AQA GCSE Biology Biology Paper 2 (Higher), June 2025: Question 3

13 marks · Standard Demand difficulty · Extended Answer

Describe tropisms, plan an investigation into the effect of light direction on seedling growth using provided equipment, identify auxin and its mechanism, and explain the survival advantage of phototropism.

Practise this question

Question

Question text

03 Tropisms help plants survive.

03.1 What is geotropism?

[2 marks]

03.2 Plan an investigation to find the effect of the direction of light on the growth of

plant seedlings.

You may use the equipment shown in Figure 3 and any other laboratory equipment.

[6 marks]

Figure 3

Extra space

Plant responses are controlled by hormones.

03.3 Which hormone controls a plant’s response to the direction of light?

[1 mark]

03.4 How does the hormone you named in Question 03.3 control the plant’s response to

the direction of light?

[1 mark]

Tick ( ) one box.

All parts of the plant have the same concentration of hormone.

The hormone has an effect when it breaks down.

*09*There is an uneven distribution of the hormone.

03.5 Explain how a plant’s response to light helps the plant survive.

[3 marks]

Mark scheme

Show the mark scheme

Question 3

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 growth (response) ignore direction of growth 1 AO1

4.5.4.1

due to gravity 1

AO /

Question Answers Mark

Spec. Ref.

03.2 Level 3: The method would lead to the production of a valid 5–6 AO1

outcome. The key steps are identified and logically sequenced. 4.5.4.1

RPA8

Level 2: The method would not necessarily lead to a valid 3–4

outcome. Most steps are identified, but the plan is not fully logically

sequenced.

Level 1: The method would not lead to a valid outcome. Some 1–2

relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative content

• place a seedling in box with slit

• place a seedling in darkness or in all-round light

• measure initial heights of shoots

• measure final heights of shoots or measure shoots with a ruler

or measure the growth of shoots

• record a named feature of appearance of seedlings

• detail of how bent shoots are measured eg use thread or

straighten them out

• repeat with several seedlings

• calculate mean height increase for each condition

• compare results (for each condition)

control variable(s)

o same number of seedlings (per pot / condition)

o same temperature

o same volume of water

o same soil type / volume

o same age of seedlings 11

o same species / type of plant

o same time left for

For Level 3, a method comparing the growth of plants in light from

one direction with plants in full light / darkness along with control

variables is required.

12 AO /

Spec. Ref.

03.3 auxin 1 AO1

4.5.4.1

AO /

Spec. Ref.

03.4 there is an uneven distribution of 1 AO1

the hormone 4.5.4.1

AO /

Spec. Ref.

03.5 leaves / plant receive(s) / 1 AO2

absorb(s) more light 4.5.4.1

4.4.1.1

(so) more photosynthesis 1 4.4.1.3

(which produces) more glucose allow (which produces) more 1

starch / carbohydrate / sugar

allow (which produces) more

(named) organic material / other

named organic substance

if no other marks awarded allow

1 mark for any two of the mark

points with no reference to

‘more’

Total Question 3 13

How to answer it

Plant Hormones & Investigating Tropisms

📋 What this question tests

This question examines content from Topic B5 (Homeostasis and Response) and Required Practical 8:

Recall & Definitions: Defining geotropism (gravitropism) and identifying auxin.
RPA 8 Experimental Design (6 marks): Planning an objective, valid investigation comparing seedling growth under directional light versus a control condition, controlling key variables, and measuring shoot response accurately.
Mechanism of Action: Explaining how auxin distribution leads to differential growth.
Evolutionary / Survival Advantage: Linking phototropism to light absorption, photosynthesis, and glucose production.

Question 03.1 • Recall [2 marks]

Definition of Geotropism

What is geotropism?

✅ Correct Answer

A growth response [1 mark]
In response to gravity [1 mark]

💡 Key Knowledge

Tropisms are directional growth responses in plants:

Phototropism: Growth in response to light.
Geotropism (Gravitropism): Growth in response to gravity.
Shoots are negatively geotropic (grow against gravity); roots are positively geotropic (grow towards gravity).

❌ Common Errors

Writing just "plants growing downwards" without mentioning gravity.
Omitting the word growth (e.g., stating just "moving towards gravity" — plants cannot move locations; they respond by growing).

