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An experiment to investigate the rate of anaerobic respiration of yeast in various respiratory substrates

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Practical Method Title "An experiment to investigate the rate of anaerobic respiration of yeast in various respiratory substrates." In this experiment, the independent variable is various different respiratory substrates being used (glucose, sucrose, maltose, lactose) and the dependent variable is the rate of respiration (measured by movement of manometer fluid which moves in relation to the amount of carbon dioxide released). Apparatus Yeast Glucose Sucrose Maltose Lactose pH7 buffer Top pan balance Stopwatch Thermometer Manometer fluid Capillary tube 20ml & 1ml syringe 100ml beakers Distilled water Water trough Kettle Stirring rod Stopwatch Spatula Background information My investigation will involve analysing how yeast respires in various different substrates: Glucose, Lactose, Maltose and Sucrose. All four of these respiratory substrates are carbohydrates. Glucose Glucose is a monosaccharide sugar, which is a 'simple sugar' that have between 3 and 10 carbon atoms per molecule. They are sweet and all soluble in H2O. It has the chemical composition C6H12O6. Glucose is a white crystalline solid but is less sweet then ordinary table sugar. Powdered dry glucose exists mainly in straight chain form. However, when glucose molecules are dissolved in water, two different ring structures are formed. See picture. Fig 1 These ring structures are more stable in solution, so that, at equilibrium, almost all of the molecules are present as rings, with the straight chain form being a relatively short-lived intermediate. The structures of ?-glucose and �-glucose differ only in the position of the -OH and -H groups attached to carbon atom number 1. Lactose Lactose is a disaccharide which is formed by condensation reactions (where water is removed) between two monosaccarides, glucose and galactose. They are joined together by a glycosidic bond. It consists of galactose and glucose molecules joined by a 1, 4 glycosidic link. Fig 2 Lactose is the only common sugar that is of animal origin. Other sugars, such as sucrose and fructose, can be found only in plants. ...read more.


Therefore the difference between the amount of carbon dioxide produced between Glucose and Sucrose at 12 minutes is statistically significant. Hence the differences are not due to chance, so the null hypothesis is rejected. Comparing Glucose and Lactose t = 5.16 - 0.48 (0.25)2 + (0.11)2 10 10 t = 4.68 V0.00746 t = 54.18 (2dp) Degrees of freedom = 10 + 10 - 2 = 18 Looking up the calculated t value in the t-tables using a degrees of freedom value of 18, the corresponding probability is less than 0.05. Therefore the difference between the amount of carbon dioxide produced between Glucose and Lactose at 12 minutes is statistically significant. Hence the differences are not due to chance, so the null hypothesis is rejected. Overall, the results of my t-test calculations have shown that the differences in the amount of carbon dioxide produced at 12 minutes between Glucose and the three other respiratory substrates is not due to chance, so there must be a biological explanation to account for the differences. The results from the t-test confirm that the results from my Standard Error and 95% confidence limits were correct and therefore reliable, even though the sample size was significantly under 30. Interpretation of Results After carrying out my experiment for each of the four respiratory substrates and representing the results on a graph, and using statistical analysis, I can conclude that Glucose is the best respiratory substrate for the yeast as this produced the greatest volume of carbon dioxide after 12 minutes. This shows that the rate of anaerobic respiration of yeast is fastest with Glucose as the respiratory substrate. The second fastest rate of respiration of yeast was with Maltose as the respiratory substrate, followed by Sucrose and Lactose respectively. After 12 minutes, the amount of carbon dioxide produced on average by the yeast (mean of the 10 repeats) with Glucose as the respiratory substrate was 5.16cm3. ...read more.


Another way in which the rate of respiration could be increased could be by adding more yeast and substrate. Adding yeast would mean there are more enzymes present which can break down the respiratory substrate, and adding excess substrate would mean a higher frequency of collisions between enzymes and substrate, leading to an increased rate of respiration, as mentioned earlier. In order for me to 'compare the rate of anaerobic respiration of yeast in various respiratory substrates' (title of investigation), I used four different respiratory substrates: Glucose, Sucrose, Maltose and Lactose. Although I gained a large amount of results from using these four respiratory substrates and made suitable and accurate conclusions, I feel that by using more respiratory substrates I could have compared the rate of respiration of yeast between a larger sample and so my results would have been of a greater depth and my investigation could have been carried out in much greater detail. By using more substrates my investigation would be expanded to account for a larger range of respiratory substrates. This larger range could have included other carbohydrate monosaccharides and disaccharides (e.g. Amylose). I only used a single monosaccharide substrate in my investigation - Glucose. To expand on this I could have used more monosaccharides such as Fructose and Galactose and compare the rate of respiration of yeast between these monosaccharides. In conclusion I felt that my investigation was carried out accurately enough to give reliable and consistent results, even though in retrospect I feel that I could have created more accurate and reliable results by taking into consideration some of the improvements I mentioned in my evaluation above. If I were to repeat my investigation I would take into account the errors produced this time and use a greater variety of respiratory substrates to compare against in order to expand on my research in this investigation. ?? ?? ?? ?? Adeel Ahmed 1 02/05/2007 ...read more.

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