My first graph shows that the optimum temperature for catalyse is 40C. This is because at 50C the enzyme became denatured and could not form an enzyme substrate complex, therefore it produced no oxygen. At 21C and 30C there was less oxygen evolved because at lower temperatures the Hydrogen Peroxide molecules had less kinetic energy and so there were fewer collisions and fewer enzyme-substrate complexes were formed, so less oxygen was evolved.
Evaluation
My results are really reliable and accurate as they prove my prediction which was that the catalyse would break down the hydrogen peroxide down best at a certain temperature, 40C. My results are good enough to support a firm conclusion and my conclusion is safe.
I have already identified anomalous results in the previous section.
In my investigation I think the following areas should be improved next time:
More repeats
Checking bung regularly
Using a more reliable water bath
Overall, I think my investigation was successful.
By varying the temperature the enzyme will react differently to each temperature this is due to the collision theory, the collision theory is when lots of collisions are made the rate of reaction will be higher than when the is relatively few collisions.
Conclusion.
By increasing the temperature of the Hydrogen Peroxide the Catalyse reacted faster as I predicted. This is because I have studied the rate of reactions in previous work. At 37 c the Catalyse worked best because that is the temperature of the human body. The rate of reaction increased as the temperature increased but denatured after 37 c.The enzyme's rate of reaction decreased rapidly when the temperature passed 37 c because the enzyme no longer fit the substrate, therefore the enzyme had to work harder to create a reaction and it eventually becomes useless and stops working.
When I heat the enzyme, it works faster because the particles have more room to move, vibrate faster and are uder less pressure.
Evaluation.
I think the procedure used was very efficient and practical. he experiment went well and was not too time consuming. The results were as I predicted. The experiment worked as well as I wanted it to. The results were satisfactory and satisfied me.
In my opinion, the experiment could have produced more accurate results than the results that were obtained. Instead of heating the Hydrogen Peroxide to the desired temperature then putting the potato in, the hydrogen peroxide could have been timed for 1 minute after being boiled so that the temperature could settle down. This might have affected the results that were obtained.
Also, instead of using the bubble counting mehtod,a gas syringe could have been used to see how much oxygen was given off. This would have given a much more accurate result than the results obtained.
The potato had to be cut and then left in the open air until it was required. Instead of the potato being left in the open air, the potato could have been kept in an air tight container until it was required. By leaving the potato in the open air for too long, the oxygen in the air may have started to react with the potato, therefore affecting the performance of the catalase,in the potato, in the hydrogen peroxide.
By putting the hydrogen peroxide in a water bath, the hydrogen peroxide would have stayed at the same, constant temperature throughout the experiment.Unfortunatly,there were not enough water baths, so we had to heat up the hydrogen peroxide to the desired temperature and then carry on with the experiment which meant that the temperature of the hydrogen peroxide fluctuated during the experiment which more than likely affected the overall results.
Also, the hydrogen peroxide was measured in a plastic measuring cylinder, which meant that the amount of hydrogen peroxide might not have been the exact amount. If an electronic liquid measurer had been used, the amount of hydrogen peroxide would have been more accurate and also the results may have been more accurate.
The distance the rubber tubing went into the water in the test tube would be another issue regarding the accuracy of theexperiment.Each of the five times the experiment was carried out, the rubber tubing was always a different distance in the test tube which means the further in the tubing was, the more water was taken up. This would affect the results because the more water taken up by the rubber tubing, the longer and the more oxygen it would take to push the water out. This means that if the experiment was done 3-5 times at the same temperature, the amount of bubbles would be likely to change.
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Out of the two methods used, this was probably the most reliable because it was clear and you could tell that gas was actually being produced because the bubbles were very easy to see.
I think this experiment was a fair test because it was timed each time with an accurate stopwatch. I am very pleased with the results I obtained.
Conclusion:
The reaction was at its fastest, when the concentration of the hydrogen peroxide was 20 vol (100%). Here there were the largest number of substrate molecules to react with the enzymes; therefore there was a greater volume of oxygen and water produced. The rate increased steadily from 19.67cm oxygen collected, to 77.67cm collected, until there was no more enzymes left for the substrate to react with, hence the graph gradually levelling out. Other factors such as increasing the temperature and increasing the enzyme concentration would increase the rate even more if used along side the increase in substrate concentration. However as these were kept constant throughout the experiment, they prevented any further increase in the rate of reaction. The rate increases when there is an increase in the concentration of the substrate, because of the collision theory. There is an increase in the substrate (hydrogen peroxide) therefore more collisions between the substrate and the enzyme (yeast) can take place, causing the rate of reaction to increase, and the activation energy (amount of energy needed for the reaction to take place) to decrease.
