Question

when the body is cold, body hair stands upright because. multiple choice the cold hair stiffens the hair shaft the hair bulb begins to freeze, making it difficult for the hair shaft to relax the hair receptors respond to cold by triggering an electrical impulse into the hair shaft contraction of an arrector pili muscle pulls the follicle vertically the skin stiffens around the hair shaft, making it difficult for the hair shaft to move

Explanation:

When the body is cold, the arrector pili muscles (tiny muscles attached to hair follicles) contract. This contraction pulls the follicle vertically, causing the body hair to stand upright. This is a physiological response (goosebumps) that in animals can trap a layer of air for insulation. The other options are incorrect as:

• Cold doesn't stiffen the hair shaft in a way that causes upright hair (first option).
• The hair bulb doesn't freeze (second option).
• Hair receptors don't trigger electrical impulses into the hair shaft (third option).
• Skin stiffening around the hair shaft isn't the cause (last option).

Answer:

contraction of an arrector pili muscle pulls the follicle vertically