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Detailed notes on Human Nutrition for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Mouth chewing, stomach churning, bile emulsifying. Cambridge wants tooth types, tooth structure, and the surface-area logic.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Incisor, canine, premolar, molar — different shapes for different jobs.
An adult human has 32 teeth, in 4 types. Each tooth's SHAPE matches its FUNCTION.
1. Incisors (8 in total — 4 upper, 4 lower at the front).
2. Canines (4 — corners of incisors).
3. Premolars (8 — between canines and molars).
4. Molars (12, including 4 wisdom teeth).
Worked qualitative. Why do herbivores have more molars and few canines?
Cambridge tip. Memorise the order: i₂c₁p₂m₃ (in each half jaw, top and bottom). Total: 32. Babies have 20 (no premolars; only 8 molars).
Enamel outside (crown), dentine in the middle, pulp inside with nerves and blood.
Three regions of a tooth:
Crown (above the gum) and root (below the gum), with the neck in between.
Layers from outside in:
| Layer | Where | Function |
|---|---|---|
| Enamel | Crown only | Hardest substance in the body. Protects from wear and acid. NO nerves. |
| Cement | Root only | Anchors the tooth to the JAW BONE via the periodontal membrane. |
| Dentine | Both crown + root | Slightly softer than enamel; main bulk of the tooth. Has tiny channels for sensation. |
| Pulp | Centre | Living tissue with NERVES and BLOOD VESSELS. Senses pain, hot, cold; supplies nutrients. |
Worked qualitative. Why does a cavity hurt only when it reaches the dentine?
Tooth decay.
Cambridge tip. Cambridge labels diagrams. Memorise: ENAMEL (crown), CEMENT (root), DENTINE (between), PULP (centre).
Chewing breaks food into small pieces; stomach churns the rest.
In the mouth:
In the stomach:
The point of all this physical break-up. Enzymes only work on a food particle's SURFACE. A cube of food 1 cm on each side has 6 cm² of surface. Cut it into 1 mm cubes and the total surface jumps to 60 cm². Cut it again to 0.1 mm and you reach 600 cm².
More surface = more enzyme reach = faster digestion.
Worked qualitative. Why doesn't a sip of orange juice need any chewing?
Cambridge tip. When asked "why chew", say "to break food into smaller pieces, INCREASING SURFACE AREA for enzyme action". The full phrase earns 2 marks.
Bile breaks big fat drops into tiny ones. Not chemical — just mechanical break-up by detergent action.
Where it happens. Small intestine (duodenum), where bile from the gall bladder is released onto incoming chyme.
The problem with fat. Fat is INSOLUBLE in water (and gut contents are watery). It forms big greasy globules → very small surface area → lipase can hardly reach it.
What bile does.
Why it matters.
Bile also neutralises acid.
Worked qualitative. A patient has had their gall bladder removed. Why might they need to eat smaller, low-fat meals?
Cambridge tip. EMULSIFICATION is the keyword. Cambridge marks 'emulsifies fat' specifically. 'Breaks down fat' loses marks because that sounds chemical.
Verbatim phrases and definitions Cambridge mark schemes credit.
Physical digestion appears every Paper 2 (3-4 marks: name a tooth/layer or explain bile). Examiner reports flag students saying 'bile digests fat' and confusing the enamel/dentine/pulp order.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (7.3); 0610/22 May/Jun 2024 — Q5 (teeth, physical digestion); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on physical digestion, written exactly the way a tutor would explain them at the board.
Question
Name the four types of human teeth and describe what each is shaped for.
Step-by-step solution
Step 1
Incisors (front, chisel-shaped): cutting and biting food.
Step 2
Canines (pointed, next to the incisors): tearing and gripping food.
Step 3
Premolars (with cusped surfaces): crushing and grinding.
Step 4
Molars (back, broad surfaces): grinding and chewing.
Answer
Incisors cut/bite, canines tear, premolars and molars crush and grind.
Question
Describe the structure of a human tooth, naming enamel, dentine, pulp and cement.