🧠 Exam Technique

Any tropism definition must have two parts: the nature of the response (growth) and the stimulus (gravity for geotropism, light for phototropism).

Mark Scheme Note: Ignore direction of growth (i.e. whether positive or negative). Just mentioning growth + gravity secures both marks.

Question 03.2 • Practical Skills (RPA 8) [6 marks]

Planning an Investigation on Directional Light

Plan an investigation to find the effect of the direction of light on the growth of plant seedlings using the equipment in Figure 3.

✅ Model 6-Mark Method

Set up groups: Place one dish of seedlings inside the box with a slit cut in the side (directional light from the lamp). Place another identical dish in a box with no slit (complete darkness) OR in open, all-round light as a control.
Measure initial length: Use a ruler to record the starting shoot height of each seedling.
Control variables: Keep the temperature, volume of water added, number of seedlings per dish, and type of seed constant for all groups.
Incubation: Leave all seedlings for a set period of time (e.g., 3 to 5 days).
Measure final growth: Measure the final height of each shoot. Use a piece of damp thread along the curve of bent shoots and measure against the ruler to get an accurate length. Record the angle or direction of bending.
Replication & Analysis: Calculate the mean increase in height for each condition and compare results.

🧠 Examiner Level Criteria (Level 3: 5–6 Marks)

To reach Level 3, your plan must be logically sequenced and achieve a valid outcome. The examiner specifically looks for:

A clear comparison: Seedlings in unidirectional light compared against seedlings in all-round light or total darkness.
Clear control variables: At least two named variables held constant (e.g., water volume, temperature).
Measurement precision: Measuring shoot height before and after with a ruler, or using thread to measure bent shoots.

❌ Why Students Lost Marks

No control group: Setting up only the box with a slit. Without an all-round light or dark control, you cannot prove the bending is caused specifically by the direction of the light.
Vague measurement: Saying "see how much they grow" instead of specifying "measure shoot height in mm using a ruler before and after".
Ignoring repeats: Using only a single seedling instead of multiple seedlings to calculate a mean.

💡 Practical Tip: Bent Shoots

Because seedlings in directional light bend towards the slit, measuring them straight with a wooden ruler is difficult. Mentioning using thread placed along the stem, then straightened against the ruler is a classic top-mark practical detail!

Questions 03.3 & 03.4 • Recall & Mechanism [2 marks]

Auxin and Uneven Growth

✅ 03.3 Hormone Name

Auxin [1 mark]

✅ 03.4 Tick Box Answer

[ ] All parts of the plant have the same concentration of hormone.
[ ] The hormone has an effect when it breaks down.
[✔] There is an uneven distribution of the hormone. [1 mark]

💡 How Auxin Works in Shoots

Auxin is produced in the shoot tip and diffuses backwards.
Light causes auxin to accumulate on the shaded side (darker side) of the shoot.
In shoots, higher auxin concentration stimulates faster cell elongation.
Cells on the shaded side grow longer than cells on the lit side, forcing the shoot tip to bend towards the light.

❌ Common Misconceptions

Believing auxin is destroyed by light. (Auxin simply diffuses / moves towards the shaded side).
Confusing shoots with roots. (In roots, high auxin levels inhibit elongation, which causes roots to bend downwards towards gravity).

Question 03.5 • Explanation & Application [3 marks]

Survival Advantage of Phototropism

Explain how a plant's response to light helps the plant survive.

✅ Model 3-Mark Explanation

Leaves receive / absorb more light [1 mark]
(So there is) more photosynthesis [1 mark]
(Which produces) more glucose (or food / carbohydrates for growth and energy) [1 mark]

🧠 Exam Technique: Use Comparative Words!

Notice that every single marking point in the official mark scheme requires the word "more" (or a comparative equivalent):

absorbs more light → more photosynthesis → produces more glucose.
Strict Marking Rule: If no comparative word is used (e.g. you only write "absorbs light for photosynthesis to make glucose"), the mark scheme restricts you to a maximum of 1 mark overall!

❌ Common Errors

Writing simply "so it can make food" without naming the biological process (photosynthesis) and product (glucose).
Claiming the plant absorbs light "for energy" without linking it to photosynthetic production of biomass/glucose.

Topics

Biology · Required Practicals · B5: Homeostasis and Response · B4: Bioenergetics · Required Practicals

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Higher), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.