Apparatus:
I have decided to use the following equipment in order to carry out my experiment:
· Water Baths
· Test Tube/Boiling tube
· 10 cm3 Measuring cylinder
· 2 cm3 of Hydrogen Peroxide
· 1 cm of circular potato chips
· Thermometer
· Borer
·Cylinder; I will use a small cylinder because in my preliminary work I saw in was very inaccurate using a larger one
· Stopwatch
Method:
At first, I will set up the apparatus as above. Get the potato so I will use a Borer to cut a cylinder of potato out of the whole one and from there I will cut up the potato cylinder into segments weighing 3g all together, using a razor. I will then put them into a flasks containing 10 cm3 place it in their designated water/ice baths along with the 10 cm3 of Hydrogen Peroxide. then put the cylinder full water of into the container of water making sure I don’t put any more gas into the cylinder because this will affect my results because im not reading the right readings. The water baths range from 10°C to 40°C, with intervals of 5°C. Time will not affect my experiment, as I will leave all the potato chips in the water baths for an equal length of time, my only variable being the temperature, with a range increasing by 5°C each time. I will use this range because I think it will improve the accuracy of my results and from my preliminary work. Also in my preliminary work I tried increasing the temperature by 2°C but it was to hard to get the exact temperature and took a lot of time. Once the Hydrogen Peroxide and water bath are at the temperature I want them to be, I will put in the potato discs and place the bung over the test tube instantly. I will then start the stopwatch; measuring the time it takes the bubbles to appear and be collect as gas in the cylinder; measuring the gas every 20sec for 5 minutes. I will repeat this two times to find a mean for this temperature. Then repeat for the following temperatures: 0°C, 20°C, 30°C, 40°C, 50°C and 60°C. Key Variables: Heat, pH, Concentration of enzyme of substrate, Potato weight, the surface area of the potato
I shall only be altering the temperature, as that is my main variable, and so I will therefore keep the others the same in order to make it a fair test. I am going to vary the temperature, from above, and control all of the other variables. The amount of Hydrogen Peroxide is carefully measured out using the small measuring cylinder; enabling me to make sure it is kept constant throughout the experiment. I will keep my variables the same by making sure that I have implied the same strategy for each test taken
Safety Precautions:
I will have to be careful when using the Hydrogen Peroxide, as it is a corrosive chemical, so I will attempt to overcome this problem by wearing goggles. Hydrogen Peroxide is a bleaching agent, so I will be wearing a lab coat so it doesn’t bleach my clothes. I will be using sharp razors during the experiment so I will have to be cautious about that. I will also use a peg to retrieve the test tubes from the boiling water baths.
Predictions:
I predict that the enzyme will become denatured, and therefore will work at a slower rate after 40 - 45°C. I think the reason for this prediction is because every enzyme has a temperature range of optimum activity. Over that temperature the enzyme is inactive. This is because as the temperature changes enough energy is supplied to break some of the molecular bonds. The active site becomes distorted and its ability to hold the substrate molecules it was intended to catalyse. When gases or liquids are heated the particles gain kinetic energy and move faster (see diagrams below). The increased speed increases the chance of collision between reactant molecules and the rate increases. However this is not the main reason for the increased reaction speed. (fig.2)
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Most molecular collisions do not result in chemical change. Before any change takes place on collision, the colliding molecules must have a minimum kinetic energy called the Activation Energy. This is shown on the energy level diagrams below. It does not matter whether the reaction is an exothermic or an endothermic energy change. Now when heated molecules have a greater kinetic energy, a greater proportion of them have the required activation energy to react. The increased chance of higher energy collisions greatly increases the speed of the reaction.
(fig.3)
From my background knowledge it is evident that as temperature increases, the rate of reaction also increases. So, it predict that the enzyme will become denatured at around 40°C, and, that as the temperature increases the reaction rate will increase due to the molecules colliding together at a higher speed (kinetic theory) due to their extra energy obtained by the increase in temperature. I predict the optimum temperature will be 30°. I also predict that the opposite of lower temperature (e.g. 10°C) will show a much low activity; in my preliminary work I saw that the rate of reaction was very low at this temperature. I predict that the graph for the total oxygen produced will look like this:
(fig3A)
When a gas is formed from a solid reacting with a solution, it can be collected in a gas syringe (see diagram below). The initial gradient of the graph eg in cm3/min gives an accurate measure of how fast the gaseous product is being formed. If the reaction is allowed to go on, you can measure the final maximum volume of gas and the time at which the reaction stops.
(fig.4)
The shape of the graph is quite characteristic (see below). The reaction is fastest at the start when the reactants are at a maximum (steepest gradient in cm3/min), the gradient becomes progressively less as reactants are used up and the reaction slows down. Finally the graph levels out when one of the reactants is used up and the reaction stops.
My prediction is supported by Collision Theory in that if I apply twice as much heat there will be twice as many collisions and therefore the rate of reaction will double This will only be so until the enzyme denatures after its optimum temperature: 35°C.
Fair test:
In this investigation I will keep constant the following
· The same volume of hydrogen peroxide in each part of the investigation.
