Relate each tooth type to physical digestion
Explain cutting, tearing and crushing from crown shape.
Section B7.3 · Physical digestion
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall large and small nutrient molecules, cell membranes and enzyme specificity.
- Use the stated diagram keys and evidence; models are not to scale.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which teeth are especially associated with cutting?
What you will learn
- Explain cutting, tearing and crushing from crown shape.
- Separate chewing from the enzyme action occurring beside it.
Different shapes support different actions
Incisors cut or bite with an edged crown. Pointed canines help grip and tear. Premolars crush and grind with cusped surfaces; molars provide broad surfaces for crushing and grinding farther back.
These functions overlap during chewing rather than acting as four isolated machines. A tooth’s action makes smaller food pieces without itself chemically changing nutrient molecules.
Connect shape to mechanism
An incisor edge concentrates contact along a cutting edge. Broad back-tooth surfaces bring food between opposing teeth to crush and grind it. Explain the mechanism rather than simply calling all teeth sharp.
Chewing increases exposed surface for digestive enzymes and mixes food with saliva. Saliva’s enzyme action is chemical; teeth’s cutting and grinding are physical. Neither is nutrient absorption.
Sources for this lesson
Pause and explain
Why do broad molar surfaces help?
Worked example
A student identifies a broad back tooth as an incisor because it breaks food. Improve the identification.
Show the worked solution
- Many teeth break pieces.
- Use broad crown and back position.
- Identify a molar with grinding/crushing function.
Answer The broad back tooth is better identified as a molar; incisors have cutting edges at the front.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Match each type to a function: incisors, canines, premolars, molars.
Give me a hint
Use cutting, tearing and grinding.
Compare my reasoning
- Incisors cut.
- Canines grip/tear.
- Premolars and molars crush/grind.
Incisors: cut; canines: grip/tear; premolars: crush/grind; molars: crush/grind.
Look for these in your work
- All four.
- Appropriate actions.
Explain why a molar’s broad crown suits crushing more than describing it simply as “white”.
Give me a hint
A functional explanation uses shape.
Compare my reasoning
- Broad surfaces oppose each other.
- Food is pressed and ground between them.
Broad opposing surfaces crush and grind food; colour does not explain that mechanism.
Look for these in your work
- Shape-to-function link.
- No colour explanation.
A bread sample is chewed with saliva. Identify two different mechanisms that can occur at the same time.
Give me a hint
Separate teeth and enzyme.
Compare my reasoning
- Teeth physically subdivide.
- Salivary amylase chemically begins starch breakdown.
Physical digestion by teeth and chemical digestion by salivary amylase can occur together.
Look for these in your work
- Both mechanisms.
- Correct agents.
Common mistakes
- All food-breaking teeth are not incisors.
- Tooth action does not replace digestive enzymes.
What can you explain now?
Why do broad molar surfaces help?
Compare with the explanation
They crush and grind food between opposing surfaces.
Shape supports the physical action.
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Make it stick
Explain how tooth shape supports a named action and exposes food surface.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.