CAIE A Level Biology 9700 · Biological molecules
A student tested an unknown food sample using four biochemical tests. The results are shown in the table.
| Test | Result |
|---|---|
| Benedict's test (on original sample) | Blue solution remains after heating |
| Benedict's test after acid hydrolysis | Brick-red precipitate forms |
| Iodine test | Blue-black colouration |
| Biuret test | Purple colouration |
Explain what these results indicate about the biological molecules present in the sample. In your answer, include the principles of the tests used.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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