The length of pollen tube depends on the distance between:(a) pollen grain and upper surface of stigma
(b) pollen grain on upper surface of stigma and ovule
(c) pollen grain in anther and upper surface of stigma
(d) upper surface of stigma and lower part of style

Correct Answer: (b) pollen grain on upper surface of stigma and ovule

Explanation:

In Angiosperms, the pollen tube arises from the pollen grains and grows towards the ovules, passing stigma, style and ovary to fuse with the eggs.

After pollination, pollen germinates on the upper surface of the stigma.

The prime function of the pollen tube is to transport sperms to the ovule where the female egg is present for the process of fertilization.

Therefore, the length of the pollen tube depends on the distance between the upper surface of stigma and ovule.