· The same concentration peroxide in each part of the investigation
· The same size equipment e.g. boiling tubes as the readings for the results will be wrong if this is not constant.
· Use the same method for each experiment so that there won’t be any major differences. Only alter the temperature.
· Keep the amount of potato the same amount 3g
· Measure the temperature with a thermometer.
·In my preliminary work I found that the cylinder that was collecting the gas was not stable and kept on slipping, loosing a lot of gas , so I would use a stand to keep it stable.
Accuracy:
In order to make my investigation go to plan I will be as accurate as I can be so I will measure to the correct measuring size.
· Use a smaller cylinder to measure liquid more precisely , I will use a small cylinder because in my preliminary work I saw in was very inaccurate using a larger one
· Measure the volume in cm³ and amount of potato in grams to make sure that they are exactly the same mass before using them in the experiment.
· Also to average out the results.
· Use a electronic timer for more accurate results
· Balance mass to 2 decimal places
· Repeat any results that look odd (anomalies). In my preliminary wotk I didn’t repeat each temperature I thought they would be more accurate if they were repeated.
Reliability:
· Do the experiment two times to ensure that there isn’t an odd result. Three is a good number to use as you can see if there is one odd one where if you just done the experiment twice then you wouldn’t know which one odd and which isn’t.
· Selecting a range for reliability
· Use a electronic timer for more accurate results
Results
10°C
20°C
35°C
40°C
45°C
Analysis:
From the graph, I am able to back up my theory. We can now see when the enzyme is most active and when it starts to denature. From the graph, I have found out that, as the temperature increases, so does the rate of reaction. I found that the optimum for a catalase is at 35°C. This is where the greatest number of collisions takes place between the enzyme and the substrate and therefore the highest rate of reaction is. This also supports my predicted graph (fig3A) the predicted graph and final graph are extremely similar and you can see the predict were correct.
The rate was higher at the higher temperatures (up to 35°C) because as the temperature is raised, so is the energy level of the enzymes and substrate molecules. This means that they have more kinetic energy so they collide more often and enzyme/subtracted lock (fig1. This therefore means that the rate increases as more oxygen is produced. The enzyme denatured between 35°C and 40°C because the weak bonds, which hold the molecule into the specific shape for one substrate, are broken. The increase in particle collisions and vibrations at higher temperatures is great enough to change the shape of the active site. The enzyme denatured so can no longer form an enzyme-substrate complex as its active site has been unalterably changed.
My prediction was correct in that there was very little activity in low temperatures (10°C) because the speed at which the enzymes and substrate molecules were moving was very slowly so there were not many collisions between them. The optimum (35°C) temperature was just above as I predicted at 30°C instead of 35°C. The temperature at which the enzyme denatured (45°C) and the activity stopped was also 5°C above what I predicted at 45°C.
Fig.1, fig.2 and fig.3 diagrams explain m analysis in illustrated detail.
Evaluation:
All the data I obtained in this experiment supports my conclusion. I’ve carried out a fair test because the only thing I’ve changed each time was the temperature. Most of the crosses lie close to the line of best-fit suggest accuracy. And also my results support the temperature and collision theory. Even though I carry out my experiment as efficiently and fairly as I could, there were still sum errors and complications in the method, which may need possible improvement. Firstly, the experiment was conducted over a number of days and consequently could not use the same potato. This is a source of error because the concentration peroxidase of in the potatoes may have been different which might have created an inconsistent rate of reaction. As I done the experiment on different days there is also the problem of room temperature. Different days had a range of different room temperatures and also I did my experiment in different places, sometimes near an open window where it was cold or sometimes near the warm sunlight. The water baths were not set at fixed certain temperature for the substances. One had to be very careful that the substances did not exceed their planned temperatures of there was danger of denaturing. If had done the experiment again I would conduct all on the same day because it is less likely there will a large change in temperature, and also for temperature accuracy I would use a electric water bath because they will stay are a unchanging temperature. I would also try to do all the practices with the potato from the same bag, same age and the same variety, so it is less likely there isn’t any large differences in concentration The accuracy of these measurements could be improved by the use of a syringe instead of a measuring cylinder, as it is a more precise piece of equipment and there are fewer margins for error. There could also have been a slight variation in surface area of the potato discs because it was very difficult to get them all the exact same size even though I was using razor. But the evidence I have obtained is not good enough to make firm conclusion; I think this is because I have not done enough temperatures. If I repeated the experiment I would also take more readings for example at every 2°C starting at 10°C because if I did this I would be able to plot a more accurate graph and it would be easier and to tell when the enzyme got to the optimum and denaturing temperatures an use a longer range of temperatures so I can know the exact temperature of the denaturing of the enzyme; in my experiment I didn’t obtain the precise temperature of denaturing; I would repeat the experiment again, but explore 35°C-55°C because in my results an graph the is around the temperature where the enzyme started denaturing.
Maybe going to 45°C/50°C would be a suitable temperature. And also I would extend the length the time, so I could and out if the time when the enzyme stops producing and see what temperature takes the fastest to run out of enzyme.
