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I have been asked to investigate the factors that affect the rate of respiration in yeast.

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Biology investigation What am I investigating? have been asked to investigate the factors that affect the rate of respiration in yeast. What could I vary? There are three factors that I could vary and these are: 1) The temperature of the yeast. 2) The pH level that the yeast is in. 3) The concentration of glucose that the yeast is in. Variable chosen I chose to change the temperature of the yeast as my variable as I feel that you can obtain an accurate temperature easily with the equipment available so the results would be more precise. Whereas with the equipment available getting the concentration of glucose or pH level of the yeast would be harder and less exact than the temperature this would lead to poor results. Fair test and other variables. To create a fair test all variables must stay the same except for the one that you are changing. These variables are: 1) The concentration of glucose, which affects the rate of respiration as it is the source of food for the yeast. 2) The pH level of the yeast, the yeast may prefer to work in either acidic conditions or alkali on even neutral. 3) Temperature, yeast may have an optimum working temperature at which respiration takes place fastest for this reason if the temperature is changing throughout the experiment then the results may not be accurate. 4) Same amount of yeast solution in each test tube, if more yeast I used respiration may take place quicker or slower. ...read more.


You must mix the glucose and yeast 1/2 an hour before starting the experiment to allow the yeast to start respiring. Practical techniques to avoid inaccuracies. Each temperature was done three times to obtain an average. The test tubes were filled using a syringe to the same volume (10cm�). The same batch of yeast was used throughout the experiment so it as always at the same glucose concentration. The temperature of the yeast was measured to find the temperature not the water around it. The size of test tube was kept the same throughout the experiment in case a larger test tube heated quicker and altered the yeast. When taking readings from the thermometer we waited for it to settle and then took the reading as accurately as possible and did no round up or down and just left it as it was. Readings from the blocked off syringe were taken to the nearest whole number as more precise readings could not be taken using the equipment available the readings were also taken when the syringe was vertical so as to try to create more accurate results. Safety considerations. As the most of the equipment is glass you have to be careful not to drop it, by holding it carefully, not waving it around. If you accidentally drop a piece of glass equipment and it breaks then you have to clear up the glass as it is a danger to others. If a thermometer breaks then as well as glass you have the liquid inside. ...read more.


From looking at the table my results seem quite accurate as the temperatures increase evenly the averages increase quiet evenly as well and also the use of an average increases accuracy by if there is one wrong result reducing its affect. From the graph my results seem accurate as well as they are all close to the line of best fit indicating accuracy. The method did work because it produced a set of results that showed that my hypothesis was right and when placed into the form of a graph gave correlation and with a line of best fit gives reliable results. From the data gathered I could give the conclusion that out of the 5 temperatures 40�c is the best or most efficient temperature for the enzymes in the yeast to work at. The inaccuracies in this experiment came from the use of the equipment. The thermometer as some readings were in between two temperatures and the collection of the gas in the syringe end was inaccurate as the scale on the syringe did not go down to a small enough reading so approximations had to be made. To increase the accuracy in this experiment more accurate apparatus could have been used, an electric thermometer and a more precise device for measuring the gas To improve this method you need to collect gas for a longer period of time on each one e.g. half an hour. You could also use a larger amount of temperatures e.g. 0c, 5c, 10c, 15c, 20c... up to a higher temperature than before e.g. 10 0�c. ...read more.

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