# A student carries out chemical tests on four different food samples, A, B, C and D. Describe the procedure and expected positive result for the iodine test and the biuret test.

> Cambridge International IGCSE Biology (0610) — 4.1 Biological molecules · Describe · 4 marks

## Mark scheme (4 marks)

1. Iodine test procedure: add iodine solution to the sample
2. Iodine test positive result: colour changes to blue-black, indicating starch is present
3. Biuret test procedure: add sodium hydroxide solution then a few drops of dilute copper II sulphate solution to the sample
4. Biuret test positive result: colour changes to purple, indicating protein is present

## Key terms

- [iodine test](https://www.gradenine.co.uk/glossary/iodine-test)
- [biuret test](https://www.gradenine.co.uk/glossary/biuret-test)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-chemical-tests-d96443b2) · Published by Druglandscape Ltd.