To investigate one factor which affects the way in which the enzyme catalase works.
To investigate one factor which affects the way in which the enzyme catalase works.
Aim: To investigate one factor which affects the way in which the enzyme catalase works.
catalase
Hydrogen peroxide ? oxygen + water
2H2O2 (aq) O2 (g) 2H2O(l)
Background: There are three main ways to affect the way and speed that the enzyme catalase works. One is to change the temperature at which it is used. This affects the rate of reaction at which hydrogen peroxide is broken down because enzymes act like inorganic catalysts, and the rate of reaction doubles every 10?c within the temperatures of 0 and 40?, but above this temperature the enzymes effectiveness slows, and then stops as it becomes denatured. The optimum temperature is around 37?c, as this is the average body temperature and enzymes are designed to work in the body.
For a reaction to occur, particles need to collide successfully. For a successful collision, molecules need to collide with enough energy to break the bonds. This is called the activation energy.
The activation energy level, which is needed, can be lowered by use of a catalyst (in this investigation using the biological catalyst, the enzyme catalase)
The concentration of the hydrogen peroxide can be changed. This affects the rate of reaction by increasing the rate as the concentration is increased, up to a certain point. It increases because if the concentration of the hydrogen peroxide is higher, then the chance of its particles coming in contact with the catalase and so being broken down is increased, therefore increasing the rate at which it is broken down and so the rate of reaction.
Another variable is pH. The optimum pH for catalase to work at is 7.6. The catalase is most effective at this pH, and its activity is affected when this is changed. By extremes in pH it could also be denatured, and so no longer work at all.
The surface area of the catalase (in this case liver) can affect the rate of reaction. This is because with increased surface area, the hydrogen peroxide has more area to come in contact with the liver, and so be broken down by the catalase, therefore increasing the rate of its reaction
In my investigation I will be measuring how the rate of reaction is affected by changing the concentration of the hydrogen peroxide. I will do this by measuring how much oxygen is produced when the liver is added to the hydrogen peroxide. I expect that in a graph of volume of oxygen collected against concentration, the volume will steadily increase, and then level off at the end. I predict the same for my rate of reaction against concentration of hydrogen peroxide. This is because, once the hydrogen peroxide gets to a certain volume, all the active sites of the catalase will already be in use, and so this is when the graphs will level off, as there will be no, or less increase in the enzymes activity.
Prediction: In this experiment I predict that the rate of reaction of the breakdown of hydrogen peroxide into oxygen and water will increase as the concentration of the hydrogen peroxide increases, up to a point where it will remain the same. This is because the increase of the substrate concentration means that there is an increase in the rate of the reaction, due to more of the enzymes active sites will be filled and the breakdown of the substrate will be faster. This is in reference to the lock and key theory.
The hydrogen peroxide, which is ...
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Prediction: In this experiment I predict that the rate of reaction of the breakdown of hydrogen peroxide into oxygen and water will increase as the concentration of the hydrogen peroxide increases, up to a point where it will remain the same. This is because the increase of the substrate concentration means that there is an increase in the rate of the reaction, due to more of the enzymes active sites will be filled and the breakdown of the substrate will be faster. This is in reference to the lock and key theory.
The hydrogen peroxide, which is the substrate molecule fits exactly into the active site of the catalase, which is the enzyme, it is the only substrate that fits into the enzymes active site, and is therefore specific, like a key is specific to a lock. (Hence the name of the theory) This is demonstrated in the diagram below.
The rate of reaction increases with the concentration of the hydrogen peroxide (substrate) up to a point and then remains the same because when you increase the substrate concentration enough, all the enzymes molecules (catalase)
Are in use, and the active sites being used, so no more hydrogen peroxide can be broken down at that time, ?the rate of reaction would remain the same.
The reason the rate of reaction increases with concentration is also to do with collision theory. More collisions increase the rate of reaction, and increased concentration increases the chance of these collisions happening.
I predict that my first graph, showing percentage concentration of hydrogen peroxide on the x-axis, and volume of oxygen collected on the y-axis will show direct proportionality, with a proportional relationship between the volume of oxygen and the concentration of the hydrogen peroxide. I predict that my second graph showing rate of reaction on the y-axis against concentration of hydrogen peroxide on the x-axis will also show direct proportionality up to a point where it will tail off (where all the active sites are occupied).
Apparatus: The amount of water and H2O2 for each reaction (cm3): H2O H2O2
Test tube 1 0 20
Delivery tube 2 2 18
Rubber bung 3 4 16
50cm3 measuring cylinder 4 6 14
10cm3 measuring cylinder 5 8 12
Hydrogen peroxide
Liver (0.2g each time)
Diagram:
Method:
* Set up the apparatus as shown in the previous diagram.
* Measure out volume needed of hydrogen peroxide and water (shown in the table in the apparatus), and add to test tube.
* Add liver to test tube and put rubber bung into test tube
* Record how much oxygen is produced in 30 seconds by looking at measuring cylinder.
* After recording results set up and repeat using required concentrations of hydrogen peroxide, using a fresh piece of liver each time.
