Practice Quiz

IB Biology Exam Prep

Category - Biology

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Which of the following best describes how muscle fibers contract?
  1. Actin filaments shorten during the early phase of contraction, and myosin filaments shorten during the later phase of contraction.
  2. Actin and myosin filaments wind tightly around each other during contraction, which shortens their lengths.
  3. Actin filaments shorten during contraction, while myosin fibers stretch.
Explanation
Correct Response: B. During muscle contraction, actin and myosin filaments slide past one another, remaining the same length as they create movement. The actin and myosin filaments do not shorten (A) or wind around one another and shorten (C), nor does one shorten and one lengthen (D) during a contraction. Instead, the actin and myosin remain the same length as they slide past one another during a contraction.
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