Final answer:
Z discs do not bisect the A bands; instead, they mark the boundaries of sarcomeres and are located at the midpoints of the I bands, not the A bands. During muscle contraction, Z discs move closer together, but the width of the A band remains unchanged.
Step-by-step explanation:
The student's question concerns the positioning of Z discs in the muscle fiber's structure. The claim that Z discs are found bisecting the A bands is false. Z discs are not located in the middle of A bands; instead, they precisely mark the boundaries of sarcomeres. The A band is found in the center of the sarcomere and consists of overlapping actin and myosin filaments, whereas Z discs run through the middle of the I band. When considering a single sarcomere, Z discs are at either end, with the A band in the middle. During muscle contraction, the Z discs move closer together, and the length of the I band decreases, but the A band remains the same width. This clearly indicates that the Z discs do not bisect the A band but are separate from it.