Sexual Reproduction In Flowering Plants — BIOLOGY STD 12 Science — Question

→ After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid.
→ One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy. This results in the formation of a diploid cell, the zygote.
→ 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).
→ 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.
→ The central cell, after triple fusion, becomes the Primary Endosperm Cell (PEC) and develops into the endosperm while the zygote develops into an embryo.