Final answer:
The arrector pili muscle causes hair to stand on end, resulting in goose bumps as a reaction to cold or emotional stress. It is not responsible for sweat production, skin pigmentation, or sensing temperature.
Step-by-step explanation:
The arrector pili muscle plays a significant role in the body's response to cold and emotional stimuli. When activated by the sympathetic nervous system, these tiny muscles, which are attached to hair follicles, contract and pull the hair upright. This action is responsible for creating goose bumps on the skin's surface. The contraction of the arrector pili muscles occurs as part of the body's thermoregulatory mechanisms. While other skin components such as sweat glands and blood vessels work to regulate temperature by sweating and changing blood flow, the arrector pili muscles are not involved in sweat production, skin pigmentation, or direct temperature sensation. They are strictly associated with elevating the hair which, in the case of animals with thick fur, provides additional insulation. In humans, the response is more related to our primitive reactions and has less of an insulating effect.
The final answer for the student's question is, the arrector pili muscle is responsible for B) Hair standing on end. This is the cause of goose bumps and is a reaction to cold or emotional stress, not directly associated with sweat production, skin pigmentation, or sensing temperature.