NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants
| Textbook | NCERT |
| class | Class – 12th |
| Subject | Biology |
| Chapter | Chapter – 2 |
| Chapter Name | Sexual Reproduction in Flowering Plants |
| Category | Class 12th Biology Notes |
| Medium | English |
| Source | last doubt |
NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants Notes asexual reproduction, sexual reproduction, discuss Sexual Reproduction in Flowering Plants Notes
NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants
Chapter – 2
Sexual Reproduction in Flowering Plants
Notes
Reproduction is the process of continuous production of offsprings. It is an important way of multiplication and perpetuation of species.
Modes of reproduction in plants can be broadly classified into two groups:
- asexual reproduction,
- sexual reproduction.
Asexual reproduction or Apomixis only takes place with a single parent. It does not involve the formation of sex organs, meiosis and fusion of gametes.
Regeneration of a whole new plant from vegetative parts of the plant is called vegetative reproduction. Its unique features of plants and can be natural or induced.
Runners, rhizomes, bulbs, corns and tubers are means of propagation.
Cutting, layering, grafting and micropropagation are artificial means of vegetative propagation. These are used for commer¬cially important plants.
A population of genetically identical plants derived from an individual is called a clone.
Plants that have lost the capacity to produce seeds e.g. banana, reproduce vegetatively.
Grafting is the technique used to improve the varieties of plants.
The flower and floral parts are the organs of sexual reproduction in angiosperms.
Sexual reproduction involves meiosis and the fusion of gametes.
The flower is a modified shoot with whorls of reproductive leaves – sepals, petals, stamens and carpels. Stamen and carpel are essential floral parts; sepals and petals are non-essential floral parts.
The calyx is the whorl of sepals. It is green in colour and protects the other parts of the bud. It prevents rapid transpiration.
Corolla is the whorl of petals. It is generally coloured, attractive and fragrant. It helps in pollination by attracting pollinators.
The androecium is the whorl of stamens. Stamen is made up of filament and anther. Anthers are bilobed and contain microsporangia (pollensac). Microsporangia produce a large number of pollen grains.
Gynoecium or pistil is the whorl of carpels. It consists of ovary, style and stigma.
Flowers that contain both stamen and pistil are called bisexual or hermaphrodite.
Stigma receives pollen grains, style provides the way to the ovary, the ovary is basal swollen part of gynoecium which contains ovules.
The ovule is an integument megasporangium where meiosis occurs and a megaspore is formed. It develops into an 8 nuclei embryosac.
Placentation is the manner in which the placenta is distributed. In the placenta, ovules are suspended.
The 8 nuclei of the monosporic embryo sac (e.g.Polygonum) are arranged such that a mature female gametophyte or embryosac contains: Two synergids, a single egg, a single secondary nucleus(2n) and three antipodals.,
Mature pollen grains are liberated from dehisced anthers. They are at a two-celled stage. The exine of pollen grains is made up of sporopollenin.
Pollination is the transfer of pollen grains to the stigma of the flower.
When the pollen grains are transferred from another to the stigma of the same flower it is called self-pollination. It occurs by autogamy and geitonogamy.
When pollen grains are transferred from the anther to the stigma of the flower of another plant it is termed cross-pollination. It takes place by the wind, water, insects, animals, bats and birds.
Allogamy represents cross-pollination where genetic recombination is ensured.
The pollen grains deposited on the stigma, after mutual recognition, absorb water and germinate and form a pollen tube.
Pollen tube traverses through stigma and style and reaches the ovary. It enters the ovule through micropyle, enters into embryo sac and releases two male gametes.
Siphonogamy is the carrying of male gametes to the egg through a pollen tube. It occurs in angiosperms.
Angiosperms exhibit double fertilization.
During fertilization, one male gamete fuses with the egg to form a diploid zygote in embryosac.
Second male gamete fuses with two polar nuclei to give rise to triploid primary endosperm nucleus inside embryosac.
After the process of fertilization, the ovule develops into a seed. The diploid zygote develops an embryo and the triploid primary endosperm nucleus forms an endosperm.
The ovary matures into a fruit.
The size, shape and colours of fruits and seeds vary enormously.
In a mature seed, the reserve food material is stored for embryo development and sustenance. In non-endospermic seeds, seeds are stored in cotyledons and in endospermic seeds, seeds are stored in endosperm.
The integuments of the ovule are transformed into seed coats.
All seeds have certain common features: an embryo, stored food and protective coverings.
Seeds are the principal means of the perpetuation of the species.
The embryo is differentiated into radicle, plumule and cotyledons. Dicot embryos have two cotyledons and monocot embryos have single terminal cotyledon.
A true fruit derived from the ovary consists of seeds and a pericarp. The pericarp is three layered-epicarp, mesocarp and endocarp.
Seed may remain dormant for some time before germination and growing into a new plant.
Amphimixis – The normal sexual reproduction is called
amphimixis – It involves meiosis and the fusion of haploid gametes.
Apomixis – It is the substitution of usual sexual reproduction which does not involve meiosis and syngamy.
Autogamy – Autõgamy results when a flower is pollinated by its own pollen.
Apogamy – It is the phenomenon in which an embryo is formed from any cell of embryosac (except egg) without fertilization.
Automixis – It is the fusion of nuclei derived both from the same zygote and from the same meiosis.
Aleurone layer – It is a layer of aleurone grains (protein grains) present on the outer surface of seeds and of maizë etc.
Coleoptile – The covering sheath of plumule in monocots.
Coleorhiza – The protective sheath of radicle in monocots.
Callus – The mass of undifferentiated cells formed in a culture medium.
Gootee – The process of air layering practised in lichi, promo- gran dates.
Grafting – Process of combining characters -of two related plants having vascular cambium.
Monogamy – The process of entry of pollen tube into ovule through integuments for fertilization.
Non-recurrent apomixis – The kind of apomixis in which the haploid egg or any other cell of haploid embryo sac develops an embryo without fertilization.
Polliniurn – Pollen grains contained in a pollen sac remain united in a single grain mass called pollinium.
Placentation – Arrangement and distribution of placenta within the ovary.
ParthenogeneSis – The kind of uniparental sexual reproduction in which an embryo is formed from an unfertilized egg.
PolyembryoflY – The phenomenon of formation of more than one embryo per ovule.
Pseudogamy – The phenomenon where pollination is needed for the development of apomictic embryò.
Scutellum – Single cotyledon of maize grain.
Siphonogamy – The process of carrying male gametes in the vicinity of female gamete by pollen tube.
Tapetum – The nutritive layer of cells around pollen sacs in anther.
Vivipary – The germination of seed within fruit while still attached to parent wall.
Viability – The ability of seeds to retain the power of germination.