AQA GCSE Combined Science: Trilogy Biology Paper 1 (Foundation), 2021: Question 4

13 marks · Standard Demand difficulty · Short Answer

Identify plant transport organs and processes, and calculate stomata density and mean values from experimental data.

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Question

The image shows a multi-part GCSE biology exam question about plant transport systems. It includes multiple-choice questions on water absorption, ion transport, and sugar translocation. Figure 5 is a microscopic view of a leaf surface showing several stomata and a cell labeled X. A calculation question asks for the number of stomata per mm squared using a provided formula. Table 1 presents data for the number of stomata on the upper and lower surfaces of five different leaves, including a mean calculation for the lower surface labeled X.
Question text

04 This question is about plant transport systems.

04.1 Which organ in a plant absorbs water from the soil?

[1 mark]

04.2 The concentration of nitrate ions in the soil is lower than the concentration of

nitrate ions inside a plant.

How would the nitrate ions move from the soil into the cells of this plant?

[1 mark]

Tick ( ) one box.

By active transport

By diffusion

By osmosis 19

Dissolved sugars are transported in the phloem.

04.3 What is the name of the process that moves dissolved sugars through the phloem?

[1 mark]

Tick ( ) one box.

Evaporation

Osmosis

Translocation

04.4 Give one use of sugars in a plant.

[1 mark]

*18* 20

Stomata are openings on the surface of a leaf.

Stomata allow gases to move into and out of a leaf.

Figure 5 shows the surface of a leaf.

Figure 5

04.5 What is cell X?

[1 mark]

Tick ( ) one box.

Guard cell

Meristem cell

Palisade cell 21

04.6 Why do the stomata open during the day?

[1 mark]

Tick ( ) one box.

To allow carbon dioxide in

To allow nitrogen in

To allow oxygen in

04.7 The area of the leaf shown in Figure 5 is 0.25 mm2.

Calculate the number of stomata per mm2 for the leaf in Figure 5.

Use the equation:

2 number of stomata

number of stomata per mm = 2

area in mm

[2 marks]

22 2

Number of stomata per mm =

A student investigated the number of stomata per mm2 on the upper and lower

surfaces of leaves.

The leaves were taken from the same plant.

Table 1 shows the results.

Table 1

Number of stomata per mm2

Leaf

Upper surface Lower surface

10 37

21 36

32 30

41 32

51 35

Mean 1 X

04.8 Calculate mean value X in Table 1.

[2 marks]

23 X =

04.9 Water vapour is lost through stomata.

Explain the difference in the number of stomata on the upper and lower surfaces of

the leaves.

Use Table 1.

[3 marks]

Mark scheme

Show the mark scheme The mark scheme provides the correct answers for questions 04.1 through 04.9. Key answers include: root for the organ, active transport for ion movement, translocation for sugar transport, and guard cell for cell X. It shows the calculation steps for stomata density (9 divided by 0.25 equals 36) and the mean calculation for the table (sum of 37, 36, 30, 32, 35 divided by 5 equals 34). The final explanation points out that fewer stomata on the upper surface reduces water loss in warmer or windier conditions.

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 root do not accept root hair (cells) 1 AO1

4.2.1

4.2.3.2

04.2 by active transport 1 AO2

4.1.3.3

04.3 translocation 1 AO1

4.2.3.2

04.4 any one from: 1 AO1

• respiration allow to release energy 4.2.3.2

do not accept to produce / make 4.4.1.3

/ create energy

allow for growth

• (used) to produce starch

• (used) to produce fat / oil

• (used) to produce cellulose

• (used) to produce amino

acids / protein

04.5 guard cell 1 AO1

4.2.3.1

4.2.3.2

04.6 to allow carbon dioxide in 1 AO2

4.2.3.1

4.2.3.2

04.7 9 1 AO2

0.25 4.2.3.2

36 do not accept if a unit is given 1

allow correct calculation using

04.8 37 + 36 + 30 + 32 + 35 170 1 AO2

allow

55 4.2.3.2

34 1

04.9 there are fewer stomata on the allow converse statements 1 AO3

upper surface of the leaves a comparative term is required

(conditions on upper surface 1 AO2

will:)

any one from:

