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

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

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.

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

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

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

Individual members of the perianth are called tepals.

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

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

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

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

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.

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.

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

Transfer of pollen grains through water is known as 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.

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.

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 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.

The process of fruit formation without fertilisation is called parthenocarpy.

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.

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.

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 seed contains the future plant or embryo, which develops into a seedling under appropriate conditions. This process 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.

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.

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

• Sexual reproduction involves the formation and fusion of male and female gametes (amphimixis) to form a zygote, with gamete formation by meiosis.
• It occurs in two phases: juvenile phase (no reproduction) and reproductive phase (sex organs active), regulated by hormones.
• It includes three main events: pre-fertilisation (gamete formation and transfer), fertilisation (fusion of gametes), and post-fertilisation (zygote and embryogenesis).
• Sexual reproduction produces genetic variation due to meiosis, recombination, and fertilisation, which is important for evolution.
• Primary sex organs (testes, ovaries) produce gametes, and organisms may be seasonal or continuous breeders depending on the reproduction pattern.

• 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).

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• Fruit: Develops from the mature ovary after fertilisation and contains seeds.
• Parthenocarpic fruit: Formed without fertilisation, usually seedless (e.g., banana).
• Structure: Fruit consists of pericarp (wall) and seeds; pericarp may be dry or fleshy.
• Pericarp layers: In fleshy fruits, it is divided into epicarp (outer), mesocarp (middle), and endocarp (inner).
• Drupe fruit: Develops from a monocarpellary superior ovary, usually one-seeded (e.g., mango, coconut).
• Types of fruits: True fruits develop from the ovary (mango, coconut); false fruits develop from other floral parts (apple, strawberry, pineapple).

• 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.

• Based on cotyledons, Seeds are classified into dicot (two cotyledons) and monocot (one cotyledon).
• Based on endosperm: Seeds are albuminous (endospermic) or exalbuminous (non-endospermic).
• Albuminous seeds: Endosperm persists and provides nutrition; cotyledons are thin (common in monocots).
• Exalbuminous seeds: Endosperm is used during development; cotyledons become thick and store food (common in dicots).
• Perisperm: In some seeds, remnants of the nucellus persist, forming perisperm (e.g., black pepper, beet).

• 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.

• 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

• 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.