Gametogenesis

Spermatogenesis is the biological process through which spermatozoa are produced from male primordial germ cells in the testes. This process involves mitotic and meiotic divisions, ultimately resulting in the formation of mature sperm cells capable of fertilizing an ovum.

Step 1: Understanding the male reproductive system. The male reproductive system is primarily responsible for the production of male gametes (sperm) and hormones like testosterone. The testes are the key structures where spermatogenesis (the production of sperm) occurs.

Step 2: Spermatogenesis in the testes. - Spermatogenesis occurs in the seminiferous tubules within the testes. - These tubules are lined by germ cells and Sertoli cells, which aid in the development of sperm.

Step 3: Explanation of other options.

Prostate gland: Produces seminal fluid that nourishes and protects sperm.

Seminal vesicles: Contribute to the production of seminal fluid.

Epididymis: Stores and matures sperm but does not produce it.

Hence, the correct answer is (D) Testes.

The female gametophyte (also known as the embryo sac in angiosperms) develops from the following:

Megaspore mother cell: Undergoes meiosis to produce megaspores, one of which develops into the female gametophyte.

Nucellus: Provides nutrition to the developing female gametophyte.

Megaspore: Directly develops into the female gametophyte through mitosis. However, the microspore mother cell is responsible for producing microspores, which develop into the male gametophyte (pollen grains). It is not involved in the development of the female gametophyte. Thus, the female gametophyte does not develop from the microspore mother cell.

Step 1: Overview of primary follicles.
Primary follicles are immature ovarian follicles containing an oocyte. Females are born with around 1 to 2 million primordial follicles in their ovaries. However, the number decreases significantly as the individual ages.

Step 2: Number of follicles during puberty.
By the time a female reaches puberty, the number of primary follicles reduces drastically to approximately 300,000 to 400,000. This reduction occurs due to a natural process called follicular atresia, where most follicles degenerate over time.

Step 3: Analysis of options.
Option (A): Incorrect. While 2 million follicles are present at birth, this number decreases before puberty.

Option (B): Incorrect. Although close, 1 million follicles is an estimate for early childhood, not puberty.

Option (C): Correct. Thousands (approximately 300,000–400,000) of primary follicles are present in the ovaries during puberty.

Option (D): Incorrect. Primary follicles are present during puberty; it is not true that none are present.

Step 4: Conclusion.
During puberty, the number of primary follicles in the ovaries is reduced to thousands due to natural follicular atresia.