Revision: Reproduction >> Sexual Reproduction in Flowering Plants Biology (Theory) ISC (Science) ISC Class 12 CISCE

A mode of reproduction involving the fusion of male and female gametes (sperm and egg) to form a zygote that develops into a new organism.

The period of growth and development before an organism becomes sexually mature is called the juvenile phase.

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.

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.

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

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

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

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

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

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

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

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.

or

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 pollination occurs within the same flower or between two flowers on the same plant, it is called self-pollination.

or

Transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant is said to be self~pollination.

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

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

When pollination occurs between flowers on two different plants of the same species, it is called cross-pollination.

or

Transfer of pollen grains from the anther of a flower from one plant to the stigma of the flower on another plant is called cross-pollination

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

Transfer of pollen grains through wind is known as anemophily.

Transfer of pollen grains through water is known as hydrophily.

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 the agency of insects is known as entomophily.

Transfer of pollen grains by birds is known as ornithophily.

Transfer of pollen grains by bats is known as chiropteriphily.

Transfer of pollen grains by snails and slugs is known as malacophily.

The fusion of the germ-cells (male and female) to form a zygote is called fertilisation.

or

The process in which male and female gametes fuse to form a diploid zygote is called fertilization. The actual union of the male and female gametes during fertilization is called syngamy.

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

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.

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

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

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

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

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

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

It is the condition in which fruit is developed without the process of fertilization. It occurs naturally in some varieties of Pineapple, Banana, Papaya, etc.

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

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

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

Seed germination is the process by which the embryo within the seed becomes active and grows into a new plant under favourable conditions.

The process by which the dormant embryo of the seed resumes active growth and forms a seedling is known as germination.

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

An embryo is the early stage of development of an organism after fertilization, when the zygote starts dividing and differentiating into tissues and organs.

Fusion of one male gamete with the egg and the other with the polar nuclei in angiosperms is called double fertilization.

The process of development of mature embryo from diploid zygote is called embryogenesis.

The fruits which develop without fertilization are called parthenocarpic fruits and this phenomenon is described as parthenocarpy.

• Sexual reproduction involves the formation and fusion of male and female gametes to form a zygote, which develops into a new organism.
• It is a slow, complex, and energy-expensive process, but it results in offspring that are genetically different from parents and from each other.
• Genetic variation arises due to meiosis, DNA recombination, and fertilisation, which is essential for evolution and natural selection.
• To maintain chromosome number, haploid gametes are formed by meiosis and fuse during fertilisation.
• Organisms must pass through a juvenile (vegetative) phase before entering the reproductive phase, which is regulated by hormones.
• Sexual maturity is marked by puberty in animals and flowering in plants; plants may be monocarpic or polycarpic.
• Based on breeding time, animals are classified as seasonal breeders or continuous breeders.

• 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.

• Pollen germination begins when a pollen grain lands on a receptive stigma, absorbs water, and forms a pollen tube using nutrients from stigmatic fluid.
• Pollen tube growth occurs through the stigma and style, with elongation restricted to the tip, carrying the male gametes toward the ovule.
• Enzymatic action of cutinase helps the pollen tube penetrate the stigma, and its path depends on whether the style is hollow or solid.

• 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.

• After fertilization, the ovule develops into a seed, the integuments form the seed coat, and the endosperm may be absorbed or persist as food material.
• The ovary develops into a fruit, and the ovary wall forms the pericarp, making the fruit a ripened ovary.
• During seed formation, structures like synergids and antipodals degenerate, while the zygote forms the embryo and the secondary nucleus develops into endosperm.

• In angiosperms, a seed is a mature fertilized ovule containing an embryo, stored food, and a protective seed coat.
• After fertilization, the zygote forms the embryo, the endosperm nucleus forms endosperm, and integuments develop into seed coats.
• Seeds show great variation in size, shape, and structure, and may bear special features like hilum, funicle, and aril.
• Seeds ensure plant survival and dispersal, provide genetic variation, and are a major source of human food and agricultural products.

• The zygote divides transversely into an apical cell and a basal cell, which further divide to form the pro-embryo.
• Cells derived from the apical region form the single cotyledon and embryonal axis, while basal derivatives contribute to the root cap and periblem.
• Monocot embryos possess one cotyledon, called the scutellum, positioned laterally on the embryonal axis.
• The radicle and root cap are enclosed by coleorhiza, and the epicotyl with shoot apex is protected by coleoptile.

A. Based on Number of Cotyledons