Investigating the effect of enzyme catalase concentration on hydrogen peroxide.

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INVESTIGATING THE EFFECT OF ENZYME CATALASE CONCENTRATION ON HYDROGEN PEROXIDE.

PLANNING.

        Background Information: Firstly it must be established that enzymes are protein catalysts. The definition of an enzyme is that it takes part in a chemical reaction but still remains intact after the reaction and is hence not spent. There are two types of enzyme reaction, these can be separated into catabolic and anabolic, anabolic reactions involve growth (i.e. photosynthesis) whereas catabolic reactions involve an enzyme breaking down a substance, for example digestion where organic compounds are broken down in respiration. One thing that all these chemical reactions have in common is that they take place in aquatic conditions.

        Enzymes have active binding sites, which will fit only certain substrates and thus, they are said to be substrate specific. Enzymes are not destroyed but merely denatured at certain temperatures or by certain pH levels. Temperature denaturisation takes place at temperatures above 60˚c but in certain human enzymes it is 45˚c. Most enzymes will work at optimum efficiency at around pH 7, which is considered neutral. At a certain or pH the active site of the enzyme may have been changed in shape, this change is likely to be irreversible, however, after the pH changes the enzyme can be reversed back. If the temperature is increased without exceeding the denaturisation barrier, this can lead to an increase of kinetic energy in the reaction between the substrate and the enzyme molecules, this can be explained as resulting in a greater collision rate, this speeds up the rate of the reaction. An accepted figure for this rate of increase is that for every 10˚c gained; this results in the reaction rate doubling. Also, by increasing the enzyme or substrate quantity, this may result in the increase of the reaction rate as more collisions take place in less time. The enzyme catalase is present in all living tissue. Catalase breaks down the chemical Hydrogen Peroxide (H2O2) into the harmless chemicals Water (H2O) and Oxygen (O2). Catalase is present in high concentration in the liver and in less concentrated conditions, in the potato.

        The source of catalase for this experiment is in potatoes. The other half of the experiment or the substrate is hydrogen peroxide, the experiment is completed by the catalyse breaking down the hydrogen peroxide, thus making it a catabolic reaction. This experiment can be summarised chemically in this way: (2H2O2→2H2O+O2). Thus, the end result is water and oxygen from a potentially poisonous chemical.

        

        Variables: The independent variable is the one that is going to be changed. In this experiment the independent variable is the quantity of potato strips positioned in the boiling tube containing hydrogen peroxide.

        The dependent variable is the variable that depends on the independent variable. This dependent variable is the number of the air bubbles being released during the reaction every minute. This method may not be of the utmost accuracy but for certain reasons due to a lack of equipment, time and human error, this method is adequate.

        To ensure that this is a fair experiment, I decided that the variables which needed controlling were:

1) How wide the potato strips are (this adds a further complication about surface area).

2) The quantity of hydrogen peroxide used as well as its concentration should be kept constant so as to avoid it affecting the rate of reaction or any other aspects of the experiment.

3) The potato strips should have all come from the same source so that there are no differences between the strips in terms of source.

4) The temperature of the experiment was important but to a certain extent we could not keep room temperature constant but it was checked with a thermometer.

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5) The time was checked constantly by a stopwatch so that this time counting would help us to work out the rate of bubble release.

6) The volume of water kept in the boiling tube into which the bubbles were being released was kept constant at 10 cm3 throughout the experiment.

        

My prediction, which I am not taking for granted, is that obviously oxygen bubbles will be produced which should eventually increase at rates, which are being recorded, and then eventually the bubble release will decrease until only water is left in the boiling tube until all the oxygen ...

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