AQA GCSE Biology Biology Paper 1 (Foundation), June 2022: Question 7
17 marks · Standard Demand difficulty · Short Answer
Identify cell structures and their functions, and analyze an osmosis investigation on potato tissue including calculations, plotting a graph, and explaining mass change.
Practise this questionQuestion
Question text
07 This question is about cells and transport.
07.1 Complete Table 5.
[3 marks]
Table 5
Name of cell part Function of cell part
Contains genetic information
Mitochondria
Controls the movement of substances into and
out of the cell
Cells in potatoes are plant cells.
Cells in potatoes do not contain chloroplasts.
07.2 What is the function of chloroplasts?
[1 mark]
07.3 Name one type of cell in a potato plant that does not contain chloroplasts.
[1 mark]
A student investigated the effect of salt concentration on pieces of potato.
This is the method used.
1. Cut three pieces of potato of the same size.
*27* 2. Record the mass of each potato piece.
3. Add 150 cm3 of 0.4 mol/dm3 salt solution to a beaker.
4. Place each potato piece into the beaker.
5. After 30 minutes, remove each potato piece and dry the surface with a paper towel.
6. Record the mass of each potato piece.
7. Repeat steps 1 to 6 using different concentrations of salt solution.
07.4 What is the independent variable in the investigation?
[1 mark]
Tick ( ) one box.
Concentration of salt solution
Mass of potato piece
Time potato is left in salt solution
Volume of salt solution
07.5 Why did the student dry the surface of each potato piece with a paper towel
in step 5?
[1 mark]
The student calculated the percentage change in mass of each potato piece.
07.6 For one potato piece:
• the starting mass was 2.5 g
• the end mass was 2.7 g.
Calculate the percentage increase in mass of the potato piece.
[2 marks]
Use the equation:
increase in mass
percentage increase in mass = × 100
starting mass
Percentage increase in mass = %
The student used the results from each potato piece to calculate the mean percentage
change in mass at each concentration.
Table 6 shows the results.
Table 6
Concentration of
Mean percentage (%)
salt solution in
3 change in mass
mol/dm
0.0 9.8
0.1 9.5
0.2 7.0
0.3 0.4
0.4 −1.4
07.7 Complete Figure 9.
You should:
• label the x-axis
• use a suitable scale for the x-axis
• plot the data from Table 6
• draw a line of best fit. 31
[4 marks]
Figure 9
07.8 What concentration of salt solution was equal to the concentration of the
solution inside the potato pieces?
Use Figure 9.
[1 mark]
Concentration =32 mol/dm3
07.9 Explain why the potato pieces in the 0.4 mol/dm3 salt solution decreased in mass.
[3 marks]
Mark scheme
Show the mark scheme
Question 7
AO /
Question Answers Extra information Mark
Spec. Ref.
07.1 must be in this order AO1
4.1.1.1
nucleus allow chromosomes 1 4.1.1.2
allow plasmid
(site of aerobic) respiration allow makes ATP 1
or releases energy
do not accept produces / makes
/ creates energy
do not accept anaerobic
respiration
(cell) membrane 1
AO /
Spec. Ref.
07.2 photosynthesis allow produce glucose / sugar 1 AO1
allow to absorb (sun) light 4.1.1.2
4.4.1.1
ignore contains chlorophyll
AO /
Spec. Ref.
07.3 root (hair) allow xylem / phloem / epidermis 1 AO1
/ meristem 4.1.1.3
4.2.3.1
4.2.3.2
AO /
Spec. Ref.
07.4 concentration of salt solution 1 AO1
4.1.3.2
RPA3
AO /
Spec. Ref.
07.5 to make sure only the potato allow (to) remove excess water 1 AO2
mass was measured / solution / liquid 4.1.3.2
or RPA3
if water / solution / liquid was left do not accept if water / solution
on (the potato), the mass would / liquid was left on (potato) the
be higher / affected mass would be lower
ignore to remove water /
solution / liquid on the outside /
surface (of potato)
AO /
Spec. Ref.
