MCAT Biology Question 151: Answer and Explanation
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Question: 151
1. 
During muscle contraction, which of the following regions decrease(s) in length?
- A. 1 only
- B. 1 and 2 only
- C. 3 and 4 only
- D. 2, 3, and 4 only
Correct Answer: D
Explanation:
We are given a diagram of a sarcomere and asked to determine which regions shorten during muscle contraction. All bands and zones of the sarcomere shorten during contraction except the A-band, which is the full length of the thick filaments. In this diagram, that is region 1. Thus, the remaining regions all shorten, making choice (D) the correct answer. Region 2 represents the I-band, region 3 represents the H-zone, and region 4 is the length of the sarcomere between Z-lines.