Which of the following is NOT a function of the skin?

The skin serves several essential functions, including protection, sensation, and thermoregulation. However, photosynthesis is not among these functions.

The skin acts as a barrier, shielding internal organs from mechanical damage, pathogens, and harmful substances, which is vital for overall protection. It also contains numerous sensory receptors that allow for the perception of touch, temperature, and pain, making sensation an essential role of the skin. Thermoregulation is achieved through processes such as sweating and altering blood flow to the skin's surface, helping to maintain a stable body temperature.

Photosynthesis, however, is a process primarily associated with plants and certain microorganisms, where they convert light energy into chemical energy, typically using chlorophyll. Humans and most animals do not have the necessary structures or mechanisms in the skin for photosynthesis to occur. Instead, humans obtain energy and necessary nutrients through their diet. Hence, it is clear why photosynthesis does not align with the functional roles of the skin.