Which term describes animals that obtain most body heat from the environment?

• A. Endotherm
• B. Poikilotherm
• C. Ectotherm
• D. Homeotherm

Answer: (C)

The main idea being tested is whether an animal relies on external sources for heat versus generating it internally. Animals that obtain most of their body heat from the environment are ectotherms. They depend on heat from surroundings—sunlight, warm rock, or heated water—to raise and regulate their body temperature, so their internal temperature tends to rise and fall with the environment. You can see this in reptiles, amphibians, and many fish and invertebrates, which bask to warm up or seek shade to cool down.

In contrast, endotherms generate most of their heat metabolically, keeping their internal temperature relatively stable regardless of the outside temperature. Homeotherms describe that stable internal temperature, often aligned with endothermy, while poikilotherms describe organisms whose body temperatures vary with the environment. The term that directly answers “obtain most body heat from the environment” is ectotherm.