AQA A-Level Biology Paper 1, June 2024: Question 4

10 marks · Medium difficulty · Practical Techniques & Data Analysis

Analyze monosaccharides in molasses, perform a reducing sugar test, calculate free sugar energy allowances, explain osmosis using a diagram, and determine changes in water potential based on air pressure differences.

Practise this question

Question

Question text

04.1 Molasses is a solution obtained from sugar beet plants. The sugars present in

molasses are sucrose, glucose and fructose.

Give the number of different types of monosaccharides present in molasses.

[1 mark]

04.2 A student used the biochemical test for reducing sugars on a clear sample of

molasses.

Describe the biochemical test for a reducing sugar.

Explain the result expected from the test on the sample of molasses.

[3 marks]

Description of biochemical test

Explanation of expected result

04.3 ‘Free sugar’ is the sugar in food and drinks released when food is crushed or when

sugar is added to food at home or by manufacturers.

Scientists recommend that no more than 5% of the energy consumed per day should

come from ‘free sugar’.

The mean daily energy requirement for a 10-year-old child is 8100 kJ

The ‘free sugar’ in one tablespoon of molasses contains 250 kJ of energy.

Calculate the number of tablespoons of molasses required for a 10-year-old child to

reach the recommendation for energy consumed in ‘free sugar’ per day.

[1 mark]

Number of tablespoons12 per day

04.4 A scientist used the apparatus in Figure 3 to investigate osmosis.

*11* Figure 3

Use your understanding of osmosis to explain why the air pressure in the

tube increased.

[3 marks]

04.5 The scientist repeated the investigation, but made one change to the molasses. The

scientist did not change the volume of molasses at the start of the investigation.

The scientist observed that the air pressure inside the tube increased by 160 kPa

compared with 800 kPa in the first investigation.

Suggest the change the scientist made to the molasses to cause this smaller increase

in air pressure.

Use the air pressure figures in a calculation to support your answer.

[2 marks]

Suggested change

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

2; 1 Accept glucose and

04.1 fructose

(1 x

AO1)

1. Heat with Benedict’s (solution/reagent); 1. Ignore water bath

unqualified

2. Red (colour/precipitate);

1. Ignore warm

3. (Because) glucose/fructose is/are reducing

1. Accept Fehling’s for

sugars

Benedict’s

OR 3

1. Reject if heat with

04.2 (Because) glucose/fructose is/are detected; (3 x acid

AO1) 2. Accept green OR

orange OR brown OR

yellow

2. Ignore emulsion

3. Reject if sucrose is

detected

1.6 / 1.62; 1 Accept 2

04.3 – A-LEVEL BIOLOGY(1x – –

AO2)

1. Molasses/solution has a lower water potential 1. Accept more

negative for lower OR

less negative for

Water (in beaker) has higher water potential; higher

2. Water moves in (across) partially/selectively 1. Accept for water

04.4 (3 x

permeable bladder; potential

AO2)

3. Increased (molasses/solution) volume 2. Accept

semi-permeable

Decreased air volume;

Suggested change Ignore reduced

temperature

1. Diluted (molasses)

1. Accept less

negative for increased

Decreased (molasses) concentration

1. Accept for water

OR potential

Increased (molasses) water potential

Decreased water potential gradient; 2

04.5 (2 x

AO3)

2. (Reduction by) 80% / 5 times 2. Accept description

OR of 1 : 4 ratio, eg 20

(cm3) molasses

(Reduction to) 20% (added) to 80 (cm3)

OR water

(Used) 1 in 5 molasses to water OR

OR 2. Accept fivefold OR

factor of 5 for 5 times

(Used) 1 : 4 molasses to water; dilution

How to answer it

Biological Molecules & Osmosis Study Guide

What this question tests

This assessment evaluates your knowledge of carbohydrate monomers (monosaccharides), practical biochemical testing procedures for reducing sugars, data manipulation and proportional calculations, and the application of water potential principles in osmosis.

Question 04.1

Types of Monosaccharides in Molasses

✅ Correct Answer

2 (Accept glucose and fructose)

💡 Key Knowledge

Molasses contains sucrose (a disaccharide made of glucose and fructose), plus free glucose and fructose. Therefore, the different types of monosaccharides present are just two: glucose and fructose.

Mark: 1 mark (1 × AO1)

Question 04.2

Biochemical Test for Reducing Sugars

✅ Correct Answer

Description: Add Benedict's reagent and heat.
Explanation: Colour changes to red (or orange/yellow/green) because glucose and/or fructose are reducing sugars that reduce copper(II) ions to copper(I) oxide.

🧠 Exam Technique

You must link the action (heating with Benedict's) to the expected observation (colour change) and the scientific reason (detection of reducing sugars).

❌ Common Errors

Students often lose marks by failing to mention heating, mentioning heating with an acid (which hydrolyses non-reducing sugars instead), or stating that sucrose is detected directly by this test.

Marks: 3 marks (3 × AO1)

Question 04.3

Energy Intake & Free Sugar Calculation

📐 Step-by-Step Calculation

Find 5% of total daily energy: 5% of 8100 kJ = 0.05 × 8100 = 405 kJ
Divide by energy per tablespoon: 405 kJ ÷ 250 kJ per tablespoon = 1.62 (Accept 1.6 or 2)

✅ Correct Answer

1.6 or 1.62 (Accept 2 if rounded up based on whole tablespoons context, though standard decimal rules apply)

Mark: 1 mark (1 × AO2)

Question 04.4

Osmosis and Air Pressure Explanation

✅ Correct Answer

Molasses solution has a lower (more negative) water potential than the water in the beaker.
Water moves across the partially/selectively permeable bladder down the water potential gradient.
This increases the volume of liquid in the bulb/tube, which decreases the volume of air, thereby increasing air pressure.

💡 Key Knowledge

Always use correct terminology: solutions have water potential (not concentration), membranes are partially permeable, and movement is by osmosis down a water potential gradient.

Marks: 3 marks (3 × AO2)

Question 04.5

Modifying Osmosis Investigations

✅ Correct Answer

Suggested change: Dilute the molasses (decrease concentration / increase water potential / decrease water potential gradient).
Calculation support: The pressure change dropped from 800 kPa to 160 kPa, which is a reduction of 80% (or a 1 : 4 ratio of molasses to water, or a fivefold dilution).

🧠 Exam Technique

When an exam question asks you to use figures in a calculation, explicitly show the math: (160 ÷ 800) = 0.2 (or 20% of original, representing an 80% decrease or a 1:4 dilution factor).

Marks: 2 marks (2 × AO3)

Topics

Biology · Practical skills · 3.1 Biological molecules · 3.2 Cells · Data analysis

Question and mark scheme from the AQA A-Level Biology examination, Paper 1, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.