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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
What this skill means
Use Benedict’s plus heat for reducing sugar, iodine for starch, biuret for protein, ethanol then water for fat, and DCPIP decolourisation for vitamin C. State both the reagent and the positive colour change.
Food-test answers are exact. Naming the nutrient without the reagent, heating step or result colour leaves marks behind. DCPIP is included in the current Cambridge 0610 Core practical content.
Reducing sugar, starch and protein
Substance
Method
Positive result
Reducing sugar
Add Benedict’s solution and heat in a water bath
Blue to green, yellow, orange or brick-red precipitate
Starch
Add iodine solution
Orange-brown to blue-black
Protein
Add biuret reagent
Blue to lilac or purple
The ethanol emulsion test for fat
Add ethanol to the sample and shake, then add water. A white cloudy emulsion indicates fat. Ethanol is flammable, so keep it away from naked flames.
DCPIP and vitamin C
Blue DCPIP is decolourised by vitamin C. When comparing samples, keep DCPIP volume and concentration constant and measure the volume of sample needed to remove the blue colour, or use another consistently defined endpoint.
Designing a fair comparison
Use equal sample volumes and concentrations, the same reagent volumes, identical heating time and temperature where relevant, and repeats. Include a known positive or negative sample when a control comparison is useful.
Use this before submitting your answer
A complete answer is specific enough for another person to repeat or assess.
✓Name the correct reagent.
✓Include heating for Benedict’s solution.
✓State the starting and positive-result colours.
✓Use a water bath and relevant safety precautions.
✓Keep sample and reagent quantities consistent in comparisons.
Try the skill in a question (3 marks)
Describe how to test a solution for reducing sugar and state a positive result.
Show the answer and marking guidance
Add Benedict’s solution to the sample.
Heat the mixture in a hot-water bath.
A green, yellow, orange or brick-red precipitate indicates reducing sugar.
Original practice content written for this site. It is not an official Cambridge question.