Is it correct to say: Writing endosperm as diploid (2n)?

Endosperm is TRIPLOID (3n) — formed by fusion of one sperm (n) with two polar nuclei (n + n).

Is it correct to say: Calling the embryo sac '8-celled'?

It is 8-nucleate but 7-CELLED (egg + 2 synergids + 3 antipodals + 1 central cell with 2 polar nuclei).

Is it correct to say: Confusing microsporogenesis (meiosis) with microgametogenesis (mitosis)?

Sporogenesis = meiosis (2n → n); gametogenesis = mitosis within the gametophyte (n → n).

Is it correct to say: Treating parthenocarpy and apomixis as the same?

Parthenocarpy = fruit without fertilisation and without seeds (banana). Apomixis = seed without fertilisation (some grasses, Citrus).

Is it correct to say: Saying self-pollination is possible in dioecious plants?

Dioecious plants have male and female flowers on separate plants — self-pollination is impossible; only cross-pollination occurs.

Is it correct to say: Believing the pollen wall is made of cellulose?

Outer exine is made of sporopollenin (most resistant biopolymer known); inner intine is cellulose + pectin.

Sexual Reproduction in Flowering Plants

Flower structure, microsporogenesis, megasporogenesis, pollination, double fertilisation, embryo and seed development — NCERT Class 12 Biology Ch 1

📐 10 formulas✏️ 3 examples🎯 6 practice⚖️ 6-7 marks🏫 CBSE📚 Class 12✓ 2025–26 syllabus

💡

Board Exam Tips

→Draw a labelled diagram of the mature embryo sac (7-celled, 8-nucleate) — asked almost every year.
→Double fertilisation and triple fusion is a 3-mark question. Learn the ploidy of every product.
→Distinguish self-pollination vs cross-pollination and their adaptations (a favourite VSA/SA question).
→Never confuse endosperm (3n) with embryo (2n). Marks are lost every year on ploidy questions.
→Apomixis, polyembryony and parthenocarpy — three 'p' terms often mixed up. Remember exact definitions.

📐 Formulas(10)

Ploidy of Embryo Sac Cells★ Board fav

Egg = n, Synergids = n, Antipodals = n, Central cell = n + n = 2 n

Double Fertilisation (Syngamy)★ Board fav

n (sperm) + n (egg) \to 2 n (zygote)

Triple Fusion★ Board fav

n (sperm) + n (polar) + n (polar) \to 3 n (PEN)

Microsporogenesis Output

1 MMC (2 n) meiosis 4 microspores (n) \to 4 pollen grains

Megasporogenesis Output★ Board fav

1 MMC (2 n) meiosis 4 megaspores (n); 3 degenerate, 1 functional

Polygonum-type Embryo Sac

Functional megaspore 3 mitoses 8 nuclei \to 7 cells

Ploidy Ledger of the Seed★ Board fav

Embryo = 2 n, Endosperm = 3 n, Seed coat = 2 n, Perisperm (nucellus) = 2 n

Pollen Grain Composition

Mature pollen = 1 vegetative cell + 1 generative cell (n each)

Exine Composition

Exine = sporopollenin (highly resistant biopolymer)

Apomixis and Polyembryony

Apomixis: seed without fertilisation; Polyembryony: many embryos in one seed

✏️ Solved Examples

1Solved Exampleeasy3 steps

A pollen grain and the egg cell of the same flower are examined. State the ploidy of each and name the process that produced them.

Identify origin of the pollen grain

MMC (2 n) meiosis microspore (n)

2Solved Exampleboard4 steps

In the embryo sac of an angiosperm, one male gamete fuses with the egg while the other fuses with the two polar nuclei. Identify the two fusion events, name the products and give their ploidy. (3 marks)

Name the phenomenon

Double fertilisation (unique to angiosperms)

3Solved ExampleHOTS4 steps

A coconut fruit contains a hard stony endocarp, a white edible kernel and coconut water. Trace the botanical identity of each part and explain why the coconut water is multinucleate.

