Topic 7 of IGCSE Biology (Cambridge 0610) is human nutrition. You need to know the need for a balanced diet (food groups and deficiency diseases), the digestive system (order of organs and the role of liver and pancreas), the digestive enzymes (amylase, protease, lipase: where produced, where they act, substrate and product), and absorption in the small intestine (how villi are adapted). This revision guide takes you through each of these with clear descriptions and exam-style tips for full marks.

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Balanced diet and deficiency diseases

A balanced diet provides all the nutrients the body needs in the right amounts: carbohydrates (energy), fats (energy, insulation, cell membranes), proteins (growth, repair, enzymes), vitamins (e.g. vitamin C for healthy skin and gums; vitamin D for calcium absorption), minerals (e.g. iron for haemoglobin; calcium for bones and teeth), fibre (roughage; keeps the gut moving), and water (hydration; many body processes). You may be asked to list the main food groups and state one role of each, or to name a deficiency disease (e.g. scurvy – lack of vitamin C; rickets – lack of vitamin D or calcium; anaemia – lack of iron).

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The digestive system: organs in order

The alimentary canal is the tube from mouth to anus. Food passes in this order: mouth → oesophagus → stomach → small intestine → large intestine → anus. The mouth is where food is chewed and mixed with saliva (which contains amylase). The oesophagus carries food to the stomach by peristalsis (wave-like muscle contractions). The stomach churns food and mixes it with gastric juice (acid and protease); it can store food temporarily. The small intestine is where digestion is completed and where absorption of digested food into the blood takes place. The large intestine absorbs water from the remaining material; the faeces are stored and then egested through the anus.

Digestion is the breakdown of large food molecules into small, soluble molecules that can be absorbed. Absorption is the uptake of these digested molecules into the blood (mainly in the small intestine). Egestion is the removal of faeces (undigested food and other waste) from the body. Do not confuse absorption with egestion: absorption is into the blood; egestion is faeces out.

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The liver and pancreas

The liver produces bile. Bile is stored in the gall bladder and released into the small intestine. Bile emulsifies fats: it breaks large fat droplets into small droplets, which increases the surface area for the enzyme lipase to act on. Bile does not digest fat (lipase digests fat); it emulsifies it. Bile also neutralises stomach acid so that enzymes in the small intestine can work. The pancreas produces digestive enzymes (amylase, protease, lipase) and releases them into the small intestine. It also produces substances that neutralise stomach acid. In exams you may need to label the digestive system and state the function of the liver (produces bile; emulsifies fats) and pancreas (produces enzymes; neutralises acid).

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Digestive enzymes: amylase, protease, lipase

Amylase breaks down starch into sugars (e.g. maltose, glucose). It is produced in the salivary glands (and in the pancreas) and acts in the mouth (and small intestine). Protease breaks down proteins into amino acids. It is produced in the stomach (and pancreas) and acts in the stomach (and small intestine). Lipase breaks down fats into fatty acids and glycerol. It is produced in the pancreas and acts in the small intestine. For each enzyme you should state: where it is produced, where it acts, substrate (what it breaks down), and product (what is formed). Do not say bile “digests” fat; bile emulsifies fat; lipase digests fat.

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Absorption: the small intestine and villi

Absorption is the uptake of digested food (glucose, amino acids, fatty acids, glycerol, vitamins, minerals) into the blood (and into the lymph for some fats). It happens mainly in the small intestine. The inner wall of the small intestine is folded into millions of tiny finger-like projections called villi. Each villus has: a large surface area (many villi; microvilli on each cell) so that more absorption can happen; a thin wall (one cell thick) so that digested food crosses quickly; a good blood supply (capillaries) so that absorbed nutrients are carried away and a concentration gradient is maintained. You may be asked to describe how villi are adapted for absorption: state these three adaptations and explain each (surface area → more absorption; thin wall → short distance; blood supply → maintains gradient and carries nutrients away).

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Exam tips and command words

• Label the digestive system: Know the order of organs and the position of liver and pancreas; state their functions.
• State the function: One clear sentence (e.g. “Bile emulsifies fats to increase surface area for lipase.”).
• Describe: Where each enzyme is produced, where it acts, and what it breaks down (substrate → product).
• Explain: Why villi are adapted for absorption (surface area, thin wall, blood supply).

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Common mistakes to avoid

• Confusing absorption (into blood) with egestion (faeces out). Digestion = breakdown; absorption = uptake.
• Saying bile “digests” fat (bile emulsifies; lipase digests).
• Not naming the substrate and product for each enzyme (e.g. amylase: starch → maltose/sugars).
• Confusing small intestine (absorption) with large intestine (water absorption; formation of faeces).

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Revision checklist

• List the main food groups and one role of each; name one deficiency disease.
• Draw or label the digestive system and state the function of stomach, small intestine, liver, pancreas.
• State where amylase, protease, and lipase are produced, where they act, and what they break down (substrate → product).
• Describe how villi are adapted for absorption (surface area, thin wall, blood supply).

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Next steps

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