Step-by-step solution
Step 1
Enamel (covering the crown): the hardest substance in the body; protects the tooth from wear.
Step 2
Dentine: a bone-like layer beneath the enamel, forming the bulk of the tooth.
Step 3
Pulp (the central cavity): living tissue containing nerves and blood vessels.
Step 4
Cement: covers the root and, with the gums, holds the tooth in its socket in the jawbone.
Answer
From the outside in: enamel (crown), dentine, then pulp (with nerves and blood vessels). Cement and the gums fix the root in the jawbone.
Question
Explain why physical digestion is important, even though chemical digestion does the actual breaking of bonds.
Step-by-step solution
Step 1
Enzymes can only act on the SURFACE of food particles.
Step 2
A large lump of food has a small surface-area-to-volume ratio, so enzymes reach only its outer layer.
Step 3
Physical digestion (chewing, churning, emulsification) breaks food into many smaller pieces.
Step 4
More, smaller pieces means a larger TOTAL surface area, so enzymes work much faster and digestion is completed in a reasonable time.
Answer
Physical digestion increases the surface area of the food for the action of enzymes, so chemical digestion happens much faster.
Examiner tip
Use the exact phrase 'increases the surface area for enzyme action' (syllabus 7.3.2).
Question
Describe the role of the stomach in physical digestion.
Step-by-step solution
Step 1
The stomach wall has muscles that contract and relax.
Step 2
These muscular contractions churn the food, mixing it with the gastric juice (acid and enzymes).
Step 3
The churning breaks the food into smaller pieces and makes a semi-liquid mixture.
Step 4
This increases the surface area of the food and mixes it thoroughly with enzymes, helping chemical digestion.
Answer
The muscular stomach wall churns the food, breaking it into smaller pieces and mixing it with digestive juices — increasing the surface area for enzyme action.
Examiner tip
The stomach's physical role is churning/mixing, which is mechanical, not chemical. Keep it separate from the action of its enzymes and acid.
Question
Explain how bile assists in the digestion of fats and oils.
Step-by-step solution
Step 1
Bile is made by the liver, stored in the gall bladder, and released into the small intestine.
Step 2
Bile emulsifies fats — it breaks large fat droplets into many tiny droplets.
Step 3
This greatly increases the surface area of the fat exposed to the enzyme.
Step 4
With a larger surface area, lipase can digest the fat much faster (into fatty acids and glycerol).
Answer
Bile emulsifies fats, breaking large droplets into many small ones and so increasing the surface area for lipase, which speeds up the chemical digestion of fat.
Examiner tip
Bile is NOT an enzyme — it only emulsifies (a physical process). The surface-area link to lipase is the marked point.
Question
A person who chews their food thoroughly digests it faster than someone who swallows large lumps. Explain why, linking physical and chemical digestion.
Step-by-step solution
Step 1
Thorough chewing is physical digestion: the teeth break the food into many small pieces.
Step 2
Many small pieces have a much larger total surface area than a few large lumps.
Step 3
Digestive enzymes act on the surface of the food, so a larger surface area means more enzyme molecules can act at once.
Step 4
Therefore chemical digestion happens faster and more completely, whereas large lumps are digested only on the outside and pass through more slowly.
Answer
Chewing increases the surface area of the food, so more enzymes can act on it at once, making chemical digestion faster and more complete. Swallowing large lumps leaves a small surface area, so digestion is slower.
Examiner tip
This connects physical and chemical digestion: physical breakdown → larger surface area → faster enzyme action.
High-scoring sample answers for physical digestion on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State what is meant by physical digestion. (1 mark)
Model answer
Physical digestion is the breakdown of food into smaller pieces without any chemical change to the food molecules.
Why this scores
One mark for 'breaking food into smaller pieces without chemical change'.
State the function of (a) the incisors and (b) the molars in physical digestion. (2 marks)
Model answer
(a) The incisors are used to cut or bite off pieces of food. (b) The molars are used to grind and crush food into smaller pieces.
