Practice question

A large bear retains body heat more effectively than a small bird, lizard, or amphibian because body size lowers the surface-area-to-volume ratio. Heat is produced throughout metabolically active tissue, which scales broadly with mass, but exchanged with the environment across body surface. As size increases, surface area grows more slowly than volume, so less heat is lost per unit mass. Bears also possess fur and subcutaneous fat that reduce conduction and convection. Birds are endothermic and insulated by feathers, but a small bird has high relative surface area and must sustain a very high mass-specific metabolic rate to remain warm. Desert lizards and amphibians rely mainly on environmental heat and typically do not maintain the same internally generated thermal gradient; amphibian skin can additionally promote evaporative cooling. Physiological state and habitat matter—a torpid bear produces less heat, and feathers can be exceptionally effective—but the geometric comparison strongly favours the large bear for retention. This principle helps explain why many cold-region endotherms are large and compact and why small endotherms require frequent feeding to offset rapid heat loss.