Also it would have been best to control the pH level of the enzyme as they do get heavily affected by level of pH. The enzymes work best at neutral and therefore in an ideal experiment the pH would have been 7 as it neither acidic nor alkaline and this is the catalyses’ optimum pH. It is the pH where it will be able to work at its best and break down the hydrogen peroxide into water and oxygen. Any change in the pH will alter or maybe denature the shape of the substrate or enzyme.
Another factor that I controlled was the Surface Area. This was the area of the enzyme, the potato. The area of the potato was cut using a potato slicer to ensure that the surfaces of the potatoes were smooth and of the same size however when we cut them into cubes with the scalpel we used a ruler to be as precise as possible. However there is no certainty that they were 100% identical. It was important to keep the surface area the same because if they were smaller or bigger then different quantities of the enzyme would be present and it would make the test unfair.
Apparatus
This diagram shows how the equipment was assembled together to obtain the results.
Range of Independent Variables
After settling on our independent variable, we chose the ranges which would entitle us to have the most suitable results for the experiment. As we had chosen to do the experiment on the concentration of the enzyme we would have to test various numbers of potato cubes in order to see how increasing the amount of enzyme does impact the reaction.
The range of the number of potato cubes we would test was initially 1-7. This is because they would give us a broad range of results and that we would be able to graph them and they you aid us to work out the rate of reaction. However we soon changed this to 6 as the amount of hydrogen peroxide was not that of equal to the amount of enzyme.
If after writing the tables we notice that there is an anomaly we would highlight that field and then repeat the test so that the results would be more accurate. This happened to us on a couple of occasions and we were able to spot it as the range of the outlier was different to the other two results. After repeating that certain experiment the outlier was disregard from our results. It was also not included when calculating our averages. This was so that our averages were more reliable and interpreting the graphs would be much easier.
Trialling
Before we did the final experiment we did a run through to check that
we knew what we were doing. This gave us a rough estimate of what the results would be, and see if our predictions were right. It also told
us how to conduct he experiment properly, and we worked out how we were going to measure the froth, In order to complete this investigation about the breakdown of hydrogen peroxide there was a choice between potato and yeast as the catalase. I tested both but chose solid potato over yeast as that requires persistent stirring, however my main motivation for selecting potato was that it could be measured more precisely than yeast. The option between counting the number of bubbles released and the volume of oxygen released was an easy pick for me. I chose to measure the volume of oxygen displacement as it is more accurate to measure and easier to record in comparison to counting bubbles which is prone to human error.
Preliminary Test Results
These are our results from the potato experiment trial. We eventually chose to measure the oxygen produced by a change in enzyme concentration.
This is a table of our results when we were using temperature as a variable. We liked this experiment as it was easy to measure and control.
This is a set of result obtained from trying the yeast experiment. I only had time to do the experiment once however in the real thing I will ensure that several repeats are done to get more reliable results. Also I discovered that counting bubbles required full concentration on the amount of bubbles produced but that it is easy to lose count. By doing the preliminary tests I found that I liked the time we let the experiment run and decided to go up to three minutes. I was very satisfied with the interval between each measurement and felt it was sufficient amount of time to pass to let something change.
Method
The first thing to do is take safety precautions which means wearing safety spectacles to ensure protection of eyes as hydrogen peroxide is a irrtant. Then begin to collect equipment and put everything in place. A potato was collected and sliced using a potato cutter for finely cut cuboid chips. Then wrap these in cling film to stop the potatoes from oxidising. With the aid of a ruler and scalpel, long chips of potato were cut in 1cm2 cube pieces. Then get a large plastic tub and fill it with water so that it is approximately half full. After get a 50ml measuring cylinder and fill it right to the brim with water from the tap. Then cover the top of the measuring cylinder, ensuring nothing escapes and carefully tip the measuring cylinder upside down and place it in the water filled tub. Attach a clamp to the cylinder to hold it still above the base of the tub but below the surface of the water. Slot the rubber tube up the measuring cylinder, which is has been made easier due to placing the measuring above the base of the tub giving a good gap and making it easier to stick the tube along. Also the bung at the other end of the tube needs to be kept out and ready for the next stages. Get a clean test tube and using a syringe pour 10 ml of 10% concentration hydrogen peroxide in to it. Then drop the enzyme into the substrate. As soon as that happens bung the top of the test tube, whilst a partner starts the stop clock at the same time. As gas starts to escape measure the effervescence every 15 seconds using the stop clock. After recording down the results, repeat the process twice, making sure that the equipment is all reset properly. Follow this process for all concentrations of the enzyme.
Data
Below are my tables of results collected from conducting the experiment. The yellow highlighted columns represent outliers which were then repeated and disregarded. They were excluded from the averages.
One potato cube:
Two potato cubes:
Three potato cubes:
Four potato cubes:
Five potato cubes:
Six potato cubes:
Seven potato cubes:
Seven potato cubes were measure however the amount of hydrogen peroxide was at a level below the cubes and therefore the each substrate did not get an equal amount of the H2O2. This meant that these results are not accurate enough and therefore we have not included them as if there are insufficient substrate molecules to occupy all of the enzymes’ active sites, the rate of reaction is affected by further as the substrate is unable to break down the greater quantity of enzyme.
Analysis of Results
The patterns within the results collected from the experiment, are best shown on a graph. This is because overall trends between the enzyme concentration and rate of reaction can be portrayed more effectively and become more obvious.
