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?

Potato

1.0 M Sucrose solution

(= 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 thee.g. Effect of sucrose concentration on the

length of potato cylinderlength of potato cylinder.

Effect of sucrose concentration on the percentage

change in length of potato cylinder

- 3.04.854.84.950.6

- 1.04.954.95.0 50.4

- 5.04.754.74.850.8

4.6

5.1

5.2

- 7.04.654.751.0

+ 3.05.155.2 50.2

+ 5.05.25 5.3 50

% change in % change in

length of potato length of potato

cylinderscylinders

Average Average

ffinal length inal length

of potato of potato

cylinders cylinders

(cm)(cm)

FFinal length inal length

of potato of potato

cylinders cylinders

(cm)(cm)

OOriginal riginal

length of length of

potato potato

cylinders cylinders

(cm)(cm)

concentration concentration

of sucrose of sucrose

solutionnsolutionn / M)/ M)

Key : + increase in lengthKey : + increase in length

-- decrease in lengthdecrease 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 %Effect on sucrose concentration on the %Effect on sucrose concentration on the %Effect on sucrose concentration on the %

change in length of potato cylinderchange in length of potato cylinderchange in length of potato cylinderchange in length of potato cylinder

-8.0-8.0-8.0-8.0

-6.0-6.0-6.0-6.0

-4.0-4.0-4.0-4.0

-2.0-2.0-2.0-2.0

0.00.00.00.0

2.02.02.02.0

4.04.04.04.0

6.06.06.06.0

0000 0.20.20.20.2 0.40.40.40.4 0.60.60.60.6 0.80.80.80.8 1111 1.21.21.21.2

Concentration of sucrose solution / MConcentration of sucrose solution / MConcentration of sucrose solution / MConcentration of sucrose solution / M

% c

hange i

n l

ength

of

pota

to%

change i

n l

ength

of

pota

to%

change i

n l

ength

of

pota

to%

change i

n l

ength

of

pota

to

cyli

nders

cyli

nders

cyli

nders

cyli

nders

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)