Below is a table of result which I obtained when conducting these experiments. Time (s) Amount of gas given off using 1cm3 of liver suspension and 1cm3 of hydrogen peroxide (cm3) 0. 0 Amount of gas given off using 2cm3 of liver suspension and 3cm3 of hydrogen peroxide(cm3) Amount of gas given off using 1cm3 of liver suspension and 3cm3 of hydrogen peroxide(cm3) 0 Amount of gas given off using 1cm3 of liver suspension and 4cm3 of hydrogen peroxide(cm3).
Amount of gas given off using 1cm3 of liver suspension and 5cm3 of hydrogen peroxide(cm3) Amount of gas given off using 0. 5cm3 of liver suspension and 5cm3 of hydrogen peroxide(cm3) 0By looking at these results I can see that the best ratio I have tested so far is the ratio of 10:1 (5cm3 hydrogen peroxide to 0. 5 cm3 liver suspension) as it gives me a good spread of results and does not happen so quickly that I cannot take results from it.
I obtained a 1cm3 syringe with which I could accurately measure to the nearest 0. 02 cm3 I used 0. 2cm3 of liver suspension and 5cm3 of hydrogen peroxide my results are in the table below. Time (s): 0. 0 Amount of gas given off using 0. 2cm3 of liver suspension and 1cm3 of hydrogen peroxide (cm3his ratio gave me good results which I can easily analyse so I have decided to use this ratio in my final experiment. I will use the concentrations 0%, 2%, 4%, 6%, 8% and 10% of liver suspension in my experiments as these should give me sensible results.
Also, after conducting these experiments I have decided to use a 1cm3 syringe as this will give me accurate results and I have decided to use a gas cylinder rather than a measuring cylinder to collect gas as this is more accurate and easy to read. Fair testing In order to ensure that my results are reliable and accurate I will endeavour to make sure that there is only one variable in all of my experiments. Given that I only wish to test one variable I will make sure that I control all other variables that could affect the amount of gas produced in my experiments.
Factors that could affect the results of my experiments are temperature, pH, apparatus and substances. To maintain a constant temperature throughout all my experiments I will conduct all of my experiments with the side arm boiling tube in an electronically heated water bath set at a temperature of 30i?? C. I have chosen this temperature as it is higher than room temperature so this will not affect it and it is not at a temperature high enough to denature the enzymes. To control pH I will add a pH buffer to the liver suspension buffering the pH at seven.
I have chosen seven as it is neutral and therefore should not affect my experiments. I will also test the pH of the liver suspension at the start of each experiment using universal indicator if the paper turns light green I will know the pH is seven. To ensure that my apparatus is in working order I will ensure that I assemble the apparatus well and double check that all connections are well made and are therefore as air tight as possible. This will mean that any all gas produced goes into the gas cylinder and does not escape the apparatus so that my results are accurate.
Given that all substance concentration that I will ask for will be mixed by the school biology department I cannot be sure exactly what is in them so unfortunately I will have to trust that all the substances I use are what they should be. Before using any of my substances I will stir them for ten seconds using a glass rod, this is to ensure that there is an even distribution of liver in my suspension so my results are accurate. Also, I will always use the same concentration of 10 vols hydrogen peroxide. Another factor which could affect my results is human error.
When I am conducting my experiments it is possible that I could inaccurately measure my substances and I could start the stop clock at the wrong time. To accurately measure all of my substances I have chosen the most accurate apparatus to measure them with. I will measure as closely as is possible with the human eye measuring my liver suspension accurate to the nearest 0. 01cm3 and my hydrogen peroxide to the nearest 0. 1cm3. Also, when injecting my hydrogen peroxide I will inject it as quickly as possible so the full amount is in the boiling tube as soon as possible.
