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Introduction

The effect of different sugar substrates on the rate of yeast respiration AIM In this investigation I will be using various sugars to see the effect on the rate of respiration of yeast. The sugars I will be using are glucose, fructose, sucrose, maltose and galactose. All the sugars used will be of a 2%concentration. In order to obtain my results I will use the same type of yeast i.e. Bakers yeast. I will place the 2% solution of the sugars in a waterbath at 35�c. Together with the sugars I will place 20cm� of yeast solution. I will measure out 25cm� of both sugar and yeast and place them into a conical flask in the same waterbath. As soon as I do this I will place the rubber bung and delivery tube which will be attached to the gas syringe and onto the flask. I will then measure the volume of Carbon Dioxide produced by the yeast every 30 seconds until the yeast stops respiring and this will repeated for each sugar. After completing my results I will draw a graph to work out the rate of respiration of yeast and also statistically analyse my results. Background Information Yeast is a unicellular (eukaryotic) fungus that reproduces asexually by budding. Cells of yeast are very active metabolically and usually respire aerobically. However when they are deprived of oxygen they switch to anaerobic respiration where it produces carbon dioxide and ethanol as waste products. These waste products are important in industry. Cells of yeast have a single nucleus and are usually egg shaped. Individual cells vary in size but nevertheless contain most of the organelles of a typical eukaryote. Yeast can reproduce both sexually and asexually. In asexual reproduction, a single cell divides by budding and separates into two cells. Some buds group together to form colonies, and others separate to grow individually into new yeast. In sexual reproduction, two cells fuse to form a diploid cell which then forms haploid spores by meiosis. ...read more.

Middle

This will allow the solutions to be maintained at the correct temperature. 4. After 15 minutes, using the two 25cm� measuring cylinders, measure out 25cm� of one of the sugars and 25cm� of the yeast solution. As soon as they are measured out, pour them into the conical flask, put the rubber bung into the flask, this will prevent Carbon Dioxide from escaping to anywhere than the gas syringe. Start the stop clock immediately to avoid loss of time. Make sure the solutions are not left out for too long before the experiments as they temperature would drop and this will slow down the activity of enzymes and will affect your results. 5. Continuously swirl the mixture. This will provide oxygen for the yeast and so will respire aerobically and this will prevent aerobic respiration from taking place. 6. After every 30 seconds note down the amount of Carbon Dioxide produced. If, no more CO2 is produced after three concordant results then stop the investigation and move onto the next. 7. Repeat the investigation for each sugar substrate five times. This will allow averages to be worked out and hence will provide more reliable results and a more reliable conclusion. 8. I will then draw tables of raw results and average results. Using my average results I will draw graphs in order to find a gradient which will enable me to calculate the rate of respiration of each sugar. I will then calculate standard deviations. I will use this because it will measure the extent to which individual measurements vary around the mean. The greater the variation among the individual measurements, the bigger the standard deviation and vice versa. I will then use the standard deviations to calculate the significance of the difference between two means via student T tests. I will carry out 3 student T tests. Variables The independent variable in my investigations will be the different sugars used. ...read more.

Conclusion

Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) 30 5 2 3 1 3 0 60 6 2 4 1 3.5 0 90 8 2.5 6 1.5 4 0 120 9 3.5 8 2 7 - 150 10.5 5 9 2.5 7.5 - 180 13 7 10 3.5 7.5 - 210 14.5 9 11.5 5 7.5 - 240 15.5 10 12 7 - - 270 15.5 12 12.5 9.5 - - 300 16 14 12.5 12 - - 330 16 15 12.5 13 - - 360 16 16 - 14 - - 390 - 16.5 - 14 - - 420 - 16.5 - 14 - - 450 - 16.5 - - - - 480 - - - - - - 510 - - - - - - 540 - - - - - - 570 - - - - - - 600 - - - - - - Average results Glucose Maltose Fructose Sucrose Galactose Lactose Time (seconds) Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) Volume of gas produced (cm�) 30 4.7 1.8 2.9 0.8 2.4 0 60 6 1.9 3.9 1.1 3 0 90 7.8 3.1 5.4 1.5 4 0 120 9.2 3.1 5.9 2 6.5 - 150 10.8 4.1 8.5 2.6 7.4 - 180 12.3 5.7 9.7 3.5 7.4 - 210 13.4 7.4 10.6 4.5 7.4 - 240 14.1 9.2 11.1 6.5 - - 270 14.5 11.6 11.7 8.9 - - 300 14.8 13.7 11.7 11 - - 330 15.1 15 11.7 12.2 - - 360 15.2 16.1 - 13.2 - - 390 15.3 16.9 - 13.2 - - 420 15.5 16.9 - 13.2 - - 450 - 16.9 - - - - 480 - - - - - - 510 - - - - - - 540 - - - - - - 570 - - - - - - 600 - - - - - - ?? ?? ?? ?? 1 ...read more.

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