What is the primary difference between syngamy and triple fusion?

Syngamy is the fusion of one haploid male gamete (n) with the haploid egg cell (n) to form a diploid zygote (2n). This event is responsible for the formation of the embryo. Triple fusion, on the other hand, involves the fusion of the second haploid male gamete (n) with the diploid secondary nucleus (2n), which is formed by the fusion of two polar nuclei. This results in a triploid primary endosperm nucleus (3n), which develops into the endosperm, providing nourishment to the embryo. Both are essential parts of double fertilisation.

Why is it called 'double' fertilisation?

It is termed 'double' fertilisation because two distinct fusion events occur simultaneously within the embryo sac. The first fusion is syngamy, where one male gamete fuses with the egg cell. The second fusion is triple fusion, where the other male gamete fuses with the central cell's secondary nucleus. This dual event is unique to angiosperms and ensures the formation of both the embryo and its nutritive tissue, the endosperm, in a coordinated manner.

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

The endosperm is typically triploid (3n). This triploid nature arises from the triple fusion event (one male gamete (n) + two polar nuclei (n+n) = 3n). The endosperm serves as the primary nutritive tissue for the developing embryo. Its triploid nature is thought to provide a genetic advantage, potentially allowing for more robust growth and nutrient accumulation compared to a diploid tissue, ensuring efficient nourishment for the growing embryo.

What is the role of the synergids and the filiform apparatus in double fertilisation?

Synergids are two cells flanking the egg cell in the embryo sac. They play a crucial role in guiding the pollen tube towards the egg cell. The filiform apparatus, a finger-like projection within the synergids, helps in this guidance by secreting chemical substances (chemotropism) that attract the pollen tube. It also helps in the absorption of nutrients and facilitates the discharge of male gametes into the embryo sac. After the pollen tube enters, one or both synergids typically degenerate.

What happens to the antipodal cells after double fertilisation?

The antipodal cells are three cells located at the chalazal end of the embryo sac, opposite to the micropylar end where the egg apparatus is situated. Their precise function is not fully understood, but they are generally believed to provide nourishment to the embryo sac before fertilisation. However, after double fertilisation, the antipodal cells typically degenerate and disintegrate. They do not directly participate in the fusion events of fertilisation.

Can double fertilisation occur without pollination?

No, double fertilisation cannot occur without pollination. Pollination is the prerequisite step, involving the transfer of pollen grains from the anther to the stigma. Without successful pollination, the pollen grain cannot germinate, form a pollen tube, or deliver the male gametes to the embryo sac. Therefore, pollination is an essential precursor that initiates the sequence of events leading to double fertilisation.

Process of Double Fertilisation

Biology

NEET UG

Version 1Updated 21 Mar 2026

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Double fertilisation is a unique and defining characteristic of angiosperms (flowering plants), involving two distinct fusion events within the embryo sac. It commences with the germination of a pollen grain on the stigma, leading to the formation of a pollen tube that penetrates the ovule. This tube delivers two non-motile male gametes into the embryo sac. One male gamete fuses with the egg cell,…

Quick Summary

Double fertilisation is a unique reproductive process in flowering plants (angiosperms) involving two distinct fusion events. It begins with a pollen grain landing on the stigma and growing a pollen tube, which carries two male gametes into the embryo sac within the ovule.

The first fusion, called syngamy, occurs when one male gamete (haploid, n) fuses with the egg cell (haploid, n) to form a diploid zygote (2n), which develops into the embryo. The second fusion, known as triple fusion, involves the other male gamete (haploid, n) fusing with the diploid secondary nucleus (2n), formed by the fusion of two polar nuclei in the central cell.

This results in a triploid primary endosperm nucleus (3n), which develops into the endosperm, a nutritive tissue for the embryo. This dual fertilisation ensures the simultaneous formation of both the new plant embryo and its food supply, making it a highly efficient reproductive strategy.

Post-fertilisation, the ovule matures into a seed, and the ovary develops into a fruit.

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Key Concepts

Ploidy Levels in Double Fertilisation

Understanding the ploidy (number of sets of chromosomes) of different cells and nuclei involved is crucial.…

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…

Distinction between Endospermic and Non-Endospermic Seeds

The fate of the endosperm after its formation determines whether a seed is classified as endospermic (or…

Double Fertilisation: — Two fusions in angiosperms.

Syngamy: — Male gamete (

n

) + Egg cell (

n

)

\rightarrow

Zygote (

2n

). Forms embryo.

Triple Fusion: — Male gamete (

n

) + Secondary nucleus (

2n

)

\rightarrow

Primary Endosperm Nucleus (PEN) (

3n

). Forms endosperm.

Ploidy: — Male gamete (

n

), Egg cell (

n

), Zygote (

2n

), Polar nuclei (

n+n

), Secondary nucleus (

2n

), PEN (

3n

), Endosperm (

3n

), Embryo (

2n

Pollen Tube: — Carries male gametes, guided by synergids.

Synergids: — Guide pollen tube via filiform apparatus; degenerate post-entry.

Antipodals: — Degenerate post-fertilisation.

Post-Fertilisation: — Ovule

\rightarrow

Seed; Ovary

\rightarrow

Fruit.

Double Fertilisation: Synergy Triple Fusion.

Synergy: Single male gamete + Egg $\rightarrow$ Zygote (2n) $\rightarrow$ Embryo. (S.E.Z.E.)

Triple Fusion: Two polar nuclei + Second male gamete $\rightarrow$ Primary Endosperm Nucleus (3n) $\rightarrow$ Endosperm. (T.S.P.E.N.E.)

Think of it as 'SEZE' for the embryo and 'TSPENE' for the endosperm. The 'T' in TSPENE reminds you it's Triploid.