Which term describes an animal whose body temperature matches the environment?

• A. Endotherm
• B. Echolocation
• C. Exoskeleton
• D. Ectotherm

Answer: (D)

Understanding how body temperature is regulated across animals helps explain why some animals heat up or cool down with their surroundings. An animal whose body temperature matches the environment is an ectotherm. Ectotherms rely on external heat sources—like sunlight or warm rocks—to raise body temperature and become less active when it’s cool, so their internal temperature fluctuates with ambient conditions. This is in contrast to endotherms, which generate metabolic heat to keep a relatively constant internal temperature, allowing more constant activity levels regardless of the environment. Common examples of ectotherms include reptiles, many fish, amphibians, and invertebrates, while mammals and birds are typically endotherms. The other terms aren’t about temperature regulation: echolocation is a sensory method for locating objects with sound, and an exoskeleton is an external skeleton, neither describing how body temperature is controlled.