I will start the stop clock at the very moment I inject the hydrogen peroxide so my results are accurate. Safety When conducting my experiments it is vital that I take the utmost care to be safe in the laboratory. I will wear safety glasses to protect my eyes as well as tucking my tie into my shirt to avoid it coming into contact with any apparatus or substances. Also, when dealing with hydrogen peroxide I will only remove the stopper from the bottle when I need to use it, I will extract it with a syringe and replace the stopper immediately.
I will do this as hydrogen peroxide is highly dangerous and can cause the spontaneous combustion of clothing if applied in high concentrations. Also I will take great care when handling glass equipment and will ensure that all apparatus is properly clamped in place before beginning my experiments. I will be aware of others around me, tidying my apparatus away so it does not pose a danger to others. Also, I will wash my hands after conducting my experiments so as not to leave any dangerous substances on my hands which may be ingested if I put my hands near my mouth.
MethodApparatus A water bath A trough A side arm boiling tube A test tube rack A gas cylinder A stopwatch A clamp and retort stand 1x 1cmi?? syringe 1x 5cmi?? syringe A bung with a space for a syringe. Thermometer Diagram Procedure Before conducting any experiments I will ensure that the gas cylinder is full of water with no air bubbles by filling it then placing my thumb over it whilst submersing it in the trough. I will also ensure that the water bath is at a temperature of 30i?? C. After collecting the listed apparatus I will set it up as in the diagram above.
I will then remove the bung and collect a liver suspension. I will begin with a concentration of 2% then proceed to use 4%, 6%, 8% and 10% as well as a control of distilled water. I will firstly take a sample of the solution in a test tube and universal indicator solution to it to in order to monitor the pH of the suspension. I will not add a buffer to control the pH as the chemicals in the buffer could interfere with the reaction and alter my results. I will measure out 0. 2cm3 of the suspension using a 1 cm3 syringe being as accurate as is possible with the naked eye when measuring.
I will inject this suspension into the side arm boiling tube and replace the bung. I will then use the 5cm3 syringe to measure out 5cm3 of hydrogen peroxide. I will place the syringe into the bung and ensure that all my apparatus is air tight. I will then quickly inject all of the hydrogen peroxide into the boiling tube whilst simultaneously starting the stop clock. I will then record the amount of gas collected in the gas cylinder at ten second intervals for a period of two minutes. I will then repeat each experiment three times for each concentration of liver.
I will record all my results on the table below. After collecting my results I will go on to test a different liver concentration until I have three sets of data for five different concentrations as well as a control. I will then tabulate these results and use the average results for each experiment to plot a graph of my results allowing me to analyse them easily. Taking the average of three experiments for each suspension will give me more reliable results as it will reduce the affect of anomalous results.
Also, to ensure that all my tests are fair I will endeavour to use exactly the same conditions for each experiment by maintaining a constant temperature and by measuring all substances as accurately as is possible. I will also ensure that my apparatus is set up in exactly the same way for each experiment. When conducting my experiments I will consider all factors which I discussed in the fair testing section of this project making my results as reliable and accurate as possible. Observations On the next page is a table showing my results for the experiments described in my plan. I will go on to analyse these results in the analysis section.
Analysis On the next page is a graph showing volume of gas produced against time for the six concentrations of liver suspension I used in my experiments. Although the graph of my results that I produced may at first appear not to agree with my predicted graph it does in fact indicate that my hypothesis was true. The lines on my graph are in the same positions as I predicted apart from the control graph which was higher than I expected. The lines did not flatten out as I predicted however, I believe this is due to the fact that I used a short time scale and the graphs would have flattened out had I used a longer time scale.
I did not use a longer time scale as it would have been pointless given that I am investigating the rate of reaction of several different liver concentrations rather than the rate of reaction changing over time in one concentration of liver. On the whole I am happy with my graphs and I think they verify my hypothesis. My graph for the reaction rate of the 2% liver concentration followed this pattern well. Initially there was a dramatic increase in the amount of gas released.
