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Specimen lab book: Osmosis
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Study Hack Lab
RP 3 · Biology
Osmosis
Lab book
Name
Specimen
Date
2 November 2026
Course
GCSE Biology
Board and specification
AQA GCSE Biology (8461), 4.1.3.2AQA GCSE Combined Science: Trilogy (8464), 4.1.3.2Apparatus and techniques: AT 1, AT 3, AT 5
Run
C29HO
Status
Finished: every stage done
Exam questions
30/30 marks
Aim
Investigate the effect of the concentration of sucrose solution on the mass of potato cylinders, and use it to estimate the concentration inside the potato cells.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
Exam questions on your data
Simulated data produced by Study Hack Lab from the student's own run (seed 20261004). Every reading, value and mark here is from that run; nothing has been retyped. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
Osmosis is the diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane. Potato cells in a solution more dilute than their contents take in water and gain mass; in a more concentrated solution they lose water and mass. Where the curve crosses zero there is no net movement: that concentration matches the inside of the cells.
percentage change in mass = (final mass − initial mass) ÷ initial mass × 100
Variables
Independent (you change)
Concentration of sucrose (sugar) solution in mol/dm³
Dependent (you measure)
Percentage change in mass of the potato cylinder in %
Control (you keep the same)
Same potato; Size of each cylinder; Volume of solution; Time in the solution; Temperature; Blotting
Prediction
As the sucrose concentration goes up from 0.0 to 1.0 mol/dm³, what will happen to the percentage change in mass of the potato?
It starts positive (a gain), falls as the concentration rises, crosses zero and becomes negative (a loss).Right first time
Your mean went from +15.6 % in distilled water to −28.2 % in 1.0 mol/dm³. In dilute solutions water moves into the cells by osmosis, so they gain mass. In concentrated solutions water moves out, so they lose mass. At one concentration there is no net movement of water: the curve crosses zero there.
What will a cylinder left overnight in distilled water (0.0 mol/dm³) be like?
Heavier, slightly bigger and firm.Right first time
Your cylinders in distilled water changed by +15.6 % on average. Distilled water is more dilute than the solution inside the cells, so water moves in by osmosis through the partially permeable cell membranes. The cells swell and push against their cell walls, so the cylinder is firm (turgid).
What will a cylinder left overnight in 1.0 mol/dm³ sucrose be like?
Lighter, smaller and soft enough to bend.Right first time
Your cylinders in 1.0 mol/dm³ changed by −28.2 % on average. The sucrose solution is more concentrated than the solution inside the cells, so water moves out of the cells by osmosis. The cells shrink and stop pushing on their walls, so the cylinder goes soft and bendy (flaccid).
Risk assessment
Hazard
Harm it could cause
Control you chose
Sharp cork borer and scalpel
Cuts to the hand if the borer or blade slips
Bore and cut on a white tile, pushing down onto the tile and away from your fingers; carry the scalpel blade down.Right first time
Water or solution near the electric balance
Electric shock, and damage to the balance
Blot each cylinder before it goes on the pan, wipe up drips at once and keep the tubes away from the balance.Right first time
Spilt sugar solution
Slipping on a wet floor; a sticky bench
Keep the tubes in their racks and wipe up spills straight away.Right first time
Glass boiling tubes
Cuts if a tube breaks
Keep tubes in a rack, not loose on the bench; report any breakage and do not pick up broken glass by hand.Right first time
2 Apparatus
✓Potato The plant tissue.
✓Cork borer and rod Cuts cylinders of the same diameter.
✓Scalpel Trims the cylinders and cuts off the skin.
✓White tile A safe surface to bore and cut on.
✓30 cm ruler (resolution 1 mm) Measures each cylinder to 30 mm.
✓Sucrose solutions: 0.0 (distilled water), 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm³ The independent variable.
✓10 cm³ measuring cylinder (resolution 0.2 cm³) Measures 10 cm³ of solution into each tube.
✓18 boiling tubes in racks, with labels One tube for each cylinder.
✓Cling film Covers the tubes so water does not evaporate.
✓Forceps Lift the cylinders out of the tubes.
✓Paper towels Blot the cylinders dry before weighing.
✓Top-pan balance (resolution 0.01 g) Weighs each cylinder.
3 Method: your choices
Which version are you doing?: AQA required practical 3: osmosis in potatoWeigh each cylinder before and after: percentage change in mass.
Zero (tare) the balance: DoneA balance that does not read zero when it is empty adds the same error to every mass.
Choose which potato to use: Bore every cylinder from one large potatoEvery cylinder has the same concentration inside its cells, so repeats agree (within about 1.5–3 percentage points).
