The testosterone secretion is controlled by:

Correct Answer: B

Rationale: Step 1: LH (luteinizing hormone) is produced by the pituitary gland and plays a key role in stimulating the Leydig cells in the testes to produce testosterone. Step 2: Testosterone secretion is directly controlled by the LH through this stimulation. Step 3: FSH (follicle-stimulating hormone) is involved in sperm production, not testosterone secretion. Step 4: Corticoadrenal hormones are related to stress response, not testosterone regulation. Step 5: Negative feedback from the posterior pituitary does not directly control testosterone secretion. Therefore, the correct answer is B (the LH) as it directly influences testosterone production.

Correct Answer: D

Rationale: The correct answer is D: muscular. The uterus is composed of smooth muscle tissue, allowing it to contract during childbirth and menstruation. This contraction is essential for the expulsion of the fetus or uterine lining. Funnel-shaped (A) and cavitary (C) describe the shape and structure of the uterus, but they do not define its primary function. Unpaired (B) is incorrect as the uterus is a paired organ in the female reproductive system.

Correct Answer: B

Rationale: The correct answer is B: consists in the fusion between the male and female gametes. Fecundation, also known as fertilization, is the process where a sperm cell fuses with an egg cell to form a zygote. This is a crucial step in sexual reproduction. The male gamete (sperm) and the female gamete (egg) come together to combine their genetic material, resulting in the formation of a new individual. The other choices are incorrect because: A) Monospermic means involving only one sperm, which is not accurate as multiple sperm may reach the egg but only one will fertilize it. C) Grafting of the egg at the Fallopian tube is not how fertilization occurs; fertilization typically takes place in the fallopian tube but does not involve grafting. D) Fecundation does not require the existence of several fecundated spermatozoa; only one sperm is needed for fertilization to occur.

Correct Answer: C

Rationale: The correct answer is C: chromosome number. Human egg cells and sperm cells both have 23 chromosomes, which is half the total number of chromosomes in a human cell (46). This is crucial for maintaining the correct chromosome number in offspring. Choices A, B, and D are incorrect because: A: Human egg cells are not motile, while sperm cells are highly motile. B: Egg cells contain a larger amount of stored food (cytoplasmic material) compared to sperm cells. D: Egg cells are larger and rounder in shape, while sperm cells are smaller and more streamlined.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.