Question

Even though each pollen grain has two male gametes, why are at least 10 pollen grains and not 5 pollen grains required to fertilise 10 ovules present in a particular carpel? 2

Answer 1

Even though 2 male gametes are there in one pollen grain, 10 pollen grains are required to fertilise 10 ovules. This is due to the presence of double fertilization in angiosperms. For one Zygote to form, One male and one egg is required. The other male gamete fuses with the polar nuclei and forms the primary endosperm nucleus (PEN).

Answer 2

During double fertilization, one of the male gamete of pollen grain fuses with egg cell, while other male gamete fuses with secondary nucleus. Thus to fertilize 20 ovules in a particular carpel, 20 pollen grains are required.