This chapter traces the full sexual reproduction cycle in flowering plants, from the structure of the flower and the development of pollen grains and the embryo sac to pollination, double fertilisation, and the formation of seeds and fruits. It is one of the highest-yield Botany chapters for NEET, packed with frequently tested facts like the 7-celled, 8-nucleate embryo sac and triple fusion, so a clear grasp of every stage directly converts into marks.
Class 12 Botany – swipe through all 8 cards to understand the whole chapter.
Flower as a Reproductive Unit
A flower is a modified shoot with four whorls stacked on the thalamus.
Determinate growth; ‘perfect’ = bisexual; ‘complete’ = all 4 whorls present.
- Accessory whorls: calyx (sepals) + corolla (petals)
- Essential whorls: androecium (stamens, male) + gynoecium/pistil (carpels, female)
- Stamen = filament + anther; carpel = stigma + style + ovary
Anther & Microsporogenesis
Each anther is dithecous and tetrasporangiate, raising pollen in four microsporangia.
Tapetum nourishes pollen; endothecium aids dehiscence. 1 MMC → 4 pollen grains.
- MMC undergoes meiosis → microspore tetrad (4 haploid microspores)
- Tapetum = innermost nutritive layer; often multinucleate
- Pollen count = MMCs × 4 (per microsporangium)
Pollen: The Male Gametophyte
A mature pollen grain has a tough two-layered wall and, usually, two cells.
~60% shed at 2-celled stage; rest 3-celled. Germ pores = thin exine spots.
- 2-celled: large vegetative cell + small generative cell
- Generative cell divides → two male gametes (3-celled)
- Parthenium pollen causes allergy/asthma
Ovule (Megasporangium)
The ovule is the cradle inside the ovary where the embryo sac forms.
Micropyle = the doorway; nucellus = nutritive tissue.
- MMC meiosis → 4 megaspores; 3 degenerate, 1 functional (monosporic)
- Hilum = funicle-ovule junction; chalaza is the basal region
- Polygonum-type development from a single functional megaspore
Embryo Sac (Female Gametophyte)
Three free-nuclear mitoses of the functional megaspore build the embryo sac.
Single most-asked fact: 7 cells, 8 nuclei — never write 8-celled.
- Micropylar end: egg apparatus = 1 egg + 2 synergids (filiform apparatus)
- Chalazal end: 3 antipodal cells
- Centre: 1 central cell with 2 polar nuclei
Pollination & Outbreeding
Pollination transfers pollen from anther to stigma; it precedes fertilisation.
Anemophily = light dry pollen + feathery stigma; hydrophily = Vallisneria, Zostera.
- Outbreeding devices: dichogamy, herkogamy, self-incompatibility, dioecy
- Geitonogamy needs an agent but is genetically self-pollination
- Cleistogamy guarantees autogamy (flowers never open)
Double Fertilisation
Unique to angiosperms: both male gametes are used, none wasted.
Discovered by Nawaschin. Triple fusion = 3 nuclei → endosperm is 3n (triploid).
- Syngamy: 1 male gamete + egg → zygote (2n) → embryo
- Triple fusion: 1 male gamete + 2 polar nuclei → PEN (3n) → endosperm
- Male gametes released into a synergid, not directly into the egg
Seed, Fruit & Apomixis
The ovule becomes the seed and the ovary becomes the fruit.
Albuminous (wheat, maize, castor) retain endosperm; non-albuminous (pea, bean) consume it.
- Integuments → testa + tegmen; perisperm = persistent nucellus (black pepper, beet)
- True fruit (ovary only) vs false fruit (thalamus, e.g. apple); parthenocarpy = seedless (banana)
- Apomixis = seed without meiosis/fertilisation → clones; polyembryony = many embryos (Citrus)
📝 Practice Sexual Reproduction in Flowering Plants — 10 NEET PYQs
Real previous-year questions · with answers & solutions
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Related Chapters in Class 12 Biology
- Reproduction in Organisms Class 12 Notes
- Human Reproduction Class 12 Notes
- Reproductive Health Class 12 Notes
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Frequently Asked Questions
Double fertilisation is the two fusion events that happen inside the embryo sac: syngamy, where one male gamete fuses with the egg to form the diploid zygote, and triple fusion, where the second male gamete fuses with the two polar nuclei to form the triploid primary endosperm nucleus. It is unique to angiosperms because both male gametes are used and none is wasted, and it was discovered by Nawaschin.
A typical mature embryo sac is 7-celled and 8-nucleate. It has an egg apparatus of one egg and two synergids at the micropylar end, three antipodal cells at the chalazal end, and one central cell with two polar nuclei, so you should never write 8-celled.
Yes, it is a very high-weightage chapter in the NEET Botany section and questions from it appear almost every year. Double fertilisation, embryo sac structure, microsporogenesis and outbreeding devices are repeatedly asked, so it is among the must-prepare chapters.
Geitonogamy is the transfer of pollen from the anther to the stigma of another flower on the same plant, so although it needs a pollinating agent it is genetically the same as self-pollination. Xenogamy is the transfer of pollen to the stigma of a flower on a different plant, which is true cross-pollination bringing genetically different pollen.
The endosperm is triploid because it forms from the primary endosperm nucleus, which is the product of triple fusion. One haploid male gamete fuses with the two haploid polar nuclei of the central cell, giving a 3n nucleus that then divides to build the nutritive endosperm tissue.