Study Hack Lab

RP 3Biology

Osmosis

Write-up template

Name
Date
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
Class and teacher

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.

Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up

A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. 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)
Dependent (you measure)
Control (you keep the same)

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?

What will a cylinder left overnight in distilled water (0.0 mol/dm³) be like?

What will a cylinder left overnight in 1.0 mol/dm³ sucrose be like?

Risk assessment

Hazard	Harm it could cause	Control

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

Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.

4 Results

The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.

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
0.0
0.0
0.2
0.2
0.2
0.4
0.4
0.4
0.6
0.6
0.6
0.8
0.8
0.8
1.0
1.0
1.0

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
0.2
0.4
0.6
0.8
1.0

Anomalies

Ring any anomalous result. Say what probably went wrong and whether you repeated it.

5 Graph

Percentage change in mass against concentration · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.

6 Analysis

Percentage change in mass
percentage change in mass = (final mass − initial mass) ÷ initial mass × 100
Answer
Mean percentage change
mean = sum of the results ÷ number of results
Answer
No change in mass
Read the concentration where your curve crosses the x-axis (0 % change in mass).
Answer
Water across the membrane
Answer

7 Conclusion and evaluation

Conclusion

Conclusion: what do your results show? Use your own numbers.

Sources of error

For each, say whether it is systematic or random, and how it affected your results.

Blotting the cylinders differently each time

Not blotting the cylinders before the final weighing

Differences between cylinders (and between potatoes)

Skin left on some cylinders

Water evaporating from open tubes

A balance not zeroed

Too short a time in the solutions

Only six concentrations, 0.2 mol/dm³ apart

Improvement

How could you improve the method? Say why it would help.

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