Hypothesis Enzymes

.. to produce more accurate results as any inaccuracies in one experiment can be compensated for in the other experiments. ? The 0% concentration of hydrogen peroxide is used as a control to show that at 0% concentration no reaction occurs. Safety To be protected safety goggles must be worn at all times during the experiment. A lab coat should be worn to protect from damage to clothing.

Cleaning apparatus must be kept near by in case of any spillage. Hydrogen peroxide is toxic and care must be taken when using it because it will blister the skin easily. Results 100% concentration Time (s) Experiment 1 Experiment 2 Experiment 3 Average Rate of reaction 30 35 22 24 27.00 0.90 60 49 44 42 45.00 0.75 90 62 54 52 56.00 0.62 120 66 59 56 60.33 0.50 150 68 62 59 66.00 0.42 180 72 64 62 66.67 0.37 210 73 65 62 68.33 0.32 240 74 68 63 69.00 0.28 270 75 69 63 69.33 0.25 300 75 69 64 69.33 0.23 330 75 69 64 69.33 0.21 360 75 69 64 69.33 0.19 390 75 69 64 69.33 0.18 80% Concentration Time (s) Experiment 1 Experiment 2 Experiment 3 Average Rate of reaction 30 20 23 18 20.33 0.68 60 37 29 28 31.33 0.52 90 53 35 39 42.33 0.47 120 59 57 48 53.00 0.44 150 64 59 57 60.00 0.40 180 66 65 66 65.67 0.36 210 69 72 70 70.33 0.33 240 70 73 72 71.67 0.30 270 70 73 72 71.67 0.27 300 70 73 72 71.67 0.24 330 70 74 72 72.00 0.22 360 70 74 72 72.00 0.20 390 70 74 72 72.00 0.18 60% Concentration Time (s) Experiment 1 Experiment 2 Experiment 3 Average Rate of reaction 30 14 18 25 16.00 0.53 60 37 39 39 38.00 0.63 90 54 50 69 52.00 0.59 120 66 57 75 61.50 0.51 150 67 65 82 66.00 0.44 180 72 67 90 69.50 0.39 210 73 70 94 71.50 0.34 240 74 74 96 74.00 0.31 270 74 74 98 74.00 0.27 300 74 74 98 74.00 0.25 330 74 74 98 74.00 0.22 360 74 74 98 74.00 0.21 390 74 74 98 74.00 0.19 Experiment 3 for 60% is anomalous. 40% Concentration Time (s) Experiment 1 Experiment 2 Experiment 3 Average Rate of reaction 30 15 16 15 15.33 0.51 60 30 33 32 31.67 0.53 90 40 46 45 43.67 0.49 120 51 57 57 55.00 0.46 150 63 67 69 66.33 0.44 180 68 77 78 74.33 0.41 210 74 82 85 80.33 0.38 240 79 84 89 84.00 0.35 270 82 86 90 86.00 0.32 300 84 87 91 87.33 0.29 330 86 89 92 89.00 0.27 360 86 89 92 89.00 0.25 390 86 89 92 89.00 0.23 20% Concentration Time (s) Experiment 1 Experiment 2 Experiment 3 Average Rate of reaction 30 14 16 12 14.00 0.46 60 27 22 25 24.67 0.41 90 32 31 29 30.67 0.34 120 35 33 31 33.00 0.28 150 40 39 36 38.00 0.26 180 46 42 39 42.33 0.24 210 52 48 47 49.00 0.23 240 55 52 51 52.67 0.22 270 58 56 56 56.67 0.21 300 61 60 60 60.33 0.20 330 65 62 61 62.67 0.19 360 65 63 61 63.00 0.18 390 65 63 61 63.00 0.16 0% Concentration No reaction for 0% Rate of reaction at 5 minutes 100% concentration 0.23 80% concentration 0.24 60% concentration 0.25 40% concentration 0.29 20% concentration 0.20 0% concentration No reaction The replicates are all written down to the nearest whole one on the gas syringe, because sometimes the gas syringe was moving so fast it could not be recognised if it was at .5 of a cm3. From these results it was able to plot a graphs of oxygen evolved and rate of reaction. Interpretation It would have been expected that when the concentration doubled so would the rate of reaction but this didnt occur. After 270 seconds the rate of reaction slows almost to a halt.