Why this scores
One mark each. Incisors → cutting/biting; molars → grinding/crushing.
Describe the structure of a human tooth. (3 marks)
Model answer
The crown of the tooth is covered by hard enamel, which protects it. Beneath the enamel is a layer of bone-like dentine that makes up most of the tooth. In the centre is the pulp cavity, which contains nerves and blood vessels. The root is covered by cement and is held firmly in the jawbone and gums.
Why this scores
Three marks from: enamel (hard, protective, on crown); dentine (bulk of tooth); pulp (nerves and blood vessels); cement/embedded in bone and gums.
Explain why physical digestion is important for chemical digestion. (4 marks)
Model answer
Physical digestion, such as chewing and churning, breaks the food into smaller pieces. This greatly increases the total surface area of the food. Because digestive enzymes act on the surface of the food, a larger surface area allows more enzyme molecules to act at the same time. This makes chemical digestion faster, so the food is fully digested in the time available.
Why this scores
Four marks: breaks food into smaller pieces; increases surface area; enzymes act on the surface; so chemical digestion is faster.
Describe the role of bile in the digestion of fats. (5 marks)
Model answer
Bile is made by the liver, stored in the gall bladder, and released into the small intestine. It emulsifies fats, which means it breaks large droplets of fat into many tiny droplets. This greatly increases the surface area of the fat. With a larger surface area, the enzyme lipase can act faster, digesting the fat into fatty acids and glycerol more quickly. (Bile is alkaline and is not an enzyme — it does not break chemical bonds itself.)
Why this scores
Five marks from: made in liver / stored in gall bladder / released into small intestine; emulsifies fat = large droplets to small droplets; increases surface area; speeds up lipase. Stating bile is not an enzyme avoids the common error.
Describe the roles of the different types of teeth and of the stomach in the physical digestion of food. (6 marks)
Model answer
Physical digestion begins in the mouth, where the teeth break food into smaller pieces. The chisel-shaped incisors at the front cut and bite off pieces of food. The pointed canines beside them tear and grip food. The premolars and molars at the back, which have broad cusped surfaces, crush and grind the food into a paste. This chewing increases the surface area of the food. The food then passes to the stomach, whose muscular wall contracts and relaxes to churn the food, breaking it up further and mixing it thoroughly with the gastric juices to form a semi-liquid. Both the teeth and the stomach therefore carry out physical digestion by breaking the food into smaller pieces and increasing its surface area, which speeds up the chemical digestion that the enzymes carry out.
Why this scores
Up to 6 marks: incisors cut; canines tear; premolars/molars grind/crush; teeth increase surface area; stomach churns/mixes food; overall point that this increases surface area for enzymes.
Definitions to memorise and the exact keywords mark schemes credit for physical digestion answers — sharpened from recent examiner reports for the 2026 0610 sitting.
Breaking food into smaller pieces WITHOUT changing the food molecules chemically. Includes chewing, churning and emulsification.
The process by which bile breaks large fat droplets into many tiny droplets, greatly increasing the surface area for lipase.
Front, chisel-shaped tooth used for cutting and biting.
Pointed tooth next to the incisors, used for tearing or gripping food.
Back teeth with cusped surfaces, used for crushing and grinding.
Hardest substance in the body; the mineral-rich layer covering the crown of a tooth.
The traps other students keep falling into on physical digestion questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Bile is associated with fat.
How to avoid it
Bile EMULSIFIES fat (a physical process). Lipase (an enzyme) DIGESTS fat (a chemical process). Bile only helps lipase by increasing the surface area.
Why it happens
All teeth crush a little.
How to avoid it
Canines are POINTED → for TEARING. Premolars and molars (broad cusped surfaces) crush and grind.
Why it happens
Both stages happen together.
How to avoid it
Physical digestion does NOT break chemical bonds. It just makes the pieces smaller. Chemical digestion (by enzymes) breaks the bonds.
The things students keep getting wrong in this sub-topic, answered.