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I have been set a task to investigate how substrate concentration affects the rate of an enzyme catalyzed reaction.

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AS Biology Coursework Aim- I have been set a task to investigate how substrate concentration affects the rate of an enzyme catalyzed reaction. I will test different concentrations of substrate (hydrogen peroxide, H2O2) with the same amount of enzyme catalase (in celery) and compare them to see if a higher substrate concentration equals a faster rate of reaction. When the enzyme catalase reacts with hydrogen peroxide, oxygen gas is evolved from the reaction. Therefore I am going to compare the rate at which oxygen is produced at different substrate concentrations using the catalyse enzyme to catalyse the reaction to see the effect that changing substrate concentration has on the rate of reaction. Prediction- I predict that as the substrate concentration increases, the rate of reaction will go up at a directionally proportional rate until the solution becomes saturated. When this saturation point is reached, then adding extra substrate will make no difference. I know through past experiments I have done that the rate of reaction steadily increases when more substrate is added because more of the active sites of the enzyme are being used which results in more reactions, so the amount of Oxygen released in a given time is higher. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. ...read more.


4) I will have started the stopwatch as soon I have put the rubber bung back on the conical flask. As soon as 20 seconds has elapsed I will look to the gas syringe and see how much oxygen gas has evolved from the reaction 5) I will keep doing this every 20 seconds until three readings from the gas syringe are identical. 6) Once this is the case I will wash the conical flask out with water and begin the experiment again using a different concentration of hydrogen peroxide solution. 7) When I have completed all of the experiments with all 5 of the different concentrations of hydrogen peroxide, I will repeat the whole experiment another 2 more times. I will be repeating it this many times incase one of the results is a bit abnormal. This could be from mistakes such as wrong concentrations added or even getting the table knocked while I was measuring the celery. By doing the experiment 3 times and taking an average I will eliminate any chance of a wrong reading showing up on the graph. Diagram- Results table- 2H202------Catalase--------> 2H20 + 02 Concentration of the solution Time elapsed 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 1st experiment 2.5 5 10 15 20 2nd experiment 2.5 5 10 15 20 3rd experiment 2.5 5 10 15 20 Average results 2.5 5 10 15 20 1 2 3 ...read more.


5g. The 1g mixture was just not enough enzyme for the amount of substrate being used. There are a few invalid readings such as where there is no difference in oxygen gas evolved at a certain time between two different concentrations. There are so many possible reasons why this could have happened. One of the enzyme mixtures may have contained more sand than the other leading to less active sites being available for the substrate molecules. Another being the celery pieces are larger in one than the other. This means that the reaction that has more surface area would have the faster rate of reaction. I could even repeat the experiment again and the average results might be a little more accurate. Limitations- To enable this experiment to be completed as accurate as possible, I repeated it three times and then used an average of all the results to best plot a graph with a line of best fit. I tried my best to keep all the variables apart from the one I was testing (Hydrogen Peroxide Concentration) the same. However and unfortunately in practice it is impossible with the basic apparatus I had to keep all measurements precisely the same. For example: There is a slight delay between pouring the celery into the beaker of Hydrogen Peroxide. This will slightly affect all the results for each individual experiment but as I carried out all the steps in the same way, it should not make any negotiable difference to the overall result. By Paul Faichney ...read more.

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