Nutrition & Digestion

IGCSE Edexcel Biology
2.24–2.32 Balanced diet, digestive system, and absorption
Key Concepts: A balanced diet provides all required nutrients in the correct amounts. Digestion breaks large insoluble molecules into small soluble ones for absorption. The digestive system includes specialised structures for mechanical and chemical digestion.

Section A — Balanced Diet and Nutrients

1. Complete the table for the main dietary components. [12]
Nutrient Role in the body Food source (example)
Carbohydrates
Proteins
Lipids (fats/oils)
Vitamin C
Vitamin D
Iron
Calcium
Dietary fibre
2. Explain why a diet high in fat can lead to cardiovascular disease. [2]
3. Explain why protein requirements are higher during pregnancy and adolescence. [2]

Section B — The Digestive System

4. State the function of each organ or structure in the digestive system. [10]
StructureFunction
Mouth / salivary glands
Oesophagus
Stomach
Small intestine
Large intestine
Liver
Pancreas
Rectum / anus
5. Describe the process of peristalsis. [3]
6. Explain the role of bile in digestion. [3]

Section C — Digestive Enzymes

7. Complete the table for digestive enzymes. [9]
Enzyme Substrate Product(s) Where produced
Amylase
Protease (e.g. pepsin)
Lipase
8. Explain why pepsin works best in acidic conditions. [2]

Section D — Absorption

9. Explain why the small intestine is well adapted for absorption of digested food. Refer to at least three structural features. [6]
10. State how the products of protein and carbohydrate digestion are transported from the small intestine to the rest of the body. [2]

Total marks: 51

Mark Scheme

1. Carbohydrates: energy source; bread/pasta/rice; Proteins: growth and repair; meat/eggs/beans; Lipids: energy store/insulation; butter/nuts/oil; Vitamin C: prevents scurvy/healthy connective tissue; citrus fruit; Vitamin D: absorption of calcium/healthy bones; fish/sunlight; Iron: makes haemoglobin; red meat/spinach; Calcium: strong bones and teeth; dairy/leafy veg; Fibre: prevents constipation/moves food through gut; vegetables/whole grains [12 — accept reasonable answers]
2. Saturated fat raises LDL cholesterol [1]; cholesterol deposits (plaques) build up in artery walls, narrowing them, which can lead to heart attacks or strokes [1] [2]
3. Protein is needed for growth and tissue repair [1]; during pregnancy the foetus is growing rapidly / during adolescence the body is growing quickly, so more protein is required [1] [2]
4. Mouth/salivary glands: mechanical digestion by teeth; salivary amylase breaks down starch; Oesophagus: carries food to stomach by peristalsis; Stomach: churns food; produces HCl (low pH) and pepsin to digest protein; Small intestine: chemical digestion (amylase, protease, lipase); absorption of products into blood/lymph; Large intestine: reabsorption of water; formation of faeces; Liver: produces bile; Pancreas: produces pancreatic juice (amylase, protease, lipase); Rectum/anus: storage and egestion of faeces [10 — 1 per structure approx.]
5. Circular muscles contract behind the food bolus [1]; longitudinal muscles relax [1]; this pushes food along the gut in a wave-like motion [1] [3]
6. Bile is produced in the liver and stored in the gall bladder [1]; it emulsifies fats (breaks large fat droplets into smaller ones) [1]; this increases the surface area for lipase to act on [1] [3]
7. Amylase: starch → maltose; salivary glands/pancreas/small intestine; Protease: protein → amino acids; stomach/pancreas/small intestine; Lipase: lipids → fatty acids + glycerol; pancreas/small intestine [9 — 3 per row]
8. Pepsin has an optimum pH of around 2 (acidic) [1]; the HCl produced by the stomach creates these conditions, allowing the enzyme's active site to function correctly [1] [2]
9. Any three features with explanations: villi increase surface area for absorption [2]; microvilli (brush border) further increase surface area [2]; thin epithelial walls = short diffusion distance [2]; good blood supply (capillaries in each villus) maintains concentration gradient [2]; lacteals absorb fatty acids and glycerol [2] [6 — 2 per point]
10. Amino acids (from protein) and glucose (from carbohydrates) are absorbed into the blood capillaries [1]; transported to the liver via the hepatic portal vein [1] [2]