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Influence of pH on the activity of potato Catalase

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Investigation 6.4 Influence of pH on the activity of potato Catalase Introduction Catalase occurs in many plant and animal tissue. It breaks down toxic Hydrogen peroxide, formed as a by-product of various biochemical reactions, into water and oxygen. The activity of most enzymes is influenced by changes in pH. In this experiment, potato discs in solutions of known pH act on hydrogen peroxide, and the rate at which oxygen is evolved is measured. This reflects the activity of the Catalase in the potato. Procedure Use a cork borer to cut cylinder shapes from a potato, use the cork borer to the diameter of 1cm. Place a ruler beside the potato cylinder and cut the potato into discs that are 1mm thick. Place the discs straight into a petri dish filled with water, you need to cut around 60 discs. To measure the rate of oxygen produced I will be using a vital piece of apparatus called a Manometer Tube, this will be filled with dye and will show us the amount of oxygen produced. Set up the apparatus as shown. First assemble the apparatus as shown, then remove the rubber bung from the neck of the boiling tube, use a syringe to put in 5cm3 of buffer solution with your starting desired pH. Immediately after you have put the buffer solution in add the hydrogen peroxide along with the 10 slices of potato. Replace the bung with and airtight seal using the help of water. Now the reaction will start to proceed, use the ruler to measure 3cm along side of the manometer. ...read more.


The rate and average time taken for the manometer to rise 3cm are both a very good indication to show that pH 7 had the most influence on the activity of potato catalase. A buffer solution contain a weak acid and a salt of weak acid, in our case we were using Citric acid-sodium phosphate. Depending on the relative concentrations of the weak acid and the salt, the solution will have a characteristic pH value. A pH buffer was used to maintain a consistent pH level in the boiling tubes. This way there was no variation in pH that might have resulted in an increase or decrease in the rate of reaction. We used a buffer in the experiment, this was an important part of the experiment as a buffer solution is resistant to changes in the pH, thus for example, if more acid was added to a buffer solution to increase the concentration of H+ ions and there fore decrease the pH, the excess H+ ions would then be neutrilised by the salt of the weak acid. There fore pH does not change, this was very helpful to our experiment as it kept the results fair and the pH could not be altered whilst the experiment was being carried out. An acid is a substance, which dissolves in water and dissociates to form H+ ions. The stronger the acid is, the more it dissociates and the more H+ ions it produces. The concentration of H+ ions in solution is used as an indication of acid strength, referred to as the pH scale. ...read more.


PH 7. This I cannot explain as I would not have thought that a single H+ ion could have changed the rate at which the gasses were given off. To obtain more reliable data it would be necessary to redesign the apparatus, this new apparatus would have to secure all the potato slices in separate holders so that each potato slices had the same amount of pH covering their surface. This not a great change to the initial design, but it could have a more accurate affect on the results and avoid confusion about how many potato slices have been put in. To make this investigation a little more accurate and interesting it would be a good idea to record the time taken for every 5mm, this means you would be able to collate a much wider range of data, and would also help with many uncertainties incurred in this experiment. This would also give your conclusion much more basis and reliability. It would also be a good idea to repeat all test and us a much more varied pH scale. To achieve more reliable results you could use the apparatus given to calculate the amount of gas given of in volume using a syringe at the end of one of the tube instead of the manometer tube, this would then tell you the volume of gas produced. You could then also measure the amount of gas given off every 10 seconds for a longer period of time, this means you would be able to collate a wide range of graphs that would clearly show how the different pH's reacted. This would lead to a better variation of graphs, including error bar graphs and more accurate rates. ...read more.

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