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

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

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

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.

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 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.
• Xenogamy is the process of transferring the pollen grains from anther to the stigma of a different plant.

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.

Transfer of pollen grains through water is known as hydrophily.

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

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

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 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.

• Flower: A modified shoot and the reproductive unit of angiosperms.
• Structure: Consists of four whorls—calyx, corolla (accessory), androecium, and gynoecium (reproductive).
• Types by sex: Flowers may be unisexual (male/female) or bisexual (both present).
• Symmetry: Actinomorphic (radial), zygomorphic (bilateral), or asymmetric.
• Based on floral parts: Flowers can be trimerous, tetramerous, or pentamerous depending on the number of parts.
• Position of ovary: Hypogynous (superior), perigynous (half inferior), epigynous (inferior).

• Flower formation begins before it is visible, triggered by hormonal and structural changes.
• These changes lead to the development of the floral primordium (early stage of flower).
• An inflorescence is formed, which bears floral buds and later develops into flowers.
• In the flower, reproductive parts differentiate into an anther (male) and a gynoecium (female).
• Androecium (stamens) is the male organ, while gynoecium is the female reproductive organ.

• A typical anther is dithecous and tetrasporangiate, having two lobes, each with two microsporangia (pollen sacs).
• Microsporangia contain sporogenous tissue, which develops into microspore mother cells that form pollen grains.
• The anther wall has four layers: epidermis, endothecium, middle layers, and tapetum.
• The tapetum provides nutrition to developing pollen, and microspore mother cells undergo meiosis to form haploid microspores.
• During anther dehiscence, the endothecium helps in rupture at the stomium, releasing pollen grains for pollination.

• Microsporogenesis is the process in which pollen mother cells (PMC) undergo meiosis to form haploid microspores (pollen grains).
• Each PMC divides meiotically to produce a tetrad of four haploid microspores.
• Microspores separate at maturity and develop into pollen grains.
• A pollen grain has a two-layered wall called sporoderm: outer exine and inner intine.
• Exine is made of sporopollenin, a tough and resistant substance, and contains germ pores for pollen tube growth.
• Intine is the inner layer made of cellulose and pectin.
• Pollen viability (ability to germinate) depends on temperature and humidity; it is short (about 30 minutes) in crops like rice and wheat but can last for months in some plant families.

• 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 is an integumented megasporangium present inside the ovary and is attached to the placenta by a stalk called the funicle.
• The nucellus is the central part containing reserve food, surrounded by one or two integuments for protection.
• The integuments leave a small opening called the micropyle at the apex, while the basal region is called the chalaza, and the attachment point is the hilum.
• The ovule is commonly anatropous, and contains an embryo sac (female gametophyte) with structures like egg cell, synergids, and polar nuclei.
• During development, the ovule arises from the placenta, and integuments grow around the nucellus to form a mature ovule.

• Meaning - Autogamy is the transfer of pollen grains from anther to the stigma of the same flower.
• Conditions for Autogamy - Requires synchrony in pollen release, stigma receptivity, and anthers & stigma close to each other.
• Complete Autogamy is Rare - In flowers where anthers and stigma are open and exposed, complete autogamy rarely occurs.
• Chasmogamous Flowers - Flowers that open normally with exposed anthers and stigma (e.g., Viola, Oxalis, Commelina).
• Cleistogamous Flowers - Flowers that never open; anthers and stigma lie close together, ensuring assured autogamy without pollinators (e.g., Viola, Oxalis, Commelina).

• Geitonogamy is the transfer of pollen from anther to the stigma of another flower on the same plant.
• It is functionally cross-pollination because it involves a pollinating agent.
• It is genetically similar to self-pollination (autogamy) since pollen comes from the same plant.
• Thus, it shows features of both self and cross-pollination.

• Pollination agents are of two types: abiotic (wind, water) and biotic (animals).
• Most plants use biotic agents, while only a few rely on wind and water.
• In abiotic pollination, pollen reaches the stigma by chance, so plants produce large amounts of pollen.
• Common animal pollinators include insects (especially bees), birds, bats and other animals.
• Flowers adapt to attract animals → bright colours, fragrance, nectar and large size.
• Animals transfer pollen while collecting nectar or pollen, helping in pollination.
• Some plants show special relationships with pollinators (e.g., insects laying eggs in flowers in return for pollination).

