Galactose
Fructose
Sorbose
Arabinose
Diagram
Method
As we are measuring the amount of Carbon Dioxide produced; the sugar and yeast solution will be weighed before and after the experiment, to see how much the yeast has respired. The more the solution looses weight, the more carbon dioxide has been created, and the more it has respired.
[Perform 3 times for each sugar (for accurate results test)]
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Measure out 5 cm3 of Sugar solution in a measuring cylinder, and put into the conical flask
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Measure 10 cm3 of yeast solution in a different measuring cylinder, and put into the conical flask.
- Weigh immediately after you mix the two solutions and record the weight.
- Leave the solution overnight.
- Weigh it again the next day, and record any changes.
Fair test
To make it a fair test; always use the same amount of sugar solution (5 cm3) and yeast (10 cm3). Always check if the equipment is clean before use to prevent contamination. Also, the same people will perform certain tasks, so the, measuring for example, will be done by the same person to get the same amount measured each time. The experiment will be repeated a few times to get accurate results and to eliminate any anomalous results. This is not a dangerous experiment so there isn’t any need for protective clothing.
Results
Analysis
The results of this experiment did not have a pattern. How well respiration occurred depended on the structure of the sugars. If the sugar substrate managed to ‘fit’ the enzyme active site properly, then this will create a ‘good’ enzyme substrate complex therefore the yeast would then respire well. In the experiment, looking at the graph, Sucrose respired best (largest positive result), and the Sorbose respired worst (largest negative result). This is probably the case because the experiment was not accurate. There were no patterns in the results. My prediction of Glucose respiring best was incorrect, in fact Sucrose respired best (highest positive percentage change (1.3%)). There was no pattern in this experiment. In theory, Glucose should have been the sugar that respired best, and lost the most amount of mass, then galactose and other hexoses(6 carbon sugars), Arabinose should have respired least because it is a pentose (5 carbon sugar). The results don’t fit with the above, galactose should have at least respired a bit but it did not, even arabinose respired more than galactose. Galactose should have respired because: in yeast cells supplied with glucose, the “GAL” genes are repressed. They are activated a thousand fold in yeast that is starved for glucose, these newly activated genes will make the yeast metabolise galactose. The experiment must have not been performed well or it could have been tampered with or our result taking was not accurate.
Evaluation
This has been very inaccurate, as the results we managed to obtain were totally nonsense. The result taking was probably the most inaccurate part of the experiment because different people took the results increasing the chance of inaccuracy. If I had to do this experiment again then I would use the same, very accurate, balance for each solution because I think this is where the experiment was at its least accurate. This was a very inaccurate experiment, this is proved by the fact that Glucose was not the sugar that respired most, but it should have been, according to (and further research)
The lock and key theory and enzyme substrate complex thing, glucose and yeast should create the ‘best’ enzyme substrate complex so in turn create the ‘best’ Product. But Sucrose respired best, an observation that explains this is that Sucrose (sugar cane) is used (in Brazil and other places) with yeast to create ethanol, therefore, it most ‘fit’ the lock and key mechanism well and metabolise well (because it does create over 4 billion gallons of fuel ethanol per year in Brazil alone). In conclusion this experiment did not go very well, it should have been Glucose that respired best because it is will create the best enzyme substrate complex(as it ‘fits’ yeast’s active site best). Repeating this experiment under more controlled conditions is a good idea because the results of this experiment were very unreliable.
