Function (biology)

Function in biology is what a part of the body or cell does in relation to the whole. It is the reason some part or process occurred in a system which evolved by natural selection.
A similar definition is "the function of a component in an organism is the contribution it makes to that organism's fitness".
The term is used especially in physiology, in phrases like "the function of the kidneys is to excrete urea from the body" or "the function of the heart is to push blood around the body". It is incorrect to use the word 'purpose' instead of 'function', because the word 'purpose' implies forethought.