The experiment will be repeated using the different temperatures.
The apparatus will be assembled as the diagram on the following page:-
Evaluation of procedures
After completing the experiment I was able to see that there were certain flaws in my method and possible sources of error which may have lead to inaccuracies in my data. One flaw in my method was chopping the potato into small chunks. Using this method would mean that getting the same surface area on the potato each time would be extremely difficult, and thus this may have led to inaccurate results. A better option would have been to grate or crush the potato and then weigh it. This would allow me to get nearly the same surface area of potato each time, and therefore the rate of reaction would be more similar for each of the repeats, improving the accuracy of my results, and therefore improving the reliability of my conclusions.
Another flaw in my experiment was that I did not check the pH of the catalase. This was a large error as the pH was supposed to remain constant and if the pH varied then this could have had a significant effect on my results. I should have checked the pH of the enzyme and made sure that I kept it constant by using a buffer solution.
The amount of temperatures I measured was also not large enough. I only did the experiment at 5 different temperatures spread over a large range. Therefore I could have had more conclusive results if I had smaller intervals between temperatures as this would allow me to have a more accurate look at what is happening at different temperatures. For example I was not able to accurately determine the optimum temperature for the enzyme catalse from looking at my graphs, as the intervals were too large and therefore the optimum temperature could have been between a large range of temperatures as well.
One of the biggest problems in this experiment was due to the catalse not being properly equilibrated to the correct temperatures. This would mean that the results were inaccurate due to a lack of precision. One way this could be improved would be to keep the enzyme within the water tank for a longer period of time and test the temperature with a thermometer to make sure it has been properly equilibrated. The catalase should remain within the water tank while the experiment is being carried out so that the temperature does not change.
There was also a problem when measuring one of the temperatures. When we measured the room temperature it was 23oC, that temperature was in fact supposed to be 20oC however the temperature in the room at the time was 23oC. The final temperature, 74oC, was supposed to be 80oC however the water tank we used was only able to sustain 74oC. To fix that problem we should have used a different water tank which was capable of sustaining a higher temperature.
Conclusions from graphs
By looking at the scatter graph with all of the points plotted on it, (graph 1) we can see that from 0oC to 23oC the volume of oxygen collected increases. At 0oC the volume of oxygen is very low with its results ranging from 10cm3-16cm3. When the temperature was raised to 23.4oC the values increased to a range of 22cm3-34cm3. We can see that the volume of oxygen collected continues to increase until the enzyme reaches its optimum temperature at around 40oC where the results range from 30cm3-47cm3. It is clear that after reaching its optimum temperature the reaction slows down and the volume of oxygen collected at 60oC fell to 7cm3-21cm3 and then fell again to a point where the reaction was only giving off very small amounts of oxygen, and its results only ranged from 3cm3-5cm3.
Therefore we can discover a general trend from this graph; as the temperature increases so does the amount of oxygen given off, until the enzyme reaches its optimum temperature whereby the reaction begins to slow down and produce less oxygen as the temperature rises, until the reaction is finally no longer able to take place.
These conclusions can be explained if we look at graph 2, the graph with the mean points plotted on it. As we can see this graph also follows the same general trend as the graph with all the points plotted. Part A of the graph is the results from 0oC-40oC. In this range we can see that the amount of oxygen given off is increasing as the temperature rises, this is because as the temperature rises the molecules will have more energy and therefore there will be more successful collisions faster and more frequently between the enzyme and its substrate, thus more oxygen will be released.
Part B of the graph shows the optimum temperature of the enzyme. This is where the enzyme reaches its maximum rate of successful collisions. There is no way of telling what the optimum temperature actually was. We know that the optimum temperature must lie between 23.4oC and 60oC however there is no way of pinpointing the temperature where the most successful collisions occurred. However from looking at my graph it is most likely that the optimum temperature lies between 30oC and 50oC. To have tightened the range of possible temperatures of where the optimum temperature of catalase might reside, I should have used smaller intervals between temperatures.
