Delayed breathing at birth is a common danger faced by newborn infants. What is a frequent cause of delayed breathing?

Correct Answer: A

Rationale: The correct answer is A: Fetal hypoxia during the birth process. Fetal hypoxia, which is a lack of oxygen to the fetus during birth, can lead to delayed breathing in newborn infants. This lack of oxygen can result from various factors such as umbilical cord compression or placental insufficiency. Maternal hypoxia (choice B) and hypercapnia (choices C and D) may affect the fetus indirectly but are not direct causes of delayed breathing in newborns. Therefore, the correct choice is A, as it directly addresses the specific cause of delayed breathing in newborn infants.

Correct Answer: A

Rationale: Step 1: Testosterone plays a crucial role in maintaining bone density. Step 2: Estrogen helps regulate bone turnover and calcium balance. Step 3: Women experience a significant drop in estrogen levels after menopause. Step 4: Decreased estrogen production leads to increased bone resorption. Step 5: Men, on the other hand, continue to produce testosterone throughout their lifetime, which helps maintain bone density. Summary: A is correct because men maintain testosterone production, while women cease estrogen production after menopause, leading to a higher risk of osteoporosis in elderly women. B, C, and D are incorrect as they do not address the hormonal changes that contribute to osteoporosis gender disparity.

Correct Answer: D

Rationale: The correct answer is D: acrosome. The acrosome is a specialized organelle in the sperm head that contains enzymes necessary for penetrating the egg during fertilization. It releases these enzymes to help the sperm penetrate the egg's protective outer layer. The flagellum (choice A) is the tail of the sperm that provides motility. The midpiece (choice B) contains mitochondria for energy production. Spermatid (choice C) is an immature sperm cell formed during spermatogenesis.

Correct Answer: B

Rationale: The correct answer is B: Epididymis. The epididymis is where maturing sperm gain increased motility and their ability to swim due to the presence of specific proteins and enzymes that facilitate this process. Sperm leave the seminiferous tubules in an immature state and undergo maturation in the epididymis through interactions with these proteins. The ductus deferens and ejaculatory duct are not involved in the maturation process of sperm and do not contribute to their motility. The seminiferous tubules are responsible for sperm production but not for the maturation of sperm motility.

Correct Answer: B

Rationale: The correct answer is B: Onset of menopause. Puberty is the period of sexual maturation and development, typically occurring in adolescence. Menopause, on the other hand, is the cessation of menstruation and fertility, usually happening in women in their late 40s or early 50s. During puberty in females, there is an increase in fat deposits beneath the skin, widening and lightening of the pelvis to prepare for childbirth, and development of the breasts as part of secondary sexual characteristics. Menopause does not occur during puberty; it is a separate phase in a woman's reproductive life cycle. Therefore, B is the correct answer.