Which of these is NOT a primary function of the hair?

The reason why absorption of nutrients is not a primary function of the hair is that hair itself does not have the biological capability to absorb nutrients. Hair is composed of a protein called keratin and is considered a non-living structure once it emerges from the scalp. Its characteristics and functions are primarily related to protection, insulation, and regulation of body temperature.

In contrast, hair provides protection by shielding the scalp from UV radiation and environmental elements, while also helping to keep debris away from the skin. It serves an insulating function by trapping air and retaining warmth during cold weather. Additionally, hair can participate in temperature regulation by helping to dissipate heat through the scalp when it is hot. These primary functions highlight the roles of hair in maintaining health and homeostasis, contrasting with the incorrect choice that misattributes a biological function to hair that is actually linked to other systems in the body.