An Investigation Into the Effects of Sugar Concentration on Yeast Activity free essay sample

An investigation into the effects of sugar concentration on yeast activity Introduction: Yeasts are eukaryotic micro organisms belonging to the kingdom fungi. Yeasts live on sugars and produce ethanol and carbon dioxide as by-products. [James Mallory, 1984]When Yeasts are given water and sucrose they convert the sucrose into glucose then convert the glucose into carbon dioxide and ethanol following the following reaction: C? H O? ( 2(C? H? OH + CO? Brady Burkhart, Terrell Grayson and Eric Kimler, 2009] Because yeasts produce ethanol and carbon dioxide they are commonly used in the fermentation of alcoholic beverages and in baking as a rising agent. [Ron Pickering, 2006] Research question: What is the effect of sugar concentration on yeast activity? Hypothesis: The expectation is that the amount of carbon dioxide produced will be directly (and linearly? ) inked to the concentration of the sugar Variables: Independent variables: †¢ Sugar concentration Constant variables: †¢ Temperature †¢ Sugar type Yeast type †¢ Type of bottle used for the experiment †¢ Volume of water †¢ Time †¢ Quantity of yeast Dependant variables †¢ Quantity of carbon dioxide produced by the yeast Apparatus: †¢ 1 Set of scales (accurate to 1 gram) †¢ 1 Measuring cup †¢ 5 Bottles †¢ 5 Thin plastic tubes (approx. 5mm gauge, 1m length) †¢ 1 Tub of water †¢ 5 Test tubes with volume markings up to 100ml †¢ 5 12 g Bags of dried Saccharomyces cerevisiae (Baker’s yeast) †¢ 472. 5 g Sucrose (table sugar) Method We started setting up our experiment by measuring different molar solutions (0M, 0. 25M, 0. M, 0. 75M and 1M) of sugar and putting them into separate bottles, along with one bag (12g) of yeast and 300ml of water. We then attached a tube going from the top of each bottle to separate test tubes which were entirely full of water and were placed upside down in a tub of water, stopping the tube from emptying and allowing carbon dioxide to be collected at the top of the test tube in bubbles. The data was collected by removing the plastic tubes leading from the bottles to the test tubes after waiting eight minutes after the experiment was started. The test tubes were then sat vertically upside down and using the measurement markings on the test tubes measured the volume of the carbon dioxide that had been produced by the yeast. Results: |Sugar Concentration |Amount of carbon dioxide produced. | |0M |0ml | |0. 25M |115ml(approx. ) | |0. M |54ml | |0. 75M |34ml | |1M |46ml | Discussion: The results of this experiment suggest that the ideal sugar concentration for yeast respiration lies around 0. 25M. Reasons for this result could include: 1. The alcohol produced by the yeast at higher sugar concentrations could have killed the yeast if the alcohol content in the solutions became enough. 2. Yeast cells may have evolved to favour sugar concentrations of around 0. 25M as it may be a common sugar concentration in the natural environment and would therefore be beneficial for the yeast to favour it. To assess more accurately where the optimal sugar concentration for yeast respiration lies the experiment could be repeated with more points between 0M and 0. M Reliability: In this experiment there were five points, one for each different sugar concentration we tried. We could have had many more points with higher sugar concentration to see how the carbon dioxide production changed at much higher levels of sugar concentration, and could perhaps have found out how much sugar is needed to increase the osmotic capacity of yeast [Stafan Hohmann, 2002. ] Many more points could have been done be tween the existing ones to increase the accuracy of the experiment. Another thing that could have been done to improve the reliability of the results would be to measure the quantity of sugar in each solution more accurately. The scales that were used did not show any values after a decimal point, meaning that if better scales had been used the accuracy could have been improved. The quantity of water in each solution could also potentially have been more accurate by using a thinner test tube, rather than a measuring cup, to measure the quantity of water in each solution. The dependant variable in this experiment was the quantity of carbon dioxide produced by the yeast. The amount of carbon dioxide was measured in test tubes submerged in water. The tube used to measure the 0. 25M solution did not have volume marks high enough to measure the volume of carbon dioxide that was produced in that solution, so the measurement on that particular result is estimated. In addition the accuracy of each of the other points could have been improved by by using test tubes that were narrower and therefore would measure more accurately. The accuracy of the results could have been improved by doing replicate readings as, in this experiment; there was only a single reading To assess more accurately where the optimal sugar concentration for yeast respiration lies the experiment could be repeated with more points between 0M and 0. 5M. The results of this experiment show a slight rise between the points at 0. 