Define mechanical and chemical digestion.

Mechanical digestion means digestion of food when it is travelling in the alimentary canal whereas chemical digestion is the phase when it breaks down into smaller particles by the action of various enzymes ...

Mechanical digestion begins in the mouth as the food is chewed. Chemical digestion involves breaking down the food into simpler nutrients that can be used by the cells. Chemical digestion begins in the mouth when food mixes with saliva. Saliva contains an enzyme (amylase) that begins the breakdown of carbohydrates.