Explain the process of spermatogenesis in human male.

OR

Define double fertilization. Explain the process giving significance.

Spermatogenesis is the process of formation of sperm occurs in the seminiferous tubules of testis. Steps involve in the formation of spermatozoa are

i. In the multiplication phase, spermatogonia are formed from primordial germ cells by mitosis.

ii. In the growth phase, primary spermatocytes are formed from the spermatogonium.

iii. In the maturation phase, primary spermatocytes undergo reductional division leading to the formation of two secondary spermatocytes. Both secondary spermatocytes undergo second reductional division and form four haploid spermatids.

iv. Spermiogenesis- is the morphological differentiation of spermatids to spermatozoa.

OR

Double fertilizations is the unique feature of anigiosperms. During double fertilisation, one male gamete fuses with the egg cell to form the zygote and another male gamete fuses with the secondary nucleus to form the primary endosperm nucleus.