Cut the skin off the ends: DonePotato skin lets water through much more slowly than the flesh, so a piece of skin slows the water moving in or out.
Trim to the same length: Measure 30 mm with the ruler for every cylinderThe starting masses agree to within a few per cent.
Choose how long to leave the cylinders in the solutions: Leave them overnight (about 20 hours)The cylinders get close to their final mass: big, clear changes (about +17 % in water, −25 % in 1.0 mol/dm³).
Blotting before you weigh: Roll each cylinder gently once on the paper towel, the same way every timeOnly a trace of liquid (under 0.03 g) is left, about the same on every cylinder.
Cover the tubes: DoneWater evaporates from an open tube, which makes the solution more concentrated.
4 Results
36 of 36 readings taken.
Mass of each potato cylinder · Three cylinders (A, B, C) in each solution. Blot and weigh before, then again after the wait.
Concentration of sucrose solution in mol/dm³
Cylinder
Initial mass in g
Final mass in g
Change in mass in g
Percentage change in mass in %
0.0
A
2.03
2.35
0.32
15.8
0.0
B
2.07
2.42
0.35
16.9
0.0
C
2.06
2.35
0.29
14.1
0.2
A
2.04
2.17
0.13
6.4
0.2
B
2.09
2.22
0.13
6.2
0.2
C
2.01
2.18
0.17
8.5
0.4
A
2.01
1.80
-0.21
-10.4
0.4
B
1.98
1.77
-0.21
-10.6
0.4
C
2.03
1.78
-0.25
-12.3
0.6
A
2.12
1.59
-0.53
-25.0
0.6
B
1.99
1.50
-0.49
-24.6
0.6
C
2.07
1.59
-0.48
-23.2
0.8
A
2.12
1.52
-0.60
-28.3
0.8
B
2.07
1.52
-0.55
-26.6
0.8
C
1.97
1.39
-0.58
-29.4
1.0
A
2.12
1.56
-0.56
-26.4
1.0
B
2.11
1.48
-0.63
-29.9
1.0
C
2.04
1.46
-0.58
-28.4
Mean percentage change in mass · Leave out any anomalous cylinder.
Concentration of sucrose solution in mol/dm³
Mean percentage change in mass in %
0.0
15.6
0.2
7.0
0.4
-11.1
0.6
-24.3
0.8
-28.1
1.0
-28.2
Anomaly: No anomalous reading.
5 Graph
Percentage change in mass against concentration
6 Analysis
Percentage change in mass
percentage change in mass = (final mass − initial mass) ÷ initial mass × 100
Calculate the percentage change in mass of cylinder A in 1.0 mol/dm³ sucrose. A loss in mass is a negative change.
-26.4 %Right first time
Mean percentage change
mean = sum of the results ÷ number of results
Calculate the mean percentage change in mass in 0.4 mol/dm³. Give your answer to 1 decimal place.
-11.1 %Right first time
Shape of the graph
Describe the shape of your curve.
Positive at low concentrations, falling as the concentration rises, crossing zero and levelling off below zero.Right first time
No change in mass
Read the concentration where your curve crosses the x-axis (0 % change in mass).
Use your curve. What concentration of sucrose solution would give no change in mass? Read it to 2 decimal places.
0.28 mol/dm³Right first time
What the crossing point means
At about 0.28 mol/dm³ your potato would neither gain nor lose mass. What does this tell you?
The solution inside the potato cells has about the same concentration as this sucrose solution, so there is no net movement of water.Right first time
Water across the membrane
3 of 3 right first timeRight first time
Why percentage change?
The table shows your three cylinders in distilled water. Why do we compare percentage changes rather than changes in grams?
The cylinders started with different masses, so the same change in grams means more for a small cylinder.Right first time
7 Conclusion and evaluation
Quantity
Your value
Accepted value
Concentration with no change in mass (your potato, careful technique)
0.28 mol/dm³
0.29 mol/dm³
Mean percentage change in distilled water (your potato, careful technique, overnight)
16 %
16 %
Conclusion
What do your results show? Pick one statement that your data support.
Below about 0.28 mol/dm³ the potato gained mass, and above it the potato lost mass.Right first time
Water moves into the cells from solutions more dilute than the cell sap and out into solutions more concentrated than it. The cell wall limits how much the cells can swell, and the loss levels off once the cells have lost most of the water they can.
Sources of error
Blotting the cylinders differently each time: systematic or random?
RandomRight first time
Different amounts of liquid are left on each cylinder (and squeezing presses water out), so repeats scatter.
Not blotting the cylinders before the final weighing: systematic or random?
