Question

what do the pollen grains and the egg became during fertilization

Answer 1

The ovary contains ovules in which are present the egg cells.
The pollen grains leave the male part and reach the stamen either by cross or self pollination. The pollen grain germinates on the stigma and forms a pollen tube through the style to the ovary . Then one pollen grain combines with an egg cell in the ovule.This forms the zygote . 
                         The Ovary forms the fruit,the ovule becomes the seed and the zygote remains inside the seed. 

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