Explain the events up to double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm.

Solution

The events seen after the pollen tube enters one of the synergids in an ovule are as follows :

Pollen tube, after reaching the ovary, enters the ovule through the micropyle and thus enters one of the synergids through filiform apparatus.
After entering one of synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid.
One of the male gametes move towads the egg cell and fuses with its nucleus thus result in the formation of the zygote (diploid cell). This is Syngamy.
The other male gamete moves towards the two polar nuclei located in the central cell and fuses to form triploid primary endosperm nucleus (PEN). This involves fusion of three haploid nuclei & hence termed as triple fusion.
Two types of fusions, syngamy & triple fusion take place in an embryosac and hence the phenomenon
is termed as double fertilisation.
After fertilisation, PEN becomes the primary endosperm cell (PEC) & develops into endosperm while zygote develops into an embryo.

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