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.

The pattern of ovule arrangement in the ovary is called placentation. 

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.

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 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.

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

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.

The female gametophyte of angiosperms is called the embryo sac. It is the haploid (n) structure inside the ovule that contains the egg cell and all supporting cells required for fertilisation and early seed development.

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

Biotic agents are living organisms, such as insects, birds, bats, and snails, that help transfer pollen grains from one flower to another, thereby assisting plant reproduction.

Abiotic agents are the non-living external means, namely wind and water, that bring about the transfer of pollen grains from one flower to another.

Transfer of pollen grains from the anther to the stigma 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 from the anther to the stigma 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 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.

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.

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.

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.

A state of metabolic inactivity in mature seeds where germination does not occur even under seemingly favourable conditions.

• Sexual reproduction involves the formation and fusion of male and female gametes (amphimixis) through meiotic division to create a diploid zygote.
• Life cycles progress from an initial juvenile phase focused purely on vegetative growth and development to a mature reproductive phase in which sex organs become functional.
• The reproductive process is strictly regulated by hormones and sequence-driven, consisting of three sequential stages: pre-fertilisation, fertilisation, and post-fertilisation.
• Pre-fertilisation focuses on gamete production and transfer, while post-fertilisation events track zygote development and the formation of embryonic structures.
• Meiotic cell division and cross-fertilisation blend parental genetic material, generating the vital variations needed to drive species adaptation and organic evolution.

• Angiosperms are flowering plants with sex organs in flowers and seeds enclosed within fruits, succeeding mainly through efficient sexual reproduction.
• Their life cycle shows alternation of generations - the diploid sporophytic phase (2n) from the zygote and the haploid gametophytic phase (n) from spores.
• They have a haplodiplontic life cycle in which the sporophyte is dominant and the gametophyte is highly reduced.
• Sporophytic phase (2n): starts from the zygote, includes the embryo, seedling, and flowering plant; dominant, long-lived, and produces spores by meiosis.
• Gametophytic phase (n): starts from spores, forms male and female gametophytes that produce gametes; microscopic, short-lived, and dependent on the sporophyte.

• 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.

• Entomophily is the transfer of pollen by insects like bees, butterflies, flies, beetles, and moths; e.g., rose, jasmine, salvia.
• Insects visit flowers for nectar or pollen and carry pollen from one flower to another, aiding pollination in many angiosperms.
• Entomophilous flowers are large, showy, brightly coloured, scented, with nectar glands; small flowers group into a conspicuous inflorescence.
• Their stigma is rough/sticky, and pollen is spiny or sticky (coated with pollenkit) to cling to insect bodies.
• Special patterns: night-blooming flowers like Cestrum nocturnum attract moths by strong scent; some produce foul odours to attract flies and beetles.
• Salvia has a lever mechanism that deposits pollen on an insect's body for transfer to another flower's stigma, promoting cross-pollination.

• Ornithophily is the transfer of pollen by birds like sunbirds and hummingbirds; e.g., bombax, callistemon, butea, erythrina, syzygium.
• Birds visit flowers to feed on nectar, and pollen sticks to their beak, head, or feathers and is carried to another flower.
• Touching the stigma of the next flower causes pollination, promoting cross-pollination and genetic variation.
• Ornithophilous flowers are bright (red, orange, yellow, blue), large, showy, and tubular, cup-, or urn-shaped to suit a bird's beak.
• They secrete abundant, dilute nectar, bear sticky pollen, and have reduced fragrance since birds rely on vision more than smell.

• Malacophily is the transfer of pollen by snails and slugs (molluscs); e.g., Chrysanthemum leucanthemum (land) and Lemna (aquatic).
• It is a type of animal-mediated pollination, much less common than by insects, wind, or birds.
• As a snail or slug crawls or feeds over a flower, pollen sticks to its body and is carried to another flower.
• On reaching the next flower, some pollen is deposited on the stigma, completing pollination.

• Fertilization is the fusion of male and female gametes to form a diploid zygote; the actual union of the gametes is called syngamy.
• In some organisms (rotifers, honeybees, and turkeys), the female gamete develops into a new organism without fertilization, which is called parthenogenesis.
• External fertilization occurs outside the body in water (algae, bony fishes, amphibians); many gametes are released, but offspring are vulnerable to predators.
• Internal fertilization occurs inside the female body (bryophytes to angiosperms; reptiles, birds, mammals); motile male gametes are produced in large numbers.
• In flowering plants, the embryo sac lies inside the ovule, so pollen on the stigma forms a pollen tube to carry the male gametes to it.

• 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.

• 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.

