Define endothermy and its relation to mammalian physiology.

• A. The maintenance of a stable, high body temperature through internal metabolic heat production; enables sustained activity.
• B. The body temperature mirrors the environment.
• C. Heat is produced only during exercise.
• D. Temperature is regulated primarily by external factors.

Answer: (A)

Endothermy means maintaining a stable, relatively high body temperature through internal metabolic heat production. In mammals, this internal heat comes from the body's own metabolism and is supported by insulation such as fur and body fat, plus regulatory systems that keep temperature within a narrow range. This internal control lets mammals stay active across a wide range of environments because enzymes and muscles work best at a consistent temperature, supporting sustained activity. Heat can be generated by processes like shivering and, in some species, non-shivering thermogenesis using brown adipose tissue. Thermoregulation also involves adjusting blood flow, sweating or panting, and behaviors to balance heat gain and loss. Because temperature is controlled internally rather than simply mirroring the environment, endothermy is a defining feature of mammals, enabling high-energy lifestyles.