Cambridge O Level Biology 5090: Human nutrition (5090) – Revision Notes

For full explanations and worked examples, read the human nutrition study guide first.

These notes cover Topic 8, Human nutrition, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4): sections 8.1 Diet, 8.2 Human digestive system and 8.3 Absorption and assimilation. The syllabus is not tiered, so everything here is for every candidate. Test yourself with the practice questions, track progress on the printable checklist, or start from the course hub. A free 10-minute diagnostic shows which topics need work first.

8.1 Diet in one table

Nutrient	Two sources	Why you need it	Deficiency
Carbohydrate	Rice, bread	Energy (respiration)	–
Lipid	Oil, butter	Energy store, insulation, membranes	–
Protein	Meat, beans	Growth and repair; enzymes, antibodies	–
Vitamin C	Citrus fruit, guava	Collagen: healthy gums, skin, blood vessels; wound healing	Scurvy: bleeding gums, bruising, slow healing
Vitamin D	Oily fish, egg yolk (and sunlight on skin)	Absorbing calcium for bones and teeth	Rickets: soft bones, bowed legs
Calcium	Milk, cheese	Hard bones and teeth; clotting; muscle contraction	Rickets
Iron	Red meat, spinach	Haemoglobin, to carry oxygen	Anaemia: tiredness, pale skin, breathlessness
Fibre	Vegetables, wholemeal bread	Bulk for peristalsis; prevents constipation	–
Water	Drinks, food	Solvent; transport; plasma	–

Balanced diet: all nutrients in the correct proportions, plus enough energy for the person’s needs. Needs vary with age, sex, activity and pregnancy.

Only vitamins C and D and minerals calcium and iron are in the syllabus. Don’t spend time on others.

8.2 The digestive system

Route of food

mouth → oesophagus → stomach → duodenum → ileum → colon → rectum → anus
                                 ↑
        salivary glands (into mouth), liver + gall bladder and pancreas
        (into duodenum) add secretions -- food never passes through them

Key definitions

• Physical digestion: breakdown of food into smaller pieces without chemical change to the food molecules.
• Chemical digestion: breakdown of large molecules into small molecules.
• Physical digestion increases surface area for enzymes in chemical digestion.
• Why digest? Large, insoluble molecules cannot be absorbed; small, soluble ones can.
• Peristalsis: waves of contraction of longitudinal and circular muscles that move food through the digestive system.
• Egestion: removal of undigested food as faeces, via the rectum and anus.

Teeth

Tooth	Shape	Job
Incisor	Chisel	Biting, cutting
Canine	Pointed	Gripping, tearing
Premolar	Cusps	Grinding, crushing
Molar	Broad, cusps	Grinding, crushing

Structure, outside in: enamel (crown, hardest) → dentine → pulp with nerves and blood vessels. Cement covers the root. The tooth is embedded in the gum.

Region functions

Region	Remember
Mouth	Ingestion; teeth; amylase on starch
Salivary glands	Saliva with amylase
Stomach	Churning; protease; hydrochloric acid
Duodenum and ileum	Amylase, maltase, protease, lipase
Liver	Makes bile; stores glycogen
Gall bladder	Stores bile
Pancreas	Alkaline secretion with amylase, protease, lipase
Ileum and colon	Absorption
Rectum and anus	Egestion

Enzymes: substrate → products

Enzyme	Substrate	Products
Amylase	Starch	Maltose
Maltase	Maltose	Glucose
Protease (pepsin, trypsin)	Protein	Amino acids
Lipase	Lipids	Fatty acids + glycerol

starch --amylase--> maltose --maltase--> glucose

Acid, pH and bile

• Hydrochloric acid kills ingested bacteria.
• The stomach is acidic; the duodenum receives the pancreas’s alkaline secretion. The protease in each place (pepsin in the stomach, trypsin in the duodenum) works best at that region’s pH.
• Bile (made in liver, stored in gall bladder) emulsifies fats into small droplets → larger surface area → faster digestion by lipase to fatty acids and glycerol. Emulsifying is physical; bile has no enzyme.

Method in steps: “Explain how bile speeds up fat digestion”

1. Bile emulsifies fat / breaks large droplets into small droplets.
2. This increases the surface area of fat.
3. More lipase can act on the fat at once.
4. Fat is broken down to fatty acids and glycerol faster.

Method in steps: “Describe peristalsis”

1. The gut wall has circular and longitudinal muscle layers.
2. They contract in waves along the gut.
3. Circular muscle contracting behind the food narrows the gut and pushes the food forward.
4. Longitudinal muscle contracting shortens and widens the gut ahead of the food.

Method in steps: following one nutrient from mouth to cell

Use this chain for “trace what happens to starch in a meal”.

