Final answer:
b) Titin links the thick filaments to the Z line.
Step-by-step explanation:
The sarcomere, the basic unit of muscle contraction, is made up of thick and thin filaments. These filaments are essential parts of the muscular system and interact to facilitate muscle contractions. The thick filaments are primarily composed of myosin, and they are centrally located in the sarcomere, extending from the M line toward but not quite reaching the Z discs. The thin filaments are primarily composed of actin and are anchored to the Z discs, extending toward the center of the sarcomere to interact with the thick filaments.
In terms of the specific protein that links the thick filaments to the Z line, the correct option is titin (option b). Titin is a massive protein that holds the record as the largest known polypeptide. It extends from the Z disc to the M line of sarcomeres, coiling around thick filaments along the way. Titin's role is to provide structural support and elasticity to the sarcomere by anchoring the thick filaments to the Z discs, which maintain the alignment and proper functioning of the muscle fibers.