# Double Fertilisation in Flowering Plants

> Double fertilisation in angiosperms — pollen tube entry, syngamy, triple fusion, the triploid PEN and post-fertilisation changes for NEET-UG Biology.

- Canonical URL: https://prepelephant.com/topics/neet-ug/biology/double-fertilisation
- Exam / course: NEET-UG · Subject: Biology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Double Fertilisation in Flowering Plants", PrepElephant, https://prepelephant.com/topics/neet-ug/biology/double-fertilisation

## Direct answer

Angiosperms are unique in performing two fusions in one embryo sac, an event called double fertilisation. The pollen tube, carrying two male gametes, enters the embryo sac through a synergid guided by its filiform apparatus. One gamete fuses with the egg cell (syngamy) to form the diploid zygote, while the other fuses with the two polar nuclei of the central cell (triple fusion) to form the triploid primary endosperm nucleus (PEN).

## What you must remember

- **Pollen tube journey:** after pollination the pollen grain germinates on the stigma and the tube grows through the style and ovary toward the ovule, showing chemotropic growth.
- **Entry into the embryo sac:** the tube enters through one of the synergids, whose filiform apparatus at the micropylar end secretes chemical signals that guide it.
- **Syngamy:** fusion of one male gamete with the egg forming the diploid (2n) zygote, which develops into the embryo.
- **Triple fusion:** fusion of the second male gamete with the two polar nuclei forming the triploid (3n) primary endosperm nucleus, from which the nutritive endosperm develops — endosperm development usually precedes embryo development.
- **Post-fertilisation changes:** the ovule matures into the seed and the ovary into the fruit; integuments become the seed coat, the ovary wall becomes the pericarp, and the antipodal cells and synergids degenerate.
- **Apomixis:** formation of seeds without fertilisation, as in some Asteraceae and grasses; polyembryony, the development of more than one embryo per seed, is seen in Citrus — both are commercially important because hybrid seeds can then be retained year after year.

## Common confusion

The recurring confusion is between the two fusions and their ploidy: syngamy gives a diploid zygote, triple fusion gives a triploid primary endosperm nucleus — so the embryo is 2n and the endosperm 3n in the same seed. Students also muddle the embryo sac cells: synergids guide the pollen tube, antipodals are simply degenerate after fertilisation, and the egg cell sits between the two synergids at the micropylar end.

## Exam-focused takeaway

NEET-UG tests this topic with match-the-following between floral parts and their post-fertilisation fates (ovule-seed, ovary-fruit, integuments-seed coat) and with assertion-reason statements such as "the endosperm of angiosperms is triploid because it arises from triple fusion". Expect statement-based questions on the filiform apparatus, on apomixis and polyembryny in Citrus, and on the sequence of post-fertilisation events. Ploidy-based one-liners on the PEN appear almost every year.

## Frequently asked questions

### Why is fertilisation in angiosperms called double fertilisation?

Because two fusion events occur in one embryo sac — syngamy of one male gamete with the egg, and triple fusion of the other with the two polar nuclei.

### What is the ploidy of the primary endosperm nucleus?

Triploid (3n), formed by the fusion of one haploid male gamete with two haploid polar nuclei.

### Through which cell does the pollen tube enter the embryo sac?

Through one of the synergids, attracted by chemical signals from the filiform apparatus at the micropylar end.

### What changes occur in the flower after fertilisation?

The ovule becomes the seed, the ovary becomes the fruit, integuments harden into the seed coat, and floral parts other than the ovary generally wither and fall.

### What is apomixis?

Seed formation without fertilisation, seen in some Asteraceae and grasses; it allows farmers to reuse hybrid seeds because the maternal genotype is preserved.