Demonstrating Osmosis in Potato
This lab will be assessed on Conclusion & Evaluation.
Introduction
Osmosis is the movement of water through a selectively permeable membrane, from a dilute to
concentrated environment. It is a form of passive diffusion. Cells can either take in or expel water
across their plasma membranes, depending upon the conditions of their environment.
Aim
To demonstrate the process of osmosis using potato, and to determine the molarity (concentration) of
the cytoplasm of the potato.
Materials
Potato
test tubes
test tube holder
electronic balance
Paper towel
cork borer
knife/razor blade
distilled water
Sucrose solutions of the following concentrations: 0.1M, 0.2M, 0.5M, 1.0M, 2.0M
250 cm3 beaker
stoppers
filter paper
sticky labels
Measuring cylinder 50 cm3
Procedure
1. Take 6 test tubes and label them A, B, C, D, E, and F.
2. Measure 40cm3 distilled water using a measuring cylinder and pour into test tube A.
3. Measure 40cm3 0.1M sucrose solution using a measuring cylinder and pour into test tube B.
Repeat with the other concentrations of sucrose solution [0.2M into C, 0.5M into D, 1.0M into
E and 2.0M into F].
4. Using a cork borer cut out 6 cylinders of potato of equal diameter and length (approx 3-4cm).
5. Take the mass of each cylinder using the electronic balance and record it.
6. Place one cylinder of known mass into each of the 6 test tubes and stopper.
7. Leave the test tubes in a place where they won’t be disturbed until next lesson.
8. Remove the potato cylinders one by one, pat dry with a paper towel and record the mass
using an electronic balance.
Results
Record any qualitative observations from the tubes before taking the second mass reading.
Complete the results tables below. Include uncertainties in the tables due to the precision of the
apparatus used.
Raw data table showing the initial and final mass of potato cylinders placed in sucrose solutions of various concentrations.
Concentration of
sucrose solution /M
[Uncertainty unknown]
0.0
0.1
0.2
0.5
1.0
2.0
Initial mass of potato
/g
[+/- 0.1g]
Final mass of potato
/g
[+/- 0.1g]
Table showing the mean, maximum and minimum changes and percentage changes in mass of potato cylinders placed in
sucrose solution of various concentrations.
Concentration
Change in
Percentage
Maximum
Maximum
Minimum
Minimum
of sucrose
mass of potato
change in
change in
percentage
change in
percentage
solution /M
/g
mass of potato mass of potato
change in
mass of potato
change in
[Uncertainty
[+/- 0.2g]
/%
/g
mass of potato
/g
mass of potato
unknown]
/%
/%
0.0
0.1
0.2
0.5
1.0
2.0
Graph
Plot a graph of percentage change in mass of potato (y axis) against concentration of sucrose
solution (x axis).
Task

Conclusion and Evaluation (CE)


State a conclusion, with justification, based on a reasonable interpretation of the data
obtained.
Evaluate weaknesses and limitations in the procedure.
Suggest realistic improvements in respect of identified weaknesses and limitations.
c=2
p=1
n=0
Concluding
Evaluating procedure(s)
States a conclusion, with
justification, based on a
reasonable interpretation of
the data.
States a conclusion based
on a reasonable
interpretation of the data.
Evaluates weaknesses and
limitations.
States no conclusion or the
conclusion is based on an
unreasonable interpretation
of the data.
Identifies some weaknesses
and limitations, but the
evaluation is weak or
missing.
Identifies irrelevant
weaknesses and limitations.
Improving the
investigation
Suggests realistic
improvements in respect of
identified weaknesses and
limitations.
Suggests only superficial
improvements.
Suggests unrealistic
improvements.