What function do actin and myosin proteins serve?

Actin and myosin are crucial proteins that play a key role in muscle contraction and movement. Together, they form the contractile apparatus of muscle fibers. Myosin heads bond to actin filaments, using energy from ATP to create the force necessary for muscle cells to shorten and contract. This process not only facilitates movement in walking, running, and flying for animals but also enables other forms of cellular movement and shape changes. Their interaction underpins the ability of organisms to perform coordinated movements, making option B the correct choice in highlighting their function.