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An investigation into the effect of Hydrogen Peroxide concentration on Yeast Catalyse activity

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Introduction

AS-Level Biology Coursework An investigation into the effect of Hydrogen Peroxide concentration on Yeast Catalyse activity Introduction Hydrogen Peroxide (H202) is a by-product of several different metabolic reactions within cells. It is a free radical, and as such can oxidise biological molecules, therefore damaging or killing the cell which produced it. To protect themselves, cells synthesise from amino acids Catalase, an enzyme which catalyses the decomposition of Hydrogen Peroxide into water and oxygen. H202 --> 2H20 + 02 Catalase lowers the activation energy required for this reaction to take place, thus speeding up the rate at which H2O2 is converted to water and oxygen. It does this by having specific active sites; places on the molecule shaped in a way that fits the shape of Hydrogen Peroxide molecules, encouraging them to bind to the enzyme there. This forms an enzyme-substrate complex. Catalase like all enzymes is a globular protein, but as well as its polypeptide chains, Catalase contains a prosthetic group, haem (also found in Haemoglobin). The Iron atom in the haem group facilitates the breaking of the bonds between atoms in the H2O2 molecules, bound to the active sites of the Catalase. The shape of the overall enzyme-substrate complex encourages this, and the release of the substrate atoms as 2 molecules of water and 1 of oxygen. ...read more.

Middle

4. After 20s, I will remove the bung from the test tube, and record the amount of gas in the cylinder. My measurement of the amount of oxygen released over the incubation time will come from the subtraction of the initial amount of gas from the final amount. 5. I will repeat steps 2 through 4, three times for each of the concentrations of H2O2. 6. To achieve concentrations of 16, 8, 4, and 2moldm-3 is simply a matter of adding water to the previous higher concentration in a proportion of 1:1 therefore halving it's concentration. To get 28moldm-3 I will add 14ml of water to 100ml of 32moldm-3, because... H2O2 is toxic and caustic, and therefore must be handled with care - it is also colourless so I will label the beaker to ensure it's not confused with water. Sources of error I decided to use the inverted cylinder method for measuring the oxygen produced because I think it would provide more reliable and accurate results than the gas syringe method. This is because the gas syringes require a certain amount of pressure to build up before the plunger will move which may effect the accuracy of readings at lower concentrations which I expect will produce little oxygen. ...read more.

Conclusion

To account for this possible weakening of the yeast solution, one would have to repeat the whole investigation, but instead of using one batch of premixed yeast solution for all the experiments, an amount of yeast solution would have to be mixed (from inert dry yeast) just before each trial. This would mean each batch of yeast used would have been in solution for the same amount of time, reducing the suspected error arising from the effective yeast Catalase concentration diminishing over time. Another possible reason for the error could be a mistake in mixing the H2O2 solution. The difference in average measurements between those for 16moldm-3 and 28moldm-3 is only 1 ml, with the measurement of 26 ml of O2 being seen at both concentrations. To determine if this is in fact the reason I would merely have to repeat the experiment for the 28moldm-3 concentration. The anomalous result is very significant in terms of the conclusions that can be drawn. Without further experimentation it is impossible to say for definite whether the result for 32moldm-3 is wrong and conclude Vmax was in fact reached at lower concentrations, (around 28moldm-3), or whether the result at 28moldm-3 is wrong and concentrations up to 32moldm-3 of H2O2 can be decomposed per second by Catalase. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

****
The introduction to this report gave a good summary of the scientific theory needed for this investigation.
The report would have benefited from a clear hypothesis so that the conclusion could have been more certain as to whether the hypothesis had been proved / disproved.
The data collection and recording are excellent.
The analysis focused too much on a potential anomalous result instead of looking at the rest of the data and offering more analysis, but was still good.

Marked by teacher Jon Borrell 18/07/2013

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