• be warmer

• be drier

• be more exposed to wind

• have more light

(so) less water will be lost 1 AO2

4.2.3.2

Total 13

How to answer it

Plant Transport and Gas Exchange

What this question tests

This question assesses your understanding of plant anatomy and physiology, specifically how substances move into and through a plant. Key topics include active transport, translocation, leaf structure (stomata and guard cells), and the ability to process experimental data using means and ratios.

Parts 04.1 — 04.4

Foundations of Plant Transport

💡 Key Knowledge

  • Roots: The organ responsible for water and mineral uptake.
  • Active Transport: Moves substances from low to high concentration (against the gradient) using energy.
  • Translocation: The movement of dissolved sugars through the phloem.

🧠 Exam Technique

Read the wording carefully. If the question asks for an organ, don't name a cell. If it asks for a process, look for specific biological terms like "translocation" rather than general descriptions.

✅ Correct Answers

  • 04.1: Root
  • 04.2: By active transport
  • 04.3: Translocation
  • 04.4: Respiration (or to produce starch/cellulose/fats)

❌ Common Errors

  • 04.1: Writing "root hair cell". A cell is not an organ!
  • 04.4: Saying sugar is used to "make energy". Energy is released, not made.
Parts 04.5 — 04.6

Leaf Structure and Gas Exchange

Identifying Cell X and its function

💡 Key Knowledge

Guard Cells: These are the pairs of cells that surround a stoma. They control the opening and closing of the pore to balance gas exchange and water loss.

Photosynthesis: Plants need CO₂ during the day for photosynthesis, which is why stomata open.

✅ Correct Answers

  • 04.5: Guard cell
  • 04.6: To allow carbon dioxide in
Parts 04.7 — 04.8

Data and Calculations

📐 Calculation 04.7: Stomata per mm²

  1. Step 1: Count the stomata. Looking at Figure 5, there are exactly 9 stomata visible.
  2. Step 2: Identify the area. The question provides the area as 0.25 mm².
  3. Step 3: Use the formula. 9 / 0.25 = 36.
Mark 1: For the setup (9 / 0.25) | Mark 2: For the correct answer (36)

📐 Calculation 04.8: Calculating Mean X

  1. Step 1: Sum the values. 37 + 36 + 30 + 32 + 35 = 170.
  2. Step 2: Divide by the count. 170 / 5 = 34.
Mark 1: For the sum (170 / 5) | Mark 2: For the correct answer (34)

❌ Calculation Traps

In 04.7, students often forget to count the stomata in the image first. In 04.8, ensure you don't include the "Upper surface" mean (1) in your calculation for the "Lower surface" mean (X).

Part 04.9

Explaining Stomata Distribution

Why are there fewer stomata on top?

🧠 How to structure a 3-mark "Explain" answer

You must link the observation to the environment and then to the biological benefit.

  1. The Observation: State that there are fewer stomata on the upper surface (using the data from Table 1).
  2. The Environment: Explain that the upper surface is more exposed to heat/sunlight/wind.
  3. The Benefit: Explain that having fewer stomata there reduces water loss (transpiration), preventing the plant from wilting.

✅ Model Answer

There are fewer stomata on the upper surface of the leaf (1 mark). This is because the upper surface is warmer and more exposed to sunlight (1 mark), so having fewer stomata means less water is lost through evaporation (1 mark).

💡 Examiner Insight

Top-level responses used comparative language (e.g., "fewer", "warmer", "less"). Simply saying "it is hot" is less effective than saying "the upper surface is hotter than the lower surface".

Topics

Biology · B1: Cell Biology · B2: Organisation · B4: Bioenergetics

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 1 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.