SystematicRight first time
Solution on the surface makes every final mass too high: gains too big, losses too small, and the crossing point too high.
Differences between cylinders (and between potatoes): systematic or random?
RandomRight first time
Each piece of tissue is slightly different, so repeats never agree exactly; cylinders from different potatoes disagree more.
Skin left on some cylinders: systematic or random?
RandomRight first time
Skin lets water through slowly, so those cylinders change less and look out of line.
Water evaporating from open tubes: systematic or random?
SystematicRight first time
The solutions get slightly more concentrated, so the crossing point comes out slightly low.
A balance not zeroed: systematic or random?
SystematicRight first time
Every mass is out by the same amount; the percentage changes are slightly wrong.
Too short a time in the solutions: systematic or random?
SystematicRight first time
The tissue has not finished changing, so every change is too small and harder to measure.
Only six concentrations, 0.2 mol/dm³ apart: systematic or random?
RandomRight first time
The crossing point is read between two points far apart, so the curve there is uncertain.
Improvement
Which change would most improve your results?
Cut every cylinder from the same potato and take a mean of three or more repeats.Right first time
Repeatable or reproducible
A student’s three cylinders in 0.6 mol/dm³ changed by −21.0 %, −22.4 % and −20.7 %. This shows their results are…
RepeatableRight first time
Repeatable: the same person, method and equipment give similar results.
Another group used their own sucrose solutions, balance and a potato from the same bag, and also found their curve crossed zero near 0.3 mol/dm³. This shows the results are…
ReproducibleRight first time
Reproducible: a different person, method or equipment gives similar results.
8 Make safe and clear up
Put the potato cylinders and the rest of the potato in the bin
Pour the solutions down the sink and rinse the boiling tubes
Wipe the balance pan and the bench dry
Return the cork borer and scalpel (blade down) to the tray, and wash your hands
9 Exam questions on your data
On your own readings, self-marked against the mark scheme, with error carried forward where it applies. Total 30/30.
01.1[1 mark]
A student investigated the effect of sucrose solution on the mass of potato. They cut cylinders of potato with a cork borer, weighed each one, left them in different concentrations of sucrose solution overnight, then blotted and reweighed them.
What was the independent variable in this investigation?
Your answer
The concentration of the sucrose solution
1/1 self-marked
Concentration of the sucrose (sugar) solution
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The concentration of the sucrose solution.
01.2[1 mark]
Give one variable the student should control.
Your answer
the time the cylinders are left in the solution
1/1 self-marked
Any one of: same potato; size (length, diameter, mass or surface area) of the cylinders; volume of solution; time in the solution; temperature; the same blotting
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The time the cylinders are left in the solution (or the volume of solution, the temperature, the size of the cylinders, the same potato).
01.3[2 marks]
The student used a cork borer and a scalpel to cut the potato.
Give one harm the cork borer or scalpel could cause, and one way to reduce the risk.
Your answer
The scalpel could slip and cut your finger. Cut on a white tile, pushing the blade down away from your fingers.
2/2 self-marked
Harm: a cut (to the hand or fingers) (ignore "sharp" on its own)
Control: cut or bore onto a white tile (a cutting board) / push or cut away from your hand (downwards) / carry the scalpel blade down / keep fingers out of the way
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The blade could slip and cut your hand. Bore and cut on a white tile, pushing down and away from your fingers.
01.4[1 mark]
Before each weighing, the student rolled the cylinder on a paper towel to blot it dry.
Suggest why the student blotted the cylinders dry before weighing them.
Your answer
So that only the mass of the potato is measured. Solution left on the outside would make the mass higher.
1/1 self-marked
So only the mass of the potato is measured / liquid left on would make the mass higher (allow: to remove excess water) (do not accept: the mass would be lower)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: So that only the mass of the potato is measured: solution left on the surface would make the mass too high.
01.5[1 mark]
Your balance had a resolution of 0.01 g. Your smallest change in mass was 0.13 g (cylinder A in 0.2 mol/dm³).
Suggest why a balance with a resolution of 0.1 g would not be suitable for this investigation.
Your answer
A balance reading to 0.1 g is less precise, so it could not show the small differences in mass between the cylinders.
1/1 self-marked
It could not detect (measure) the small differences in mass / it is less precise (it reads to only 0.1 g)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: A balance that reads to 0.1 g is less precise: it would round a change such as 0.13 g to the nearest 0.1 g, so it could not show the small differences between the cylinders.
02.1[2 marks]
Table 1 shows your results for cylinder B, in distilled water.
