Both types of digestion start in the
mouth. The teeth are responsible for
mechanical digestion by grinding and
chewing food to break it into smaller
pieces. This makes it easier for chemical
digestion to occur. Saliva in the mouth has
special chemicals 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.