NCERT Textbook: Reproduction in Organisms | Biology Class 12 - NEET PDF Download

 Page 1


Biology in essence is the story of life on earth. While individual
organisms die without fail, species continue to live through
millions of years unless threatened by natural or anthropogenic
extinction. Reproduction becomes a vital process without
which species cannot survive for long. Each individual leaves
its progeny by asexual or sexual means. Sexual mode of
reproduction enables creation of new variants, so that survival
advantage is enhanced. This unit examines the general
principles underlying reproductive processes in living organisms
and then explains the details of this process in flowering plants
and humans as easy to relate representative examples. A related
perspective on human reproductive health and how
reproductive ill health can be avoided is also presented to
complete our understanding of biology of reproduction.
Chapter 1
Reproduction in Organisms
Chapter 2
Sexual Reproduction in
flowering Plants
Chapter 3
Human Reproduction
Chapter 4
Reproductive Health
2022-23
Page 2


Biology in essence is the story of life on earth. While individual
organisms die without fail, species continue to live through
millions of years unless threatened by natural or anthropogenic
extinction. Reproduction becomes a vital process without
which species cannot survive for long. Each individual leaves
its progeny by asexual or sexual means. Sexual mode of
reproduction enables creation of new variants, so that survival
advantage is enhanced. This unit examines the general
principles underlying reproductive processes in living organisms
and then explains the details of this process in flowering plants
and humans as easy to relate representative examples. A related
perspective on human reproductive health and how
reproductive ill health can be avoided is also presented to
complete our understanding of biology of reproduction.
Chapter 1
Reproduction in Organisms
Chapter 2
Sexual Reproduction in
flowering Plants
Chapter 3
Human Reproduction
Chapter 4
Reproductive Health
2022-23
PANCHANAN MAHESHWARI
(1904-1966)
Born in November 1904 in Jaipur (Rajasthan) Panchanan Maheshwari
rose to become one of the most distinguished botanists not only of India
but of the entire world. He moved to Allahabad for higher education
where he obtained his D.Sc. During his college days, he was inspired
by Dr W. Dudgeon, an American missionary teacher, to develop interest
in Botany and especially morphology. His teacher once expressed that
if his student progresses ahead of him, it will give him a great satisfaction.
These words encouraged Panchanan to enquire what he could do for
his teacher in return.
He worked on embryological aspects and popularised the use of
embryological characters in taxonomy. He established the Department
of Botany, University of Delhi as an important centre of research in
embryology and tissue culture. He also emphasised the need for initiation
of work on artificial culture of immature embryos. These days, tissue
culture has become a landmark in science. His work on test tube
fertilisation and intra-ovarian pollination won worldwide acclaim.
He was honoured with fellowship of Royal Society of London (FRS),
Indian National Science Academy and several other institutions of
excellence. He encouraged general education and made a significant
contribution to school education by his leadership in bringing out the
very first textbooks of Biology for Higher Secondary Schools published
by NCERT in 1964.
2022-23
Page 3


Biology in essence is the story of life on earth. While individual
organisms die without fail, species continue to live through
millions of years unless threatened by natural or anthropogenic
extinction. Reproduction becomes a vital process without
which species cannot survive for long. Each individual leaves
its progeny by asexual or sexual means. Sexual mode of
reproduction enables creation of new variants, so that survival
advantage is enhanced. This unit examines the general
principles underlying reproductive processes in living organisms
and then explains the details of this process in flowering plants
and humans as easy to relate representative examples. A related
perspective on human reproductive health and how
reproductive ill health can be avoided is also presented to
complete our understanding of biology of reproduction.
Chapter 1
Reproduction in Organisms
Chapter 2
Sexual Reproduction in
flowering Plants
Chapter 3
Human Reproduction
Chapter 4
Reproductive Health
2022-23
PANCHANAN MAHESHWARI
(1904-1966)
Born in November 1904 in Jaipur (Rajasthan) Panchanan Maheshwari
rose to become one of the most distinguished botanists not only of India
but of the entire world. He moved to Allahabad for higher education
where he obtained his D.Sc. During his college days, he was inspired
by Dr W. Dudgeon, an American missionary teacher, to develop interest
in Botany and especially morphology. His teacher once expressed that
if his student progresses ahead of him, it will give him a great satisfaction.
These words encouraged Panchanan to enquire what he could do for
his teacher in return.
He worked on embryological aspects and popularised the use of
embryological characters in taxonomy. He established the Department
of Botany, University of Delhi as an important centre of research in
embryology and tissue culture. He also emphasised the need for initiation
of work on artificial culture of immature embryos. These days, tissue
culture has become a landmark in science. His work on test tube
fertilisation and intra-ovarian pollination won worldwide acclaim.
He was honoured with fellowship of Royal Society of London (FRS),
Indian National Science Academy and several other institutions of
excellence. He encouraged general education and made a significant
contribution to school education by his leadership in bringing out the
very first textbooks of Biology for Higher Secondary Schools published
by NCERT in 1964.
2022-23
Each and every organism can live only for a certain period
of time. The period from birth to the natural death of an
organism represents its life span. Life spans of a few
organisms are given in Figure 1.1. Several other organisms
are drawn for which you should find out their life spans
and write in the spaces provided.  Examine the life spans
of organisms represented in the Figure 1.1. Isn’t it both
interesting and intriguing to note that it may be as short
as a few days or as long as a few thousand years?  Between
these two extremes are the life spans of most other living
organisms. You may note that life spans of organisms are
not necessarily correlated with their sizes; the sizes of
crows and parrots are not very different yet their life spans
show a wide difference. Similarly, a mango tree has a much
shorter life span as compared to a peepal tree. Whatever
be the life span, death of every individual organism is a
certainty, i.e., no individual is immortal, except single-celled
organisms. Why do we say there is no natural death in
single-celled organisms? Given this reality, have you ever
wondered how vast number of plant and animal species
have existed on earth for several thousands of years?  There
must be some processes in living organisms that ensure
this continuity.  Yes, we are talking about reproduction,
something that we take for granted.
CHAPTER 1
REPRODUCTION IN ORGANISMS
1.1 Asexual
Reproduction
1.2 Sexual
Reproduction
2022-23
Page 4


