An Experiment to investigate change in the' rate of reaction' of potato Catalase enzymes due to varied concentrations of hydrogen peroxide.

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Michelle Rothwell

An Experiment to investigate change in the’ rate of reaction’ of potato Catalase enzymes due to varied concentrations of hydrogen peroxide.

Definition of an Enzyme: - Enzymes are biological catalysts which control all the      

                                              chemical reactions inside cells

How Enzymes work.

Enzymes are biological catalysts; these are in all living creatures, these catalysts speed up the rate of reactions.  Most enzymes are globular proteins; their molecules are round in shape. The enzymes speed up the process of conversion of substrates into products.

The shape of the enzyme molecule is what is important; they have an area, like a gap in the molecule, which is, called the active site.  The substrate molecule(s) “plug in” to the active site on the enzyme molecule.  The molecules can then be broken down (or built up) far more quickly than if they were moving around randomly.

An enzyme will only catalyze it’s “own” particular reaction i.e. it is very specific.  This is explained by the fact that each enzyme has it’s own particularly shaped active site and only one type of substrate will fit in.  A cell contains many hundreds of enzymes, all catalyzing different reactions.  Even though the enzyme takes part in the reaction it is freed afterwards and can be used again and again.  Because of this enzymes are needed in very small amounts.

There are various factors that affect the rate of reaction between the enzyme and the substrate:

  • Temperature – an increased temperature can speed up the rate of reaction but each individual enzyme has its own optimum temperature (maximum); if an enzyme goes over its optimum temperature it becomes denatured.  When this happens an enzyme is permanently changed and is no longer functional.  If the temperature is too low, the enzymes do not have sufficient Kinetic energy to move, and there is less chance of them colliding with the substrate molecules.
  • pH – changes in pH affect the attraction between the enzyme and the substrate and therefore the rate of reaction Enzymes have a level of pH where they are most effective, most commonly this is pH7.
  • Enzyme concentration
  • Substrate concentration
  • Three elements Lead, Mercury and Cyanide, which act as poisons to enzymes.  

Catalase.

Catalase is a catalyst for the conversion of hydrogen peroxide into water and oxygen.

                                                                Catalase

     Hydrogen peroxide ---------→---------Water + oxygen

Catalase is a very efficient enzyme (40,000,000 molecules/second).  It is important as it detoxifies the hydrogen peroxide and prevents the formation of carbon dioxide in the blood.  The pH for the optimum activity for Catalase is pH 7.

Outline Plan:

The Experiment: - to investigate change in the rate of reaction of potato Catalase enzymes due to varied concentrations of hydrogen peroxide (the substrate).

Diagram of Equipment

Independent Variable: -

        My independent variable is the different concentrations of hydrogen peroxide. I will find out the rate of reaction using these different concentrations of hydrogen peroxide .I will use a certain range of concentrations of hydrogen peroxide starting from 0.25M to 2.0M.  Although I am changing concentration of hydrogen peroxide, I still have to keep the volume the same, by keeping the volumes constant I am only having to measure the one dependant variable (hydrogen peroxide) this makes my experiment a fair and reliable test.

Dependent (output) variable: will be the volume of oxygen produced, in a set period of time, I will measure the volume of oxygen produced in order to work out the rate of the reaction.  

Accurate results: -

        To achieve the most accurate results I will use a calibrated test tube with the smallest measurement available to measure the oxygen, hydrogen and water. I will measure the oxygen by collecting it in a test tube instead of using the method of counting the gas bubbles. I am not using the latter method due to its inaccuracy, the bubbles can be larger or smaller than the last, and also if the reaction were quick I would have had difficulties counting every bubble.

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        I shall not mix the different concentrations, especially because the concentration is my dependent variable. I can do this by labeling beakers clearly, clean apparatus after use of the individual concentrations.

Reliable results: -

        I want reliable results so I shall do each different concentration three times. I will then check that the results for each concentration to see if they are similar, if there is an anomalous result I shall find out why and find out what happened to cause it and repeat the experiment.

I will also use a thermometer so that I can check ...

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