Table 1
Initial mass in g
Final mass in g
2.07
2.42
Calculate the percentage change in mass of the cylinder.
Your answer
16.9
Working: change in mass = 2.42 − 2.07 = 0.35 g
percentage change = 0.35 ÷ 2.07 × 100
= 16.9 %
2/2
0.35 ÷ 2.07 × 100 (change in mass ÷ initial mass × 100)
16.9 (%)
Full marks. Clear and precise.
Model answer: change in mass = 2.42 − 2.07 = 0.35 g
percentage change = 0.35 ÷ 2.07 × 100
= 16.9 %
02.2[1 mark]
Another student put three potato cylinders in 0.8 mol/dm³ sucrose solution. Table 2 shows their results.
Which cylinder gave an anomalous result?
Select one row.
Table 2
Cylinder
Initial mass in g
Final mass in g
Percentage change in mass in %
A
2.65
2.07
-21.9
B
2.57
2.03
-21.0
C
2.60
2.37
-8.8
Your answer
cylinder C
1/1
Cylinder C: it lost much less mass than the other two, which agree with each other
Full marks. Well done. Cylinder C (-8.8 %) is far from the other two, which agree with each other.
Model answer: Cylinder C. Its percentage change is -8.8 %: it lost much less mass than the other two, which agree with each other.
02.3[2 marks]
Look again at Table 2.
Calculate the mean percentage change in mass.
Do not use the anomalous result. Give your answer to 1 decimal place.
Your answer
-21.5
Working: mean = (-21.9 + -21.0) ÷ 2
= -21.5 %
2/2
(-21.9 + -21.0) ÷ 2 (the anomaly left out)
-21.5 (%)
Full marks. Clear and precise.
Model answer: mean = (-21.9 + -21.0) ÷ 2
= -21.5 %
02.4[1 mark]
Figure 1 shows your mean percentage change in mass for each concentration, with a curve of best fit.
Figure 1
Determine the concentration of sucrose solution that would cause no change in the mass of the potato.
Your answer
0.28
1/1
0.28 mol/dm³ (where the curve crosses the x-axis; ± half a small square)
Full marks. Your answer meets all the points for this question.
Model answer: About 0.28 mol/dm³, where the curve crosses the x-axis (no change in mass).
02.5[1 mark]
Your curve crosses the x-axis between 0.2 and 0.4 mol/dm³.
Suggest one way to find the concentration with no change in mass more accurately.
Your answer
Use more concentrations between 0.2 and 0.4 mol/dm³, at smaller intervals.
1/1 self-marked
Use more concentrations between 0.2 and 0.4 mol/dm³ (smaller intervals near the crossing point); allow more repeats at each concentration
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: Repeat with more concentrations between 0.2 and 0.4 mol/dm³ (for example every 0.05 mol/dm³), so the curve near the crossing point is better defined.
03.1[3 marks]
The cylinders in distilled water (0.0 mol/dm³) gained mass.
Explain why the cylinders in distilled water gained mass.
Your answer
Water moved into the cells by osmosis. It moved from a dilute solution outside to a more concentrated solution inside the cells, through a partially permeable membrane.
3/3 self-marked
Water entered (moved into) the cells by osmosis
From a dilute solution (outside) to a more concentrated solution (inside the cells); allow: from a high water concentration to a low water concentration; allow: water potential
Through a partially permeable membrane
Self-marked: 3 of 3 marks. This is your own judgement against the mark scheme.
Model answer: Water moved into the potato cells by osmosis, from the dilute solution outside (distilled water) to the more concentrated solution inside the cells, through the partially permeable cell membranes.
03.2[2 marks]
The cylinders in 1.0 mol/dm³ sucrose solution lost mass.
Explain why the cylinders in 1.0 mol/dm³ sucrose solution lost mass.
Your answer
Water moved out of the cells by osmosis because the solution inside the cells is more dilute than the sucrose solution outside.
2/2 self-marked
Water moved out of the cells (potato) by osmosis
The solution inside the cells is less concentrated (more dilute) than the solution outside; allow: from a dilute to a more concentrated solution; allow: high to low water concentration
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: Water moved out of the potato cells by osmosis, because the solution inside the cells was less concentrated (more dilute) than the 1.0 mol/dm³ sucrose solution outside.
03.3[2 marks]
Your mean percentage change in mass was -11.1 % in 0.4 mol/dm³ and -28.2 % in 1.0 mol/dm³.
Explain why more mass was lost in the 1.0 mol/dm³ solution than in the 0.4 mol/dm³ solution.
Your answer
More water left the cells because there is a steeper concentration gradient between the cells and the solution.
