Which organ system is essential for locomotion and maintaining posture?

The muscular system is essential for locomotion and maintaining posture due to its primary function of enabling movement through muscle contractions. Muscles work in coordination with the skeletal system, contracting to create movement at the joints, which facilitates activities such as walking, running, and other forms of physical activity.

In addition to enabling movement, the muscular system is crucial for maintaining posture. Muscles stabilize the body in various positions, supporting the spine and allowing for balance. This stability is necessary for standing, sitting, and performing physical tasks where alignment and support are vital.

While the nervous system plays a significant role in controlling and coordinating muscle movements, and the endocrine system regulates various body functions including growth and metabolism, it is the muscular system itself that directly engages in locomotion and posture. The integumentary system, which includes skin, hair, and nails, primarily serves protective and sensory functions rather than locomotion. Therefore, the muscular system is the correct choice for the organs involved in movement and maintaining posture.