RBSE Class 12 Biology Notes Chapter 2 Sexual Reproduction in Flowering Plants

These comprehensive RBSE Class 12 Biology Notes Chapter 2 Sexual Reproduction in Flowering Plants will give a brief overview of all the concepts.

RBSE Class 12 Biology Chapter 2 Notes Sexual Reproduction in Flowering Plants

→ Flower is modified shoot having whorls of floral leaves, sepals, petals, stamens and carpels. The sepals and petals are non-essential parts whereas stamens and carpels are essential parts.

→ Collectively the sepals are called calyx and petals are called corolla. These both are non-essential parts of flower. Whereas stamens and carpel are essential parts.

→ Sexual reproduction involves some events, 

• Pre-fertilization events i.e., development of pollen grains, development of ovules and pollination.
• Fertilization and
• Post fertilization events i.e., development of embryo and endosperm and formation of fruit and seed.

→ Stamens are the male reproductive organs of flower. They collectively form the male whorl or androecium. They also called microsporophylls.

→ Each stamen has three parts:

1. Filament,
2. Anther and
3. Connective.

→ Majority of plants have dithecous anthers i.e., anthers are bilobed having two pollen chambers in each lobe. But in some plants monothecous anthers are also found (single lobe, two pollen chamber).

→ The pollen chambers represent microsporangia.

→ In a transverse section a typical microsporangium appears circular in outline. Its wall has four layers:

1. Epidermis, 
2. Endothecium, 
3. Middle layer and
4. Tapetum.

→ Formation of microspores or pollen grains from the pollen mother cell (PMC) or sporogenous tissue occurs inside microsporangia and is called microsporogenesis.

→ Pollen grains are male gametophytes. Each pollen grain represents the first cell of male gametophyte.

→ In mature pollen grain, two cells i.e., vegetative cell and generative cell are found at the time of liberation.

→ Gynoecium (megasporophyll) represents female reproductive part of the flower.

→ The gynoecium may consist of single carpel, two carpels, three carpels or many carpels.

→ Each carpel or pistil has three parts:

1. ovary, lower swollen part,
2. style, a tube like part above ovary and
3. Stigma, the tip of styla.

→ The ovary bears ovule. The ovule represent the megasporangium. Each ovule has an embryosac.
 
→ the process of formation of megaspores from the megaspore mother cell (MMC) is called megasporogenesis.

→ The fully developed female gametophyte or embryo sac is an oval and multicellular haploid structure. It is embedded in the nucellus towards micropylar end.

→ A mature monosporic polygonum type of embryo sac is 7- celled and 8-nucleated structure at the time of fertilization. It has 3-cells at the micropyler end, A single central cell with two polar nuclei and three antipodal cells.

→ Pollination is the transfer of pollen grains from anther to the stigma.

→ Pollination is classified into two types: Self-pollination and cross-pollination.

→ Self pollination involves of pollen grains from anthers to stigma of the same form or of another flower borne on the same plant.

→ Cross pollination is the transfer of pollen grains from anther of one flower to the stigma of another flower borne on a different plant of same species.

→ Cross pollination is performed with the help of an external agency. These agencies may be anemophily, hydrophily entomophily, ornithophily, chiropterophily or malacophily.

→ The pollen grains deposited on the stigma absorb water and nutrients. As a result pollen grain germinates to produce pollen tube. Only one pollen tube reaches the ovule and release two male gametes inside the embryo sac.

→ In angiosperms fertilization involves two process-syngamy and triple fusion. Hence, it is called double fertilization.

→ Syngamy is the fusion of one of the two malegametes with the egg nucleus to form a diploid zygote.

→ Triple fusion involves fusion of second male gamete with the secondary nucleus (2n) forming a triploid nucleus called the primary endosperm nucleus.

→ the diploid zygote represents the first cell of the sporophytic generation. By continuous mitotic divisions, it develops into the embryo. The triploid primary endosperm nucleus forms the endosperm for naurishment of the embryo.

→ The ovule after fertilization, change into seeds and ovary forms the fruit.

→ In a mature seed, the reserve food material may be stored in the cotyledons or in endosperm, the integuments of ovule are transformed into seed coats.

→ The embryo formed from zygote, is differentiated into radicle, plumule and cotyledons. The embryo of dicots possesses two cotyledons whereas those of monocots possesses single terminal cotyledon.

