Sweating cools the body because
- A. sweat is colder than the body
- B. sweat carries away dissolved urea
- C. the sweat glands use up energy in secreting it
- D. evaporation of the water in sweat takes latent heat from the skin
Explanation
Changing liquid water into vapour requires a large amount of latent heat, and that heat is drawn from the skin surface, so the body cools only when the sweat actually evaporates. This is why sweating is far less effective on a humid day, when evaporation is slow and the sweat simply drips off. Sweat leaves the body at body temperature, so it is not cold when secreted.
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