Whilst the experiment is being carried out the results have to be collected at set 30second intervals so to do this they are to be written down in a table like the sample of the one on the next page.
The table below is the table that is going to be used to record the results of gas collected throughout the reaction.
After all the results have been collected and averages have been worked out they will be shown in various ways, at least two graphs will be drawn and a table which shows the rate of reaction will be drawn. The first graph that will be drawn is a volume of gas collected to enzyme concentration, and also two showing the average volume of gas collected to time, but the second of these graphs will be a larger scale of 60seconds of the first graph and this shall be used to calculate the rate of reaction.
The graphs shall look something like those below,
From working out the averages of each set of results the graphs above can be drawn also from the second graph the table below can be filled in.
And from the table above the table below can be filled in and the data can be used to calculate the rate of reaction.
Results
Tables for use in analysis
From graph 3 on a previous page the table below could be completed.
Now because all the data for the above table has been filled in the table below could also be filled in.
Analysis
By looking at all the graphs, which have been created from the set of results on a previous page I am are able to come up with various conclusions. From graph 1 I am are able to see that 20-25 disks and 30-35disks have produced in total a similar amount of gas. From the graph 2, the first line graph, we are able to see a trend in each number of disks, although there is no set trend throughout all sets of disk. For the set of 15 disks as the experiment begins to reach 3 minutes it starts to level off, whereas for all the other sets of disks they don’t level off and keep climbing.
For each set of results the gradient of the line on the graph is steeper, this is because the more potato disks that are put in the conical flask increases the surface area therefore this increases the chances of successful collisions between the enzyme and substrate. Also when there is a higher concentration of enzyme there are more active sites for the substrates to attach to. With enzymes thought to be like a lock with which only 1 substrate is able to fit into it is obvious that if there are more enzyme molecules in the mixture then there is a greater chance of a substrate molecule finding an active site it can attach to. The enzyme catalase (found in the potato) attracts hydrogen peroxide and they bond at the active site on the enzyme to produce and enzyme-substrate complex, this then becomes a product that is released. Therefore there is going to be a higher rate of reaction within the runs that had 35 potato disks in the mixture than those that only had 15 disks because there are more enzymes with active sites for the substrate to bond with. The diagram below shows the enzyme and substrate complex idea.
If the experiment had taken place over a longer period of time the lines on graph 2 would level off and run horizontally straight. This would happen because one of two reasons, either all the substrate would be used up or there would be no more substrate that fit the enzymes.
From the second table on the previous page, we can see that where 15, 20 and 25 disks were present there was less gas collected than what was expected, although when 30 disks were used there was more gas produced than that which was expected compared with 35 disks. From the table we can see that once 30 disks are being used the experiment is giving off a worthy amount of gas.
As the only point where the number of disks actually doubles is at the use of 15 disks and use of 30 disks it is unable to make an accurate decision as to whether of not the rate of reaction doubles for the experiment which I had carried out, this would not be an accurate result for all experiments of the same purpose because there may have been things which I had done different that would cause this to happen. From the results that have been taken for 15 disks and 30 disks you can see that the results have more than doubled, in fact they have almost quadrupled. To investigate further if the rate of reaction does double another two sets of results would have to be taken for 40 disks and 50 disks. By doing this there would be more sets of results at which the number of disks being used has doubled and therefore more results to make a conclusion from.
Evaluation
There are various limitations that could affect the results and if any of these were to alter in anyway they could cause an incorrect, biased or anomalous results. Various limitations are,
- The accuracy at which the potato disks were cut. With the thickness of the potato disks being 1mm thick it is hard to cut them accurately by using a ruler and knife. There are few ways in which this would be possible to get round and they would be 1. Use less potato disks but a higher thickness 2. Create a device that would be able to cut more than one disk at once and have it so they are all cut at 1mm thickness.
- The accuracy of measuring out 20cm³ of hydrogen peroxide. As the hydrogen peroxide was measured out using a 10cm³ syringe it meant more than one syringe full of the substrate was needed. The problem with using a syringe is that you can easily have air bubbles in the liquid and you can never make it perfect on 10cm³. The only way really to make this more accurate would be by using a different measuring device, but one that was accurate enough would be rare to find in a college.
- If the room temperature were to alter at all during the experiment that could change the speed of the reaction as if it was to increase it would speed the reaction up and if it were to decrease it would slow it down. This is not a factor that can be controlled.
- Another limitation is at the point when the potato disks are added to the hydrogen peroxide, because at the same time you have to try to place the bung in the top of the conical flask and start the stopwatch. If you make a fault at this point then it will cause the rest of your results for that run to be slightly out. This is because as soon as the enzymes and substrate are placed together they start to react and give off the gas that is produced so some of the gas produced can be lost to the atmosphere.
- From the view of problems with the potato there are various, 1. Due to different potatoes having to be used throughout the experiment there could have been different concentrations of catalase found in each. So therefore if there were more catalase in one potato this would have caused the reaction to take place faster. 2. Some of the cylinders of potato that were being used had area’s which had begun to go off so this could have cause a ‘deformation’ throughout all the potato and it may have affected the catalase in the potato. Due to this there may have been areas where the catalase either didn’t react fully or didn’t react at all.
As well as the limitations with the actual experiment there are limitations with recording the data,
- If the line on the gas syringe was in the middle of two markers some people would read it off as .5 where as other people would round it either up or down so that could alter the graphs and therefore alter the rates of reaction.
- The readings being taken every 30seconds was unable to be accurate because as the stopwatch hits the 30seconds the gas syringe could move by the time the reading is being taken. This can’t really be made more accurate unless two people took the reading with one person watching the stopwatch and the other taking the reading.
