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AT1 practical assessment – yeast respiration

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27th September 2001 AT1 practical assessment - yeast respiration AIM => investigate one thing that will change the rate of yeast respiration. When yeast respires, it is anaerobic, so the equation for yeast respiration is: Glucose => ethanol + carbon dioxide + energy There are two things that could change the rate of this respiration. These are; * A change in concentration * A change in temperature Increasing the concentration of glucose increases the rate of respiration because, based on the collision theory, there will be more glucose particles to collide with the active site of the yeast enzymes. Increasing the temperature will increse the rate of respiration because the molecules will have more energy. This means they will be moving faster, and will collide with the active site of the enzymes more often and with more force. PRELIMINARY WORK => To help me decide which variable to investigate, and what measurements I would use, I did some preliminary research and experiments. I did three experiments. These were: A 'control' experiment, which was carried out at room temperature using; 25ml water 1g yeast 1.5g glucose This gave us 2ml of carbon dioxide over 4 minutes. ...read more.


This was to measure the carbon dioxide, by the displacement of the water, after 3 minutes. Once this had been recorded, I repeated the experiment three times to make it fair and ensure there were no inaccurate results. Then I increased the temperature in the water bath to 20(C, and did the experiment again. I continued to do this with the measurements going up in 10s, so I had 6 results ranging from 10 C to 60 C. I made the experiment safer by using a kettle rather than a bunsen to heat water, and by wearing safety goggles. PREDICTION => I predict that increasing the temperature will increase the rate of reaction. The reaction will produce approximately 3ml of extra carbon dioxide for every 10 C the temperature is increased by. I am basing this prediction on two things, the collision theory, and my preliminary work. The collision theory, as mentioned earlier, says that increasing the temperature will speed up the respiration, because the glucose particles will have more energy, and they will collide with the active site of the yeast particles with greater frequency and force. I think that the amount of carbon dioxide will increase in 3ml amounts because of the results of my preliminary work. ...read more.


As the respiration took place, more glucose was being used up, and so the concentration was decreasing. If I were to do this experiment again, I would change the following things: * Use a more accurate way to measure the temperature of the water bath, and keep it constant. * Use a more accurate time measurement. * Use a fresh yeast, glucose and water mixture for each experiment. However, this was not possible because we did not have enough mixture for the whole group to do this. The only problem with this would have been making sure we kept the whole batch of yeast stirred up, so the yeast did not settle. These measures would ensure I got more accurate results. To extend the investigation, I could investigate how the concentration affects the rate of respiration as well. This would enable me to compare the two variables and decide which has the greatest effect. I had an anomalous (wrong or unusual) result. I pointed this out on my graph, by circling it in blue. I think this was caused by some of the inaccuracies mentioned above, because it is not a largely wrong result, just outside of the curve. My investigation has clearly showed that temperature affects the rate of respiration. ...read more.

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