1. Teeth chew bread into small pieces: physical digestion, larger surface area.
2. Salivary amylase starts digesting starch to maltose in the mouth.
3. Pancreatic amylase continues in the duodenum; maltase turns maltose into glucose in the small intestine.
4. Glucose is absorbed through the villi of the ileum into the capillaries.
5. The hepatic portal vein carries it to the liver, which can store it as glycogen.
6. Body cells take glucose from the blood and use it in respiration: assimilation.

Swap in protein (protease, amino acids, capillaries, built into new proteins) or fat (bile, lipase, fatty acids and glycerol, lacteal) to practise the other two chains.

Worked reminder: surface area and chewing

A 3 cm cube of food has surface area 6 × 3 × 3 = 54 cm². Chewed into 1 cm cubes, it makes 27 cubes with total area 27 × 6 × 1 × 1 = 162 cm²: three times as much, for the same volume.

8.3 Absorption and assimilation

• Absorption: movement of nutrients from the intestines into the cells lining the gut and then into the blood, by diffusion, osmosis and active transport. Main site: small intestine.
• Assimilation: uptake and use by cells of nutrients from the blood (e.g. amino acids built into proteins; glucose stored as glycogen in the liver).

Villus checklist

Feature	How it helps
Villi (finger-like projections of the ileum wall)	Large internal surface area
Microvilli on epithelial cells	Increase surface area further
Epithelium one cell thick	Short diffusion distance
Capillary network	Absorbs glucose, amino acids, water, ions; blood flow keeps the gradient steep
Lacteal	Absorbs fatty acids and glycerol into lymph

Water and the hepatic portal vein

• Water is absorbed in the small intestine and the colon; most is absorbed in the small intestine.
• The hepatic portal vein carries most absorbed molecules and ions from the ileum to the liver.

Worked reminder: reading water data

In a model of one day, 9.0 dm³ of water enters the small intestine; 7.6 dm³ is absorbed there and 1.3 dm³ in the colon.

% absorbed in small intestine = 7.6 / 9.0 × 100 = 84.4 %
% absorbed in colon           = 1.3 / 9.0 × 100 = 14.4 %
left in faeces                = 9.0 − 7.6 − 1.3 = 0.1 dm³

This fits the syllabus point: most water is absorbed in the small intestine.

Must-know distinctions

• Digestion vs absorption: digestion makes molecules small; absorption moves them into the blood.
• Absorption vs assimilation: absorption is into the blood; assimilation is cells taking nutrients out of the blood and using them.
• Egestion vs excretion: egestion removes undigested food; excretion removes waste made by metabolism.
• Bile vs lipase: bile emulsifies (physical); lipase digests (chemical).
• Amylase vs maltase: amylase stops at maltose; maltase makes glucose.
• Capillary vs lacteal: capillaries take glucose and amino acids; lacteals take fatty acids and glycerol.

Quick self-test

1. Name the deficiency disease caused by a lack of iron and give two symptoms.
2. Name the two nutrients whose deficiency can cause rickets.
3. What is a balanced diet?
4. Why must starch be digested before it is absorbed?
5. Give the function of canines.
6. Name the part of a tooth that contains nerves.
7. Where is bile made, and where is it stored?
8. Give the products of lipase action.
9. State the function of hydrochloric acid in the stomach.
10. A 2 cm cube of food is cut into 1 cm cubes. By what factor does the surface area increase?
11. Name the vessel that absorbs fatty acids and glycerol in a villus.
12. Which blood vessel carries absorbed nutrients from the ileum to the liver?

Answers

1. Anaemia; any two of tiredness, weakness, pale skin, shortness of breath.
2. Vitamin D and calcium.
3. A diet with all the nutrients in the correct proportions and enough energy for the person’s needs.
4. Starch molecules are large and insoluble, so they cannot pass through the gut lining into the blood; they must be broken down to small, soluble glucose.
5. Gripping and tearing food.
6. The pulp.
7. Made in the liver; stored in the gall bladder.
8. Fatty acids and glycerol.
9. It kills ingested bacteria.
10. Two: 24 cm² becomes 48 cm².
11. The lacteal.
12. The hepatic portal vein.

Where marks are usually lost

• Writing “amylase breaks starch into glucose”: the product is maltose.
• Calling bile an enzyme, or saying it “breaks down fat” without “into smaller droplets”.
• Giving “makes the stomach acidic for pepsin” when asked for the function of hydrochloric acid, instead of killing bacteria.
• Stating that the liver stores bile. The liver makes bile; the gall bladder stores it.
• Saying villi “absorb more” without linking to increased surface area.
• Mixing up the vessels: fatty acids and glycerol go into the lacteal, not the capillaries.
• Saying most water is absorbed in the colon. Most is absorbed in the small intestine.
• Describing a balanced diet as “eating equal amounts of every food group”.
• Naming only one tooth tissue when asked for structure: give enamel, dentine, pulp (with nerves) and cement.

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028, version 4, Cambridge International Education. Topic 8: Human nutrition (8.1 Diet; 8.2 Human digestive system; 8.3 Absorption and assimilation).