Practice question

Warm-blooded animals, more precisely endothermic homeotherms, use metabolic heat and physiological regulation to keep core temperature relatively stable across a range of environmental temperatures. Birds and mammals adjust insulation, blood flow, evaporation, shivering, and behaviour to balance heat production and loss. Cold-blooded animals are generally ectothermic, obtaining much of their heat from the environment, so body temperature and physiological rate vary more strongly with external conditions. They can still regulate behaviourally by basking or seeking shade. Hibernation is not exclusive to warm-blooded species; many ectotherms undergo seasonal dormancy, often termed brumation in reptiles. Ectotherms typically have lower, not higher, food demands because they do not continuously fuel intense thermogenesis. Body size also does not provide an absolute distinction: both groups contain small and large species. Stable internal temperature is therefore the biologically meaningful contrast among the choices. Even this distinction has exceptions. Some endotherms use torpor and become temporarily heterothermic, while large active fishes or insects may retain metabolically produced heat regionally. “Warm-blooded” and “cold-blooded” are convenient labels, but endothermy, ectothermy, homeothermy, and poikilothermy describe mechanisms more precisely.