Human Reproduction — BIOLOGY STD 12 Science — Question

The process of formation of spermatozoa (sperms) from diploid spermatogonia is called spermatogenesis.

It includes the following phases:

Multiplication phase: The male germ cells (spermatogonia) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers.

Growth phase: Spermatogonia grow and increase in size and form primary spermatocytes. Each spermatogonium is diploid and contains 46 chromosomes.

Maturation phase or formation of spermatids: Some of the spermatogonia called primary spermatocytes periodically undergo meiosis. A primary spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal haploid cells called secondary spermatocytes, which have only 23 chromosomes each. The secondary spermatocytes undergo the second meiotic division to produce four equal haploid spermatids.

Differentiation phase: The spermatids are transformed into spermatozoa (sperms) by the process of spermiogenesis. The sperm’s head gets attached to Sertoli cells to draw nourishment and are finally released from the seminiferous tubules by the process called spermiation.