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Investigating the Effect of Ethanol Concentration on the Rate of Respiration in Yeast.

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Introduction

Investigating the Effect of Ethanol Concentration on the Rate of Respiration in Yeast Respiration is the process by which the energy in food molecules is made available for an organism to do biological work. Respiration produces ATP, which is the form of energy, made by most organisms, and they use it for their survival. Yeast cell, along with all other cells respire, and I am going to investigate the effect on the rate of respiration when I add various concentrations of alcohol to it. Scientific Theory: There are many factors that can affect the rate of respiration in a yeast cell. In my experiment, I am going to develop this with how an alcohol affects the rate at different concentrations. The equation for aerobic respiration is C6H12O6 + 6O2 6CO2 + 6H2O + Energy ... Is the standard equation before the alcohol is added. As the alcohol is the factor I am assessing, then the concentrations of the yeast solution, and how much sugar I am adding, need to be determined before I can add the different volumes of alcohol, in this case Ethanol. I am going to do this by carrying out preliminary experiments. Glucose concentration is an important part in the reaction as this helps the reaction to get started. If too much glucose is added, then this has an osmotic effect on the yeast cell, pulling all the water out of them and preventing the from respiring. This then kills the yeast cell. Also, if not enough glucose is added then the reaction cannot begin, as it does not have enough raw materials to react with the yeast. Either way, the amount of glucose that is added has an effect on the rate of respiration, as it is the substrate for the enzymes in yeast.. Temperature can also affect how fast and how efficient the reaction is. If the yeast is heated to a temperature above 45'C, then the enzymes within the yeast are denatured. ...read more.

Middle

This is not efficient, as it cannot keep a constant temperature, therefore it is not accurate. Also this method is not safe as Ethanol can be ignited from the Bunsen burner due to it being flammable. As I am using different concentrations of ethanol, I need to ensure that I collect various results from a variety of ethanol concentrations. I aim to use at least 5 different concentrations of ethanol, so that I can obtain a range of results. Safety is important in any experiment that is carried out. So, as I am using ethanol, I need to ensure that this is dealt with great care and kept away form any naked flame that are around, due to it being highly flammable. I also need to ensure that it is kept under a lid as it evaporates, and also does not smell too pleasant either. I also need to ensure that all hair is tied back and I wear goggles at all times. Method: 1. Make up at least 5 concentrations of chosen ethanol concentration and place into test tubes. This is done by adding a volume of ethanol and making it up with water. E.g. for a 40% solution, 4ml ethanol can be added along with 6ml of distilled water. 2. Weigh out yeast and glucose and make up solutions as required. This is done by adding required weight of yeast/sugar and adding a volume of distilled water t it. 3. Heat the yeast solution in the water bath at 30'C, so that it is ready for respiration. Whilst this is heating, set up the apparatus for collecting gas as shown in the diagram. (Appendix 5) 4. Add required amount of Yeast solution to the conical flask, and record the temperature. If needed place in the water bath to increase the temperature as a constant temperature is needed. 5. Next add required amount of sugar solution and immediately after add the required amount of ethanol (if no alcohol is added add 10ml of distilled water instead). ...read more.

Conclusion

Time was also a large limiting factor in my experiment. I found it hard to get all of the concentrations I had hoped for as to set up and carry out the experiment took time, as well as cleaning and washing apparatus and making up fresh ingredients each time. So, I was only able to achieve the concentrations that I have in my results. Space within my working area also prevented me from carrying out my experiment as accurately as I should. So my results could be more accurate. The results I obtained anyway I think support my hypothesis well, yet not extremely well. I predicted that as the ethanol concentration increased then the volume of Carbon Dioxide produced would decrease. This occurred yet not as consistently as I would have hoped it to. I think that this is due to the limiting factors in my experiment that I have just discussed. If I were to carry out this experiment again then the major element I would change would be the time scale. I would allow myself a reasonable time period, yet enough to ensure that fresh yeast was used every day, and maybe have a one-day limit for this. Also I would probably change how I dissolved my sugar in the water. The way that I done it was accurate, yet not extremely accurate as not all the sugar dissolved. I could possible heat the solution to allow the sugar to dissolve, then cool to room temperature to ensure a fair test. Also, I could extend my preliminary experiments more and vary the amount of sugar I used more. I also think that I could use a variety of alcohols, for example propanol or butanol, and see whether they have a different effect on the yeast, or that they change the way it respires. I think that that would be all I would change as overall my experiment and the equipment was well used. 1 Biology Coursework A2 Nikki Jagait 13T 1 ...read more.

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3 star(s)

***
A good plan including relevant background theory. In places more detailed explanations and greater specificity would have been useful. The analysis of results could be more objective.

Marked by teacher Adam Roberts 05/09/2013

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