Chemical digestion — Cambridge IGCSE Combined Science
Chemical digestion into small soluble molecules, and what amylase, protease and lipase break down, their products and where they act.
Revision notes
1 short note, in the order of the specification. Each one in short:
Chemical digestion is the breakdown of large insoluble molecules into small soluble molecules, carried out by enzymes, so they can be absorbed into the blood. Amylase breaks starch into simple reducing sugars, protease breaks protein into amino acids, and lipase breaks fats and oils into fatty acids and glycerol. Pancreatic enzymes act in the small intestine.
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4 exam-style questions (12 marks), each with its mark scheme.
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6 cards: flip them, mark what you knew, and practise the rest.
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The whole of human nutrition on one page, so you can see where this subtopic fits.
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Quick check questions
What is chemical digestion?
Show answer
The breakdown of large insoluble molecules into small soluble molecules.
Supplement What does lipase break down fats and oils into?
Show answer
Fatty acids and glycerol.
Supplement Where is amylase secreted?
Show answer
Salivary glands and pancreas.
Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026