School-based assessment
Practical related tasks
Osmosis in Living Tissue
To determine the water potential of potato
tissue.
Curriculum Link
C1 Water for Living
Movement of water in and out of cells by osmosis
Background
How can we determine the water potential of
potato tissues?
1.0 M Sucrose solution
Potato
(= 342 g sucrose in 1 L of solution)
Apparatus and Chemicals
Procedure (1)
A series of sucrose solution of
different concentration.
Procedure (2)
Cut potato cylinders into length of 5 cm.
Blot dry the potato cylinders and put them into a Petri dish.
Procedure (3)
Immerse 2 potato cylinders in
each tube that contains different
concentration of sucrose
solution.
After 40 mins, take out the
potato cylinders, blot dry and
measure the length of the potato
cylinders.
Result Table
1. Tabulated result :
Notice the position of independent variable,
dependent variable in the table.
Units and suitable conversions should be shown
clearly and correctly
Title of the table should be written correctly according
to the aim of the experiment.
e.g. Effect of sucrose concentration on the
length of potato cylinder.
Effect of sucrose concentration on the percentage
change in length of potato cylinder
Original
concentration length of Final length
of potato
of sucrose
potato
cylinders
solutionn / M) cylinders
(cm)
(cm)
Average
final length
of potato
cylinders
(cm)
% change in
length of potato
cylinders
0
5
5.3
5.2
5.25
+ 5.0
0.2
5
5.2
5.1
5.15
+ 3.0
0.4
5
5.0
4.9
4.95
- 1.0
0.6
5
4.9
4.8
4.85
- 3.0
0.8
5
4.8
4.7
4.75
- 5.0
1.0
5
4.7
4.6
4.65
- 7.0
Key : + increase in length
- decrease in length
Graph
Notice the choice of axes
x-axis – for independent variable (unit should be stated)
y-axis – for dependent variable (unit should be stated)
Notice the rule of using short straight lines to join
the points or the smooth curve to join the points
Title of graph should be added correctly and related
to the aim of the experiment
e.g. Effect of sucrose solution on the % change in length of potato
cylinders
Effect on sucrose concentration on the %
change in length of potato cylinder
% change in length of potato
cylinders
6.0
4.0
2.0
0.0
0
0.2
0.4
0.6
0.8
1
-2.0
-4.0
-6.0
-8.0
Concentration of sucrose solution / M
1.2
Laboratory Report
Title
Aims
Theory/Background (optional)
Apparatus
Design of experiment
Procedure
Precautions and safety measures
Results (including data and observations)
Discussions (including possible sources of errors and
improvements to be made)
Conclusion
Questions for further thought (optional)
Assessment Criteria – Area A (Max:10)
Assessment criteria – Area B (Max:10)
Assessment Criteria – Area B (Cont’d)