Found Mixed-Results In How Teachers Should Respond To Scientific Questions Biology Experiments for Teachers – Enzymes: Catalase

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Biology Experiments for Teachers – Enzymes: Catalase

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

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

Liver and yeast samples are soaked in hydrogen peroxide. Oxygen is evolved and the student is asked to extend the experiment to try and decide if an enzyme in the tissues is responsible. The experiments and questions will take about an hour.

First knowledge. The existence of inorganic catalysts; enzymes denatured by boiling; the oxygen illuminates a glowing splint.

Advance preparation and materials – per group

20 volume hydrogen peroxide 50 cm3

movie

liver, about 1 cm cube

distilled water 20 cm3

dry yeast about 1 g

clean sand about 1 g

activated charcoal granules, about 1 g

Apparatus – per group

test-tube rack and 4 test-tubes

forceps or finder for pushing the liver into the test-tube

4 spirit labels or markers

filter funnel

Bunsen burner

filter paper

test-tube holder

mortar and pestle

Experiment

The investigation below is a somewhat critical examination of plant and animal tissues to see if

they contain catalase.

(a) Write the three test-tubes 1-3.

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

(c) Cut the liver into 3 pieces.

(d) In tube 1 add a small piece of liver, and in tube 2 add a pinch of dry yeast.

(e) Insert the sparkling splint into tubes 1 and 2, bringing it close to the liquid surface or the top of the foam.

1 Describe what you saw happening and the effect of 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 came from hydrogen peroxide or from the solid?

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

(f) In tube 3 put some charcoal granules and observe the reaction.

5 Can charcoal be an enzyme? Explain your answer.

6 Assuming that (i) that the gas in (f) is the same as before and (ii) that the charcoal is almost pure carbon, does the charcoal result 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 the liver and yeast, which decomposes 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 do it, (iii) the observations

results and (iv) your conclusions.

(h) Wash the test tubes. Design and perform an experiment to see if the supposed enzyme in plant and animal material can be extracted and still retain its properties. The experiment must include a control.

8 Briefly describe your method, your results and your conclusions.

9 Assuming that liver and yeast each have an enzyme that splits hydrogen peroxide, is there any evidence to show that it is the same enzyme? What should be done to know this for sure?

Discussion – answers

1 Effervescence should be observed in each case but it is stronger in yeast than in liver. The glowing splint should glow again.

2 Oxygen is produced.

3 There is no evidence to show whether the liquid or solid gave the gas. If students think that a solid is unlikely to give off a gas they may be reminded of marble and hydrochloric acid where it is the solid that produces carbon dioxide. It seems less likely, however, that yeast and liver both give oxygen when treated with hydrogen peroxide, than that hydrogen peroxide should give oxygen when treated with different substances.

4 Currently, there is no evidence that an enzyme is involved.

5 A gas escapes but is not strong enough to re-ignite a lighted splint. Charcoal can’t

can be an enzyme because (a) it is an element and (b) it is produced at very high temperatures that destroy enzymes.

6 Charcoal, as an element, cannot produce oxygen. The gas must come from

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 is produced.

8 The student should grind the samples with a little sand and distilled water, filter and test the filtrate with hydrogen peroxide. Oxygen will evolve with a force proportional to that witnessed when the original substances were tested.

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

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

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