Evaporation via sweating as primary heat loss on hot days

Steps:

• Identify scenario: Air temperature exceeds body temperature, limiting conduction, convection, and radiation for heat loss.
• Recall thermoregulation: Body relies on evaporation when environmental heat prevents passive transfer.
• Evaluate options: Focus on mechanisms promoting active heat dissipation rather than conservation or production.
• Select best: Increased sweat production enables evaporative cooling, the most effective method here.

Why D is correct:

• Evaporation of sweat absorbs heat via the latent heat of vaporization (about 2420 J/g), directly cooling the skin and blood.

Why the others are wrong:

• A: Narrower vessels (vasoconstriction) reduce skin blood flow, conserving heat by limiting dissipation.
• B: Flat hairs reduce insulation minimally in humans and do not actively remove heat.
• C: Ceasing shivering stops heat generation but does not facilitate heat loss.

Final answer: D