Enzyme Lab Report - Notes PDF

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Monday, March 25, 2019 SBI4U3 Investigating the Rate of Hydrogen Peroxide Decomposition by the Enzyme Catalase Obtained from Yeast at Various Concentrations of Hydrogen Peroxide Introduction This experiment was done to understand the effect of hydrogen peroxide concentration (H2O2) on the rate of decomposition of H2O2 into oxygen and water when using catalase. The enzyme catalase was obtained from yeast. A filter paper disk saturated with yeast was placed in H2O2. After the decomposition reaction, the oxygen produced on the disk rose it to the top of the solution. It is expected that with higher H2O2 concentrations, the decomposition reaction would occur faster. This results from the greater number of H2O2 molecules leading to a greater number of collisions with the catalase per unit of time. Materials and Methods A hole puncher was used to make small disks from filter paper. A small plastic cup was filled with a room temperature yeast solution of 20 g/L (2% yeast). A different small plastic cup was filled with room temperature 3% H2O2 to a height of 1.5 centimetres. Forceps were used to submerge a filter paper disk in the yeast solution for fifteen seconds. The filter paper disk was then taken out of the solution and patted dry on the paper towel for one second. After it was moderately dried, the filter paper disk was placed at the bottom of the H2O2 cup for one second before being released. The elapsed time from when the filter paper disk exited the yeast solution to when it entered the H2O2 was two seconds. The time between the filter paper disk entering the H2O2 to when the filter paper disk rose to the surface of the H2O2 solution was measured and recorded in a raw data table. This procedure was performed ten times, and the cup of H2O2 was replaced after every 4 trials to avoid the effect of catalase build up in the solution on successive trials. The process of submerging the filter paper disks in a 20 g/L yeast solution, drying and placing them at the bottom of an H2O2 cup was repeated with the following various H2O2 concentrations: 2.5%, 2%, and 1.5%. 10 trials were done for each concentration. Discussion Data & Trend Analysis The trendline in Figure 1 below is polynomial of degree 2. Based on this trendline, as concentration of H2O2 increases, the average time it takes for the filter paper disk to reach the surface of the H2O2 solution decreases. With reference to the proximity of the data points to the trendline in Figure 1, there are no anomalies in the data. The data collected and general trend supports the expectations for the results of the experiments. Increasing the concentration of the substrate, H2O2, increases the amount of substrate available to react. This increases the chances of H2O2 binding to the active sites of catalase, the enzyme. The speed at which the substrate binds to the enzyme therefore increases, allowing the enzyme to catalyze more reactions at a time. This decreases the rate of reaction and causes the filter paper disk to rise faster.

Figure 1 Average rise time of 10 trials of filter paper disks due to decomposition of hydrogen peroxide sped up by catalase. Disks were placed in 2% yeast, dried for 1 second, then placed in varying concentrations of hydrogen peroxide at 1.5%, 2%, 2.5% and 3% with solution heights of 1.5 centimetres. Error bars show standard deviation for the 10 trials at each of the corresponding concentrations. Error Analysis The variation in the data was most likely due to varying amounts of yeast on the disk for each trial and inconsistent temperatures of H2O2 solution. Varying amounts of yeast on each disk were due to inconsistent sizes of paper disks created by the hole puncher. The amount of yeast also differed due to the nature of random movement of molecules, meaning different numbers of yeast molecules were absorbed by each disk. This affected the number of enzymes available to catalyze the decomposition of H2O2 which increased or decreased the time taken for the disk to float to the surface. The inconsistent H2O2 solution temperatures was due to the cold tap water used to create the diluted H2O2 solutions. Since room temperature water was not provided, the use of the cold tap water to create solutions of varying concentrations affected the temperature of the solution. The 3% H2O2 positive control was room temperature. However, with lower concentrations of H2O2, more tap water was added and the colder the solution became. The colder temperatures slowed the molecules’ movement and less H2O2 collided with the yeast which slowed the rate of decomposition and increased the time taken for the filter paper disk to float. One way to reduce this source of error would be to use room temperature water that had been stored in the same room as the H2O2 for a few hours to ensure the H2O2 and the water were the same temperature and that the varying solutions of H2O2 created would also be the same temperature....