The Affect of Substrate Concentration on the Rate of Reaction of the Enzyme Catalase.

Biology Coursework Samantha Brown 11C

Plan

The aim of this investigation is to discover how the concentration of the substrate hydrogen peroxide affects the rate of reaction with the enzyme catalse.

I predict that the higher the concentration of substrate become, the faster the rate of the catalase reaction will be. I believe this because if there are more substrate molecules present with the catalse enzymes then more collisions between the two will occur. This collision theory will cause an increase in the number of hydrogen peroxide molecules that are broken down into water and oxygen by the catalase enzyme, compared to if the concentration of substrate was smaller.

To discover the rates at which the catalase enzyme will break down hydrogen peroxide at different concentrations of the substrate, a solution of hydrogen peroxide and this slices of liver will be placed into a test tube. A bung will be placed in the top of the test tube with a delivery tube coming out of it, which leads to a gas syringe. As the catalse breaks down the hydrogen peroxide, gas should be produced, which will then travel through t he tube. This will then go into the syringe, pushing the plunger out and therefore measuring the volume of gas produced. The gas produced should be oxygen as the equation for the reaction is:

Hydrogen peroxide water + oxygen

2H₂O₂ H₂O O₂

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Hydrogen peroxide water + oxygen

2H₂O₂ H₂O O₂

The experiment will be carried out 10 times - twice for each of 5 different concentrations of the substrate. In order to make the experiment a fair test the only variable will be the substrate concentration. The amounts of the enzyme, time the enzyme is allowed to work for, and temperature will be kept constant at all times. The experiment will be carried out twice in order to give reliable evidence, as the average of the two will be calculated. Having two sets of results will also allow us to spot any possible anomalies.

Analysing Evidence

The trend of my results seems to be that as the concentration of hydrogen peroxide used increases, so does the rate of reaction with the enzyme catalase. This proves my prediction that as the Concentration of H₂O₂ increases so does the rate of reaction to be correct. This occurs because as the substrate (H₂O₂) concentration increases there are more molecules of the substrate for the catalase enzymes to react with. When the hydrogen peroxide is in weak solution not only do the catalase enzymes collide with substrate molecules, they also collide with water molecules. This means that fewer collisions between catalase and H₂O₂ molecules occur, slowing the rate of reaction. If the hydrogen peroxide is in a stronger solution there will be more H₂O₂ molecules for the catalase enzymes to collide with. This means that there is more chance of a reaction between the H₂O₂ molecules and catalase enzymes taking place and so the rate of reaction is higher. This is proved by my results as at a concentration of 1.25% the average rate of reaction between H₂O₂ and catalase is 0.38cm³/min, where as at 10% concentration the average rate of reaction increases to 237.875cm³/min.

The biggest increase in average rate of reaction occurs at 7.5% concentration as the rate increases from 5.56cm³/min (at 5% concentration), to 185.18cm³/min. I believe this to be because the substrate concentration is nearing the % needed for the enzymes to work at their optimum rate.

Evaluating Evidence

I believe that the investigation was a success as it provided the necessary results to prove our prediction correct. I think that the method we used was reliable as all groups’ data was very similar and only one anomalous result was recorded. This result was provided by group 3 and is that at 10% concentration of H₂O₂ the rate of reaction is 52.3cm³/min. This is much lower than the results provided by other groups e.g. The average rate of reaction for 10% was 237.875cm³/min. (I did not include the anomalous result when calculating this average as I realised it would cause my results to be inaccurate).

The anomalous result was probably caused by the fact that our method was not as accurate as possible. E.g. The main problem our method of gas from the reaction displacing water inside boiling tubes. This difficulty lies in making sure that all water inside boiling tubes (inside a water bath) remains inside until the gas produced in the reaction begins to displace it. It is very easy to lose some of the water whilst trying to position the delivery tube which the gas will eventually flow through under the boiling tube in the water bath. Another problem was that the reaction could quite easily start before the delivery tube has been positioned in the water bath, and so some gas could escape before it is ready to be measured. These problems would be solved if, instead of using a water bath and the displacement method of gas collection, a gas syringe was used. This way virtually as soon as the reaction started the gas would be collected-the only delay being the time taken to insert a bung into the boiling tube.

If I wished to investigate this hypothesis further I could repeat the experiment but with a wider range of concentrations and sources of catalase enzyme; I could use different types of animal liver, fresh liver and frozen liver to see how this affected my results. Potato and celery could also be used as sources of catalase. This would make my results more accurate as it would show a wider range of the catalase used and how different conditions it is kept in can affect its efficiency. I would probably also use the improvements to my method mentioned above to make my results more accurate. However I believe that for the purposes of the investigation I was carrying out the results my method provided were reliable and sufficient.