In model physical science systems, the rate of a chemical reaction typically doubles every 10oC increase in temperature. In biological systems, however, where biochemical reactions tend to be enzyme catalyzed, the dependence of rate on temperature is more complex. A particular enzyme will possess an optimal temperature. For example, ectotherms (i.e. 'cold blooded') can either occupy a habitat of constant temperature for optimal enzyme activity, such as the deep ocean, or their physiological processes may have adapted for a range of temperature. Temperature regulation in endothermic animals depends on the internal generation of heat to maintain a chemical environment for optimal enzyme function.