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To investigate one of the variables to show its effect on the rate of the reaction.

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GCSE Practical Assessment: Biology Investigation Aim: To investigate one of these variables to show its effect on the rate of the following reaction: Variables to choose between: 1. The concentration of the substrate molecule (H2O2) 2. The mass of the potato (indirect way of measuring the concentration of the enzyme) The Reaction: Hydrogen Peroxide Water + Oxygen 2H2O2 2H20 + O2 For this experiment I have decided to vary the concentration of the substrate molecule (H2O2) Background information: Hydrogen Peroxide is a toxic chemical, produced by many living organisms as a product of the biochemical reactions occurring in the cells. As hydrogen peroxide is poisonous it must be removed quickly. The enzyme Catalase speeds up the reaction that breaks down hydrogen peroxide into water and oxygen. Catalase can be found in potato cells. When hydrogen peroxide is added to the potato as a liquid, the catalase in the potato breaks down the hydrogen peroxide into water and oxygen - two substances that are essential for our bodies. Therefore catalase is essential in our bodies to break down H2O2. Prediction: I predict that as the substrate concentration increases, the rate of reaction will go up at a directly proportional rate until the solution becomes saturated with the substrate hydrogen peroxide. When this saturation point is reached, then adding extra substrate will make no difference or vice versa, as the substrate concentration decreases the rate of the oxygen production will decrease as well. ...read more.


Each enzyme has an optimum pH at which its active site best fits the substrate. Variation either side of pH results in denaturising of the enzyme and a slower rate of reaction. Safe Test: Keeping a safe test is also very important for the safety of me and other people around me. To ensure that my experiment is safe, I will carry out the following precautions: * Goggles should be warn to protect my eyes from the hydrogen peroxide or in case another accident occurred. * Be careful when cutting and grating the potato. Try not to be distracted whilst doing this or you could end up cutting yourself. * I should act in a sensible and safe manner, carefully working with the equipment and being aware of any dangers. Results: These are the results I have collected from my experiments: 0.5m Concentration-Amount of Oxygen collected: Time (seconds) 1st test (cm3) 2nd test (cm3) 3rd test (cm3) Average (cm3) 30 11 5 9 8.3 60 20 11 14 15 90 24 16 20 20 120 28 19 25 24 150 32 23 29 28 180 35 26 33 31.3 210 39 29 35 34.3 240 41 32 39 37.3 270 43 35 42 40 300 45 37.5 44 42.2 330 47 39.5 46 44.2 360 49 41 48 46 390 50 43 50 47.6 420 51 45 51.5 49.2 450 52 47 53 50.6 480 52 49 53.5 51.5 510 52 50.5 54 52.2 540 52 51.5 54 52.5 570 52 51.5 54 52.5 600 52 51.5 54 52.5 1.0m Concentration-Amount of Oxygen collected: Time (seconds) ...read more.


The other equipment that I used was otherwise accurate enough as the mass balance was accurate to two decimal places and the measuring cylinder I used to measure out the hydrogen peroxide, as I have said was graded in steps of 5cm� therefore as I was measuring out 20cm� that was accurate enough. * A slight experimental error was that there was a small time between the hydrogen peroxide being introduced into the conical flask and the bung creating a seal to the delivery tube, although I don't believe that enough oxygen could escape in that time to make a real difference to my results. A possible larger error was that parts of the skin of the potato were used in the experiment; this is not good as the skin of the potato doesn't contain any of the enzyme catalase, and therefore could have affected my results significantly, finally another error could have been that as I had grated the potato not all the subsequent pieces of potato would have been the same size, therefore would have a different surface area and therefore would allow differing amounts of the enzyme to come into contact with the hydrogen peroxide. * To improve the accuracy of the investigation I could use more precise apparatus, also I could take readings of the experiment for 15 minutes or longer instead of just 10 minutes, To extend on the investigation I could investigate if the surface area of the potato affects the rate of reaction, this would show me if the variable I didn't control had a drastic effect on my results. Dhiraj Aery ...read more.

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