Using these potato strips, there are several ways in which you could react the enzymes and the hydrogen peroxide together.
- You could mush up the potato into a puree, and use the mass of the experiment in order to measure the number of enzymes. Then, you could place inside a centrifuge and spin for several minutes before slowly decanting away the clear supernatant at the top of the centrifuging. The enzymes would be inside this supernatant. According to mass then, you could place them into the substrate. Then, time it, and measure the time given off.
Or
- You can use the potato slices in order to obtain a different sort of results, in which you could measure the amount of oxygen released from the experiment. There are 2 main ways of measuring the rate of reaction of the enzymes in this sort of reaction. You can count the number of bubbles formed, or you can measure the amount of oxygen given off by using a measuring cylinder. I think that this would be much more useful.
I have decided on method 2, due to the fact that I have already done a SC1 coursework on enzymes using a centrifuge, and also, in order to do the exact experiment that I am going to do. This is to test what effect the surface area has on the experiment (or the number of enzymes reacting at any one point in time).
Method
Using the fact that now I have prepared the potatoes that I am going to use (see above), then I have to decide how to carry out the experiment, to the most exact detail. You must remember that water is heavier than gas, and so the oxygen will displace the water filled in the measuring cylinder, and will build up in the measuring cylinder. Therefore, I can try and measure at intervals what the amount of oxygen there is.
The 2 ways of going about this experiment is to measure the oxygen given off, or to count the number of bubbles of oxygen given off by the experiment. In order to obtain a good set of results, I have decided to try my hands at both, and if one does not give satisfactory results, then I will drop that method, and carry on with the other only. There are a few other things that you should have ready, such as distilled water, in order to change the concentration of the water if necessary, and then to keep the concentration constant. Therefore, if you are going to make a tricky sort of concentration, then it is best if you go and make that concentration in a large scale, so that the rest of the experiments can use the same concentration of Hydrogen Peroxide, so that even if it isn’t exact, the experiment should remain much more fairer than if all the concentrations were of slightly different values. In this way, I can then narrow the gap for inaccuracies in the end, and in the graph that I produce in the end; I will have a much more fairer and more accurate graph, due to (hopefully) fewer anomalies.
HYPOTHESIS
I think that the results will be directly proportional, and so that if the number of potatoes were to increase from 1 to 5, then I think that the time in which to change the same amount of substrate into
PRELIMINARY RESULTS
For 1 potato, using a molarity of 0.5
For 5 potatoes with molarity of 1M
In the end, I have decided not to wait for too long in the experiment, but instead, I will have to make time count, and so I have decided not to go on further than for 5 minutes (i.e 300 seconds) otherwise, it would be a waste of time. Therefore, I have decided to go for the combination of 0.5M concentration because, at a minimum (with only 1 potato slice), in the preliminaries, It has come out as 289 seconds, which is just below the 5 minute mark. Therefore, it should be easier to record the results when the time comes to record those long experiments, but should not in turn be too quick when it comes to recording the time when I have to try and measure the experiment when it is at maximum, which will be at 0.5M with 5 potato slices.
I have found out that the measuring cylinders do not all start from 0 when you have turned them upside down, and so then there is a little space before I can start reading. However, I have also found that when I plug the bung onto the top of the reaction tube, there has to be some loss for the compressed air, and this is squeezed out through the side tubing, and into the measuring cylinder. Therefore, the few mm of space left in the measuring cylinder when turned upside down is cancelled out. However, 1 problem which I have found to be significant is that of which I cannot place the bung on quick enough. When I pour the aqueous solution of H2O2 over the potatoes, there is a vigorous reaction, as it is quick enough to react in that small space of time. However, I cannot catch all of this, as I have not even had enough time to pour all of the solution in before the experiment has started to react violently, and a lot of gas has escaped. However, as this gas does not seem to go into the measuring solution, this shouldn’t make too much of a difference to the experiment, as I cannot catch this all for all the experiments. A greater problem was one of shaking, and making sure that the experiment was not shaken, as that would mean increasing the movement of the molecules. If more movement was given to only 1 or 2, this would make the experiment unfair, as this means giving the molecules more energy, and then this means that the particles would have more collisions in a certain space of time, and so should increase the rate of reaction.
