Chapter 15

If more food energy is consumed than is expended, explain the possible fates of the excess energy.

The basal metabolic rate (BMR) is about \(72 \mathrm{kcal} / \mathrm{hr}(301 \mathrm{~kJ} / \mathrm{hr})\) in an average human, with nearly all the energy converted to heat. If we could not lose this heat, our temperature would rise until we boiled (although we would die long before reaching that temperature). How long would that take? If an amount of energy \(\Delta U\) is put into a liquid of mass \(m\), the temperature change \(\Delta T\) (in \({ }^{\circ} \mathrm{C}\) ) is given by the following formula: $$ \Delta T=\Delta U / m \times C $$ Here, \(C\) is the specific heat of the liquid. For water, \(C=\) \(1.0 \mathrm{kcal} / \mathrm{kg}-{ }^{-} \mathrm{C}\). Calculate how long it would take for BMR heat to boil your body fluids (assume 42 liters of water in your body and a starting body temperature at \(\left.37^{\circ} \mathrm{C}\right)\).

Why is it dangerous to engage in heavy exercise on a hot, humid day?

Different groups of homeotherms have different body temperatures. Why might that be?