In double fertilisation, the triploid primary endosperm nucleus is formed by the fusion of one male gamete with:

The two polar nuclei of the central cell

Maize and castor are albuminous seeds because they:

Retain the endosperm as a food store in the mature seed

Consume the endosperm completely during development

Lack an endosperm from the start

Sexual Reproduction in Flowering Plants — the Flower, Double Fertilisation and the Seed

This is one of the highest-yielding NEET chapters, and it rewards learning the development of the two gametophytes — the male in the anther, the female in the ovule — as parallel stories, then meeting them at double fertilisation, an event unique to flowering plants. The single most examined fact is what double fertilisation produces: one sperm makes the zygote (2n), the other makes the endosperm (3n), and this triploid endosperm is a flowering-plant signature. Around this centre sit the counts (how many cells and nuclei in the pollen grain and embryo sac), and special cases like apomixis and polyembryony that examiners love. Keep the male and female tracks side by side and the ploidy numbers stop being a jumble.

The Two Gametophytes

Male and female development, side by side
Stage	Male (in anther)	Female (in ovule)
Mother cell	Microspore mother cell (2n)	Megaspore mother cell (2n)
After meiosis	4 microspores; all survive	4 megaspores; usually only 1 survives
Gametophyte	Pollen grain — 2 cells (vegetative + generative)	Embryo sac — 7 cells, 8 nuclei

ℹ️ The 7-cell, 8-nucleus embryo sac — count it once and never forget

The mature embryo sac (female gametophyte) is a favourite counting question, and the numbers only look odd until you place them. It has eight nuclei but only seven cells, because one cell — the large central cell — contains two nuclei (the polar nuclei), while every other structure is single-nucleate. The arrangement is: at the micropylar end an egg apparatus of three cells (one egg + two synergids); at the chalazal end three antipodal cells; and in the middle the one central cell with two polar nuclei. Three plus three is six single-nucleate cells, plus the one central cell makes seven cells, and the two polar nuclei bring the nucleus count to eight. Fixing "7 cells, 8 nuclei" and the reason for the mismatch answers a whole family of questions, including which cell the second sperm fuses with (the central cell) and why the endosperm ends up triploid.

Pollination and Double Fertilisation

Pollination is the transfer of pollen to the stigma. Autogamy is self-pollination within a flower; geitonogamy is between two flowers of the same plant (genetically still self); xenogamy is between different plants (the only genuinely cross type).
After landing, the pollen grain germinates and its pollen tube grows down the style, guided by the synergids, and enters the ovule usually through the micropyle (porogamy). The two male gametes are discharged into the embryo sac.
Then the defining event: one male gamete fuses with the egg → zygote (2n) (syngamy), and the other fuses with the two polar nuclei → primary endosperm nucleus (3n) (triple fusion). Two fusions, hence double fertilisation.

🎯 Why double fertilisation is worth calling a landmark

Almost every animal, and most other plants, fertilises with a single fusion — one sperm, one egg, one zygote. Flowering plants do something no other group does: both male gametes are used, in two separate fusions, and this is why the event is singled out as a landmark of angiosperms. The pay-off is the endosperm. Rather than stocking the seed with food in advance — expensive if the ovule is never fertilised — the plant waits until fertilisation is assured, then triggers endosperm formation at the same moment as the zygote. The endosperm is nutritive tissue that feeds the developing embryo, and because it forms from one sperm plus two polar nuclei it is triploid (3n) — a ploidy you will not find in the animal body and a reliable giveaway that a tissue is angiosperm endosperm. So the "extra" fertilisation is not redundancy but an economical coupling of food supply to successful fertilisation, and the triploid endosperm is the fingerprint it leaves behind.

Seed, Fruit and Special Cases

After fertilisation the ovule → seed and the ovary → fruit. The zygote grows into the embryo, and the seed coat forms from the ovule's integuments. A fruit formed without fertilisation is a parthenocarpic (seedless) fruit.
Seeds are albuminous (endosperm persists — maize, castor, wheat) or non-albuminous (endosperm used up during development — pea, bean, groundnut). This persist-or-not distinction is directly examined.
Apomixis is seed formation without fertilisation (an asexual seed, genetically identical to the parent — useful in hybrid seed technology). Polyembryony is more than one embryo in a seed, as in many citrus fruits.

⚠️ Match each fruit/seed part to the floral part it came from

A whole class of questions gives you a mature structure and asks which floral part produced it, and the mapping is fixed: ovary → fruit, ovule → seed, zygote → embryo, primary endosperm nucleus → endosperm, integuments → seed coat, outer ovary wall → pericarp. The trap is that the numbers of things do not change through the transformation — the ploidy of a part is set at fertilisation and carried forward — so the embryo stays 2n and the endosperm stays 3n right through into the seed. A second, subtler trap: in some fruits the thalamus (not the ovary) swells to form the edible part — a false fruit, the apple being the standard example — so "the edible part develops from the ovary" is not always true. Learning the source-of-each-part table forwards and backwards is what turns these into free marks.

