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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) .
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.
• Sporogenous tissues- It is compactly arranged homogenous cells which are present at centre of each microsporangium when
the anther is young.
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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.
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
2. Intine :-
-Thin and continuous layer
- Made of cellulose and pectin
3. Germ pores
- apertures on exine where sporopollenin is absent
- forms pollen tube.
4. A plasma membrane surrounds cytoplasm of pollen grain.
MATURE POLLEN
— A mature pollen consist of 2 cells with nucleus (Vegetative and Generative)
VEGETATIVE CELL
Bigger
Abundant food reserve
Large irregular nucleus
Responsible for the development of pollen grain
GENERATIVE CELL
Small
Involves in syngamy (fuse with an egg)
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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) .
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.
• Sporogenous tissues- It is compactly arranged homogenous cells which are present at centre of each microsporangium when
the anther is young.
Copyright © myCBSEguide.com. Mass distribution in any mode is strictly prohibited.
1/7
, myCBSEguide
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.
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
2. Intine :-
-Thin and continuous layer
- Made of cellulose and pectin
3. Germ pores
- apertures on exine where sporopollenin is absent
- forms pollen tube.
4. A plasma membrane surrounds cytoplasm of pollen grain.
MATURE POLLEN
— A mature pollen consist of 2 cells with nucleus (Vegetative and Generative)
VEGETATIVE CELL
Bigger
Abundant food reserve
Large irregular nucleus
Responsible for the development of pollen grain
GENERATIVE CELL
Small
Involves in syngamy (fuse with an egg)
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