Question

explain the pollination leading to the formation of a seed in an angiosperm

Answer 1

Fertilisation leads to formation of zygote which forms embryo.
Embryo is the progenitor of the next generation.
Double fertilisation in Angiosperms ensures that proper nutrition is provided to the embryo. (Formation of endosperm due to triple fusion).

Post fertilisation changes taking place are:
1. Embryo development. (Zygote gets converted to embryo)
2. Endosperm development. (PEN gets converted to endosperm)
3. Formation of seeds. (Ovules are converted to seeds)
4. Formation of fruits. (Ovary is converted to fruit)

Other changes are:
Style, Stigma, Anthers, Sepals, Petals wither away. Ovary wall gets changed to fruit wall (Pericarp).

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Answer 2

When the pollengrains fall on the stigma, the pollen tube enters one of the synergids and release two male gamets.