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Biology Experiments for Teachers – Enzymes: Catalase

Security. Although the risks in the following experiments are negligible, you are advised to consult the latest version of ‘Safeguarding in the School Laboratory’ published by The Association for Science Education (ase.org.uk) before starting any experiment.

Contour. Catalase is an enzyme that occurs in the cells of many living organisms. Some of the energy-releasing reactions in the cell produce hydrogen peroxide as an end product. This compound, which is toxic to the cell, is broken down into water and oxygen by the action of catalase. 2H2O2 = 2H2O + O2

Liver and yeast samples are dropped into hydrogen peroxide. Oxygen is evolved and the student is asked to extend the experiment to try to decide whether an enzyme in the tissues is responsible. The experiments and questions last about an hour.

Prior knowledge. The existence of inorganic catalysts. enzymes denatured by boiling. oxygen flashes a glowing splint.

Preparation and materials in advance – per group

20 volumes of hydrogen peroxide 50 cm3

splints

liver, about 1 cubic cm

distilled water 20 cm3

dry yeast about 1 g

clean sand about 1 g

activated carbon granules, about 1 g

Device – per group

test tube rack and 4 test tubes

forceps or seeker to push the liver into the test tube

4 alcohol labels or indicator

filtering funnel

Bunsen burner

filter paper

test tube holder

mortar and pestle

Experiment

The following investigation is a fairly critical examination of plant and animal tissues to determine whether

they contain catalase.

(a) Label three test tubes 1-3.

(b) Pour about 20 mm (deep) of hydrogen peroxide into each tube.

(c) Cut the liver into 3 pieces.

(d) To tube 1 add a small piece of liver and to tube 2 add a pinch of dried yeast.

(e) Place a shiny splint in tubes 1 and 2, bringing it close to the surface of the liquid or to the top of the foam.

1 Describe what you saw happen and the effect on the glowing splint.

2 How do you interpret these observations?

3 Is there any evidence from this experiment so far to show whether the gas is coming from the hydrogen peroxide or the solid?

4 Is there evidence at this stage that an enzyme is involved in the production of gas in this reaction?

(f) In tube 3 place some grains of carbon and observe the reaction.

5 Could carbon be an enzyme? Explain your answer.

6 Assuming (i) that the gas in (f) is the same as before and (ii) that the carbon is almost pure carbon, does the result with carbon help you decide the source of the gas in this and the previous experiments?

(g) Suppose the hypothesis is advanced that there is an enzyme in liver and yeast which decomposes hydrogen peroxide into oxygen and water. design and perform a control experiment to test this hypothesis.

7 Record (i) the experiment, (ii) your reasons for carrying it out, (iii) the observed

results and (iv) your conclusions.

(h) Rinse the test tubes. Design and carry out an experiment to see if the hypothesized enzyme in the plant and animal material can be extracted and retain its properties. The experiment must include control.

8 Briefly describe your process, results and conclusions.

9 Assuming that liver and yeast contain an enzyme that breaks down hydrogen peroxide, is there any evidence that it is the same enzyme? What would have to be done to know for sure?

Discussion – answers

1 Effervescence should be observed in all cases but is more pronounced with yeast than with liver. The glowing splint should light up again.

2 Oxygen is produced.

3 There is no evidence to indicate whether the liquid or the solid gives the gas. If students think that a solid is unlikely to give off a gas, they might recall marble and hydrochloric acid in which the solid produces carbon dioxide. However, it seems less likely that yeast and liver give off oxygen when treated with hydrogen peroxide than that hydrogen peroxide should give oxygen when treated with various substances.

4 So far, there is no evidence of enzyme involvement.

5 A gas will come off but not fast enough to re-ignite a glowing splint. coal could not

to be an enzyme because (a) it is an element and (b) it has been produced by very high temperatures that would destroy enzymes.

6 Coal, as an element, could not emit oxygen. The gas must come from the

hydrogen peroxide.

7 (i) The experiment should involve boiling the tissues and then placing them in hydrogen peroxide.

(ii) If an enzyme is involved,

(iii) no gas will be produced.

8 The student should grind the samples with some sand and distilled water, filter and test the filtrate with hydrogen peroxide. Oxygen will evolve with a valence commensurate with that observed when testing the original substances.

The student must boil half of each extract and show that it loses its activity.

9 There appears to be no fundamental reason why yeast and liver should not have different enzymes that catalyze the decomposition of hydrogen peroxide. To be certain at this point, the enzymes should be extracted and their chemical composition determined.

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