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Effect of Concentration of Enzyme on the Rate of Reaction

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Objective of Experiment: Hydrogen peroxide (H2O2), a very pale blue liquid which appears colorless in a dilute solution, is naturally produced as a by-product of oxygen metabolism. Aerobic organisms such as human beings use oxygen for respiration or oxidation of nutrients. During reduction of molecular oxygen to water, hydrogen peroxide is produced. Conversions of amino acids into "fuel" molecules and conversion of lipids to carbohydrates are two examples of reactions that produce hydrogen peroxide. Hydrogen peroxide is extremely toxic to living cells as it can damage DNA, protein and lipid membranes and may even be a causative factor in cancer. However, there are some human immune system cells that actually use hydrogen peroxide to kill foreign invaders. Hydrogen peroxide can decompose spontaneously into water and oxygen as shown in the chemical equation below: 2H2O2 � 2H2O + O2 However, the rate of decomposition of hydrogen peroxide itself in living cells is very slow. This can result in the accumulation of a substantially threatening amount of hydrogen peroxide in the living cells. Thus a type of protein called enzyme is used to catalyse the decomposition of hydrogen peroxide. The enzyme which is used in the decomposition of hydrogen peroxide is catalase. The chemical equation below shows the decomposition of hydrogen peroxide with catalase: 2H2O2 2H2O + O2 Enzyme is a catalytic protein that catalyses specific chemical reaction in the body. It is in the form of a globular protein molecule which has a tertiary structure. The features of enzyme include specific in the reaction it catalyses, speed up reaction, not used up in the reaction and effective in catalysing a reaction in small amount. Catalase, which is an enzyme used in the decomposition of hydrogen peroxide, can be found in animal and plant tissues, and is especially abundant in organs such as potato tubers, corms, in the fleshy parts of fruits and animal liver. ...read more.


12. The test tube was shaken gently throughout the experiment to ensure the mixture in the test tube mixed well. 13. The volume of oxygen gas evolved in the measuring cylinder was measured every 30 seconds for 4 minutes. 14. Steps 2 to 13 were repeated by using 2, 3, 4 and 5 spatulas of blended potato. 15. After that, all the measurements were recorded in a table. 16. Graphs of different catalase concentrations were plotted against time in the same graph paper. 17. The initial rate of reactions for different catalase concentrations were calculated by finding the gradient of the graphs. 18. Finally, a graph of initial rate of reaction against enzyme concentration was plotted. (280 words) Observation: Tables: Table 1 shows the different amount of potato extract used and its corresponding amount of buffer solution and hydrogen peroxide solution used. Quantity of potato extract Volume of buffer solution/ cm3 Volume of hydrogen peroxide solution/ cm3 1 spatula full 10 2.5 2 spatula full 10 2.5 3 spatula full 10 2.5 4 spatula full 10 2.5 5 spatula full 10 2.5 Table 2 shows the volume (cm�) of oxygen gas released every 30 seconds for 4 minutes for different quantity of potato extract used. Quantity of potato extract Time taken/s 30 60 90 120 150 180 210 240 Volume of oxygen gas evolved/cm� 1 spatula full 5 6 7 8 9 10 10 11 2 spatula full 6.5 10 11 13 15 17 18 19 3 spatula full 14 20.5 25.5 29 30 32 34 35 4 spatula full 17 25 34 37 39.5 41 42 44 5 spatula full 18 28.5 36 43 45 46.5 47.5 49 (163 words) Table 3 shows the concentrations of enzyme and their corresponding initial rate of reaction. Concentration of enzyme catalase/ arbitrary unit Initial rate of reaction/ cm�s-1 1 0.0333 2 0.119 3 0.198 4 0.315 5 0.413 Graphs: Six graphs are plotted. ...read more.


To improve this, the blended potato should be prepared in 1 molar solution and then been diluted to create different concentrations. Besides that, when blended potato is being transferred from spatula to test tube, some of the potato stuck at the of the spatula. This may affect the rate of reaction because less blended potato was added into the test tube thus the test tube contained less catalase to speed up the decomposition of hydrogen peroxide. h. It would also have been better to have repeated the experiment for each concentration more times to make the results more reliable and so it could be sure that the results were not obtained by chance. This may have eliminated anomaly in the results. i. Comparison of the results in this experiment was made with results of others groups of students who also conducted the experiment. The results were approximately similar to each other. All the data that obtained from the experiment had the same pattern although there were some differences. 13. There were no apparent anomaly in the results and none of the sources of error or limitations of the experiment were sufficient to cause the results unreliable. However, the sources of error and limitations in the results may have made the results slightly less accurate. 14. Further investigation could be conducted if there were more time given to investigate the rate of decomposition of hydrogen peroxide. It could be investigated how temperature, pH and substrate concentration (concentration of hydrogen peroxide) influenced the rate of decomposition of hydrogen peroxide. Conclusion: An increase in the concentration of enzyme can result in the rate of enzymatic reaction to be higher as there are more active sites provided by the enzymes for the substrate molecules to bind and form more products, given that the substrate molecules are in excess. Hence, the higher the amount or concentration of blended potato, the higher the rate of reaction between the blended potato and hydrogen peroxide at which the volume of oxygen gas evolved at a given time increases as the concentration of blended potato is increased. ...read more.

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