AQA GCSE Biology Biology Paper 1 (Higher), June 2025: Question 4

16 marks · Standard Demand difficulty · Short Answer

Investigate the effect of temperature on the rate of photosynthesis in pondweed, perform rate calculations with units, and explain plant diseases and mineral deficiencies.

Practise this question

Question

Question text

04 A student investigated the effect of temperature on the rate of photosynthesis in

pondweed.

Figure 4 shows how the student set up the apparatus.

Figure 4

This is the method used.

1. Prepare five tubes of pondweed as shown in Figure 4.

2. Place one tube into each of five water baths set at different temperatures.

3. Wait two minutes.

4. Measure the time taken for each piece of pondweed to release 10 bubbles.

04.1 What is the independent variable in the investigation?

[1 mark]

Table 4 shows the results.

Table 4

Temperature Time taken for pondweed to

in °C release 10 bubbles in seconds

10 84

20 43

30 27

*15* 40 25

50 33

04.2 Calculate the rate of photosynthesis at 20 °C.

Give your answer to 3 significant figures.

Give the unit.

[4 marks]

Rate (3 significant figures) =

17Unit =

04.3 Explain the difference in the rate of photosynthesis at 40 °C compared with the rate

of photosynthesis at 10 °C.

[3 marks]

04.4 Give two other factors that affect the rate of photosynthesis.

Do not refer to temperature in your answer.

[2 marks]

04.5 Describe one way the method could be changed to obtain more accurate results for

the rate of photosynthesis.

[1 mark]

A gardener noticed that some plants were not growing as well as usual.

04.6 Describe two ways the gardener could identify a plant disease.

[2 marks]

04.7 One of the plants had purple spots on its leaves and the leaves fell off.

What disease is the plant most likely to have?

[1 mark]

04.8 A different plant had yellow leaves, but no spots.

Explain why plants may develop yellow leaves.

[2 marks]

Mark scheme

Show the mark scheme

Question 4

AO /

Question Answers Extra information Mark

Spec Ref.

04.1 temperature 1 AO2

4.4.1.2

RPA6

AO /

Spec Ref.

04.2 allow correct calculation in other AO1

units eg bubbles per minute / 4.4.1.2

hour RPA6

10 1

or × 10 1

43 43

0.23255… 1

0.233 allow student’s incorrectly 1

calculated value to 3 significant

figures

allow use of other values for

time from Table 4

(unit) bubbles per second unit must be consistent with 1

student’s answer for MP3

AO /

Spec Ref.

04.3 allow converse for 10 °C if

clearly stated

rate / photosynthesis is faster / allow as the temperature 1 AO3

o increases, the rate (of

higher (at 40 C)

photosynthesis) increases

reactants / particles / molecules allow reactants / particles / 1 AO2

/ enzymes have greater (kinetic) molecules / enzymes move

energy faster

(so) collide more frequently allow (so) more collisions in a 1 AO2

given time

allow more successful collisions 4.4.1.2

4.2.2.1

AO /

Spec Ref.

04.4 any two from: 2 AO1 17

• light intensity / level if neither point awarded allow 4.4.1.2

• colour / wavelength of light 1 mark for light unqualified

• carbon dioxide

(concentration)

• (mass of) chlorophyll allow number of chloroplasts

ignore water / humidity

do not accept wind

AO /

Spec Ref.

04.5 allow bubbles for gas / oxygen AO3

do not accept incorrect gas 4.4.1.2

RPA6

collect gas / oxygen in a (gas) allow measure the volume of 1

syringe gas / oxygen in a (gas) syringe

or ignore use a gas syringe

collect gas / oxygen in an allow measure the volume of

inverted measuring cylinder gas / oxygen in an inverted

measuring cylinder

ignore collect gas / oxygen in a

measuring cylinder

ignore use an inverted

measuring cylinder

allow other correct methods

AO /

Spec Ref.

