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In this investigation I intend to explore the one of the factors that affects the rate of reactions. My research from textbooks and the Internet suggests that this depends on several factors; temperature, pressure, pH and concentration.

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In this investigation I intend to explore the one of the factors that affects the rate of reactions. My research from textbooks and the Internet suggests that this depends on several factors; temperature, pressure, pH and concentration. After research and careful consideration, in my experiment I am going to investigate how a change in temperature could affect the rate of reaction. Using the enzyme in potatoes (peroxidase) reacting with hydrogen peroxide. Rate of reaction increases by: * An increase in temperature * An increase in concentration * An increase in surface area * A catalyst increases the rate but doesn't take part in the reaction The collision theory is when particles of substances collide with each other and there is a reaction. The higher the temperature the more energy the particles have for a faster reaction, more likely that the enzymes/substrates with collide an lock. An increase in temperature increases reactions rates because there is more heat energy in the particles therefore the collisions happens faster. Enzymes work slower at low temperatures because the movement of particles is slower. Molecules have less energy to collide; enzymes and substrates don't find each other and lock. Each enzyme works most effectively at a certain temperature called the optimum temperature. Which is around 50?C, but over this temperature the enzyme rapidly decreases in rate of its action and becomes denatured from the heat. (fig.1) In an enzyme-catalyzed reaction, the substrate (the substance to be acted upon) binds to the active site of the enzyme. The active site has a specific three-dimensional shape that corresponds to the appropriate substrate. This assures that only the substrate can bind to the enzyme and prevents the thousands of other compounds present in the cell from binding to the enzyme and interfering with the reaction. Once the substrate binds to the enzyme it is called an enzyme-substrate complex. This complex goes through the biochemical reactions and the products(s) ...read more.


10?C) will show a much low activity; in my preliminary work I saw that the rate of reaction was very low at this temperature. I predict that the graph for the total oxygen produced will look like this: (fig3A) When a gas is formed from a solid reacting with a solution, it can be collected in a gas syringe (see diagram below). The initial gradient of the graph eg in cm3/min gives an accurate measure of how fast the gaseous product is being formed. If the reaction is allowed to go on, you can measure the final maximum volume of gas and the time at which the reaction stops. (fig.4) The shape of the graph is quite characteristic (see below). The reaction is fastest at the start when the reactants are at a maximum (steepest gradient in cm3/min), the gradient becomes progressively less as reactants are used up and the reaction slows down. Finally the graph levels out when one of the reactants is used up and the reaction stops. My prediction is supported by Collision Theory in that if I apply twice as much heat there will be twice as many collisions and therefore the rate of reaction will double This will only be so until the enzyme denatures after its optimum temperature: 35�C. Fair test: In this investigation I will keep constant the following � The same volume of hydrogen peroxide in each part of the investigation. � The same concentration peroxide in each part of the investigation � The same size equipment e.g. boiling tubes as the readings for the results will be wrong if this is not constant. � Use the same method for each experiment so that there won't be any major differences. Only alter the temperature. � Keep the amount of potato the same amount 3g � Measure the temperature with a thermometer. �In my preliminary work I found that the cylinder that was collecting the gas was not stable and kept on slipping, loosing a lot of gas , so I would use a stand to keep it stable. ...read more.


One had to be very careful that the substances did not exceed their planned temperatures of there was danger of denaturing. If had done the experiment again I would conduct all on the same day because it is less likely there will a large change in temperature, and also for temperature accuracy I would use a electric water bath because they will stay are a unchanging temperature. I would also try to do all the practices with the potato from the same bag, same age and the same variety, so it is less likely there isn't any large differences in concentration The accuracy of these measurements could be improved by the use of a syringe instead of a measuring cylinder, as it is a more precise piece of equipment and there are fewer margins for error. There could also have been a slight variation in surface area of the potato discs because it was very difficult to get them all the exact same size even though I was using razor. But the evidence I have obtained is not good enough to make firm conclusion; I think this is because I have not done enough temperatures. If I repeated the experiment I would also take more readings for example at every 2�C starting at 10�C because if I did this I would be able to plot a more accurate graph and it would be easier and to tell when the enzyme got to the optimum and denaturing temperatures an use a longer range of temperatures so I can know the exact temperature of the denaturing of the enzyme; in my experiment I didn't obtain the precise temperature of denaturing; I would repeat the experiment again, but explore 35?C-55?C because in my results an graph the is around the temperature where the enzyme started denaturing. Maybe going to 45�C/50�C would be a suitable temperature. And also I would extend the length the time, so I could and out if the time when the enzyme stops producing and see what temperature takes the fastest to run out of enzyme. ...read more.

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