Experiment to investigate the activity of enzyme catalase at different pHs.

PH2, PH4, PH7, PH9, PH12

        To ensure that it is a fair test I will have to make sure the following variables are kept the same

1g of mushroom, 15cm2 pH buffer, equal amount of hydrogen peroxide as pH buffer. I must also time all experiments for 2 minutes.

Trail Run

        

        I am going to trial 2 different concentrations of hydrogen peroxide to find out which is best to use for my experiments.

Apparatus 

We set up the following apparatus as shown in the diagram.

• Test tube rack

• 2 boiling tubes

• Rubber bung and delivery tube

• Stop watch

• Top-Hand balance

• Measuring cylinder

Safety

In order to ensure the experiment is carried out safely I must clear all my things form my desk and place my bag at the back of the classroom. I will also wear safety glasses to protect my eyes from the chemicals I will be using.

        

Method

        We set the apparatus up as shown in the diagram above, but kept the hydrogen peroxide separate from the PH buffer and the mushroom. Then we did the following in order.

• Measured out equal amounts (15cm ) of Hydrogen peroxide and pH buffer in separate measuring tubes.

• Filled a measuring tube ¾ full of water.

• Fed the delivery tube from the top of the rubber bung into the water

• Mixed the hydrogen peroxide with the ph buffer and mushroom into the same measuring cylinder.

• Placed the bung on top of the measuring cylinder with the hydrogen peroxide, mushroom and pH buffer in.

• Started the stopwatch

• Started counting the bubbles

• Stopped counting after 2 minutes

• Recorded the results

Trial Run Results

These are the results I found using two different concentrations:

        

As you can see the rate of reaction was much greater using 20% concentration, so this will be the one we will use for our experiments.

Results

        

        These are the results of the enzyme catalase reaction with 1g of mushroom. We used hydrogen peroxide with a 20% concentration for the reactions. We put 15 cm of hydrogen peroxide in a test tube with 1g of mushroom and 15cm of ph buffer. We trailed each ph 3 times for accuracy. The pH buffer provided a way of changing which pH the reaction was taking place within and allowed us to se clearly which pH was best for the reaction.

Conclusion

        From the results obtained pH 9 was the optimum pH for the enzyme activity. I can tell this from the graph as the most amount of bubbles were given off using pH 9.

        The graph shows the pattern of enzyme activity. The pattern shows that the enzyme activity increases the closer the pH is to pH 9. Once the pH goes over 9 the rate of reaction decreases again. This confirms my theory.

        The graph clearly shows the denaturing effect on the enzyme as the solution becomes more acid or alkali concentrated and the rate of reaction decreases. The following diagram shows what was happening to the catalase enzymes in my experiment when I was using extremes of pH (pH2 + pH12). This also shows why the rate of reaction slowed the further the pH from 9.

        The conclusion drawn from the results support my theory but not my prediction. I predicted that a pH of 7 would be the optimum pH for the reaction. This was not the case; pH 9 gave slightly more bubbles. I do not think this was an error in my readings. All enzymes are different and pH 7 was a good estimate for the pH as this is neutral (neither acid nor alkali). The graph and table clearly conform my theory on the denaturing effect of different pHs.

Evaluation

        The experiment was carried out over two days. This leaves many factors open to change. Namely the fact different types of mushrooms were used. This may have had major affects on the accuracy of our pH averages. I did not find any anomalous results in my repeats for each pH as the results were consistent with each other so I am inclined to believe the change in mushroom type had not adverse affects on the overall reliability of my experiment.

        In some places my experimental process was weak. Instead of counting the bubbles given off, to make the experiment more reliable I could have measured the exact volume of the gas given off using a gas syringe.

        As I have stated my repeats for each pH were close in value. Though they do not support my prediction as pH 9 gave off the most bubbles. My results show a clear trend in enzyme activity and show that pH 9 gave off only marginally more bubbles.

        Testing all the pH values from 1-12 could extend the experiment. This would give a wider band of results making the experiment more accurate again. This would also confirm the theory further. I could also test different sources of the enzyme catalase e.g. (liver) and see if the pattern was similar.