases
which are found only either in male or female. Such diseases are called Sex-linked disease. For
example haemophelia, colour blindness etc. are found in male only. These diseases are not found
even though they are carrier of the disease i.e. they transfer the diseases from one generation to
other. Breast-cancer is found usually in females but very rare in males.
Activity-1
Observation of dominant and recessive characters in Humans.
Methods
Observe the various dominant and recessive characters found in your classmates. Study them
well and compare the characters as mentioned above. Make a table and draw your conclusion.
Variation
Every organism shows difference to the other organism of the same species as well as of other
species. These changes occur due to the number of reasons like environment and the genetic
make-up of organisms. Since not two organisms in the universe are exactly same. They show
variation among themselves, even the identical twins of a parent differ in some or more extent.
Variation may be defined as morphological or a physiological change in organisms due to either
genetic or environmental reason. Variation may be somatogenic or blastogenic.
1. Somatogenic variations (Environmental Variations) are those acquired by an organism due
to the influence of environment. They are not inherited from generation to generation. Some
examples of such variation are development of muscles in an athelete, loss of tail or leg of
an individual in an accident etc.
2. Blastogenic variations (Hereditary Variations) are those arise due to changes in the germ
cells. These are inheritable; some examples of these variations are colour of skin, colour of
hair etc.
The type of variation mentioned above are continuous variations. Sometimes sudden variations
are seen in an individual, which are called discontinuous variations. For example, disability of
babies by birth, six-fingered limb in human, cut a lip by birth, Discontinuous variation is also
termed as mutation. Mutation theory was suggested by Hugo De Vries of Holland in 1901AD.
Mutation
A sudden heritable change in the genetic material of an organism is called mutation. The various
factors like UV, X-rays, etc. are responsible for mutation. It's useful to think of mutation as a
process that creates genetic variation. We often refer to a mutation as a genetic variation itself.
This approach can be useful when it comes to a gene associated with a disease The disease
allele carries a mutation, a DNA change that compromises the protein's function. However, this
approach gives mutation a bad name.
290 Blooming Science Book 10
Differences between Mutation and Variation
Mutation Variation
1. A sudden heritable change in the genetic 1. The structural difference that provides
material of an organism is called mutation. individuality to each member of a species
is called variation.
2. The various factors like UV, X-rays, etc. 2. The structural and functional differences
are responsible for mutation. of genes, environmental factors are
responsible in variation.
Let's Learn
1. Mendel choose pea plants for his experiment but not other because it is a seasonal plant with
different pair of contrasting characters and life cycle is completed within three months.
2. Mendel would not be succeeded in his experiment if he used frog instead of pea plants.
It is because a frog reproduces by crossing only. Thus, purity of characters cannot be
checked in them. Similarly they need special climatic conditions to survive, thus it was
difficult to have.
3. Blue eyed offspring may be formed from brown-eyed parents. It is because, if the brown
eyed parents are not pure i.e., they are hybrid, they have blue-eyed character as recessive.
The recessive character is expressed in next generation and the blue-eyed offspring is
formed. It is clear by the following illustration.
Hybrid brown eyed parents
Bb Crossing Bb
Gamete formation B B bb
New generation BB Bb Bb bb
Pure Brown Hybrid Pure
eyed Brown eyed Blue eyed
Points to Remember
1. Transformation of characters from parents into offspring is called heredity and the
dissimilarity between the individuals of same species is called variation.
2. The branch of Biology concerned with the study of the mechanism of heredity and
variation is called Genetics. Gregor Johann Mendel is known as the Father of Genetics.
3. DNA and RNA are two types of nucleic acids responsible for heredity.
4. In a cross, the character which can express itself is called dominant character and that
which is covered by dominant character is called recessive character.
Blooming Science Book 10 291
5. External morphological appearance of an organism is phenotype and genetic make
up of an organism is called genotype of that organism.
6. Hybrid is that individual which has its phenotype and genotype different.
7. Mendel did his experiment on pea plant (Pisum sativum) and found 100% dominant
in F1 generation while in F2 generation 75% pea plants were dominant.
8. Major Mendel’s laws are:
a. Law of dominance
b. Law of segregation
c. Law of independent assortment
9. The gradual change from one generation to another generation is called continuous
variation.
10. The sudden and unexpected change from one generation to another generation is called
mutataion.
Project Work
To varify Mendel's law
Observe some corn cob after removing the husks. Select a cob having different
colours in seed, generally the seeds are found in two colours like yellow and white,
yellow and pink etc. Separate the seeds from cob, divide into two groups according
to colour and count their numbers
Corn cub with different colours.
