Diagram
Analysis
Data handling-
The data obtained from this investigation have been recorded in a table showing the time, enzyme concentration and rate of reaction. This means that the results of the experiment are presented in a clear and orderly fashion that allows patterns in the results to become more obvious. Patterns within the results collected from the experiment, are best shown on a graph, see separate sheet. This is because overall trends between the enzyme concentration and rate of reaction can be portrayed more effectively and become more obvious, also anominal results will stand out.
The reaction was fastest at an enzyme concentration of 100%. At this enzyme concentration there were the greatest number of free active sites available to the substrate molecules so that they could be broken down into the products water and oxygen.
The rate increased steadily from 10% up to a concentration of 100%. The initial rates of reaction in each of the five concentrations are very quickly (indicated by a steep curve) and then gradually slow down (curve levels off). Because the amount of hydrogen peroxide are the same in all of the five reactions the total amount of oxygen eventually produced will be the same if the investigation was left for a sufficient amount of time.
To compare the rates of these five reactions, in order to look at the effect of enzyme concentration on reaction rate, I will look at the initial rate of reaction. This is the fairest way to compare the rates of reactions as once the reaction is under way; the amount of substrate in each reaction begins to convert to product at different rates in each of the five reactions. It is only at the beginning of the reaction that we can be sure that difference in reaction rate are caused only by difference in the catalase concentration.
The results of this investigation are as I predicted in the hypothesis: "The reaction will increase with increasing enzyme concentration when molecules of hydrogen peroxide are freely available. However, when molecules of the substrate are in short supply, the increase in rate of reaction is limited". The reasons for this are that there are number of variables that influence the decomposition of hydrogen peroxide in the presence of Catalase. Some of which can be classified as limiting factors i.e. the reaction is dependant or "limited" by their availability, to be able to function effectively; these include enzyme concentration, temperature and substrate concentration. All of these factors are required for an efficient reaction to take place, even when one is freely available the reaction can still be limited by the availability of the others. When I increased the enzyme concentration, it meant that there were more free active sites for the substrate molecules so that a greater quantity of substrate molecules could be broken down into products quicker. However past a certain point, which in my investigation was at an enzyme concentration 100% at time 4.5 minutes, there were many free active sites but insufficient substrate molecules to occupy them. Increasing the enzyme concentration further without increasing the substrate concentration will have no effect on the rate of reaction, which will eventually remain constant. When the enzyme catalase converted the substrate molecules into oxygen another molecule was produced, water. This product will make the solution more dilute. This will slow the reaction down, as it will be harder for the substrate molecules to find the active sites of the enzymes. Therefore making it a more dilute solution.
Evaluation
In this investigation, I measured the rate of reaction with enzyme concentrations of 10%, 20%, 40%, 80% and 100%. This is a sufficient and wide enough range of concentrations to draw accurate conclusions. I did each of the tests for the five different concentrations three times and calculate a mean average; this way I made the results more accurate.
As a precaution, I limited my contact with the boiling tubes, as my body heat will raise the temperature, increasing the rate of reaction or expanding the gas inside the test tube causing anominal results. I should have monitored the temperature using a thermometer to ensure that it remained constant and not disrupt the results of the experiment by affecting the activity of the Catalase. A major limitation of this investigation was the time. It meant that only 5 different enzyme concentrations could be measured. This means that only very general, overall trends can be identified across the results. Patterns between these values can only be approximated and are not necessarily accurate. Next time I will plan to do concentrations at even intervals every 10% for example 10%, 20%, 30%, 40%, 50%, 60% etc
I collected my results using a qualitative technique. This means I used my observation to record the amount of oxygen gas produced in the upside down measuring cylinder. This is an inaccurate technique as many human errors could occur. To improve the accuracy of the results I could use a quantitative technique, such as using a manometer.
PH affects the rate of any enzyme-controlled reaction in future to rule out any contamination or inaccurate results, I will do a control test to see whether the PH of the tested solution is neutral and not acidic/basic, as this will affect the results.
I choose the time range to collect results at every 30 seconds (0.5 minutes). I think that this is insufficient to detect any accurate trends. Next time I will record the results at 10-second intervals, this will allow me to get an even more accurate set of results for the five concentrations.
Contamination of the hydrogen peroxide solution may have cause anominal results. To improve the accuracy of the results I could do a control test of 0% catalase concentration to see if there is any enzyme contaminating the hydrogen peroxide solution. Also to see whether it is the enzyme, which is converting the hydrogen peroxide.
From the graph "Chart 1", it is clear that concentration 10% and 20% do not fit the trend followed by the other solutions on the graph. They are anomalies. Although they have only slight inaccuracies, they are an indicator of possible errors in the investigation. These may have occurred in either the measurement of the quantities of the enzyme. Another possibility was that changes in room temperature caused the rate of reaction to increase or the gas inside the boiling tube to expand, forcing more oxygen bubbles up the tube. Although minimal contact was made with the apparatus during the investigation, slight undetected variations in the room temperature may have led to inaccuracies. All the other possible causes are discussed above.
The shape of the graph is as I predicted showing that as enzyme concentration increases so does the rate of reaction. This is because at a greater enzyme concentration, there are more free active sites available for the substrate and so more products can be made in a shorter length of time. However, it is not possible to take precise readings from the graph between the plotted points since insufficient readings were taken. To be able to do this, intermediate enzyme concentrations would have to be measured so that the shape of the graph would be more exact.
Because the amount of hydrogen peroxide is the same in all five reactions, the total amount of oxygen eventually produced will be the same. For further work I will test this theory out by carrying the investigation until no more oxygen gas is produced.
