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Hydrogen peroxide is a toxic by-product of metabolism in organisms and must be decomposed into its products water and oxygen (in the form of effervescence) in order not to be harmful to the cells of the organism.

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Biology Method - Skill AB BACKGROUND KNOWLEDGE Hydrogen peroxide is a toxic by-product of metabolism in organisms and must be decomposed into its products water and oxygen (in the form of effervescence) in order not to be harmful to the cells of the organism. The enzyme catalase speeds up the decomposition. Catalase catalyses the following reaction: 2H2O2 2H2O + O2 INDEPENDENT VARIABLE: in this experiment the independent variable i.e. the one that is controlled, is the pH level of the solution in which the potato chip is immersed. The independent variable in this particular experiment is not the only factor that affects the rate of the decomposition reaction of H2O2, there are many other factors which are confounding in this experiment: CONFOUNDING VARIABLES: * Temperature of the substrate, buffer solution and the enzyme - the buffered H2O2 solution will be incubated in an electric water bath at temperature 20?C (as this is the optimum temperature for this particular type of catalase as it is found in a plant). Also, the Buchner flask will be placed in an electric water bath of temperature 20?C so that, when the potato sample has been cut and placed in the Buchner flask it will remain at the optimum temperature. ...read more.


* Concentration of buffered solution in the buffered H2O2 solution added to the potato chip - the total volume of solution added to the potato chip amounts to 100cm3, in order to completely submerge the potato sample in the solution in a 200ml Buchner flask with approximate base diameter of 9cm. Also a larger volume will reduce percentage errors. H2O2 solution naturally decays so the solutions used in this experiment must all be from the same sample. DEPENDANT VARIABLE: if the volume of oxygen produced which is a method for measures the rate of the reaction. This depends on the pH level of the solution and is therefore, the dependent variable. It will be measured using a gas syringe in an airtight system in order to produce useful and reliable quantitative results. The method will be repeated in order to produce a full range of results. Method NOTE: Goggles must be worn at all times and care taken when using the scalpel 1. Label a boiling tube pH3 (ignoring pH1 and pH2 due to preliminary experiments) and add 5cm3 of 1% hydrogen peroxide (H2O2) using a graduated pipette. 2. Add 5cm3 pH3 buffer solution to boiling tube pH3, seal with a rubber bung and shake vigorously. ...read more.


to stop friction having a restricting effect on the movement of the plunger. 14. When the reaction is complete or after ten minutes, dispose of the waste contents from the boiling tube with side arm, rinse and dry the boiling tube with side arm and dropping funnel and reset the plunger on the gas syringe to nought. 15. Repeat stage 1 - 14, twice, using fresh samples of 1% H2O2 and buffered pH3 solution. Cut a fresh potato sample from the remaining sample in the cork borer (N.B when this supply runs out cut another cylinder from the same area of the same potato). 16. Repeat stages 1 - 15 using increasing pH buffer solutions of intervals of 1 pH level, from pH4 to pH12 (chosen due to my preliminary investigation, where no reaction took place for the extreme pH buffer solutions i.e. pH1, 2, 13 and 14). 17. Record the data in table 2 for each buffered solution and calculate the averages for each individual buffered solution. 18. Construct a graph of the volume of oxygen produced against the pH level of the buffer solution for each individual buffer solution and work out the rate of the reactions by calculating the gradient of each graph. Diagram 1 ...read more.

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