Biology Experiments for Teachers – Enzymes: Catalase

Safety. Although the hazards in the following experiments are negligible, 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 embarking on any experiment.

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

Samples of liver and yeast are dropped into 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 the questions take about one hour.

Prior knowledge. The existence of inorganic catalysts; enzymes denatured on boiling; oxygen relights a glowing splint.

Advance preparation and materials – per group

20 volume hydrogen peroxide 50 cm3

splint

liver, about 1 cm cube

distilled water 20 cm3

dried 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 seeker for pushing liver into test-tube

4 labels or spirit marker

filter funnel

Bunsen burner

filter paper

test-tube holder

mortar and pestle

Experiment

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

they contain catalase.

(a) Label three test-tubes 1-3.

(b) Pour about 20 mm (depth) 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) Insert a glowing splint into tubes 1 and 2, bringing it close to the liquid surface or into the upper part of the froth.

1 Describe what you saw happening 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 indicate whether the gas is coming from the 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 place a few granules of charcoal 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 to decide on 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 to oxygen and water; design and carry out a control experiment to test this hypothesis.

7 Record (i) the experiment, (ii) the reasons which led you to conduct it, (iii) the observed

results and (iv) your conclusions.

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

8 Describe briefly your procedure, your results and your conclusions.

9 Assuming that liver and yeast each contain an enzyme which splits hydrogen peroxide, is there any evidence to show that it is the same enzyme? What would have to be done to find this out for certain?

Discussion – answers

1 Effervescence should be observed in each case but it is more vigorous with yeast than with liver. The glowing splint should relight.

2 Oxygen is being produced.

3 There is no evidence to indicate whether the liquid or solid is giving the gas. If the students think that a solid is unlikely to give off a gas they could be reminded of marble and hydrochloric acid in which it is the solid producing the carbon dioxide. It seems less likely, however, that yeast and liver would both give off oxygen when treated with hydrogen peroxide, than that hydrogen peroxide should give oxygen when treated with diverse substances.

4 So far, there is no evidence of an enzyme being involved.

5 A gas will come off but not sufficiently rapidly to relight a glowing splint. Charcoal could not

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

6 Charcoal, as an element, could not be giving off oxygen. The gas must be coming from the

hydrogen peroxide.

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

(ii) If an enzyme is involved,

(iii) no gas will be 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 be evolved with a vigour 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 no fundamental reason why yeast and liver should not have different enzymes which catalyse the decomposition of hydrogen peroxide. To be certain on this point, the enzymes would have to be extracted and their chemical composition determined.

How Teachers Influence The Performance Of Biology In High Schools

Biology plays a key role in industrialization and other sectors of the economy. Biology is a practical subject, which equips students with concepts and skills that are useful in solving the day-today problems of life. The study of biology aims at providing the learner with the necessary knowledge with which to control or change the environment for the benefit of an individual, family or community.

In general, the importance of biology to humanity can be outlined as follows:

(i) The learning of biology helps us to know how to use natural resources more efficiently in industry e.g. in bio-technology, food production, building and textile and paper industries.

(ii) The learning of biology helps us to understand changes in the environment and the factors affecting these changes, in order to know how human needs are influenced.

(iii) The learning of biology is important in helping mankind to find effective ways of preventing, treating and curing diseases and home management techniques e.g. better methods of food preservation, efficient food preparation and care of the family

(iv) The learning of biology is important in helping the improvement of agricultural yields through scientific research.

There has been public outcry and concern by parents, teachers, educationists in Kenya about poor performance in science subjects and mathematics in national examinations.

But do you know the biology teacher has a role to play in this poor performance?

Biology as a science subject requires an integration of both theoretical and practical work to make it easily understood by the students. The largest proportion of teachers still use the conventional lecture method while teaching biology.

Teacher expectations have a bearing on the attitude and science anxiety levels of the learners particularly when the learners are aware of the level of expectation the teacher has of them.

In relation to the teaching and learning of biology, attitudes begin to develop on the first encounter between the teacher and the learner, once formed they play a key role in determining students’ learning and performance in biology.

Authoritarian and impersonal teacher- student interaction in class could be the major factor that contributes to negative attitude of the students towards learning biology. On the other hand, democratic and personal teacher-student interaction in class elicits positive attitude towards learning biology

The teaching approach, methodology and how the professional skills and practices of the teacher are displayed may be dependent on the level of science anxiety the biology teacher has.

A teacher who suffers from career dissatisfaction is likely to contribute negatively in terms of performance of the learners in biology; this is because the teacher will have lower self-efficacy and high levels of anxiety. This kind of teacher is likely to develop negative attitude towards the students and his/her interaction with the students will be negative and this may contribute to a negative attitude of the students towards biology with the likelihood of the students developing high levels of anxiety towards the subject.

Therefore, teacher perceptions, teaching methods applied, the type of teacher -pupil classroom interactions, teacher expectations of students in terms of performance and science anxiety levels of the teachers- partly contributed by lack of job dissatisfaction or satisfaction are the key factors that influence performance in biology in Kenyan secondary schools.