Practice question

Endotherms generate most of the heat used to regulate body temperature through metabolism. Oxidation of carbohydrates and fats releases energy, much of which appears as heat rather than mechanical work. Birds and mammals can increase heat production through shivering muscles, non-shivering thermogenesis in brown adipose tissue, hormonal effects, and ordinary organ activity. Insulation and controlled blood flow then reduce or redistribute heat loss, while sweating or panting removes excess heat. Environmental heat can contribute, and many endotherms bask or seek shelter to reduce energetic costs, but it is not their primary heat source. Low oxygen would restrict aerobic metabolism and impair thermogenesis rather than support it. Reflective skin or covering may reduce solar heat gain but cannot replace heat generation. Sustained endothermy allows enzymes, nerves, and muscles to operate at relatively stable temperatures and enables activity in cold environments or at night. Its cost is high demand for oxygen and food. Endothermy should be distinguished from homeothermy: the former names the internal heat source, whereas the latter describes relative constancy of body temperature; hibernating endotherms may temporarily become heterothermic.