In what ratio can you find them? Observe carefully by counting and draw
your conclusion by discussing with your friends.
Exercise
1. What are heredity and Genetics?
2. Who is Gregor Johann Mendel? Why is he called the Father of Genetics?
3. Why did Mendel select pea plant for his experiment? What characters of pea plants were
selected by Mendel for his experiment?
4. Would Mendel have succeeded if he had used toad instead of pea plants for his experiment?
Give reasons.
5. What are dominant and recessive characters? Clarify your answer by giving examples.
292 Blooming Science Book 10
6. Write short notes on:
i. phenotype ii. genotype iii. hybrid
vi. dihybrid cross
iv. allele v. monohybrid cross ix. m utation
vii. polyhybrid cross viii. unit character
7. What percentage of dominant character of pea plant was found in F1 and F2 generations
respectively in Mendel’s experiment?
8. If blue-eyed offspring is formed from black-eyed parents, what type of character is the
blue eye, dominant or recessive? Write with reason.
9. Explain the law of dominance in short with chart.
10. What is the law of segregation? Write with illustration. Tt
11. Study the table alongside and answer the questions.
a. Name the filial generation shown. T TT tT
b. Which law is used to explain it? t tT tt
c. Write the percentage of tall character.
d. Which factors show hybrid tall and pure short characters respectively?
12. Show in genetic diagram of the result of crossing between pure long-winged and pure short-
winged drosophila upto second filial generation. Here long-winged is dominant character.
Also write phenotype and genotype ratio.
13. When black and brown dogs are crossed, all the dogs of F1 generation are found black.
Give reason of not forming brown dogs.
14. In what ratio will red-flowered and white-flowered pea plants be seen when red (RR) and
white (rr) flowered pea plants are crossed together? Show by chart (up to F2 generation).
Also write phenotype and genotype.
15. What is sex linked disease? Write with examples.
16. Write some important heridity characters seen in human being.
17. What is gene? Where is it located? What is its main function?
18. What is variation? Why is it necessary?
19. What is discontinuous variation? Write with examples.
20. Write difference between:
(i) Genotype and phenotype
(ii) Dominant and recessive characters
(iii) Hereditary and environmental variation.
(iv) Variation and mutation
Blooming Science Book 10 293
21. Choose the correct alternatives from the following options.
i. Who is called father of genetics?
a. Mendel b. D.H. Morgan
c. Madam curie d. Charles Darwin
ii. In which cross only one unit character is involved?
a. Polyhybrid b. Dihybrid
c.Monohybrid d. None of them
iii. The genotype for pure tall character is:
a. Tt b. tt
c. TT d. PP
iv. What happens when there is sudden change in chromosome?
a. Fertilization b. Pollination
c. Mutation d. Both ‘a’ and ‘b’
v. The major causes of mutation are:
a. Variation b. Evolution
c. UV rays and unwanted chemicals d. None of the above
294 Blooming Science Book 10
Chapter Environmental
Pollution and
20 Management
Learning Outcomes Estimated Periods: 6+3
On the completion of this unit, the students will be able to:
write about pollution and its types.
describe air, water and soil pollution with their causes and effects.
tell the preventive measure pollution in daily life..
explain water and forest management.
Human population is entirely dependent on various natural resources which are over used
due to population growth. Excessive pressure in natural resources cause environmental
degradation. So, the problem of floods, landslide and soil erosion occurs. Deforestation and
depletion of habitat of wild birds and animals are taking place. Over use of natural resources
have created imbalance in the environment. It disturbs the life of man, birds, animals and overall
ecosystem.
The reduction in quality and quantity of any component of the environment generally called
environmental degradation.
Environment degradation can be defined as any alternation in the composition or state or the
environmental which directly or indirectly causes harm to us.
Pollution
Physical, chemical and biological change in the natural qualities of air, water and soil is called
pollution. It affects the health of the common people and cultural heritage also. The agents of
pollution are called pollutants. It is found in the form of solid, liquid and gas. Heat and noise are
also a kind of pollutants. It harms human beings, animals, birds, forests, historical monuments
and non-living components.
The air, water and land are getting polluted due to population growth. The problem of
environmental pollution is increasing day by day in Nepal. There are different types of pollution.
