Chemical digestion Cambridge IGCSE Biology (9–1) revision
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In plain words
Starch, protein and fat molecules are too big to get through the gut wall. Enzymes act like scissors, snipping them into pieces small enough to be absorbed. There's a different enzyme for each kind of food.
Three things to know
- Amylase breaks starch into sugars. It is made in the salivary glands and the pancreas, and works in the mouth and small intestine.
- Proteases break proteins into amino acids. Pepsin works in the stomach (acid); trypsin, from the pancreas, works in the small intestine (alkaline).
- Lipase, from the pancreas, breaks fats into fatty acids and glycerol. Hydrochloric acid in the stomach kills microbes and gives pepsin the acid it needs.
Tips and tricks
- Learn a table: enzyme, what it breaks down, what it makes, where it's made.
- Large insoluble molecules are broken into small soluble ones "so they can be absorbed". Finish the sentence.
It lands in your notebook with its questions as flashcards.
Chemical digestion: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which enzyme breaks down starch?
Amylase is in saliva and pancreatic juice.
What are the products of fat digestion?
Lipase breaks fats down.
Where does pepsin work?
It needs the acid conditions of the stomach.
What are proteins broken down into?
Proteases do this.
Which organ makes amylase, protease and lipase?
Pancreatic juice is released into the small intestine.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Chemical digestion
Cambridge IGCSE Biology (9–1) 0970 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Name the enzyme that digests each of these, and its products: starch, protein, fat.[3]
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Starch: amylase, giving sugars (maltose). Protein: protease, giving amino acids. Fat: lipase, giving fatty acids and glycerol.
Give two functions of the hydrochloric acid in the stomach.[2]
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It kills microorganisms in the food, and it provides the acid pH that pepsin (the protease) needs.
Explain why food has to be digested.[2]
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Large, insoluble molecules cannot pass through the wall of the gut. They must be broken into small, soluble molecules that can be absorbed into the blood.
Answers: Chemical digestion
- 1. Starch: amylase, giving sugars (maltose). Protein: protease, giving amino acids. Fat: lipase, giving fatty acids and glycerol.
- 2. It kills microorganisms in the food, and it provides the acid pH that pepsin (the protease) needs.
- 3. Large, insoluble molecules cannot pass through the wall of the gut. They must be broken into small, soluble molecules that can be absorbed into the blood.