• The embryo is the young developing plant formed from the zygote after fertilisation, developing at the micropylar end of the embryo sac.
• A typical dicot embryo has an embryonal axis with two laterally attached cotyledons that store food and act as first seed-leaves.
• On the axis, the epicotyl (above cotyledons) ends in the plumule (shoot tip), and the hypocotyl (below) ends in the radicle (root tip), covered by a protective root cap.
• In Capsella bursa-pastoris, the zygote divides transversely into a larger basal cell (forms the suspensor) and a smaller terminal cell (forms the embryo proper).
• The basal cell forms a 6–10 celled suspensor; its first cell becomes a haustorium absorbing nutrients, and its lowermost cell (hypophysis) forms part of the radicle and root cap.
• The terminal cell forms the octant stage (8 cells: upper tier → plumule and cotyledons, lower tier → hypocotyl and radicle), then the dermatogen (future epidermis) at the globular stage.
• In the heart-shaped stage, two lobes grow into cotyledons; further growth curves the embryo through the torpedo stage into the mature horseshoe-shaped embryo, and the suspensor degenerates.

• In monocots (e.g., grasses), the embryo has a single cotyledon called the scutellum, set laterally on the embryonal axis; it is shield-shaped and absorbs nutrients from the endosperm.
• Two protective sheaths unique to monocots are present: the coleoptile encloses the shoot (plumule), and the coleorhiza surrounds the radicle and root cap.
• An epiblast (vestigial second cotyledon) lies opposite the scutellum; the radicle at the lower end forms the primary root, covered by a root cap.
• After double fertilisation, the zygote divides transversely into a small terminal cell (embryo proper) and a large basal cell (suspensor).
• The suspensor pushes the embryo into the endosperm to absorb nutrients; the terminal cell forms the plumule and the single massive scutellum.
• The scutellum grows fast, pushing the plumule sideways into a lateral depression on the axis.
• The coleoptile and coleorhiza then differentiate, giving a mature embryo with scutellum, laterally displaced plumule, radicle, epicotyl, and epiblast (if present).

• Parthenocarpy is the formation of fruit without fertilisation, giving seedless fruits called parthenocarpic or "virgin fruits" (Greek parthenos = virgin, karpos = fruit).
• These fruits lack embryo and endosperm, so no viable seeds are formed.
• In its mechanism, hormones like auxins, gibberellins, or cytokinins mimic the post-fertilisation environment, causing the ovary wall (pericarp) to divide and enlarge into a pulpy, seedless fruit.
• Natural (genetic) parthenocarpy occurs spontaneously without pollination, as in banana and pineapple.
• Environmental parthenocarpy is triggered by conditions like low temperature or frost, as in some pears in cold climates.
• Chemically induced (artificial) parthenocarpy results from spraying hormones on unpollinated flowers, as in tomato, seedless grapes, and citrus.

• 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.

• After double fertilisation, the flower shifts to a developmental phase: the ovule matures into a seed, and the ovary ripens into a fruit.
• A seed is a mature, fertilised ovule with an embryo enclosed in a protective seed coat and a food reserve (endosperm or cotyledons).
• The seed coat has a tough outer testa and a thin inner tegmen, both from the ovule's integuments.
• A typical seed also has the embryo (radicle, plumule, cotyledons), endosperm (3n food reserve), a micropyle for water and oxygen entry, and a hilum marking attachment.
• Albuminous seeds retain the endosperm for food storage, as in wheat, maize, castor, and coconut.
• Non-albuminous seeds absorb the endosperm fully and store food in cotyledons, as in pea, bean, and groundnut.
• A fruit is the ripened ovary; in fleshy fruits, the pericarp has three layers - epicarp (skin), mesocarp (fleshy/edible), and endocarp (hard or papery).
• Seeds protect and nourish the embryo and allow dormancy, dispersal, and genetic variation.
• Fruits protect and disperse seeds, store nutrients, and have commercial value as food and raw materials.

• 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).

• A seed is a fertilised, mature ovule with an embryo, stored food (endosperm), and a protective seed coat (outer testa, inner tegmen).
• The embryo consists of the radicle (→ root), plumule (→ shoot), embryonal axis, and cotyledons (one in monocots, two in dicots); endosperm is triploid (3n).
• Dicot seeds have two cotyledons and store food in them (pea, bean); monocot seeds have one cotyledon (scutellum), a bulky endosperm, and a coleoptile and coleorhiza (maize, wheat).
• Albuminous seeds retain the endosperm (wheat, castor); ex-albuminous seeds store food in cotyledons (pea, groundnut).
• The seed attaches by a funicle, leaving a hilum, with a micropyle above it for water entry.
• Seed dormancy is the failure of a viable seed to germinate even in favourable conditions; germination needs water, suitable temperature, and oxygen.
• True fruits form only from the ovary (mango); false fruits include other floral parts (apple); parthenocarpic fruits are seedless and form without fertilisation (banana).