• Meaning - Anemophily is pollination by wind; more common among abiotic pollinations (e.g., grasses, corn cob).
• Pollen Characteristics - Pollen grains are light and non-sticky, so they can be easily carried by wind currents.
• Floral Structure - Flowers have well-exposed stamens for easy pollen dispersal and a large, feathery stigma to trap airborne pollen.
• Ovule & Inflorescence - Each ovary has a single ovule; flowers are numerous and packed into an inflorescence (e.g., corn cob/tassels).
• Colour & Nectar - Flowers are not colourful and do not produce nectar (no need to attract insects).
• Pollination Efficiency - Produces large amounts of pollen to compensate for the chance factor of pollen reaching the stigma.

• Meaning - Hydrophily is pollination by water; rare in flowering plants, limited to about 30 genera, mostly monocotyledons (e.g., Vallisneria, Hydrilla, Zostera).
• Pollen Characteristics - Pollen grains are long and ribbon-like; protected from wetting by a mucilaginous covering.
• Vallisneria Mechanism - Female flower reaches the water surface via a long stalk; male flowers/pollen are released onto the surface and carried passively by water currents.
• Seagrasses Mechanism - Female flowers remain submerged; pollen grains are released inside the water (e.g., Zostera).
• Water Hyacinth & Water Lily - Flowers emerge above water level and are pollinated by insects or wind, not water.
• Colour & Nectar - Flowers are not colourful and do not produce nectar; produce large amounts of pollen due to the chance factor of reaching the stigma.

• Zoophily (animal pollination) involves animals like insects (bees, butterflies), birds and bats transferring pollen.
• Bees are the most important pollinators among all animals.
• Flowers attract animals using bright colours, fragrance and nectar.
• Pollen sticks to the animal’s body and gets transferred to another flower’s stigma, causing pollination.
• Insect-pollinated flowers are usually large, colourful, fragrant, nectar-rich and have sticky pollen grains.

• Pollen-pistil interaction is the series of events from pollen landing on the stigma to fertilisation.
• The pistil recognises compatible pollen and rejects incompatible or foreign pollen using specific proteins.
• Compatible pollen germinates on the stigma and forms a pollen tube by absorbing nutrients.
• The pollen tube grows through the style and reaches the ovule, entering through a synergid in the embryo sac.
• The pollen tube releases male gametes, enabling fertilisation and seed formation.

• Artificial hybridisation is used in crop improvement to combine desirable traits of different plants.
• It ensures that only selected (desired) pollen is used for pollination.
• Emasculation → removal of anthers from bisexual flowers before they release pollen.
• Bagging → covering the flower to prevent unwanted pollen contamination.
• When stigma becomes receptive, desired pollen is applied, and the flower is rebagged for fruit development.

• Endosperm is a nutritive tissue formed from the triploid primary endosperm nucleus (PEN) after fertilisation.
• The PEN undergoes repeated mitotic divisions, and the embryo and endosperm develop simultaneously inside the ovule.
• Other cells of the embryo sac degenerate, while endosperm formation provides nourishment to the developing embryo.
• Nuclear type is the most common; divisions occur without wall formation initially, forming free nuclei, and walls develop later.
• Cellular type shows immediate wall formation after each division, making it cellular from the beginning.
• Helobial type is intermediate; first division forms two unequal cells (micropylar and chalazal), followed by nuclear divisions and later wall formation.

• Embryogenesis is the process of development of the zygote into an embryo, which begins after fertilisation and some endosperm formation.
• The embryo develops at the micropylar end of the embryo sac.
• The zygote divides to form a two-celled proembryo: a terminal (embryonal) cell and a basal (suspensor) cell.
• The suspensor pushes the developing embryo into the endosperm and helps in nutrient supply, while the embryonal cell forms the main embryo.
• The embryo passes through stages like the octant and heart-shaped stage, forming structures such as cotyledons, plumule, radicle, and hypocotyl.
• In monocots, a single cotyledon (scutellum) is present with protective sheaths, the coleoptile (plumule) and coleorhiza (radicle), while in dicots, two cotyledons are formed.

• 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.

• Polyembryony is the formation of more than one embryo in a single seed, leading to multiple seedlings.
• It was first observed by Leeuwenhoek in Citrus (orange) seeds.
• Polyembryony can occur due to development from the zygote or other tissues like the nucellus and integuments.
• Types include true polyembryony (embryos in the same embryo sac) and false polyembryony (embryos in different embryo sacs).
• Cleavage polyembryony occurs when the zygote splits into many parts, while adventive polyembryony occurs from nucellus or integument cells.
• It is important in horticulture and increases chances of survival by producing multiple seedlings.