What is the primary difference between syngamy and triple fusion?

Syngamy, also known as generative fertilisation, is the fusion of one male gamete (haploid, $n$) with the egg cell (haploid, $n$), resulting in a diploid ($2n$) zygote. This zygote develops into the embryo. Triple fusion, or vegetative fertilisation, is the fusion of the second male gamete (haploid, $n$) with the two polar nuclei (each haploid, $n$, or a diploid secondary nucleus, $2n$) in the central cell, leading to the formation of a triploid ($3n$) primary endosperm nucleus (PEN). The key difference lies in the participating female nuclei and the ploidy and fate of the resulting structures.

Why is double fertilisation considered unique to angiosperms?

Double fertilisation is unique to angiosperms because no other group of plants exhibits this specific dual fusion event. While some gymnosperms show a form of 'double fertilisation' where one sperm nucleus fuses with the egg and another degenerates or fuses with a ventral canal cell without forming a viable structure, it does not lead to the formation of a nutritive triploid endosperm in the same coordinated manner as in angiosperms. The simultaneous formation of both the embryo and its dedicated triploid food source (endosperm) is an angiosperm innovation.

What is the ploidy level of the endosperm and why is it significant?

The endosperm is typically triploid ($3n$). This triploid nature arises from the fusion of one haploid male gamete ($n$) with two haploid polar nuclei ($n+n$). The significance of its triploidy is thought to be related to its vigorous growth and ability to accumulate abundant food reserves. A triploid tissue often exhibits hybrid vigour, which could lead to more efficient nutrient storage, ensuring a robust food supply for the developing diploid embryo. This coordinated development ensures that resources are only invested in the endosperm if a viable embryo is formed.

What happens to the synergids and antipodal cells after double fertilisation?

After double fertilisation, the synergids and antipodal cells typically degenerate. The synergids play a crucial role in guiding the pollen tube towards the egg cell and facilitating the release of male gametes. Once their function is served, they are no longer needed and undergo programmed cell death. Similarly, the antipodal cells, located at the chalazal end of the embryo sac, also degenerate. Their exact function is still debated, but they are thought to be involved in providing nourishment or absorbing nutrients for the embryo sac before fertilisation. Their degeneration after fertilisation indicates their transient role.

Can double fertilisation occur if the pollen grain is incompatible?

No, double fertilisation cannot occur if the pollen grain is incompatible. Plant species have evolved sophisticated mechanisms to prevent self-pollination or cross-pollination with incompatible species, known as pollen-pistil interaction. If the pollen is incompatible, it will either fail to germinate on the stigma, or the pollen tube will be inhibited from growing through the style, or it may even fail to enter the ovule. These mechanisms ensure that only genetically compatible pollen successfully reaches the embryo sac and participates in fertilisation, preventing the formation of non-viable seeds or hybrids.

Double Fertilisation

Biology

NEET UG

Version 1Updated 21 Mar 2026

Explore This Topic

Definition Deep Explanation Core Principles NEET Importance Problem Strategy Practice Problems MCQ Practice Quick Revision

Double fertilisation is a unique and defining characteristic of flowering plants (angiosperms), involving two distinct fusion events within the embryo sac. The first fusion, known as syngamy or generative fertilisation, occurs between one male gamete and the egg cell, leading to the formation of a diploid zygote. This zygote subsequently develops into the embryo. The second fusion, termed triple f…

Quick Summary

Double fertilisation is a hallmark process in flowering plants, involving two distinct fusion events within the embryo sac. It commences when a pollen grain germinates on the stigma, forming a pollen tube that carries two male gametes to the ovule.

Upon reaching the embryo sac, typically via a synergid, the pollen tube releases these gametes. The first fusion, called syngamy, involves one male gamete fusing with the egg cell to form a diploid ( $2n$ ) zygote, which develops into the embryo.

The second fusion, known as triple fusion, sees the other male gamete uniting with the two polar nuclei (or the secondary nucleus) in the central cell, resulting in a triploid ( $3n$ ) primary endosperm nucleus (PEN).

The PEN subsequently develops into the endosperm, a vital nutritive tissue for the growing embryo. This dual fertilisation ensures the simultaneous formation of both the new plant embryo and its dedicated food supply, a highly efficient evolutionary strategy unique to angiosperms.

Vyyuha

Your 6-Month Blueprint, Updated Nightly

AI analyses your progress every night. Wake up to a smarter plan. Every. Single.…

Key Concepts

Ploidy Levels in Double Fertilisation

Understanding the ploidy (number of sets of chromosomes) of different structures involved in double…

Role of Synergids and Filiform Apparatus

The synergids are two specialized cells located adjacent to the egg cell at the micropylar end of the embryo…

Endosperm Development and Types

The primary endosperm nucleus (PEN) undergoes repeated mitotic divisions to form the endosperm, which serves…

Double Fertilisation: — Unique to angiosperms, two fusion events.

Syngamy: — Male gamete (

n

) + Egg cell (

n

)

\rightarrow

Zygote (

2n

). Forms embryo.

Triple Fusion: — Male gamete (

n

) + Two polar nuclei (

n+n

)

\rightarrow

Primary Endosperm Nucleus (PEN) (

3n

). Forms endosperm.

Ploidy: — Male gamete (

n

), Egg (

n

), Zygote (

2n

), PEN (

3n

), Endosperm (

3n

Synergids: — Guide pollen tube via filiform apparatus, degenerate after gamete release.

Antipodals: — Degenerate, function unclear (possibly nutritive).

Products: — Zygote

\rightarrow

Embryo; PEN

\rightarrow

Endosperm; Ovule

\rightarrow

Seed; Ovary

\rightarrow

Fruit.

Significance: — Coordinated development of embryo and food source, efficient resource use.

To remember the ploidy levels: Egg is N (n), Male is N (n), Zygote is 2N, PEN is 3N, Endosperm is 3N. Think: 'E-N-M-N, Z-2N, P-3N, E-3N'. Or, for the fusions: 'Syngamy = Egg + Sperm = Zygote (2n), Triple = Polar + Sperm = Endosperm (3n)'. The 'Triple' in Triple Fusion directly reminds you of '3n'.