Lesson 7 of 9
Enzymes
Goal: Describe enzymes as biological catalysts.
Enzymes are biological catalysts. They speed up the breaking down of large food molecules into small ones.
An enzyme breaks a large starch molecule into small sugar molecules. The enzyme is not used up.
- Large molecules cannot be absorbed. Molecules of starch, protein and lipid are too big to pass through the wall of the small intestine.
- Enzymes break them into small molecules. These pass through the wall into the blood, and the blood carries them to your cells.
- Digestive juices contain enzymes. Saliva, the juices in the stomach and the juice from the pancreas all have them. Each enzyme works on one kind of nutrient.
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Key words in this lesson
Lipid A fat or an oil, which the body can store for energy
Protein The nutrient used to build new tissue for growth and repair
Digestion Breaking large food molecules into small ones
Enzyme A substance that speeds up the chemical reactions of digestion
Stomach A bag where food is mixed with acidic juices
Small intestine Where digestion is completed and food is absorbed into the blood