Physical digestion Physical digestion is the mechanical breaking up of food into smaller pieces. It occurs in the mouth by the teeth, and in the stomach by mixing and churning. Physical digestion does not change the chemical structure of the food molecules.
Chemical digestion Chemical digestion is the breaking down of large food molecules into smaller ones, using special chemicals called digestive enzymes. Enzymes are chemicals produced by cells. They cause chemical changes to occur. The enzymes themselves do not change. Enzymes in the digestive system break down food into simpler molecules.
Large food molecule Smaller food molecules
Enzyme A chemical made in a living cell which can speed up a chemical reaction without itself being changed.
Enzyme Enzyme unchanged
Fig. 5 Enzymes in the digestive system help break food down into smaller molecules but remain unchanged themselves.
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There are many enzymes involved in numerous chemical reactions in the body such as digestion, growth and the breakdown of waste products. Enzymes are essential for life. Digestive enzymes are made in the mouth, stomach, pancreas and small intestine. Each enzyme is different and will only act on one type of food molecule. Therefore, they are specific to this type of food molecule. For example, an enzyme that breaks down fat will not break down protein.
10.6 The mouth
Physical digestion in the mouth Food is broken down into smaller pieces using the teeth. An adult has 32 teeth. There are four types of teeth.
