What is the effect of pH on the activity of the enzyme catalase?

pH strips of paper. The numbers 0-7 represent an acidic pH, and 7-14 represent a low, otherwise known as a ‘basic’ pH. The optimum pH for catalase is seven. In this lab, we aimed to test this statement by investigating the effect of pH on the activity of catalase, (which has an optimum pH of 7). We used liver as a source of catalase as liver is one of the central detoxifying organs in the body, and therefore needs catalase in order to breakdown Hydrogen Peroxide.Prediction:        Before the outcome of the experiment was known, I predicted that beaker number three, which contained no added acidic substances, would produce the greatest amount of bubbles. The greatest amount of bubbles would demonstrate that the solution produced oxygen, and therefore showing that the catalase had successfully broken down the Hydrogen Peroxide into water and oxygen. Since enzymes work best in their optimum pH, I believed that as the optimum pH of catalase is in fact 7, it would therefore work best in water, which also has a pH of 7. I also thought that beakers number 1 and 5, would work the least efficiently, and therefore produce the least amount of bubbles. My prediction was due to the fact that beaker number 1 had the largest amount of HCL (Hydrochloric acid) added, which was and is bound to increase the acidity level of a substance, (unless it’s a biological organism or a buffer). As for beaker number 5, it had the largest amount of NaOH which is bound to lower the pH of a substance. As the new acidity level would most likely be very different from catalase’s optimum pH, it would stop breaking down the Hydrogen Peroxide and become denatured.Procedure:Gather 5 beakers with the following contents:Beaker # 1: 20 ml of water & 10 drops of HCL (Hydrochloric acid)Beaker # 2: 20 ml of water & 5 drops of HCLBeaker # 3: 20 ml of waterBeaker # 4: 20 ml of water & 5 drops of NaOH (Sodium Hydroxide)Beaker # 5: 20 ml of water & 10 drops of NaOHMeasure the acidity of each beaker by putting a drop of each solution on pH paper. Record the results in a table.Then, pour 5ml of each of the 5 solutions into 5 different beakers. Use a pipette in order to add 5 drops of liver puree to the 5 solutions.Add 2.5 ml of Hydrogen peroxide (H202) to the beakers.Measure the volume, (in millilitres), of the bubbles produced in each of the beakers. Record the results in a table.       Data:Beakers Contents        pH of substance Added contents  Volume of bubbles (ml)1       10 drops of HCl and 20ml of water       2       5 drops of liver puree & 2.5 ml of Hydrogen peroxide (H202)     122       20ml of water and 5 drops of HCL        4       5 drops of liver puree & 2.5 ml of Hydrogen peroxide (H202)     103       20ml of water   7       5 drops of liver puree & 2.5 ml of Hydrogen peroxide (H202)     0.84       20ml of water and 5 drops of NaOH       9       5 drops of liver puree & 2.5 ml of Hydrogen peroxide (H202)     25       10 drops of  NaOH and 20ml of water     11      5 drops of liver puree & 2.5 ml of Hydrogen peroxide (H202)     1.9Conclusion:        Enzymes work within certain limits. One of these limits is pH, (otherwise known as the acidity level), at which an enzyme has an ‘optimum’ pH, which is basically the pH at which the enzyme works best. The further away an enzyme is from it’s optimum pH, the less efficiently it begins to work, eventually becoming denatured. Nevertheless, that is precisely what our results did not show.        The volume of the bubbles in beaker number 1, which contained 20 ml of water and 10 drops of Hydrochloric acid (HCl), (making the solution have a pH of 2), were 12ml. In beaker number 2, there were 20 ml of water and 5 drops of HCl, and the pH was 4. The bubbles produced a volume of 10 ml. Beaker number 3 only contained 20ml of water. Once the liver puree and hydrogen peroxide had been added, the bubbles rose to a volume of approximately 0.8ml. Beaker number 4 held 20ml of water and 5 drops of Sodium Hydroxide (NaOH), which had a pH of 9. The bubbles had a volume of 2ml. Finally, beaker number 5 contained 20 ml of water and 10 drops of NaOH. It had a pH of 11, and once the liver puree and Hydrogen peroxide had been added, the bubbles rose to roughly 1.9ml.        If we relied on our results alone, we would be able to conclude from this experiment, that the higher the pH of a substance, the better the enzyme works. However, this is completely untrue. What our results should have shown is that the addition of HCl and NaOH merely inhibit the activity of the catalase.        For beaker number 1, the volume of the bubbles should have been relatively low, as this proves that the catalase unsuccessfully broke down the Hydrogen Peroxide, and there were therefore fewer oxygen bubbles. On the other hand, our beaker number 4 and 5 had a plausible result, as they too had a low volume of bubbles after the addition of NaOH. This showed that the NaOH did in fact inhibit catalase activity as fewer bubbles were produced. Beaker number 3 should have had the highest volume of bubbles as it contained catalase’s optimum pH. This would have shown that catalase worked most effectively as it produced the largest amount of bubbles and therefore correctly broke down the Hydrogen Peroxide into water and Oxygen.Evaluation:        Clearly, as our experiment did not have successful results, there were many sources of error, human errors and limitations. To begin with, one human error was that we accidentally muddled the beakers up on a number of occasions. Upon gathering all the 5 beakers, we assigned each person in our group with a beaker. That person then had the task of investigating that particular beaker. However, certain members of our group were unhappy with the beaker which they had then been assigned, and began arguing amongst themselves. By the end of multiple discussions, a few people had forgotten which beaker belonged to them. And so, as there was a limited amount of time, and we were too lazy to regather equipment, one or two people randomly picked a beaker which they assigned their number to. At this point, there was a lot of confusion over the beakers. In order to solve the problem, we attempted to place the beakers in a consecutive order on the work surface. By mistake, some beakers were placed in the wrong order, and we were unsure as to whom they belonged to. We guesstimated the number of each of the beakers, and continued to work. In order to resolve this issue, though it would have consumed more time, we should have worked as a group, and dealt with one beaker at a time. This would have made the experiment far easier, and we would have definitely obtained better results.        Another human error was the amount of Hydrochloric acid and Sodium Hydroxide added to the beakers. For beaker number 2, we were supposed to add 5 drops of HCl. However, after adding a few drops, we had lost count, as so we practically guessed the remaining drops which we would have to add. Though this probably wouldn’t have made such a large difference in terms of the entire experiment, it could have still affected our results. To improve this error, we should have been more careful in measuring and adding the drops of HCl.        Finally, we didn’t measure the volume of the bubbles incredibly accurately. In beaker number 2, there was a disagreement between members in our group whether the bubbles rose 9ml or 11ml. Without properly measuring the volume, we simply assumed, by taking the average, that the bubbles were 10ml in height. To improve this, we should have accurately measured the volume of the bubbles in the cylinder.