Sexual Reproduction in Flowering Plants
SHORT NOTES
Parts of flower Female Gametophyte/Embryo Sac
All flowering plants show sexual reproduction. Ovules generally differentiate a single megaspore mother cell
A complete flower consists of calyx, corolla, androecium and (MMC) in micropylar region of nucellus.
gynoecium. In majority of flowering plants, one megaspore remains
Androecium is the male reproductive structure that consists functional and 3 degenerate. The functional megaspore
of a whorl of stamens. develops in to the female gametophyte (embryo sac).
Gynoecium is the female reproductive structure that consists The typical angiosperm embryo sac (female gametophyte)
of a whorl of carples (pistils). possess 8-nucleate and 7-celled condition at maturity.
Each pistil has three parts. Pollination
Stigma: Landing platform for pollen grains. Pollination is the transfer of pollen grain from anther to the
Ovary: Basal bulged part of pistil, has ovarian cavity stigma of the same flower (self pollination) or of different
(locule). Placenta is located inside ovarian caviity. flower (cross pollination) of the same species.
A typical stamen is composed of filament and anther. Self pollination is of two types i.e, autogamy and geitonogomy.
Filament: It is a long slender stalk. The proximal end of Autogamy can be promoted by cleistogamy.
the filament is attached to the thalamus or the petal of the Xenogomy (cross pollination) is the only type of pollination
flower. which brings genetically different types of pollen grains on
Anther is terminal and generally bilobed structure and the stigma.
each lobe having two theca i.e., they are dithecous. Geitonogamy functionally similar to cross pollination and
The anther is a four-sided (tetragonal) structure consisting of genetically it is similar to autogamy (self pollination).
four microsporangia located at the corners two in each lobe. Wind and water are common abiotic pollinating agents.
The microsporangia develop further & become pollen sacs. Wind Pollination requires light, non-stickly pollen so
They extend longitudinally all through the length of an anther that they can be transported by wind currents. Well exposed
and are packed with pollen grains. stamens and large often feathery stigma to trap air borne
pollen, single ovule in each ovary and numerous flowers in
Structure of Microsporangium an inflorescence.
A typical microsporangium near circular, which is generally In majority of aquatic plants like water hyacinth and water lily,
surrounded by four wall layers. flowers emerge above water & are pollinated by insects or wind.
The outer 3 wall layers perform the function of protection In most water-pollinated species, pollen grains are protected
and help in dehiscence of anther to release the pollen. The from wetting by a mucilaginous covering.
innermost wall layer tapetum nourishes the developing pollen Insect-pollinating flowers are large, colourful, fragrant
grains. and rich in nectar.
Microsporogenesis is a process of formation of microspores Nectar & pollen grains are usual floral rewards.
from PMC (Pollen Mother Cell). In some species, floral rewards are in providing safe places to
lay eggs, eg, Amorphophallus. A species of moth and Yucca
Pollen Grain cannot complete their life cycles without each other.
It represents the male gametophyte.
Outbreeding Devices
It has prominent two layered wall-exine and intine.
Flowering plants have developed many out breeding devices
The outer layer exine is made up of sporopollenin and the to discourage self pollination and to encourage cross
intine is made up of pectin and cellulose. pollination. For example:
Pollen grains of many species causes severe allergies. Pollen release and stigma receptivity are not synchronised.
Pollen grains are rich in nutrients. Anther and stigma are placed at different positions so that
Pollen variability: depends on both temperature and pollen cannot come in contact with stigma of the same flower.
humidity. Self-incompatibility is a genetic mechanism which
Pollen of a large number of species can be stored for years in prevents self-pollen from fertilizing the ovules by inhibiting
liquid nitrogen (–196°C) in pollen banks for crop breeding pollen germination or pollen tube growth in the pistil.
programmes. Production of unisexual flowers.
1
SHORT NOTES
Parts of flower Female Gametophyte/Embryo Sac
All flowering plants show sexual reproduction. Ovules generally differentiate a single megaspore mother cell
A complete flower consists of calyx, corolla, androecium and (MMC) in micropylar region of nucellus.
gynoecium. In majority of flowering plants, one megaspore remains
Androecium is the male reproductive structure that consists functional and 3 degenerate. The functional megaspore
of a whorl of stamens. develops in to the female gametophyte (embryo sac).
Gynoecium is the female reproductive structure that consists The typical angiosperm embryo sac (female gametophyte)
of a whorl of carples (pistils). possess 8-nucleate and 7-celled condition at maturity.
Each pistil has three parts. Pollination
Stigma: Landing platform for pollen grains. Pollination is the transfer of pollen grain from anther to the
Ovary: Basal bulged part of pistil, has ovarian cavity stigma of the same flower (self pollination) or of different
(locule). Placenta is located inside ovarian caviity. flower (cross pollination) of the same species.
A typical stamen is composed of filament and anther. Self pollination is of two types i.e, autogamy and geitonogomy.
Filament: It is a long slender stalk. The proximal end of Autogamy can be promoted by cleistogamy.
the filament is attached to the thalamus or the petal of the Xenogomy (cross pollination) is the only type of pollination
flower. which brings genetically different types of pollen grains on
Anther is terminal and generally bilobed structure and the stigma.
each lobe having two theca i.e., they are dithecous. Geitonogamy functionally similar to cross pollination and
The anther is a four-sided (tetragonal) structure consisting of genetically it is similar to autogamy (self pollination).
four microsporangia located at the corners two in each lobe. Wind and water are common abiotic pollinating agents.
The microsporangia develop further & become pollen sacs. Wind Pollination requires light, non-stickly pollen so
They extend longitudinally all through the length of an anther that they can be transported by wind currents. Well exposed
and are packed with pollen grains. stamens and large often feathery stigma to trap air borne
pollen, single ovule in each ovary and numerous flowers in
Structure of Microsporangium an inflorescence.
A typical microsporangium near circular, which is generally In majority of aquatic plants like water hyacinth and water lily,
surrounded by four wall layers. flowers emerge above water & are pollinated by insects or wind.
The outer 3 wall layers perform the function of protection In most water-pollinated species, pollen grains are protected
and help in dehiscence of anther to release the pollen. The from wetting by a mucilaginous covering.
innermost wall layer tapetum nourishes the developing pollen Insect-pollinating flowers are large, colourful, fragrant
grains. and rich in nectar.
Microsporogenesis is a process of formation of microspores Nectar & pollen grains are usual floral rewards.
from PMC (Pollen Mother Cell). In some species, floral rewards are in providing safe places to
lay eggs, eg, Amorphophallus. A species of moth and Yucca
Pollen Grain cannot complete their life cycles without each other.
It represents the male gametophyte.
Outbreeding Devices
It has prominent two layered wall-exine and intine.
Flowering plants have developed many out breeding devices
The outer layer exine is made up of sporopollenin and the to discourage self pollination and to encourage cross
intine is made up of pectin and cellulose. pollination. For example:
Pollen grains of many species causes severe allergies. Pollen release and stigma receptivity are not synchronised.
Pollen grains are rich in nutrients. Anther and stigma are placed at different positions so that
Pollen variability: depends on both temperature and pollen cannot come in contact with stigma of the same flower.
humidity. Self-incompatibility is a genetic mechanism which
Pollen of a large number of species can be stored for years in prevents self-pollen from fertilizing the ovules by inhibiting
liquid nitrogen (–196°C) in pollen banks for crop breeding pollen germination or pollen tube growth in the pistil.
programmes. Production of unisexual flowers.
1
