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Enzyme Investigation.

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AS Biology Coursework Enzyme Investigation Introduction In this experiment, I will see how the substrate concentration affects the rate of reaction in the break down of hydrogen peroxide, using the enzyme catalase. Hydrogen peroxide breaks down into water and oxygen. This type of reaction, where molecules are broken down into smaller pieces is called an anabolic reaction. Background Information In this experiment, catalase will be used to break down hydrogen peroxide into water and oxygen. Catalase is an enzyme, which is found in every cell in the body. It is a very fast acting enzyme, because it is needed to break down hydrogen peroxide as quickly as possible. 2H2O2 2H2O + O2 Enzymes are a special group of proteins that act as biological catalysts. They are made of proteins, which are made up by amino acids. They speed up the rate of reactions in biochemical reactions (Mr. Nias' notes). Without enzymes, these biochemical reactions in living cells would either not take place or take place too slowly to sustain life. Energy is required to make reactions happen. This energy is called activation energy. When enzymes are used in a reaction, the activation energy barrier is lowered and the reaction is able to take place more easily because the enzyme attaches itself to the substrate molecule. Enzyme molecules are larger than the substrate molecules. A part of the enzyme is called the active site; this is where the bond formation or destruction takes place. The 'lock and key' hypothesis suggests that the active site and substrate molecule shapes compliment each other, so they fit together. E.g. Bond Destruction Enzyme Substrate Products Active Site Enzyme-Substrate Complex This reaction is reversible. The 'induced fit' hypothesis suggests that the shape of the active site changes according to the shape of the substrate molecule. After the reaction, the active site returns back to its original shape. E.g. Bond Destruction Enzyme Substrate Products Active Site Enzyme-Substrate Complex Active site has changed shape The 'lock and key' hypothesis explains how specificity applies to enzymes. ...read more.


* At 60 seconds, read off the gas burette the amount of oxygen that has been collected and stop the experiment. * Repeat this for all 5 concentrations, 3 times each, so that the results obtained are reliable. Risk Assessment Throughout the experiment, safety glasses will be worn and care will be taken with the hydrogen peroxide to minimise skin contact with the solution for myself and others. This is because hydrogen peroxide is harmful. The carrot will be grated carefully and not cut into pieces with a knife so that the risk of cut fingers is prevented. Justification for Materials Used I decided to use the gas burette in my experiment as it gave a more accurate and precise reading that using a gas syringe would have given. It would also give more reliable results than counting bubbles would have. I decided not to use a manometer because the gas burette gave accurate readings of oxygen collected, therefore it gave accurate results. Also it was easier to use than a manometer. I used a syringe to measure out the volume of hydrogen peroxide instead of a beaker. This is so that the volume used was accurately measured. Also only a small amount of hydrogen peroxide was needed in the test, so measuring 20mm3 was easier in a syringe than in would have been in a beaker. The electric weighing scales were used to measure out the grated carrots accurately. This was accurate as the scales gave a mass reading of up to 2 decimal places. The mass of grated carrot used was 5g because I thought that this mass would be enough for the experiment, as only 20mm3 of hydrogen peroxide was going to be used. The grater was used to ensure that the surface area of the carrot was kept the same throughout the whole of the experiment. This was to make sure the test was fair each time the carrots were used. ...read more.


This is because I did do three repetitions of my experiment. They all had similar results. Also I did not have any anomalous results, therefore I think my experiment went well and my results are reliable. Limitations and Technique In my experiment, I had been limited with time. If I did have more time, I would have done each experiment slower and this may have reduced the sources of error. This would have made my results more accurate and reliable. My method of measuring the amount of oxygen produced in the break down of hydrogen peroxide could have been better. This is because I had to insert the hydrogen peroxide in the test tube, start the stop watch, and seal the test tube with the rubber bung and delivery tubes all at the same time and this could have led to some error. Improvement I would improve my experiment by using more care in accurately measure out the carrot and hydrogen peroxide, therefore the sources of error would be reduced. Also I would remove the rubber bung from the test tube when it had been 60 seconds after the experiment had begun. This is so that even when the reaction is going on, no more oxygen can be collected in the gas burette, therefore I would have a more accurate reading of the oxygen collected. I would also use gloves when the carrot would be grated so that the carrots would not be contaminated by skin contact. Instead of a beaker of tap water, I would use a proper water bath that would always be kept at a constant temperature. This way the temperature would not change and will not affect the reaction. Validity of Conclusion I think my prediction is acceptable. It had been backed up with scientific information. My results and graph had also proved my prediction to be correct, as it had shown similar trends with my predicted graph and the typical graph. The results had shown exactly what I had written in the prediction. Mahvish Mamsa 61D ...read more.

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