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Factors affecting the rate of respiration in immobilised yeast balls

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Introduction

Jaysukh Kerai 10V - SC1 Science Investigation Report - 02/02/03 Title of investigation: Factors affecting the rate of respiration in immobilised yeast balls Input Variable to be investigated: The input variable that I will be investigating is the temperature and im gay 4 rreal. Variables to be controlled: The fixed volume, concentration of the glucose solution will have to be sustained throughout the entire investigation in order to maintain a fair test. The number and the size of the beads will also have to be kept the same, although it (size) may vary slightly, it should not have a major impact on the results. Prediction: I predict that the rate of respiration in immobilised yeast will increase with the temperature, until a particular temperature has been reached. I anticipate that as the temperature doubles, the rate of respiration will also double; that is to say that the temperature is precisely proportional to the rate of respiration. The yeast balls will respire and in effect rise, this makes this experiment an anaerobic respiration one. Scientific reason to explain prediction: All enzymes have an optimum temperature as to when they actually operate best. Yeast cells are not an exception; they convert glucose into carbon dioxide and alcohol plus energy by the use of the enzyme zymase. Enzymes are actually catalysts, which speed up reactions. These yeast cells undertake the conversion by performing anaerobic respiration. Incidentally, another name for this process is fermentation. This means that the rate at which these enzymes operate is likely to be constant until a certain temperature is reached. Furthermore, most enzymes denature within roughly 45�C, the optimum temperature will probably be around 37�C - 40�C (body temperature). The yeast balls will respire and in effect rise because the glucose solution will diffuse through the thin layer of jelly into the yeast cell, then the yeast balls will release carbon dioxide. ...read more.

Middle

As the investigation was repeated three times for each temperature, there are four results columns: 1st Experiment, 2nd Experiment, 3rd Experiment and Average. From my results, I was able to plot a graph to show temperature against time using the averages I worked out in 'Table B'. Error bars were also included, to show the accuracy of my times recorded. The idea of the error bars is that the longer the bar, the less reliable or accurate the results are. As you can see from my graph, at 20�C the size of the bar is very long. This evidently, means that my result at that particular point is not very accurate. However my other error bars are quite short in length, this means that my results in that particular area are more accurate. It is therefore evident from the graph that, as the temperature is increased, the time taken for the balls to raise decreases; however, this does not show the rate of respiration. Therefore, another graph was drawn to show the temperature against the rate of respiration. To calculate this (rate of respiration) the final averages were taken and was divided by one. Table A for these calculations are shown. From the graph, a best fit curve was drawn and it is clear that this particular enzyme in yeast cells is most active between 50�C and 60�C, which is obviously the optimum temperature. This result does not match up to my prediction; maybe because the atmospheric conditions in which we did the experiment was cold, (it was snowing at the time). Therefore, the enzymes probably needed extra heat to get them operating. I believe if we had done this investigation in warmer atmospheric conditions the optimum temperature would be around 40�C (body temperature). According to the best fit curve, this temperature is at 59�C. It is apparent from the graph that as the temperature increases then, so does the rate of respiration. ...read more.

Conclusion

because it would take longer for the water bath of larger volume to decrease in temperature, thus affecting the temperature of the boiling tube and consequently the results. Another reason why there was an anomalous result could have been the size of the immobilised yeast balls. A further reason could be that there are a different number of yeast cells in each ball; however, this would affect the result minimally. Although it is more likely to have been the temperature that caused the anomalous data. The volume of the water in the water bath was not kept constant, if we had done so, it may have strengthened our dependability and reliability of our results. The hardest thing to control was indeed the temperature, we were unable to keep it constant, because the temperatures kept on declining dramatically (sometimes by 7 �C). In order to keep the temperature as accurate as possible we had to add some more hot water, this what made the volume of the water inconstant. During each preliminary experiment, we were very busy doing something or another, one time we missed the balls rising to the surface of the glucose solution, so we had to estimate roughly what time each ball rose. This caused that particular result to be very unreliable. We estimated on the counts of our previous repeats and the time that was running. Apart from that, the other preliminary experiments went accordingly. As a whole, I would say our results were relatively reliable enough to say that the conclusion is correct. Furthermore, other groups obtained the same pattern of results in reference to the graphs. If we had, another chance to repeat the experiment the yeast balls should be recently made so that they would work properly, instead of being stored and possibly becoming defective. Further work could be carried out to ensue that the results sustained are accurate and reliable and if given more time, more results could have been acquired, therefore giving a more accurate average. ...read more.

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