Describe how the biuret test is carried out on a food sample and explain what each possible result indicates.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Add a small amount of the food sample to a clean test tube.
Add a few drops of sodium hydroxide solution to the tube and swirl.
Add a few drops of dilute copper(II) sulphate solution and swirl again.
If a purple colour appears, protein is present in the sample.
If the solution remains blue, no protein is detected.
Add a few drops of sodium hydroxide solution to the tube and swirl.
Add a few drops of dilute copper(II) sulphate solution and swirl again.
If a purple colour appears, protein is present in the sample.
If the solution remains blue, no protein is detected.
Examiner tips
- Use the exact sequence of reagents and note the colour change
- Mention the colour of the solution before adding copper(II) sulphate
Common mistakes
- Mixing the reagents in the wrong order
- Failing to describe the colour change of the solution
Mark scheme (4 marks)
- Add sodium hydroxide solution to the sample (in a test tube)
- Add a few drops of dilute copper(II) sulphate solution
- A purple colour indicates that protein is present in the sample
- If the solution remains blue, no protein is present in the sample
Key terms in this question
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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