→ The fruits vary in their size, shape and colour. A true fruit derived from ovary consists of seeds and pericarp. The pericarp consists of three layers-epicarp, mesocarp and endocarp.

→ The life cycle of angiosperm is completed by the germination of seeds.

→ Flower: Modified shoot of angiosperms which bear sexual parts.

→ Calyx s Outer whorl of flower consists of green sepals.

→ Corolla: Second whorl of flower consists of coloured petals.

→ Androecium: The male reproductive whorl formed of stamens.

→ Gynoecium: the female reproductive whorl formed of carpels.

→ Sexual reproduction: Formation and fusion of male and female gametes to form new individual, is called sexual reproduction.

→ Stamen s Male reproductive organ of a flower.

→ Anther s The swollen bilobed structure at the terminal end of a filament of stamen.

→ Pollen chamber: A chamber present in anther which has pollen grains.

→ Microsporangium: The pollen chamber represents microsporangium.

→ Sporogenous cell: The cell of cellular mass inside very young anther, which produces microspores, is called sporogenous cell.

→ Tapetum: Inner most layer of microsporangium.

→ Microsporogenesis: Formation of microspores or pollen grains from the pollen mother cell.

→ Pollen grain: Male gametophyte which has a vegetative cell and a generative cell.

→ Pollinium: When all the pollen grains of a sporangium form a single mass called pollinium.

→ Sporoderm s The wall or covering of the pollen grain is called sporoderm.

→ Exine: Outer layer at wall of pollen grain.

→ Intine: Inner layer of wall of pollen grain.

→ Pollen bank: Collection of pollen grains of a large number of species in liquid nitrogen at -196°C.

→ Gamete s Haploid reproductive structure having male or female haploid nucleus.

→ Gynoecium: Female reproductive part of a flower.

→ Apocarpous: If the carpels are free, such condition is called apocarpous.
 
→ Syncarpous: If the carpels are united, such condition is called syncarpous.

→ Ovary: The basal swollen part of the carpel which bears ovule.

→ Style: Long, tubular part above the ovary is called style.

→ Stigma: A button like structure at the apex of style is called stigma.

→ Ovule: Ovule represent the megasporangium, where female gametophyte is developed.

→ Nucellus: The main body of an ovule is composed of parenchymatous cells, this tissue is called nucellus.

→ Integuments: Nucellus is surrounded by one or two cellular coats called integuments.

→ Funide: The structure which attaches ovule with placenta.

→ Micropyle: A pore formed by integuments.

→ Embryosac: The chamber, inside the ovule having egg apparatus, antipodals and secondary nucleus.

→ Egg apparatus: Haploid structure consists of one egg cell and two synergids.

→ Polar nuclei s The nuclei coming from micropylar and chalazal end and combine to form secondary nucleus.

→ Antipodols: The group of three cells lies at chalazal end inside embryo sac.

→ Megasporogenesis: The process of formation of megaspore from megaspore mother cell is called megasporogenesis.

→ Pollination: The process of the transfer of pollens from anther to stigma is called pollination.

→ Autogamy: Transfer of pollens from anther to stigma in same flower.

→ Cleistogamy: Pollination process in flowers which never blossom.

→ Geitonogamy: Transfer of pollen grains from anther of a flower to stigma of another-flower borne on same plant.

→ Xenogamy: Cross pollination is also called xenogamy.

→ Protandry: When anthers mature earlier in a bisexual flower.

→ Protogyny: When stigmas mature earlier in a bisexual flower.

→ Anemophlly: Pollination by wind.

→ Hydrophily: Pollination by water.

→ Entomophily: Pollination by birds.

→ Chiropterophily: Pollination by bats.

→ Fertilization: Fusion of male and famel gametes is called fertilization. 

→ Zygote s The diploid structure produced by fusion of male and female gametes.

→ Endosperm J A structure produced by fusion of a male gamete with secondary nucleus, which provides nourishment to developing embryo.

→ Embryo: A very young plant inside seed having, plumule radicle and cotyledons.

→ Seed: A compact structure developed from ovule after fertilization and embryogenesis.

→ Fruit: Mature and ripened ovary is called fruit.

→ Apomixis: The development of reproductive propagules without meiosis and syngamy is called apomixis.

→ Polyembryony: The phenomenon of development of more than one embryo in a seed is called polyembryony.