Physical digestion Cambridge IGCSE Biology revision
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In plain words
Before enzymes can get to work, food has to be broken into small pieces. Chewing and churning don't change what the food is made of, they just smash it up. A sugar cube and the same sugar as powder are the same stuff, but the powder dissolves far faster.
Three things to know
- Physical digestion breaks food into smaller pieces without changing its molecules. This gives a larger surface area for enzymes to work on.
- Teeth: incisors cut, canines tear, premolars and molars crush and grind. A tooth has hard enamel outside, dentine under it, and a pulp in the middle with nerves and blood vessels.
- The stomach churns food with its muscular walls. Bile, made in the liver and stored in the gall bladder, breaks fat into tiny droplets (emulsification).
Tips and tricks
- Bile is not an enzyme. It doesn't break fat molecules down, it only splits big drops into small ones.
- "Increases the surface area for enzymes" is the reason behind every bit of physical digestion.
It lands in your notebook with its questions as flashcards.
Physical 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.
What does physical digestion do?
The molecules themselves are unchanged.
Which teeth are used for grinding?
Their broad, ridged surfaces crush food.
What is the hard outer layer of a tooth?
Enamel is the hardest substance in the body.
What does bile do to fats?
This is emulsification.
Where is bile made?
It is stored in the gall bladder until it is needed.
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.
Physical digestion
Cambridge IGCSE Biology 0610 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Explain why chewing food helps digestion.[2]
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It breaks the food into smaller pieces, giving a larger surface area for enzymes to act on.
State the function of incisors and of molars.[2]
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Incisors bite and cut food. Molars grind and crush it.
Describe the role of bile in digestion.[3]
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It emulsifies fats, breaking large drops into small droplets, which gives lipase a larger surface area. It is also alkaline, so it neutralises the acid from the stomach.
Answers: Physical digestion
- 1. It breaks the food into smaller pieces, giving a larger surface area for enzymes to act on.
- 2. Incisors bite and cut food. Molars grind and crush it.
- 3. It emulsifies fats, breaking large drops into small droplets, which gives lipase a larger surface area. It is also alkaline, so it neutralises the acid from the stomach.