NCERT Textbook: Reproduction in Animals | Science & Technology for UPSC CSE PDF Download

 Page 1


REPRODUCTION IN ANIMALS
REPRODUCTION IN ANIMALS
D
o you recall the processes of
digestion, circulation and
respiration which you have
studied in your previous classes? These
processes are essential for the survival
of every individual. You have also learnt
about the process of reproduction in
plants. Reproduction is essential for the
continuation of a species. Imagine what
would have happened if organisms had
not reproduced. You will realise that
reproduction is very important as it
ensures the continuation of similar
kinds of individuals, generation after
generation.
You have already learnt in your
previous class about reproduction in
plants. In this chapter, we shall learn
how reproduction takes place in
animals.
6.1 Modes of Reproduction
Have you seen the young ones
of different animals? Try to name some
of the young ones by completing
Table 6.1 shown in examples at S. No.
1 and 5.
You must have seen the young
ones of various animals being born.
Can you tell how chicks and
caterpillars are born? How are kittens
and puppies born? Do you think that
these young ones looked the same
before they were born as they do now?
Let us find out.
Just as in plants, there are two modes
by which animals reproduce. These are:
(i) Sexual reproduction, and
(ii) Asexual reproduction.
6.2 Sexual Reproduction
Try to recall reproduction in plants
which you studied in Class VII. You will
remember that plants that reproduce
sexually have male and female
reproductive parts. Can you name these
parts? In animals also, males and
females have different reproductive parts
or organs. Like plants, the reproductive
parts in animals also produce gametes
that fuse to form a zygote. It is the zygote
which develops into a new individual.
This type of reproduction beginning
from the fusion of male and female
gametes is called sexual reproduction.
Let us find out the reproductive parts
Table 6.1
S. No. Animal Young one
1. Human Baby
2. Cat
3. Dog
4. Butterfly
5. Hen Chick
6. Cow
7. Frog
2024-25
Page 2


REPRODUCTION IN ANIMALS
REPRODUCTION IN ANIMALS
D
o you recall the processes of
digestion, circulation and
respiration which you have
studied in your previous classes? These
processes are essential for the survival
of every individual. You have also learnt
about the process of reproduction in
plants. Reproduction is essential for the
continuation of a species. Imagine what
would have happened if organisms had
not reproduced. You will realise that
reproduction is very important as it
ensures the continuation of similar
kinds of individuals, generation after
generation.
You have already learnt in your
previous class about reproduction in
plants. In this chapter, we shall learn
how reproduction takes place in
animals.
6.1 Modes of Reproduction
Have you seen the young ones
of different animals? Try to name some
of the young ones by completing
Table 6.1 shown in examples at S. No.
1 and 5.
You must have seen the young
ones of various animals being born.
Can you tell how chicks and
caterpillars are born? How are kittens
and puppies born? Do you think that
these young ones looked the same
before they were born as they do now?
Let us find out.
Just as in plants, there are two modes
by which animals reproduce. These are:
(i) Sexual reproduction, and
(ii) Asexual reproduction.
6.2 Sexual Reproduction
Try to recall reproduction in plants
which you studied in Class VII. You will
remember that plants that reproduce
sexually have male and female
reproductive parts. Can you name these
parts? In animals also, males and
females have different reproductive parts
or organs. Like plants, the reproductive
parts in animals also produce gametes
that fuse to form a zygote. It is the zygote
which develops into a new individual.
This type of reproduction beginning
from the fusion of male and female
gametes is called sexual reproduction.
Let us find out the reproductive parts
Table 6.1
S. No. Animal Young one
1. Human Baby
2. Cat
3. Dog
4. Butterfly
5. Hen Chick
6. Cow
7. Frog
2024-25
in humans and study the process of
reproduction in them.
Male Reproductive Organs
The male reproductive organs include a
pair of testes (singular, testis), two sperm
ducts and a penis (Fig. 6.1). The testes
produce the male gametes called
sperms. Millions of sperms are produced
by the testes. Look at Fig. 6.2 which
shows the picture of a sperm. Though
sperms are very small in size, each has
a head, a middle piece and a tail. Does
it appear to be a single cell? Indeed, each
sperm is a single cell with all the usual
cell components.
Fig. 6.1: Male reproductive
organs in humans
What purpose does the
tail in a sperm serve?
