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Investigating How the Concentration of the Enzyme Catalase in Celery Tissue Alters the Rate of Reaction with Hydrogen Peroxide.

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AS INTERNAL ASSESSMENT Investigating How the Concentration of the Enzyme Catalase in Celery Tissue Alters the Rate of Reaction with Hydrogen Peroxide. I am going to investigate how the concentration of an enzyme (the enzyme catalase) affects the rate of reaction it is involved in. To investigate this problem, a knowledge of enzymes and more specifically the enzyme catalase (or peroxidase) is required. Enzymes are described as biological catalysts. Like any catalyst, enzymes help to speed up chemical reactions without actually being altered by the reaction. If you wrote down the equation of an enzyme or indeed any catalyst-controlled reaction the molecules in the enzyme would not appear as part of the equation, but are written above the line indicating the direction of reaction. This means that enzymes help to speed up reactions, which occur naturally but very slowly and can be used time and time again as they are not altered by the reactions they take place in. For this reason, they are very useful in living organisms. Enzymes help to speed up a reaction by lowering its activation energy. This is the energy required to break or form the bonds of a substrate to change it into the product of the reaction. Normally the activation energy of a reaction is too high for the reaction to take place without fairly high amounts of energy input. However enzymes lower this energy so that when the products are heated up (by relatively high body temperatures) they are given enough energy to change into the substrate of the reaction. The structure of an enzyme allows it to temporarily hold a substrate (by temporarily bonding with it) in such a way that the substrate can react more easily and form the reaction's products. Enzymes are globular proteins (ones with an obvious 'ball' shape), which possess a cleft, or depression to which another molecule can bind at a position called the active site. ...read more.


Both the enzyme and substrate will be in a liquid solution meaning that they can move about relatively freely. The more these molecules move about the greater the chance that the substrate will bump into the enzyme's active site and thus the greater the chance that the enzyme will catalyse the break down of the substrate. This means that an increase in temperature will result in an increase in the rate of reaction. However, if the temperature increases a lot, the enzyme may become damaged. This is because the enzyme is moving about so quickly that some of the bonds (particularly the ones between the hydrogen atoms of the amino acids) begin to break. This can alter the shape of the enzyme and more importantly its active site, meaning that the substrate can no longer bind to it and be catalysed. Thus the rate of reaction rapidly decreases. In our experiment, it will be very difficult to control the temperature of the substrate and enzyme. However, if the experiment is carried out in similar conditions, the temperatures are unlikely to change significantly. By using a thermometer, we can measure the temperature throughout and thus take this into account when drawing conclusions. The temperature could be controlled by placing the apparatus in a water bath and adding hot of cold water accordingly, or using an electronically controlled water bath. This would be the fairest way to conduct the experiment. However this would be very difficult to do, as the apparatus is very large. Also as the temperatures are likely to stay very similar (as the experiments are carried out in similar conditions) the temperature can simply be measured and any fluctuations taken into account when drawing up conclusions. * PH LEVEL- The pH of the conditions an enzyme is in can also affect its rate of reaction. pH is a measure of the acidity of a substance but is also a measure of concentration of hydrogen ions. ...read more.


Hopefully the results should be repeated at least 3 times so that 3 values for each concentration are obtained. * The pH of the solution can be taken once and the temperature recorded so that these two factors can be taken into account when drawing conclusions. Volume of celery extract (ml) Volume of distilled water (ml) % Concentration 0 10 0 1 9 10 2 8 20 3 7 30 4 6 40 5 5 50 6 4 60 7 3 70 8 2 80 9 1 90 10 0 100 Table to show concentration values for celery solution and their respective volumes of celery extract and distilled water. In the interest of safety the experiment must be carried out in a careful manner. Hydrogen peroxide is a flammable substance but will not come into contact with any flames throughout the experiment. It is also a very powerful bleach and so should be kept away from the hair, eyes, skin and clothes. The enzyme may also be an irritant to the skin or eyes. If spillage occurs your hands must be washed immediately at the nearest sink and safety goggles must be worn. When using glassware, especially the brittle collecting tubes we must be careful. When tabulating the results, volumes of celery extract and water as well as their respective percentage concentrations must be present along with the volumes of oxygen collected in a table. The temperatures, pH, total volumes of solution as well as the concentration and volume of hydrogen peroxide used must be noted. Averages of volumes of oxygen collected must be calculated and recorded. The rates of reaction for these averages must also be calculated and recorded on the table. When plotting a graph of results, firstly amount of oxygen produced can be plotted against concentration, to give an overview of the course of each reaction. On this graph, the steepest part of the graph is the initial rate of reaction. Then rate of reaction can be plotted against concentration. For the graph, all 5 experiments should be plotted on the same graph so that comparisons can easily be made. ...read more.

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