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Introduction

Investigation into the initial rate of hydrogen peroxide decomposition when the enzyme catalase is used. When Hydrogen Peroxide is broken down there are two products, Oxygen and water. However, the breakdown of Hydrogen Peroxide requires the enzyme catalase which catalyses the reaction. Catalase is found in microbodies and in this experiment the source of catalase is yeast. The formula for the decomposition of Hydrogen peroxide is: (Catalase) H2O --> H2O + O2 The reaction is an anaerobic one, meaning it happens in the absence of oxygen. To measure the rate of the enzyme reaction I will collect the oxygen produced in the reaction over a two-minute period. Also, I will vary the concentration of the hydrogen peroxide each time. So my experiment will look at how the concentration of H2O2 affects the speed of an enzyme controlled reaction. Enzymes, such as catalase, are used to speed up a specific reaction. Each enzyme has an active site in which the break down of the substrate occurs. However, each enzyme's active site is shaped to fit one type of substrate and is said to be specific to the substrate. The specificity of an enzyme to its substrate is known as the 'Lock and Key' theory. Enzymes are globular proteins made up of amino acids and s in any globular protein; there are four types of bonding that give the protein its three-dimensional structure. The four types of bond are disulphide bond, hydrogen bond, ionic bond and hydrophobic interactions. When it has been shaped the amino acids that make up the enzyme's active site and called catalytic amino acids. The aim of this investigation is to find out how substrate concentration will affect the initial rate of reaction. Substrate concentration is an independent variable while the rate of reaction is a dependent variable. An independent variable is a variable that the values have already been chosen for, while the dependent variable is the result or measurement taken that would relies upon the value of the independent variable. ...read more.

Middle

If H2O2 is spilled then it should be covered with a mineral absorbent and then diluted with water. My results are as follows: O2 Collected (cm3) H2O2 (ml) H2O (ml) Time (sec) 1st 2nd 3rd Average 1 4 10 7 6 5 6 1 4 20 8 7 6 7 1 4 30 8 8 8 8 1 4 40 9 9 8 8.7 1 4 50 9 9 9 9 1 4 60 9 10 9 9.3 1 4 70 9 10 9 9.3 1 4 80 9 10 10 9.7 1 4 90 9 10 10 9.7 1 4 100 9 10 11 10 1 4 110 9 11 11 10.3 1 4 120 9 11 11 10.3 O2 Collected (cm3) H2O2 (ml) H2O (ml) Time (sec) 1st 2nd 3rd Average 2 3 10 4 7 12 7.7 2 3 20 4 9 16 9.7 2 3 30 8 11 18 12.3 2 3 40 9 14 20 14.3 2 3 50 12 17 24 17.7 2 3 60 15 22 28 21.7 2 3 70 19 26 33 26 2 3 80 22 28 36 28.7 2 3 90 25 31 40 32 2 3 100 27 33 43 34.3 2 3 110 28 35 46 36.3 2 3 120 29 36 47 37.3 O2 Collected (cm3) H2O2 (ml) H2O (ml) Time (sec) 1st 2nd 3rd Average 3 2 10 8 11 12 10.3 3 2 20 11 14 15 13.3 3 2 30 13 16 18 15.7 3 2 40 15 18 19 17.3 3 2 50 16 19 21 18.7 3 2 60 17 20 22 19.7 3 2 70 18 21 23 20.7 3 2 80 22 22 24 22.7 3 2 90 27 23 25 25 3 2 100 33 23 26 27.3 3 2 110 35 24 27 28.7 3 2 120 37 25 27 29.7 O2 Collected (cm3) ...read more.

Conclusion

Another reason why my results are unreliable is that the surface area was not the same each time. If the yeast in one experiment had a much higher surface area then it was going to have a much faster initial rate of reaction than an experiment where yeast had a small surface area. This is likely to be why my 2ml H2O2 experiment came out higher than my 3ml and 4ml H2O2 experiments On my graphs I have circled what I think are anomalous results. My first anomalies occur on my 2ml H2O2 graph. Between 40seconds and 60seconds the O2 collected is 14.3cm3, 17.7cm3 and 21.7cm3. I think that, although the graph on the whole is unreliable, these are anomalous because they do not fit the best-fit curve. On the 3ml H2O2 graphs I have circled two points as these points dip below the best fit curve and then back up again. At 70seconds and 80seconds the O2 collected is 20.7cm3 and 22.7cm3. A possible reason for this could have been that the tube might have been blocked, maybe by the way that the measuring cylinder was held. It might have been different if the measuring cylinder was clamped so it couldn't move and therefore couldn't squash the tube. By holding the measuring cylinder it was possible that it may have been pressed down on the tube briefly. This would of held the O2 in the tube and then when it was released the O2 would have all come out at once, resulting in the points moving back to the best-fit line. On the 5ml H2O2 graph I have circled one point. This point is after 30seconds and misses the best-fit curve by about 4cm3; it has 30cm3 whereas the curve crosses 30seconds at 34cm3. The reason for this anomaly could have been the same as above or possible because of a reading inaccuracy. Also, when holding the measuring cylinder, it was not always held perfectly upright, and therefore could have given a false reading but this is likely to have been the same throughout the experiment. ...read more.

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