Acountercurrent heat exchanger enables an animal to see concept 40.3 (page 883) increase heat loss by evaporation slow metabolism when food is not available reduce the loss of body heat to the environment absorb heat from the environment produce more heat when needed

The correct answer is: reduce the loss of body heat to the environment. A countercurrent heat exchanger works by transferring heat from one part of the body to another that has cooled down. For example, in dolphins, body parts of a high surface area such as flippers are rich in veins. Blood running through these veins that is cooled down is run close to arteries containing warmed-up blood, and some of the heat energy from the arteries is transferred to the veins, thereby allowing the dolphin to conserve heat energy.