By 
Safety. Although the dangers in the following experiments are negligible, it is recommended that you consult the latest edition of ‘Safeguards in the School Laboratory’ published by the Association for Science Education (ase.org.uk) before embarking on any experiment.
Scheme. Catalase is an enzyme found in the cells of many living organisms. Some of the energy release reactions in the cell produce hydrogen peroxide as the end product. This compound, which is toxic to the cell, is divided into water and oxygen by the action of catalase. 2H2O2 = 2H2O + O2
Liver and yeast samples are poured into hydrogen peroxide. Oxygen is generated and the student is asked to extend the experiment to try to decide if 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 reignites an incandescent splint.
Preparation and previous materials – by group
20 volumes of hydrogen peroxide 50 cm3
splint
liver, about 1 cubic cm
distilled water 20 cm3
dry yeast about 1 g
clean sand about 1 g
activated charcoal granules, about 1 g
Device – per group
rack for test tubes and 4 test tubes
forceps or finder to push the liver into a test tube
4 labels or spirit marker
funnel filter
Bunsen lighter
filter paper
test tube holder
mortar and pestle
To experience
The following investigation is a fairly critical examination of plant and animal tissues to see if
contain catalase.
(a) Label three test tubes 1-3.
(b) For approximately 20mm (depth) of hydrogen peroxide in 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 dry yeast.
(e) Insert an incandescent ferrule into tubes 1 and 2, bringing it closer to the surface of the liquid or towards the top of the foam.
1 Describe what you saw happen and the effect on the incandescent splint.
2 How do you interpret these observations?
3 Is there any evidence from this experiment so far that indicates whether the gas is from hydrogen peroxide or from the solid?
4 Is there any evidence at this stage that an enzyme is involved in gas production in this reaction?
(f) In tube 3 put some charcoal granules and observe the reaction.
5 Could charcoal be an enzyme? Explain your answer.
6 Assuming (i) that the gas in (f) is the same as before and (ii) that the charcoal is almost pure carbon, does the result with charcoal help you decide the source of the gas in this and the experiments? previous? ?
(g) Suppose the hypothesis is advanced that there is an enzyme in the liver and yeast that breaks down hydrogen peroxide into oxygen and water; design and conduct a control experiment to test this hypothesis.
7 Record (i) the experiment, (ii) the reasons that led you to carry it out, (iii) the
results and (iv) its conclusions.
(h) Wash the test tubes. Design and conduct an experiment to see if the putative enzyme from plant and animal material can be extracted and still retain its properties. The experiment must include a control.
8 Briefly describe your procedure, your results, and your conclusions.
9 Assuming liver and yeast each contain an enzyme that breaks down hydrogen peroxide, is there any evidence to show that it is the same enzyme? What would one have to do to find out for sure?
Discussion – Answers
1 Effervescence should be observed in all cases, but it is more vigorous with yeast than with liver. The incandescent ferrule should reignite.
2 Oxygen is being produced.
3 There is no evidence to indicate whether the liquid or the solid is giving off the gas. If students think that a solid is unlikely to emit a gas, they might recall marble and hydrochloric acid where it is the solid that produces carbon dioxide. However, both yeast and liver seem less likely to emit oxygen when treated with hydrogen peroxide than hydrogen peroxide when treated with various substances.
4 So far, there is no evidence that an enzyme is involved.
5 A gas will come out, but not fast enough to relight an incandescent ferrule. Coal could not
be an enzyme because (a) it is an element and (b) it has been produced by very high temperatures that would destroy the enzymes.
6 Charcoal, as an element, could not be emitting oxygen. The gas must come from
hydrogen peroxide.
7 (i) The experiment should include boiling the tissues and then placing them in hydrogen peroxide.
(ii) If there is an enzyme involved,
(iii) gas will not be produced.
8 The student must grind the samples with a little sand and distilled water, filter and test the filtrate with hydrogen peroxide. Oxygen will develop with vigor proportional to that observed when the original substances were tested.
The student must boil half of each extract and show that it loses its activity.
9 There does not appear to be a rationale why yeast and liver should not have different enzymes that catalyze the breakdown of hydrogen peroxide. To be certain on this point, one would have to extract the enzymes and determine their chemical composition.