I will be changing the temperature of the yeast, and I intend to use these temperatures: 20, 30, 40, 50, 60, 70, and 80 (oC), although it does not matter what exact temperatures I use, as long as they are at a suitable range. I will just use the temperatures which are most convenient when I am making the water baths.
I will measure how much water will be displaced by Carbon Dioxide in 3 minutes, in cm.
Temperature is my independent variable.
Volume of carbon dioxide produced in 3 minutes is my dependent variable.
I will also control the concentration of yeast (this will be 10%), the concentration of glucose (also 10%). I will always use 10cmof glucose, and 10cm of yeast. I will not change the time taken to collect the carbon dioxide (3 minutes) or the volume of liquid paraffin (2 drops) or volume of diazine green (2 drops). The reason I won’t change any of these is because they might affect the volume of carbon dioxide produced, which would make my experiment unfair.
This is my planned method:
Glucose solution (at a concentration of 10%) will be boiled to remove all the oxygen, and then cooled. 10cm of this will be added to 10cm of a 10% concentration yeast mixture. This will then be poured in a test tube. 2 drops of diazine green will be added so I can tell when all the oxygen has been used up in aerobic respiration. It will be blue when oxygen is present and pink when it is not. I will put the test tube with the other apparatus as shown in my diagram (without the rubber bung in the test tube). I will add 2 drops of paraffin in the test tube to prevent oxygen getting into the suspension. When the suspension appears pink, I will start the experiment by placing the rubber bung in the test tube and measuring how much carbon dioxide is produced in 3 minutes. Each time I use a new temperature, I will use a new set of yeast, glucose, paraffin and diazine green. I will then repeat the experiment, making sure each time that anaerobic respiration has started (i.e. mixture is pink).
These are the temperatures I plan to use:
20 oC 30 oC, 40 oC, 50 oC, 60 oC& 70 oC although as long as the temperatures I use have a suitable range, it does not matter if the temperatures are exact or not, for example 22 oC is just as good as 20 oC.
Diazine green can be dangerous if it gets into your eyes, so I will wear safety goggles. I will ensure that no obstructive items such as bags are on the floor at the time of the experiment. As I will be using glass apparatus I will have to be careful it doesn’t break and cut me.
To ensure my results were reliable I will do 3 repeats in total of the same temperature. If the results look similar enough I can assume they are reliable and I will keep them. If they do not, I will redo them until they look reliable. This will keep my results accurate.
There are many possible causes of error that could affect my results:
- If the yeast and glucose mixture is not the same temperature of the water.
- If the temperature of the water bath (and hence the glucose and yeast mixture) goes down during the experiment, so will the rate.
- If the paraffin does not completely cover the mixture and oxygen can get into the mixture, aerobic respiration would start.
- If a mixture is not completely mixed there will be less successful collisions per second between the reactants which will decrease the rate.
- Different volumes of water in the water bath will affect how much it changes the temperature of the yeast and glucose mixture.
Preliminary experiment:
I wanted to see if I needed to make any changes to my experiment, so I carried out the experiment as planned so far, and I got the following results:
I did two runs, so I could see anomalies if I got any.
During this experiment I noticed that the contents of the test tube where bubbling over into the delivery tube. Another problem was that I could not see the colour of the diazine green in the mixture so it was hard to tell when aerobic respiration had fully stopped. Also as the mixture bubbled over the paraffin had no effect. These are probably the reasons that my results don’t show a good trend. This means I am going to have to modify my experiment:
Modified Method
I will carry out my experiment as I planned before, but I will use 6 drops of diazine green instead of 2, because with 2 drops I couldn’t see the colour so I couldn’t tell when aerobic respiration had stopped, but should definitely be able to with six. Also I will only use 5cm of the yeast mixture and 5cm of the yeast mixture so that the mixture doesn’t bubble over. I am going to also use 6 drops of paraffin so there is no way that oxygen can get in and trigger aerobic respiration. Also I am going to take 3 runs for each temperature rather than 2, and work out an average.
