AQA GCSE Biology Biology Paper 1 (Higher), 2024: Question 5

11 marks · Standard Demand difficulty · Extended Answer

Plan and explain an investigation into how different salt solution concentrations affect the mass of potato pieces, using the results graph to explain osmosis and differences in mass loss.

Practise this question

Question

Question text

05 A student investigated the effect of concentration of salt solution on the mass of

uncooked potato pieces.

Figure 4 shows the results.

Figure 4

05.1 Plan a method that could be used to obtain the results in Figure 4.

[6 marks]

05.2 Explain the result for the potato pieces in the 0.6 mol/dm3 salt concentration.

[3 marks]

05.3 Explain why the result for the potato pieces at 1.0 mol/dm3 was different from the

result at 0.6 mol/dm3.

[2 marks]

Mark scheme

Show the mark scheme

Question 5

AO /

Question Answers Mark

Spec Ref.

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

outcome. The key steps are identified and logically sequenced. 4.1.3.2

RPA3

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

outcome. Most steps are identified, but the method 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:

• (measure and) record mass of potato pieces

• place potato pieces into different concentrations of salt solution

o use at least 3 different concentrations of salt solution

• leave potato pieces in salt solutions

• remove potato pieces from salt solutions

• blot potato pieces dry

• (measure and record mass of potato pieces and) calculate

change in mass

• repeat each concentration

o repeat each concentration 2 more times

• calculate mean change in mass

Control variables

• use same size / mass potato pieces

• use same potato or use same type of potato

• use same blotting technique

• ensure no skin on potato pieces

• keep potato pieces in solution for the same amount of time (≥10

minutes)

• keep potato pieces in solutions at the same temperature

For Level 1, the method must allow the determination of the

change in mass for a piece of potato.

For Level 3, the method must allow the production of the graph inMARKSCHEME–– –

Figure 4.

AO /

Question Answers Extra information Mark

Spec Ref.

05.2 (pieces) lost mass because 1 AO2

water left cells / potato 4.1.3.2

RPA3

(because) the solution in the allow (because) the solution 1

cells / potato is less outside the cells / potato is more

concentrated than outside concentrated than inside

(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

water left cells / potato by allow water left cells by diffusion 1

osmosis through a partially / selectively /

semi permeable membrane

AO /

Spec Ref.

05.3 (pieces at 1.0 mol/dm3) (pieces at 1.0 mol/dm3) 1 AO3

lost more mass because more lost more mass because more

water left potato / cells osmosis occurred out of the

potato / cells

(because) there is a steeper allow there is a greater 1 AO2

concentration gradient (at difference in the concentration 4.1.3.1

1.0 mol/dm3) between inside and outside the 4.1.3.2

cells / potato at 1.0 mol/dm3 RPA3

Total Question 5 11

How to answer it

Potato Mass Change and Osmosis

What this question tests

Planning a valid biology investigation, explaining results using osmosis and concentration gradients, and linking answers to the graph. You need to know how to make a fair test, how to calculate change in mass, and how water moves in and out of potato cells.

Overall difficulty: Low Demand

This question is mainly about practical method recall and simple osmosis explanations. Full marks come from a clear, logical method and using the correct biological vocabulary.

Question 5.1 — Plan a method that could be used to obtain the results in Figure 4

6 marks — method planning

✅ Correct answer

Measure and record the mass of each potato piece before the investigation.
Place potato pieces into different concentrations of salt solution, using at least 3 concentrations.
Leave the potato pieces in the solutions for the same amount of time.
Remove the pieces and blot them dry.
Measure and record the mass again, then calculate the change in mass.
Repeat each concentration at least 2 more times and calculate a mean change in mass.

💡 Key knowledge

Osmosis is the movement of water through a partially permeable membrane.
Potato pieces should be similar size/mass and from the same potato or same type.
Keep the temperature the same.
Use the same blotting technique each time.
Make sure the potato pieces have no skin if that is part of the method you describe.

