AQA AS Level Biology Paper 2, November 2021: Question 8

8 marks · Medium difficulty · Practical Techniques & Data Analysis

Analyze enzyme activity and reaction products using a multi-part question based on a sequence of reactions catalyzed by GOx and HRP enzymes.

Practise this question

Question

Question 08 containing four sub-questions about enzymes GOx and HRP. Figure 9 shows a reaction pathway where glucose and oxygen produce gluconic acid, hydrogen peroxide, water, and green pigment. Figure 10 is a bar chart comparing the relative activity of GOx and HRP when trapped inside cages (T) versus not trapped (NT), with error bars showing plus or minus 2 standard deviations.
Question text

08 A scientist investigated a sequence of reactions catalysed by two enzymes, GOx and

HRP. Figure 9 shows this sequence of reactions.

Figure 9

08.1 Use Figure 9 to identify all of the products formed when this sequence of reactions is

completed.

[1 mark]

08.2 The scientist joined DNA molecules together to make tiny cages. The cages are

exactly 20 nm long, 20 nm wide and 17 nm deep.

He trapped one GOx molecule and one HRP molecule together in each cage.

The GOx molecule and HRP molecule fill 9% of the cage volume.

The volume of a GOx molecule is eight times larger than an HRP molecule.

Use this information to calculate the volume of a GOx molecule. Give the appropriate

unit with your answer.

Show your working.

[3 marks]

Answer

The scientist investigated the activity of GOx and HRP enzymes when they are:

• trapped inside cages (T) and

• not trapped (NT), but free in solution with no cages.

Figure 10 shows his results.

The error bars show ± 2 standard deviations.

± 2 standard deviations include 95% of the data.

Figure 10

08.3 What can you conclude from Figure 10 about the effect of trapping GOx and HRP

inside cages?

[3 marks]

*0248.*4 The design of the scientist’s investigation did not include a suitable control.

Suggest a suitable control.

[1 mark]

Mark scheme

Show the mark scheme Mark scheme for Question 08 detailing correct answers for parts 08.1, 08.2, 08.3, and 08.4, including the calculation for volume, analysis of error bars, and suggestions for enzyme controls.

Question Marking Guidance Mark Comments

08.1 All three correct and no other substances = 1 mark

1 Accept in any order

Gluconic acid, water, green pigment;

08.2 Correct answer for 3 marks = 544 and nm ;;;

Accept for 2 marks:

612 (cage volume occupied by enzymes)

OR

68 (volume of HRP)

OR

544 (correct answers with no unit)

Accept for 1 mark:

6800 (cage volume)

08.3 1. (Trapping) increases enzyme/GOx/HRP activity; 3. Accept for ‘standard

deviations’, error bars

2. Difference/increase is significant

OR 3

Difference is not (likely to be) due to chance;

3. (Because) SDs do not overlap;

08.4 Denatured enzymes Accept any valid

method of

OR denaturing/inactivation

Inactivated enzymes 1

OR

– LOGY – – JUNE 2021

Empty cages (in water);

TOTAL 8 15

How to answer it

Enzyme Immobilisation & Experimental Design

What this question tests

This multi-part question assesses your ability to interpret biochemical pathway diagrams, execute multi-step volumetric calculations with dimensional awareness, analyze graphical data including standard deviations, and understand the core principles of biological controls and enzyme immobilisation.

Part 08.1

Identifying Products from a Reaction Sequence

✅ Correct Answer

Gluconic acid, water, green pigment

Awarded 1 mark for listing all three correct substances with no extraneous chemicals.

💡 Key Knowledge

Look at the directional arrows pointing away from the enzymes in Figure 9. Substrates enter (glucose, oxygen, colourless pigment) and products leave (gluconic acid, water, green pigment).

Part 08.2

Enzyme Volume Calculation

📐 Step-by-Step Calculation

  1. Calculate total cage volume: 20 nm × 20 nm × 17 nm = 6800 nm³ (1 mark)
  2. Calculate volume occupied by enzymes (9%): 6800 × 0.09 = 612 nm³ (Part-mark awarded)
  3. Set up algebraic ratio: Let HRP volume = x . Since GOx is 8 times larger, GOx volume = 8x .
  4. Total enzyme volume = 8x + x = 9x = 612 nm³ .
  5. Volume of HRP ( x ) = 612 / 9 = 68 nm³ .
  6. Volume of GOx ( 8x ) = 68 × 8 = 544 nm³ .
Final Answer: 544 nm³ (3 marks)

❌ Common Errors & Traps

  • Missing Units: Forgetting to write nm³ loses the final accuracy mark even if the math is correct.
  • Ratio Confusion: Dividing by 8 instead of setting up the combined ratio of 9 parts (8 parts GOx + 1 part HRP).
Part 08.3

Interpreting Graphical Data with Error Bars

✅ Correct Answer

An eligible 3-mark response must cover three pillars:

  • Trapping (T) increases enzyme activity compared to not trapped (NT).
  • The difference is statistically significant.
  • Because the standard deviation error bars do not overlap.

🧠 Exam Technique & Examiner Insight

Examiners note that top-tier students immediately link non-overlapping error bars to statistical significance. Never say "results are not due to chance" without explicitly referencing that error bars do not overlap.

Part 08.4

Suggesting a Suitable Control

✅ Correct Answer

Any one of the following:

  • Denatured enzymes (trapped inside cages)
  • Inactivated enzymes
  • Empty cages (in water)
Awarded 1 mark.

💡 Key Knowledge

A control in enzyme investigations must show that the active tertiary structure of the enzyme is specifically required for the observed change, ruling out non-specific interactions caused by the DNA cage itself or inactive protein mass.

Topics

Biology · Practical skills · 3.1 Biological molecules · Data analysis · Experimental design

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.