In . . . . . . pollen grains cause allergy.

The pollen tube usually enters the embryo sac through:

By which process does the tip of the pollen tube rupture within the embryo sac?

In some cereals like wheat and rice, pollen grains lose viability within a certain period of their release. In members of the families $Rosaceae$, $Leguminosae$, and $Solanaceae$, the viability is maintained for a different period. Choose the correct option for these two periods respectively.

Which of the following in the female gametophyte of an angiosperm helps in guiding the pollen tube for fertilizing the egg?

In pollen grains released at the $2$-celled stage,where are the male gametes formed?