04.6 any two from: 2 AO1

• reference to a gardening ignore use / search the internet 4.3.3.1

manual / website / app unqualified

• take (infected plants) to a

laboratory / scientist / expert

• use testing kits that contain

monoclonal antibodies

AO /

Spec Ref.

04.7 (rose) black spot allow other correct diseases 1 AO1

such as rust 4.3.3.1

do not accept nitrate /

magnesium deficiency

do not accept tobacco mosaic

virus or TMV

AO /

Spec Ref.

04.8 a shortage of magnesium (ions) allow a shortage of nitrate / iron 1 AO1

(ions) 4.3.1.4

4.3.3.1

which causes chlorosis ignore chlorosis unqualified 1

(so) less chlorophyll ignore fewer chloroplasts

(magnesium is needed) to make allow (nitrate / iron is needed) to

chlorophyll make chlorophyll

lack of light (1)

causes chlorosis or causes

chlorophyll to break down (1)

Total Question 4 16

How to answer it

Photosynthesis Investigation & Plant Pathology

What This Question Tests

This practical and recall question assesses key concepts from AQA GCSE Biology Paper 1 (Topics 4.4 Bioenergetics & 4.3 Infection and Response):

Required Practical 6 (Photosynthesis): Identifying scientific variables, calculating rates from raw laboratory data to specified significant figures with correct derived units, and evaluating experimental accuracy.
Enzyme & Kinetic Theory: Explaining temperature effects on reaction rates using kinetic energy and collision frequency.
Limiting Factors: Recalling limiting factors of photosynthesis beyond temperature.
Plant Pathology & Mineral Deficiencies: Diagnosing plant fungal diseases (rose black spot), identifying disease-identification methods, and explaining mineral deficiency symptoms (magnesium deficiency leading to chlorosis).

Question 04.1 • 1 Mark

Independent Variable Identification

Identifying the variable changed by the experimenter

✅ Correct Answer

Temperature

1 Mark: AO2 (Application of RPA6 practical knowledge)

🧠 Exam Technique

Independent variable: The thing you deliberately change (e.g., water bath temperature).
Dependent variable: The thing you measure (e.g., time taken for 10 bubbles to emerge).
Look at the left-hand column of the data table—it almost always shows the independent variable!

Question 04.2 • 4 Marks

Rate Calculation at 20 °C

Calculate rate to 3 significant figures with units

📐 Step-by-Step Calculation

Identify data: From Table 4, at 20 °C, time for 10 bubbles = 43 s .
Set up rate formula:
Rate = number of bubbles ÷ time in seconds
Rate = 10 ÷ 43 [1 mark]
Calculate unrounded value:
0.232558... [1 mark]
Round to 3 significant figures:
The 4th figure is 5, so round up: 0.233 [1 mark]
Determine the unit:
bubbles per second (or bubbles/s ) [1 mark]

❌ Common Errors to Avoid

Inverting the division: Calculating 43 ÷ 10 = 4.3 calculates seconds per bubble, not the rate of photosynthesis.
Incorrect rounding: Writing 0.23 (2 s.f.) or 0.232 (rounding down incorrectly) loses Mark 3.
Missing or mismatched unit: Writing just "seconds" or leaving the unit line blank. If you converted time to minutes ( (10 ÷ 43) × 60 = 14.0 ), your unit must match: bubbles per minute .

Question 04.3 • 3 Marks

Explaining Rate Difference (40 °C vs 10 °C)

Linking temperature change to kinetic energy and collision theory

✅ Mark Scheme Model Answer

The rate of photosynthesis is faster / higher at 40 °C than at 10 °C. [1 mark]
Particles / molecules / enzymes / reactants have greater kinetic energy (or move faster). [1 mark]
Therefore, they collide more frequently (or there are more collisions per second / more successful collisions). [1 mark]

Converse accepted: You can explain why the rate is slower at 10 °C (less kinetic energy, fewer collisions per second).

