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the effect of ethanol on the rate of anaerobic respiration

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Skill P: The effect of ethanol on the rate of anaerobic respiration of sucrose by yeast Aim: This is an experiment to investigate at which rates the different sugar-yeast-ethanol-mixtures move to the end of the 1mm capillary tube using five different ethanol concentrations. Background theory: Saccharomyces cerevisiae is a species of budding yeast. Yeast is used in bread making and brewing. In brewing yeasts ferment fruit or grain to produce alcoholic drinks. In bread making yeasts produce carbon dioxide which helps the bread to rise. The alcohol evaporates during baking. It is believed that yeast was originally isolated from the skin of grapes. Yeast contains many enzymes including sucrase which breaks down sucrose into glucose and fructose. The official name for sucrase is beta-fructofuranosidase (1, 11). Carbohydrates are a group of substances that are important in many biological processes. They provide energy-rich nutrients to organisms and are used to build up their body structures; all carbohydrates contain hydrogen, carbon and oxygen. The carbohydrate sucrose is a disaccharide of one glucose sugar and one fructose sugar joined by a glycosidic bond. Glucose and fructose are both monosaccharides, and structural isomers and both respire to give off the same products (2). When oxygen is not available, oxidative phosphorylation and the Krebs cycle cannot take place. This is also true for organisms or cells which don't contain the machinery to carry these out. In these circumstances, respiration takes place without oxygen- anaerobic respiration. In anaerobic respiration, glycolysis takes place as usual, producing pyruvate and a small yield of 2 ATP (3). Glycolysis is the lysis of glucose. It is a multi-step process in which a glucose molecule with six carbons is broken down into two molecules of pyruvate, each with three carbon atoms. Energy from ATP is needed in the first steps, but energy is released in later steps, when it can be used to make ATP. ...read more.


Ethanol increases the acidity by allowing more H+-ions into the cytoplasm, which will affect the pH, which will affect the enzyme activity. Most enzymes work fastest at a pH of around 7. Some however have a different optimum pH. pH is the measure of the concentration of hydrogen ions in a solution. The lower the pH the higher the hydrogen ion concentration. Hydrogen ions can interact with the R groups of amino acids, affecting the way in which they bond with each other and therefore affect their 3D arrangement. A pH which is very different from the optimum pH can cause denaturation of an enzyme (9, 10).Sucrose cannot be broken down by sucrase as fast as when using 0.0% ethanol concentration. When using an ethanol concentration of 10.0% the rate of anaerobic respiration will be even slower than when using an ethanol concentration of 5.0% because ethanol affects the membrane permeability of yeast even more and lets more hydrogen ions into the cytoplasm of yeast. The length of movement will be twice as long as the length of movement when using 20.0% of ethanol concentration. When using the ethanol concentration of 15.0% the rate of anaerobic respiration will be even slower and the length of movement will be shorter than when using an ethanol concentration of 10.0%. When using the ethanol concentration of 20.0% the rate of anaerobic respiration will be the slowest of all five ethanol concentrations and this concentration will have the shortest length of movement. A graph to show the effect of ethanol on the rate of anaerobic respiration of sucrose (predicted) Apparatus list (for one investigation only excludes repeats): Item quantity Concentration and volume Accuracy Activated yeast suspension 25cm3 10% concentration, 1g every 10 cm3 - Sucrose solution 25cm3 0.25M - Beaker 5 100cm3 - Stop clock 1 - 1 sec Goggles 1 - - Plastic syringe 7 10cm3 1cm3 Plastic syringe 7 5cm3 0.5cm3 Plastic syringe 5 1cm3 0.1cm3 Text marker 1 - - Distilled water 100cm3 pH 7 ...read more.


These limitations could result in anomalies which make the practical not as accurate and reliable as it could be. To attempt more accurate results we could have used more data, i.e. a longer time and repeated the experiment four times for each mixture containing a different ethanol concentration to get more accurate averages of distance displaced in a given time. The method went well and there are no modifications to make except to ensure that the yeast has the same temperature throughout the whole investigation as once the windows were open and the biology lab was cooler compared to other days. Use a thermometer to measure the temperature of the yeast and make sure that it is room temperature. Further make sure there are no human errors made, like forgetting to start the stop watch or parallax errors, like not reading off at eye level the distance the mixture moved. Do more repeats than three as it can happen easily that the results given off in one go are different from the next results, repeat the investigation for each ethanol concentration until you get vaguely similar results and always make sure the lower the ethanol concentration in the mixture the longer the distance moved in a short time. Bibliography: 1) Advanced biology by Jones and Jones 2) Advanced sciences : Biology 1 3) Advanced sciences : Biology 2 4) Biological sciences 1 and 2 5) Advanced biology by Michael Kent 6) Class notes 7) Research paper: Influence of magnesium ions on heat shock and ethanol stress responses of Saccharomyces cerevisiae by Rosslyn M. Birch, Graeme M. Walker 8) Research paper: The effect of ethanol on the plasma membrane permeability of spoilage yeast by Celia Quintas, Emilia Lima-Costa and Maria C. Loureiro-Dias 9) Research paper: Ethanol production during Bath Fermentation with Saccharomyces cerevisiae: Changes in glycolytic enzymes and internal pH by K. M. Dombek and L. O. Ingram 10) Research paper: Mechanism of ethanol inhibition of fermentation in Zymomonas mobilis by Yehia A. Osman and Lonnie O. Ingram 11) Internet: www.wikipedia.co. ...read more.

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