Question 1Multiple choice · 1 mark
Which reagent is used to test for protein, and what is the positive result?
| reagent | positive result | |
|---|---|---|
| A | DCPIP solution | blue |
| B | biuret solution | purple |
| C | ethanol | purple |
| D | biuret solution | blue |
Show answer
Answer: B
Free Food tests questions for IGCSE Biology (0610), part of Biological molecules & enzymes. Each question has the answer and the marking points an examiner would look for.
Generate a full Food Tests worksheet →All Biological molecules & enzymes questionsWhich reagent is used to test for protein, and what is the positive result?
| reagent | positive result | |
|---|---|---|
| A | DCPIP solution | blue |
| B | biuret solution | purple |
| C | ethanol | purple |
| D | biuret solution | blue |
Answer: B
A food sample is tested.
Benedict’s solution (heated): orange-red
biuret solution: purple
iodine solution: orange-brown
ethanol, then water: clear
Which nutrients are present?
Answer: C
Benedict’s test can be semi-quantitative.
Describe how you could compare the reducing sugar content of two fruit juices.
| Part | Answer and marking points | Marks |
|---|---|---|
| same volumes, same heating time, compare colour/precipitate same volume of each juice and Benedict’s solution B1 heat in a water bath for the same time B1 compare colours (blue → green → yellow → orange → red) B1 | 3 |
A student tests foods for fats and for reducing sugars.
Describe the test and the positive result.
Explain why Benedict’s test can give an estimate of how much reducing sugar is present.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | shake with ethanol, add water, cloudy white emulsion shake the sample with ethanol B1 pour into water B1 a cloudy white emulsion shows fat B1 | 3 |
| (b) | more sugar, more red precipitate more reducing sugar reduces more copper(II) ions / forms more (brick-red) precipitate B1 so the colour changes from blue through green, yellow and orange to brick red as the amount increases (allow: only a rough estimate unless volumes and heating time are kept the same) B1 | 2 |
A student tests a sample of crisps.
Describe the result if the crisps contain fat, using the ethanol emulsion test.
Explain why a control test with water is carried out alongside each food test.
State a safety precaution for the ethanol emulsion test.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | cloudy white emulsion a cloudy white emulsion forms B1 | 1 |
| (b) | compare colour to compare the colour and show the reagent alone does not give a positive result B1 | 1 |
| (c) | no naked flames keep ethanol away from flames (it is flammable) B1 | 1 |
A student tests a food sample for starch, reducing sugar, protein and fat.
Describe the test for reducing sugar, including the positive result.
Describe the test for protein, including the positive result.
Describe the test for starch.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | Benedict’s, heat, brick red add Benedict’s solution B1 heat in a water bath B1 blue to brick red/orange B1 | 3 |
| (b) | biuret, purple add biuret reagent B1 blue to purple/violet B1 | 2 |
| (c) | iodine, blue-black add iodine solution B1 orange-brown to blue-black B1 | 2 |
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