Fig. 6.3 : Female reproductive organs in
humans
Female Reproductive Organs
The female reproductive organs are a pair
of ovaries, oviducts (fallopian tubes) and
the uterus (Fig. 6.3). The ovary produces
Oviduct
Ovary
Uterus
Head
Middle piece
Tail
Fig. 6.2 : Human sperm
REPRODUCTION IN ANIMALS 67
Sperm
duct
Testis
Penis
2024-25
Page 3


REPRODUCTION IN ANIMALS
REPRODUCTION IN ANIMALS
D
o you recall the processes of
digestion, circulation and
respiration which you have
studied in your previous classes? These
processes are essential for the survival
of every individual. You have also learnt
about the process of reproduction in
plants. Reproduction is essential for the
continuation of a species. Imagine what
would have happened if organisms had
not reproduced. You will realise that
reproduction is very important as it
ensures the continuation of similar
kinds of individuals, generation after
generation.
You have already learnt in your
previous class about reproduction in
plants. In this chapter, we shall learn
how reproduction takes place in
animals.
6.1 Modes of Reproduction
Have you seen the young ones
of different animals? Try to name some
of the young ones by completing
Table 6.1 shown in examples at S. No.
1 and 5.
You must have seen the young
ones of various animals being born.
Can you tell how chicks and
caterpillars are born? How are kittens
and puppies born? Do you think that
these young ones looked the same
before they were born as they do now?
Let us find out.
Just as in plants, there are two modes
by which animals reproduce. These are:
(i) Sexual reproduction, and
(ii) Asexual reproduction.
6.2 Sexual Reproduction
Try to recall reproduction in plants
which you studied in Class VII. You will
remember that plants that reproduce
sexually have male and female
reproductive parts. Can you name these
parts? In animals also, males and
females have different reproductive parts
or organs. Like plants, the reproductive
parts in animals also produce gametes
that fuse to form a zygote. It is the zygote
which develops into a new individual.
This type of reproduction beginning
from the fusion of male and female
gametes is called sexual reproduction.
Let us find out the reproductive parts
Table 6.1
S. No. Animal Young one
1. Human Baby
2. Cat
3. Dog
4. Butterfly
5. Hen Chick
6. Cow
7. Frog
2024-25
in humans and study the process of
reproduction in them.
Male Reproductive Organs
The male reproductive organs include a
pair of testes (singular, testis), two sperm
ducts and a penis (Fig. 6.1). The testes
produce the male gametes called
sperms. Millions of sperms are produced
by the testes. Look at Fig. 6.2 which
shows the picture of a sperm. Though
sperms are very small in size, each has
a head, a middle piece and a tail. Does
it appear to be a single cell? Indeed, each
sperm is a single cell with all the usual
cell components.
Fig. 6.1: Male reproductive
organs in humans
What purpose does the
tail in a sperm serve?
Fig. 6.3 : Female reproductive organs in
humans
Female Reproductive Organs
The female reproductive organs are a pair
of ovaries, oviducts (fallopian tubes) and
the uterus (Fig. 6.3). The ovary produces
Oviduct
Ovary
Uterus
Head
Middle piece
Tail
Fig. 6.2 : Human sperm
REPRODUCTION IN ANIMALS 67
Sperm
duct
Testis
Penis
2024-25
SCIENCE 68
Boojho recalls that the size
of eggs in animals varies.
The egg may be very small
as in humans, much larger
as in hens. Ostrich egg is
the largest!
Fertilisation
The first step in the process of
reproduction is the fusion of a sperm
and an ovum. When sperms come in
contact with an egg, one of the sperms
may fuse with the egg. Such fusion of
the egg and the sperm is called
fertilisation (Fig. 6.5). During
fertilisation, the nuclei of the sperm and
the egg fuse to form a single nucleus.
This results in the formation of a
fertilised egg or zygote (Fig. 6.6). Did
Fig. 6.5 : Fertilisation
Fig. 6.4 : Human Ovum
Nucleus
Sperms
Ovum
Fusing
nuclei
The process of fertilisation is the
meeting of an egg cell from the mother
and a sperm cell from the father. So,
the new individual inherits some
characteristics  from the mother and
some from the father. Look at your
brother or sister. See if you can recognise
some characters in them similar to those
of your mother or your father.
Fertilisation which takes place inside
the female body is called internal
fertilisation. Internal fertilisation
occurs in many animals including
humans, cows, dogs and hens.
Fig. 6.6 : Zygote
female gametes called ova (eggs)
(Fig. 6.4). In human beings, a single
matured egg is released into the oviduct
by one of the ovaries every month.
Uterus is the part where development of
the baby takes place. Like the sperm,
an egg is also a single cell.
you know that the zygote is the
beginning of a new individual?
