MCAT Biology Question 93: Answer and Explanation
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Question: 93
3. Hemoglobin's affinity for O2:
- A. increases in exercising muscle tissue.
- B. decreases as blood PaCO2 decreases.
- C. decreases as blood pH decreases.
- D. is higher in maternal blood than in fetal blood.
Correct Answer: C
Explanation:
According to the Bohr effect, decreasing the pH in the blood decreases hemoglobin's affinity for O2. This makes choice (C) the correct answer. The affinity is generally lowered in exercising muscle to facilitate unloading of oxygen to tissues, eliminating choice (A). A decrease in the PaCO2 would cause a decrease in [H+] or increased pH—which increases hemoglobin's affinity for O2, eliminating choice (B). Finally, choice (D) is incorrect because hemoglobin's affinity for O2 is higher in fetal blood than in adult blood.