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Investigate how the concentration of the substrate hydrogen peroxide (H2O2) affects the rate of reaction of the enzyme catalase in yeast cells.

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Introduction Enzymes were discovered be Edward Buncher towards the 19th century. Enzymes such as catalase are globular protein molecules found in all living cells. They are biological catalysts, which are used to speed up a reaction rate within the cell. They reduce the level of activation energy needed in a reaction, increasing the rate of reaction by doing that. The higher the activation energy, the slower the reaction is going to be. Figure 1, below shows the amount of activation energy needed with and without an enzyme. Figure 1: The activation energy of a reaction is smaller than in the presence of an enzyme Enzyme-substrate complex An area on the surface of an enzyme is known as the active site. The substance that the enzyme acts on is called the substrate. The substrate fits into the active site (shapes fit together); therefore their shapes are complimentary to each other. Each enzyme has a different active site; making enzymes specific, because only a substrate with a complimentary shape to the active site will fit. When enzymes denature, the bonds that are holding the active site together start to break making the shape of the active site no longer complimentary to the substrate's shape. The denaturing of enzymes means that the tertiary structure of the polypeptide chain has changed and caused a change in its three dimensional shape. The 'Lock and Key' hypothesis states that the enzyme is like a lock and the substrate like a key; so to lock or unlock something you will have to have the exact lock and the exact key or else you would not be able to do anything with either the key or the lock. This is exactly how the enzyme-substrate complex works. Figure 2 shows how the enzyme breaks a large molecule into a smaller molecule. The same enzyme will also catalyse the reverse reaction; it will then join the smaller molecules together again to form larger molecules. ...read more.


Variables The independent variable will be the substrate (hydrogen peroxide), as its volume will change throughout every test, because different concentration will be used. I will use 10cm3 of hydrogen peroxide for every test, as I believe that it is the best measurement that could be used in this investigation. 5cm3 will not produce reliable results as it could be not good enough for producing enough amount of oxygen. The dependent variable will be the total amount of oxygen produced, as it cannot be changed. The concentrations to be used are: 5%, 7.5%, 10%, 12.5%, 15%, 17.5% and 20%. The range will be 2.5 in between each concentration. Each result will be repeated 3 times, this is to make sure that the results of each test is as accurate as possible and that the test was fair. The variables which will have to be kept constant throughout the experiment are: * Temperature * pH * The substrate concentration * The volume of substrate added The reason why I choose these variables to be controlled is because they are what will affect my experiment's results the most. In my method I will explain how I will be controlling them. Fair testing A good range (2.5) in between the hydrogen peroxide was used. The same volume of the yeast solutions will also be used. Equipments which need to be washed will be washed with distilled water between each test; this is to make sure that everything is decontaminated. The temperature (25�C) will be controlled throughout the experiment. Each experiment should be allowed to proceed its maximum time (5 minutes), and each concentration will be repeated three times (ensuring that valid and accurate data are collected). Equipments The equipments to be used during the experiment are: * Goggles * Clamps * Syringe * Burette * Conical flask * Measuring cylinder * Thermometer * Beaker * Bung * Water bath set at 25�C * Stop clock Diagram of apparatus The diagram below shows how the apparatus looks like when it is used during the experiment. ...read more.


Hereby more enzyme-substrate complex can be formed. The increased rate of reaction will mean that more oxygen is formed. This increase in productivity of oxygen will form more oxygen filled bubbles. Each concentration rose on the first graph, but the second graph had three anomalous results. Collision theory states that effective collisions between reactant molecules must occur in order for the reaction to occur. Particles must collide successfully in order for the rate of the reaction to increase. This proves that my prediction was right. The rate of 12.5% concentration was higher than that of 7.5 %. The same prediction went for all my results for the first graph. Evaluation Possible errors that could have risen with my experiment is that the fact that the experiment was carried out over two lessons. We did not receive the actual set, but an identical one instead; therefore results could have been affected. The syringe in the second set did not insert all hydrogen peroxide into the conical flask, remains of hydrogen peroxide remained in the syringe thereby catalase did not break down as much hydrogen peroxide as it could have. This also means that not the same volume for each concentration was used throughout the experiment. The temperature of yeast also decreased during the reaction, it was a variable, which I could not control. The data obtained could have been affected by these possible errors. If I were to do the experiment again, I would improve it by carrying out the experiment in one go and by using the same syringe throughout the experiment, and also by using a water bath (at 25�C) to put the conical flask in so that the temperature of the yeast cells and the hydrogen peroxide remains the same, in order that the reaction's results are not affected. I will also make sure that everything is airtight so that no oxygen bubbles are formed before the start of the reaction. ...read more.

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