DIAGRAM
SAFETY PRECAUTIONS
1. Due to the fact that H202 can be harmful and an irritant, gloves should be worn throughout the experiment.
2. Eye protection should also be worn to prevent any of the substances from entering the eyes.
3.The test tube should always be tilted at an angle away from the conductor of the experiment, to prevent the inhalation of the solution.
TABLE 3
TABLE 4
METHOD
- Before starting the experiment, make the different concentration percentages by diluting the 10% concentration provided as shown in table 4 above.
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Add 0.4g of liver catalase to an 18*150cm3 boiling tube. Add 4cm3 of hydrogen peroxide solution at a concentration of 6% to another boiling tube (also of a volume of 18*150cm3). Use a pipette to measure out the volumes of hydrogen peroxides. It is very important to accurately measure the amounts of Hydrogen Peroxide, catalase and water to ensure a fair test.
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Pour the hydrogen peroxide solution into the boiling tube containing the catalase, place a cork stopper on it and immediately put the gas syringe bung on the end of the cork, at the same time start the stopwatch. Before this process, ensure that all of the substances (liver catalase and H2O2) are at room temperature.
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Bubbles should start to rise up the tube and the gas syringe will move outwards, as soon as the gas syringe passes the 10cm3 mark stop the stopwatch and note the elapsed time down to the nearest 1/10th of a second.
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Repeat the experiment with hydrogen peroxide concentrations of 4%, 2%, 1%, and 0%, using liver catalase of 0.4g in each process. The 0% concentration of hydrogen peroxide solution is done as a control solution to show that at 0% concentration no reaction occurs.
- Repeat all the tests at least five times so that an average can be obtained. Repeating the experiments several times will help to produce better and more accurate results, as any inaccuracies in one experiment should be compensated for by the other experiments. Note all the results in a table such as the one below.
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After the experiments with the 6%, 4%, 2%, 1% and 0% concentrations of hydrogen peroxide, take out the enzymes and drop it into another 4cm3 of 4% hydrogen peroxide solution. This is not to be included in your data table but the results should be stated in your qualitative data and accounted for in your conclusion.
The rate can then be worked out by
Rate=10cm3
Average time taken for the trial (s).
This gives the rate in cm3 of oxygen produced per second, this is because I am timing how long it takes to produce 10cm3 of oxygen. From these results a graph can be plotted with concentration on the x-axis and rate on the y-axis.
TABLE FIVE
TABLE SHOWING THE DATA COLLECTION BASED ON THE RATE OF THE PRODUCTION OF 10ml OF THE GAS IN ALL THE FIVE TRIALS EACH IN THE FIVE EXPERIMENTS
Example
For trial one, the rate for the experiment with the 6% concentration of the H202 can be calculated as
R = 10cm3
19.82
=0.504cm3s-1
QUALITATIVE DATA
During the cause of the experiment, some data was collected which were not quantifiable, hence, were not written down in the quantitative data section. Below is a table containing those observations.
CONCLUSION
Considering the hypothesis that I put forward that “If all other factors such as temperature and pH are kept constant, increasing the substrate concentration will increase the activity of the enzyme to a point where it will reaches a maximum and remains constant because at its maximum rate the active sites of all the enzyme molecules in solution are occupied by a substrate molecule”, My data supports the first half of my hypothesis, since the rate as one moves down from 6% to the lower concentration, the rate of enzyme activity significantly decreases from
0.504cm3s-1 to 0.363cm3s-1, to 0.280cm3s-1, to 0.034cm3s-1 then to
0cm3s-1.
This can be explained that, as the concentration of the hydrogen peroxide s increased, the amount of substrate available increases therefore; there are more portions on the substrates for the active sites of the enzymes to bond and react with. As the concentration is effectively diluted with the preceding experiments, the amount of substrate available reduces therefore there is an imbalance between the amount of enzymes present and the amount of substrate available, since there will be more enzymes compared to the amount of substrate present. Therefore the enzymes have to “queue” and “compete” for the substrate available since only a few are present due to the reduction in the concentration, most of the enzymes are left in the solution without reacting. This was accounted for by further reacting the enzymes with 4cm3 of 4% enzyme solution. During this reaction, the liver catalase that was reacted with the lower concentrations of the hydrogen peroxide solution were found to react more with the 4% solution than those that were reacted with the higher concentrations of the solutions. This was because the enzymes that reacted with the lower concentrations of the solutions still had active sites which were untouched therefore these active sites now reacted with the new substrate that were in the 4% concentration while those that were in the higher concentrations of the solutions reacted with the new 4% solution but at a lower rate. This was because most of the active sites in these enzymes had already bonded in the first solution that they were in therefore there are only few left to react with the new solution. (As explained in the IB Clegg Biology Textbook, page 58)
My experiment did not cater for the second half of my hypothesis, which stated, “At a particular concentration onwards, the rate of activity will even out”. This was not catered for because the concentration the highest concentration used was 6% of Hydrogen peroxide solution, which is relatively low compared to the size of the enzyme used, therefore the rate of activity continued to increase throughout the reaction. But upon referring to the experiment conducted by sally Morgan on the “review my life” website quoted below, since she used up to 20% of hydrogen peroxide solution, and only 2cm3 yeast solution, she found out that from the 20% concentration and 16% concentration, the rate of activity was fairly the same. This was due to the fact that when you have higher amount of substrate for the same amount of enzymes, as the concentration increases from a certain point onwards, the rate of enzyme activity remains the same. This is due to the fact that as the concentration increases, al of the active sites of he enzymes would be occupied therefore adding more substrate will not affect the activity because there will be no further enzymes to react with the added substrate therefore the rate evens out.
It should be noted however that, the 0% concentration was only performed as a control experiment to show that enzymes are very specific and that they only react with a small group of a particular substrate therefore for the 0% solution in which there was only distilled water, there was no reaction because the catalase in the liver does not react with water but rather breaks down hydrogen peroxide to water and oxygen, as shown in the equation above. For the one percent concentration, It was found out that the time taken for the gas to be produced was very long due to the fact that at that concentration, the amount of enzymes present is very minimal therefore all of the solution had to react with the enzymes for the required amount of gas o be produced. Thus, the greatest amount of time consumed more than any of the other concentrations in the solution.
EVALUATION
Even though the experiment went along as planed to some extent, it did not really expose all the details I was looking forward to proof from my hypothesis. This was basically because the concentrations used in the experiment were much lower there fore I couldn’t get to the place where it would even out.
Also, the method designed for the collection of the gas was not very precise since the same person had to add the two substances, start the stop watch, cork the test tube and place the gas syringe over the corked test tube at the same time. Therefore most of the oxygen being produced might therefore have been lost to the atmosphere.
Again, it was noticed as the experiment was taking place that as the catalase was being added to the hydrogen peroxide solution, it started to react with the solution on the sides of the test tube before getting to the actual mixture in the test tube therefore some of the oxygen from the reaction might have been lost through that pre reaction before the main reaction in the main solution in the test tube.
Also, because different syringes were used, it took more time for some of the syringes to start moving because some of them were relatively tighter as compared to the others.
Below is a table to illustrate the errors, how they affected the experiment and steps to improve upon it next time.
BIBLIOGRAPHY
The effects of substrate concentration on enzyme activity, review my life, 9th December 2012
<<>>.
Enzymes, definition, factors that affect the efficiency of enzymes, effect of substrate concentration of enzymes
<<International Baccalaureate biology text book written by C. J. Clegg, page 52 to 58>>
by
davidboss (student)
