Q4. Which hormone does the corpus luteum secrete in large amounts, and why is it needed?
Progesterone, which is essential for maintaining the endometrium; such an endometrium is needed for implantation of the fertilised ovum and the other events of pregnancy (NCERT page 35).
Q5. In the textbook’s typical 28-day ovulatory model, around which day would ovulation occur, and in which phase do days 20–25 fall?
Approximately day 14 in this model, not a fixed prediction for every individual (NCERT page 35); days 20–25 fall in the luteal phase, when the corpus luteum is active (NCERT Figure 2.9, page 34).
Q6. Assertion: menstruation does not occur during pregnancy. Reason: the corpus luteum regresses immediately after implantation. Are both true, and does the reason explain the assertion?
The assertion is true: during pregnancy all events of the menstrual cycle stop and there is no menstruation (NCERT page 35). The reason is false, so it cannot explain the assertion: NCERT says the corpus luteum degenerates in the absence of fertilisation (page 35), not after implantation. Beyond the NCERT text: after implantation, hCG from the embryo maintains the corpus luteum (Open RN, Nursing Health Promotion, 2025), and the corpus luteum keeps up its hormone output until the placenta can secrete the hormones needed (NCI SEER Training Modules, Ovaries).