Liver and Hydrogen Peroxide experiment
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Liver and Hydrogen Peroxide experiment Aim: To see how different concentrations of hydrogen peroxide affects the enzyme activity and rate of reaction. Hypothesis: I believe that when the concentration of the substrate (hydrogen peroxide) increases this will cause the rate of reaction to increase. I believe this because enzyme activity and substrate concentration affect the rate of reaction. As the concentration of enzymes increase so does the number of active sites. If there is excess substrates present. This will then cause the rate of reaction to increase in the proportion of excess substrate molecules and enzymes. The rate of reaction depends on the rate of formation of enzyme - substrate complexes. As the substrate concentration increases the rate of reaction will increase until all enzyme molecules are being used up. After this point it doesn't matter how much more substrate you add the rate of reaction will not increase anymore as the enzymes are working as fast as they can to break down the substrate. The rate reaches maximum velocity and remains constant. Basically with the highest concentration the enzymes will be able to collide with more substrate molecules. Here are 2 graphs to show the increase of rate of reaction as enzyme and substrate concentration increase.
Next the liver will be placed in the pestle with some sand. Using the mortar I will grind the liver into smaller pieces. After this the liver will be transferred into a test tube. This will then be put into a test tube rack. After I will then make my 6 concentrations. I will start off with my highest concentration which is 10% Hydrogen peroxide (10 Cm3). To make the other concentrations for instance my lowest add 5 Cm3 of hydrogen peroxide and the 5 Cm3 of water etc. Using the syringe I will collect my first concentration which will be the 10cm3 hydrogen peroxide (Highest). After the syringe will be placed onto the bung. The hydrogen peroxide can be inserted into the test tube with the liver when ready. The liver needs to be at the bottom of the test tube. If not liver may be left un-reacted therefore it will not be a very precise test. An effected way is to use tweezers when placing the liver in the test tube. Next place the bung on top off the test tube. Make sure rubber tube is connected to the bung and gas syringe. After keep stop watch ready in one hand and then insert hydrogen peroxide from the syringe into the test tube.
The anomalous results could have been down to the equipment not being cleaned properly after each experiment. The equipment may have contained extra catalase therefore this will increase the number of active site for the enzymes causing the hydrogen peroxide being broken down quicker. Another factor was that the room temperature rose as the day went on. It was cool in the morning and then got hotter. Temperature affects the enzymes and substrate by causing the molecules to move faster. This causes the molecules to collide more often. And therefore the rate of reaction was increased. This could be used to explain why the time for the lower concentrations was so small a measurement. Surface area of the liver could have been a factor. The liver was not cut up equally so there for the larger the surface area the molecules have a bigger surface to work on. More useful collisions are made. This could have also been down to human error where measurements were inaccurate. For instance the concentration of the hydrogen peroxide was measured wrong. Also equipment was not cleaned properly. Considerations when doing the experiment again: If I was to do the experiment again I would make sure that the equipment was cleaned properly. Also measurements are taken more accurately and precisely. I will have to make sure the temperature is constant throughout the whole experiment. ?? ?? ?? ??
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Here's what a teacher thought of this essay
Overall, the investigation is based on sound biochemistry and the author demonstrates at least a partial understanding of the factors affecting reaction rates in living organisms. The interaction of substrate and enzyme concentration needed clarification at the start.
Substrate concentration was not calculated at any stage, a surprising omission.
The DV was not specifically addressed in the report and readers will be a little confused by this.
The data collected was not wholly accurate or reproduceable, almost certainly due to the preparation of the liver.
A fair effort overall, but with a number of key weaknesses that would certainly undermine the overall grade.
Marked by teacher Ross Robertson 01/03/2013
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