Explanation
The sarcomere is the distance between two Z-lines in a muscle fiber. Therefore, the correct answer is option A: Z-line to Z-line.
The sarcomere is the basic unit of contraction in skeletal muscle. It is composed of thin filaments made of actin and thick filaments made of myosin. The Z-line is a dark line that marks the boundary between adjacent sarcomeres, and it serves as an anchor point for the thin filaments. The A-band is a region that contains both thick and thin filaments, while the I-band is a region that contains only thin filaments.
During muscle contraction, the sarcomeres shorten as the thin and thick filaments slide past each other. This shortening results in the contraction of the entire muscle fiber, which generates force and produces movement.
Therefore, the distance between two Z-lines in a muscle fiber is known as the sarcomere, which is the functional unit of skeletal muscle contraction.
