MCAT Biology Question 86: Answer and Explanation

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Question: 86

11. Some people with anxiety disorders respond to stress by hyperventilating. It is recommended that these people breathe into a paper bag and then rebreathe this air. Why is this treatment appropriate?

  • A. Hyperventilation causes an increase in blood carbon dioxide, and breathing the air in the bag helps to readjust blood levels of carbon dioxide.
  • B. Hyperventilation causes a decrease in blood carbon dioxide, and breathing the air in the bag helps to readjust blood levels of carbon dioxide.
  • C. Hyperventilation causes an increase in blood oxygen, and breathing the air in the bag helps to readjust blood levels of oxygen.
  • D. Hyperventilation causes a decrease in blood oxygen, and breathing the air in the bag helps to readjust blood levels of oxygen.

Correct Answer: B

Explanation:

When people hyperventilate, their respiratory rate increases. When the respiratory rate increases, more carbon dioxide is blown off. This causes a shift to the left in the bicarbonate buffer equation, and the blood becomes more alkaline. Breathing into the bag allows some of this carbon dioxide to be returned to the bloodstream in order to maintain the proper pH.

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