75M and 1M, however it is not possible to assess whether this is significant using the current experimental design The reliability of the date could be improved by taking replicate readings and in addition possibly taking further readings at higher concentrations. The reliability of the experiment could possibly also be improved by optimising the water temperature for yeast respiration (around 35? C) [Slaa, J. , Gnode, M. , and Else, H, 2009] this may have created larger volumes of carbon dioxide and could therefore have made the differences in quantity greater. In addition the reliability of the results could have been improved by using fresh, pressed yeast rather than dried yeast as dried yeast does not retain all of the activity it had in it’s original pressed state [L. I. K. Ebbutt, 1960] Another factor which could have affected the reliability of the results was the face that the carbon dioxide which was measured was not given time to settle before the volume was measured Validity: Volumes of Solutions – The volumes and concentrations in this experiment were incorrect as instead of making a solution that was a total volume of 300ml we added 300ml of water to various amounts of sugar. This is something that could have greatly affected the validity of the results. †¢ Water temperature – The temperature of the water used to make the solutions in thi s experiment as no measurement of water temperature was taken during this experiment. To improve the validity of the experiment accurate thermometers could have been used to measure water temperature before beginning the experiment. Water motion No measure of water motion was taken during this experiment. If the water was still moving after the solutions had been mixed it could have affected the validity of the results. To improve this the solutions could have been left for a few moments until the water had definitely stopped moving or the solutions could have been mixed by an automated system, meaning that there would be no difference in water motion, †¢ Oxygenation of water – The oxygenation of the water used to make the solutions in this experiment was not measured or deliberately manipulated. This is a factor which could directly affect the validity of the results. To improve this factor the water could have been poured by an automated system, meaning that the height the water was poured from in relation to the container would always be the same, and that the water would be poured at the same rate. †¢ Yeast (type) – Although the yeast used in this experiment were all the same type and came from the same box, the yeast in each solution came from a different packet, meaning that there could be slight differences in the yeast used in each solution. To improve this factor the yeast could have been mixed to ensure that the yeast that was used in each solution was the same. †¢ Quantity of yeast The only control of the quantity of yeast used in this experiment was that the yeast came from separate packages which were supposed to contain the same amount. To improve the validity of the experiment the yeast could have been weighed using a set of scaled, or been measured in volume before being used in the experiment. †¢ Time – The timing in this experiment was done using a stopwatch. Although the stopwatch timing was presumably correct there could have been a slight delay between the plastic tubes being removed from the test tubes which were used to measure carbon dioxide volume. This could affect the validity of the experiment as some of the results could have been from a slightly longer period. To improve the validity an automated system could have been used to remove human error from the timings in this experiment. Conclusion: The results suggest that the optimum sugar concentration for respiration of yeast is 0. 25M. However due to flaws in the experimental design it was not possible to accurately assess where the optimal concentration lies. In addition there were insufficient data to assess validity and reliability, and therefore the experiment should be repeated taking into account the improvements suggested above. References: †¢ [L. I. K. Ebbutt, 1960, Microbiology[pdf]. Great Britain: The Distillers Co. , Ltd. , Glenochil Research Station, Menstrie, Clackmannanshire. Received 21 October 1960. available at http://mic. sgmjournals. org/content/25/1/87. full. df+html [accessed 14:24, 11. 11. 2012]] †¢ [Slaa, J. , Gnode, M. , and Else, H, 2009, Journal of Organic Chemistry [pdf]. , The Netherlands: Vrije Universiteit, Amsterdam. Received October 2009. Available at http://www. pieternieuwland. nl/Menu_Items/Projecten/Symposium/symposium2009-2010/organisatie/docs/Article%20Yeast%20and%20fermentation. pdf [accessed 14:20, 11. 11. 2012]] †¢ [Stafan Hohmann, 2002. Osmotic Stress Signali ng and Osmoadaptation in Yeasts, Microbiology and Molecular Biology, Vol. 66  no. 2  300-372. Available at http://mmbr. asm. org/content/66/2/300. hort [accessed 14:10, 11. 11. 2012]] †¢ [James Mallory, 1984. Collin’s Concise Encyclopedia. 4th edition. 59 Grosvenor Street, London: Peerage books] †¢ [Brady Burkhart, Terrell Grayson and Eric Kimler, 2009. Yeast Fermentation Optimization Project#4 [pdf]. 17th September 2009. Available at http://unitopslab. okstate. edu/yeast%20fall%202%2009. pdf [accessed 15:08, 11. 11. 2012]] †¢ [Ron Pickering, 2006. The economic importance of yeast: baking and brewing, Complete Biology for IGCSE. Oxford University Press Edition. Singapore: KHL Printing Co. Pte Ltd. ]