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To investigate the effect of catalase concentration on the rate of decomposition of hydrogen peroxide

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Introduction

´╗┐Anglo-Chinese School (Independent) Life Sciences and Biology Department Name: Natasha Lee Varella (20) Class: 5.04 Biology practical 5 Research Question To investigate the effect of catalase concentration on the rate of decomposition of hydrogen peroxide by using four different catalase concentrations varied using different number of potato discs which are 2 potato discs, 4 potato discs, 6 potato discs and 8 potato discs respectively and the air pressure measured using a Vernier data logger is used to determine the rate of decomposition. Introduction Enzymes are biological catalysts that catalyze biochemical reactions in living cells and remain chemically unchanged at the end of the reaction. In an enzyme-catalyzed reaction, the substrate binds to the active site and forms enzyme-substrate complex with the enzyme. The enzyme then breaks the bonds in the substrate. The product of the reaction then leaves the enzyme, which remains unchanged after the reaction.[1] [2]Figure 1. Free substrate colliding with a free enzyme, resulting in the catabolic reaction. Enzymes work by lowering the activation energy for a reaction, thus increasing the rate of the reaction. Thus, as the rate or enzyme concentration increases, the rate of reaction increases, assuming that enzyme concentration is a limiting factor. Due to the three-dimensional shape of the enzyme, its active site is specific and only acts on a particular substrate. In the liver, Hydrogen peroxide is a toxic by-product of fatty acid oxidation. When it is left alone, it is relatively stable and thus, each molecule of hydrogen peroxide can stay in the body for a few years. As hydrogen peroxide is active and harmful to cells and tissues of organisms, its decomposition therefore needs to be speeded up greatly in order to prevent it from intoxication in the cell. Catalase is a common enzyme found in nearly all living organisms exposed to oxygen that catalyzes the decomposition of hydrogen peroxide to water and oxygen. ...read more.

Middle

15 second intervals are used for each set of data. Air Pressure/ (± 0.01) kPa Time/s Replicate 1 Replicate 2 Replicate 3 Replicate 4 Replicate 5 0 104.21 102.79 107.43 102.34 103.26 15 104.56 102.90 109.55 102.62 103.53 30 104.85 103.07 109.55 102.90 103.69 45 105.19 103.29 109.85 103.07 103.83 60 105.30 103.29 110.03 103.18 104.10 75 105.42 103.35 110.39 103.24 104.31 90 105.48 103.69 110.70 103.35 104.59 105 105.65 103.74 110.58 103.41 104.79 120 105.82 103.74 110.45 103.69 104.98 135 105.87 103.97 110.94 103.57 105.20 150 105.99 103.80 111.12 103.52 105.37 165 106.10 103.80 111.18 103.85 105.54 180 105.99 104.08 111.06 104.02 105.66 Table 2.2 5 replicates of Experimental Data collected from the Vernier data logger with a Gas Pressure Sensor for experiment carried out using 4 potato discs. 15 second intervals are used for each set of data. ________________ Air Pressure/ (± 0.01) kPa Time/s Replicate 1 Replicate 2 Replicate 3 Replicate 4 Replicate 5 0 102.86 104.74 104.74 110.58 103.93 15 104.97 104.91 104.91 111.30 102.67 30 105.31 105.37 105.37 111.60 102.95 45 105.48 106.05 106.05 111.73 103.07 60 105.65 106.40 106.40 111.96 103.47 75 105.88 106.68 106.68 112.15 103.76 90 106.34 106.97 106.97 112.21 104.05 105 106.57 107.37 107.37 112.27 104.33 120 106.91 107.65 107.65 112.45 104.62 135 107.25 108.11 108.11 112.69 104.96 150 107.71 108.40 108.40 112.93 105.31 165 107.88 108.68 108.68 112.99 105.60 180 108.17 109.03 109.63 112.93 105.83 Table 2.3 5 replicates of Experimental Data collected from the Vernier data logger with a Gas Pressure Sensor for experiment carried out using 6 potato discs. 15 second intervals are used for each set of data. Air Pressure/ (± 0.01) kPa Time/s Replicate 1 Replicate 2 Replicate 3 Replicate 4 Replicate 5 0 104.73 102.84 104.08 103.43 101.30 15 105.71 105.14 105.88 104.52 103.75 30 106.80 105.36 107.28 105.32 104.47 45 107.43 106.06 108.46 105.94 105.19 60 107.66 106.28 109.53 106.34 105.81 75 108.18 106.63 110.32 107.20 106.40 90 107.95 106.92 111.44 107.54 106.98 105 108.47 107.20 111.84 107.88 ...read more.

Conclusion

To improve on this, an instrument of lower tolerance can be used instead and the weight of each potato disc can be measured to ensure that they contain the same number of plant cells and hence a relatively same amount of catalase. However, this limitation can never be totally gotten rid of. Thirdly, although there was an attempt to standardize the diameter and thickness of the potato discs to 8mm in diameter and 2mm in thickness, the amount of catalase present in each potato discs cannot be measured and thus, although the sizes of the potato discs are the same, they may contain different amounts of catalase as they come from different parts of the potato. Thus, it is not accurate to say that the number of potato discs placed into the test tube is proportional to the concentration of catalase used in the experiment. To improve on this, instead of using potato discs as a source of enzyme catalase, yeast can be used as a catalase substitute as the concentration of catalase present in yeast can be weighed and measured. Finally, although there was an attempt to standardize the volume of hydrogen peroxide used in each experiment, random error might have occurred due to parallax error when reading off the meniscus of the measuring cylinder when measuring out 10ml of hydrogen peroxide. The volume of hydrogen peroxide solution might have been read above or below the meniscus, resulting in the amount of hydrogen peroxide molecules to vary from experiment to experiment. The concentration of hydrogen peroxide molecules would thus be affecting the rate of decomposition as well, masking the overall results. In order to see the meniscus more clearly, a piece of paper with a red marking on it could be held up behind the measuring cylinder until the reflection of the red marking is visible on the outline of the meniscus. This method allows greater ease in reading the measurement. ...read more.

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4 star(s)

A very accomplished report on an investigation into the effect of changing enzyme concentration on the rate of reaction, using potato and hydrogen peroxide. The writer uses a data logger to record gas pressures caused by oxygen released from the reaction. The method is clearly set out and the results well tabulated. The data is thoroughly processed with both mean values and standard deviation calculated.

To gain the highest grade at A' Level, the student needs to make some improvements to the conclusion. An overall trend is identified and explained. But with so much data available, there is plenty of opportunity to analyse the effect of increasing enzyme concentration in depth. The writer does not refer to any particular data points in the graphs, and anomalies are not identified and discussed.

However, the overall quality of the essay is very good and reflects an excellent understanding of enzyme biology.

4 stars

Marked by teacher Ross Robertson 26/04/2013

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