MCAT Biology Question 103: Answer and Explanation
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Question: 103
13. The world record for the longest-held breath is 22 minutes and 0 seconds. If a sample were taken from this individual during the last minute of breath-holding, which of the following might be observed?
- A. Increased hemoglobin affinity for oxygen
- B. Decreased PaCO2
- C. Increased hematocrit
- D. Decreased pH
Correct Answer: D
Explanation:
Holding one's breath for a prolonged period would result in a drop of oxygenation and an increase in PaCO2. The increased carbon dioxide would associate with water to form carbonic acid, which would dissociate into a proton and bicarbonate anion. Further, the low oxygen saturation would eventually lead to anaerobic metabolism in some tissues, causing an increase in lactic acid. These would all lead to a decreased pH.