MCAT Biology Question 157: Answer and Explanation
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Question: 157
7. Which of the following INCORRECTLY pairs a type of muscle fiber with a characteristic of that fiber?
- A. Red fibers—rich in mitochondria
- B. Red fibers—high levels of myoglobin
- C. White fibers—fast-twitching
- D. White fibers—predominantly uses aerobic respiration
Correct Answer: D
Explanation:
Red fibers are slow-twitching fibers that have high levels of myoglobin and many mitochondria. They derive their energy from aerobic respiration and are capable of sustained vigorous activity. This eliminates choices (A) and (B). White fibers, on the other hand, are fast-twitching fibers and contain lower levels of myoglobin and fewer mitochondria. Because of their composition, they derive more of their energy anaerobically and fatigue more easily. This eliminates choice (C) and makes choice (D) the correct answer.