Increase in temperature Volume increases (Gas expands)
This is because as the temperature of the gas increases, the particles get more energy. This causes the particles to move faster and collide with each other and the walls of the container. If the gas cannot expand, the pressure would increase. If the pressure is kept constant while the temperature is increased, then the gas will expand.
Plan
I have planned to experiment I will take a yeast culture solution (enzyme) 3ml, and mix it with 20ml of hydrogen peroxide (substrate), the substrate will be between 4 vol. and 14 vol. Accurately measure the rate of reaction by collecting the amount of oxygen discharge (given off).
I am using yeast catalyse as opposed to catalyse from apples, potatoes, or liver because it is easier to get the desired amount of yeast catalyse by simply measuring it off. To obtain catalyse from a substance such as potato would involve crushing it and with that method, you would never be sure of the concentration of the catalyse. If the catalyse were used up then another potato would have to be crushed and this could produce catalyse of a totally different concentration, which would lead to inaccuracies in the experiment making this an unfair test.
To ensure this is a fair test all the variables except for the concentration of Hydrogen Peroxide must be kept the same for all the experiments. Variables that must not be altered include: -
Temperature, yeast concentration, type of yeast, batch of yeast, volume of yeast, volume of hydrogen peroxide, air pressure and humidity.
Prediction
I predict that the rate of reaction will subsequently increase proportional with the increase in substrate (hydrogen peroxide)
Scientific reasons for this
I predict that as the substrate concentration increases twofold the final volume of oxygen shall also increase twofold. The rate of reaction will go up at a directly proportional rate until the solution becomes saturated with the substrate hydrogen peroxide. When this saturation point is reached, then adding extra substrate will make no difference.
The rate steadily increases when more substrate is added because more of the active sites of the enzyme are being used which results in more reactions so the required amount of oxygen is made more quickly. This is duo to the concentration of hydrogen peroxide is doubled, there would be twice as many substrate molecules in the same time. Therefore there is twice as many successful collisions, doubling the rate of reaction. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. This is because the maximum number of reactions are being done at once so any extra substrate molecules have to wait until some of the active sites become available.
Catalyse has 4 active sites per enzyme molecule: hence it has a very fast rate of reaction (4 substrates molecules can be catabolise simultaneously.
108 molecules of H2 O2 can be catabolised.
Preliminary
In the preliminary we set out the equipment we were going to use which was: safety glasses, water basin, hydrogen peroxide, yeast culture, boiling tube, retort stand and clamp, pipette, bun/cork, measuring cylinder.
Diagram
I found these were good results, so I have decided to use 0%, 20%, 40%, 60%, 80%, 100% as my concentration. I will do my real experiment three times.
Conclusion:
My results show me that the higher the concentration of a substrate, the quicker the reaction rates of that substrate and the enzyme working on it. The 100% concentration produced the most 02 in the shortest time, which gives it a higher reaction rate than the others. This shows that my prediction was correct, the highest concentration would produce the most 02 in the shortest time. In addition, the anticipated results I produced in my plan were correct, as the lines are almost identical to the lines produced in my results. The next highest reaction rate is the 60% concentration, this is because it had the second highest concentration therefore there would have been the second most amount of collisions. As my prediction and background information show, more collisions produces more reactions. The results then show that in order the reaction rate gets lower as each concentration gets lower. My graphs also show that the reaction rate for 00% concentration is quickest because its line is steepest therefore it shows again that more O2 was produced in a shorter time.
My results support my prediction, because as I said, the higher concentration the quicker more of the O2 is produced. Therefore, my prediction was correct, from what my results show.
Variables – In this investigation, the variables that affect the activity of the enzyme, Catalyse, were considered and controlled so that they would not disrupt the success of the experiment.
I) Temperature – As temperature increases, molecules move faster (kinetic theory). In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. As the temperature continues to rise, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function, as the active site no longer accommodates the substrate. The enzyme is denatured.
To control this variable, the temperature was maintained at a constant level that allowed the enzyme to work effectively (room temperature, approximately 23°C).
ii) PH – Any change in pH affects the ionic and hydrogen bonding in an enzyme and so alters it shape. Each enzyme has an optimum pH at which its active site best fits the substrate. Variation either side of pH results in denaturation of the enzyme and a slower rate of reaction.
