What is the primary function of the human skeleton?

The primary function of the human skeleton is to provide support, protect internal organs, and facilitate movement. The skeleton creates a rigid framework that supports the body's shape and structure, allowing humans to stand upright and maintain proper posture. This support is essential for other bodily functions and activities.

Additionally, the skeleton protects vital internal organs such as the heart, lungs, and brain. For instance, the rib cage safeguards the heart and lungs from physical damage, while the skull encases and protects the brain.

Moreover, the skeleton plays a crucial role in facilitating movement. Bones serve as levers that muscles pull on to produce movement, and joints allow for flexibility and rotation. This coordination between bones and muscles is vital for all types of physical activity, whether it's walking, running, or performing intricate tasks.

The other options do not primarily relate to the main functions of the skeleton. Energy for cellular functions comes from metabolic processes within cells, hormonal regulation is controlled by the endocrine system, and the production of heat relates more to metabolic processes and muscle activity rather than directly to the skeletal system.