Fair test: To make this experiment a fair test, I will keep the mass of liver the same each time, and time for 30 seconds each time. I will also try to keep the temperature of the hydrogen peroxide solution at room temperature, as temperature can affect the rate of reaction. I will do this by measuring the temperature before the start of each reaction, not after as the reaction could be endothermic or exothermic. I will try and put the bung on as quickly as possible after the liver goes in so that none, or not a lot of the oxygen escapes without being measured. I will also not shake or stir the hydrogen peroxide and liver at all, as this could increase the rate of reaction due to the substrate particles coming in contact and so being broken down more by the liver.
Preliminary work: Before I carried out this experiment I did some preliminary work to decide on what volumes, concentrations and masses to use. For example when using a lot of liver a vigorous reaction occurred so I decided to use 0.2g rather than any higher masses. I decided on the concentration of the hydrogen peroxide as well, as there is enough difference between each concentration for a change in the rate of reaction to be noticed.
Accuracy: To make this experiment accurate, I will try to keep all the conditions other than the variable of concentration the same each time, so that nothing effects the rate of reaction other than that. To make it more accurate, I will repeat the experiment, and all 5 reactions again, so that if the second results back up the first set, I know that it is reliable. If there are any anomalous results then I will repeat them ones a further time also.
Safety: To make this experiment safe, the workspace must be clear, goggles must be worn, and the experiment must be done standing up.
I will record the results in a table like the following:
Vol. H2Ocm3
Vol. H2O2
Concentration H2O2 %
st time vol. O2 collected cm3 in 30 seconds
2nd time vol. O2 collected cm3 in 30 seconds
Temp ?C
st time
2nd time
2
3
4
5
Results:
(The original concentration of 100% is at 1.76 moles)
Vol. H2Ocm3
Vol. H2O2 cm3
Concentration H2O2 %
st time vol. O2 collected cm3 in 30 seconds
2nd time vol. O2 collected cm3 in 30 seconds
Temp ?C
st time
2nd time
0
20
00
25
26
20
20
2
2
8
80
23
22
20
20
3
4
6
60
8
9
20
20
4
6
4
40
1
2
20
20
5
8
2
20
5
4
20
20
I found the rate of reaction by using the following equation:
Vol. Of O2
30 seconds
Average Vol. O2 cm3
Rate of reaction cm3/s
25.5
0.85
2
22.5
0.75
3
8.5
0.62
4
1.5
0.38
5
5.5
0.18
Conc. % H2O2
Average O2 collected
00
25.5
2
80
22.5
3
60
8.5
4
40
1.5
5
20
5.5
Conclusion: From looking at my results I can see that their general pattern agrees with my prediction, as far as when the concentration of the hydrogen peroxide increases the rate of reaction increases to a point, where the reaction levels off, although this is not extremely clear on my rate of reaction graph. This is due to the lock and key theory, where the substrate molecules hydrogen peroxide enters the active sites of the enzyme catalase and so is broken down. The more of these hydrogen peroxide particles there are in relation to water particles (the concentration) the more likely this is to happen. The reason that the results should tail off is because with increased concentration the reaction comes to a point where all of the catalases active sites are being used, ?the reaction can not possibly go any faster.
Looking at my graph showing rate of reaction against concentration it does start to level off, and if the concentration of the hydrogen peroxide had been increased further, or I had used less liver then it would have levelled off further, due to there being more substrate molecules ?less more active sites in use, or less active sites in the first place. Looking at both of my graphs I can say that they're general trend supported my prediction, although there were a few anomalous results which I shall talk about further in my evaluation.
Evaluation: I think that my results are fairly reliable, but are not perfect and I believe that this is due mainly to human error. I could have made errors when measuring out the liquids, due to my eyesight and the accuracy of the measuring equipment used. This could have been improved by using a burette, which is a glass tube with a calibrated scale, and a tap, which is longer and thinner than measuring cylinders making it more accurate. Another thing, which could have affected the accuracy of the results, was the surface area of the liver. Although it was the same mass each time, the shape of it from it being cut can effect the surface area which effects the rate of reaction due to more active sites being available when the surface area is increased. This could be improved by using the same piece of liver for each reaction, as the liver is not actually effected by the reaction, it still has the same active sites available for each reaction.
As I have said in my conclusion, my results did follow the general pattern of increasing with concentration as I said in my prediction. But looking at my graphs I can see a couple of anomalous results. These can be seen best on my second graph which shows the rate of reaction against the concentration of the hydrogen peroxide. They are at 20% and 60%. These odd results are most likely due to human error. These could be improved by repeating the experiment more times to get more results to compare them with, or as I mentioned earlier by using more accurate equipment like the burette. Although there were these anomalous results, they still followed the general pattern, so I think that from my results I can draw a firm conclusion.
To do further work on investigating factors which affect the rate of reaction of the breakdown of hydrogen peroxide, the experiment could be done, but instead of making concentration the variable, changing the temperature each time, or by changing the pH of the solution each time. (Both mentioned in greater detail in my background knowledge).
Another thing that could make a more accurate experiment to make a firmer conclusion would be to use a wider range of concentrations hydrogen peroxide. As I mentioned earlier, the molarity of the 100% solution of hydrogen peroxide was 1.76 moles, so by using a higher concentration of hydrogen peroxide, it would have been easier to see the tail off of the rate of reaction at the end of the experiment.
Clare Mann 11F 1