In this experiment, the pH was kept constant using a pH 7 buffer, selected to maintain a pH level suited to the enzyme by being equal to the natural environment of the enzyme
iii) Substrate Concentration – When there is an excess of enzyme molecules, an increase in the substrate concentration, produces a corresponding increase in the rate of reaction. If there are sufficient substrate molecules to occupy all of the enzymes’ active sites, the rate of reaction is unaffected by further increases in substrate concentration as the enzymes are unable to break down the greater quantity of substrate.
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vi) Enzyme Concentration – Provided there is an excess substrate, an increase in enzyme concentration will lead to a corresponding increase in rate of reaction. Where the substrate is in short supply (i.e. it is limiting) an increase in enzyme concentration has no effect.
iv) Inhibition – Inhibitors compete with the substrate for the active sites of the enzyme (competitive inhibitors) or attach themselves to the enzyme, altering the shape of the active site so that the substrate is unable to occupy it and the enzyme cannot function (non-competitive inhibitors). Inhibitors therefore slow the rate of reaction. They should not have affected this investigation, however, as none were added.
v) Enzyme cofactors – cofactors are none protein substances which influence the functioning of enzymes. They include activators that are essential for the activation of some enzymes. Coenzymes also influence the functioning of enzymes although are not bonded to the enzyme.
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Safety/Fair:
For this test, I will have to make sure everything is done with safety and fairness. Throughout the whole experiment safety glasses must be worn, as Hydrogen Peroxide can be dangerous if it gets into your eyes. All other Lab rules must be followed also. To make sure the experiment is fair I must make sure nothing is changed for different experiments. I will use the same apparatus for each different experiment and I will make sure the same types of yeast and Hydrogen Peroxide are used. The equipment should be kept the same to ensure all results are taken without any advantages or disadvantages. Everything in the experiment should be kept the same apart from the concentration of the Hydrogen Peroxide. Each time the yeast will be replaced with another 3ml of yeast, as it will have been used to react with the Hydrogen Peroxide in the experiment before.
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.
· Measure the volume in cm³ and amount of yeast in mm to make sure that they are exactly the same volumes before using them in the experiment.
· Do the experiment three 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.
· Also to average out the results.
Take as many readings as possible
Controls
Controls are used to see if there is a reaction coming from the apparatus, to make it a fair test.
- I would put some water in the test tube to see if the glass reacts with it.
- I would do the same for hydrogen peroxide and see if the glass reacts with it.
- Finally with the yeast
Method
Diagram
Equipment list
Boiling tube
Delivery tube
Retort stand and clamp
Container of water
Yeast culture
Water
Pipette
Cork/bung
Stop watch
Measuring cylinder
To test out how the concentration of hydrogen peroxide affects the rate of reaction first set up the apparatus above.
First I would put on my safety glasses and tuck in my tie. After that, I would place the concentration of hydrogen in to the test tube. Put 3ml of yeast into the pipette and then put it in the test tube containing the hydrogen peroxide whilst you put it all in you should start the stopwatch. Then look at the amount of gas if any, that has flowed through the delivery tube and has pushed the water out of the measuring cylinder. Do this for 1 minute and the stop measuring. Then the same procedure for the concentration of 0%, 20%, 40%, 60%, 80%, 100%. For 1 minute repeat each time 3 times.
Results Table
Observations and Measurements – In the boiling tubes it was clear that a reaction was taking place by the observation of bubbles of oxygen gas being released creating a ‘fizzing’ in the boiling tubes.
Analysis
from my graph I can see that my prediction was correct. As when the concentration of substrate(Hydrogen Peroxide) is increased, the rate of reaction increases at a directly proportional rate. My results also show me that the higher the concentration of a substrate, the quicker the reaction rates of that substrate and the enzyme working on it. The 100% concentration produced the most 02 in the shortest time, which gives it a higher reaction rate than the others. This shows that my prediction was correct, the highest concentration would produce the most 02 in the shortest time. In addition, the anticipated results I produced in my plan were correct, as the lines are almost identical to the lines produced in my results. The next highest reaction rate is the 75% concentration, this is because it had the second highest concentration therefore there would have been the second most amount of collisions. As my prediction and background information show, more collisions produces more reactions. The results then show that in order the reaction rate gets lower as each concentration gets lower. My results support my prediction, because as I said, the higher concentration the quicker more of the O2 is produced. Therefore, my prediction was correct, from what my results show. I have a straight-line graph and it has not levelled off. If my graph had start to level off at the top, at this point virtually all the active sites are occupied so the active sites are said to be saturated with Hydrogen Peroxide. Increasing the Hydrogen Peroxide Concentration after the point of saturation has been reached will not cause the rate of reaction to go up any more. All the active sites are being used so any extra Hydrogen Peroxide molecules will have to wait until an active site becomes available. This is like getting a taxi if all the taxi is being used up; you have to wait for an available one. Th enzymes would be the taxi and the substrate passengers.
