An animal that produces its own heat and maintains a steady body temperature.

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

Answer: (A)

Endotherms generate heat inside the body through metabolic processes, which lets them keep a relatively constant internal temperature even when the surrounding environment changes. This internal heat production, or thermogenesis, is what sets them apart from ectotherms, which rely on external heat sources and have body temperatures that vary with the environment. The description also aligns with having a steady body temperature, a hallmark of organisms that regulate their heat internally. While some terms describe constant temperature (homeothermy) or the occasional switch between endothermy and ectothermy (heterothermy), the defining feature in the statement is producing heat internally to maintain a stable body temperature, so the best fit is an endotherm.