AQA GCSE Combined Science: Trilogy Biology Paper 1 (Foundation), 2022: Question 2

17 marks · Standard Demand difficulty · Short Answer

Identify leaf adaptations, calculate cell size using magnification, explain diffusion gradients, and analyze an investigation into the effect of light color on the rate of photosynthesis.

Practise this question

Question

Figure 2 shows a cross-section of a leaf with the palisade layer and pores labeled X. Figure 3 depicts four cells (A-D) with different concentrations of carbon dioxide molecules inside and outside. Figure 4 shows an experimental setup with pondweed in a beaker of water under a funnel and test tube, collecting gas bubbles. Table 2 shows the rate of photosynthesis for blue, green, and red light. Figure 5 is a blank graph grid for a bar chart.
Question text

02 Figure 2 shows a section through a leaf.

Figure 2

02.1 Give one way that the palisade layer is adapted for photosynthesis.

[1 mark]

02.2 Gases pass into and out of the leaf through small pores in the surface of the leaf.

What are the small pores labelled X called?

[1 mark]

Tick ( ) one box.

Guard cells

Stomata

Xylem vessels 7

02.3 A student viewed a section of a leaf using a microscope.

The student measured the length of one of the palisade cells.

The cell image measured 28 mm in length when viewed at a magnification of ×400

Calculate the real length of the palisade cell in millimetres (mm).

Use the equation:

image length

real length =

magnification

[3 marks]

Real length = mm

Convert the real length of the cell from millimetres to micrometres (μm).

1 mm = 1000 μm

Real length = μm

02.4 Carbon dioxide can move into and out of cells.

What is the process by which carbon dioxide can move into and out of cells?

[1 mark]

Tick ( ) one box.

Active transport

Diffusion

Osmosis 8

Figure 3 shows a diagram of four cells.

Each cell is surrounded by carbon dioxide molecules.

Figure 3

02.5 Which cell will carbon dioxide move into at the fastest rate?

Give a reason for your answer.

[2 marks]

Tick ( ) one box.

A B C D

Reason

A student investigated the effect of different colours of light on the rate

of photosynthesis.

*08* Figure 4 shows some of the apparatus the student used.

Figure 4

The student placed the apparatus in blue light, then in green light and then in red light.

The student measured the rate of photosynthesis in each colour of light.

02.6 What two measurements should the student make to calculate the

rate of photosynthesis?

[2 marks]

02.7 Give two variables the student should keep the same in this investigation.

[2 marks]

Table 2 shows the results.

Table 2

Rate of photosynthesis in

Colour of light

arbitrary units

Blue 9

Green 1

Red 11 8

02.8 Complete Figure 5.

You should:

• label the y-axis

• use a suitable scale

• plot the data from Table 2 as a bar chart

• label each bar.

[4 marks]

Figure 5

02.9 Look at Table 2.

What colour of light should be used to grow plants in a greenhouse?

[1 mark]

Tick ( ) one box.

Blue Green Red

Mark scheme

Show the mark scheme The mark scheme details 17 marks across 9 sub-questions. It includes answers for leaf adaptations (chloroplasts), identification of stomata, a three-step magnification calculation (28/400 = 0.07mm = 70µm), identification of diffusion, explanation of concentration gradients, experimental measurements (bubbles and time), control variables (temperature, light intensity), and criteria for a 4-mark bar chart.

Question 2

AO /

Question Answers Extra information Mark

Spec. Ref.

02.1 cells contain (many) allow positioned nearest to the 1 AO1

chloroplasts light 4.1.1.3

or 4.2.1

at the top of the leaf 4.2.3.1

4.4.1.1

allow cells are closely packed

or

no gaps between cells

allow chlorophyll for chloroplast

AO /

Spec. Ref.

02.2 stomata 1 AO1

4.2.3.1

4.2.3.2

AO /

Spec. Ref.

02.3 28 1 AO2

(real length) =

400 4.1.1.1

4.1.1.2

(real length in mm =) 0.07 1

4.1.1.5

RPA1

(real length in μm =) 70 allow answer given for length in 1

– OMBINED SCIENCE: TRImm correctly multiplied by 1000LOGY– –

AO /

Spec. Ref.

10 02.4 diffusion 1 AO1

4.1.3.1

AO /

Spec. Ref.

no marks if wrong cell chosen

02.5 A 1 AO3

Reason any one from: 1 AO2

• steeper (diffusion) gradient

• bigger difference in allow higher concentration of 4.1.3.1

concentration of carbon carbon dioxide outside the cell

dioxide inside and outside the than inside the cell

cell allow particles / molecules for

carbon dioxide

AO /

Spec. Ref.