Some of the major types of pollution found in Nepal are as follows:
i) Air pollution
ii) Water pollution
iii) Land pollution
iv) Noise pollution
Blooming Science Book 10 295
1. Air Pollution
Air mixed with dust, smoke and harmful bacteria
is called impure air. When the stench of garbage
mixes with air, it is called air pollution. There are
gases, chemicals, dust particles and other harmful
gases in polluted air. It causes harm to humans,
animals, birds, vegetation and many other cultural
heritage.
Air pollution can be defined as an undesirable change in our air, which directly or indirectly
causes harm to us.
Activity-1
Study the factors that produced air pollution in your surrounding area. Ask some
local people, what factors are there to produce air pollution. Write in short about
causes, effects and remedial measures adopted to control such pollution in your
area.
Effects of Air Pollutions
i) The polluted air is harmful to health of living beings.
ii) It also affects plants, trees, birds and animals
iii) It affects the eyes and breathing of people. Due to this, fatal diseases like cancer may
attack.
iv) It harms the cultural heritage also.
v) It is difficult for the entire living beings to survive if air pollution is increased in
environment.
vi) Polluted air causes various airborne diseases to the human beings.
vii) Mixing of industries gases in the air cause acid rain
2. Water Pollution
The source and capacity of water does not increase
if it is not well managed. The garbage, drains and
sewage coming out of industries and factories
pollute the water sources. It is known as water
pollution. Harmful germs and bacteria cause water
pollution.
Water pollution can be defined as an undesirable
change in water, which directly or indirectly cause
harm to us.
It causes the scarcity of pure and clean drinking water. The water of Bagmati and
Bishnumati in Kathmandu has been excessively polluted. Similarly, the historical pond
of Patan, Bhaktapur and Janakpur are also facing the problems of water pollution. The
polluted river and tank water is of no use for any purpose.
296 Blooming Science Book 10
Activity-2
Visit a near by water souce to your community or school. Study the factors that produces water
pollution of your area. Ask some local people, what factors are making water polluted.
Write down a report about causes and effects of water pollution and suggest some points to the
local people to prevent from water pollution.
Effects of water pollution:
i) Groundwater contamination from pesticides causes reproductive damage within wildlife
in ecosystems.
ii) Sewage, fertilizer, and agricultural run-off contain organic materials that when discharged
into water sources, increase the growth of algae, which causes the depletion of oxygen.
iii) Swimming in and drinking contaminated water causes skin rashes and health problems
like cancer, reproductive problems, typhoid fever and stomach sickness in humans.
iv) Industrial chemicals and agricultural pesticides that end up in aquatic environments can
accumulate in fish that are later eaten by humans cause many diseases.
v) Ecosystems are destroyed by the rising temperature in the water, as coral reefs are affected
by the bleaching effect due to warmer temperatures.
vi) Human-produced litter of items such as plastic bags and rings can get aquatic animals
caught and killed from suffocation.
vii) Water pollution causes flooding due to the accumulation of solid waste and soil erosion in
streams and rivers.
viii) Oil spills in the water causes animal to die when they ingest it or encounter it. Oil does
not dissolve in water so it causes suffocation in fish and birds.
3. Land/ Soil Pollution
Generally, the deterioration in quality of land is
known as land pollution. It degrades the fertile
upper crust of the earth.
Land pollution can be defined as an undesirable
change in land, which directly or indirectly
causes harm to us.
The land pollution degrades quality of soil. The
germs that protect the soil also die due to the
pollution in land. It causes decline in soil fertility.
The land is a valuable gift of nature. Its pollution
causes imbalance in the environment.
Blooming Science Book 10 297
Activity-3
Visit a near by place of your community/school where the household wastes are dumped.
Study the factors that cause soil and other forms pollution of that particular area.
Write a report with causes, effects and preventive measures of pollution caused by such
wastages in particular community.
Effects of soil pollution
i) The bad smell spreads from the polluted land destroys the surrounding places.
ii) It destroys the fertility of soil.
iii) It spoils the beauty of the natural environment.
iv) Soil pollution also causes pollution to water resources.
v) Earthworms and micro-organisms die due to soil pollution. They improve quality of soil.
Preventive measures of pollutions (air, water and soil)
i) Wastages ejected from homes and factories must be managed by '3R' Principle.(Reduce,
Reuse & Recycle).
ii) The use of compost manure must be encouraged.
iii) Proper drainage system must be built for collection of wastage.
iv) The use chemical fertilizers of insecticides, pesticides, etc. must be reduced.
v) Afforestation must be done.
vi) The industrial area must be constructed far from city and chimney of the industries must
be made tall.
vii) Alternative source of energy like solar, wind, etc. should be used.
viii) Over population should be controlled.
ix) Various awareness programs should be conducted.
x) Nuclear tests in water sources must be banned.