The theoretical maximum rate of reaction is when all the sites are being used but in reality this theoretical maximum is never reached due to the fact that not all the active sites are being used all the time. The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum. The time taken to fit into and leave the active site is the limiting factor in the rate of reaction.
H2O2 molecules in the same volume, therefore more O2 can be produced.
The diagram of this is shown in my plan.
From the research I found I could make a scientific and persist estimate of what the graph should of look like. My research was correct like my plan.
Anomalies
I had no anomalous results; this was because I worked with precision and skill. If I had had anomlisious results, it might have been because of the delay between putting the bung on the test tube when the yeast was added. It took roughly the same amount of time to put the bung on all the experiments,
Evaluation
I am pleased with my results, as they are accurate and well produced with precision and skill. I know they are produced with precision and skill because there are no anomalous results. As I predicted it is a straight-line graph.
From my results, I have found that the higher the concentration of Hydrogen Peroxide, the quicker the reaction rates, producing oxygen.
I have succeeded in what I planned to do, which was to find out how the concentration of H2O2 affects the amount of oxygen produced in an enzyme catalysed reaction. The results I got were what I had expected and predicted and I did not get any anomalous results. The results I got were what I wanted so I was fairly happy with them.
The experiment could have been made more accurate by using other ways of doing things that were important to the experiment. Measurements that are more accurate could have been used as the measuring cylinders used were only to either every 0.5cm2 or 1cm2. This is not very accurate. Using a gas syringe, which measures much more accurately, could have solved this. Another inaccuracy is when the experiment was started, the measuring cylinder may have still had some air bubbles inside it, and this is not fair as air is not pure oxygen, and it has CO2 and Nitrogen in it. This makes the results slightly less accurate.
To help make this experiment more accurate, I repeated it three times and then used the average of all the results to plot a graph with a line of best fit. I tried to keep all the variables except for the concentration of Hydrogen Peroxide the same for all the experiments. However, in reality it is impossible to keep all the variables precisely the same. For example:
a) There is a slight delay between pouring yeast into the hydrogen peroxide, putting the bung on and starting the stopwatch. This will slightly affect all the results but as I carried out all the three steps in the same way for all the experiments, it should not make any difference to the overall result.
b) It is also impossible to precisely measure out the amounts of Hydrogen Peroxide, Yeast, and Water each time. As the scale on the pipettes shows the volume to the nearest mm3 the volume of the solutions that I used should be correct to the nearest mm3. The volume of gas in the test tube to start with is slightly affected by the amount which the bung is pushed down each time, if the bung is pushed down further then the volume in the tube will be less and the gas will reach faster.
c) Due to the fairly slow speed of our reactions, it is only possible to measure the time of the reaction to the nearest 0.1-second even though the stopwatch shows the measurements to the nearest 0.01 second.
The experimental techniques were customarily enough that the they provided adequately accurate data to compose an accurate rate of reaction graph.
Improvements
I have stated many the improvements in my evaluation. You could use pipettes to a high degree of accuracy. Also the length of the delivery tube may of effect the result so a different shorter delivery tube. I have thought of a different layout for the experiment
Diagram
I could use a smaller quantity of substrate next time, to see if the rate of reaction levels off. I could use ad different enzyme such as liver, potatoes, or celery. To see if this has an adverse effect on the rates of reaction. I have used controls to take more readings.
I could have more repeats. An elaborate description of improvements is found in my plan.
Extend
I could use a catalyse from a different source to see if this effect the experiment. In addition, I could completely change the substrate and enzyme. I could also see if having the yeast in solid form effect the experiment. I could add some inhibitors into the experiment and see what effect they have on the rate of reaction. I could add the same amount of a non-competitive inhibitants and competive inhibitor at different times to see what effect each one has at each time.
Bibliography
Nelson biology and chemistry
Collins encyclopaedic dictionary