MCAT General Chemistry Question 290: Answer and Explanation

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Question: 290

3. All of the following statements are true regarding human respiration EXCEPT:

A. when a person's breathing is hampered by conditions such as asthma or emphysema, the blood [H⁺] increases.
B. exercise stimulates deeper and more rapid breathing, which increases blood plasma pH.
C. slow, shallow breathing allows CO₂ to accumulate in the blood.
D. hyperventilation can result in the loss of too much CO₂, causing the accumulation of bicarbonate ions.

Correct Answer: D

Explanation:

D Choices A and C can be eliminated because they create the same effect. A decrease in breathing rate causes less CO₂ to exchange, leading to an increase in CO₂ remaining in the blood (i.e., increased CO₂ concentration). Consequently, this shifts the equilibria shown in Figure 1 to the right, which results in increased H⁺ concentration, and decreased pH. Choice B is the opposite effect. Deeper, more rapid breathing expels more CO₂, decreasing the CO₂ in the blood and increasing pH. Hyperventilation may involve the loss of too much CO₂. This loss will shift the equilibria shown in Equation 1 to the left. Loss of bicarbonate ions will result, making choice D the only statement that is NOT true.

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