Digesting starch and protein in detailSpec 7.4.6, 7.4.7
In short
Starch is digested in two steps: amylase from the salivary glands and pancreas breaks starch down to maltose, then maltase on the membranes of the small intestine epithelium breaks maltose down to glucose. Protein is digested by proteases: pepsin works in the acidic stomach, and trypsin works in the alkaline small intestine.
Starch
- Amylase from the salivary glands and the pancreas breaks starch down to maltose.
- Maltase breaks maltose down to glucose. Maltase is on the membranes of the epithelium lining the small intestine.
- Glucose is small and soluble, so it can be absorbed into the blood.
Protein
| Protease | Where it works | Conditions |
|---|---|---|
| Pepsin | Stomach | Acidic, because of the hydrochloric acid in gastric juice |
| Trypsin | Small intestine | Alkaline, because of the bile mixed with the food |
Each enzyme has an optimum pH. Pepsin works best in acid and trypsin works best in alkali. Both are proteases, so both break down protein.
(opens full size in a new tab)Amylase does not make glucose directly. It makes maltose, and maltase then makes glucose. Link each enzyme to its own product.
Quick check
What is chemical digestion?
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The breakdown of large insoluble molecules into small soluble molecules.
What does lipase break down fats and oils into?
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Fatty acids and glycerol.
Where is amylase secreted?
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Salivary glands and pancreas.
Supplement Which enzyme breaks maltose down to glucose, and where is it found?
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Maltase, on the membranes of the epithelium lining the small intestine.
Supplement Why does trypsin work in the small intestine but pepsin does not?
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Trypsin works in alkaline conditions and pepsin works in acidic conditions; bile makes the small intestine alkaline.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026