Temperature has a more severe affect on enzymes since high temperature can completely destroy or denature the enzyme. At temperature below the optimum the enzyme-substrate reaction is like a normal chemical reaction. As the temperature increases the particles gain more kinetic energy and so move about faster and collide with more energy resulting in more enzyme-substrate complexes being formed. However, above the optimum temperature the enzyme shape changes and so the substrate does not fit properly and so the activity of the enzyme decreases rapidly. The predicted graph for the effect of temperature on enzyme activity would look like this:
In this investigation I use the enzyme catalase. Catalase is found in most animals and plant cells since it breaks down hydrogen peroxide, which is produced as a product of many chemical reactions in the cell. Hydrogen peroxide is toxic and so is broken down by the enzyme catalase into oxygen and water.
Hydrogen peroxide → oxygen + water.
The activity of catalase can be measured by counting the number of oxygen bubbles produced in the reaction in a specific amount of time.
Analysis and conclusions
The results of the experiment are shown in the table and presented in the graph. The graph shows the average number of oxygen molecules. The pattern produced is similar to the predicted graph I presented in the planning. From 15 oC to 35 oC the number of oxygen bubbles produced increased. This is because the increasing temperature increased the kinetic energy of the enzyme and hydrogen peroxide particles. This resulted in the particles moving about faster and more collisions happening. Therefore, more enzyme-substrate complexes formed and more chemical reactions took place. In other words the hydrogen peroxide was broken down faster which is why the number of oxygen bubbles produced increased. The graph shows that the optimum temperature was 35 oC. At higher temperature, the enzyme shape was changed so more of the enzyme particles stopped working (the enzymes were being denatured). At the highest temperature of 70 oC only a few enzyme molecules were working which is why so few bubbles of oxygen were made. I estimate that at about 75 oC all the enzyme molecules would have been denatured. My results agree with my prediction although I said that the enzymes would denature at 40 oC.
Evaluation
The design of the experiment was good enough to allow me to produce data to help me investigate my aim. The results in my replicates are fairly similar and I was able to fit a line of best fit to the data which suggests that my experiment and data are reliable. The two main anomalous results were the one repeat at 45 oC where the number of bubbles (49) was probably too low for that temperature, and at 55 oC where all the bubble counts were too high. The graph shows why these data might be anomalous since they do not fit the trend. The temperature at 55 oC may not have been 55 oC and was probably lower since the number of bubbles produced was higher than expected. At error at 45 oC might have occurred because the water might have been too hot when that repeat was done, or the number of bubbles had not been counted accurately. The fact that I was able to produce a reasonable line of best fit suggests that the range of temperatures I used was adequate. However, there are a number of improvements that I would make if I had the equipment and time.
- I would use water baths to control the temperature. A water bath would electronically adjust the temperature so that it would stay constant during the experiment.
- I would use a measuring cylinder instead of just a test tube to collect the oxygen in so that I could measure the volume of oxygen produced. Counting bubbles was not easy especially at around the optimum temperature and also the sizes of the bubbles change. If it was possible then I would use a gas syringe to collect and measure the oxygen.
- The other way I could do this experiment is to use a weighing balance. Since the oxygen gas is escaping I could measure the loss in mass of the reacting mixture.
Even though I did not have this equipment I was still able to produce reliable results and make a conclusion.
I could use the same apparatus to investigate the effect of pH on enzyme activity or enzyme concentration. To change the pH, I could use acid or alkali mixed with the hydrogen peroxide and again count the number of bubbles of oxygen produced. To change enzyme concentration I could use different sized pieces of potato. However, one of the problems with this would be that the surface area would be different. Therefore, it might be better to investigate surface area in stead. I would keep the mass of potato the same but chop it into different numbers of pieces.
