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Biology investigation to investigate how selected variable affects the rate of fermentation in yeast.

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Biology investigation to investigate how selected variable affects the rate of fermentation in yeast Planning I think that the easiest way to measure the rate of fermentation in yeast is to measure a waste product of respiration. When the yeast is unable to respire aerobically it respires anaerobically producing alcohol and carbon dioxide. I could measure either of these two things to measure the rate of reaction. To measure the volume carbon dioxide is easier. I will do this by counting the number of bubbles of carbon dioxide through a wine trap with water in it. This gives a good indication of how fast fermentation is occurring. I predict that as the temperature rises so will the rate of reaction in the yeast and therefore the volume of carbon dioxide produced. However when temperatures exceed 40�C the rate of reaction will start to decline and beyond 70�C the reaction will cease and if temperatures are significantly below 40�C (20�C) there will be very little or no reaction. I am of this opinion because of the way enzymes are affected by temperature and because yeast contains enzymes. I know that enzymes have an optimum working temperature of about 40�C and that below this they fail to work effectively and above it they become denatured and fail to work. ...read more.


Step 2 When the water has heated to the correct temperature (15�C above chosen temperature) pour 50cm� into the 75cm� tripour and 100cm� into the water bath. Measure the temperature, which should have fallen to about 7�C above the required temperature. Place the remaining water back onto the heat and leave with the Bunsen burner on a low heat setting. Step 3 Add the sugar, weighed previously, to the water that is in the 75cm� tripour. Using the stirring rod, stir the solution until all of the sugar has been fully dissolved. Then pour this solution into the fermentation vessel. Step 4 Using the funnel add the yeast to the fermentation vessel and replace bung. Next add 2ml of water to wine trap. Then with finger on the bung shake the vessel vigorously for about 40-60 seconds. After this, remove bung and as quickly as possible replace with wine trap. Immediately immerse the fermentation vessel complete with wine trap into the water bath. Step 5 Using the thermometer check that the temperature of the water bath is exactly as desired. If it is too low then add hot water from the large beaker being heated by the Bunsen burner, using the pipette dropper. If it is too high then add cold water. ...read more.


The results from repeat reading are slightly different in most cases but never by anything greater than 4. This does however show that the results could have been better. A 3rd repeat of the experiment would have been preferred enabling me to produce a more accurate average. Unfortunately I didn't have time. There was one difficulty in counting the numbers of bubbles. As mentioned earlier the heated water which was added to the water bath caused the top of the fermentation vessel to heat rapidly and the air inside to expand forcing air through the wine trap producing bubbles. These had to be distinguished from carbon dioxide bubbles which were to be counted. Had I had more advanced equipment I would have liked to use a thermostat and some means of electronic heater to control the temperature of the water bath and produce more accurate readings. I had biased my suggested temperature values to be more concentrated around the 40�C mark but I think that it may be worth doing more in this range perhaps trying to do it at 1�C intervals, from say 35�C - 45�C. This would be difficult however and would require more advanced equipment such as a thermostat and electric heater immersed within the water bath. With this level of accuracy it may be worth then using a gas measuring syringe to measure accurately the volume of carbon dioxide produced. ?? ?? ?? ?? 1 Lewis Buckley 10A (T/A) ...read more.

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Here's what a teacher thought of this essay

4 star(s)

A really good report on the effect of temperature on rate of fermentation. To improve on this I thought you could have included more detail on the theory side of enzymes, how they work and what happens when they become denatured. I think it would also have benefitted from an explanation of what fermentation is.
The analysis was good but do not forget to use data from the results section to support what you are saying.
Method very good.

Marked by teacher Jon Borrell 08/01/2013

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