The first task of the digestive system is to break down food into a fine pulp (mechanical digestion). When the food is physical broken down, digestive chemicals break the food down into small molecules (chemical digestion). The mouth is the organ in which the process of digestion begins. It starts the process of mechanical digestion by grinding the food with teeth. Also in the mouth, an enzyme called salivary amylase begins to break down long starch molecules into maltose.