How is it that cold-blooded animals do not generate heat?
You are correct that one of the byproducts of chemical reactions within the body is heat. However, these processes do not generate enough heat for an endotherm to stay warm. Endotherms have evolved ways to stimulate the body cells to continuously burn up energy to stay warm. The hypothalamus of endotherms acts as a thermostat, signaling the body cells to generate heat through metabolism by releasing hormone into the blood. Ectotherms do not have the same mechanism to generate heat to stay warm. That is why ectotherms need a lot less food. Animals that are moving or doing work would of course burn up energy. Endotherms burn up energy even when they are at rest just to generate heat. Endotherms therefore have much higher basal metabolic rates than ectotherms in order to maintain an elevated body temperature. Small endotherms have proportionally greater surface areas per unit volume than large ones, so small endotherms lose heat more quickly to the environment, and they need to burn up th
