NCERT Textbook: Sexual Reproduction in Flowering Plants | 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 explains the details of
reproductive processes 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
Sexual Reproduction in
flowering Plants
Chapter 2
Human Reproduction
Chapter 3
Reproductive Health
2024-25
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 explains the details of
reproductive processes 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
Sexual Reproduction in
flowering Plants
Chapter 2
Human Reproduction
Chapter 3
Reproductive Health
2024-25
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.
2024-25
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 explains the details of
reproductive processes 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
Sexual Reproduction in
flowering Plants
Chapter 2
Human Reproduction
Chapter 3
Reproductive Health
2024-25
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.
2024-25
Are we not lucky that plants reproduce sexually? The
myriads of flowers that we enjoy gazing at, the scents and
the perfumes that we swoon over, the rich colours that
attract us, are all there as an aid to sexual reproduction.
Flowers do not exist only for us to be used for our own
selfishness. All flowering plants show sexual reproduction.
A look at the diversity of structures of the inflorescences,
flowers and floral parts, shows an amazing range of
adaptations to ensure formation of the end products of
sexual reproduction, the fruits and seeds.  In this chapter,
let us understand the morphology, structure and the
processes of sexual reproduction in flowering plants
(angiosperms).
1.1 FLOWER – A FASCINATING ORGAN OF
ANGIOSPERMS
Human beings have had an intimate relationship with
flowers since time immemorial.  Flowers are objects of
aesthetic, ornamental, social, religious and cultural value
– they have always been used as symbols for conveying
important human feelings such as love, affection,
happiness, grief, mourning, etc.  List at least five flowers
of ornamental value that are commonly cultivated at
1.1 Flower – A Fascinating
Organ of Angiosperms
1.2 Pre-fertilisation : Structures
and Events
1.3 Double Fertilisation
1.4 Post-fertilisation: Structures
and Events
1.5 Apomixis and
Polyembryony
CHAPTER 1
SEXUAL REPRODUCTION IN
FLOWERING PLANTS
2024-25
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 explains the details of
reproductive processes 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
Sexual Reproduction in
flowering Plants
Chapter 2
Human Reproduction
Chapter 3
Reproductive Health
2024-25
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.
2024-25
Are we not lucky that plants reproduce sexually? The
myriads of flowers that we enjoy gazing at, the scents and
the perfumes that we swoon over, the rich colours that
attract us, are all there as an aid to sexual reproduction.
Flowers do not exist only for us to be used for our own
selfishness. All flowering plants show sexual reproduction.
A look at the diversity of structures of the inflorescences,
flowers and floral parts, shows an amazing range of
adaptations to ensure formation of the end products of
sexual reproduction, the fruits and seeds.  In this chapter,
let us understand the morphology, structure and the
processes of sexual reproduction in flowering plants
(angiosperms).
1.1 FLOWER – A FASCINATING ORGAN OF
ANGIOSPERMS
Human beings have had an intimate relationship with
flowers since time immemorial.  Flowers are objects of
aesthetic, ornamental, social, religious and cultural value
– they have always been used as symbols for conveying
important human feelings such as love, affection,
happiness, grief, mourning, etc.  List at least five flowers
of ornamental value that are commonly cultivated at
1.1 Flower – A Fascinating
Organ of Angiosperms
1.2 Pre-fertilisation : Structures
and Events
1.3 Double Fertilisation
1.4 Post-fertilisation: Structures
and Events
1.5 Apomixis and
Polyembryony
CHAPTER 1
SEXUAL REPRODUCTION IN
FLOWERING PLANTS
2024-25
4
BIOLOGY
homes and in gardens. Find out the names of five more flowers that are
used in social and cultural celebrations in your family.  Have you heard
of floriculture – what does it refer to?
To a biologist, flowers are morphological and embryological marvels
and the sites of sexual reproduction.  In earlier classes, you have read the
various parts of a flower.  Figure 1.1 will help you recall the parts of a
typical flower. Can you name the two parts in a flower in which the two
most important units of sexual reproduction develop?
1.2 PRE-FERTILISATION: STRUCTURES AND EVENTS
Much before the actual flower is seen on a plant, the decision that the plant
is going to flower has taken place. Several hormonal and structural changes
are initiated which lead to the differentiation and further development of
the floral primordium. Inflorescences are formed which bear the floral buds
and then the flowers. In the flower the male and female reproductive
structures, the androecium and the gynoecium differentiate and develop.
You would recollect that the androecium consists of a whorl of stamens
representing the male reproductive organ and the gynoecium represents
the female reproductive organ.
Figure 1.1 A diagrammatic representation of L.S. of a flower
2024-25
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 explains the details of
reproductive processes 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
Sexual Reproduction in
flowering Plants
Chapter 2
Human Reproduction
Chapter 3
Reproductive Health
2024-25
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.
