Sexual Reproduction in Flowering Plants

NCERT Line-by-Line Breakdown for NEET 2026

1. Pre-Fertilization: Stamen, Microsporangium & Pollen

A. Stamen & Microsporangium

The stamen consists of the Filament (long and slender stalk) and the Anther (terminal, generally bilobed). The proximal end of the filament is attached to the thalamus or petal of the flower.

Wall Layers of Microsporangium:

• Epidermis, Endothecium, Middle Layers: Outer three layers perform protection and help in dehiscence of anther to release pollen.
• Tapetum: Innermost layer. Nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus (multinucleate/polyploid).

B. Microsporogenesis & Pollen Grain

The process of formation of microspores from a Pollen Mother Cell (PMC) through meiosis is called Microsporogenesis. The microspores are arranged in a cluster of four cells (Microspore Tetrad).

When mature, the pollen grain contains two cells:
1. Vegetative Cell: Bigger, has abundant food reserve and a large irregularly shaped nucleus.
2. Generative Cell: Small and floats in the cytoplasm of the vegetative cell. Spindle-shaped with dense cytoplasm.

*In over 60% of angiosperms, pollen grains are shed at this 2-celled stage.

2. Pre-Fertilization: Pistil, Megasporangium & Embryo Sac

Gynoecium represents the female reproductive part. May be monocarpellary or multicarpellary (syncarpous/apocarpous). Pistil has three parts: Stigma, Style, and Ovary.

The Megasporangium (Ovule)

• Funicle: Stalk attaching ovule to placenta.
• Hilum: Junction between ovule and funicle.
• Integuments: Protective envelopes.
• Micropyle: Small opening at the tip where integuments are absent.
• Chalaza: Basal part of the ovule (opposite to micropyle).
• Nucellus: Mass of cells enclosed within integuments, having abundant reserve food materials.

Megasporogenesis & Embryo Sac

Process of formation of megaspores from the Megaspore Mother Cell (MMC). MMC undergoes meiosis to form 4 megaspores. Three degenerate, and only one remains functional.

• Micropylar End: Egg Apparatus (1 Egg cell + 2 Synergids). Synergids have Filiform apparatus to guide pollen tube.
• Chalazal End: 3 Antipodal cells.
• Center: Large Central Cell containing 2 Polar Nuclei.

3. Pollination & Outbreeding Devices

Transfer of pollen grains to the stigma of a pistil.

Agents of Pollination

• Wind (Anemophily): Pollen are light, non-sticky. Well-exposed stamens, large feathery stigma. Often single ovule per ovary. Examples: Grasses, Corn cob.
• Water (Hydrophily): Rare (about 30 genera, mostly monocots). Examples: Vallisneria, Hydrilla, Zostera (marine seagrass). Pollen protected by mucilaginous covering.
• Animals (Entomophily/Ornithophily): Majority of flowering plants. Flowers are large, colorful, fragrant, and rich in nectar.

Outbreeding Devices & Pollen-Pistil Interaction

Continuous self-pollination leads to inbreeding depression. Devices to prevent it: Dichogamy (unsynchronized release), Herkogamy (different positions), Self-incompatibility (genetic mechanism), and production of Unisexual flowers.

Pollen-Pistil Interaction: A dynamic process involving pollen recognition followed by promotion or inhibition of the pollen. Chemical dialogues occur between pollen and pistil.

4. Double Fertilization

A unique event strictly found in Angiosperms.

1. Syngamy: One male gamete (n) fuses with the Egg cell (n) → forms Zygote (2n). Develops into embryo.
2. Triple Fusion: The other male gamete (n) fuses with the two polar nuclei (n+n) in the central cell → forms Primary Endosperm Nucleus (PEN) (3n). Develops into endosperm.

Since two types of fusions (syngamy and triple fusion) take place in an embryo sac, the phenomenon is termed Double Fertilization.

5. Post-Fertilization Events

A. Endosperm

Endosperm development precedes embryo development. Why? To provide assured nutrition to the developing embryo.
Most common type is Free-nuclear endosperm (e.g., coconut water is free-nuclear endosperm, white kernel is cellular endosperm).

B. Embryo

Develops at the micropylar end. Stages: Proembryo → Globular → Heart-shaped → Mature embryo.

• Dicot Embryo: Embryonal axis and two cotyledons. Portion above cotyledons is Epicotyl (terminates in Plumule); below is Hypocotyl (terminates in Radicle).
• Monocot Embryo: Only one cotyledon called Scutellum (situated laterally). Shoot apex is enclosed in Coleoptile; Root cap is enclosed in Coleorhiza.

C. Seed & Fruit

Seed: Fertilized ovule. Contains seed coat, cotyledon(s), and an embryo axis. Can be Albuminous (retains endosperm, e.g., Wheat) or Non-albuminous (endosperm consumed, e.g., Pea). Residual nucellus is called Perisperm (e.g., Black pepper, Beet).

Fruit: Ripened ovary. Wall of ovary becomes fruit wall (Pericarp).
• True fruits: Develop only from ovary (Mango).
• False fruits: Thalamus contributes to fruit formation (Apple, Strawberry, Cashew).
• Parthenocarpic fruits: Develop without fertilization. Seedless (Banana).

6. Apomixis and Polyembryony

• Apomixis: Form of asexual reproduction that mimics sexual reproduction. It is the production of seeds without fertilization. (Found in some species of Asteraceae and grasses). Important for the hybrid seed industry to prevent segregation of traits.
• Polyembryony: Occurrence of more than one embryo in a seed. Often caused by nucellar cells dividing and protruding into the embryo sac (e.g., Citrus, Mango).

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