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Investigating how varying the concentration of substrate (hydrogen peroxide) affects the rate of reaction with the enzyme catalase.

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Introduction

AS Level Biology Coursework Investigating how varying the concentration of substrate (hydrogen peroxide) affects the rate of reaction with the enzyme catalase. * Abstract of experiment I carried out the following experiment to investigate how varying the concentrations of hydrogen peroxide affects the rate of reaction with catalase in the form celery. I tested the rate of reaction at 5 different concentrations of hydrogen peroxide and found that the higher the concentration the faster the rate of reaction goes. The following write up explains my experiment in detail: * Aim In this experiment I want to look at how the concentration of hydrogen peroxide affects the rate of reaction with catalase. Here hydrogen peroxide is the substrate and catalase is the enzyme. * Introduction REFERENCES: Biology 1 Advanced Sciences http://gened.emc.maricopa.edu/bio/bio181/BioBk/BioBookEnzym.html. Enzymes are protein molecules that can be called biological catalysts. A catalyst is a molecule that speeds up a chemical reaction, the catalyst will remain unchanged at the end of the reaction. Metabolic reactions that occur in living organisms are catalysed by enzymes. Enzymes are globular proteins. The molecules are coiled into a precise three-dimensional shape, with hydrophilic R-groups on the outside of the molecules ensuring that they are soluble. The enzyme I will use in this experiment is catalase, it is found in food such as potato, celery and liver. Catalase works to remove hydrogen peroxide from cells. Catalase increases the speed of reaction that decomposes hydrogen peroxide and produces water and oxygen. Formula: Catalase Hydrogen peroxide Water + Oxygen 2H2O2 2H2O O2 The way catalase works to decompose hydrogen peroxide can be explained by the lock and key theory, like all enzymes, catalase has an active site. The active site of an enzyme is an area to which another molecule can bind. This molecule is called the substrate. It has a lock and key structure because the active site's shape allows the substrate to fit perfectly. ...read more.

Middle

At this point I needed to consider whether the amount of juice produced when the celery is mashed would affect the reaction rate. I found it difficult to measure the amount of juice the celery produced so to keep the experiment fair I will only use the solid mush not the juice. As my aim is to investigate how the concentration of substrate affects the rate of reaction I needed to chose the different concentrations of hydrogen peroxide that I would test. I carried out my preliminary experiment at different concentrations and have decided to use five concentrations of hydrogen peroxide. This will give me a wide range of results. I will use concentrations of 100%, 70%, 40%, 10% and 0%. In each case I will use distilled water to dilute the hydrogen peroxide. My 0% will be the control, it will be 5ml of distilled water. I am not expecting to see a reaction here. See table below to see amounts of hydrogen peroxide and distilled water to be used: Amount of hydrogen Amount of distilled peroxide (ml) water (ml) 100% 5 0 70% 3.5 1.5 40% 2 3 10% 0.5 4.5 0% 0 5 I will also carry out the experiment with 100% hydrogen peroxide on celery that has been in boiling water to see if that affects the rate of reaction. Here I would expect to see no reaction, as the celery would have been denatured by temperature. Another consideration I have taken into account is whether to use fresh celery each time or if it was all right to use frozen celery. I thought maybe freezing the celery would denature the enzymes but when I tested this, frozen celery produced a reaction, so I have decided to use the frozen celery and defrost it. This means I won't have to worry about getting fresh celery. After carrying out my preliminary experiment I have decided to do my experiment as follows: * Plan I will first set up the apparatus (listed before) ...read more.

Conclusion

Also the readings could be affected by my speed of reaction of reading off the measuring cylinder. > The precision of measuring the amounts of hydrogen peroxide, celery and water I used each time could have also affected my results, as it was difficult to be completely accurate. To make the measurements more accurate I could have used pipettes rather than pouring the hydrogen peroxide and water. I could also improve this experiment in the following ways: If I had the time I would do more repeats at each of the concentrations of hydrogen peroxide. This would make the average I took more accurate as it would mean errors, which could have been made in one experiment, would not affect the over all result so much. To improve the accuracy of reading the amount of oxygen given off at timed intervals, I could ask someone to start and stop the stop-clock and call out time intervals while I recorded the amount of oxygen given off at each time interval. This would mean my readings might be more accurate. Also to improve this experiment I should extend it to include more time intervals. I think if I had continued to take readings every 10 seconds for another minute it would have produced a better graph as my curve would have flattened off more as the solution became saturated. I could repeat this experiment for more concentrations of hydrogen peroxide so I could have more rates of reaction to compare. This would make my results more reliable. I conclude that my final conclusion is valid because the evidence shows that my prediction was correct. This is seen in my results, on the graph it shows that the 100% concentration of hydrogen peroxide has the fastest rate of reaction. I feel that any uncertainties play little affect in making my conclusion any less valid as they can be justified by the inaccuracies I stated at the start of this evaluation. December 2001 Elanor Parsons 1 1 ...read more.

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