Introduction Catalase breaks down H2O2 (hydrogen
peroxide) into water and oxygen. 
H2O2 is a toxic substance formed during
anaerobic respiration. Aim To determine the effects of pH on catalase enzyme activity. Materials and method We used four different concentrations (pH values) of a buffer
solution of sodium phosphate Na2PO4 between
pH 4 and pH 8. 3cm³ of shredded potato (containing catalase)
was placed in a flask, with 10cm³ of buffer solution at the
lowest pH. A rubber bung equipped with both a syringe and a
delivery tube was placed in the neck of the flask. The other end of
the delivery tube was placed in a beaker containing water. The air
in the flask was displaced by the injection of
H2O2 solution. The air was allowed to bubble
out through the delivery tube into the beaker. A measuring cylinder
was filled with water and inverted carefully into the beaker over
the end of the delivery tube. Timing was begun immediately after
the oxygen bubbles began. After five minutes, the volume of oxygen
present in the measuring cylinder as a result of the reaction in
the flask was determined. This was repeated for all buffer
concentrations. A control set-up was used in the exact manner as
above - but instead of using buffer solution each time, the same
quantity of distilled water was used. Results and discussion The relative reaction rate (volume of oxygen evolved during five
minutes) was plotted against pH. The control showed the same enzyme
activity each time the experiment was run. The relative reaction
rate increased with pH - up to the optimum value (around 6.3) and
then decreased at higher pH values. Possible errors
The amount of oxygen given off is not measured accurately here and
not all air may have been expelled from the flask. Comment We have already seen that temperature affects
the reaction rate - we must keep it constant so that it does not
affect the results of this experiment.
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