🧠 Top Examiner Tip

Always state "collide more frequently" or "more collisions per unit time" rather than just "more collisions". In GCSE science, rate depends on collisions per second.

Do NOT say the enzymes are denatured at 40 °C! Looking at Table 4, the time at 40 °C is 25 s (the fastest rate in the table). Denaturation only begins at 50 °C where the time increases to 33 s.

Question 04.4 • 2 Marks

Other Limiting Factors of Photosynthesis

Recall factors other than temperature

✅ Any Two From:

Light intensity (or light level / wavelength / colour of light)
Carbon dioxide concentration
Amount / mass of chlorophyll (or number of chloroplasts)

2 Marks: 1 mark per valid factor. If neither full point is given, 1 compensatory mark is awarded for unqualified "light".

❌ What NOT to Write

Water: Although a reactant in the word equation, water shortage affects stomatal closure rather than directly acting as a limiting factor in standard GCSE photosynthesis questions. The mark scheme explicitly states: "ignore water / humidity".
Wind: Explicitly rejected by examiners: "do NOT accept wind".
Temperature: Explicitly barred by the question instruction ("Do not refer to temperature").

Question 04.5 • 1 Mark

Improving Experimental Accuracy

Upgrading gas collection from bubble counting

💡 Why Bubble Counting is Inaccurate

Bubbles are different sizes, human counting is prone to error, and rapid bubbling can cause bubbles to merge or be miscounted.

✅ Acceptable Improvements (1 Mark)

Collect the gas/oxygen in a gas syringe (to measure volume).
Collect the gas/oxygen in an inverted measuring cylinder (or graduated tube) filled with water.
Measure the volume of oxygen produced rather than counting bubbles.

Examiner note: Do NOT just say "use a gas syringe" without mentioning gas collection or volume measurement.

Question 04.6 • 2 Marks

Ways to Identify a Plant Disease

Practical methods available to gardeners and farmers

✅ Any Two From (1 Mark each):

Check a gardening manual / gardening website / plant app.
Take the infected plant / sample to a laboratory / plant pathologist / expert.
Use a testing kit containing monoclonal antibodies.

❌ Common Error

Writing simply "search the internet" or "look online" is too vague and gets 0 marks. You must specify a gardening website, plant identification app, or gardening guide.

Question 04.7 • 1 Mark

Identifying Symptoms: Purple Spots

Fungal diseases in plants

✅ Correct Disease

Rose black spot

Allow: "black spot" or "rust".
Do NOT accept: Tobacco Mosaic Virus (TMV) or mineral deficiencies.

💡 Disease Profile: Rose Black Spot

Pathogen type: Fungus.
Symptoms: Purple or black spots develop on leaves, which often turn yellow and drop early.
Effect on plant: Reduces photosynthetic leaf area → less glucose produced → stunted growth.

Question 04.8 • 2 Marks

Why Plants Develop Yellow Leaves

Mineral deficiencies & chlorophyll synthesis

✅ Model Answers (Any Pair)

Route 1 (Magnesium deficiency - Most Common):

Shortage / deficiency of magnesium ions (or nitrate / iron ions) [1 mark]
So less chlorophyll is made / magnesium is needed to produce chlorophyll / causes chlorosis [1 mark]

Route 2 (Light deficiency):

Lack of light [1 mark]
Causes chlorophyll breakdown / causes chlorosis [1 mark]

🧠 Exam Tip: Ion vs Nutrient

Always specify the exact ion and its role:

Magnesium ions: Required to synthesise the green pigment chlorophyll. Without it, leaves suffer chlorosis (yellowing).
Nitrate ions: Needed to make amino acids and proteins (deficiency causes stunted growth).
Do not confuse "fewer chloroplasts" with "less chlorophyll"—chlorophyll is the pigment that gives the green colour.

Topics

Biology · Required Practicals · B3: Infection and Response · B4: Bioenergetics · Required Practicals

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 1 (Higher), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.