MCAT Question A Day - 6/18/13 - 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 H1 and HCO32. This suggests that in active tissues, pH will tend to
A. decrease.
B. increase.
C. remain the same.
D. first increase and then decrease.
The correct answer is (A). If carbon dioxide contributes to H1 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.
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