Investigating the effect of temperature on yeast respiration.

        It will be vitally important throughout the experiment that a fair test will be kept. The amount of water in the beaker should not change, the amount of water in the water bath and burette should not change throughout. The boiling tube should be filled to the same level with yeast throughout the test because if there is a different amount of yeast every time the amount of respiration will be different, the yeast will be accurately measured each time. Everything within reason should be kept the same, apart from the temperature. The temperature is going to have the main effect on the results as explained with the collision theory. I will keep checking the temperature of the beaker to make sure it is correct, I will measure this with a thermometer. The equipment I am going to use is as follows:

• Heat-proof mat
• Bunsen burner
• Tripod
• Gauze
• Beaker
• Thermometer
• Boiling tube
• Rubber bung
• Delivery tube
• Water bath
• Burette
• Clamp stand x 2

Firstly, we stood a tripod with a gauze on top of it, supporting a beaker containing water onto a heat proof mat. A boiling tube containing a quantity of yeast plugged with a rubber bung with a delivery tube attached was then suspended into the beaker, which was being controlled so it was kept at the correct temperature. Therefore the suspended yeast was left to respire in the climate I wished. 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.

Analysis:

        Like predicted my graph shows that as the temperature is increased, the speed of the respiration also increases. However once the temperature reached 40º 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 0ºC and 20ºC. Like expected the line has a rapid increase before reaching its optimum temperature at 40ºC. From this point on the line quickly decreases to low amounts of respiration. The graph for trial two begins with a mild increase between 0ºC and 20ºC before the large increase expected. This experiment reached its optimum peak at 35ºC and began to decrease from there. The rapid diminish began at 40ºC where the rate of respiration fell largely, it reached its lowest point of respiration at 60ºC before making a small increase toward the end of the experiment. The graph of the final trial commenced with a small increase between 0ºC and 20ºC and it was from this point of which the respiration took the largest increase. The amount of respiration continued to raise up until the 40ºC mark. A rapid diminish now took over and sent the respiration to its lowest point at 60ºC before it rose slightly by 0.20ml. The average graph begins with a line moving positively as the temperature increases. Between the points of 20ºC and 35ºC there is a noticeable, rapid increase. The amount of gas collected continues to rise when measured at the 40ºC point. From this point onwards there is a rapid decline in the amount of respiration. There is very little respiration between the points of 0ºC and 20ºC, also there is a very little amount of respiration between the points of 60ºC and 80ºC. I found that the optimum peak of two of my three experiment runs was 40ºC, therefore my average optimum peak was 40ºC.

        The results I achieved can be explained using the scientific theorems, as stated above. The lock and key hypothesis is proved, by the fact that my results showed that the respiration begins to decrease after 40ºC and there very little activity due to the fact that the enzymes active site is becoming denatured. The collision theory is proved in my results because there is clear evidence to show us that as the temperature increased the amount of respiration increased due to the extra energy provided by the heat. However this is not always the case, as the enzymes active site, became denatured after 40ºC. Therefore no matter how much temperature was applied the rate of respiration would still be low.  

        My results were as close as I would have hoped to a perfect fit. I did not expect a complete exact match of my prediction. Also I did not expect to see a precise relation between temperature and respiration, for example I did not expect to see that for every 10ºC the respiration would double. There was no major anomalous results recorded from the three trials, and I feel my processed average is fairly accurate and success when compared to my original prediction.

Evaluation:

        The procedure I carried out was not really that difficult, although it was rather time consuming and care had to be taken to keep a measure on time. Attaching the delivery tube under the burette also proved to be rather awkward, as it had to be done quickly and correctly. I found it rather the apparatus was reasonably straight forward to set up, which meant not that much time was spent arranging the set-up. The yeast was left to acclimatise in the beaker for five minutes which mean the timer had to be left continually running, once the five minutes was over the delivery tube had to be connected to the burette which was suspended into the water, held by a grip. Once the delivery tube was connected to the burette the timer was then left to count down ten minutes until the amount of gas collected in the burette was to be measured and the delivery tube was to be disconnected from the burette. A thermometer was placed into the beaker, to take a constant measure of the temperature to ensure it was kept correct. The water in the beaker was circulated regularly to guarantee the heat was being spread throughout the beaker. The experiments were carried out continually, in sequence and overall twenty-one experiments were preformed. If more funds were made available my experiments may have been more accurate, for example if I had used apparatus more accurate than a burette to measure the amount of gas collected. To improve upon my method, I could have used an electrically thermostatically controlled water bath. This would have meant that I would not have needed to use a Bunsen burner to heat my water beaker containing the yeast. I would have merely had to place the boiling tube containing the yeast into the electrically thermostatically controlled water bath, where it would have been kept at the correct temperature without any worry. The temperature could have also been altered depending on the need of the temperature, this would have made my experiment not only easier to carry out but it would have also given a more accurate measure. I was unable to use an electrically thermostatically controlled water bath as sufficient funds were unavailable.

My results that I achieved from the series of tests were all parallel to my original forecast. I did not expect a complete match when I first predicted the outcome of my experiment. However what I did achieve was close to my original prediction and I am thoroughly pleased with the final outcome. I recorded no major anomalous results although on my second run of the experiment the optimum peak was at 35ºC and from that temperature the amount of respiration fell. Unlike this on the other two trials of the experiment the optimum peak fell at 40ºC, therefore the average optimum peak was 40ºC, like originally predicted. This difference may have been caused due to a problem with the method, for example the temperature may have risen during the experiment due to overheating with the Bunsen burner. The temperature of the water beaker may have fallen slightly when performing the test at 40ºC, 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 40ºC the respiration rate begins to fall due to denaturisation of the enzyme structures.