🧠 Exam technique

To reach the top level, your method must allow the examiner to see how you would produce the graph in Figure 4.
Write steps in a logical order: measure first, treat the potato, measure again, then calculate change.
Include enough detail to show it is a fair test.
Use the phrase mean change in mass to show you are dealing with repeats properly.

❌ Common errors

Only saying “put potato in salt solution” is too vague.
Forgetting to mention repeat readings and a mean.
Not stating that the potato pieces must be the same size/mass.
Not mentioning blotting dry, which changes the mass reading unfairly.
Missing the link to different concentrations of salt solution.

📐 Calculations / data handling

Initial mass of potato piece = measure before placing in solution.
Final mass = measure after removal and blotting dry.
Change in mass = final mass − initial mass.
Do this for each repeat.
Calculate the mean change in mass for each concentration.

Good answer phrasing: “I would calculate the mean change in mass for each concentration so the graph is reliable.”

How marks are awarded: the mark scheme rewards a method that is complete, valid, and logically sequenced. Top answers mention the key practical stages and controls, not just the idea of “testing osmosis”.

Question 5.2 — Explain the result for the potato pieces in 0.6 mol/dm³ salt concentration

3 marks — explain using osmosis

✅ Correct answer

The potato pieces lost mass because water left the cells by osmosis.

This happened because the solution outside the cells was more concentrated than inside the potato cells, so water moved out through the partially permeable membrane.

💡 Key knowledge

Water moves from a region of higher water concentration to lower water concentration.
The outside salt solution at 0.6 mol/dm³ is more concentrated than the potato cell contents.
The cell membrane is partially permeable, so water can move through it.

🧠 Exam technique

Say water left the cells and then name the process: osmosis.
To get the second mark, explain the concentration difference between inside and outside.
Use “more concentrated / less concentrated” or “more dilute / less dilute”.

❌ Common errors

Saying “salt entered the potato” instead of water leaving.
Writing “water moves from high solute concentration to low solute concentration” — this is the wrong way round.
Forgetting to mention osmosis.
Referring only to “amount of water” without explaining concentration.

Examiner insight: students often lost the second mark by describing the result only as “water left the potato” without explaining why it moved out. The best answers include both the direction of movement and the reason.

Question 5.3 — Explain why the result at 1.0 mol/dm³ was different from 0.6 mol/dm³

2 marks — compare the two concentrations

✅ Correct answer

The pieces at 1.0 mol/dm³ lost more mass because more water left the potato cells.

This was because there was a steeper concentration gradient / a greater difference in concentration between the potato cells and the surrounding solution.

💡 Key knowledge

A higher salt concentration means the outside solution is even more concentrated.
This causes more osmosis out of the potato.
Greater water loss means a larger decrease in mass.

🧠 Exam technique

Compare directly with 0.6 mol/dm³: “at 1.0 mol/dm³, more water left”.
Use the phrase steeper concentration gradient for full marks.
Make sure the explanation is about osmosis, not just “more salt”.

❌ Common errors

Saying it was different because “1.0 is bigger than 0.6” without explaining why that matters.
Talking about salt moving out of the cells instead of water moving out.
Not linking the bigger concentration difference to a bigger water loss.

📐 Calculation-style thinking for graphs

Even though this is not a number-crunching question, you should still read the graph carefully:

At 0.6 mol/dm³, the change in mass is about −0.20 g.
At 1.0 mol/dm³, the change in mass is about −0.29 g.
The more negative value means a greater loss of mass.

Trap: do not say “lost less mass” when the graph value is more negative.

Quick revision summary

✅ What to remember

Use a fair test.
Measure mass before and after.
Use several salt concentrations.
Repeat and calculate a mean.
Explain mass loss by osmosis.

❌ Biggest exam traps

Missing repeats.
Not blotting dry.
Wrong direction of osmosis.
No explanation of concentration difference.

Topics

Biology · Required Practicals · B1: Cell Biology · Required Practicals

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 1 (Higher), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.