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# Investigation into the Affect of Temperature on Yeast Activity.

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Introduction

INVESTIGATION INTO THE AFFECT OF TEMPERATURE ON YEAST ACTIVITY AIM: To investigate the affect of temperature on yeast activity. APPARATUS: 1 test tube, 1 boiling tube, rubber bung and delivery tube, test tube rack, 250ml beaker, tripod, gauze, Bunsen burner, stopwatch, 2 measuring syringes, thermometer, safety goggles, 250ml of glucose solution and 250ml of yeast solution. DIAGRAM: METHOD: 1) Set up the apparatus as shown in the diagram. Put on safety glasses and fill the 250ml beaker with water to slightly over half way. Also fill roughly 3/4 of the test tube with water. 2) Measure out 10ml of glucose solution in one syringe and 10ml of yeast solution in the other. Add these two solutions together in the boiling tube. 3) Light the Bunsen burner and heat the water in the water bath to 15oC. When the water has reached temperature place the boiling tube into the beaker. 4) When the contents of the boiling tube have reached 15oC remove it from the beaker and fit the rubber bung and delivery tube. Place the loose end of the delivery tube into the test tube containing water. 5) Gently shake the glucose and yeast solution and start the stopwatch when the first bubble appears in the test tube. Time how many bubbles are released from the delivery tube in 1 minute. 6) Record the result and measure the temperature of the glucose and yeast solution to check it has remained at 15oC. If not, disconnect the rubber bung and delivery tube and place the boiling tube back into the beaker. Heat the glucose and yeast solution back up to temperature slowly. ...read more.

Middle

The average bubble count was calculated using the following equation: (Test 1 + Test 2 + Test 3 + Test 4 + Test 5) / 5 = Average bubble count Temperature (oC) Bubble Count (bubbles per minute) Average Test 1 Test 2 Test 3 Test 4 Test 5 15 3 4 3 5 3 3.6 25 11 10 21 15 11 13.6 35 21 20 33 27 22 24.6 40 17 17 30 26 18 25.6 45 29 28 16 27 30 26 50 16 15 17 20 17 17 60 8 2 0 1 0 2.2 65 0 0 0 0 0 0 ANALYSIS: The results of my experiment show that higher temperatures up to a point somewhere between 45oC and 50oC, where all respiration stops, increase the rate of yeast respiration. My results can be presented in simple line graphs, with temperature (oC) on the 'x' axis and number of carbon dioxide bubbles produced through respiration on the 'y' axis. When arranged in the line graphs it becomes apparent that my results for the experiments, excluding test 5, are significantly inconsistent. In an attempt to counteract this I calculated the average bubble count. This provided a fairly precise curve of best fit and straight line. From the graphs I am able to find the following trends and patterns in my results: * As the temperature increased the rate of yeast respiration increased, up to 45oC where a decrease in respiration began occur - this displays a direct positive correlation followed by a direct negative correlation. * The rate of yeast respiration does not increase with temperature in a linear fashion. ...read more.

Conclusion

I also found a strange pattern in my results table that did not related to the averages or the graphs. It showed a significant increase in the amount of bubbles produced on test 3 of each temperature, which rose by roughly 12 bubbles when compared to tests 1 and 2 that were quite similar. There is a possible reason for this pattern: after test 2 at each temperature the temperature of the yeast and glucose solution had fallen, so I reheated it back to temperature. Doing this must have re-acclimbatised the yeast and caused it to produce bubbles at an increased rate. However, once the temperature fell again after reheating, lower bubbles counts were obtained for tests 4 and 5, so averaging out the results. The evidence I have obtained in this experiment is reliable enough to support the conclusion that the rate of yeast respiration increases with temperature up to 45oC, and then the zymase enzyme becomes denatured. However, I do not believe that the evidence is strong enough to support a numerical conclusion; such as if the temperature is doubled then the rate of respiration is doubled. More accurate experiments would need to be carried out before any reliable numerical conclusions could link the respiration rate of yeast and temperature. A useful extension for this investigation would be to measure the rate of yeast respiration beginning from a temperature of 45oC and increase the temperature very slightly, for example, in 2oC or 3oC intervals, until respiration no longer occurred. This would find the approximate point where the zymase enzyme becomes denatured as well as the optimum functional temperature for the enzyme indicated by the highest respiration rate. Also, to further extend this investigation, I could examine another factor affecting yeast activity, such as the concentration of glucose or yeast solution. Nick Hawkshaw Page 1 4/30/2007 ...read more.

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