Inhibition:
The inhibitor decreases the rate of reaction because it alters the shape of the active site or either blocks the active site so that the enzyme cannot form the enzyme-substrate complex.
I predict with reasons that the more concentration of catalase I use the higher the rate of reaction will be. Reason for this prediction is because every enzyme has a temperature range of optimum activity. Outside that temperature range the enzyme is rendered inactive. This occurs because as the temperature changes enough energy is supplied to break some of the molecular bonds. When these forces are disturbed and changed the active site becomes altered in its ability to accommodate the substrate molecules it was intended to catalase. Most enzymes in a human body shut down beyond certain temperatures.
Catalase is a common found in living organisms. Its functions include the decomposition of to and . Catalase has to be very fast acting to keep the hydrogen peroxide levels low and it is one of the fastest acting enzymes known. The reaction of catalase in the decomposition of hydrogen peroxide is:
2H2O2 → 2H2O + O2
Pilot test apparatus:
For our pilot test we are going to use downward displacement of water to collect hydrogen gas in a graduated test tube. The reason we are doing a pilot test is because it enables us to carry out the experiment in the way we feel is most effective- also we will be able to find which way is the most appropriate form of measuring the amount of gas. It will also confirm whether or not the equipment we are using is good.
Method:
Firstly we will find the amount of time taken to collect 20cm3, 50cm3 and 100cm3 of gas with the highest concentration of catalase (0.10%) and the lowest amount of catalase (0.02%). To show a range of results we will repeat each one 3 times, this will ensure us that the test is consistent and reliable.
Also we will collect the amount of gas collected every 10 seconds for a minute. Again using the highest concentration of catalase (0.1%) and the lowest concentration of catalase (0.02%). This will give us an idea of results to expect, and an appropriate way to carry out the experiment.
Pilot test results
The time taken in seconds to produce certain volumes of gas
This table shows the amount of gas collected (cm3) every 10seconds for a minute
I will measure the amount of time it takes to produce 50cm3 of hydrogen gas. The volume will be kept the same. The reason for this is because from my pilot test it is obvious that it will be too difficult as there is a huge difference in results between the concentrations of catalase in order for it to be a practical test. It took 10-20 seconds to displace 100cm3 of water with a catalase concentration of 0.1% but after the same amount of time with 0.02% it only produced 30cm3 of gas, therefore it is difficult to choose a suitable time scale.
Although the reaction will be very quick with 0.1% of catalase concentration when timing how long it takes to displace water to reach 50cm3 it is practical and has a more suitable time scale. This is clear from my pilot test results. However when using a concentration of 0.02% it will take a while longer but less time than if we were collecting 100cm3, as from my pilot test it took 10 minutes so we abandoned it.
We will keep the apparatus the same as this was a reliable and practical way, however we may encounter a few errors in our results- as air bubbles may form, and also the bunk not being placed quick enough etc.
These are the variables which may affect my results:
Safety measures:
Safety precautions are a serious matter to the practical as a whole and not carrying out any precautions cause danger to me as well as those around me. The following is a list of the procedures that I will take out:
1. Wearing appropriate goggles, apron and safety gloves
2. Work in centre of table with plenty of space.
3. When using hydrogen peroxide there are many factors that need to be taken into consideration because it is corrosive and causes burns. It is also irritant to the eyes and skin. It’s a dangerous product and can cause explosive reactions and causes internal damage if swallowed due to release of oxygen.
4. Work standing up and with chairs under tables and not in the way.
Method
- I will set out my apparatus as I did for my pilot test, before I do this I will wash my equipment with distilled water and dry it thoroughly- especially the test tube as I do not want the concentration of catalase to weaken as this could effect the results
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Using a syringe I will place 5cm3 of H202 into a boiling tube.
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Using another clean syringe, because using the old one could again affect the results I will place 2cm3 of catalase into the same test tube. As soon as possible I will place the bung directly on the test tube so very little gas is lost
- Simultaneously, start the stopwatch.
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When it reaches 50cm3 stop the stop watch and record the time.
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repeat the procedure 5 times in order to get an accurate average of how much time is taken to collect 50cm3 of oxygen
- Repeat this procedure with the other concentrations of catalase.
Apparatus
A table to show the effect of the different concentrations of catalase on the time taken to collect 50cm3 of oxygen in seconds by the decomposition of hydrogen peroxide.
2 of the results had to be re-done, marked on the graph with a (*). The ones marked on the graph are the new results.
- * old result: 42.79
- ** old result: 37.97
Rate of reaction graph
Graph to show the different averages of the oxygen produced at different concentrations of catalase.
This graph shows the averages of the time taken to produce 50cm3 of oxygen; averages were taken by adding up all 5 repeats of each level of concentration, this has been plotted onto one graph, it shows the speed of decomposition of Hydrogen Peroxide when catalysed with catalase. When using a catalase concentration 0.02% it is clearly shown that it takes a very long time to make 50cm³ of Oxygen, hence the steep line on the graph. This changes very dramatically; this is shown by the steep drop in the graph. The reaction decreases rather fast as the concentration of catalase decreases. Gradually I would expect the reaction to stop working completely as the enzymes will denature. I would have further investigated however Hydrogen Peroxide can be corrosive when highly concentrated.
In conclusion as you increase the concentration of catalase, the rate of reaction increases just as I had predicted, as you increase the concentration of the enzymes catalase there will be more enzymes molecules in a given volume, which can react with the substrate hydrogen peroxide to produce oxygen. The rate of reaction increases because there are more chances of a successful collision, increasing the chances of successful collisions increases the chances of an enzyme-substrate complex being formed. This only happens up to a certain point, when all the active sites on an enzyme are being used, after this the rate of reaction cannot increase anymore because the substrate has nothing to react with, and therefore stays at a constant rate
Although the results have a validated satisfactory graph of the amount of oxygen produced, and established a conclusion that is acceptable, the results were not perfect. Two errors occurred when readings were taken, these errors were re-done to get a more accurate and similar result to the other tests that were repeated. This could have been due to the fact that the bung needed to be replaced at the same time to prevent the loss of oxygen, and the stopwatch to be started. This transaction was done as concurrently as rationally possible, but there was certainly some delay, so a little gas would have been lost; also gas could have been lost at other connections. This would have slightly affected the results. The fact that I may also have delayed in stopping the stopwatch or may have stopped it too early could also have effected the readings also considering the fact that readings were taken by eye, and although they were taken by looking at the scale as near to right angles as possible, there may well have been possible errors. I did not monitor any changes in the temperature of the hydrogen peroxide and this may have altered my results slightly, this was very hard to control because we had a rubber bung at the end of the test tube, so there was no where for a thermometer to go. I could have controlled the temperature of the hydrogen peroxide better by putting it in a water bath, to try and keep the temperature more constant.
Evaluation
The procedure of this experiment could be improved, although the results do give an adequate conclusion. Improvements would simply remove certain errors, and improve the accuracy of results. Using slightly different procedures could reduce the delay between putting in the hydrogen peroxide and replacing the bung and starting the stopwatch. The best solution would be to find a method that doesn’t require the bung to be removed and replaced each time.