Analysing
My results show that below 20 oC, anaerobic respiration has hardly started and is too slow to allow a measurable volume of carbon dioxide to be evolved in three minutes. This is because the reactants rarely collide frequently enough and with enough energy to react because the temperature is too low. At temperatures above 20 oC, measurable respiration starts, and rate of anaerobic respiration increases as temperature increases, because as the temperature increases, the reactant particles collide more frequently and with more force, so the number of successful collisions per second increases. This increase in rate stops when the temperature reaches an optimum temperature where rate is at the highest. On my graph the optimum temperature appears to be at 48 oC, but it could be anywhere between 42 oC and 52 oC. At temperatures above 48 oC, the rate appears to decrease as temperature decreases because the enzymes are beginning to denature. As temperature increases, the active sites of the enzymes slowly misshape until they completely denature and anaerobic respiration cannot take place. At temperatures above 48 oC, as temperature increases the rate of respiration decreases because the enzymes are losing their active sites so the substrate particles cannot react as often. At 76 oC the rate is zero and respiration has completely stopped because all of the enzymes have been denatured and the active sites have been lost so the reaction cannot take place.
My graph shows this trend clearly. At 20 oC the line starts as the rate increases until the highest point which is at 48 oC. The highest point on the true line of best fit however could be anywhere between the two points either side of 42 oC and 52 oC.
Calculations
To work out the average volume of carbon dioxide produced in 3 minutes (cm), I added the 3 runs from one temperature together and divided the sum by three because:
Mean value = _Sum of values__
Number of values
Conclusion
I can conclude that as temperature increases, the rate of anaerobic respiration in yeast increases, until an optimum temperature where the rate is highest. At temperatures higher than this temperature, as temperature increases, rate decreases, until all the enzymes have fully denatured, all the active sites have been lost, and the rate is zero.
This is exactly as I predicted; I predicted that as temperature increases, the rate will also increase, until a certain optimum temperature, after which, the rate will decrease until the rate is zero as respiration has stopped completely. The experiment has verified my prediction.
Evaluation
My experiment was successful. The results showed a good trend and the results were accurate and repeatable. I can tell they are repeatable because the repeats in my results table are consistent. I have also shown this on my graph by adding error bars. This shows how they work:
I have not included errors bars at temperatures where all three readings were the same.
I had one anomaly (the 2nd reading at 48 oC), possible reasons are
- If the yeast and glucose mixture was not the same temperature of the water.
- If a temperature of the water bath went down during the experiment, this would have lowered the rate.
- If the paraffin did not completely cover the mixture, oxygen could have got into the mixture causing aerobic respiration.
- If the mixture was not completely mixed there would be less successful collisions per second between the reactants.
- Different volumes of water in the water bath will affect how much it changes the temperature of the yeast and glucose mixture.
To improve the experiment I could use a gas syringe instead of a measuring cylinder as they are more accurate. I would attach it to the delivery tube, but I would no longer need to use a bucket to hold water, and I could use a conical flask instead of a test tube so the yeast and glucose mixture doesn’t bubble over, but if I did this I would need a larger volume of liquid paraffin to cover the glucose and yeast mixture. Also I could use a thermostatically controlled water bath instead of water in a beaker, because this would keep the temperature of the water bath constant so the temperature of the yeast and glucose mixture would not change throughout the experiment and would keep my results more accurate. This diagram shows what I would use:
Extended experiment:
I could repeat the experiment with the aim of find the optimum temperature for anaerobic respiration in yeast. I would repeat the experiment with the above improvements but use the following temperatures instead:
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52 (oC)
If I wanted I could also find a more accurate optimum temperature by using a small range of results at small intervals, for example if the highest reading was at 47 oC, I could then measure the rates of respiration at the following temperatures:
46.5, 46.6, 46.7, 46.8, 46.9, 47.0, 47.1, 47.2, 47.3, 47.4, 47.5 (oC)
This would give me a more accurate optimum temperature, as the optimum temperature is only as accurate as the temperature intervals are small.
Another experiment I could do would be to find the temperature at which all the enzymes in yeast involved in anaerobic respiration are fully denatured. I would repeat the experiment with the same changes (conical flask, gas syringe and thermostatically controlled water bath) but used the following temperatures instead:
66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76 (oC)
Then I could find this a more accurate value, for example if 70 oC was the lowest temperature which gave all the volumes of carbon dioxide produced in 3 minutes (cm) as 0, then I would do the same but with the temperatures:
74.1, 74.2, 74.3, 74.4, 74.5, 74.6, 74.7, 74.8, 74.9, 75.0 (oC), and then the lowest of these values which gave which gave average volume of carbon dioxide produced in 3 minutes as 0 would be the temperature at which all the enzymes in yeast fully denature (to 1 decimal place).
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