What is the phenomenon called when one male gamete fuses with the egg cell to form the zygote and the other male gamete fuses with the two polar nuclei to produce a triploid primary endosperm nucleus?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Double fertilisation
The pollen tube releases two male gametes into the embryo sac. One male gamete fuses with the egg cell; this fusion is syngamy and it forms the diploid zygote. The other male gamete fuses with the two polar nuclei in the central cell; this is triple fusion and it forms the triploid primary endosperm nucleus (PEN). Because two fusions take place in one embryo sac, the whole event is called double fertilisation. It is found only in flowering plants.
Option (1) Fertilisation — Incorrect. Fertilisation in general means the fusion of a male and a female gamete. Here that is only the first fusion (syngamy). The question describes two separate fusions, so the general term does not name it.
Option (2) Triple fusion — Incorrect. Triple fusion is only the second fusion: one male gamete with the two polar nuclei. It does not include the fusion of the other male gamete with the egg.
NCERT Extract:
Double Fertilisation – “… The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN) (Figure 1.13a). As this involves the fusion of three haploid nuclei it is termed triple fusion. Since two types of fusions, syngamy and triple fusion take place in an embryo sac the phenomenon is termed double fertilisation, an event unique to flowering plants.”