07.6 0.2 2.7 − 2.5 1 AO2
×100 allow ×100 4.1.3.2
2.5 2.5
RPA3
8(%) 1
if no other mark awarded allow 1
mark for
2.5 − 2.7
×100 = − 8 (%)
2.5
AO /
Spec. Ref.
07.7 max 3 marks for bar chart AO2
Mark with 4.1.3.2
07.8 correct scale and axis labelled scale must take up at least 50% 1 RPA3
(concentration (of salt solution) of grid
in mol/dm3)
all points plotted correctly allow a tolerance of ± ½ small 2
square
allow 3 or 4 correct plots for 1
mark
curved line of best fit ignore line extended beyond 1
0.4 mol/dm3
ignore line joined point to point
22 with straight lines
AO /
Spec. Ref.
07.8 correct answer from their line allow a tolerance of ± ½ small 1 AO2
Mark with drawn on Figure 9 square 4.1.3.2
07.7 RPA3
ignore line joined point to point
with straight lines if a line of best
fit is drawn
if no line of best fit is drawn,
allow an answer in the range
0.31 – 0.33 (mol/dm3)
AO /
Spec. Ref.
07.9 allow ‘pieces’ for potato AO2
throughout 4.1.3.2
RPA3
water moves out of cells / potato 1
by osmosis allow by diffusion through a 1
partially / selectively / semi
permeable membrane
(because) the solution in the allow (because) the solution 1
cells / potato is less outside the cells / potato is more 23
concentrated than outside concentrated than inside
or
(because) the solution in the allow (because) the solution
cells / potato is more dilute than outside the cells / potato is less
outside dilute than inside
allow correct references to water
concentration / potential
ignore reference to amount of
water or salt
do not accept water moves from
an area of high (solute)
concentration to an area of low
(solute) concentration
Total Question 7 17
How to answer it
Cell Biology & Osmosis Required Practical
This 17-mark question assesses fundamental cell biology and the core Osmosis Required Practical (RPA 3):
- Organelle Recall (AO1): Structure and precise function of nucleus, mitochondria, cell membrane, and chloroplasts.
- Plant Cell Specialisation (AO1): Identifying cells lacking chloroplasts due to location underground.
- Practical Methodology (AO1/AO2): Identifying experimental variables and understanding control steps (drying tissue).
- Maths & Graphical Skills (AO2): Calculating percentage mass change, plotting non-linear calibration curves, and reading isotonic points (x-intercept).
- Scientific Explanation (AO2): Applying the principle of osmosis to mass changes in hypertonic solutions.
Part (a): Cell Structure & Function
Questions 07.1, 07.2 & 07.3 [5 Marks Total]
✅ Correct Answers
- 07.1 Table Completion:
Cell Part Function Nucleus (1) Contains genetic information Mitochondria Site of (aerobic) respiration / releases energy (1) (Cell) membrane (1) Controls the movement of substances into and out of the cell - 07.2 Chloroplast Function: Photosynthesis / produces glucose / absorbs light energy (1).
- 07.3 Cell without chloroplasts: Root hair cell (or root / xylem / phloem / meristem / epidermal cell) (1).
❌ Common Errors & Traps
- Energy Trap: Writing that mitochondria "produce" or "create" energy loses the mark. Energy cannot be created—it is released during respiration.
- Anaerobic Trap: Specifying "anaerobic respiration" for mitochondria is incorrect; anaerobic respiration happens in the cytoplasm.
- Structure vs. Function: Stating chloroplasts "contain chlorophyll" describes their structure, not their function.
- Potato Anatomy: Writing "leaf cell" or "stem cell" for 07.3. Potato tubers grow underground, as do root hair cells, where light cannot reach.
