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An investigation to look at the affect of changing temperature on the speed of fermentation of yeast.

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Introduction

An investigation to look at the affect of changing temperature on the speed of fermentation of yeast Introduction Yeast is a microbe that can respire anaerobically (without oxygen). The reaction for this experiment is: Glucose (with yeast) = ethanol + carbon dioxide C6HL2O6 = 2C2H5OH + 2CO2 Preliminary Plan We set up the equipment as below: We used the temperatures 10?C, 20?C, 30?C, 40?C, 50?C, 60?C and 70?C. We got the yeast to the right temperature by either melting ice in it to cool it down or putting it in a water bath to heat it up. We then placed three spatulas of glucose (sugar) into the beaker with the yeast. We then put the tube into the beaker to collect the carbon dioxide. We placed this tube into the water bath with the measuring cylinder full of water, upside down over the top of it. Then as the carbon dioxide filled the measuring cylinder the water level decreased. We timed this for 3 minutes with a stopwatch then read the amount of carbon dioxide that had been produced and recorded it. We did this seven times for each of the temperatures. When we examined our results we could see that they weren't very accurate. This was because of the markings on the measuring cylinder. We then decided to use a new method. ...read more.

Middle

Energy diagram In the yeast enzyme there is an active site. This has a specific shape especially for use in fermentation. Only a glucose molecule is the right shape to be a substrate for the yeast enzyme active site. When the glucose molecule has enough kinetic energy it slots into the yeast enzymes active site (key fitting into lock). The reaction has then been catalysed and the products can't stay in the active site so they are released. These products are ethanol and carbon dioxide. Studying my predicted graph the optimum temperature for the reaction is 40?C because it is the activation energy. The glucose molecules have enough kinetic energy to collide and lock onto the yeast enzymes active sites. After 40?C some of the enzymes begin to denature (change shape) but not all at once. When they denature the glucose molecules can't lock onto the active sites anymore. At around 70?C all of the enzymes become denatured and the active sites have changed shape so no glucose molecules can lock on therefore there is no fermentation. Results table Temperature (?C) Amount of CO2 produced in 5 mins (cm3) Average amount of CO2 Produced in 5 minutes (cm3) Run 1 Run 2 10 3.4 3.8 3.6 20 11.1 14.1 12.6 30 19.0 20.5 19.6 40 32.5 20.2 26.4 50 26.2 19.2 22.7 60 3.2 9.7 6.5 70 0 0.6 0.3 Conclusion My graph shows that the results of my experiment are what I predicted. ...read more.

Conclusion

They followed the pattern of my predicted results. There were two anomalous results. These were 20?C and 60?C. For my results to gain in reliability I would need to find out what factors could have affected my final results and then remedy them. I don't think the yeast was kept at the exact temperature all the way through the experiment. Once we had gotten the yeast to the temperature we wanted we took it out of the water bath and began the experiment. While we did the experiment we didn't keep the temperature the same, it probably started to go to room temperature. This would have affected my results and could explain my anomalous ones. To prevent this from happening, while doing the experiment we should keep the yeast in the water bath and make sure it remains at the desired temperature. Another factor that could have made our results unreliable is the sugar. We added three spatulas of sugar but they weren't at an equal level. To make sure this doesn't affect our experiment if we did it again I would make sure that each spatula of sugar was either flat or the same level. Another improvement that I could make to my method is to seal the rubber tube and thermometer better into the bung. I felt that in the experiment carbon dioxide could have leaked out of the bung and therefore caused anomalous results. ...read more.

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