The biological implications and consequences of temperature
Although no organism has learned to use thermal energy as a source of metabolism, the chemical reactions that are life are continually responding to exchanges of energy with other molecules -- that is, they respond to temperature. It's why animals have evolved the mechanism of fever (raising their body temperature) to defend against some infections.
Since the chemical reactions that take place in their bodies depend on temperature, animals often care what their temperature is. Some animals adjust their temperature by absorbing heat from their environment. Such animals (for example, lizards) are called ectotherms. They control temperature by moving to where they can absorb more heat, such as into the sun, or where they can absorb less heat, such as into the shade. As a result, their temperature fluctuates considerably through the day and night.
Other animals generate thermal energy internally. These endotherms burn fat and sugar to convert them to thermal energy and so stabilize their body temperatures. It is possible to be an ectotherm and find an environment with a relatively stable temperature to maintain a constant body temperature. So while an ectotherm, such as a snake or turtle, can have a wildly varying body temperature as it moves in and out of the sun (making it a poikilotherm, poikilo- means varied or irregular), other ectotherms such as marine fish stay in water of quite stable temperature to keep their temperature nearly constant. This makes some fish homeotherms (homeo- means same or similar). Properly functioning endotherms will be homeotherms as the point of generating internal energy is to maintain a constant temperature.
Joe Redish and Karen Carleton 11/20/11
Last Modified: July 13, 2019