02.6 (number / amount of) bubbles allow volume of gas / oxygen 1 AO1

4.4.1.2

RPA5

time allow suitable time eg 1 / 5 / 10 1

– OMBINED SCIENCE: TRIminutesLOGY – –

AO /

Spec. Ref.

do not accept colour of light

02.7 ignore time AO3

any two from: 2 4.4.1.2

• temperature (of water) RPA5

• light intensity allow amount of light

or ignore light unqualified

distance of light (from

pondweed)

• concentration of carbon allow amount / mass of sodium 11

dioxide (in water) hydrogen carbonate (in water)

allow type / size of plant

ignore volume of water / solution

AO /

Spec. Ref.

02.8 y-axis labelled: 1 AO2

rate of photosynthesis in 4.4.1.2

arbitrary units RPA5

suitable scale 1

all bars plotted correctly allow ± ½ a small square 1

the bars can be in any order

all bars labelled correctly– OMBINED SCIENCE: TRILOGY – 1 –

AO /

Spec. Ref.

02.9 blue 1 AO3

4.4.1.2

RPA5

12Total Question 2 17

How to answer it

Leaf Structure and Photosynthesis

What this question tests

This question assesses your understanding of leaf adaptations, microscopy calculations, and the process of diffusion. It also tests your ability to design a required practical investigation into the rate of photosynthesis and present data in a bar chart.

Part (02.1 - 02.2)

Leaf Anatomy & Gas Exchange

Correct Answers

  • 02.1: Palisade cells contain many chloroplasts (or are closely packed/at the top of the leaf).
  • 02.2: The small pores (X) are Stomata.

Key Knowledge

The palisade layer is the main site of photosynthesis. It is located at the top of the leaf to absorb maximum sunlight. Stomata are controlled by guard cells to allow CO₂ in and O₂ out.

Part (02.3)

The Magnification Calculation

Step-by-Step Calculation

  1. Identify the values: Image length = 28 mm, Magnification = ×400.
  2. Apply the formula: Real length = 28 / 400.
  3. Calculate in mm: 28 / 400 = 0.07 mm. [2 marks]
  4. Convert to micrometres (μm): Multiply by 1000. 0.07 × 1000 = 70 μm. [1 mark]

Common Calculation Traps

Students often forget to convert units. Always check if the question asks for mm or μm. To go from mm to μm, you multiply by 1000. If you get a real length that is larger than the image length, you have likely multiplied instead of divided!

Part (02.4 - 02.5)

Diffusion & Concentration Gradients

Correct Answers

  • 02.4: Diffusion
  • 02.5: Cell A. Reason: It has the steepest concentration gradient (the biggest difference between CO₂ outside and inside).

Exam Technique

When asked about the "rate" of diffusion, always look for the difference in concentration. In Figure 3, Cell A has many dots outside and very few inside. This "steep" gradient makes molecules move much faster.

Part (02.6 - 02.7)

Investigating Photosynthesis

Measuring Rate

To find a rate, you need a quantity and a time. In the pondweed experiment, we measure:

  • Number of bubbles (or volume of oxygen).
  • A specific time period (e.g., 1 minute).

Control Variables

To make it a fair test, keep these the same:

  • Temperature of the water.
  • CO₂ concentration (using sodium hydrogen carbonate).
  • Distance of the light source from the plant.

Misconception Alert

Do not list "colour of light" as a control variable here. That is the independent variable (the thing you are changing). You cannot keep the thing you are testing the same!

Part (02.8 - 02.9)

Data & Graphing

How to draw the Bar Chart (02.8)

  • Y-axis: Label it "Rate of photosynthesis in arbitrary units". Use a scale of 0 to 10 (1 unit per major grid line).
  • X-axis: Label three distinct bars: Blue, Green, and Red.
  • Plotting: Blue bar to 9, Green bar to 1, Red bar to 8.
  • Accuracy: Ensure bars are equal width and clearly separated.

Conclusion (02.9)

Blue light should be used. The table shows it has the highest rate of photosynthesis (9 arbitrary units), which will lead to the fastest plant growth.

Topics

Biology · B1: Cell Biology · B2: Organisation · B3: Infection and Response · B4: Bioenergetics

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 1 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.