The straight lines show this on the graphs. At this point virtually all of the active sites are occupied so the active sites are said to be saturated with hydrogen peroxide. Increasing the concentration at this point will not cause the rate of reaction to go up any more. . All the active sites are being used so any extra Hydrogen Peroxide molecules will have to wait until an active site becomes available. The theoretical maximum rate of reaction is when all the sites are being used but in reality this theoretical maximum is never reached due to the fact that not all the active sites are being used all the time. The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum.

The time taken to fit into and leave the active site is the limiting factor in the rate of reaction. There is something obviously wrong with the results because the rate of reaction should be highest at 100% concentration. These could be some of the explanations to illustrate why the experiment went wrong Limitations 1. The experiment was repeated 3 times to and an average was taken improve accuracy. The results were used to plot graphs with a lone of best fit.

It was unrealistic to think that all the variables could be kept the same. 2. There was a slight delay between pouring the hydrogen peroxide into the conical flask, inserting the bung and starting the stopwatch. This will slightly affect the results but the three steps were carried out in the same way for each experiment so it shouldnt have made a very big difference in the overall results. 3. One of the most inaccurate pieces of apparatus used was the measuring cylinder this is extremely inexact because if the meniscus isn’t exactly on the line the measurement is wrong.

This brings in a fairly large percentage error. 4. The volume of gas in the conical flask is very slightly affected by how far the bug is pushed down in each experiment, if the bung is pushed down further then the volume in the conical flask will be less so more oxygen will be pushed into the gas syringe early in the experiment and this might have affected the results. 5. The gas syringe only had measurements for 1 whole number this could have affected the results because no decimal places could be used. 6.

The amount of catalase in each potato couldnt be measured this would affect the results because some parts of the potato could have more catalase than the rest. 7. The water bath was difficult to keep at the constant temperature due to heat loss to the surroundings more hot water would have to be added to heat it up again but this is imprecise. 8. The hydrogen peroxide could have been at different temperatures due to the room warming and cooling.

9. The potato ran out so another potato was used this could have influenced the results because this potato could have contained a different concentration of catalase. 10. The balance only measures to 2 d.p. this might have affected the results because slightly different masses of potato could have been used. 11. The gas syringe may have been slightly sticky making it harder for the oxygen to push, to register the true result.

Improvements 1. To gain a more accurate result more replicates could be taken to get a more actual average. 2. There is no way to rectify the time taken between pouring in the hydrogen peroxide, putting in the bung and starting the stopwatch. Although it does help if there are assistants to help so each person only has to do one job.

3. Instead of using a measuring cylinder a pipette or a burette would have been far more precise pieces of equipment. 4. A conical flask with a pressure line could have been used this would show how far to push in the bung. 5.

A decimal place gas syringe would give more accurate readings. 6. The catalase cant be measured in potato a much better catalase substitute would be yeast this can be weighed and measured. Also once the potato is used another would have to be used and this could produce catalase of a totally different concentration. 7.

An electrically monitored water bath would be useful this could keep the water in the correct temperature range accurately. 8. The hydrogen peroxide should be kept at a constant temperature by putting it into an electrically monitored water bath and taking and recording its temperature before it is added to the catalase. 9. A different source of catalase should be used one thats concentration can be measured e.g.

yeast. 10. A balance with more decimal places would have made the results more exact. 11. The gas syringes should be made so that it has a non-stick surface inside so it doesnt become stiff.

The plotted results on the graph go up to produce a curve of best fit levelling off at the end. The main anomaly is the fact that the rate of reaction at 40% concentration is far higher than that at 100% concentration. Another one of the anomalies in the results was the 3rd experiment at 60% concentration this went completely wrong. These were probably due to and experimental error involving some of the limiting factors mentioned above.