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Determine what effect pH has on the rate of reaction in the presence of the enzyme catalyse.

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Catalase Design Experiment Aim To determine what effect pH has on the rate of reaction in the presence of the enzyme catalyse. Observing the enzyme activity on potato rods will discover this. The amount of carbon dioxide produced indicates the rate of reaction. Hypothesis The enzyme will have an optimum pH of around neutral. Either side of the optimum pH will have relatively high rates of reaction and far away from the optimum pH will have a low rate of reaction. The enzyme catalase is found in many tissues including potato and liver. It is important because it breaks down the hydrogen peroxide formed in metabolism. Hydrogen peroxide is toxic and if it were not broken down it would kill the cells. As it does this, it liberates carbon dioxide that can be collected. 2H2O2 2H2O + O2 Variables Constants * Volume of buffer solution (3cm�) - controlled because different values will affect the reaction by acting on the catalase in a different way and possibly produce different volumes of gas - which is not an accurate test. * Volume of hydrogen peroxide (2cm�) - this is what the catalase reacts with and in turn liberates gas - would produce different volumes off gas if not constant. ...read more.


Modifications Step 6 was changed because the tipping of the hydrogen peroxide was making inaccuracies within the experiment, as it was extremely difficult to ensure all hydrogen peroxide was emptied from the test tube. This technically meant that different amounts of gas would be liberated. There was also another motive to this modification - the bung would act as a piston and drives any air left into the glass delivery tube out into the upturned test tube. Results The amount of gas liberated when catalase enzyme reacts with H2O2 with varied pH environments pH 4 6 7 8 9 CONTROL Replicate 1 (Cm�) 1.25 5.80 4.01 3.50 3.34 0 Replicate 2 (Cm�) 1.32 2.80 4.42 3.72 3.65 0 Mean Values (Cm�) 1.285 2.80 4.215 3.61 3.495 0 Mean volume of O2 per slice per minute (Cm�) 0.0257 0.056 0.0843 0.0722 0.0699 0 Anomalies The result for the first replicate of pH6 is obviously anomalous when in comparison to the surrounding results. I am putting this down to the sources of error within the experiment. Sources Of Error * The hydrogen peroxide could not be fully emptied from its container as each time the boiling tube was tipped, hydrogen peroxide would leak out-but re-enter when the boiling tube was returned to its upright position. ...read more.


The three-dimensional structure of an enzyme has many different crevices, which will only allow certain substrates to join. Just like a lock and key, there must be a perfect fit between the enzyme and substrate for the reaction to occur. Once this combination occurs, the biological reaction will be able to take place at an extremely higher rate. The forces that maintain the shape of the enzyme include salt bridges, hydrogen bonds, disulphide bonds, and hydrophobic interactions. Any chemicals or temperature changes can alter these forces within the enzyme, and limit the ability of the enzyme to catalyse a reaction. pH denatures catalase enzyme as it alters the forces stated above. In this experiment, catalysis of the decomposition of hydrogen is studied with the use of a potato extract. Hydrogen peroxide is a chemical that is produced in certain human cells, and would be deadly if consumed. A catalyst, which is found in red blood cells, prevents the accumulation of this chemical. With the use of a potato extract, the biological reaction that occurs in every human body can be observed. Conclusion My hypothesis was proved correct as the results show - the graph shows a peak over the optimum pH7 and a smooth decreasing slope either side away from the optimum -which was expected. ...read more.

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