IGCSE Biology (0610)

Carrying out food tests

What this topic tests, the mistakes that cost marks, and one exam-style question worked through step by step.

Key ideas and common mistakes

Identifying a food test requires both naming the correct reagent and stating the specific substance detected (e.g., iodine for starch), not just one or a vague answer like 'sugar' or omitting the reagent.
A positive test for starch is shown by iodine solution changing specifically to blue-black, not just any dark or blue colour.
To test for vitamin C, use DCPIP solution, which is the specific reagent for it, rather than the reagents used for sugars, starch, protein or fat.
Identifying the correct reagent for a protein test requires naming the specific test (Biuret solution), not just one of its components (e.g., copper sulfate), as partial or incomplete names do not indicate full understanding.
Identifying the correct reagent for testing protein presence (Biuret solution), not just describing the expected colour change or naming a reagent for another food group like Benedict's for sugars.
A positive ethanol emulsion test for fat is shown by the formation of a cloudy white emulsion, not just a color change or whiteness.
Common mistake: Students must mention the cloudy or milky appearance, not simply 'turns white'.

Identify the solution used and state the conclusion for this test.

Try it first, then show the working

Naming iodine but concluding 'sugar is present', or giving the conclusion without the reagent, does not gain the mark.
Answer: The solution is iodine solution and the conclusion is that starch is present in the yam.
Examiner's mark scheme: 'iodine in potassium iodide' accepted for the reagent; 'positive for starch' accepted for the conclusion

Answer: The solution is iodine solution and the conclusion is that starch is present in the yam.

20 exam-style questions on Carrying out food tests, each marked to the scheme.