CHAPTER - 1
SEXUAL REPRODUCTION IN FLOWERING PLANTS
FLOWER – It is the modified stem of a plant.
STRUCTURE OF A FLOWER:
WHORLS
Non – Essential (sterile) Essential ( fertile )
Calyx Corolla Androecium Gynoecium
Outermost whorl of - whorl of petals - Whorl of stamens -Whorl of pistils
sepals inside calyx - Male reproductive part -Female reproductive
of the flower part of the flower
, Sexual Reproduction in Flowering Plants
- The process by which male and female gametes from two parents combine to
generate new creatures is known as sexual reproduction.
- Flower is the main reproductive organ of a plant which contains the male and female
reproductive organs.
- Flowers are structurally divided into the following different whorls:
○ Calyx - group of sepals, usually green in colour.
○ Corolla - group of petals, brightly coloured.
○ Androecium - male reproductive part of a flower consisting of the stamen having filament
and anther.
○ Gynoecium - female reproductive part of a flower known as pistil or carpel consisting of
stigma, style and ovary.
There are three stages involved in sexual reproduction in flowering
plants:
i) Pre-fertilization
ii) Double fertilization
iii) Post-fertilization
Pre-Fertilisation: Structures and Events
STRUCTURE OF STAMEN:
- Typical stamen consists of two parts, long and slender stalk called filament
and terminal bilobed structure called anther.
o Filament–Sterile part which connects the anther to the thalamus or petals of the flower.
o Anther-Fertile part, within which are formed pollen grains.
, - Anther is usually bilobed, each lobe has two theca and thus known as dithecous. Each
theca has two microsporangia (four in total) and thus a typical angiosperm anther is
tetrasporangiate.
- Each microsporangium develops and become the pollen sac that produces a large
number of microspores known as pollen grains.
MICROSPORANGIUM:
Each microsporangium is surrounded by four wall layers:
o Epidermis : it is the outermost wall layers which performs the function of protection.
o Endothecium : it is present in the form of radial bands and helps in the dehiscence
of anther.
o Middle layers : 1-3 layers, helps in the formation of pollenkit.
o Tapetum : innermost wall layer, provides nourishment to the developing pollen
grains and also secretes sporopollenin which forms the outer wall of pollen grains.
- The centre of each microsporangium consists of homogenous mass of sporogenous
tissue.
- Each cell of the sporogenous tissue has the potential to undergo meiosis and produce
four haploid microspores or pollen grains.
Protective and helps in the
Dehiscence of pollen grains.
Provides nourishment to
the developing pollen
grains.
FIG: Walls of Microsporangium
MICROSPOROGENESIS:
- The process of formation of microspores from pollen mother cell through
meiosis is called microsporogenesis.
- The sporogenous tissue of microsporangium is differentiated into microspore
SEXUAL REPRODUCTION IN FLOWERING PLANTS
FLOWER – It is the modified stem of a plant.
STRUCTURE OF A FLOWER:
WHORLS
Non – Essential (sterile) Essential ( fertile )
Calyx Corolla Androecium Gynoecium
Outermost whorl of - whorl of petals - Whorl of stamens -Whorl of pistils
sepals inside calyx - Male reproductive part -Female reproductive
of the flower part of the flower
, Sexual Reproduction in Flowering Plants
- The process by which male and female gametes from two parents combine to
generate new creatures is known as sexual reproduction.
- Flower is the main reproductive organ of a plant which contains the male and female
reproductive organs.
- Flowers are structurally divided into the following different whorls:
○ Calyx - group of sepals, usually green in colour.
○ Corolla - group of petals, brightly coloured.
○ Androecium - male reproductive part of a flower consisting of the stamen having filament
and anther.
○ Gynoecium - female reproductive part of a flower known as pistil or carpel consisting of
stigma, style and ovary.
There are three stages involved in sexual reproduction in flowering
plants:
i) Pre-fertilization
ii) Double fertilization
iii) Post-fertilization
Pre-Fertilisation: Structures and Events
STRUCTURE OF STAMEN:
- Typical stamen consists of two parts, long and slender stalk called filament
and terminal bilobed structure called anther.
o Filament–Sterile part which connects the anther to the thalamus or petals of the flower.
o Anther-Fertile part, within which are formed pollen grains.
, - Anther is usually bilobed, each lobe has two theca and thus known as dithecous. Each
theca has two microsporangia (four in total) and thus a typical angiosperm anther is
tetrasporangiate.
- Each microsporangium develops and become the pollen sac that produces a large
number of microspores known as pollen grains.
MICROSPORANGIUM:
Each microsporangium is surrounded by four wall layers:
o Epidermis : it is the outermost wall layers which performs the function of protection.
o Endothecium : it is present in the form of radial bands and helps in the dehiscence
of anther.
o Middle layers : 1-3 layers, helps in the formation of pollenkit.
o Tapetum : innermost wall layer, provides nourishment to the developing pollen
grains and also secretes sporopollenin which forms the outer wall of pollen grains.
- The centre of each microsporangium consists of homogenous mass of sporogenous
tissue.
- Each cell of the sporogenous tissue has the potential to undergo meiosis and produce
four haploid microspores or pollen grains.
Protective and helps in the
Dehiscence of pollen grains.
Provides nourishment to
the developing pollen
grains.
FIG: Walls of Microsporangium
MICROSPOROGENESIS:
- The process of formation of microspores from pollen mother cell through
meiosis is called microsporogenesis.
- The sporogenous tissue of microsporangium is differentiated into microspore