Biology in essence is the story of life on earth. While individual
organisms die without fail, species continue to live through
millions of years unless threatened by natural or anthropogenic
extinction. Reproduction becomes a vital process without
which species cannot survive for long. Each individual leaves
its progeny by asexual or sexual means. Sexual mode of
reproduction enables creation of new variants, so that survival
advantage is enhanced. This unit examines the general
principles underlying reproductive processes in living organisms
and then explains the details of this process in flowering plants
and humans as easy to relate representative examples. A related
perspective on human reproductive health and how
reproductive ill health can be avoided is also presented to
complete our understanding of biology of reproduction.
Chapter 1
Reproduction in Organisms
Chapter 2
Sexual Reproduction in
flowering Plants
Chapter 3
Human Reproduction
Chapter 4
Reproductive Health
2022-23
PANCHANAN MAHESHWARI
(1904-1966)
Born in November 1904 in Jaipur (Rajasthan) Panchanan Maheshwari
rose to become one of the most distinguished botanists not only of India
but of the entire world. He moved to Allahabad for higher education
where he obtained his D.Sc. During his college days, he was inspired
by Dr W. Dudgeon, an American missionary teacher, to develop interest
in Botany and especially morphology. His teacher once expressed that
if his student progresses ahead of him, it will give him a great satisfaction.
These words encouraged Panchanan to enquire what he could do for
his teacher in return.
He worked on embryological aspects and popularised the use of
embryological characters in taxonomy. He established the Department
of Botany, University of Delhi as an important centre of research in
embryology and tissue culture. He also emphasised the need for initiation
of work on artificial culture of immature embryos. These days, tissue
culture has become a landmark in science. His work on test tube
fertilisation and intra-ovarian pollination won worldwide acclaim.
He was honoured with fellowship of Royal Society of London (FRS),
Indian National Science Academy and several other institutions of
excellence. He encouraged general education and made a significant
contribution to school education by his leadership in bringing out the
very first textbooks of Biology for Higher Secondary Schools published
by NCERT in 1964.
2022-23
Each and every organism can live only for a certain period
of time. The period from birth to the natural death of an
organism represents its life span. Life spans of a few
organisms are given in Figure 1.1. Several other organisms
are drawn for which you should find out their life spans
and write in the spaces provided.  Examine the life spans
of organisms represented in the Figure 1.1. Isn’t it both
interesting and intriguing to note that it may be as short
as a few days or as long as a few thousand years?  Between
these two extremes are the life spans of most other living
organisms. You may note that life spans of organisms are
not necessarily correlated with their sizes; the sizes of
crows and parrots are not very different yet their life spans
show a wide difference. Similarly, a mango tree has a much
shorter life span as compared to a peepal tree. Whatever
be the life span, death of every individual organism is a
certainty, i.e., no individual is immortal, except single-celled
organisms. Why do we say there is no natural death in
single-celled organisms? Given this reality, have you ever
wondered how vast number of plant and animal species
have existed on earth for several thousands of years?  There
must be some processes in living organisms that ensure
this continuity.  Yes, we are talking about reproduction,
something that we take for granted.
CHAPTER 1
REPRODUCTION IN ORGANISMS
1.1 Asexual
Reproduction
1.2 Sexual
Reproduction
2022-23
4
BIOLOGY
Figure 1.1 Approximate life spans of some organisms
4
2022-23
Page 5


