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How Does the Changing Temperature Affect the Rate of Fermentation by Yeast.

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How Does the Changing Temperature Affect the Rate of Fermentation by Yeast Aim: My aim is to find out the effect of changing temperature on the rate of fermentation by yeast. Introduction: Fermentation is another name for the production of energy from food without using oxygen. When yeast ferments glucose the process can be represented by the following word equation - Glucose alcohol + carbon dioxide + energy Yeast is a single celled, microscopic fungus that uses sugar as food. Yeast reproduces asexually by budding a 'daughter' cell. This then becomes detached and follows an independent existence. Fermentation is important in everyday life because it has a variety of uses. Brewers exploit fermentation to produce alcoholic drinks, and bakers use the carbon dioxide to make bread rise. Key factors, which could affect the speed of fermentation, are temperature (which I am investigating), amount of yeast, amount of glucose solution and concentration of the glucose solution. The rate of reaction could be measured by the amount of gas given off during fermentation - the number of bubbles or volume of gas. Prediction: I have chosen 5 temperatures or variables at which I will measure the rate of fermentation: 20?C, 30?C, 40?C, 50?C and 60?C. I think that the optimum temperature, where the rate of fermentation will be quickest is 40?C. I think that the rate of reaction will be slow at 20?C and increasing at 30?C. I think that above 40?C the reaction will slow down again. Scientific reason: All enzymes are made of protein, and proteins are denatured at high temperatures (above about 50�C). ...read more.


65 0.0 0.2 2.0 0.0 0.1 * I have decided not to use the results from pupil 3 because they are not like the results of the other pupils and therefore may be inaccurate. Rate of reaction: Temperature/ �C Rate of reaction - cm�/minute 20 Gas collection = 1 = 0.5 Time 2 30 Gas collection = 2 = 1 Time 2 35 Gas collection = 2.6 = 1.3 Time 2 40 Gas collection = 3.6 = 1.8 Time 2 50 Gas collection = 3.6 = 1.8 Time 2 60 Gas collection = 0.8 = 0.4 Time 2 65 Gas collection = 0.1 = 0.05 Time 2 Conclusion: The graph showing class results shows that as the temperature of the yeast suspension increased, the rate of fermentation (shown by the volume of gas collected) increased. The readings taken at temperature 40�C and 50�C were very similar, after which the level of activity fell as the temperature was increased. This would seem to indicate that the optimum temperature for activity of yeast in glucose solution falls somewhere between 40�C and 50�C. The graph shows that there is a relationship between the rate of activity of the yeast (amount of gas produced) and the temperature of the glucose solution into which the yeast is placed. Comparison of original prediction with conclusion: In my original prediction I thought that the optimum temperature, where the rate of fermentation would be quickest was at 40?C - my conclusion shows this to be nearly correct, as from class results the optimum temperature was shown to be somewhere between 40?C and 50?C. ...read more.


I got one anomalous result, which occurred at 60�C. I thought that it was anomalous because the rate of fermentation of yeast at 60�C should not have been the same as the rate of fermentation at 40�C or 50�C. It is a much higher result than I expected. I think that this result occurred because the enzyme in the yeast had not been denatured, as it had not been at 60�C for long enough. If it had been denatured, or even partially denatured it would not have given anywhere near as high a result. To get more information for my conclusion I would do my experiment with more temperatures, to get a wider set of results to analyse, and to know what the effect of temperature on the rate of fermentation really is, as at the moment I do not really have enough results. To provide extra evidence to support the results that I have, I would like to carry out the following experiments: * I would carry out the same experiment using different sugar solutions, for example fructose or sucrose and see whether using different sugar solutions affected the rate of fermentation. I would mix the yeast and sugar solution together once they were both at the correct temperature. I would still measure the rate of fermentation by recording the volume of gas over a specified time. * It would be interesting to investigate the effect of the room temperature of the laboratory on the rate of fermentation, as I believe that the results obtained would vary if the experiment was carried out in a very hot room, for example a 40�C laboratory or a very cold 10�C laboratory. Alison Hines 4L ...read more.

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