AQA GCSE Combined Science: Trilogy Biology Paper 1 (Foundation), 2020: Question 3

9 marks · Standard Demand difficulty · Short Answer

Investigate transpiration from leaves by comparing mass loss when different leaf surfaces are covered with grease, then use the results to calculate water loss and interpret stomata distribution.

Practise this question

Question

Question text

03 Water is lost from the leaves of plants through pores called stomata.

03.1 What is the loss of water from a leaf called?

[1 mark]

Tick ( ) one box.

Osmosis

Respiration

Transpiration

03.2 Which cells control the size of stomata?

[1 mark]

Tick ( ) one box.

Guard cells

Phloem cells

Xylem cells 14

A student investigated the water loss when different surfaces of leaves were covered

in grease.

The grease blocks the stomata.

This is the method used.

1. Remove four similar leaves from one plant.

2. Put grease on different surfaces of the leaves as shown in Figure 4.

3. Record the mass of each leaf and attach the four leaves to a string.

4. After 24 hours record the mass of each leaf again.

Figure 4

Table 2 shows the results.

Table 2

Leaf Surfaces covered with Mass of leaf at Mass of leaf Loss in mass

grease start in grams after 24 hours in after 24 hours in

grams grams

A Upper and lower 2.01 1.97 X

B Only upper 2.00 1.87 0.13

C Only lower 2.01 1.96 0.05

D None 1.9815 1.83 0.15

03.3 Calculate value X in Table 2.

[1 mark]

Value X = g

03.4 The loss in mass of water was measured after 24 hours.

Calculate the mass of water lost in grams per hour for leaf D.

[2 marks]

Mass of water lost per hour = g

The student concluded:

‘More water is lost from the lower surface of a leaf than from the upper surface.’

03.5 What evidence is there in Table 2 to support the student’s conclusion?

[1 mark]

03.6 What do the results in Table 2 show about the number of stomata on the

surfaces of a leaf?

[1 mark]

Tick ( ) one box.

There are more stomata on the lower surface.

There are more stomata on the upper surface.

There are the same number of stomata on both surfaces.16

03.7 The investigation was done at 20 °C

How would the mass of water lost be different if the investigation was done at 25 °C?

Give a reason for your answer.

[2 marks]

Difference

Reason

Mark scheme

Show the mark scheme

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 transpiration 1 AO1

4.2.3.2

03.2 guard cells 1 AO1

4.2.3.1

4.2.3.2

03.3 0.04 (g) 1 AO2

4.2.3.1

4.2.3.2

03.4 AO2

0.15 allow 1 4.2.3.1

24 4.2.3.2

= 0.0062(5) (g) allow 0.006 / 0.0063 / 6 × 10-3 /

or 6.3 × 10-3 (g)

= 6.2(5) × 10-3 (g)

03.5 any one from: 1 AO3

4.2.3.1

• leaf B lost more mass / water allow B lost 013 g of mass / 4.2.3.2

than leaf C water and C lost 0.05 g of mass

or / water

leaf C lost less mass / water

than leaf B

allow lower surface lost 0.13 g

of mass / water and upper

surface lost 0.05 g of mass /

water

• when lower surface covered

less mass / water was lost

(than when upper surface

covered)

• when upper surface covered

more mass / water was lost

(than when lower surface

covered)

03.6 there are more stomata on the 1 AO3

lower surface 4.2.3.1

4.2.3.2

03.7 ‘it’ refers to the mass of water

lost

more (mass / water) lost 1 AO3

4.2.3.2

(because) evaporation / 1 AO2

transpiration would be faster 4.2.3.2

Total 9

How to answer it

Transpiration and Stomata Investigation

What this question tests

This question tests your knowledge of transpiration, stomata and guard cells, plus your ability to use data from a table, calculate loss in mass, work out a rate per hour, and use evidence to support a conclusion. It also checks whether you understand how temperature affects transpiration.

Question overview

Part	Topic	Marks	Main skill
03.1	Name of water loss from leaves	1	Recall
03.2	Cells controlling stomata	1	Recall
03.3	Calculate missing mass loss	1	Data handling
03.4	Calculate water loss per hour	2	Rate calculation
03.5	Use evidence from the table	1	Interpretation
03.6	Conclusion about stomata number	1	Inference
03.7	Effect of higher temperature	2	Explanation

Total = 9 marks. This is a typical GCSE biology/data question: easy marks from recall, then methodical marks from reading the table carefully.

Part 03.1

What is the loss of water from a leaf called?

✅ Correct answer

Transpiration

1 mark for choosing the correct term.

💡 Key knowledge

Transpiration = loss of water vapour from leaves.
Water mainly leaves through the stomata.

❌ Common errors

Choosing osmosis — this is movement of water through a partially permeable membrane.
Choosing respiration — this is energy release in cells, not water loss from leaves.