Water resource, Wetland and Watershed
Water is a very essential substance found on the earth. Living beings cannot survive without
it. It is used for drinking, bathing, washing, cooking, irrigation etc. It is also used to produce
hydroelectricity and to run industries. Our country is very rich in water resources. We have our
Himalayan regions covered with snow. The melted snow is also one of the main source of water.
The region which is always wet with water and contains water up to the depth of 6 meter is very
good for the aquatic bird's habitat. They are called wetlands. Ponds, lakes and swamp lands are
its examples. The catchment or watersheds are the areas from where the water runs in different
directions to different rivers. It forms a river system. Some main watersheds of our country are
Bagmati watershed, Fewatal watershed, Arun watershed, etc.
Importance of water resources, wetland and watersheds:
1. By the conservation and proper management of watersheds, the living standard of local
people can be increased.
298 Blooming Science Book 10
2. By the proper management of watersheds and wetland biodiversity can be conserved.
3. By the proper management of water agriculture conditions can be improved.
4. They support to conserve forest too.
5. They check natural disaster like flood, landslide, soil erosion etc. if they are managed
properly.
6. They provide continuous source of water.
7. They improve the economic condition of a nation by promoting tourism.
The ways of conservation of wetlands and watersheds
Wetlands and water sheds are conserved by the following ways:
1. Afforestation is the best way for it. It is because forest plays an important role in water
cycle and holds water at the surface.
2. Construction of check dams also conserves watersheds. It reduces the speed of running
water by which soil erosion minimizes.
3. Public awareness is also an effective method for conservation of watersheds and wetlands.
The local people should be educated through interaction programms, drama and
documentary show. Their support will play a vital role to conserve such regions.
4. By minimizing the pollution of water caused by industries, cities, use of insecticides and
chemical fertilizers. Pollution plays a negative role to balance the environment of water
shed. Thus, such activities should be minimized and controlled.
Water management
One third of the earth is covered with water; we use water for drinking, sanitation, generating
electric power, irrigation and transportation. But due to the excessive urbanization fresh water
resources are being exploited.
The process of organizing, developing, distributing and conserving water resources is called
water management. It means successfully managing the available resources of water initializing
its effect towards our environment. It includes prohibiting pollution of surface water sources
like ponds and rivers, over exploitation of underground water, poorly constructed water supply
system etc.
Ways to manage water resources
1. Conducting programme of afforestation to stop drought of streams and rivers.
2. Reducing the trend of treating water chemically.
3. Prohibiting industries to throw chemical wastes in water resources and stopping mixing of
sewage in water.
4. Preserving and utilizing rain water for various purposes instead of over exploiting of
surface water.
5. Properly organizing and running water supply system.
Conservation and management of forest
Forest is one of the most important natural resource. It provides us timber, medicinal herbs,
recreation, fodder, water, etc. It also helps to maintain the water cycle and prevents from various
Blooming Science Book 10 299
natural disasters like flood, landslides, soil erosion etc. It even develops our economic status as
it is a part of tourism industry. So, it is very important to conserve forest.
The process of making plans and policies for the conservation, protection and proper regulation
of forest is called forest management.
Ways to manage forest
1. Proper management of water shed.
2. Protection and promotion of wildlife.
3. Emphasizing community forests and conservation areas.
4. Utilizing forest resources in a sustainable way.
5. Awareness of people against deforestation.
6. Giving more priority to planting and re-planting of trees.
Points to Remember
1. The reduction in quality and quantity of any component of the environment generally
called environment degradation.
2. Physical, chemical and biological change in the natural qualities of air, water and soil is
called pollution.
3. Air pollution can be defined as an undesirable change in our air, which directly or
indirectly causes harm to us. Air pollution can be defined as an undesirable change in our
air, which directly or indirectly causes harm to us.
4. Water pollution can be defined as an undesirable change in water, which directly or
indirectly cause harm to us.
4. Land pollution can be defined as an undesirable change in land, which directly or
indirectly causes harm to us.
6. The region which is always wet with water and contains water up to the depth of 6
meter is very good for the aquatic bird's habitat. They are called wetlands.
7. The process of organizing, developing, distributing and conserving water resources
is called water management.
8. The process of making plans and policies for the conservation, protection and proper
regulation of forest is called forest management.
Project Work
Organize a talk programme to increase the public awareness about various types of
environmental pollution; their causes, effects and preventive measures in your community
followed by a cleaning campaign of the community with local people.
300 Blooming Science Book 10
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