Part C of my graph shows the amount of oxygen collected dropping due to the increase in temperature. This can be explained by the lock and key model:-
As the temperature increased beyond the optimum temperature of the enzyme the molecules started to collide more vigorously until some of the substrate was no longer able to fit into the active site of the enzyme due to the active site becoming denatured and changing shape.
Graph showing Rate of Reaction against temperature
From this graph we can see that the rate of reaction increases as the temperature increases until around the 40oC mark where the rate of reaction slows down as the temperature increases. This can once again be explained by the kinetic theory. The kinetic theory states that when substances are heated they gain more energy and begin to vibrate faster. Therefore when the enzyme and substrate are heated up they begin to collide with each other more frequently and the rate of successful collisions increases. This would suggest that that as the temperature increases the rate of reaction would continue to increase; however we can see that after around 40oC there is a decrease in the rate of reaction. This is because of the enzyme denaturing and thus the rate of successful collisions will decrease.
It is once again difficult to judge the optimum temperature and would look to lie between 30oC and 50oC. However we can see that the graph does not look like a smooth curve. This could suggest that there is a slightly positive skew; however I think that the odd shape was just due to the large spread of my data, and the inaccuracies.
Therefore we can see that one effect of temperature on the enzyme catalase is that as the temperature increases so too does that rate of reaction, until the enzyme becomes denatured.
Safeness of conclusions
The conclusions I have made from my graphs are limited by the inaccuracies and anomalies in my data. There were a total of seven outliers within my results, which meant that I only had 43 useful results. However the non-anomalous results were also not very reliable due to the large spread of data. If we look at graph 1 we can see that the error bars were very large, thus my conclusions may not be very safe. Also the error bars for the set of results at 23oC and 40oC overlapped, the highest result for 23.4 was higher than the lowest result at 40.
I also worked out the standard deviations for each set of data at each of the temperatures. Only the results for 74oC produced a low standard deviation of 0.79, however this data had a lot of outliers in it as well. The other temperatures all had very high standard deviation with the results for 40oC reaching over 6. This meant that my results were very spread out and as such were not very reliable, and therefore I cannot draw safe conclusions
To make the conclusions more secure, I think that I should have collected more data for more frequent intervals between temperatures. I think that the amount of repeats that were done was fine, however if I had collected data for more different temperatures then I could have made more accurate and reliable conclusions
Table 2: Rate of reaction
Standard deviation
Standard deviation is worked by using this formula:
You subtract the mean result from each of the repeats and then square the result. You do this for every result individually and then add up all the results. You then divide this value by the total number of results minus 1, and finally square root the answer to get the standard deviation. This is then repeated for all of the temperatures.
Table 3: Standard deviation
Standard deviation is a good measure of spread for my data. It is essentially worked out by measuring the concentration of data around the mean. The closer to zero the standard deviation is the less spread out my data is. As we can see almost all of the standard deviations are quite large apart from that of the 74oC class. Therefore this large spread of data indicates that my results are not very reliable. Although the 74oC class seemed to have a lower standard deviation than the rest, this class also had 3 outliers in the data, which means that even these results had some inaccuracies in them.
Table 1: Table of results
From looking at the different temperatures I measured we can see that there were irregular class intervals. This is because the temperature of 23oC was supposed to be 20oC however the room temperature on that day was 23oC. The temperature of 74oC was also supposed to be 80oC, however the water bath we used was not able to reach 80oC and the maximum it could sustain was 74. This would not largely affect the analysis of the graph however the inconsistent intervals may limit the safety of any conclusions drawn.
We can see from this table of results that there is a very wide range of data; the 40oC class had a very large range of 17cm3, thus showing large levels of inaccuracy. The data also has a lot of outliers as visible (shaded results), showing that the experiment must have had some major flaws in it to give such inaccurate results. These vast amounts of outliers meant that I only had 43 useful results, also hindering my ability to make accurate conclusions.
