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An investigation into how the amount of oxygen is produced by changing one variable effects the decomposition of Hydrogen Peroxide in the presence of the enzyme.

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INTRODUCTION: An investigation into how the amount of oxygen is produced by changing one variable effects the decomposition of Hydrogen Peroxide in the presence of the enzyme. AIM: To investigate the affect of varying the concentration of H2O2 in a catalyse reaction of an enzyme. THEORY: Enzymes exist in all living things. They are known as Biological Catalysts as they dramatically increase the rate at which reactions occur within living organisms, without being 'used up' or effecting the reaction in any other way. In this investigation I intend to explore the one of the factors that will affect the rate of enzyme catalysis. My research from textbooks and the Internet suggests that this depends on several factors; temperature, pressure, pH and concentration of H2O2. After research and careful consideration, I have decided to first look at how a change in H2O2 concentration could affect the rate of reaction. Enzymes are proteins of a very specific shape. They work by capturing the molecules that they react with (called their "substrate"). The reaction happens and then the products of the reaction are released. The enzyme is then free to react again. Vital to this is the shape of the enzyme. It must exactly fit with the substrate like two pieces of a jigsaw puzzle. It's also often described as a "key" (the substrate) fitting into a "lock" (the enzymes active site). Hence giving the theory the name, "The Lock And Key Theory." Anything that alters the shape of the enzyme alters the shape of the active site and so the substrate cannot fit in and the enzyme no longer works. ...read more.


Where the substrate is in short supply (i.e. it is limiting) an increase in enzyme concentration has no effect. My dependant variable is going to be concentration of H202 and I will change this by combining the H202 with water (different amounts of each) to keep the total volume the same. This is important to insure a fair test. PREDICTION: I predict that the Hydrogen peroxide will breakdown to oxygen and water in the presence of Catalase. The reaction will increase with increasing concentration when molecules of hydrogen peroxide are freely available. The collision theory states simply that the more H202, the more collisions and therefore a faster rate of reaction. However, when the substrate molecules begin to out-number those of the enzyme, the collisions will decrease and so will the rate of reaction. Therefore I predict the rate of reaction will increase steadily with the higher percentage concentration of H202, although the rate will decrease slightly towards the top end of the graph due to the substrate molecules beginning to out-number the enzyme molecules. (see predicted graph) APPARATUS: * YEAST SOLUTION (10%)- This will be my source of enzyme. * H2O2 (20%)- This will be my substrate for the experiment * VARIETY OF BEACONS- to contain the water * TEST TUBES- To contain the solution and collect the end result. * SYRINGES- to insert the substrate to the yeast solution * TEST TUBE RACK- To keep the test tubes in. * STOPWATCH To time the reaction. * WATER- To collect the oxygen in in. * DELIVERY TUBE- to transport the oxygen. ...read more.


The reaction increased with the increasing concentration because molecules of hydrogen peroxide were freely available. This is shown because the graph shows that there is a steady incline and strong positive correlation until it peaks at a concentration of about 4% H2O2 where the graph begins to level out (this is where the number of H2O2 molecules are beginning to out number the yeast molecules and so the collisions in the reaction begin to decrease, thus creating the graph to slow the steep incline). EVALUATION: I experienced no anomalous results in my experiment which shows that it was done accurately and I think that all in all my experiment was fair and that my results were reliable. If I was to do the experiment again there are a few things I would do differently if the circumstances (i.e. better facilities and equipment) were different. Firstly, I would do it all in one go rather than over a period of two lessons as this may have slightly altered my results. To make the experiment more accurate I could have used a more precise way of measuring the amount of gas collected instead of just using a ruler, this would have made my results more reliable. If I could do the experiment again I would take more readings so that my results would be more reliable. My results are definitely enough to draw a firm conclusion from, that hydrogen peroxide broke down into oxygen and water in the presence of the Catalase. The reaction increased with the increasing concentration because molecules of hydrogen peroxide were freely available. To find out more about how concentration can affect a catalase reaction you could investigate the effect of changing conc. of enzyme such as yeast or potato. ...read more.

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