Explain why sexual reproduction in angiosperms is said to take place through double fertilisation and triple fusion. Also draw a labelled diagram of embryo sac to explain the phenomena.

Explanation

An angiospermic plants sexually reproduces by the fromation of male and female gametes. The male is a pollen which contain two male nuclei and female gamete is egg cell produced in ovule (female gametophyte)
The pollen grains germinarte on the stigma of a flower and the resulting pollen tube grow through the tissue of stigma and style and each near the egg apparatus. The two male gametes are discharge within the embryo sac. One of the male gamete fuses with the egg cell to from a diploid zygote
This fusion is know a fetilisiton or syngamy. The second male gamete fuses wiht the diploid secondary nucleus and forms the triploid Primary Endsoperm Nucleus (PEN) . This fusion is is know as triple fusion.
Because of the involvement of two , this event in angiosperms is termed as double fertilisation. The zygote then develops into embryo and PEN develops into endosperm which provides nourishment to the developing embryo