Practice MCAT Question - Q128 - Answer!
When carbon dioxide diffuses from tissue cells to the blood, it combines with water to form carbonic acid. Then, the enzyme carbonic anhydrase causes the ionization of carbonic acid into H+ and HCO3-. This suggests that in active tissues, pH will tend to
A. decrease.
B. increase.
C. remain the same.
D. first increase and then decrease.
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The correct answer is (A). If carbon dioxide contributes to H+ concentration, then the more carbon dioxide that is produced, the more acidic the tissue will become and the more pH will decrease (acids have a pH less than 7, while alkaline substances have a pH greater than 7). Active tissues carry out more cellular respiration and, therefore, produce more carbon dioxide.