2024-25
Page 4


REPRODUCTION IN ANIMALS
REPRODUCTION IN ANIMALS
D
o you recall the processes of
digestion, circulation and
respiration which you have
studied in your previous classes? These
processes are essential for the survival
of every individual. You have also learnt
about the process of reproduction in
plants. Reproduction is essential for the
continuation of a species. Imagine what
would have happened if organisms had
not reproduced. You will realise that
reproduction is very important as it
ensures the continuation of similar
kinds of individuals, generation after
generation.
You have already learnt in your
previous class about reproduction in
plants. In this chapter, we shall learn
how reproduction takes place in
animals.
6.1 Modes of Reproduction
Have you seen the young ones
of different animals? Try to name some
of the young ones by completing
Table 6.1 shown in examples at S. No.
1 and 5.
You must have seen the young
ones of various animals being born.
Can you tell how chicks and
caterpillars are born? How are kittens
and puppies born? Do you think that
these young ones looked the same
before they were born as they do now?
Let us find out.
Just as in plants, there are two modes
by which animals reproduce. These are:
(i) Sexual reproduction, and
(ii) Asexual reproduction.
6.2 Sexual Reproduction
Try to recall reproduction in plants
which you studied in Class VII. You will
remember that plants that reproduce
sexually have male and female
reproductive parts. Can you name these
parts? In animals also, males and
females have different reproductive parts
or organs. Like plants, the reproductive
parts in animals also produce gametes
that fuse to form a zygote. It is the zygote
which develops into a new individual.
This type of reproduction beginning
from the fusion of male and female
gametes is called sexual reproduction.
Let us find out the reproductive parts
Table 6.1
S. No. Animal Young one
1. Human Baby
2. Cat
3. Dog
4. Butterfly
5. Hen Chick
6. Cow
7. Frog
2024-25
in humans and study the process of
reproduction in them.
Male Reproductive Organs
The male reproductive organs include a
pair of testes (singular, testis), two sperm
ducts and a penis (Fig. 6.1). The testes
produce the male gametes called
sperms. Millions of sperms are produced
by the testes. Look at Fig. 6.2 which
shows the picture of a sperm. Though
sperms are very small in size, each has
a head, a middle piece and a tail. Does
it appear to be a single cell? Indeed, each
sperm is a single cell with all the usual
cell components.
Fig. 6.1: Male reproductive
organs in humans
What purpose does the
tail in a sperm serve?
Fig. 6.3 : Female reproductive organs in
humans
Female Reproductive Organs
The female reproductive organs are a pair
of ovaries, oviducts (fallopian tubes) and
the uterus (Fig. 6.3). The ovary produces
Oviduct
Ovary
Uterus
Head
Middle piece
Tail
Fig. 6.2 : Human sperm
REPRODUCTION IN ANIMALS 67
Sperm
duct
Testis
Penis
2024-25
SCIENCE 68
Boojho recalls that the size
of eggs in animals varies.
The egg may be very small
as in humans, much larger
as in hens. Ostrich egg is
the largest!
Fertilisation
The first step in the process of
reproduction is the fusion of a sperm
and an ovum. When sperms come in
contact with an egg, one of the sperms
may fuse with the egg. Such fusion of
the egg and the sperm is called
fertilisation (Fig. 6.5). During
fertilisation, the nuclei of the sperm and
the egg fuse to form a single nucleus.
This results in the formation of a
fertilised egg or zygote (Fig. 6.6). Did
Fig. 6.5 : Fertilisation
Fig. 6.4 : Human Ovum
Nucleus
Sperms
Ovum
Fusing
nuclei
The process of fertilisation is the
meeting of an egg cell from the mother
and a sperm cell from the father. So,
the new individual inherits some
characteristics  from the mother and
some from the father. Look at your
brother or sister. See if you can recognise
some characters in them similar to those
of your mother or your father.
Fertilisation which takes place inside
the female body is called internal
fertilisation. Internal fertilisation
occurs in many animals including
humans, cows, dogs and hens.
Fig. 6.6 : Zygote
female gametes called ova (eggs)
(Fig. 6.4). In human beings, a single
matured egg is released into the oviduct
by one of the ovaries every month.
Uterus is the part where development of
the baby takes place. Like the sperm,
an egg is also a single cell.
you know that the zygote is the
beginning of a new individual?
2024-25
REPRODUCTION IN ANIMALS 69
Why do fish and
frogs lay eggs in
hundreds whereas a
hen lays only one
egg at a time?
Have you heard of
test tube babies?
