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Biology SC1 Investigation - Hydrogen Peroxide and Enzymes

Biology SC1 Investigation

Background Science

Catalase is an enzyme found in all living cells. It makes Hydrogen Peroxide decompose into water and oxygen.

You can represent this in the equation:

2H₂O₂ =2H₂O + O₂

Enzymes: Enzymes are able to increase the rate of reaction without actually being consumed in the process. In all, enzymes are very efficient. Small quantities at low temperatures are able to produce results, which would require high temperatures and a violent reaction from any normal chemical means. Although increases in temperature may speed up the reaction, enzymes are unstable when heated.

There are three important definitions that are used when talking about enzymes: -

The substance that enzymes act on is the substrate.

The substance formed by the reaction is the product

The site on which the enzyme takes place is called the active site.

Enzyme function can be explained by the Lock and Key Hypothesis: the active site of an enzyme (the lock) has a specific shape in which only the precise amount of substrate (the key) will fit – forming an enzyme-substrate complex. Therefore producing a product.

All enzymes have the following 4 properties:

·     All enzymes are proteins

·     Enzymes are catalysts

·     Enzymes are denatured by high temperatures

·     Enzymes work best at a certain pH (normally 7)

The Effect of Enzyme concentration:

As long as the concentration of the substrate is much higher than the enzyme concentration, the rate of reaction is directly proportional to the enzyme concentration. This is because, as the enzyme concentration rises, the number of active sites that are available to interact with the substrate also rises, this raises the rate of product formation: -

   Rate Of

   Reation

Enzyme Concentration

Enzymes are also used in fermentation where yeast is used to produce alcohol.

Aim of the Experiment

To see how different concentrations of yeast affects how much oxygen is given off in 1 minute, when 10cm³ of yeast (which contains catalyse) is mixed with 10cm³ of hydrogen peroxide

Apparatus List

·      90cm³ Yeast

·      90cm³ Hydrogen Peroxide

·      1 Stopwatch

·      1 Burette

·      1 Water Bath

·      1 Boiling tube

·     1 Delivery tube

Plan

For my experiment I shall be using the concentration of yeast as a variable as I already know that temperature and pH have an effect on the production substances. I shall use the concentrations of 1%, 0.5% and 0.1% so that there is a range of high to low results. Each of these I shall repeat 3 times to make sure the results are reliable.

Safety: Risk Assessment

Predictions

I predict that as I increase the concentration of yeast the amount of oxygen produced should increase proportionally:

   Rate Of

   Reation

Enzyme Concentration

This is because I know from my background knowledge that this shall happen, this is because, as the enzyme concentration rises, the number of active sites that are available to interact with the substrate also rises, this raises the rate of product formation.

Bibliography

The Living World by Michael Roberts - Publisher: Nelson

Encarta Encyclopaedia ’96 - Publisher: Microsoft

Teachers notes on Enzymes
Method

I shall start by making the concentrations of yeast that I have chosen (1%, 0.5% & 0.1%). I shall do this by mixing the yeast with an amount of water. If I were to make 10ml of the 0.5% concentration of yeast then I would need 5ml of water and 5ml of yeast (As the yeast we are supplied with comes at a 1% concentration). To make the 0.1% concentration I would need 1ml of yeast and 9ml of water, I would not need to add water for the 1% concentration as it already starts at this strength, therefore I shall need just 10ml of yeast.

            After making these concentrations and putting them each in their separate boiling tubes I would then set up my apparatus as shown in the diagram below. I would then put 10ml of hydrogen peroxide into one of the boiling tubes, quickly put a cork with a delivery tube on it in to the top of the boiling tube, place the u-bend of the tube into the burette and time three minutes with a stop-watch.

            When three minutes has finished I shall then measure how much oxygen has been produced by the reaction and record these results. I shall repeat this experiment with each mixture three times (nine results in total) to insure that there are no inconsistent results.

Diagram:

Results

1^st Set Of Results

2^nd Set Of Results

3^rd Set Of Results

Table of Average Results

Analysis

I found out that the concentration of the yeast did affect the amount of substrate that was produced; this can be shown by these graphs:

 In my experiment the rate of reaction was fastest at the 1% concentration and became slower the lower the concentration was. This is because as the concentration of yeast is increased, there are more active sites that are available to interact with the substrate, which increases the rate of product formation, as there are more active sites to produce the product. There were no differences from my prediction and my actual results, this was because I used the right amount of each substance and my experiment went well enough to produce the results I expected.

Evaluation

The experiment went well, this is because I had no anomalous results and the results agreed with my prediction. I think I had accurate results as they were as I predicted and also there were no abnormal patterns that occurred. If I were to make one improvement on my method, it would be to have a larger range of concentrations of yeast to prove that the results continue proportionally. I did not have any anomalous results as my experiment was done well and precisely. I feel that if I had used a larger range of concentrations for my experiment such as 0.1% - 2.0% concentration my method would be improved as my best-fit line would probably become more precise and it would help even more to prove that the oxygen produced would increase proportionally. If I were to extend the range of concentration, the oxygen would increase proportionally.

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