Food and energy
A balanced diet supplies the seven food groups in the right proportions: carbohydrates, proteins, lipids (fats), vitamins, minerals, fibre and water.
Roles of each group
| Group | Main role | Example sources |
|---|---|---|
| Carbohydrate | Quick / main energy source | Bread, rice, pasta |
| Protein | Growth and repair, enzymes | Meat, fish, beans |
| Lipid | Long-term energy store, insulation | Oils, butter, nuts |
| Vitamins | Specific functions (e.g. C — collagen) | Fruit, vegetables |
| Minerals | E.g. calcium for bones, iron for haemoglobin | Dairy, leafy greens, red meat |
| Fibre | Aids movement of food through the gut | Wholegrains, vegetables |
| Water | Solvent, transport, regulation | Drinks, food |
Food tests (you must know these for the practical paper)
| Test | Reagent | Positive result |
|---|---|---|
| Starch | Iodine solution | Blue-black |
| Reducing sugar (e.g. glucose) | Benedict's solution + heat | Brick-red precipitate |
| Protein | Biuret reagent | Lilac / purple |
| Lipid | Ethanol + water | White cloudy emulsion |
Always set up a control (e.g. distilled water) so you can compare colour changes.
Energy from food
Energy content is measured in kilojoules (kJ) or kilocalories (kcal). A simple lab method burns a known mass of food under a boiling tube of water and uses:
energy (J) = m × c × ΔT
where m is the mass of water (g) — and 1 cm³ of water has a mass of 1 g — c is 4.2 J/g/°C, and ΔT is the temperature rise. Divide by the food mass to get J per g.
Sources of error: heat lost to the surroundings (always an underestimate), incomplete combustion, water heating non-uniformly.
CCEA tip
The food test table is high-yield: every paper has at least one B1/B1 question on a positive result. Memorise the colours exactly — "blue-black", not "dark", and "brick-red", not "orange".
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