Conclusion
I found, from my results, that when the substrate concentration is increased on the enzyme, the rate of reaction increases as well. This shows that increasing the concentration will increase the rate of reaction.
The graph goes through the origin, as when the concentration was 0% the enzyme would not react with the distilled water because there was no substrate in the solution. At the beginning of the graph there was direct proportion, as the concentration went up so did the gas volume. Then the slope of the graph showed us that the rate slowed down but was still going up. This may have happened, as there was a build up of substrate so the rate slowed down. Then the rate of reaction started to pick up and the end of the graph showed that the increase in concentration meant an increase in the rate. This probably happened as the enzymes were working at a much faster rate and so taking in more substrate molecules at once. On the graph, from 0 to 6 volumes the concentration was proportional to gas volume. From 6 to 13 volumes the rate slowed down, as there may have been a build up of excess substrate. From 13 to 20 the rate started to get higher at a steady rate, showing that the enzymes were working harder and so taking in more hydrogen peroxide molecules. When the concentration was at 0 volumes there was no reaction with the enzyme. This shows that the enzyme only reacts with hydrogen peroxide. At 4 volumes and 6 volumes the gas volume is not a lot as the enzymes have a less chance of colliding with a hydrogen peroxide molecule, because the concentration is very low. Overall the curve showed that the concentration was not proportional to the gas volume but, as the concentration increased so did the gas volume. At 20 volumes the graph did not begin to flatten off, instead it was still rising. This showed that more substrate concentration was needed for the enzymes to work as hard as possible and this would be where the graph would flatten off.
In my prediction I said the rate would double, I could not measure this as my graph line was a curve. My hypothesis was supported in that the as the substrate concentration increases so does the rate of reaction. I said there would be a proportional rise but there wasn’t on my graph. This was probably a result of there being excess substrate between 6 and 13 volumes. I said that the graph would flatten off at the end but that did not happen. This was as the concentration of the hydrogen peroxide was not enough because it had been diluted so that it would be safe to use at school.
Relating to scientific theory, the curve of the graph starts to go up as the concentration gets higher as the enzyme molecule will collide more with the hydrogen peroxide molecule if there is a lot of it. There is a slow build up of substrate molecule as each enzyme has one active site. This leads to a build up of substrate. Also the reaction gets extra energy from the heat of the water bath. I also found that Catalase uses catabolism as it changed a complex molecule, hydrogen peroxide, to simple molecules, water and oxygen. My graph did not have a v-max, where the graph flattens off, as the line of best did not even begin to flatten off.
I found that when the substrate concentration is increased on the enzyme, the rate of reaction increases as well. Therefore increase in substrate = increase in rate. My hypothesis was true but the graph did not curve, as more substrate concentration was needed.
Evaluation
The graph and data I obtained was what I thought would happen, increase in substrate = increase in rate, but the graph did not even begin to flatten off. This shows that a much greater concentration was needed for the graph to flatten off and also for the enzymes to be working at their hardest. All my results seem pretty accurate, but I thought that the following concentrations were the best results: 4 volumes, 6 vols, 15 vols, 17 vols and 20 vols. 10 and 13 vols, I thought were not as accurate as there may have been a build up of substrate and so that may have been why the rate had slowed down there. The graph had no anomalies on it. The error bars on the graph show that the experiment and its replicate displaced nearly the same amount of water, indicating that the results were quite accurate and reliable.
The method had weaknesses in it. Firstly more replicates were needed. There were 2 concentrations I was unsure about, 10 and 13 vols. Though they were not anomalies, if I had done more replicates I may have got a better line for the line of best fit. Also the results would have been more accurate. This cannot be helped, as there is a certain limit of time I had and the only way to get more replicates was if I worked more efficiently in my time limit.
The boiling tube had to be shaken so that the liver was not pushed up by the froth created by the reaction. This meant that the liver would react better with the hydrogen peroxide. The problem with this action is that it was very hard to shake the boiling tube the same amount each time a concentration was being tested. If the boiling tube racks had bigger holes in it, as in width, I could shake the boiling tube in there. This way the amount of times I shake the boiling tube in a minute will almost be the same every time I do it. This will also make the experiment fairer.
I thought I did not use enough concentrations between 10 vols and 0 vols. This meant in that region, the trend of the line could be different. If I had done more concentrations between 10 vols and 0 vols my results would be more valid and accurate. Just like doing more replicates, there is a time factor involved. That is there would probably not be enough time to do more concentrations. Also I would like a much stronger concentration so that if I repeated the experiment, this time I may have a v-max. The concentration I would suggest is 40 vols.
During the experiment I used the same piece of liver every time. While doing this sometimes a tiny piece of the liver would flake off. This meant the liver’s weight would change and so there may have been fewer enzymes to react with the hydrogen peroxide. Also the surface area would change so it could react more or less with the hydrogen peroxide. To prevent this, I think a new piece of liver should be used every time a concentration is being tested, but while doing this, the surface area of the liver could change every time a new piece of liver is cut. This means that the liver has to be liquidated, using a liquidiser, so that every new piece of liver has the same surface area. Ofcourse, every piece of liver would weigh the same.
I had another problem with the liver, after cutting it; it was taken to the bench on a watch glass. While moving the piece of liver, the mass of it would have gone down as blood was left behind on the scales and when I put it in the boiling tube, blood would have been left on the watch glass. Therefore in moving it around the liver may have lost 0.1g. To prevent this form occurring, the liver from which I took a cutting from could have been drained of its blood or if that was not possible the watch glass could have been teared on the scales. The liver could then be weighed on the watch glass. The watch glass could be taken back to the bench. This way less blood will be lost.
In my graph there were no anomalies. The results were not extremely precise, as the graph did not level off at the end. This was, as more concentration was needed for the graph to level off. If the graph had levelled off I could have found the v-max of the graph. This would tell me what concentration the enzymes are working the hardest, as there is an abundance of substrate molecule. The flaws or weaknesses in my method probably affected the outcome of my results. This means they are not 100% valid. The error bars on the graph show the replicates to my experiment were very close to each other.
The changes below are to fix the flaws in my method:
The experiment would be carried out the same way but now there would be a liquidiser and a rack to shake my boiling tube in. This would liqidise the liver so the surface area would be the same overtime the liver was changed. Also the special rack I talked about earlier on where the rack would help me shake the boiling tube at a constant rate. I would want a higher concentration of hydrogen peroxide (preferably 40 volumes). I must also make sure that I use my time efficiently, as I did not when I did this experiment. Below is a diagram of the new apparatus I will use.
