CBSE Class 11-science Answered

During pollination, the pollen grains germinate on the stigma.

This results in the formation of pollen tube which grows through the style and reaches the ovule.

When the pollen tube enters the sac, two male gametes are discharged.

One male gamete fuses with the egg cell and forms a zygote.

The second male gamete fuses with the diploid secondary nucleus and produces the triploid primary endosperm nucleus (PEN).

Because the fusion occurs twice, it is called double fertilisation.

The zygote develops into an embryo, while the primary endosperm nucleus develops into endosperm.

The endosperm provides nourishment to the developing embryo.

The synergids and antipodals of the egg apparatus degenerate after fertilisation.

At the end of this cycle, ovules develop into seeds which give rise to a new plant (sporophyte) while ovaries develop into fruits.