Which of the following statements about spermatogenesis is not true?
A) The spermatogonium forms the primary spermatocyte.
B) The primary spermatocyte forms two secondary spermatocytes.
C) The secondary spermatocytes each form two spermatids.
D) Each spermatid forms two sperm.
The Correct Answer and Explanation is:
The correct answer is D) Each spermatid forms two sperm.
Explanation:
Spermatogenesis is the process by which sperm cells (spermatozoa) are produced from spermatogonia (germ cells) in the testes. This process involves several stages of cell division and differentiation. Let’s break down the phases involved to clarify why option D is incorrect.
- Spermatogonium to Primary Spermatocyte (A):
- The spermatogonium is the initial diploid (2n) cell located in the seminiferous tubules of the testes. Through mitotic division, one spermatogonium forms a primary spermatocyte. This stage is correct, as it accurately describes the initial step in spermatogenesis.
- Primary Spermatocyte to Secondary Spermatocytes (B):
- The primary spermatocyte is a diploid (2n) cell that undergoes the first meiotic division (Meiosis I), producing two haploid (n) secondary spermatocytes. Each secondary spermatocyte contains half the number of chromosomes as the primary spermatocyte, making this stage also correct.
- Secondary Spermatocytes to Spermatids (C):
- The secondary spermatocytes undergo the second meiotic division (Meiosis II), which results in the formation of spermatids. Each secondary spermatocyte divides to produce two spermatids. Spermatids are haploid (n) cells that are not yet fully differentiated into mature sperm, so this statement is also correct.
- Spermatid to Sperm (D):
- Each spermatid undergoes a process called spermiogenesis, where it matures into a sperm cell, but one spermatid forms one sperm. Spermatids undergo significant changes in structure: they develop a tail, lose excess cytoplasm, and form the head and midpiece. This results in one functional sperm per spermatid, not two. Therefore, the statement “Each spermatid forms two sperm” is incorrect.
Thus, the correct answer is D, as it misrepresents the final step of spermatogenesis. Each spermatid forms only one sperm cell, not two.