Some enzymes have the effect of changing a single-stage reaction requiring a large amount of energy into a multi-stage process involving only small amounts of energy. All cells produce a large number of enzymes (a typical cell contains about 3000 different enzymes); the function of a cell is determined by the nature of the enzymes present in it. Some cells release enzymes which act outside the cell, e.g. the cells lining parts of the alimentary canal produce enzymes which digest food.