Digestion is the mechanical and chemical breakdown of food into small molecules that cells absorb and use. Chemical digestion breaks apart food on a molecular level through chemical reaction. Once food is digested, its nutrients are absorbed into the body and carried to the cells. Both types of digestion start in the mouth. The teeth are responsible for mechanical digestion by grinding and chewing food to break to into smaller piece. This makes it easier for chemical digestion to occur. Saliva in the mouth has special chemical in it called enzymes. An enzyme is a type of protein that regulates nearly all chemical reactions in cells. Enzymes start breaking the food into simpler molecules the body can use.