After the first ten seconds this slowed significantly, the amount of gas released still increased but it increased much more slowly and steadily. This was because the catalase broke down the hydrogen peroxide into water and oxygen slowly and steadily. The reason for the graph continuously going up slowly throughout the entire two minute period was because there was little catalase compared to hydrogen peroxide meaning that even by the end of the two minutes there was still a lot of hydrogen peroxide which had not been decomposed and so the enzymes were still working at the same rate.
I think that if I had let the experiment continue for a longer time period the gradient of the graph would have flattened to zero as all of the hydrogen peroxide would have been decomposed. My line is approximately straight showing me that the reaction rate was roughly the same throughout the experiment however, the gradient is steepest at approximately sixty seconds meaning that the rate was highest here. In order to compare the rates of reaction of all my graphs I will need to calculate the rate of reaction for each graph. I will do this by dividing the amount of oxygen produced by the time taken to produce it.
This will give me a rate in cmi?? of oxygen per second (cmi?? /s). I have chosen to take the rates of reaction from the points on the graphs after thirty seconds. Although it may seem that the maximum rate is at ten seconds and so I should take this rate I think this is due to the hydrogen peroxide I injected displacing air in the apparatus. I have chosen thirty seconds as I think this is sufficient time for the experiment to have settled after the initial burst of gas and it is not too late that some of the reactions had begun to slow down.
The rate of reaction at thirty seconds for the 2% concentration suspension is as follows: 3. 83cmi?? 30s =0. 13cmi?? /s (2dp) I chose to take my rates to two decimal places as this is accurate enough for me to analyse my rate graph well and it is not so accurate that it would be difficult to plot on a graph. My graph for the rate of reaction of the 4% concentration liver suspension further supports my hypothesis. It has the same initial increase in gas from when I injected the hydrogen peroxide, it then continues to slope upwards but not as fast as before.
As I predicted the 4% graph slopes up at a higher gradient than the 2% solution graph. This can be seen by simply looking at the graph. As predicted the gradient of each line is higher than the one that preceded it. This is because as the concentration of the suspension increases there is more catalase to break down the hydrogen peroxide into its component parts. I will now proceed to compare the gradients and rates of reaction for each concentration.
On this graph the gradient of the line and the rate of reaction are the same thing as gradient=change in Y Change in X And rate of reaction=amount of gas produced (change in Y axis) Time (change in x axis) Below is a table showing the rates of reaction for each of my concentrations of catalase including the control experiment of 0% catalase. As before I will take the gradient of the line after thirty seconds. concentration of liver suspension amount of gas produced (cmi?? ) time (s) rate of reaction (cmi?? /s).
On the next page is a graph of my results, I have plotted concentration of liver suspension against rate of reaction, this will better show my results and will help to verify my hypothesis. As you can see from the graph there is clearly a relationship of proportionality between the rate of reaction and the concentration of liver suspension as I predicted in my hypothesis. I have added a best-fit line to my graph to better show this trend.
As I predicted the line is slopes upwards showing that as the concentration of liver suspension increases the rate of reaction increases, this is due to the fact that there was more catalase to collide with the hydrogen peroxide in the higher concentrations. One problem with these results is that my control experiment seems to have a rate of reaction however, this is simply due to the initial burst of gas at the start of the experiment when the hydrogen peroxide that I injected displaced air in my apparatus.
Although this effectively means that all of my results are wrong I can still draw sensible conclusions from my graphs as every one of my results had the same displacement of air so when comparing my results this in fact has no effect. If there had been no displacement of air in my apparatus I think this line would have been straight and through the origin showing that rate of reaction and concentration of liver suspension are directly proportional.
I will not attempt to subtract the gas displaced by the hydrogen peroxide from my results as this could further magnify any inaccuracies in my experiments and I do not need to in order to draw reliable conclusions from my graph. The conclusion I have come to by looking at my graphs is that my hypothesis was correct. I think that as the concentration of the liver suspension increases so does the rate of reaction proportionally.