Part 03.2

Which cells control the size of stomata?

✅ Correct answer

Guard cells

1 mark for the correct cell type.

💡 Key knowledge

Guard cells open and close the stomata.
This helps control gas exchange and water loss.

❌ Common errors

Xylem transports water, but does not control stomata.
Phloem transports sugars, but does not control stomata.

Part 03.3

Calculate value X in Table 2

📐 Calculations

Step 1: Use loss in mass = start mass − mass after 24 hours

Step 2: For leaf A: 2.01 − 1.97 = 0.04

Step 3: Add the unit: 0.04 g

✅ Correct answer

X = 0.04 g

1 mark for the correct subtraction and answer.

🧠 Exam technique

Always read the column heading carefully: here it says loss in mass after 24 hours in grams.
Write the unit g.

❌ Common errors

Doing 1.97 − 2.01 and getting a negative value.
Forgetting the unit.
Copying a number from the table instead of calculating it.

Part 03.4

Calculate the mass of water lost in grams per hour for leaf D

📐 Calculations

Step 1: Find total mass lost for leaf D from the table: 0.15 g

Step 2: Time = 24 hours

Step 3: Rate per hour = 0.15 ÷ 24

Step 4: 0.15 ÷ 24 = 0.00625 g per hour

Step 5: Acceptable rounded answers include 0.00625 g , 0.0063 g , 0.006 g or 6.25 × 10⁻³ g

✅ Correct answer

0.00625 g per hour

Also acceptable: 6.25 × 10⁻³ g per hour

1 mark for setting up 0.15 / 24
1 mark for the correct answer

🧠 Exam technique

The question asks for per hour, so you must divide by 24.
If your calculator gives a long decimal, round sensibly.
Include the unit g.

❌ Common calculation traps

Using the wrong leaf — the question says leaf D.
Subtracting the masses again instead of using the loss already given.
Multiplying by 24 instead of dividing.
Missing out per hour.

Part 03.5

What evidence in Table 2 supports the student's conclusion?

✅ Correct answers

Any one of these gains the mark:

Leaf B lost more water than leaf C.
Leaf C lost less water than leaf B.
When the lower surface was covered, less water was lost than when the upper surface was covered.
When the upper surface was covered, more water was lost than when the lower surface was covered.

Best evidence with figures:

Leaf B lost 0.13 g and Leaf C lost 0.05 g .

1 mark for one clear piece of evidence from the table.

💡 Key knowledge

Leaf B had the upper surface covered, so water could still escape mostly from the lower surface. Leaf C had the lower surface covered, so less water escaped.

🧠 Exam technique

For an evidence question, quote data from the table if possible.
Compare two results directly.
Use phrases like more than or less than.

❌ Common errors

Repeating the conclusion without giving table evidence.
Talking about the wrong leaves.
Not making a comparison.

Part 03.6

What do the results show about the number of stomata on the surfaces of a leaf?

✅ Correct answer

There are more stomata on the lower surface.

1 mark for ticking the correct statement.

💡 Key knowledge

More water was lost when the lower surface was left uncovered.
That suggests there are more stomata on the lower surface.

❌ Common errors

Choosing “same number on both surfaces”.
Choosing “more on the upper surface” because the wording of the experiment is confusing.

Part 03.7

How would the mass of water lost be different at 25 °C? Give a reason.

✅ Correct answer

More water would be lost.

Reason: evaporation / transpiration would be faster.

1 mark for saying more mass/water lost
1 mark for linking this to faster evaporation or faster transpiration

💡 Key knowledge

Higher temperature gives water molecules more kinetic energy.
This makes evaporation from leaf cells faster.
So the rate of transpiration increases.

🧠 Exam technique

The question asks for two things: difference and reason.
Write them as two separate statements to be safe.
The mark scheme allows either mass or water lost.

❌ Common errors

Saying less water would be lost.
Giving no reason.
Saying “photosynthesis is faster” — that is not the marking point here.

Examiner insight

🧠 What separated strong answers

Using the exact biology terms: transpiration and guard cells.
Showing the calculation clearly before giving the final answer.
Using actual table values as evidence in part 03.5.
Linking higher temperature directly to faster evaporation/transpiration.

❌ Where students lost marks

Mixing up upper and lower surfaces in the grease experiment.
Forgetting that grease blocks stomata.
Not dividing by 24 in the rate calculation.
Writing a general statement instead of evidence from the table.

Full mark answer checklist

03.1 Transpiration
03.2 Guard cells
03.3 0.04 g
03.4 0.15 ÷ 24 = 0.00625 g per hour
03.5 Leaf B lost more water than leaf C / use the data 0.13 g vs 0.05 g
03.6 More stomata on the lower surface
03.7 More water lost because evaporation/transpiration would be faster

Topics

Biology · B2: Organisation · B7: Ecology

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 1 (Foundation), 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.