Key takeaways

Male gametophyte = pollen grain (2 cells); female gametophyte = embryo sac (7 cells, 8 nuclei).
Embryo sac: 3 antipodals + 1 central cell (2 polar nuclei) + egg apparatus (1 egg + 2 synergids) = 7 cells, 8 nuclei.
Double fertilisation: sperm + egg → zygote (2n); sperm + 2 polar nuclei → endosperm (3n). Unique to flowering plants.
The 3n endosperm is nutritive tissue for the embryo and a signature of angiosperms.
Autogamy (within a flower) and geitonogamy (same plant) are self; xenogamy (different plants) is true cross-pollination.
Ovary → fruit, ovule → seed, zygote → embryo, integuments → seed coat; a false fruit (apple) develops from the thalamus.
Albuminous seeds keep the endosperm (maize, castor); non-albuminous use it up (pea, groundnut).
Apomixis = seed without fertilisation (clone of parent); polyembryony = many embryos in one seed (citrus).

Practice questions (8)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

In double fertilisation, the triploid primary endosperm nucleus is formed by the fusion of one male gamete with:
1. The two polar nuclei of the central cell
2. The egg cell
3. The two synergids
4. The three antipodal cells
Show answer
Answer: A — The two polar nuclei of the central cell
One sperm fuses with the two polar nuclei of the central cell, giving a 3n primary endosperm nucleus (triple fusion). The other sperm fuses with the egg to make the 2n zygote, so choosing the egg here describes syngamy, not the endosperm-forming fusion.
A mature embryo sac of a typical flowering plant has:
1. 7 cells and 8 nuclei
2. 8 cells and 8 nuclei
3. 7 cells and 7 nuclei
4. 4 cells and 8 nuclei
Show answer
Answer: A — 7 cells and 8 nuclei
The central cell holds two polar nuclei while all six other cells are single-nucleate, giving 7 cells but 8 nuclei. The "8 cells" option forgets that the two polar nuclei share one cell, which is exactly the point the count tests.
Double fertilisation is considered a characteristic feature of:
1. Angiosperms (flowering plants)
2. Gymnosperms
3. Pteridophytes
4. Bryophytes
Show answer
Answer: A — Angiosperms (flowering plants)
Only flowering plants perform double fertilisation, using both male gametes to make a zygote and a triploid endosperm. Gymnosperms and the other groups fertilise with a single fusion and lack the triploid endosperm, so they cannot show this event.
Transfer of pollen from an anther to the stigma of a different flower on the same plant is called:
1. Geitonogamy
2. Xenogamy
3. Autogamy
4. Apomixis
Show answer
Answer: A — Geitonogamy
Between two flowers of the same plant is geitonogamy — genetically still self-pollination, since both flowers share one genotype. Autogamy is within a single flower and xenogamy is between different plants, so those describe the narrower and the truly cross cases respectively.
After fertilisation, the ovule and the ovary develop respectively into the:
1. Seed and fruit
2. Fruit and seed
3. Embryo and endosperm
4. Seed coat and pericarp
Show answer
Answer: A — Seed and fruit
The ovule becomes the seed and the ovary becomes the fruit — reversing them, as the second option does, is the standard mistake. The embryo and endosperm form inside the seed from the zygote and the primary endosperm nucleus, so they are parts of the seed rather than the whole ovule and ovary.
Formation of a seed without fertilisation, producing an offspring genetically identical to the parent, is called:
1. Apomixis
2. Polyembryony
3. Parthenocarpy
4. Syngamy
Show answer
Answer: A — Apomixis
Apomixis produces a seed asexually, so the offspring is a clone of the parent — valuable for keeping hybrid vigour in seed technology. Polyembryony is many embryos in one seed and parthenocarpy is a seedless fruit, so neither describes a fertilisation-free seed that clones the parent.
The pollen tube usually enters the ovule through the micropyle. This mode of entry is called:
1. Porogamy
2. Chalazogamy
3. Mesogamy
4. Geitonogamy
Show answer
Answer: A — Porogamy
Entry through the micropyle is porogamy, the usual route. Chalazogamy is entry through the chalaza and mesogamy through the integuments — both are exceptions — while geitonogamy is a type of pollination, not a route of pollen-tube entry.
Maize and castor are albuminous seeds because they:
1. Retain the endosperm as a food store in the mature seed
2. Consume the endosperm completely during development
3. Lack an endosperm from the start
4. Form two embryos each
Show answer
Answer: A — Retain the endosperm as a food store in the mature seed
Albuminous (endospermic) seeds such as maize, castor and wheat keep the endosperm as a nutritive reserve in the mature seed. Non-albuminous seeds such as pea and groundnut use the endosperm up during development, which is the contrast the second option describes.