Pocket Notes — Sexual Reproduction in Flowering Plants
Key definitions
- Microsporogenesis — MMC → microspores by meiosis.
- Megasporogenesis — MMC → 4 megaspores; 1 functional.
- Syngamy — male gamete + egg → zygote (2n).
- Triple fusion — male gamete + 2 polar nuclei → PEN (3n).
- Double fertilisation — syngamy + triple fusion (unique to angiosperms).
- Apomixis — asexual seed formation.
- Parthenocarpy — seedless fruit without fertilisation.
- Polyembryony — >1 embryo per seed.
Numbers to remember
| Structure | Ploidy | Cells / Nuclei |
|---|---|---|
| MMC | 2n | 1 |
| Microspore tetrad | n each | 4 |
| Pollen grain (mature) | n | 2-celled (vegetative + generative) |
| Female gametophyte (embryo sac) | n | 7-celled, 8-nucleate |
| Zygote | 2n | 1 |
| PEN → endosperm | 3n | 1 |
Embryo sac layout
- Micropylar end: egg + 2 synergids (egg apparatus, with filiform apparatus)
- Middle: central cell + 2 polar nuclei
- Chalazal end: 3 antipodals
Pollen wall
- Exine — sporopollenin, most resistant biomolecule known, has germ pores
- Intine — cellulose + pectin
Pollen viability
- Rice, wheat: ~30 min
- Rosaceae, Solanaceae, Leguminosae: months
- Storage: liquid N₂ at −196°C (pollen banks)
Pollination types
- Autogamy — same flower
- Geitonogamy — different flower, same plant
- Xenogamy — different plant
Outbreeding devices (avoid self-pollination)
- Dichogamy (timing), heterostyly (height), self-incompatibility, dioecy
Fertilisation route
Compatible pollen → stigma → tube grows through style → enters ovule via micropyle (porogamy) → into embryo sac via synergid → releases 2 male gametes.
Post-fertilisation fates
- Ovule → seed · Ovary → fruit
- Integuments → seed coats · Nucellus → sometimes perisperm
- Endosperm nourishes embryo (persistent in monocots; often consumed in dicots).
Fruit types
- True fruit — ovary only
- False fruit — thalamus + ovary (apple, cashew, strawberry)
- Parthenocarpic — no fertilisation (banana)
Frequently asked
- Why is double fertilisation unique? — Two fusions in one embryo sac (syngamy + triple fusion), only in angiosperms.
- Why is endosperm triploid? — Formed from 1 male gamete + 2 polar nuclei = 3n.
- Which cell in pollen forms the tube? — Vegetative cell (larger).
- Which is more resistant, exine or intine? — Exine (sporopollenin, heat/enzyme/acid-resistant).