(a) Identify A, B and C in the given diagram and write their functions.          

(b) Mention the role of gamete and zygote in sexually reproducing organisms.

In the diagram given above:

(a) A is the Stigma.

Function: The stigma is a sticky surface where the pollen lands and later germinates.

B is the Pollen tube.

Function: It carries the pollen from stigma to the egg cell in the ovary for fertilization.

C is the Egg cell.

Function: It fuses with the male gamete and leads to the formation of zygote.

(b) The gametes play an important role in the sexually reproducing organisms as they carry a genetic instructions that is a haploid set of chromosomes that the new organism needs to grow, develop and complete its life cycle.. These gametes upon fusion result in the formation of zygote, which develops into a new individual.

Zygote is the diploid cell formed by the fusion of male and female gametes during fertilization in sexual reproduction. Zygote is the first stage in the development process of an organism and it contains the complete set of genetic information of both the parents, essential for the growth of the new organism.