12 test tubes
Pipette
Stopwatch
Test tube rack
Glucose, fructose, sucrose and lactose
Water bath
Yeast
Plan:
- You will be provided with a yeast culture already set up. It will be labelled A (glucose) B (fructose) C (sucrose) and D (lactose) and contained in a water bath to allow fermentation to begin.
- Using a pipette transfer culture A into three fermentation tubes, make sure it goes right to the top of the tube. We are doing it three times to ensure we have enough results to do the t-test
- Insert the fermentation tubes into test tubes upside down, and record the height of the bubble. Make sure the test tubes are labelled.
- Put them back into the water bath.
- Record the height of the bubble every two minutes, of each test tube. Do this until the reaction is complete i.e. the bubble would not get any larger.
- Repeat this for the next substrate and so on.
- Record all results in a table so that t-test can be used to calculate the standard deviation of the different substrates to see whether there is a significant difference between them. Allowing the hypothesis to be proved correct or incorrect.
t-test
standard deviation
HYPOTHESIS
The rate of anaerobic respiration will be faster when using the monosaccharides glucose and fructose then it would be using sucrose or lactose.
NULL HYPOTHESIS
There will be no significant difference in the rates of reaction when using different substrates.
VARIABLES
The independent variable is time it will be tested against the dependant variable (amount of carbon dioxide produced), whilst keeping fixed variables constant i.e. lab, volume, temp and concentration of yeast and substrate in the mixture. A control variable must be set up in which no substrate is added.
SAFETY PRECAUTIONS
During the experiment standard lab safety procedures must be carried out i.e. no bags left on the floor, no running and lab coats must be worn.
RESULTS
Height Of Bubble (cm)
The table shows that there wasn’t any anaerobic respiration in lactose. Newborn babies have an enzyme that can break down and digest lactose, but this fades with time. Yeast does not contain the enzyme lactase or any bacteria that can break it down. Glucose and fructose have the same chemical formula but are arranged differently. Glucose is more readily oxidised than fructose, which is why it has the fastest rate. Sucrose is made up of glucose and fructose, the rate is considerably slower this is because it has to be broken up into its’ components before it releases more energy.
A table to show the rates of reactions that the class obtained at 10 minutes
Rate Of Reaction (cm/min)
T- test is used when we have a range of measurements; it is used to find the difference between two means. It will also compare the standard deviation of the different substrates.
Mean (glucose) (X1) = 27.7/9=3.1
Standard Deviation (glucose)
SD = 103.14 – (27.7)/9
8
SD (glucose) = 0.53
Mean (sucrose) = 22.4/14 = 1.6
Standard Deviation
SD = 57- (22.4) /14
13
SD (Sucrose) = 0.35
Using T-test
In the test the degrees of freedom is n1+n2-2 therefore it is 9+14-2=21
The table value for 14 with a probability of 0.05 and 21 degrees of freedom is 2.080. Our calculated value for t is 7.52. Since this is greater than 2.080, the null hypothesis can be rejected.
CONCLUSIONS
From the graph you can see that glucose has the most rapid reaction, this proves the fact that glucose is used in our bodies for a quick release of energy. We store glucose as glycogen and break that down when we don’t have enough glucose and we need it. As you can see sucrose is the slowest and that is because it is a disaccharide and took longer to release the energy. Brewers would be very interested in the results I got, because the brewery wants to make as much beer as quick as the can. Therefore they would most definitely use glucose in the fermenter, because it has the fastest rate of reaction.
Sucrose and fructose are equally as important to our bodies and us; this is because most of the time we need a slow release of energy that is controlled by enzymes. In order for this to happen the enzyme that releases energy from glucose would be turned off, and the enzymes for sucrose and other disaccharides would take over. Sucrose allows for a gradual release of energy not a sudden one. When we sit a lot of our muscles are used and they need energy, but they require a gradual slow release of energy, therefore sucrose would be used. When we are sprinting we need a sudden and rapid release of energy this is were we would use glucose. If the glucose has no oxygen to respire with it will do so anaerobicly and will release a waste product called lactic acid which can be converted to release more energy. Far more energy is released with aerobic respiration 36 ATP molecules compared to 2 ATP molecules from anaerobic respiration.
My hypothesis had been proved correct, and that was that the monosaccharides would have a faster rate of reaction than disaccharides. You couldn’t really put a rate on lactose, it does not respire anaerobicly with yeast, its’ structure is far to complicated to do so, it is a big molecule.
EVALUATION
When transferring the fermentation tubes into the test tubes upside down a bubble always appeared it was unavoidable. This had a big effect on the results as we could not start from zero, if you extrapolate the graph back the line would hit the x axis at approximately 0.5 cm, so we would have to take this away from our results so that it seems that we started at zero. Taking reading from three different tubes takes its time so some tubes would stay in the waterbath about 20 seconds longer than I intended, this would bring in a little inaccuracy into the results.
Allthough there are limitations due to the apparatus and techniques used, the results are still reliable. This is because I can make relevant conclusions from them and test my hypothesis, it couldn’t be perfect but good implementation skills ensured that they were good enough.