Factors affecting enzyme functioning
Sub units: Temperature | Experiment: the effect of temperature on trypsin activity | pH | Experiment: the effect of pH on catalase activity | Enzyme concentration | Experiment: the effect of enzyme concentration on amylase activity | Substrate concentration | Experiment: the effect of substrate concentration on amylase activity | Maximising reaction rates

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.

Question

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.

Experimental demonstration of the effect of pH on enzyme activity

Graph showing the effect of pH on catalase activity

Sub units: Temperature | Experiment: the effect of temperature on trypsin activity | pH | Experiment: the effect of pH on catalase activity | Enzyme concentration | Experiment: the effect of enzyme concentration on amylase activity | Substrate concentration | Experiment: the effect of substrate concentration on amylase activity | Maximising reaction rates


 

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