Which of the following is NOT a function of the skeletal system?

The skeletal system has several vital functions, including protecting soft body organs, storing certain minerals and fats, and forming blood cells through the bone marrow.

When considering the choice that does not belong to the functions of the skeletal system, it's important to focus on the fact that defending against viruses, bacteria, fungal infections, and parasites is not a role of the skeletal system. Instead, this function is primarily associated with the immune system, which is responsible for recognizing and combating pathogens.

The skeletal system's involvement in other functions underscores its significance in providing structural support, facilitating movement, and hosting the body's hematopoietic (blood-forming) processes. Therefore, identifying the immune response as outside the skeletal system's responsibilities clarifies why this choice is correct.