Biology in essence is the story of life on earth. While individual
organisms die without fail, species continue to live through
millions of years unless threatened by natural or anthropogenic
extinction. Reproduction becomes a vital process without
which species cannot survive for long. Each individual leaves
its progeny by asexual or sexual means. Sexual mode of
reproduction enables creation of new variants, so that survival
advantage is enhanced. This unit examines the general
principles underlying reproductive processes in living organisms
and then explains the details of this process in flowering plants
and humans as easy to relate representative examples. A related
perspective on human reproductive health and how
reproductive ill health can be avoided is also presented to
complete our understanding of biology of reproduction.
Chapter 1
Reproduction in Organisms
Chapter 2
Sexual Reproduction in
flowering Plants
Chapter 3
Human Reproduction
Chapter 4
Reproductive Health
2022-23
PANCHANAN MAHESHWARI
(1904-1966)
Born in November 1904 in Jaipur (Rajasthan) Panchanan Maheshwari
rose to become one of the most distinguished botanists not only of India
but of the entire world. He moved to Allahabad for higher education
where he obtained his D.Sc. During his college days, he was inspired
by Dr W. Dudgeon, an American missionary teacher, to develop interest
in Botany and especially morphology. His teacher once expressed that
if his student progresses ahead of him, it will give him a great satisfaction.
These words encouraged Panchanan to enquire what he could do for
his teacher in return.
He worked on embryological aspects and popularised the use of
embryological characters in taxonomy. He established the Department
of Botany, University of Delhi as an important centre of research in
embryology and tissue culture. He also emphasised the need for initiation
of work on artificial culture of immature embryos. These days, tissue
culture has become a landmark in science. His work on test tube
fertilisation and intra-ovarian pollination won worldwide acclaim.
He was honoured with fellowship of Royal Society of London (FRS),
Indian National Science Academy and several other institutions of
excellence. He encouraged general education and made a significant
contribution to school education by his leadership in bringing out the
very first textbooks of Biology for Higher Secondary Schools published
by NCERT in 1964.
2022-23
Each and every organism can live only for a certain period
of time. The period from birth to the natural death of an
organism represents its life span. Life spans of a few
organisms are given in Figure 1.1. Several other organisms
are drawn for which you should find out their life spans
and write in the spaces provided.  Examine the life spans
of organisms represented in the Figure 1.1. Isn’t it both
interesting and intriguing to note that it may be as short
as a few days or as long as a few thousand years?  Between
these two extremes are the life spans of most other living
organisms. You may note that life spans of organisms are
not necessarily correlated with their sizes; the sizes of
crows and parrots are not very different yet their life spans
show a wide difference. Similarly, a mango tree has a much
shorter life span as compared to a peepal tree. Whatever
be the life span, death of every individual organism is a
certainty, i.e., no individual is immortal, except single-celled
organisms. Why do we say there is no natural death in
single-celled organisms? Given this reality, have you ever
wondered how vast number of plant and animal species
have existed on earth for several thousands of years?  There
must be some processes in living organisms that ensure
this continuity.  Yes, we are talking about reproduction,
something that we take for granted.
CHAPTER 1
REPRODUCTION IN ORGANISMS
1.1 Asexual
Reproduction
1.2 Sexual
Reproduction
2022-23
4
BIOLOGY
Figure 1.1 Approximate life spans of some organisms
4
2022-23
5
REPRODUCTION IN ORGANISMS
Reproduction is defined as a biological process in which an
organism gives rise to young ones (offspring) similar to itself. The offspring
grow, mature and in turn produce new offspring. Thus, there is a cycle
of birth, growth and death. Reproduction enables the continuity of the
species, generation after generation. You will study later in Chapter 5
(Principles of Inheritance and Variation) how genetic variation is created
and inherited during reproduction.
There is a large diversity in the biological world and each organism
has evolved its own mechanism to multiply and produce offspring.
The organism’s habitat, its internal physiology and several other factors
are collectively responsible for how it reproduces.  Based on whether
there is participation of one organism or two in the process of
reproduction, it is of two types. When offspring is produced by a single
parent with or without the involvement of gamete formation, the
reproduction is asexual. When two parents (opposite sex) participate in
the reproductive process and also involve fusion of male and female
gametes, it is called sexual reproduction.
1.1  ASEXUAL REPRODUCTION
In this method, a single individual (parent) is capable of producing
offspring. As a result, the offspring that are produced are not only
identical to one another but are also exact copies of their parent.
Are these offspring likely to be genetically identical or different?
The term clone is used to describe such morphologically and
genetically similar individuals.
Figure 1.2 Cell division in unicellular organism: (a) Budding in
yeast; (b) Binary fission in Amoeba
(b) (a)
Let us see how widespread asexual reproduction is, among different
groups of organisms. Asexual reproduction is common among
single-celled organisms, and in plants and animals with relatively simple
organisations. In Protists and Monerans, the organism or the parent
cell divides by mitosis into two to give rise to new individuals (Figure1.2).
Thus, in these organisms cell division is itself a mode of reproduction.
2022-23