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To find out how different sugar concentrations affect the respiration of yeast

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A2 Biology Coursework Aim To find out how different sugar concentrations affect the respiration of yeast, I shall do this by conducting a simple safe experiment, which will involve the timing of the yeasts respiration, when mixed with different sugar concentration solutions. Introduction Yeast is single celled specie of fungi and is commonly used to make bread. Yeasts are commonly found wherever sugar occurs. It has been used for thousands of years to ferment sugar into ethanol i.e. alcohol. Yeast added to dough ferments the sugar in the dough to produce carbon dioxide. Also yeast is a heterotroph as it needs to consume a ready made supply of carbon. Yeast contains an enzyme called zymase, which will only bind with glucose molecules. During fermentation, it breaks down hydrolyses starch into complex sugars, then simple sugars, and finally ethanol and carbon dioxide. Respiration is a process that takes place in all living cells. Yeast can respire aerobically or anaerobically, however for alcohol to be produced yeast must respire anaerobically. Respiration converts sugars taken in by the organism into energy. It is the controlled breakdown of carbohydrates to make energy. The normal form of energy for most living organisms is adenosine triphosphate (ATP), the other products of respiration are carbon dioxide and water. The reaction taking place in aerobic respiration is: C6H12O6 + 6O2� 6CO2 + 6H2O + ATP (ATP) ...read more.


A catalyst is a substance that speeds up a chemical reaction without being used up in the reaction itself. In a chemical reaction a certain amount of energy needs to be supplied in order for the reaction to take place this called the activation energy, enzymes lower the activation energy required for the reaction to take place. Prediction I predict that as I increase the concentration of glucose the rate of reaction will increase therefore the fermentation of yeast will increase. This is because the glucose acts as the substrate concentration which is binding to the enzyme zymase which is in the yeast. There will be a increase in the speed of the reaction as the glucose (substrate) is added this is because substrate concentration affects the rate of reaction up to a certain point. The higher the substrate concentration the faster the reaction but only to a certain point as there will be too many substrate molecules and there will be no difference. Also I predict that glucose and fructose will have the fastest rate of reaction upon the fermentation of the yeast this is because glucose and fructose are both monosaccharide's and the others have more than one sugar molecule therefore they will take longer because they have to undergo hydrolysis and then start there reaction also the higher the temperature the faster the rate of reaction, this is due to the kinetic energy as the enzymes are more likely to collide with the substrate and fill the active site. ...read more.


8) Using the rubber tubing allow it to run from the top of the rubber bung down into the large bowl of water and through a tight gap of the burette. 9) Start the stopwatch as soon as you add the rubber bung and both mixtures are getting mixed. 10) Record how long it takes until no more Carbon Dioxide is released and the level of water stops and doesn't get reduced any more. 11) For each different sugar Concentration follow out Steps 1 - 10. Variables * Concentration of Solution - this must be kept the same as altering this will increase or decrease the rate of reaction and therefore won't give an accurate reading. * The temperature must be kept the same at all times as altering this means there will be more or less kinetic energy which means the rate of reaction can be affected. * Also there must be the same amount of yeast used in each individual boiling tube as more yeast will slow the reaction down and will respire more slowly. * Change of pH may result in a change in the bonds of the enzyme. The active site will be disrupted and the enzyme will be denatured. * Also when you shake the boiling tube u might shake it more for one and less for the other therefore it will interfere how fast the rate of reaction will occur. By Mohammed Nabeel ...read more.

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