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Investigating the effect of temperature on yeast respiration.

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Investigating the effect of temperature on yeast respiration. Planning: With references to my theories I predict that when performing the experiment, the rate and speed of respiration of yeast will increase with temperature rise, up until a certain point around the area of 40�C and onwards. After this point the enzyme site will become de-natured, meaning the substrate can no longer fit into the site and the protein bonds from the enzyme will begin to snap. My prediction is based upon two scientific theorems, "lock and key" hypothesis and the "collision" theory. The lock and key hypothesis, is where the substrate, the "key", fits into the active site on the enzyme, the "lock". Once this has occurred they then bind together and a reaction takes place, the active site on the enzyme unlocks the substrate to form one or more new substances leaving the enzyme ready to perform the binding process again. However the enzyme can only bind with a substrate that fits the shape of the active site, unique to that enzyme and once the temperatures pass 40�C the sensitive active site becomes altered drastically, this process can hardly ever take place, and this is called denaturisation. Therefore, it is upon that information which my prediction is based, when I say that the temperature will have an effect on the respiration of the yeast up until a certain point around the area of 40�C and onwards. The second piece of information on which my prediction is based is the "collision" theory. ...read more.


After an acclimatisation period, the delivery tube was attached to a burette which was held by a clamp stand under the water level, in the water bath. As the yeast respired, the bubbles of gas travelled through the delivery tube into the burette, where this apparatus collected the gas and a measurement was able to be taken. My experiment will be set up as shown in this fully labelled diagram below: Obtaining Evidence: The evidence was obtained across seven experiments, these firstly helped me to achieve raw data. I then processed the data and found averages for the seven temperatures. Temperature (�C) Gas collected (ml), After 10 minutes Average Experiment 1 Experiment 2 Experiment 3 0 1.00 0.80 0.40 0.73 20 0.90 2.20 1.00 1.37 35 16.90 16.40 16.60 16.63 40 17.00 15.00 18.80 16.93 50 10.20 12.20 8.40 10.27 60 2.25 0.40 1.40 1.35 80 0.50 1.00 1.60 1.03 Analysis: Like predicted my graph shows that as the temperature is increased, the speed of the respiration also increases. However once the temperature reached 40� the rate of respiration began to decrease, due to the active sites becoming denatured. It follows a trend and a pattern, like was suggested, with reference to the lock and key hypothesis and collision theory. The graph for experiment one begins with the line moving negatively very slightly between the points of 0�C and 20�C. Like expected the line has a rapid increase before reaching its optimum temperature at 40�C. ...read more.


The temperature of the water beaker may have fallen slightly when performing the test at 40�C, due to under heating with the Bunsen burner. These problems could have been prevented, had there been enough funds available to supply me with an electrically thermostatically controlled water bath. The method I used was far from floorless, but despite that it still turned out successful, as there was no major anomalous results. If I felt it was necessary, further work could be done to improve the test, for example I could test with amount of respiration after 20 minutes, and I could leave the yeast to acclimatise for 10 minutes rather than only 5 minutes. I could attempt the experiment with the yeast in a conical flask rather than a boiling tube, to enquire into whether any different results could be found. Overall I feel it was a successfully completed experiment which went to plan and was carried out with no major problems or drawbacks. The results all prove my initial predictions, and they are evidence that both the lock and key hypothesis and collision theory are taking place in reactions. As predicted my results show that temperature has an effect on the rate of respiration of yeast. The further the temperature is increased the higher the rate of respiration. This is until a certain point where the enzymes active site becomes denatured due to the heat. This is shown in my results as on average, from 40�C the respiration rate begins to fall due to denaturisation of the enzyme structures. Chris Scrimgour ...read more.

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