2/2 self-marked
More water left the cells (potato)
Because there is a steeper concentration gradient (a greater difference in concentration between the inside and outside of the cells)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: More water left the cells by osmosis, because there was a steeper concentration gradient: a greater difference between the concentration inside the cells and the 1.0 mol/dm³ solution.
04.1[2 marks]
Another student did not blot the cylinders before the final weighing. They used their graph to find the concentration with no change in mass.
Explain how not blotting would affect the concentration they found.
Your answer
The final masses would be too high because of the solution on the surface, so the curve crosses the x-axis at a higher concentration. The concentration found would be too high.
2/2 self-marked
Solution on the surface makes the final masses too high (the percentage changes too high: gains bigger, losses smaller)
So the concentration found (the crossing point) is too high
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: Solution left on the surface makes every final mass too high, so the percentage changes are too high and the curve is moved up. It crosses the x-axis at a higher concentration, so the concentration found is too high.
04.2[1 mark]
Why did the student calculate the percentage change in mass, not just the change in mass?
Tick (✓) one box.
✓ The cylinders had different starting masses. (your choice)
A percentage is always more accurate than a mass.
A change in mass cannot be negative.
The balance only reads to 0.01 g.
Your answer
The cylinders had different starting masses.
1/1
The cylinders had different starting masses.
Full marks. That is exactly what the mark scheme is looking for.
Model answer: The cylinders had different starting masses, so percentage change lets them be compared fairly.
04.3[1 mark]
The student put three cylinders in each concentration.
Give one reason for using three cylinders at each concentration.
Your answer
So that a mean can be calculated, which reduces the effect of random errors.
1/1 self-marked
To calculate a mean (which reduces the effect of random errors); or to identify anomalies; or to check the results are repeatable
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: So a mean can be calculated, which reduces the effect of random errors (or so an anomaly can be identified).
05[6 marks]
A student wants to investigate the effect of different concentrations of sugar solution on the mass of potato.
The student has: a potato, a cork borer, a scalpel, a ruler, a white tile, a balance, boiling tubes, paper towels and sugar solutions of different concentrations.
Plan an investigation to find the effect of sugar solution concentration on the mass of potato.
Your answer
1. Use a cork borer to cut cylinders from the same potato and cut them all to the same length (3 cm) on a tile, with the skin removed.
2. Blot each cylinder dry and record its mass on a balance.
3. Put each cylinder in a boiling tube with 10 cm³ of sugar solution, using at least five different concentrations (0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm³).
4. Leave them for the same time (overnight) at the same temperature.
5. Remove each cylinder, blot it dry in the same way and reweigh it.
6. Calculate the percentage change in mass for each cylinder.
7. Repeat each concentration two more times and calculate the mean percentage change.
6/6 self-marked
Cut potato pieces of the same size (cork borer, same length) from the same potato
(Measure and) record the mass of each potato piece
Place the potato pieces into different concentrations of sugar solution
Use a range of at least five different concentrations
Remove the pieces and blot them dry
Reweigh and calculate the change (percentage change) in mass
Repeat each concentration (2 more times) and calculate the mean
Leave them for the same time (at least 10 minutes; overnight) at the same temperature
Same volume of solution; same blotting technique
Self-marked: Level 3, 6 of 6 marks. You ticked 9 of 9 indicative points. This is your own judgement against the mark scheme.
Model answer: 1. Use a cork borer to cut cylinders from the same potato and cut them all to the same length (3 cm) on a tile, with the skin removed.
2. Blot each cylinder dry and record its mass on a balance.
3. Put each cylinder in a boiling tube with 10 cm³ of sugar solution, using at least five different concentrations (0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm³).
4. Leave them for the same time (overnight) at the same temperature.
5. Remove each cylinder, blot it dry in the same way and reweigh it.
6. Calculate the percentage change in mass for each cylinder.
7. Repeat each concentration two more times and calculate the mean percentage change.
Unseen data: the same skills, new apparatus
01[2 marks]
A student weighed a disc of beetroot, left it in a salt solution for a day, blotted it and weighed it again. Its mass went from 4.43 g to 4.73 g.
Calculate the percentage change in mass of the disc. Give your answer to 1 decimal place.
A student put cylinders of sweet potato into sucrose solutions and recorded the mean percentage change in mass.
Table 2
Concentration of sucrose in mol/dm³
Mean percentage change in mass in %
0.0
+14.6
0.2
+11.0
0.4
+2.0
0.6
−11.1
0.8
−18.1
Estimate the concentration of sucrose that would give no change in mass. Assume the change in mass falls in a straight line between the two concentrations either side of zero.