The results were as I predicted in the hypothesis. I predicted, "As the concentration of the substrate increases, the rate of reaction should also increase, until the substrate molecule fills all the active sites on the enzyme molecule, or until there are no more enzyme molecules to react. However, in when there is a lower concentration of the substrate molecules, the increase in rate of reaction is limited and will have little effect." This is because a number of factors influence the decomposition of hydrogen peroxide, such as temperature, concentration of substrate, and concentration of enzymes. The reaction is dependant by their availability. These factors are needed for the reaction to take place efficiently. For example in this experiment, the substrate concentration was varied, but the the enzyme concentration was the same, I tried to keep the temperature constant all the way through the experiment, however, due to the limitations, and lack of resources the temperature fluctuated slightly. The reaction took place sufficiently, up until a certain point, when all the enzyme molecules' active sites were filled with the substrate molecules. So if the enzyme concentration was increased as well as the substrate concentration, then the rate of reaction would increase dramatically, and if you heat it to 37 C too.
Limitations and improvements:
In my results there is an anomalous result. This means it doesn't exactly fit the pattern. However to overcome this problem I repeated the concentration with the anomalous result a fourth time, and ignored the anomalous result, when taking the average, as this would have shown up on the graph as completely out of place. I haven't ignored this result completely though, on graph 1, where I plotted the averages, I included the anomalous result in pencil, to show that there was one, but I didn't include it in the averages, hence it drawn on in pencil. This result occurred as I didn't wash out the hypodermic needle in between two repeat tests, so a hydrogen peroxide bubble was lodged in it causing the next lot of hydrogen peroxide to be injected in to dribble out of the needle and down the boiling tube. This meant that not all the substrate molecules were mixed with the enzyme molecules, showing up in the results as if it had been a lower concentration test. Rather than the 60% (12 vol) that it was. It was easily rectified though, all it needed doing to it was to wash the needle out each time and after that all the results followed the pattern.
In this experiment the concentrations ranged from 4vol to 20vol going up each time by 4 vol. However a control concentration should have been included to show that the substrate concentration affects the rate of reaction, and to show that it is the variable, substrate concentration, that is measured. The control concentration would have been 0% (0 vol), in other words, 100% water.
Another limitation is that as the yeast and hydrogen peroxide didn't mix properly the reaction might not have reacted to the highest potential. The only way to stir the 2 reactants is to use a stirring rod, however, that would mean taking out the bung to stir it causing a huge volume of oxygen to be lost. If I had access to better equipment, I would use an electronic magnetic stirrer.
Although the temperature was kept as constant as possible there could have been very slight temperature changes in the room which could not be controlled. I would also need to control the amount of sunlight, by keeping the hydrogen peroxide in brown bottles in the shade. A test tube rack was used to try and limit the amount of physical contact with the boiling tubes, I failed to use test tube tongs, so I still held the boiling tubes when taking them from the test tube rack to the clamp. The failure to do this meant the results could have been affected, as the extra heat from my hands might have increased the temperature of the boiling tube, causing increase in the rate of reaction.
Due to limited time and resources, there was no possible way to control the pH, or the exact temperature. Therefore this might have led to a change in the rate of reaction. I can only presume that the pH was the same all the way through the experiment, as there was nothing within the room that could have altered the pH dramatically.
The major limitation in this experiment was the time. Meaning that only 5 concentrations could be used, and there was not enough time to repeat each test more than 3 times, therefore only general, overall trends could be identified in the results. They can only be approximated and are not necessarily accurate.
A further cause of inaccuracy is individual operator error, for example whilst reading the meniscus, to measure the volumes, slightly different eye-level positions would cause slight over or under estimations.
To make this experiment more accurate in the future, a greater number of substrate concentrations between those already recorded should be tested reducing the possibility of any anomalous results. To reduce the chance even more, repeat each test far more than 3 times. In the experiment I could have recorded how much gas was collected every 10 seconds, up to 1 minute, for an even more accurate set of results.
If I had had the equipment and the time, I would have used an incubator to keep the temperature constant. I tried to keep the syringes as accurate as possible, i.e. as 2cm of yeast was used I used a 2cm syringe and checked to see if the meniscus was lined up to the correct mark. For the hydrogen peroxide, 4cm was being used, there was no 4cm syringes available so I used the closest size to it which was a 5cm syringe, and checked the meniscus again. However, again if I had the correct resources, I would have used a micropipette as this can measure extremely small measurements, such as a tenth of a millimetre.
My results were moderately reliable as all the repeat tests were within 1cm of each of the same concentration tests. E.g., for the 20% concentration, the 3 results were; 20, 19 and 20. Causing the average to be 19.67 to 2dp. However my result's unreliability was mainly due to the fact only one variable could be controlled, all other factors that increased the rate of reaction could not be kept constant. In spite of this, the experiment has proved my hypothesis.
Eval- to improve
Concentration of Catalase (enzyme) - the more concentrated the quicker the reaction.
? Concentration of Hydrogen Peroxide - the more concentrated the quicker the reaction.
? pH - enzymes have to be at the right pH to work properly.
? Mass of celery - the more mass the faster the reaction.
? Size of celery discs / Surface area - the more surface area the more chance of collisions and therefore a quicker reaction.
? Freshness of celery - if the celery is old it might not work as well
I will increase the accuracy of my investigation by comparing my data with another person who is investigating the same temperatures; I will then take an average between the two sets of data to get a more accurate result.