The measuring cylinder is at a slight angle, because it is extremely hard to try and make the measuring cylinder stand straight. Therefore, when trying to read off the side when at an angle, the water will not be exactly at the level that it you read it as. Therefore, you have to make a compromise.
The fact that the bubbles are different sizes means that I believe it to be ineffective, and so I will only do the Oxygen given off, but at intervals of 10 seconds, up to 5 minutes, or 5ml, whichever comes first. If I had decided on a figure such as every 2 seconds, then I could be forcing myself into making mistakes, and the pressure of trying to do too many tasks at one time with limited time is hard, such as looking at the measuring cylinder, and then taking down the results, as well as trying to make sure that it is not wrong, and then trying to make a compromise, so as to get a fairly accurate result. (be careful – Hydrogen Peroxide is a bleach – always wear safety goggles)
RESULTS
1 potato, with 0.5M solution
Using 2 potato slices, 0.5M
3 potato slices, 0.5M
3 potato slices, 0.5M
4 potato slices
5 Potatoes
The surface area of the potato slices can be worked out in cylindrical form. The diameter of the potato borer is 0.5 cm (or 5mm), while the length of the potato slices are 1 cm long, and so we can work out the Surface area by the formula:
S.A. = ((2*π* 0.252) + (π*0.5* 1))* number of potato slices
By using this equation, I can find out the total surface area of the potato slices inside the tube reacting at one time.
Also, in order to work out the rate of reaction, I will have to find out what (1 / Time) would be, as this is the rate of reaction.
ANALYSIS
From these full sets of full results, I can draw out graphs, 1 for each table, and then a 6th graph to compare all 5 averages. These results have worked out quite close to my predictions, as they have all sped up as the surface area has increased. This is due to the fact that more active sites of the enzymes are present, and so this means that more reactions are taking place at any certain time, which means that more substrate is being changed into product in the same amount of time. If the results were exactly perfect, then on the graphs, the gradients on the graphs would be going up in proportion (e.g. If the gradient for 1 potato was 1, then the gradient for the 5 potatoes should have come out as a gradient of 5). Also, on the graphs, I have to work out the error bounds, as they are not quite perfect results, but could be all wrong by a certain degree. Therefore, I must draw error bars in the graphs. Also, I will point out any anomalies if there seems something out in the graph. The graphs for the oxygen given off against Time are curved, but the graphs for oxygen against the rate of reaction (1 / Time) should be straight.
EVALUATION
I think overall, this experiment has gone very well, due to the results being so close to each other, and not much of an anomaly on the graphs. Also, I think that I have proved my hypothesis right and wrong – right in that it did speed up the result when you had a greater surface area, but also I did get it wrong in that
This is an interesting site on the Internet that I have found, as this has the same experiment with roughly the same methods as the ones, which I have used in the experiment, in which they have done this experiment using the centrifuge, and a little more sophisticated equipment.
Problems could have come from the fact that not all the potato’s surface was showing, such as the parts that were touching the surface of the tube, and the fact that the potatoes were touching each other. Therefore, the trend seemed to be that of the potatoes not quite keeping up to my hypothesis of that of staying in harmony of proportionality. In order to make sure these results were OK, I would do more repeats next time round.
I think an ideal extension to this experiment would be to redo the experiment, but using the centrifuge, and then to compare results, to see if the results would have come out much different.
Also, you could redo this experiment with different enzymes, such as lipase, which is also found inside the human anatomy.
Then again, you could have tried out other forms of the enzyme, or potato, such as mashed potato form, or cubic form. Or, I could vary something else, not Surface area, such as temperature, or concentration of the hydrogen peroxide. Even, you could try and make the experiment as a whole work at a different temperature as a constant, e.g. 30 degrees centigrade, and then go and vary something like the concentration, and then compare back.
As for improvements to this experiment, I could go and try to get more results. Also, I could try more accurate equipment, and I would make all things much more accurate, by not depending completely on the eye (such as on the tilting measuring cylinder), but instead by more use of accurate equipment such as scales. Also, I could go and try to become more useful with the equipment myself – I personally am prone to mistakes. Therefore, the ideal experiment would be performed by hi-tech robots (sadly, they don’t have these in schools nowadays).
