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Potato and Osmosis Investigation

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Introduction Potatoes contain the enzyme Catalyse which catalysis the breakdown of Hydrogen Peroxide (H2O2) into oxygen and water, the equation for this is: 2H2O2 2H2O + O2 Catalyse Hydrogen Peroxide water + oxygen Catalyse The breakdown of the H2O2 is caused by the enzyme catalyse breaking it down using the lock and key theory. The lock and key theory is where, (in this experiment), the catalyse molecule has an 'active site' which part of a hydrogen peroxide molecule fits into (i.e. lock and key theory). Once a Hydrogen Peroxide molecule has met a catalyse molecule, chemical bonds form between them and then water molecules attack the bonds and weaken them. The hydrogen molecule then breaks up into water and oxygen. The oxygen given off is what we are going to measure in this experiment to calculate the rate of reaction (speed at which the reaction takes place) under certain conditions (in this experiment it will be temperature). This diagram is the enzyme breaking down the substrate, using the lock and key theory. This is what happens when the particles collide with each other (see paragraph below for information on how they collide). There are four different conditions in which the rate of reaction can speed up or slow down, and they are based on the idea of the collision theory. The collision theory is the theory that when particles collide with each other they will react. The more force they collide with the more likely they are to react instead of just bouncing off each other. The rate of reaction depends on how often and how hard the particles react, the more often the particles collide and react with each other, the faster the rate of reaction. There are four different conditions that can effect the rate of reaction by increasing, the chances of the particles colliding. The different conditions that can effect the rate of reaction are as follows: Concentration The stronger the concentration the faster the rate of reaction because there is more particles to be broken down, so more chance that they collide. ...read more.


it when cutting to avoid cutting yourself * Cut potato on a flat surface and not in hand to avoid cuts Method 1. Collect apparatus and set up as shown in diagram 2. With the 1cm borer, bore out some potato and cut 3 pieces with a scalpel to 1cm long. Each piece will have a surface area of 4.17cm2. 3. Add 3ml of H2O2 to each test tube using a syringe. 4. Place one test tube into a 40?C water bath using a test tube holder to hold it in there. Make sure the water is 40?C or as close as it can get. 5. Get the stopwatch ready and put 1ml of washing up liquid into a syringe. 6. Add a potato piece to the hydrogen peroxide and straight after, add the washing up liquid and start the stopwatch at the same time. 7. After one minute, pick up the test tube and measure the height of the foam (including the washing up liquid) with the ruler and record the results in mm. 8. Repeat after every minute until the tenth minute (include the tenth minute) and record results. 9. Do this in the 40?C water bath, 3 times using different test tubes. You do this to find an average. 10. Repeat the whole of the above procedure for 60?C, 80?C (both in a water bath), 20?C (about room temperature, so don't use water bath or ice) and 0?C (do this by putting the ice in the tub, and putting the test tube in with the ice. Try to get it as near to 0?C as possible, as it will not reach exactly 0?C). Record all results. Results Rate of reaction of the breakdown of H2O2, by catalyse in potatoes, over 10 minutes at 0?C Time/ Min Height of foam (including washing up liquid)/mm 1 2 3 4 Average (minus height of washing up liquid) ...read more.


This was not expected because the colder the experiment is done at, the slower the particles should move. So that means that the rate of reaction should be slower for a colder experiment but it was not. Possible reasons for this are that there was more catalyse in the piece of potato in the 0?C experiment than the 20?C experiment, causing the 0?C experiment to have a rate of reaction just as fast. If the experiment was done again, it could be improved in several different ways, like the catalyse being measured in the potatoes some how, to ensure that the amount of catalyse is equal in each experiment to make it a fair test. It could also be improved if I had more time to complete it and the cracked test tube result could be repeated. Also there should have been a lot more care in taking the results to avoid measuring poorly and maybe double check the measurement each time so there are no anomalous results. This experiment probably wasn't the most accurate ways of measuring the rate of reaction, however with more time the experiment could be improved by taking more results to be more accurate and doing the experiment at more temperatures. You could also take more results to find a more accurate average. Some other methods of measuring the rate of reaction is to measure the amount of oxygen given off by attaching a tube going to a syringe so when oxygen is given off the syringe will move back. Then you measure the distance it has gone back. I think this is a better way of measuring it because it is more accurate than just measuring the bubbles because some oxygen from the experiment can escape through the bubbles so your not measuring all the oxygen, so it is not a fair test. To further investigate the rate of reaction you could try it with different enzymes, particles and quantities of everything used to see which ones work best and to get more accurate results. ...read more.

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