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Investigate how concentration of the enzyme catalase in celery tissue alters the rate of reaction with hydrogen peroxide.

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Problem: Investigate how concentration of the enzyme catalase in celery tissue alters the rate of reaction with hydrogen peroxide. An enzyme, a biological catalyst, accelerates a chemical reaction, without changing the reaction's outcome and can be recovered from amongst the end products. For just about every reaction in a living organism there is an enzyme to catalyse it. For a chemical reaction to occur two conditions must be satisfied: the reacting molecules collide at the correct orientation to each other; and the second is that the reactants contain enough energy to bring about the breakage of appropriate chemical bonds. The energy can come from heat energy but the temperature needed is hard to obtain and maintain in an organism and is harmful to cells, amongst other things. In addition to raising the temperature, the rate of reaction can be altered by increasing the pressure, the presence of a catalyst, the concentration of reactants and the surface area across which the reaction occurs, although these factors may not apply to all reactions. This energy, required by the substrate to react and form an end-product, is called the activation energy. The diagram below shows how activation energy is changed by an enzyme-induced reaction. Fig 1.1 Activation Energy and Enzyme-catalysis, influence of. An enzyme decreases the activation energy and therefore rate of reaction increases, because molecules now have energy greater than, or can easily acquire enough energy to reach, the new activation energy. An enzyme must combine with a substrate for it to catalyse the reaction. By certain analytical techniques, we can see that an enzyme is a globular protein molecule, which has a specific tertiary structure and shape. A protein molecule is made of polypeptides which is a series of amino acids linked together by peptide bonds. A protein molecule can consist of one polypeptide, linear chain, or several chains making a globular structure, maintained by Van der Waal's forces (between all molecules) ...read more.


50 6.5 11.6 14.5 None Achieved - 25 4.6 5.8 6.3 None Achieved - 0 2.6 2.6 2.6 None Achieved - None Achieved indicates that the experiment was not repeated in order to get another set of results to calculate averages of my data. An example of the use of a Statistical Technique Below I have utilised standard deviation to obtain a graph of the class results, minimising the anomalies, which would otherwise affect the shape of the line graph and have plagued mine. Standard deviation is a measure of how widely values are dispersed from the average value (the mean). Equation for Standard Deviation: Already I have used Microsoft(r) Excel to create a spreadsheet of the data and a graph. Furthermore, the spreadsheet program has the capability to calculate the standard deviation of a set of data, so that one doesn't have to go through the lengthy calculation process required for such a huge set of data. After calculating the standard deviation and average of each column of data for each minute, and thus each concentration, I will use the data to evaluate whose data is best to use in a graph "The Average Rate of Reaction between Hydrogen Peroxide and Catalase for the class". As my graph showed that there were some anomalous results, the use of the class results will help me to come to a logical conclusion, hopefully reflecting my results in some way. This table is similar to the table shown two pages back; it includes everybody's results, but no repeat results obtained by anyone have been replicated here. Nobody obtained a complete set of replicate results, so including them would change the value of some deviation/average values, disrupting any pattern I hope to observe. This table, and the next two, shows the standard deviation calculated for each column of results for the volume of oxygen collected (cm3) and also the average volume of oxygen collected. ...read more.


After looking at my own results and plotting them on a graph, I became aware of the inadequacies of the data I had. To counter this I used the class' data and standard deviation and average/mean calculations, to create a graph which would have less anomalous results. I used a combination of these to analyse the data to find out what had happened, and I tried to estimate what should have happened as I had anomalous results. The 'Class Average Graph' did have some slightly linear lines but still they had a slight curvature, indicating a slow down in reaction velocity over the three minutes. The processing of the results was in no way biased in order to show the reaction slowed down, for example, the standard deviation was added and subtracted from the mean. Even though my data was error-ridden, it did show a similar pattern. Certain factors will have a greater effect on the validity of the conclusion I made earlier on, but these are not major sources of error repeated over time that could have totally changed the outcome of the experiment. The amount of sunlight would remain relatively unchanged, bubbles would have a very minimal effect on the rate of reaction and the liquidising of the celery extract would certainly not have a major impact on the experiment (unless something was obviously wrong it). Although, the temperature of the samples and transfer of solutions remain as dubious aspects of this experiment and I would have liked to use a thermostatically controlled water bath and a different strategy for the latter. The temperature could account for the drop in rate of reaction after an initial rate of reaction: the temperature of the reactants increased as the reaction progressed changing the rate of reaction. A different strategy for the transfer of solutions would include modifying the equipment, or finding new equipment; the limitation of the apparatus can hinder the effectiveness of the strategy, or the strategy needs to be modified using suggestions made earlier. ...read more.

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