The induced fit theory suggests that enzymes have some flexibility and that once the enzyme and substrate are bound; the enzyme alters shape to accommodate the substrate.
In this investigation, the enzyme, or catalase, concentration was the independent variable whereas the substrate concentration- hydrogen peroxide- remained the same throughout. The rate of an enzyme controlled reaction is always proportional to the enzyme concentration and this is supported by the graph drawn from the results. Although the gradient was not completely constant, the graph did continue to show an overall increase in the rate of the reaction as the catalase concentration increased.
When the catalase concentration was at 20%, the volume of oxygen released was low as was the rate of reaction: 9 cm3 min-1. This was because although there was a high concentration of hydrogen peroxide, there was a limited number of catalase active sites therefore the number of catalase- hydrogen peroxide complexes formed were low.
As the concentration of catalase increased so did the number of active sites available for the hydrogen peroxide to bind to. The higher the concentration of enzyme, the higher the probability that there would be collisions -resulting in more enzyme-substrate complexes. Furthermore, at a catalase concentration of 60%, the average rate was 26 cm3min-1 and this increased further when the catalase concentration was pure/100%, resulting in oxygen gas being produced at a rate of 39 cm3 min-1
In conclusion, the rate of reaction is proportional to the enzyme concentration; as the catalase concentration increased so did the rate at which oxygen gas was produced. The graph drawn supports this as it shows a line with a positive gradient.
Evaluation.
Although the graph shows the expected proportional trend of enzyme concentration against rate of reaction, there were some anomalies which resulted from the differences between the groups’ results. For example, group 3’s results for the volume of oxygen released with a catalase concentration of 20% was significantly higher than the other group’s which ranged from 14 cm3 to 20 cm3 in comparison with group 3’s result of 29cm3 . Furthermore, when 40 and 60% catalase was reacted with hydrogen peroxide, group 3’s results were again higher than other group’s where 56 and 69 cm3 of oxygen gas was recorded. These were especially high against the mean volumes which were calculated to be 34 and 52cm3 respectively. However, group 6 recorded volumes lower than the calculated mean and recorded 36 cm3 of oxygen gas being produced against the mean of 52 cm3 when the concentration of catalase was 60%. Again, for 80% catalase solution, the recorded value was lower than the mean of 66 cm3, with group 6 having recorded 49 cm3 of oxygen been given off. The final anomalous result highlighted in the results table comes from group 9 who recorded a volume of 93 cm3 of oxygen gas. Again, this is anomalous, as like others before it, it is significantly higher than the mean which in this case was 78 cm3.
Reasons for such anomalies range from biological variation of the catalase -as the solutions consisted of a suspension of yeast cells- to variation between some group’s methods, specifically differences in the time it took to remove the rubber bung.
However the most influential would have come from the fact that not all groups would have shook the bottle of ‘pure’ catalase before using a pipette to measure out the required volume for the required concentration. As a result, those groups who did not shake the bottle would have found that the catalase settled at the bottom, therefore would have taken out a highly concentrated volume of catalase. This error was probably the cause of high anomalies such as group 3’s results for 20, 40 and 60% catalase and explains why a much higher volume of oxygen was recorded for 20, 40 and 60%. As mentioned previously, the rate of reaction is proportional to the enzyme concentration; the high anomalies may be due to the higher concentration of enzyme. An improvement on this would be to either obtain a pure source of the enzyme catalase or alternatively, use a magnetic stirrer to ensure the catalase would be prevented from settling.
The second most significant reason for errors would be the time it took for different groups to replace the bung in the boiling tube once the reaction between the hydrogen peroxide and catalase had begun. Those groups who took a longer time replacing the bung would have seen a lower volume of gas produced as oxygen would have been lost in the time it took to place the stopper in. this reason could account for anomalies such as from group 6 who recorded a volume of 36 cm3 of oxygen with 60% catalase when the average was calculated to be 52 cm3. Furthermore, this reason could also account for the anomalous result from the same group which again recorded a lower volume when reacting 80% catalase and recorded that 49 cm3 of oxygen was produced in 2 minutes when the mean showed 66 cm3 to be the average. The reason why this is ranked as the second most influential error is because all groups would have allowed at least some gas to escape as it was near impossible for anyone to place the bung in securely as soon as the reaction began. However, a way to improve this would be to perhaps suggest that all groups waited a certain amount of time once the reaction had started e.g. 5 seconds before placing the bung in.
The next influential error would have come from the biological variation of the yeast suspensions containing the catalase. As they are living cells there would no doubt have been some variation between the catalase concentrations in each cell. The reason for ranking this third in relative influence of errors is that it is unlikely that any one group would have used samples of catalase that consisted of those yeast cells that only contained high concentrations of catalase or low concentrations. Furthermore, group 9’s high anomalous result of 93 cm3 of oxygen for 100% catalase against the mean of 78 cm3 may suggest that their catalase was more pure than other groups. However, I think it is more likely that in this instance this group may not have remembered to have shaken the bottle of catalase therefore would have extracted more catalase and less solvent. A way to improve this would again be to use a magnetic stirrer to ensure that the suspension was equally distributed with those yeast cells containing a high concentration of catalase, and those containing a low concentration of catalase.
Finally the least influential error would have been the number of concentrations of catalase used. Although a wide range of concentrations was used, it may have been useful to make up other, closer together concentrations such as 25, 30 and 35% to observe the effect of enzyme concentration more accurately. However, for those higher concentrations this would be difficult to do as the reactions were so rapid. The reason for ranking this as least influential is that the concentrations used had already provided evidence that as enzyme concentration increases, so does the rate of reaction.