Investigating the effect of Enzyme Concentration on the Rate of Reaction.

Investigating the effect of Enzyme Concentration on the Rate of Reaction

By Jas Singh 10D

Catalase is an enzyme, found in our cells, which speeds up the breakdown of the toxic chemical hydrogen peroxide into oxygen and water. The aim of this practical is to investigate the effect of changing the concentration of catalase on the speed of breakdown.

Hypothesis: I believe that the rate of reaction will increase when the catalase concentration is increased. This is because as the concentration of catalase in the solution increases, the more liver cells there will be and so more oxygen bubbles will be produced forcing the paper to rise to the surface faster. This shows that the reaction has occurred faster, and therefore proves that when the catalase concentration was increased, the reaction took place faster. Here is an equation to what I believe will happen:

2H202 O2 + 2H20

Here is how I think the graph will look like:

Method: (ON SHEET.)

Results:

Conclusion: From my results, I conclude that as the concentration of the catalase was increased, the rate of the reaction also increased. By discovering these results, I have also proved that they support my hypothesis. I said: “the rate of reaction will increase when the catalase concentration is increased.” This is exactly what happened in my experiment. As the liver-coated paper was dropped into the hydrogen peroxide, the reaction began to take place. The paper sank downwards, and as the coating of catalase was being broken down, oxygen was being produced as a result of the reaction. These oxygen bubbles grew in number as more catalase was being broken down. Eventually the oxygen pushed the paper back upwards and surfaced the paper. As we used the different concentrations, the speed of the reaction varied. This explains why as the concentration of the catalase increased the speed increased also. With more catalase to break down, more oxygen would be produced quicker, and so would push it up faster. That is why the higher concentrations made the paper rise to the surface the quickest. Time related to what was going on in the experiment. For instance, the longer time it took for the paper to reach the top of the test tube, the slower the enzymes were working. And the shorter time it took for the paper to reach the top of the test tube, the faster the enzymes were working. The shape of my graph was interesting. In my hypothesis, I had predicted a negative correlation for the line of best fit, with a constant gradient. But my graph showed that the line rapidly shot up at first, and then curved gradually downwards towards the end. There are two reasons for this. Firstly, the rapid upward shoot at the beginning was caused by a human error. I mistakenly did this experiment last, and this meant that all the other concentrations of the catalase were already in the solution. Thus, the readings I produced for the 0 g/l enzyme concentration were incorrect. The correct reading should have shown the time for the concentration to be very high, as the reaction would take place very slowly, and producing an accurate downwards curve on my graph. The second reason, for the curve, is as follows. After all the previous experiments, the oxygen in the substrate was being depleted. After all the previous enzymes had reacted with the oxygen, the new enzymes in the new solution would not have as much oxygen to work on, and so they would start to react less quickly. It doesn’t matter how much catalase you add; the substrate would just get used up. Based on this evidence I believe that if you increased the concentration further and further it would continue to curve until there were no oxygen molecules left to work on, and then the line would have to finish. Also, I can conclude something else. The higher the rate of collisions, the faster the rate of the reaction. I can say this because – as the graph shows – the higher concentrations took much less time to work than the low concentrations. I conclude that this is because when the concentration is higher, the more enzymes there are. This will mean that there will be more collisions between the substrate and the enzyme, and this will lead to a faster reaction. With more enzymes, this would lead to an increase in the number of enzyme-substrate complexes produced. This would mean that with more complexes, the reaction would take place quicker, and thus I also conclude that with a higher concentration, more enzyme-substrate complexes will form, and a quicker reaction.

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Evaluation: I believe my results were fairly reliable, and give a good solid basis to work out my conclusions from. I can say this because as although I did manage to gather a few anomalous results, my averages matched a familiar pattern that I had come to expect it to be similar to. Thus, I can say that my results were reliable and I could work out a successful conclusion from them. As I tested each concentration three times I believe my results would now give a reliable average which I can work from, and that I can trust. By testing each concentration three times, I could now gather an average result. If I for example had only tested each concentration one, then if it happened to be an anomalous result then I would not know, and would have to trust the result even if it was completely wrong. But by doing three results I could identify (if any) the anomalous results, and gather an average that is more likely to be accurate. However there were some faults with my experiment. The first one is the fact that between readings I did not remember to wipe clean my forceps – which could have a negative effect on the readings. Although sometimes I did remember other times I failed to do so. This means that some of my results could be wrong as the old concentration would still be on the forceps, and ruin what I thought to be for example to be 3g/l concentration of catalase and turn it into a 3.5g/l concentration of catalase. In fact by looking at my results and graph you can see that often my first result is far different to my other results. This affected my average as a result. Also, as with most experiments, given the time I could have been able to produce more results for the different concentrations. This would have made my experiment a more fairer one and provided me with a more correct average and better overall readings. But in the short time I was allowed to obtain my results I believe achieving three results was good. So to improve my experiment I would do more repeats of the different concentrations and gather more readings, and I would make sure to clean the forceps after changing concentrations every time. Another problem with my experiment was the fact that sometimes when I dropped the paper into the solution; the paper would accidentally stick to the side of the tube. This made it difficult to time, as I could not stop the timer, as it would make the experiment not be a fair test. Also, even if I had stopped the timer, it would be difficult to accurately know exactly when to stop and start the timer. To avoid this problem, I would use a wider test tube to conduct the experiment in. As for reliability, I believe the reliability of my results obtained was fairly good. My range of results, however, was slightly worrying. I seemed to obtain a result on most of my various concentrations that was far away from the rest. If you look at my graph, the anomalous results are circled in blue. But O1 and O2 are extremely different to the other results. As I explained earlier, I sometimes forgot to clean the tweezers between the concentrations and this might have affected some of the results I obtained, and in turn this would have affected my average. So I have decided to see what averages I would have obtained if I do not count the possible anomalous results I obtained.

As you can see, some of the averages without the anomalous results are quite different than the previous averages including the anomalous results. But it still gives the basic sort of shape on a graph that I obtained with my previous results. I believe that my experiment, the way I conducted it, could be repeated, with no alterations. However, if you did alter the experiment the way I would have wanted to be have to be altered, the results you would obtain would be much more accurate. I have already picked out the results I believe to be anomalous, and have pointed them out to you on my graph. The concentrations most affected by the anomalous results were the 1 g/l and the 4 g/l. Both of these incorrect results that I have identified are significantly slower than the other results in that category. This could have been caused by a contamination of the hydrogen peroxide, which could have become contaminated after the tweezers were not cleaned properly allowing other concentrations to enter the solution. Another way these results could have occurred was if the paper had got stuck to the edge, and I have explained this earlier in the evaluation. To make the results more reliable, there are a few other things I could have done. Firstly, I could have experimented with higher concentrations, and seen what the effect was. By doing this I could see whether my assumption of the curve on the graph levelling off was true or not. Second of all, I could have simply done more repeats to make my average for each concentration more accurate. To extend my investigation, I could see whether or not it was actually oxygen being given off during the reaction. How do we know that it is oxygen? To test this, I would trap some of the bubbles given off and put a glowing splint into the oxygen. If it lit up the splint, then oxygen is present. Also, I could test to see whether or not catalase is actually an enzyme, for again how are we to know? To test this, I would heat (and by doing this, denature) what I thought was the enzyme, and repeat the experiment. If the reaction failed to take place or took place extremely slower, then I would know that the denatured substance was an enzyme, as we know that by denaturing an enzyme by heating it beyond its capacity makes the enzyme stop working.