It can be seen from the data that there is a correlation the concentration of hydrogen peroxide and the oxygen produced per 15 second. The enzyme concentration is directly proportional to the rate of reaction for the decomposition of hydrogen peroxide in the presence of catalase (the rate of reaction increases with increasing enzyme concentration). This result can be explained by the idea that both the hydrogen peroxide and catalase are compromised of particles and that these individual particles collide and react if above a certain level of energy. All my results follow this upward trend quite accurately for all concentrations of the enzymes and illustrate that I correctly hypothesises. There is a good match for my identified relationship on my graph showing the oxygen displacement with four potato cubes however it is weaker on the graph of one potato cube as the points are more together than the other ones.
The line of best fit when the concentration of the hydrogen peroxide produced is a straight line on my graphs which show there was a linear relationship between the two values. It highlights that the amount of oxygen displaced is constantly increasing as the reaction progresses. However it also shows that the some of the points do not fit exactly and although they have only slight difference, they can indicate possible errors in the investigation. This may have occurred in the measurement of the quantities of the enzyme and substrate and also variations in the room temperature may have led to inaccuracies. If, however we let the experiment run longer then we would have seen a gradual steadying of the reaction, by a curve forming as the line of best fit.
Also from the graphs it is clear that the range bars of the graphs showing one, two and three potato cubes are not very accurate. I know this because the range bars overlap and this is not a sign of accurate data. However the repeats for each measure were very close together with merely a centimetre or two separating some of them. My most accurate experiment involved six potato cubes of catalase as the graph clearly indicates that most of the point are the same, on all three occasions of repeating the experiment and the data with the range bars are all different and do not overlap.
The gradients were obtained from the graphs showing the amount of oxygen produced at each set of potato cubes. This gave the rate of reaction in volume of oxygen produced in cm³ of the reaction of the breakdown of hydrogen peroxide by the catalase in potatoes. The graph of the rate of reaction is a straight line going upward. This met my expectation as it showed my hypothesis to be correct and that the amount of oxygen displaced would increase as the amount of potato concentration increased and is further proved by the graph showing that the rate of reaction is steadily increasing at a constant speed.
Conclusion
After conducting the experiment and analyzing the data I can rightfully conclude that as I correctly hypothesized, changing the concentration of the enzyme catalase causes the breakdown of hydrogen peroxide to happen faster. This is proven by my results in the graphs that all show a positive correlation and as the concentration increases so does the amount of gas.
Diagram to show the process of the Lock and Key theory
Lock and key is a common way to describe the enzyme-substrate interaction. It is a model for the interaction suggesting that the enzyme and the substrate possess specific shapes that fit exactly into one another, the binding site know as the Active site. Like a key into a lock, only the correct size and shape of the substrate (the key) would fit into the active site (the key hole) of the enzyme (the lock).
With more of the potato molecules inside the solution of hydrogen peroxide, it is more likely that a collision will take place as molecules must collide in order to for a reaction to take place. This means that a reaction is more likely to take place, in a shorter time, making the rate of reaction quicker. More collisions are needed because only one in every 10 to the 14 collisions lead to a successful reaction taking place. The more reactions that take place increases the amount of oxygen produced in the time.
Evaluation of Method
The method that I followed was done to ensure that the best possible results would be gathered. For example care was taken when using the syringes to collect the hydrogen peroxide by having the bottom lined up to the base of the syringe and ensuring there was no air in the syringe to precisely collect the right amount of substrate.
A different test tube would be used each time to minimise any leftover substance affecting the next reaction. By taking several readings for each enzyme concentration, it enabled me to average the results to minimise the extent of any inaccuracies. However one major factor we could have improved to get more precise results was to use a measuring cylinder that had accurately marked graduations on the very top of it. Also to further improve a 25cm3 measuring cylinder could have been used for more accurate results. Another way in which the accuracy of the results could have been improved would have been to record for an even shorter period of time – perhaps 90 seconds, and use the extra time for more repeats of the experiment to acquire even more reliable results. To make our experiment more accurate, better and more advance methods could have taken place to stop human error in affecting the quality of data.
Evaluation of Data
It can be seen that the results I have obtained seem fairly reliable. Howver the graphs show that range bars do overlap and the result. Some experiments which should have had identical rates actually had different ones. A cause could have been incorrect measurement of hydrogen peroxide as the syringe used to measure it was not washed between measurements. Also if once the potato had been cut, fewer anomalies would have occurred, if we completely prevented it from oxidising. This could have been done by keeping in a cooling fridge rather than wrap the enzyme potato in cling film which was not as effective as we would have like.
Despite this, overall the results show the same pattern, a correlation between the concentration of hydrogen peroxide and the amount of oxygen produced and the speed of the reaction. And also the ranges of my data were all in close quantity which does show that the data is fair and that the scale of my graphs just makes the range bars overlap.
I also tried to make my lines of best fit go through most of the points that I plotted to make my data seem dependable.
To improve the data, ICT could have been used to measure the experiment and draw up more accurate graphs and I believe that my lines of best fit were not as accurate was they could have been due to a bumpy ruler.
Evaluation of Conclusion
The conclusion I have made detailing the amount of concentration of enzyme is accurate as my collected data fully supports it and shows that as the concentration of the enzyme (potato) increases the faster the breakdown of the substrate (hydrogen peroxide). The graphs I have created fully back up my hypothesis as they show a positive correlation.
If this experiment was to be completed again I would make certain that the result collected would be as accurate as possible and cut out the risks of human error. I would also try to use better equipment for precision and use more technological advanced apparatus however I am aware that this requires a lot of money and therefore would concentrate on making our equipment was set up as best as it could be in order to ensure more accurate results. I would also like to spread this over a larger amount of time so that more results can be recorded and consequently the results would be more reliable and would help us make better conclusion.
Sahlia Khan Candidate No. 6412