As menstruation ends estrogen levels in the blood rise rapidly. What is the source of the estrogen?

Correct Answer: B

Rationale: The correct answer is B: Developing follicles. After menstruation, the developing follicles in the ovaries produce estrogen. This estrogen is responsible for thickening the endometrium in preparation for potential implantation of a fertilized egg. The corpus luteum produces progesterone, not estrogen. The endometrium is the inner lining of the uterus and is not a direct source of estrogen. Stromal cells of the ovaries are supportive cells and do not produce estrogen.

Correct Answer: A

Rationale: Rationale: Elevated levels of transcortin in a pregnant woman lead to an increase in total plasma cortisol concentration. Transcortin binds to cortisol, increasing its total concentration but reducing the amount of free (non-protein-bound) cortisol. Choice A is correct as total cortisol concentration increases due to transcortin binding. Choices B and D are incorrect as free cortisol concentration decreases. Choice C is incorrect as total cortisol concentration is elevated, not decreased.

Correct Answer: C

Rationale: The correct answer is C: gametes. Gonads produce sex cells, which are haploid cells involved in reproduction. Gametes are the mature, haploid male or female germ cells (sperm or egg) produced by the gonads. Zygotes are formed when gametes fuse during fertilization, not produced by gonads. Interstitial cells are found in the testes and produce hormones, not sex cells. Spermatids are immature male germ cells that develop into sperm, not the primary sex cells produced by gonads.

Correct Answer: D

Rationale: The correct answer is D, follicle-stimulating hormone (FSH). FSH promotes the growth and maturation of primary follicles in the ovary each month. It stimulates the follicles to develop and produce estrogen. LH surge triggers ovulation. A and B are involved in the menstrual cycle, but they do not specifically promote the growth of primary follicles. C is not a hormone involved in the process.

Correct Answer: C

Rationale: The correct answer is C: Primary spermatocyte. Primary spermatocytes are diploid cells that undergo meiosis to produce four haploid cells, which develop into sperm. First, primary spermatocytes undergo meiosis I to form two secondary spermatocytes. Then, meiosis II occurs in each secondary spermatocyte to produce a total of four spermatids, which eventually mature into sperm. Explanation for why other choices are incorrect: A: Spermatids are already haploid cells formed from the division of secondary spermatocytes, not primary spermatocytes. B: Spermatogonium are diploid cells that divide by mitosis to produce primary spermatocytes, not directly giving rise to sperm. D: Ovum is a female gamete that undergoes meiosis to produce one mature egg cell, not sperm.