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The Effect Of Glucose Concentration On The Activity Of Various Yeasts

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Introduction

The Effect Of Glucose Concentration On The Activity Of Various Yeasts Aim / Prediction - I intend to investigate what effect, if any, varying concentrations of a glucose solution has on the activity of two different types of yeasts. I predict that yeast activity will continue to rise as the concentration of the glucose solution increases, but will maybe have an optimum point at which the yeast can no longer withstand the high concentration in glucose. This applies to both of the yeasts, although I think that bread-making yeast will be more tolerant of glucose than brewers yeast. There will be a positive correlation between glucose concentration and yeast activity. Null Hypothesis (HO) - Varying glucose concentrations will have no effect on yeast activity. Alternative Hypothesis (H1) - Varying glucose concentrations will have no effect on yeast activity. Background - Yeast is any of a number of microscopic, unicellular fungi important for their ability to ferment carbohydrates in various substances. Most cultivated yeasts belong to the genus Saccharomyces; those known as brewer's yeasts are strains of Saccharomyces cerevisiae. Yeasts are used generally in the making of bread and alcohol, but their cultivation and use in large quantities are used industrially in a wide range of fermentation processes. Glucose Carbon Dioxide + Ethanol The yeast metabolises the sugar and produces carbon dioxide and ethanol, which takes place either aerobically or anaerobically. According to the theory of natural selection, changes take place in populations because individuals with the most favourable characteristics are most likely to survive and produce young. ...read more.

Middle

This has given the 5% solution (5% glucose). ii) Stir thoroughly with a glass rod. 6. 0% solutions should be 100% pure deionised water. 100% solutions should be 100% 1.00M glucose. As it is a 100ml measuring cylinder, translations into a percentage are fairly simple. For example, a 55% solution would need 55ml of the 1.00M glucose solution diluted to 100ml with deionised water, so this would mean adding 55ml glucose : 45ml water, for the 55% solution. NB: the above is the easiest method, though if this becomes a wasteful technique, a simple sum can be used to reduce the volumes of liquids used. For example, rather than using a 100ml measuring cylinder, use a 50ml measuring cylinder, therefore, halving the volumes of deionised water and glucose solution required. The 55% solutions would now need 27.5ml of the 1.0M glucose solution diluted up to 50ml with deionised water (22.5ml) and this would still be a 55% glucose solution. 7. Transfer the 100ml of the measuring cylinder to a 100ml beaker and label it appropriately. 8. Place it in the water bath. 9. Repeat the above procedure, increasing the amount of glucose each time accordingly (usually 5ml). Do this until all 21 concentrations have been made up. (0% 100%) Stand all labeled beakers in the water bath at 30o c. 10. Firstly, using the bakers yeast, weigh out 5 separate lots of 0.5g into weigh boats. Transfer each of the weigh boats contents into each of the 5 side armed test tubes, ensuring not to disturb the displacement measuring cylinders. ...read more.

Conclusion

Also, the addition of oxygen may have improved the results obtained as well. Yeast prefer to work aerobically, therefore, different results may have been obtained if oxygen was passed through the solution and subtracted from the final volume of gas collected. Obviously, the available apparatus was a problem here. When yeast respires anaerobically, they may produce different volumes of CO2 - a lower yield to when they respire aerobically. Although the water baths did keep the temperature steady within a few degrees Celsius, which was easier than using a Bunsen burner, they could never really keep the temperature constant which would have produced a much fairer test. One big improvement that could have been made to the experiment would have been to replicate each test, on each concentration of the glucose 3 times. If the mean result of these three tests were taken, it would have produced much more accurate results. Obviously the time it would have taken to do this would have made it virtually impossible to carry out. Finally, another problem, which may have accounted for anomalous results, is the idea that the mass of the yeast used each time (0.5g), may not have actually reflected the size of the population as some of the 0.5g of yeast may have in fact been dead to start with, making each test unfair. Anomalous results - These are highlighted on the graphs. All of the above factors may have accounted for the production of these freak results. Unless several repetitions were carried out to attempt to 'iron' out these results, it would be almost impossible to avoid them. Andrew Muir 01/05/07 1 ...read more.

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