MCAT Biology Question 129: Answer and Explanation
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Question: 129
9. The two graphs below show the relative activities of two enzymes in solutions of varying pH. Which of the following choices correctly identifies the two enzymes?
- A. 1—chymotrypsin; 2—pepsin
- B. 1—pepsin; 2—carboxypeptidase B
- C. 1—lactase; 2—aminopeptidase
- D. 1—enteropeptidase; 2—amylase
Correct Answer: B
Explanation:
The first graph shows maximal activity at a very acidic pH, implying that this is an enzyme acting in the stomach. The second graph shows maximal activity around pH 8.5, implying that this is an enzyme acting in the duodenum. The only choice that matches the first graph with a stomach enzyme (pepsin) and the second with a duodenal enzyme (carboxypeptidase B) is choice (B).