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How Does Temperature Affect the Rate of Respiration of Yeast?

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How does temperature affect the rate of respiration of yeast? Introduction Respiration usually happens in the presence of air (oxygen), this is called aerobic respiration. However respiration can also happen without oxygen and this is called anaerobic respiration. Yeast contains single-celled organisms which respire aerobically if oxygen is available. When the yeast is mixed with sugar or glucose solution, it soon starts to respire. The yeast uses sugar and oxygen dissolved in the water to produce carbon dioxide, water and energy by aerobic respiration. This is the chemical equation for aerobic respiration. Yeast Glucose + oxygen -----------------> carbon dioxide + water + energy C6H12O6 6O2 6CO 2 6H2O 2880 kJ / mole When all the oxygen has been used up, the yeast continues to respire anaerobically. Under anaerobic conditions, the yeast produces carbon dioxide and ethanol (alcohol) rather than carbon dioxide and water. This is the chemical equation for anaerobic respiration. Yeast Glucose -----------------> ethanol + carbon dioxide + energy C6H12O6 2C2H5OH 2CO2 210 kJ / mole We call this process alcoholic fermentation. As with aerobic respiration, this reaction does not take place in one go, but in a series of steps. Although yeast can survive during anaerobic respiration, it does not grow and multiply as it would during aerobic respiration. Anaerobic respiration releases much less energy than aerobic respiration, only 210kJ compared to 2880kJ. In anaerobic conditions most energy remains locked in the ethanol. We can show this by burning some ethanol, the energy is given out in heat form. One problem is that alcohol is poisonous in large amounts. ...read more.


However this may at some point peak and therefore from then on it will decrease in respiratory rate. My reason for the above prediction is that yeast can respire both aerobically and anaerobically. In the experiment the yeast will be respiring anaerobically and breaking down the glucose stored in it as a waste product of this process it will also form CO2 and alcohol in the form of ethanol. This respiration process is called fermentation. The yeast breaks down the glucose using a series of enzymes. I think from this that the more glucose that is present in the yeast the more will be broken down and therefore more CO2 and ethanol will be produced as waste products at a faster rate until it reaches a certain temperature and the amount of CO2 will reduce. Variables and Constants Here is a list of dependant variables. These can have an affect on my experiment and this is how I will control them if possible. Amount of yeast solution Amount of glucose solution Amount of shaking Light conditions Time Apparatus AMOUNT OF YEAST SOLUTION The amount of yeast solution is crucial, more yeast means more glucose will be respired and more products created. An imbalance will upset the results. The yeast solution will be measured out each time using a measuring cylinder to make sure we have the same amount every time. AMOUNT OF GLUCOSE SOLOUTION The amount of glucose solution will affect the results also, as more glucose would speed up the experiment, and therefore not make it fair. ...read more.


For this, I checked everything was set up correctly at the beginning of each new temperature in the same way. To obtain more reliable results I would want to: * Measuring the same amount of dried yeast on scales and to measure the water in a measuring cylinder to make sure I use the same concentration of yeast and water. * Prepare the yeast solution at the same time and leave at the temperature. * Not activating the yeast so as to prevent any getting a 'head start' over the others. * This would ensure that all the preparations are the same and would give continuity. This would help give more reliable results throughout. I think my results are quite reliable for the level that I did the experiment at. They proved that my prediction was right so they must have been fairly reliable but not very accurate. But I would not go and publish these results. I would probably want to calculate the point where the enzymes begin to stop respiring in yeast. At this stage, I shouldn't think there is to be much more I could do. I wouldn't want to investigate any other variables or reactions at this time. By looking at my graph I found two anomalous result, I have circled them in red to show where they are. I think the two points are anomalous because they should have decreased in the amount of CO2 produced not increased. These could be that different groups of people were doing the experiment. The group that did the experiment for 60� might have used a different make of syringe or it might have happenedthrough human error. ...read more.

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This laboratory investigation into the effect of temperature on respiration begins well with a thorough and well researched introduction. It provides a solid foundation for the investigation however more care does need to be taken to reference information more appropriately. The main section of the report is too brief and does miss key elements essential to any good laboratory report including a labelled method diagram and graphs of the experimental results. More care also needs to be taken when evaluating the results simply stating that the results supported the prediction is insufficient, more links need to be made between the result and the science behind respiration.

Marked by teacher Cornelia Bruce 17/03/2013

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