SAT Subject Biology Practice Question 197: Answer and Explanation

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Question: 197

7. Which of the following uses a countercurrent exchange system?

I. Gills

II. Kidneys

III. Intestines

IV. Lungs

A. I and III only
B. II and IV only
C. I, II, and III
D. I, II, and IV
E. I, II, III, and IV

Correct Answer: D


Gills, kidneys, and lungs all rely on countercurrent exchange for the intake of oxygen and/or release of waste compounds. The intestines do not feature countercurrent exchange.

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