Explain the events up to double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm?
(ii) The events seen after the pollen tube enters one of the synergids in an ovule is as follows: (a) After reaching the ovary, pollen tube enters the ovule through the micropyle and thus enters one of the synergids through filiform apparatus. (b) After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid. (c) One of the male gametes moves towards the egg cell and fuses with its nucleus and results in the formation of the zygote (diploid cell). This is called syngamy. (d) The other male gamete moves towards the two polar nuclei present in the central cell and fuses to form triploid primary endosperm nucleus (PEN) i.e., there is a fusion of three haploid nuclei and hence termed as triple fusion. (e) Two types of fusions-syngamy and triple fusion-take place in an embryo sac. Hence the phenomenon is termed double fertilisation. (f) After fertilisation, the primary endosperm nucleus becomes the primary endosperm cell (PEC) and develops into endosperm while zygote develops into an embryo.
