Question

Select the MOST CORRECT answer. Countercurrent exchange...

		occurs in the gills of most fish when water and blood flow in opposite directions allowing gas exchange.
		does not require energy for gas exchange, as oxygen and carbon dioxide move down their concentration gradient.
		is a process used in capillary beds of mammalian lungs.
		Both a) and b) are correct and c) is incorrect.
		a), b) and c) are all correct. Regarding human reproduction (select the MOST CORRECT statement): At the time of ovulation, the released ovum has not completed meiosis. In the absence of pregnancy, the corpus luteum degenerates and plasma progesterone levels decline. Fertilization results in the formation of a zygote, which is a single diploid cell that implants in the uterus. Both a) and b) are correct and c) is incorrect a), b) and c) are all correct

Answer 1

ANSWER :

1. The countercurrent exchange occurs in the gills of most fish when water and blood flow in opposite directions allowing gas exchange, and it does not require energy for gas exchange, as oxygen and carbon dioxide move down their concentration gradient. Hence option (a), and (b) are correct answers, but (c) is incorrect.

2. When a secondary oocyte or ovum released from the ovary, it has completed meiosis-I but meiosis-II completes after the fertilization with the sperm. The corpus luteum is an endocrine body formed in the ovary of females, and primarily responsible for maintaining initial pregnancy via secreting progesterone hormone, but in the absence of fertilization it begin to degenerate and lead to decline in the progesterone hormone.

The zygote is the first diploid cell forms after the fertilization, and invaginated into the endometrium of uterus for further embryological development.

Hence option (a), (b), and (c) all are correct answer choice.