Final answer:
The striations in skeletal muscle cells are caused by the precise arrangement of actin and myosin myofilaments within the sarcomeres of myofibrils.
Step-by-step explanation:
The striations of a skeletal muscle cell are produced primarily by the arrangement of myofilaments. Skeletal muscle fibers contain highly organized structures called myofibrils, which in turn are composed of repeated units called sarcomeres. Within sarcomeres, actin (thin filaments) and myosin (thick filaments) are arranged in a precise pattern that leads to the characteristic striped, or striated, appearance. The alternating light and dark bands visible under a microscope correspond to different parts of the sarcomere where these myofilaments overlap or do not overlap. Therefore, the correct answer is related to the organization of actin and myosin myofilaments within the muscle cell.