Revision: Reproduction >> Sexual Reproduction in Flowering Plants Biology Science (English Medium) Class 12 CBSE

A circular arrangement of floral organs at the same level on the thalamus is called a whorl.

The swollen terminal part of the pedicel on which all floral whorls are arranged is called the thalamus or receptacle.

When calyx and corolla are not differentiated, the floral envelope is called the perianth.

Individual members of the perianth are called tepals.

A modified, compressed reproductive shoot of angiosperms bearing sepals, petals, stamens, and carpels, meant for sexual reproduction, is called a flower.

When microspores of a tetrad do not separate and remain attached together in groups, they are called compound pollen grains.

A compact mass formed when all microspores within a pollen sac remain united as a single structure is called a pollinium.

The process of formation of microspores from the sporogenous tissue is said to be microsporogenesis.

The region where the exine is absent and through which the pollen tube emerges is called a germ pore.

The protective wall or covering of a pollen grain is called the sporoderm.

A yellowish, sticky, oily substance covering the exine of insect-pollinated pollen grains is called pollenkitt.

The study of external morphology of mature pollen grain is called palynology.

The structure in flowering plants that develops into a seed after fertilization is called the ovule.

Transfer of pollen grains from the anther to the stigma of a flower is called pollination.

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Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower or of another flower of usually the same species.

When pollen grains from the anther are transferred to the stigma of the same flower, it is known as autogamy.

When pollens of a flower pollinate any other flower present on the same plant, it is said to be geitonogamy

Xenogamy is the transfer of pollen grains from the anther of one plant to the stigma of another plant of the same species, resulting in genetic variation.

Ornithophily is bird pollination, where the pollen grains of the flower are distributed by specialised birds for pollination. They usually have small sizes and long beaks e.g. Sun birds and humming birds. Some ornithophilous plants are Bombax, Callistemon (Bottle Brush), Butea, etc.

Transfer of pollen grains through wind is known as anemophily.

When pollination of flowers occurs at the surface of water, it is called epi-hydrophily. 

When pollination of flowers occurs below water, it is said to be hypo-hydrophily.

Transfer of pollen grains through water is known as hydrophily.

Pollination in which pollen grains are transferred from the anther to the stigma with the help of animals such as insects, birds, bats and other animals.

The recognition and acceptance or rejection of pollen by the pistil, from pollen deposition on the stigma to pollen tube entry into the ovule, is called pollen–pistil interaction.

The controlled crossing of selected male and female parent plants to produce genetically superior offspring is called artificial hybridization.

Union of the second male gamete with two polar nuclei to form endosperm, along with fertilization, is called double fertilization.

The process in which a zygote undergoes meiosis to form haploid spores in some algae and fungi is called zygotic meiosis.

All events occurring after fertilization and formation of the zygote during sexual reproduction are called post-fertilization events.

The process by which the embryo present in the seed develops into a seedling under appropriate conditions is called germination.

The process by which the zygote develops into an embryo through mitotic divisions and cell differentiation is called embryogenesis.

Endosperm is a nutritive tissue formed after fertilisation in flowering plants. It is usually triploid and provides food to the developing embryo.

The embryo is the young developing plant formed from the zygote after fertilisation. It develops at the micropylar end of the embryo sac.

Seed is defined as a fertilized mature ovule which possesses an inactive embryo and reserve food for its further development.

Apomixis is the production of seeds without fertilisation and is a form of asexual reproduction that mimics sexual reproduction.

Presence of more than one embryo within a single seed is called polyembryony.

Apomixis is a type of asexual reproduction that mimics sexual reproduction, i.e., the production of seeds without pollination and fertilization.

• A typical anther is dithecous, having two anther lobes, each with two microsporangia containing pollen grains.
• Archesporial cells divide to form primary parietal layers (anther wall) and primary sporogenous tissue.
• The anther wall consists of epidermis, endothecium, middle layers, and tapetum; the tapetum provides nutrition to developing pollen.
• Microspore mother cells (2n) undergo meiosis to form four haploid microspore.
• During anther dehiscence, contraction of endothecium causes rupture at the stomium, releasing pollen grains for pollination.

• Pollen grains act as male gametophytes and are usually spherical, measuring about 25–50 μm in diameter.
• Each pollen grain has a two-layered wall (sporoderm) consisting of a thick outer exine and a thin inner intine.
• The exine contains sporopollenin, which makes pollen grains highly resistant and helps in their fossil preservation.
• Germ pores are present where the exine is absent; dicots usually have three pores, while monocots have one pore.
• The intine protrudes through the germ pore during germination to form the pollen tube.
• In insect-pollinated plants, pollen grains are coated with pollenkitt, which aids in insect attraction and pollination.
• Pollen viability varies widely, lasting minutes in cereals and months in some dicots; pollen can be preserved at –196°C in pollen banks.
• After release, the pollen grain divides into a vegetative cell and a generative cell, and the generative cell later forms two male gametes.

• The ovule consists of a central nucellus surrounded by one or two integuments that provide protection.
• Based on integuments, ovules are unitegmic, bitegmic, or ategmic, depending on the number present.
• The integuments enclose the nucellus leaving a small opening at the apex called the micropyle.
• The ovule is attached to the placenta by a stalk called the funicle; the point of attachment is the hilum, and the basal region is the chalaza.
• During development, the ovule arises from the placenta, and integuments grow around the nucellus to form the mature ovule.

• The functional megaspore enlarges and forms the female gametophyte (embryo sac) by mitotic divisions.
• The megaspore nucleus divides to form eight nuclei, arranged in a definite pattern inside the embryo sac.
• Three nuclei form the egg apparatus at the micropylar end, three form antipodals at the chalazal end, and two polar nuclei fuse to form a diploid secondary nucleus.
• The mature Polygonum-type embryo sac is monosporic, 8-nucleate but 7-celled, and is the most common type in angiosperms.

• Seed is the fertilised ovule and final product of sexual reproduction in angiosperms.
• It consists of seed coat, cotyledons and embryo axis; food is stored mainly in cotyledons or endosperm.
• Seeds may be albuminous (endosperm present) or non-albuminous (endosperm absent); perisperm may persist in some seeds.
• Dormancy and dehydration help seeds survive adverse conditions and allow long-term storage.
• Seeds ensure dispersal, protection, nourishment of embryo, genetic variation and agricultural sustainability.