Cell physiology (including cellular electrophysiology) is the biological study of the cell's mechanism and interaction in its environment. The term "physiology" refers to all the normal functions that take place in a living organism. Absorption of water by roots, production of food in the leaves, and growth of shoots towards light are examples of plant physiology.  The heterotrophic metabolism of food derived from plants and animals and the use of movement to obtain nutrients (even if the organism itself remains in a relatively stationary position) are characteristic of animal physiology.