If I varied the temperature of the experiment, this would be very hard, as to get both the Hydrogen Peroxide and the yeast suspension solution to that specific temperature would be difficult.
If I varied the level of pH, this would also be very difficult. To get both solutions to be the same pH then to vary them is possible, but it would take too long in the time I have been given.
At school we only have two different types of yeasts, so to vary the yeast species would not be an advisable choice.
I could vary the concentration of yeast suspension solution, but I chose to vary the concentration of Hydrogen Peroxide because as it would be easier to measure out and to carry out the experiment quickly, as I need to repeat the experiment many times.
Preliminary work
In the preliminary work I will carry out a ‘test run’ as it seems to be. Therefore, I can find the suitable measurements of the solutions of Hydrogen Peroxide and the yeast suspension. So that the reaction will work the better therefore, my results will be of a higher quality and more accurate.
I set up the apparatus as u can see in my method section. I carried out seven experiments to see which quantities, concentrations and equipment would work best at. I tried to collect oxygen in a measuring cylinder so I could accurately calculate the amount of oxygen given off at a given solution, but the cylinder was filled with oxygen after a few seconds. I decided that the best way to carry out the experiment was to count the number of bubbles given off, working on the assumption that each oxygen bubble given off by the reaction is approximately of the same volume. My results are shown below:
From the table of my results you can see that the best result was experiment number 7. This gave off oxygen bubbles at counting speed and showed me that I would need to use one centimetre cubed of yeast suspension solution and fifteen centimetre cubed of the Hydrogen Peroxide solution.
Prediction
I would expect from analysing my preliminary work that the quickest and most vigorous reaction would be when the concentration is 100%. I would expect the order from the quickest and vigorous reaction to the lowest reaction will be, 75%, 66%, 50%, 33%, 25% and then the slowest to react would be the 10% concentration.
I would expect 100% to react quickest because it has the most Hydrogen Peroxide molecules in it. With more molecules inside the solution, it is more likely that a collision of the two molecules will take place. Some molecules must collide if the solution to react. 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 1 in every 10¹³ collisions lead to a successful reaction taking place. I got this information from a revision GCSE guidebook for Biology. The more reactions that take place increases the amount of oxygen produced.
Method
Apparatus:
· two syringes
· large beaker of water
· conical flask
· bung
· delivery tube
· syringe tube
· 20 volume Hydrogen Peroxide solution
· 20 volume yeast suspension solution
· two small conical flasks
· stop watch
· ‘V’ shapes glass tube or oxygen output
· 500ml of water
· water for changing concentration
· safety goggles
Diagram
We set up the apparatus as shown in the diagram above from the list of apparatus above too. The first thing I will do will be to put on my safety glasses as this test needs to be made safe before anything can be done. I will measure out a rough amount of Hydrogen Peroxide into one small conical flask, and an unmeasured amount of yeast suspension solution into the other small conical flask. I will pour out 15 CCs of Hydrogen Peroxide into the large conical flask. I will measure out the 15 CCs of Hydrogen Peroxide by using one of the syringes. From the small conical flask I will measure out 1 CC of the yeast suspension solution. I will mix the yeast suspension solution before I measure it out using the other syringe. I will do this because as it is a suspension, it could be denser because of the living cells at the bottom than the top, so I will stir the solution well. All of my measurements will be made as precise as possible to keep the experiment accurate and fair. The next thing that I must do is to put the delivery tube and bung together and place the delivery tube, with the glass ‘V’ shaped tube on the end of it. These two pieces of apparatus will be placed at the bottom of 500ml of water in the beaker. I will connect the syringe of yeast suspension solution to the syringe connector on the bung. Once this is connected I will add the yeast solution into the large conical flask, which contains the Hydrogen Peroxide. As soon as I started the reaction I will start the stopwatch. I will count the number of oxygen bubbles that are given off in the first 30 seconds, as this the my time I have allowed myself to count the bubbles to make it a fair test. I will record my results in a table, so I can compare them to my other results.
I will carry out every experiment I do three times, so I can get a range of results for each experiments. I will also take an average so the results. I will be comparing the averages after I have done the experiments. I will do seven different experiments in total. They can be seen on the next page. If I make a mistake during an experiment, I will continue and still record down the result, and redo the experiment again.
Fair Test
To make it a fair test I will use the same apparatus every time, but I will wash the apparatus out thoroughly each time in case they are contaminated. I will do this so one experiment will not have any advantages or disadvantages than the other. I will stir the yeast suspension solution to make the suspension even, so the denser and the less dense molecules are mixed. I will use different Hydrogen Peroxide and different yeast solutions for every experiment, because most or all of the solutions will be used during reaction.