Boojho and Paheli’s teacher once told
them in the class that in some women
oviducts are blocked. These women
are unable to bear babies because
sperms cannot reach the egg for
fertilisation. In such cases, doctors
collect freshly released egg and
sperms and keep them together for a
few hours for IVF or in vitro
fertilisation (fertilisation outside the
body). In case fertilisation occurs,
the zygote is allowed to develop for
about a week and then it is placed in
the mother’s uterus. Complete
development takes place in the uterus
and the baby is born like any other
baby. Babies born through this
technique are called test-tube
babies. This term is actually
misleading because babies cannot
grow in test tubes.
female lays hundreds of eggs. Unlike
hen’s egg, frog’s egg is not covered by a
shell and it is comparatively very
delicate. A layer of jelly holds the eggs
together and provides protection to the
eggs (Fig. 6.7).
You will be surprised to know that
in many animals fertilisation takes
place outside the body of the female.
In these animals, fertilisation takes
place in water. Let us find out how
this happens.
Activity 6.1
Visit some ponds or slow-flowing
streams during spring or rainy
season. Look out for clusters of
frog’s eggs floating in water.
Write down the colour and size of
the eggs.
During spring or rainy season, frogs
and toads move to ponds and slow-
flowing streams. When the male and
female come together in water, the
As the eggs are laid, the male
deposits sperms over them. Each
sperm swims randomly in water with
the help of its long tail. The sperms
come in contact with the eggs. This
results in fertilisation. This type of
fertilisation in which the fusion of a
male and a female gamete takes place
outside the body of the female is called
external fertilisation. It is very
common in aquatic animals such as
fish, starfish, etc.
Fig. 6.7 : Eggs of frog
2024-25
Page 5


REPRODUCTION IN ANIMALS
REPRODUCTION IN ANIMALS
D
o you recall the processes of
digestion, circulation and
respiration which you have
studied in your previous classes? These
processes are essential for the survival
of every individual. You have also learnt
about the process of reproduction in
plants. Reproduction is essential for the
continuation of a species. Imagine what
would have happened if organisms had
not reproduced. You will realise that
reproduction is very important as it
ensures the continuation of similar
kinds of individuals, generation after
generation.
You have already learnt in your
previous class about reproduction in
plants. In this chapter, we shall learn
how reproduction takes place in
animals.
6.1 Modes of Reproduction
Have you seen the young ones
of different animals? Try to name some
of the young ones by completing
Table 6.1 shown in examples at S. No.
1 and 5.
You must have seen the young
ones of various animals being born.
Can you tell how chicks and
caterpillars are born? How are kittens
and puppies born? Do you think that
these young ones looked the same
before they were born as they do now?
Let us find out.
Just as in plants, there are two modes
by which animals reproduce. These are:
(i) Sexual reproduction, and
(ii) Asexual reproduction.
6.2 Sexual Reproduction
Try to recall reproduction in plants
which you studied in Class VII. You will
remember that plants that reproduce
sexually have male and female
reproductive parts. Can you name these
parts? In animals also, males and
females have different reproductive parts
or organs. Like plants, the reproductive
parts in animals also produce gametes
that fuse to form a zygote. It is the zygote
which develops into a new individual.
This type of reproduction beginning
from the fusion of male and female
gametes is called sexual reproduction.
Let us find out the reproductive parts
Table 6.1
S. No. Animal Young one
1. Human Baby
2. Cat
3. Dog
4. Butterfly
5. Hen Chick
6. Cow
7. Frog
2024-25
in humans and study the process of
reproduction in them.
Male Reproductive Organs
The male reproductive organs include a
pair of testes (singular, testis), two sperm
ducts and a penis (Fig. 6.1). The testes
produce the male gametes called
sperms. Millions of sperms are produced
by the testes. Look at Fig. 6.2 which
shows the picture of a sperm. Though
sperms are very small in size, each has
a head, a middle piece and a tail. Does
it appear to be a single cell? Indeed, each
sperm is a single cell with all the usual
cell components.
Fig. 6.1: Male reproductive
organs in humans
What purpose does the
tail in a sperm serve?
Fig. 6.3 : Female reproductive organs in
humans
Female Reproductive Organs
The female reproductive organs are a pair
of ovaries, oviducts (fallopian tubes) and
the uterus (Fig. 6.3). The ovary produces
Oviduct
Ovary
Uterus
Head
Middle piece
Tail
Fig. 6.2 : Human sperm
REPRODUCTION IN ANIMALS 67
Sperm
duct
Testis
Penis
2024-25
SCIENCE 68
Boojho recalls that the size
of eggs in animals varies.