Classify the fruit

Coconut is a fibrous drupe

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Writing endosperm as diploid (2n)
✓Endosperm is TRIPLOID (3n) — formed by fusion of one sperm (n) with two polar nuclei (n + n).
2
Calling the embryo sac '8-celled'
✓It is 8-nucleate but 7-CELLED (egg + 2 synergids + 3 antipodals + 1 central cell with 2 polar nuclei).
3
Confusing microsporogenesis (meiosis) with microgametogenesis (mitosis)
✓Sporogenesis = meiosis (2n → n); gametogenesis = mitosis within the gametophyte (n → n).
4
Treating parthenocarpy and apomixis as the same
✓Parthenocarpy = fruit without fertilisation and without seeds (banana). Apomixis = seed without fertilisation (some grasses, Citrus).
5
Saying self-pollination is possible in dioecious plants
✓Dioecious plants have male and female flowers on separate plants — self-pollination is impossible; only cross-pollination occurs.
6
Believing the pollen wall is made of cellulose
✓Outer exine is made of sporopollenin (most resistant biopolymer known); inner intine is cellulose + pectin.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
Name the type of pollination in which pollen is transferred from anther to stigma of the same flower. Give one advantage and one disadvantage.
Q2
How many meiotic and mitotic divisions are required to form the mature embryo sac of an angiosperm starting from one megaspore mother cell?
Q3
State the ploidy of (i) nucellus, (ii) antipodal cells, (iii) primary endosperm nucleus, (iv) seed coat, (v) embryo.
Q4
Why is emasculation followed by bagging performed in hybridisation programmes?
Q5
Name any two devices developed by flowers to encourage cross-pollination.
Q6
In which part of the ovule does the female gametophyte develop and what is the type of embryo sac development called?

📝 Notes

Sexual Reproduction in Flowering Plants

NCERT Chapter 1 traces the sexual reproductive cycle of angiosperms — from the microscopic sporogenous tissue inside the anther, through pollination and double fertilisation, to the mature seed and fruit.

The flower is a modified shoot

Four whorls sit on a thalamus:

Calyx (sepals) and corolla (petals) — accessory whorls, protective and attractive.
Androecium (stamens) — male reproductive whorl. Each stamen = filament + anther. A typical dithecous anther has four microsporangia arranged in two lobes.
Gynoecium (carpels) — female reproductive whorl. Each carpel = ovary + style + stigma. The ovary encloses ovules containing the embryo sac.

Microsporogenesis to pollen

Diploid microspore mother cells inside each microsporangium undergo meiosis to yield tetrads of haploid microspores. Each microspore matures into a pollen grain with a hard exine of sporopollenin — a chemically-inert biopolymer that lets pollen survive fossilisation.

Megasporogenesis to embryo sac

Inside the ovule, the nucellus differentiates a single megaspore mother cell. Meiosis produces four megaspores; three degenerate. The chalazal (functional) megaspore undergoes three mitotic divisions, generating the classical 7-celled, 8-nucleate Polygonum-type embryo sac.

Pollination

Transfer of pollen from anther to stigma.

Autogamy — same flower.
Geitonogamy — different flower of the same plant (functionally cross, genetically self).
Xenogamy — different plant. Only this brings genetic variation.

Agents: wind (anemophily), water (hydrophily), insects (entomophily), birds and bats. Flowers show remarkable co-adaptations — long-tubed corolla for hummingbirds, sticky pollen for insects, feathery stigma for wind.

Double fertilisation — unique to angiosperms

The pollen tube discharges two male gametes into the embryo sac:

Syngamy: sperm (n) + egg (n) → zygote (2n) → embryo.
Triple fusion: sperm (n) + two polar nuclei (n + n) → primary endosperm nucleus (3n) → endosperm.

Both fusion events happen inside the same embryo sac, hence "double" fertilisation.

Post-fertilisation events

Zygote → embryo (dicot: two cotyledons, epicotyl, hypocotyl; monocot: single cotyledon called scutellum).
Primary endosperm nucleus → endosperm (nuclear → cellular → mature).
Ovule → seed; ovary → fruit; ovary wall → pericarp.
Integuments harden into seed coat (testa + tegmen).

Special cases worth memorising

Apomixis — seeds without fertilisation (many grasses). Useful in hybrid seed technology because progeny are clones of the mother.
Polyembryony — many embryos in one seed (Citrus, mango).
Parthenocarpy — fruit without fertilisation, seedless (banana, grapes).

Quick sanity checks

Every angiosperm seed has a triploid endosperm.
The pollen grain shed at anthesis is either 2-celled or 3-celled — never more.
If a plant is dioecious, cross-pollination is obligatory.