Which of the following best describes the term sarcomere?

• A. A type of muscle fiber responsible for slow, sustained contractions
• B. The basic contractile unit of a muscle fiber
• C. A protein that binds to actin during muscle contraction
• D. The region where myosin heads attach to actin filaments

Answer: (B)

Verified step by step guidance

1. Understand that the term 'sarcomere' is related to muscle structure and function.
2. Recognize that a sarcomere is a segment within a myofibril, which is a component of muscle fibers.
3. Identify that the sarcomere is the basic contractile unit of a muscle fiber, meaning it is the smallest functional unit that can contract.
4. Note that the sarcomere is defined by the region between two Z-lines (or Z-discs) in a myofibril.
5. Understand that during muscle contraction, the sarcomere shortens as actin and myosin filaments slide past each other, which is facilitated by the attachment of myosin heads to actin filaments.