IGCSE · Biology 0610 · Biological molecules & enzymes

Biological molecules: IGCSE Biology questions with answers

Free Biological molecules questions for IGCSE Biology (0610), part of Biological molecules & enzymes. Each question has the answer and the marking points an examiner would look for.

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Biological molecules practice questions

Question 1Structured · 5 marksA* challenge

A student tests foods for fats and for reducing sugars.

(a)

Describe the test and the positive result.

[3]
(b)

Explain why Benedict’s test can give an estimate of how much reducing sugar is present.

[2]
Show answers and mark scheme
PartAnswer and marking pointsMarks
(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
Question 2Structured · 3 marksA* challenge

Benedict’s test can be semi-quantitative.

Describe how you could compare the reducing sugar content of two fruit juices.

[3]
Show answers and mark scheme
PartAnswer and marking pointsMarks
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
Question 3Structured · 5 marks

Carbohydrates, fats and proteins are made from smaller molecules.

(a)

Name the smaller molecules from which starch, proteins and fats are made.

[3]
(b)

Name the chemical elements found in carbohydrates.

[1]
(c)

Name one element found in proteins but not in carbohydrates.

[1]
Show answers and mark scheme
PartAnswer and marking pointsMarks
(a)glucose; amino acids; fatty acids and glycerol
starch: glucose B1
proteins: amino acids B1
fats: fatty acids and glycerol B1
3
(b)C, H, O
carbon, hydrogen and oxygen B1
1
(c)nitrogen
nitrogen (or sulfur) B1
1
Question 4Structured · 3 marks

A student tests a sample of crisps.

(a)

Describe the result if the crisps contain fat, using the ethanol emulsion test.

[1]
(b)

Explain why a control test with water is carried out alongside each food test.

[1]
(c)

State a safety precaution for the ethanol emulsion test.

[1]
Show answers and mark scheme
PartAnswer and marking pointsMarks
(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
Question 5Structured · 7 marks

A student tests a food sample for starch, reducing sugar, protein and fat.

(a)

Describe the test for reducing sugar, including the positive result.

[3]
(b)

Describe the test for protein, including the positive result.

[2]
(c)

Describe the test for starch.

[2]
Show answers and mark scheme
PartAnswer and marking pointsMarks
(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
Question 6Structured · 3 marks

A student carries out food tests on milk.

(a)

Milk gives a purple colour with biuret solution. State what this shows.

[1]
(b)

Name the type of sugar in milk and the test you would use for it.

[2]
Show answers and mark scheme
PartAnswer and marking pointsMarks
(a)protein present
protein is present B1
1
(b)reducing sugar (lactose); Benedict’s
lactose (a reducing sugar) B1
Benedict’s test B1
2

More Biological molecules & enzymes questions

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Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in