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Comparing the respiratory rate of yeast with different sugars.

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Comparing the respiratory rate of yeast with different sugars Situation "A baker used uses sugars to make his bread dough 'rise'. He wanted to find out which sugar, of a number of sugars would give the best results" Introduction The raising agent within the dough is yeast, and this along with numerous sugars will be the focus of this investigation. The reason the yeast is a raising agent is because of fermentation. When flour is mixed with water, sugar and yeast, the yeast feed on the sugar. As the yeast release carbon dioxide and alcohol, the gas becomes trapped as bubbles in the dough, causing it to rise. Yeast is a unicellular fungus that has the ability to respire both aerobically and anearobically. Yet in order to produce carbon dioxide and ethanol it must respire anaerobically. This is one of the first facts about this investigation; in order for the bread to rise the yeast is produce carbon dioxide and respiring anaerobically. Respiration itself consists of a number of 'redox' reactions in which certain substrates are oxidised to become 'carbon dioxide' and 'oxygen' is reduced to water. ...read more.


The higher the difference in the structure of the sugar the less likely it is to match with the active sites in the yeast. I believe that the most suited from the disaccharide's will be maltose as it is formed from two molecules of glucose which can be split apart and then used. Fructose will be slower than maltose as it is only formed from one polymer of glucose. Plan I will make an active solution of yeast (that is a dry mass of yeast combined with de-ionised water) to eliminate and factors that could produce anomalous data. This I will then add 25cm3 of this solution to 25cm3 of a sugar solution via a 60cm3 syringe. The sugar solution of each of the 5 sugars will be 0.25M in strength, this has be shown to be the optimum concentration, for higher than this level can lead to detrimental osmotic problems. I will then empty the syringe of excess air and attach it to a 300mm capillary tube held within a clamp stand. ...read more.


The control experiment will consist of using the yeast solution on its own and measuring the respiratory rate, this will show that it is the sugar that has an effect on the respiratory rate of yeast and no other factor. The dependant variable in this experiment is the amount of CO2 produced. This will be obtained by dividing the time the solution takes to reach the mark on the capillary tube, by the distance it travelled to that mark. This will give the level of Co2 production per second. This measurement will be given in Co2/s in relation to the amount of yeast. This data , once collected will be logged in a data table and then present in suitable graphs and charts to show trends and identify anomalies. Apparatus * 60cm3 syringe. * Capillary tube. * Beaker. * Active yeast solution. * 5 sugar solutions of 0.25M (glucose, fructose, maltose, sucrose, lactose). * Stop watch. * Clamp stand. * Chinagraph pencil. Al the apparatus I intend to use is very low risk , and no special precautions will be needed, such as gloves or goggles. The 2 solutions have minimal risk if they came into contact with ones skin there could be possible irritation. Human biology Hugo Metcalfe 20513 ...read more.

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