Question

Describe the process of spermatogenesis with a diagram.

Hint:

Spermatogonium → primary spermatocyte → secondary spermatocytes → spermatids → spermatozoa.

Answer 1

Step 1: Definition and site:
Spermatogenesis is the process by which male gametes (spermatozoa) are formed from primary germ cells in the seminiferous tubules of the testis; it begins at puberty under the influence of a rise in gonadotropin-releasing hormone (GnRH), which stimulates the pituitary to release LH and FSH.

Step 2: Multiplication phase:
The undifferentiated germ cells lining the tubule, called spermatogonia (2n), divide repeatedly by mitosis to increase in number; some spermatogonia periodically enter meiosis, transforming into primary spermatocytes (2n).

Step 3: Meiotic phase:
Each primary spermatocyte completes meiosis I to form two haploid secondary spermatocytes (n); each secondary spermatocyte then rapidly undergoes meiosis II to form two spermatids (n) each — so one primary spermatocyte ultimately gives rise to four spermatids.

Step 4: Spermiogenesis and spermiation:
The round, non-motile spermatids are then transformed into slender, motile spermatozoa through spermiogenesis — a process involving loss of most cytoplasm, condensation of the nucleus, and formation of the acrosome (head cap) and flagellum (tail). Sertoli cells nourish the developing germ cells throughout, and mature sperm are finally released into the lumen of the tubule (spermiation).

Final Answer:
Spermatogenesis: spermatogonia (mitosis) → primary spermatocyte → (meiosis I) secondary spermatocytes → (meiosis II) spermatids → (spermiogenesis) spermatozoa, nourished by Sertoli cells and controlled by FSH, LH and testosterone. (Diagram: concentric layers in the seminiferous tubule from spermatogonia at the base to sperm at the lumen.)