CBSE Class 12 Biology: Reproduction in Flowering Plants — Notes 2026

Flower Structure and Functions

• Calyx (sepals): outermost; protects developing flower bud; chlorophyll; photosynthesis in some species
• Corolla (petals): attract pollinators (colour, scent, nectar); in some flowers fused into tube
• Androecium (stamens): anther (pollen grains) + filament; gynoecium (carpel): stigma + style + ovary

Microsporogenesis and Male Gametophyte

• Pollen grain develops in anther; microsporocyte (2n) → meiosis → 4 microspores (n) → pollen grains
• Pollen grain structure: exine (outer, sporopollenin — extremely resistant) + intine (inner, cellulose)
• Male gametophyte: pollen germinates → pollen tube; tube cell + generative cell (→ 2 male gametes)

Megasporogenesis and Female Gametophyte

• Megasporocyte (2n) in ovule → meiosis → 4 megaspores; 3 degenerate; 1 functional
• Functional megaspore → 3 mitotic divisions → 8-nucleate cell → embryo sac (female gametophyte)
• 7-celled embryo sac: egg cell + 2 synergids (at micropyle end); 3 antipodals (chalazal end); 2 polar nuclei (central cell)

Pollination

• Self-pollination (autogamy): same flower; cleistogamous flowers (Viola, Oxalis) forced self-pollination
• Cross-pollination: different plants; agents — insects (entomophily), wind (anemophily), water (hydrophily)
• Adaptations: colourful petals + nectar (insect); light dry pollen + dangling anthers (wind); sticky pollen (insect)

Double Fertilisation

• Pollen tube enters ovule through micropyle; releases 2 male gametes into embryo sac
• Syngamy: male gamete 1 + egg cell → zygote (2n); Triple fusion: male gamete 2 + 2 polar nuclei → primary endosperm nucleus (3n)
• Double fertilisation unique to angiosperms; ensures endosperm develops only when egg is fertilised

Seed and Fruit Development

• Zygote → embryo (via embryogenesis); endosperm nucleus → endosperm (food reserve)
• Ovary wall → fruit (pericarp); ovule → seed; cotyledons absorb endosperm in monocots (e.g., maize)
• Parthenocarpy: fruit without fertilisation (banana, seedless grapes); induced by gibberellins or auxins

CBSE Board Focus

• Reproduction in plants: 5–7 marks; double fertilisation mechanism, embryo sac structure, pollination types
• Draw and label: T.S. anther, embryo sac (all 7 cells), pollen grain
• Parthenocarpy and apomixis: define; give examples; compare with normal reproduction