Safety
When carrying out the experiment I will wear safety glasses in case of spillage or if the substances spit during reaction. Hydrogen Peroxide is very toxic and if it gets in my eyes it may cause blindness.
Stop watch
I will start the stop watch at the point of input of the yeast suspension solution. I will only be timing the first 30 seconds on the experiment, as if I did this for longer, then I would need more time to do the experiment as I am pushed for time. The oxygen bubbles will be counted and written into a table in the results. They can be seen in the results section.
To change the concentration of the Hydrogen Peroxide solution, as it is 20 volume at the moment I will use the table I have created below to work out the amounts of each substance:
This table I will use to calculate the exact concentrations of Hydrogen Peroxide. This will save my the bother and the time of the day of calculating the amounts on the day of the practical.
Results:
The results I gained from the experiment are shown in the tables below, the first tables show all the results for each experiments. The last table shows the average figures from all seven experiments.
TEST 1: FULL 20 VOL.
The first test number is incorrect, as the result is outside the range of the other results. I will not count this in my average result
TEST 2: 3/4 15 VOL.
TEST 3: 2/3 13.2 VOL.
TEST 4: 1/2 10 VOL.
TEST 5: 1/3 6.6 VOL.
TEST 6: 1/4 5 VOL.
TEST 7: 1/5 4 VOL.
Results table of the average readings.
Conclusion
My results show me that the higher the concentration of a substrate, the quicker the reaction rates of the substrate and the enzyme working on the substrate. The 100% Volume concentration produced the most oxygen in the 30 second time allowance. This is because it had the highest concentration. This gives it a higher production of oxygen bubbles than my other six results. This shows that my prediction was correct. The reaction with the highest concentration of Hydrogen Peroxide would produce the most oxygen. My anticipated results that I produced in my Planning section were correct. These were, in order of most oxygen produced to least:
100% 20 VOL
75% 15 VOL
66% 13.2 VOL
50% 10 VOL
33% 6.6 VOL
25% 5 VOL
10% 4 VOL
The next highest reaction rate is the ¾ concentration, or 15 Volume Hydrogen Peroxide. This is because it had the second highest concentration therefore there would have the second most amounts of collisions when the Hydrogen Peroxide and the yeast were brought together for reaction. As my prediction and background information shows, the more collisions there are, the more reactions there are. The results then show that in the reaction rate gets lower as each concentration gets lower. My graph that I have drawn also shows that the reaction rate for the 20 Volume concentration is quickest because it’s line is steepest therefore it shows once again that more oxygen was produced quicker than when there was a less concentration of Hydrogen Peroxide.
My results support my prediction. I said in my prediction that the higher concentration the Hydrogen Peroxide, the more oxygen would be produced. The results follow an almost perfect pattern.
Evaluation
From my results I have found that the higher the concentration of Hydrogen Peroxide, the quicker the rate of the reaction, thus more oxygen being produced.
I have succeeded in what I had planned to do, which was to find out how the concentration of Hydrogen Peroxide affects the amount of oxygen produced in an enzyme catalysed reaction. The results I got were not a surprise and were what I had expected and predicted from the start. I did get one result which was abnormal, but I put this down to the lack of my accuracy. The results I got were what I wanted, so I am happy with them.
The experiment could have been made more accurate by using other ways of doing things that were important to the experiment. More accurate measurements could have been perfected by not using measuring cylinders, which were only to either 0.5cm² or 1cm² degree of accuracy. This is not very accurate. I would use a gas syringe, which measures much more accurately, could have solved this problem. Another inaccuracy was when we cleaned out the measuring cylinders, they could of still contained some Hydrogen Peroxide, water or yeast. This would give that test either an advantage or a disadvantage. I know that the temperature can effect the rate of a reaction. The temperature was not the same on both days, as one of the days was hot, and the other overcast. So this may have changed the results slightly. The enzymes may have denatured in some experiments because of the yeast solution could have been uneven. So some heavier enzymes could of sunk to the bottom and lighter enzymes as the top. I stirred the yeast suspension solution to solve this problem, but maybe using fresh yeast could perfect the results furthermore. Making sure that the oxygen bubbles were inside the allowed time of thirty seconds was difficult, having an adjudicator to calculate too could help in this problem. The more different concentrations of Hydrogen Peroxide would prove the whole experiment was correct without a doubt. Another thing to be done would be to do more repeats for each concentration. This would make results more accurate when finding averages.