Part (b): Practical Methodology & Controls
Questions 07.4 & 07.5 [2 Marks Total]
✅ Correct Answers
07.4 Independent Variable:
- ☑ Concentration of salt solution (1)
07.5 Why dry potato pieces with paper towel?
- To ensure that only the mass of the potato was measured (1)
OR to remove excess liquid on the outside which would falsely increase the mass (1).
🧠 Exam Technique
- Identifying Variables: The Independent variable is what I (the experimenter) deliberately change (salt concentration). The Dependent variable is what is measured (mass change).
- Surface Liquid: Always state that excess liquid on the surface adds to the mass. Simply saying "to clean it" or "to remove water" without explaining that it is surface liquid will not gain credit.
Part (c): Percentage Change Calculation
Question 07.6 [2 Marks]
📐 Step-by-Step Calculation
Data: Starting mass = 2.5 g , End mass = 2.7 g
- Step 1: Calculate the absolute increase in mass
Increase = End mass − Starting mass
Increase = 2.7 − 2.5 = 0.2 g - Step 2: Use the percentage equation provided
Percentage increase = (increase in mass ÷ starting mass) × 100
Percentage increase = (0.2 ÷ 2.5) × 100 = 8%
• 1 mark for correct substitution: (0.2 ÷ 2.5) × 100 or [(2.7 − 2.5) ÷ 2.5] × 100
• 1 mark for correct final answer: 8%
❌ Calculation Traps
- Dividing by the wrong mass: A classic error is dividing by the end mass (0.2 ÷ 2.7) rather than the starting mass (0.2 ÷ 2.5).
- Sign errors: Always check if mass increased or decreased. Here mass increased from 2.5 to 2.7, so the answer must be positive (+8%).
Part (d): Graph Drawing & Determining Internal Concentration
Questions 07.7 & 07.8 [5 Marks Total]
🧠 Graph Plotting Criteria (07.7) [4 Marks]
- Axis Label & Unit (1 mark): Label x-axis clearly as "Concentration of salt solution in mol/dm³".
- Scale (1 mark): Linear, sensible scale (e.g. 0.0, 0.1, 0.2, 0.3, 0.4) occupying at least 50% of the grid width.
- Plotting Data (2 marks):
• (0.0, 9.8), (0.1, 9.5), (0.2, 7.0), (0.3, 0.4), (0.4, −1.4)
• All 5 correct = 2 marks; 3 or 4 correct = 1 mark. Points must be within ±½ small square. - Line of Best Fit (1 mark): A single, smooth curved line passing close to all points. Do not join points dot-to-dot with a ruler.
✅ Finding Internal Concentration (07.8) [1 Mark]
Question: What concentration of salt solution was equal to the concentration of the solution inside the potato pieces?
- Where to look: Find where the curve crosses the horizontal 0.0 line (zero percentage mass change).
- Expected value: Between 0.31 and 0.33 mol/dm³ (or the exact value from your line drawn on Figure 9, within ±½ square).
Part (e): Explaining Mass Loss via Osmosis
Question 07.9 [3 Marks]
✅ Model 3-Mark Answer
Potato pieces in the 0.4 mol/dm³ salt solution decreased in mass because:
- Direction of water movement: Water moved out of the cells / potato pieces (1).
- Transport process: By osmosis (or diffusion through a partially permeable membrane) (1).
- Concentration gradient: Because the solution outside the potato was more concentrated than the solution inside the cells (OR the solution inside the potato was more dilute / had a higher water concentration) (1).
❌ Examiner Pitfalls to Avoid
- "Salt moved out": Salt ions do not cause the mass change; it is entirely due to water moving out.
- Vague concentration claims: Never just say "there is a concentration gradient". You must specify: the outside solution is more concentrated in solute (or has a lower water concentration) than the inside of the potato cell.
- Solute vs Solvent Confusion: Never write "water moves from high solute concentration". Water moves from high water concentration to low water concentration.
Topics
Biology · Required Practicals · B1: Cell Biology · Required Practicals
Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 1 (Foundation), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.