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An experiment to investigate how the rate of enzyme reaction is affected by the pH

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An experiment to investigate how the rate of enzyme reaction is affected by the pH Aim & Hypothesis/Null Hypothesis The aim of this experiment is to find out whether pH levels affect the working rate of reaction of the enzyme catalase as it breaks down hydrogen peroxide. My prediction (hypothesis) is that the rate of reaction depends on the pH of the environment that the enzyme is placed in. I also predict that the enzyme will have an optimum functioning pH that it works best at (i.e. has the highest rate of reaction at a particular pH level). As the pH level approaches this optimum, the rate of reaction will increase, then peak at the optimum pH, then after this point, the rate of reaction will begin to decrease again (see fig.1 below) My null hypothesis is that the pH level will have no effect on the rate of reaction, and it is against this that I will be testing. Biological Background Knowledge Enzymes are substances that act as catalysts, so they increase the rate of chemical reactions. They are specific, so may only catalyse one reaction. They are also not used up during the reaction, meaning they can be used over and over again. ...read more.


At extremes of pH, the enzyme may become denatured, i.e. loses the ability to combine with the substrate, and therefore loses its catalytic properties. The graph below shows the effect of pH on enzyme activity, and how the rate varies (once the reaction has been initialised.) It can be seen that there is an optimum pH at which the enzyme functions best. Procedure Equipment Type/Volume/ capacity of item Justification for using Item Stopclock Minutes, Seconds, Hundredths of seconds measurement Allows accuracy of time measurement - I will be checking volume of gas produced every 20 seconds. Clamp & Stand --- Allows gas syringe to be kept horizontal for accuracy of gas measurement. Ensure clamp has rubber ends to protect glass gas syringe, in case of breakages. Electronic Balance Grams, Milligrams measurement Allows accuracy of measurement of potato. I will be using 5cm cubed of potato, therefore this item of equipment will be suitable for measuring it on. Pipette --- This item will allow me to obtain the H2O2 without my skin coming into contact with it. I can then put the correct amount into the burette (the burette is graduated in cm cubed so I can measure it this way, the pipette does not have to be graduated as well.) ...read more.


Variables Inputs Constants Outputs PH Level Concentration of catalase Concentration of hydrogen peroxide Volume of potato Volume of hydrogen peroxide Volume of catalase Volume of buffer solution Temperature of buffer solution Temperature of hydrogen peroxide Rate of Reaction Amount of Oxygen produced Amount of Water produced Of the output variables, I will only be measuring the amount of oxygen produced and the rate of reaction. To control the variables that must be kept constant, I will ensure that all volumes of substances are measured carefully and accurately each time. The temperature of the solutions will be checked (using a thermometer) at the beginning of each repeat of the experiment, and any variant will be noted. The pH level will be controlled by adding a certain amount of acid and alkali together to form the buffer solution, and the volume of this solution will be kept the same each time. Safety * Wear gloves and safety glasses at all times during the experiment * Ensure hair is tied back * Do not run around the laboratory * Clean up all spillages promptly and carefully * Dispose of all left-over solutions appropriately * Be careful with glass equipment & clear up any broken glass if breakages occur See risk assessment sheet for further safety procedures. ...read more.

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