Investigating the breakdown of hydrogen peroxide by the enzyme catalyse in potatoes.

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Investigating the breakdown of hydrogen peroxide by the enzyme catalyse in potatoes

Introduction

This is an experiment to examine how the concentration of the substrate hydrogen peroxide affects the rate of reaction of the enzyme catalase.

Prediction

I hypothesise that the experiment will give results to show that as the substrate concentration increases, the rate of reaction will go up at a directly proportional rate until the solution becomes saturated with the substrate hydrogen peroxide and when molecules of the substrate are in short supply, the increase in rate of reaction is limited and will have little effect.

Background Information

Enzymes such as Catalase are protein molecules which are found in living cells. They are used to speed up specific reactions in the cells. They are all very exact as each enzyme just performs one particular reaction. The catalase enzyme is also found in food such as potato and liver. It is used for removing Hydrogen Peroxide from the cells. Hydrogen peroxide is a liquid which is slightly more viscous than water and appears a colourless substance in a dilute solution. It is a combination of hydrogen and oxygen, with a chemical symbol of H2O2.  It has strong oxidizing properties and in high concentrations, it can be unstable and even poisonous however in a lower concentration it can work well as a disinfectant and antiseptic and is commonly found in many homes. Hydrogen peroxide is naturally produced in organisms as a by-product of oxidative metabolism.

Catalase speeds up the decomposition of Hydrogen Peroxide into water and oxygen as shown in the equations below.

The decomposition increases at a rapid pace due to the shape of its active site which matches the shape of the Hydrogen Peroxide molecule. A reaction like this, where a molecule is broken down into smaller pieces, is known as an anabolic reaction.

Variables

To ensure that our experiment was fair we identified the key different factors, which could affect the results. We then went on to explore the dependant and independent variables. What we change is the independent variable and the result of this determines our dependant variable.

Independent Variable

The independent variable we chose to do for this experiment was the number of 1cm3 potato cubes placed in the test tube which was to find out how fast the breakdown of hydrogen peroxide by the enzyme catalyse takes place by changing the concentration of the enzyme. The greater the number of cubes, the greater the enzyme concentration. We chose to do the so that we could measure if the more catalyse there is the more collisions there are.  

The advantages of using this as the independent variable is that it is simple to measure due to being able to change the amount reasonable easy. Cling film was used to stop the potato from oxidising and therefore there was little problem in trying to preserve the potato whilst we conducted our trials.

However a limitation to this was that we had to ensure that all the potato cubes had the same surface area in order for the experiment to be more valid however I tried to compensate for this, by taking multiple readings for each enzyme concentration so that inaccuracies are minimised once averaged.

Dependent variables

The dependant variable for our experiment was measuring the amount of oxygen displacement as this was affected by the independent variable.  This would help figure out how fast the hydrogen peroxide was being broken down by the catalase. This is because when hydrogen peroxide reacts with the enzyme catalase the products are water and oxygen and as the measuring cylinder was already filled with water, the amount of oxygen being released would be uncomplicated to measure.

Control Variables

In this investigation, the variables that affect the activity of the enzyme, Catalase, were considered and controlled so that they would not disrupt the success of the experiment.  During the experiment we kept a number of things constant to make it fair such as the substrate concentration. To control the substrate concentration, identical quantities of the substrate were used for each reading.  To ensure that this was measured precisely, 10ml syringes were used to accurately extract the hydrogen peroxide. This was done as the rate of reaction would be affected by the level of substrate concentration in relation to enzyme concentration. As well as that the amount of hydrogen peroxide stayed the same, at 10ml, to ensure that the results would be fair.

Also the temperature was a variable controlled by maintaining the room temperature at a fairly constant level, 23°C to allow the enzyme to work effectively. This was achieved by using a test tube rack so that the heat from my hands did not affect the reaction. It was important to control this variable because as temperature increases, molecules move faster (kinetic theory).  In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed.  As the temperature continues to rise the enzyme molecules shape is broken, denatured, and the active site can no longer work and therefore no reaction can take place.

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Also it would have been best to control the pH level of the enzyme as they do get heavily affected by level of pH. The enzymes work best at neutral and therefore in an ideal experiment the pH would have been 7 as it neither acidic nor alkaline and this is the catalyses’ optimum pH. It is the pH where it will be able to work at its best and break down the hydrogen peroxide into water and oxygen. Any change in the pH will alter or maybe denature the shape of the substrate or enzyme.

Another factor that I ...

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**** A very good GCSE level experiment report, containing a clear method based on a relevant trial experiment. Results tables, conclusions and data interpretations are clear but the evaluation needed more detailed suggestions for improvements to the method. Planning: A testable hypothesis has been formulated and stated concisely. Biological knowledge was used to explain the prediction. The key variables were described but not all were controlled in the course of the experiment. The writer needs to double check the spelling of technical terms- catalyze is not the same as catalase. To improve: All written methods should usually now contain a risk assessment table to show the risks, hazards and emergency procedures to be used in an experiment. The background research would benefit from more in depth research using selected secondary resources. Carrying out: The results were recorded clearly and accurately in tables but some headings needed additional information added. The range and number of observations was good. Analysis and Evaluation: The graph was not included in this report but the student obviously used numerical evidence to to process the data for the conclusion. The student drew a conclusion consistent with the evidence and explained it using scientific knowledge and understanding. The possible explanation for anomalous results was given and how the results support the original prediction. The evaluation could be improved by giving concrete suggestions for improvements to the method. The suggestion 'use ICT' does not explain how this improves the reliability of the evidence. The proposed equipment or modification should be given in detail.