2024-25
Are we not lucky that plants reproduce sexually? The
myriads of flowers that we enjoy gazing at, the scents and
the perfumes that we swoon over, the rich colours that
attract us, are all there as an aid to sexual reproduction.
Flowers do not exist only for us to be used for our own
selfishness. All flowering plants show sexual reproduction.
A look at the diversity of structures of the inflorescences,
flowers and floral parts, shows an amazing range of
adaptations to ensure formation of the end products of
sexual reproduction, the fruits and seeds.  In this chapter,
let us understand the morphology, structure and the
processes of sexual reproduction in flowering plants
(angiosperms).
1.1 FLOWER – A FASCINATING ORGAN OF
ANGIOSPERMS
Human beings have had an intimate relationship with
flowers since time immemorial.  Flowers are objects of
aesthetic, ornamental, social, religious and cultural value
– they have always been used as symbols for conveying
important human feelings such as love, affection,
happiness, grief, mourning, etc.  List at least five flowers
of ornamental value that are commonly cultivated at
1.1 Flower – A Fascinating
Organ of Angiosperms
1.2 Pre-fertilisation : Structures
and Events
1.3 Double Fertilisation
1.4 Post-fertilisation: Structures
and Events
1.5 Apomixis and
Polyembryony
CHAPTER 1
SEXUAL REPRODUCTION IN
FLOWERING PLANTS
2024-25
4
BIOLOGY
homes and in gardens. Find out the names of five more flowers that are
used in social and cultural celebrations in your family.  Have you heard
of floriculture – what does it refer to?
To a biologist, flowers are morphological and embryological marvels
and the sites of sexual reproduction.  In earlier classes, you have read the
various parts of a flower.  Figure 1.1 will help you recall the parts of a
typical flower. Can you name the two parts in a flower in which the two
most important units of sexual reproduction develop?
1.2 PRE-FERTILISATION: STRUCTURES AND EVENTS
Much before the actual flower is seen on a plant, the decision that the plant
is going to flower has taken place. Several hormonal and structural changes
are initiated which lead to the differentiation and further development of
the floral primordium. Inflorescences are formed which bear the floral buds
and then the flowers. In the flower the male and female reproductive
structures, the androecium and the gynoecium differentiate and develop.
You would recollect that the androecium consists of a whorl of stamens
representing the male reproductive organ and the gynoecium represents
the female reproductive organ.
Figure 1.1 A diagrammatic representation of L.S. of a flower
2024-25
5
HUMAN REPRODUCTION
SEXUAL REPRODUCTION IN FLOWERING PLANTS
1.2.1 Stamen, Microsporangium and Pollen Grain
Figure 1.2a shows the two parts of a typical stamen – the long and slender
stalk called the filament, and the terminal generally bilobed structure
called the anther. The proximal end of the filament
is attached to the thalamus or the petal of the flower.
The number and length of stamens are variable in
flowers of different species.  If you were to collect a
stamen each from ten flowers (each from different
species) and arrange them on a slide, you would
be able to appreciate the large variation in size seen
in nature.  Careful observation of each stamen
under a dissecting microscope and making neat
diagrams would elucidate the range in shape and
attachment of anthers in different flowers.
A typical angiosperm anther is bilobed with
each lobe having two theca, i.e., they are dithecous
(Figure 1.2b). Often a longitudinal groove runs
lengthwise separating the theca. Let us
understand the various types of tissues and their
organisation in the transverse section of an anther
(Figure 1.3a). The bilobed nature of an anther is
very distinct in the transverse section of the anther.
The anther is a four-sided (tetragonal) structure
consisting of four microsporangia located at the
corners, two in each lobe.
The microsporangia develop further and
become pollen sacs.  They extend longitudinally
all through the length of an anther and are packed
with pollen grains.
Structure of microsporangium: In a transverse
section, a typical microsporangium appears near
circular in outline.  It is generally surrounded by four wall layers (Figure
1.3b)– the epidermis, endothecium, middle layers and the tapetum. The
outer three wall layers perform the function of protection and help in
dehiscence of anther to release the pollen.  The innermost wall layer is
the tapetum.  It nourishes the developing pollen grains. Cells of the
tapetum possess dense cytoplasm and generally have more than one
nucleus.  Can you think of how tapetal cells could become bi-nucleate?
When the anther is young, a group of compactly arranged homogenous
cells called the sporogenous tissue occupies the centre of each
microsporangium.
Microsporogenesis : As the anther develops, the cells of the sporogenous
tissue undergo meiotic divisions to form microspore tetrads.  What would
be the ploidy of the cells of the tetrad?
Figure 1.2 (a)A typical stamen;
(b)three–dimensional cut section
 of an anther
(b)
(a)
2024-25