CBSE Class 12 Biology
Revision Notes
CHAPTER-02
SEXUAL REPRODUCTION IN FLOWERING PLANTS
Reproduction ensures continuity of species generation after generations as the older individuals
undergo senescence and die. Flowering plants shows sexual mode of reproduction and bears
complex reproductive units as male and female reproductive units along with accessary structures.
Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen.
A typical angiospermic flower consists of four whorls of floral appendages attached on the
receptacle: calyx, corolla, androecium (male reproductive organ consisting of stamens) and
gynoecium (composed of ovary, style and stigma) .
Fig.: 2.1 L.S of a typical Bisexual flower
Pre-fertilisation: Structures and Events
• Several structural and hormonal changes lead to formation and development of the floral
primordium. Inflorescence is formed that bears floral buds and then flower.
• In flowers, male (androecium) and female (gynoecium) differentiate and develops in which male
and female gametes are produced.
Stamen, Microsporangium and Pollen Grain :
• Stamen consists of long and slender stalk called filament and generally bilobed anthers. Each lobe
contains two theca (dithecious).
• The anther is four-sided structure consisting of four microsporangia, two in each lobes.
• Microsporangia develop further and become pollen sacs which contain pollen grains.
• Microsporangium is generally surrounded by four layered walls- the epidermis, endothecium,
middle layer and tapetum. Innermost layer tapetum nourishes the developing pollen grains.
, Fig.: 2.2 (a) A typical stamen;
(b) three-dimensional cut section of an anther
• Sporogenous tissues- It is compactly arranged homogenous cells which are present at centre
of each microsporangium when the anther is young..
Microsporogenesis- The process of the formation and differentiation of microspores (pollen
grains) from microspore mother cells (MMC) by reductional division is called microsporogenesis.
• The cells of sporogenous tissues undergo meiotic division to form microspore tetrad. As the
anther mature and dehydrate, the microspore dissociate and develops into pollen grains.
Fig.: 2.3 (a) Transverse section of a young anther;
(b) Enlarge view of one microsporangium showing wall layers;
(c) A mature dehisced anther
Pollen grain represents the male gametophytes. Pollen grains are made of 2 layered Wall,
1. Exine :- Made of sporopollenin- most resistant organic matter known.It can withstand high
temperatures and strong acids and alkali. No enzyme can degrade sporopollenin
Revision Notes
CHAPTER-02
SEXUAL REPRODUCTION IN FLOWERING PLANTS
Reproduction ensures continuity of species generation after generations as the older individuals
undergo senescence and die. Flowering plants shows sexual mode of reproduction and bears
complex reproductive units as male and female reproductive units along with accessary structures.
Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen.
A typical angiospermic flower consists of four whorls of floral appendages attached on the
receptacle: calyx, corolla, androecium (male reproductive organ consisting of stamens) and
gynoecium (composed of ovary, style and stigma) .
Fig.: 2.1 L.S of a typical Bisexual flower
Pre-fertilisation: Structures and Events
• Several structural and hormonal changes lead to formation and development of the floral
primordium. Inflorescence is formed that bears floral buds and then flower.
• In flowers, male (androecium) and female (gynoecium) differentiate and develops in which male
and female gametes are produced.
Stamen, Microsporangium and Pollen Grain :
• Stamen consists of long and slender stalk called filament and generally bilobed anthers. Each lobe
contains two theca (dithecious).
• The anther is four-sided structure consisting of four microsporangia, two in each lobes.
• Microsporangia develop further and become pollen sacs which contain pollen grains.
• Microsporangium is generally surrounded by four layered walls- the epidermis, endothecium,
middle layer and tapetum. Innermost layer tapetum nourishes the developing pollen grains.
, Fig.: 2.2 (a) A typical stamen;
(b) three-dimensional cut section of an anther
• Sporogenous tissues- It is compactly arranged homogenous cells which are present at centre
of each microsporangium when the anther is young..
Microsporogenesis- The process of the formation and differentiation of microspores (pollen
grains) from microspore mother cells (MMC) by reductional division is called microsporogenesis.
• The cells of sporogenous tissues undergo meiotic division to form microspore tetrad. As the
anther mature and dehydrate, the microspore dissociate and develops into pollen grains.
Fig.: 2.3 (a) Transverse section of a young anther;
(b) Enlarge view of one microsporangium showing wall layers;
(c) A mature dehisced anther
Pollen grain represents the male gametophytes. Pollen grains are made of 2 layered Wall,
1. Exine :- Made of sporopollenin- most resistant organic matter known.It can withstand high
temperatures and strong acids and alkali. No enzyme can degrade sporopollenin
