AQA A-Level Biology Paper 1, June 2024: Question 7

9 marks · Medium difficulty · Practical Techniques & Data Analysis

Design a results table, explain differences in enzyme activity between apple varieties, suggest a method modification to increase reaction rate, and select the correct procedure to measure enzyme activity.

Practise this question

Question

Question text

07.1 A student investigated the activity of the enzyme polyphenol oxidase (PPO) in

apple tissue.

When apple tissue is exposed to air, PPO catalyses a reaction between colourless

phenol compounds in apple tissue and oxygen.

Figure 7 shows the reaction.

Figure 7

PPO

phenol compounds + oxygen → brown pigment

The student measured the time taken for the brown pigment to appear in two apple

varieties (D and E).

Method

1. Cut a 1 cm cube of apple tissue from variety D.

2. Put the cube on a plate and leave the plate at 30 °C

3. Measure the time for the brown pigment to appear.

4. Repeat steps 1 to 3 two more times.

5. Repeat steps 1 to 4 with apple tissue from variety E.

The student obtained the results shown below, but did not record the data in a

results table.

Variety D = 15 min 50 s, 18 min, 14 min 30 s

Variety E = 6 min 30 s, 8 min, 7 min

In the box labelled Figure 8, design a suitable results table.

• Enter the student’s results into the table.

• Calculate the mean results and include these in the table.

• Use 1 decimal place for both mean results.19

[3 marks]

Figure 8

07.2 Suggest and explain why the results for variety D are different from the results

for variety E.

[2 marks]

07.3 The student repeated the investigation but made one change to the method used to

prepare the apple tissue.

The student then observed shorter times for the brown pigment to appear in both

apple varieties.

Suggest the change the student made to the method of preparing the apple tissue.

Explain why the brown pigment appeared in a shorter time.

Do not suggest using a different volume or mass of apple.

[3 marks]

Change to method

Explanation

07.4 The student wants to change the procedure to obtain a measure of PPO activity either

in terms of how much substrate is used or how much product is produced.

Which change in procedure will provide a successful measure of PPO activity for

the student?

Tick ( ) one box.

[1 mark]

Measure the increase in oxygen concentration in the air around the

cube of apple tissue on a plate.

Measure the intensity of brown colour by comparing apple tissue with

a colour chart showing a range of apple tissues of known pigment

concentration.

Measure the intensity of colour produced from brown apple tissue in

a biuret test.

Measure the percentage of light transmitted through a cube of brown

apple tissue using a colorimeter.

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

1. Variety and D and E in left column; Accept if no table

lines are shown,

2. Time and ‘/ min’ and Mean (time) ‘/ min’ in

figures clearly written

column heading only;

in rows and columns

3. Correctly calculated times and means calculated

Accept tables where

to one decimal place;

mean is given in

Examples achieving 3 marks middle column and

time is given in right

Mean /

Variety Time / minutes column

minutes

1. Accept type OR

15.8/15.83/16 apple for variety

16.1 OR 16.2 1. Accept D and E in

D 18

OR 16.3 either order

14.5/15 2. Accept mean

values shown in rows

rather than in columns

6.5/7

2. Accept brackets

E 8 7.2 OR 7.3 OR “in” for solidus

07.1 (3 x

2. Ignore average for

AO2)

7 mean

2. Accept min OR

mins for minutes

Apple Time / s Mean / s

2. Accept seconds OR

secs OR sec for

D 950

seconds

1080 966.7 2. Reject mixed units

eg “/ minutes and

seconds”

3. Accept correct

E 390 times and correct

means however

presented

480 430.0

– A-LEVEL BIOLOGY – –

1. More phenol/substrate in E 1. and 2. Accept the

converse for D

14 OR

1. Ignore oxygen

More PPO/enzyme in E 2

07.2 2. Ignore ESC

OR (2 x

AO2)

Higher PPO/enzyme activity in E;

2. (So) more enzyme-substrate/E-S complexes

(form);

1. Use (enzyme’s) higher/optimum temperature; Mark in groups, 1, 2

and 3. OR 4, 5 and 6

2. More kinetic energy

OR 7, 8 and 9

(So) more active enzyme;

3. 6. and 9. Accept E-

3. (Causing) increased rate of reaction S complexes for

OR enzyme-substrate

complexes

(Causing) more enzyme-substrate

complexes/collisions;

3. 6. and 9. Accept a

description of

OR increased rate, eg

‘speeds up reaction’

4. Use (enzyme’s) lower/optimum temperature

OR 3 max 1 and 4 Accept

07.3 (3 x change in

Use (enzyme’s) optimum pH; temperature

AO3)

5. Less denaturation;

(So) more active enzyme;