The egg may be very small
as in humans, much larger
as in hens. Ostrich egg is
the largest!
Fertilisation
The first step in the process of
reproduction is the fusion of a sperm
and an ovum. When sperms come in
contact with an egg, one of the sperms
may fuse with the egg. Such fusion of
the egg and the sperm is called
fertilisation (Fig. 6.5). During
fertilisation, the nuclei of the sperm and
the egg fuse to form a single nucleus.
This results in the formation of a
fertilised egg or zygote (Fig. 6.6). Did
Fig. 6.5 : Fertilisation
Fig. 6.4 : Human Ovum
Nucleus
Sperms
Ovum
Fusing
nuclei
The process of fertilisation is the
meeting of an egg cell from the mother
and a sperm cell from the father. So,
the new individual inherits some
characteristics  from the mother and
some from the father. Look at your
brother or sister. See if you can recognise
some characters in them similar to those
of your mother or your father.
Fertilisation which takes place inside
the female body is called internal
fertilisation. Internal fertilisation
occurs in many animals including
humans, cows, dogs and hens.
Fig. 6.6 : Zygote
female gametes called ova (eggs)
(Fig. 6.4). In human beings, a single
matured egg is released into the oviduct
by one of the ovaries every month.
Uterus is the part where development of
the baby takes place. Like the sperm,
an egg is also a single cell.
you know that the zygote is the
beginning of a new individual?
2024-25
REPRODUCTION IN ANIMALS 69
Why do fish and
frogs lay eggs in
hundreds whereas a
hen lays only one
egg at a time?
Have you heard of
test tube babies?
Boojho and Paheli’s teacher once told
them in the class that in some women
oviducts are blocked. These women
are unable to bear babies because
sperms cannot reach the egg for
fertilisation. In such cases, doctors
collect freshly released egg and
sperms and keep them together for a
few hours for IVF or in vitro
fertilisation (fertilisation outside the
body). In case fertilisation occurs,
the zygote is allowed to develop for
about a week and then it is placed in
the mother’s uterus. Complete
development takes place in the uterus
and the baby is born like any other
baby. Babies born through this
technique are called test-tube
babies. This term is actually
misleading because babies cannot
grow in test tubes.
female lays hundreds of eggs. Unlike
hen’s egg, frog’s egg is not covered by a
shell and it is comparatively very
delicate. A layer of jelly holds the eggs
together and provides protection to the
eggs (Fig. 6.7).
You will be surprised to know that
in many animals fertilisation takes
place outside the body of the female.
In these animals, fertilisation takes
place in water. Let us find out how
this happens.
Activity 6.1
Visit some ponds or slow-flowing
streams during spring or rainy
season. Look out for clusters of
frog’s eggs floating in water.
Write down the colour and size of
the eggs.
During spring or rainy season, frogs
and toads move to ponds and slow-
flowing streams. When the male and
female come together in water, the
As the eggs are laid, the male
deposits sperms over them. Each
sperm swims randomly in water with
the help of its long tail. The sperms
come in contact with the eggs. This
results in fertilisation. This type of
fertilisation in which the fusion of a
male and a female gamete takes place
outside the body of the female is called
external fertilisation. It is very
common in aquatic animals such as
fish, starfish, etc.
Fig. 6.7 : Eggs of frog
2024-25
SCIENCE 70
Development of Embryo
Fertilisation results in the formation of
zygote which begins to develop into an
embryo [Fig. 6.8(a)]. The zygote divides
repeatedly to give rise to a ball of cells
[Fig. 6.8(b)]. The cells then begin to form
groups that develop into different tissues
and organs of the body. This developing
structure is termed an embryo. The
embryo gets embedded in the wall of the
uterus for further development
[Fig. 6.8(c)].
The embryo continues to develop in
the uterus. It gradually develops body
Fig. 6.8 : (a) Zygote formation and development of an embryo from the zygote; (b) Ball of cells
(enlarged); (c) Embedding of the embryo in the uterus (enlarged)
How could a single cell
become such a big
individual?
(b)
(a)
(c)
Uterus
Embedding
embryo
Ovary
Ovulation
Zygote
Uterus
wall
Developing
embryo
Though these animals lay
hundreds of eggs and release
millions of sperms, all the eggs
do not get fertilised and develop
into new individuals.
This is because the eggs and
sperms get exposed to  water
movement, wind and rainfall.
Also, there are other animals in
the pond which may feed
on eggs. Thus, production
of large number of eggs and
sperms is necessary to
ensure fertilisation
of at least
a few of them.
2024-25