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Experiment to Investigate Factors Affecting the Rate of Respiration in Yeast

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Experiment to Investigate Factors Affecting the Rate of Respiration in Yeast Aim: To investigate the factors affecting the rate of respiration in yeast. Introduction: The keys to this investigation are 'enzymes'. Enzymes are how organisms respire. They work on a 'lock and key method', as illustrated below: We can see in the first diagram that the two parts, the enzyme and substrate (lock and key), fit together perfectly, at around 40?C. However, we can see that as the temperature of the environment is raised to 80?C the enzymes begin to 'denature', which means that the substrate will no longer fit into the enzyme. This means that the rate of respiration will be fairly low or even negligible, in comparison to the 40?C environment. This means that during my investigation I will have to be careful that I do not raise the temperature too high, otherwise the enzymes will denature and will not produce a good set of results. Preliminary Work Factors Affecting the Rate of Respiration in Yeast: Factors that affect the rate of respiration in yeast include: * Temperature. The temperature will affect the rate of respiration in yeast as it makes the yeast respire slowly at a low temperature and faster at a higher temperature, until the temperature reaches an optimum level. I expect that once the temperature has reached an optimum level that the rate of respiration will descend, and if the temperature is too warm then the yeast will die. ...read more.


I then realised that this must mean that the yeast had stopped respiring. The following results were recorded: Preliminary Results (40?C) Time (m) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Displacement Chamber Reading (ml) 9 9 9 9 11 12 13.5 14.5 15.5 17 17.5 17.5 18 18 18 18 18 Volume of CO2 produced (ml) 0 0 0 0 2 3 4.5 5.5 6.5 8 8.5 8.5 9 9 9 9 9 I can see from the results and graph on the previous page, that the trend was that the longer we left the yeast, the higher the volume of CO2 produced. This trend occurred from 4 minutes until 16 minutes. I can assume from these results that the best time to leave the experiment for would be 15 minutes, in case there would be any change after 12 minutes in another environment. Actual Method Fair Test: The following measures will be kept constant to make sure that this investigation is fair: * The % of Glucose concentration will be kept constant, to avoid a fluctuation in results * There will always be 10cm3 of solution in the test tube * A 1g ball of yeast will be used, and changed each experiment * An accurate pair of electronic scales will be used to avoid human error * The test tube will be washed out after each experiment * An accurate measuring cylinder will be used, because we are only measuring very slight changes in volume * An accurate stopclock will be used (accurate to 100th/s) ...read more.


Because we did not take results every minute, we failed to realise this until the experiment had finished, we had packed up our apparatus and it was no longer available. Had we repeated the experiment with 60?C water used all the way through, I expect that the graph would look more like the predicted graph shown earlier. I believe that this experiment could have been improved by firstly repeating the 60?C experiment. Then I could have improved accuracy by using a more sensitive electronic scale, and by having a proper displacement chamber, instead of the makeshift one we used. A proper displacement chamber would have allowed us to measure the volume of gas produced in more accuracy than by reading it off a scale. Another problem I had was that when I was reading the volumes from the displacement chamber, I had to bend down to the level of the chamber (about table height) to read the measurement off - whilst I was still holding the apparatus in place. It would have been easier to do this and to avoid human error by using a clamp and retort stand to hold the measuring cylinders in place, instead of having to do this by hand. However, under the circumstances, and without taking these improvement points into consideration, the experiment proved that the temperature of the environment that yeast is placed in does affect its rate of respiration. John Major 11C Biology Coursework JC ...read more.

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