6. (Causing) increased rate of reaction

(Causing) more enzyme-substrate

complexes/collisions;

7. Crush/grind/blend/chop the apple (tissue);

– A-LEVEL BIOLOGY7–. Accept cube for–

apple

8 (So) more PPO/phenol/substrate in contact with 7. Accept dice OR 15

oxygen/air; homogenise OR cut

up OR slice for crush

9. (Causing) increased rate of reaction

If oxygen is

(Causing) more enzyme-substrate

suggested, no mark

complexes/collisions;

for oxygen but MP8

and MP9 are available

Measure the intensity of brown colour by 1

comparing apple tissue with a colour chart showing

07.4 (1 x

a range of apple tissues of known pigment

concentration. AO3)

How to answer it

Enzyme Activity & Experimental Design Study Guide

What this question tests

This sequence assesses core practical competencies: designing functional results tables, processing raw time data into means using consistent significant figures, explaining enzyme-substrate kinetics (enzyme concentration, surface area, and collisions), and selecting valid quantitative methods to measure enzyme reaction rates.

Question 07.1 — Results Table Design & Calculations

Constructing a Results Table and Calculating Means

✅ Correct Answer Structure

Your designed table must contain:

Columns/Rows: Variety (D and E) clearly labelled in the left-hand column or rows.
Headings: Time and Mean clearly stated with correct units ( min or s ).
Calculations: Correctly computed means to 1 decimal place .

📐 Step-by-Step Calculations

Raw data for Variety D: 15 min 50 s (15.83 min), 18 min, 14 min 30 s (14.5 min)

Convert seconds to fractions of a minute (e.g., 50 ÷ 60 = 0.83).
Sum the times: 15.83 + 18.0 + 14.5 = 48.33 min.
Divide by 3: 48.33 ÷ 3 = 16.1 (or 16.2 / 16.3 depending on rounding of recurring decimals). Alternatively, use total seconds: (950 + 1080 + 870) / 3 = 966.7 s.

❌ Common Errors

Mixing units in table headings (e.g., writing / minutes and seconds in the heading). Pick either minutes (as decimals) or seconds throughout.
Failing to round mean values to the requested 1 decimal place .
Omitting column units.

Mark allocation: [3 marks] — 1 mark for correct column/row headers with units, 1 mark for correct data entry, 1 mark for correct means to 1 decimal place.

Question 07.2 — Explaining Enzyme Results

Comparing Enzyme Kinetics in Varieties D and E

💡 Key Knowledge

Variety E showed significantly shorter times for the brown pigment to appear, meaning PPO activity is higher in variety E than variety D.

🧠 Exam Technique & Mark Scheme Points

To score full marks, state one difference in composition/concentration and link it to the rate of complex formation:

Point 1: More phenol/substrate (or more PPO/enzyme) present in variety E.
Point 2: Therefore, more enzyme-substrate ( E-S ) complexes are formed per unit time.

Mark allocation: [2 marks] — 1 mark for stating higher substrate/enzyme concentration in E, 1 mark for explaining more E-S complexes form.

Question 07.3 — Modifying Experimental Methods

Increasing Surface Area to Speed Up Enzyme Reactions

✅ Correct Change to Method

Crush, grind, blend, chop, dice, homogenise, or slice the apple tissue.

💡 Scientific Explanation

Breaking up the tissue increases the surface area of the apple.
This brings more PPO enzyme and phenol substrate into direct contact with oxygen in the air.
Results in an increased frequency of successful collisions and more E-S complexes forming, speeding up the appearance of the pigment.

❌ Common Errors

Students frequently lose marks by suggesting changing the volume or mass of the apple, which was explicitly forbidden in the question stem. Stick strictly to physical preparation modifications.

Mark allocation: [3 marks max] — 1 mark for the method change (crush/chop), 1 mark for linking to increased surface area/contact with oxygen, 1 mark for explaining increased rate of reaction / more E-S complexes.

Question 07.4 — Practical Technique Selection

Measuring Enzyme Activity Quantitatively

✅ Correct Box to Tick

[✔] Measure the intensity of brown colour by comparing apple tissue with a colour chart showing a range of apple tissues of known pigment concentration.

🧠 Why the Other Options Are Incorrect

Oxygen concentration in air: PPO uses oxygen up from the surrounding air, but measuring gas volume changes around a solid apple cube is imprecise and difficult to isolate.
Biuret test: Tests for peptide bonds / proteins, not the brown melanin pigment produced by PPO.
Colorimeter with solid tissue: A colorimeter requires light to pass through a solution (liquid filtrate), not an opaque solid cube of apple tissue.

Mark allocation: [1 mark]

Topics

Biology · Practical skills · Required Practicals · Data analysis · 3.1 Biological molecules · AS practicals (1–6)

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.