F4 EXP04: Practical 4.1

Practical 4.1

Demonstration of the break-down action

of enzymes (Book 1A P. 5)

Objective:       To study the break-down action of catalase on hydrogen peroxide

Biological principle and experiment design:                                                                          (6 marks)

Hydrogen peroxide is a toxic by-product of some metabolic reactions. Many plant and animal tissues contain

an enzyme called catalase (1) which catalyses the breakdown of hydrogen peroxide into oxygen and water.

                                                                Catalase

Hydrogen peroxide(1)                             Oxygen (1) + water (1)

To demonstrate the catalytic activity of catalase in cells, living tissues such as potato are placed in hydrogen peroxide. The reaction is observed and the gas released is collected for identification. If the gas is oxygen, it

should be able to relight a glowing splint (1).

We predict that the living tissues placed in hydrogen peroxide will give out oxygen which can relight

a glowing splint (1)

Results:                                                                                                                                  (6 marks)

Table showing the test results of the collected gases from different samples by glowing splints.

Sample	Observation
L: Liver + Hydrogen peroxide solution	Glowing splint is relighted
P: Potato + Hydrogen peroxide solution	Glowing splint is relighted
C: Hydrogen peroxide solution	No observable change / The glowing splint goes out
l: Liver + distilled water	No observable change / The glowing splint goes out
p: Potato + distilled water	No observable change / The glowing splint goes out
c: Distilled water	No observable change / The glowing splint goes out

Result Interpretation:                                                                                                           (4 marks)

1          Describe and explain for the result of the samples L and P.

The glowing splints of samples L and P relight. (1)

This is because the tissues contain catalase (1)

which catalyzes the breakdown of hydrogen peroxide (1)

to release water and oxygen (1).

Discussion:                                                                                                                            (10 marks)

2     Explain the purpose of setting up the sample C. (2)

Sample C acts as a control set-up (1)

which is used to ensure that the release of oxygen is not due to hydrogen peroxide itself (1).

3     Explain the purpose of repeating the experiment with distilled water instead of hydrogen peroxide. (2)

The sample with distilled water works as a control (1)

which is used to ensure the release of oxygen is only due to the reaction between the living tissues and hydrogen peroxide (1).

4     This experiment cannot directly show that the breakdown of hydrogen peroxide is due to the action of enzyme (catalase).

(a)   What is shown by the result of this experiment? (1)

The living tissues may contain a substance which reacts with hydrogen peroxide to release oxygen.

(b)   What further experiment should be done to ensure that the reaction is catalyzed by enzyme? (2)

The experiment can be repeated with the use of boiled tissues instead of the fresh tissues (1).

If there is no release of oxygen / no catalytic action, we can ensure that the breakdown of hydrogen peroxide to oxygen is due to the action of enzyme/catalase (1)

5      Explain whether this experiment is a fair test or not. (3)

This experiment is a fair test (1).

It because there is only one independent variable (i.e. the samples in test tubes) (1).

Other variables (e.g. the volume and the concentration of hydrogen peroxide, the total volume of the samples and the reaction temperature etc.) (1) are kept as constant (1).

Conclusion:                                                                                                                            (2 marks)

Potato and liver tissues can cause the breakdown of hydrogen peroxide to release oxygen

/ Both tissues contain substances which can cause the breakdown of hydrogen peroxide to release oxygen (1).

The breakdown action may be due to the presence of enzyme in the tissues (1). This needs further investigation to confirm.

Challenging question                                                            (2 mark)

Someone suggest that the experimental result can be improved by using the tissue extracts after grinding with distilled water instead of using the whole tissues. Do you agree? Why?

Grinding of the tissues with distilled water can increase the contact area of the tissues with the

substrates / can effectively release the enzymes inside cells (1)

This can speed up the breakdown action of the enzyme (1).