Human Reproduction

Placenta; it maintains the corpus luteum to sustain progesterone production

Step 1: After implantation, the trophoblast cells of the developing placenta begin secreting hCG. Step 2: hCG acts on the corpus luteum and prevents its degeneration. Step 3: The corpus luteum, maintained by hCG, continues to secrete progesterone, which is essential to maintain the endometrium and support early pregnancy. Step 4: Option B is wrong — FSH (not hCG) from the anterior pituitary stimulates follicle development. Step 5: Option C is wrong — the corpus luteum secretes progesterone but does NOT produce hCG; it is the placenta (trophoblast) that does. Option D is wrong — the endometrium

Acrosomal enzymes dissolve zona pellucida → sperm enters → meiosis II of oocyte completes → polar body released → haploid nuclei fuse → zygote formed

Step 1: The acrosome at the tip of the sperm head contains hydrolytic enzymes. These enzymes dissolve the zona pellucida, allowing the sperm to penetrate. Step 2: Sperm contact with the plasma membrane of the oocyte triggers a cortical reaction that prevents polyspermy (no additional sperms can enter). Step 3: The sperm entry stimulates the secondary oocyte to complete meiosis II, releasing the second polar body and forming a haploid ovum (ootid). Step 4: The haploid sperm nucleus and haploid ovum nucleus then fuse to form a diploid zygote (46 chromosomes). Step 5: Options B, C, and D all plac

One primary spermatocyte gives 4 functional sperms; one primary oocyte gives only 1 functional ovum and 3 polar bodies

Step 1: In spermatogenesis, meiosis is equal — both divisions produce cells of equal size. One primary spermatocyte → 2 secondary spermatocytes → 4 spermatids → 4 functional sperms. Step 2: In oogenesis, meiosis is unequal. Meiosis I produces one large secondary oocyte and one tiny first polar body. Step 3: Meiosis II (after fertilisation) produces one large ootid (functional ovum) and one tiny second polar body. Step 4: The first polar body may divide into two, giving a total of 3 polar bodies and 1 functional ovum. Step 5: The unequal division ensures the ovum retains maximum cytoplasm and n

Spermatogenesis would be impaired because higher temperature denatures enzymes required for sperm production

Step 1: Spermatogenesis is a highly temperature-sensitive process. The enzymes and cellular processes involved function optimally at 2–2.5°C below normal body temperature (37°C). Step 2: This is why the testes descend into the scrotum outside the body cavity — the scrotum acts as a temperature regulator. Step 3: If testes remain in the abdomen (a condition called cryptorchidism), the higher temperature inside would inhibit or destroy spermatogenesis, leading to infertility. Step 4: Option B is incorrect — Leydig cells are less temperature-sensitive and continue to secrete androgens even in cry