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The Effect of Substrate Concentrationon the Rate of Yeast Fermentation

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GCSE Assessment - The Effect of Substrate Concentration on the Rate of Yeast Fermentation The aim of this investigation is to discover how the concentration of sugar affects the rate of fermentation by yeast cells. Fermentation is an anaerobic process and can be represented by the following equation. (enzymes in yeast) glucose � ethanol + carbon dioxide + a little energy C6H12O6 � C2H5OH + CO2 + a little energy Results These are the results gained for my experiment: Sugar Concentration 0% 2.5% 5% 7.5% 10% Initial Gas (mm) 8 8 9 9 11 Increase 3 mins 8 9 10 9 13 Increase 6 mins 8 9 10 10 16 Increase 9 mins 8 9 11 11 21 Increase 12 mins 8 9 11 11 27 Increase 15 mins 8 9 11 12 32 Increase 18 mins 8 9 11 12 41 Increase 21 mins 8 9 11 12 55 Rate mm of gas per min 0 0.1 0.2 0.2 2.1 These are the results gained from the whole class: NAME 5Z2 - PHR 0% 2.50% 5% 7.50% 10% Clark 0.24 0.38 0.52 1 3.42 Cooper 0.14 0.2 0.24 0.29 2.14 Dagnell 0.19 0.38 0.33 0.48 2.62 Davies 0.38 ...read more.


Molecules are in a state of a motion and therefore collide. The more collisions that take place the faster the rate of fermentation. If the concentration is high, the number of glucose molecules is abundant, therefore the probability that the enzymes (in yeast) come into contact with these molecules is high. This in turn increases the rate of fermentation. If the concentration is low, however, the number of glucose molecules is less and therefore the rate of fermentation decreases. The conversion of glucose to carbon dioxide and ethanol takes place in the active site of the enzyme. Enzymes are protein chains of amino acids. Their molecules are very precise three-dimensional shapes. The shape includes a 'dent' which is exactly the right size and shape for a molecule of the enzyme's substrate (in this case glucose) to fit into. This 'dent' is called the active site. When the glucose molecule slots into the active site, the enzyme changes it, pulling it out of shape and making it split into product molecules. The product molecules (in this case carbon dioxide and ethanol) ...read more.


When carbon dioxide is produced some of it may dissolve into the solution and does not appear as gas, this again may cause errors. Human error also adds to the problem of inaccurate readings. As one of the products is ethanol, it can intoxicate some of the yeast cells which would die. Also, as fermentation takes place the sugar and yeast gets less and results produced may not be reliable. Therefore the procedure could have been altered in order to produce accurate results. During the experiment, there was a lack of control of other variables, such as temperature. Also, the yeast solution (before it is given to us) may not be well shaken, which leaves an unbalanced number of yeast cells. The experiment could be improved in several ways. In order to control temperature, a water bath could be used to keep a constant temperature. The test tubes could be substituted for ones which have a scale down the side, in order to improve readings of carbon dioxide. Also, more sugar concentrations could be used to give a wider range of results. For example, the following concentration could be used instead: 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18% and 20%. This would produce more accurate results. Abdul Raja 5L ...read more.

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