Question

Define spermatogenesis. Describe the process of spermatogenesis with the help of schematic diagram.

Hint:

Track how the chromosome number changes from spermatogonium to spermatid to mature sperm.

Answer 1

Step 1: Understanding the Concept:
Spermatogenesis is the process by which male germ cells inside the testis produce mature, haploid sperm cells (spermatozoa), starting from diploid cells and passing through cell division and a change in shape.

Step 2: State where it happens.
It occurs inside the seminiferous tubules of the testis, in a layer of cells called the germinal epithelium.

Step 3: Describe the stages in order.
Diploid germ cells called spermatogonia (2n) present in the tubule lining multiply repeatedly by mitosis to increase in number.
Some spermatogonia grow in size and become primary spermatocytes (2n), which then undergo the first meiotic division (meiosis I) to form two secondary spermatocytes (n, haploid).
Each secondary spermatocyte undergoes the second meiotic division (meiosis II) to produce two spermatids (n), so one primary spermatocyte ultimately yields four haploid spermatids.
These spermatids, though already haploid, do not look like functional sperm yet, so they go through a transformation process called spermiogenesis, in which they develop a head, a midpiece with mitochondria, and a tail, becoming mature spermatozoa.
Finally, the fully formed sperm heads are released from the Sertoli cells into the lumen of the seminiferous tubule, a step called spermiation.

Step 4: Note the schematic flow (diagram in words).
Spermatogonium (2n) → mitosis → Primary spermatocyte (2n) → meiosis I → two Secondary spermatocytes (n) → meiosis II → four Spermatids (n) → spermiogenesis → four Spermatozoa (n), released into the tubule lumen by spermiation.

Final Answer:
Spermatogenesis is the formation of haploid sperm from diploid spermatogonia through mitosis, meiosis I, meiosis II, and spermiogenesis, ending with spermiation into the seminiferous tubule.