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Experiment to investigate the the rate of carbohydrate fermentation by Yeast

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Experiment to investigate the the rate of carbohydrate fermentation by Yeast Aim: To investigate the effect yeast on glucose and other respiratory substrates such as sucrose and starch. I will measure the amount of carbon dioxide bubbles produced using a respirometer. The more bubbles produced in a given time, the higher the rate of respiration. I will achieve this by reacting the yeast (Saccharomyces cerevisiae) with glucose, sucrose and starch at constant temperature, PH, mass and volume. I will keep the temperature constant by using an electronic water bath. This will ensure a fair test because varying temperatures cause varying rates of reaction. I will keep the PH constant by using a buffer solution. This will also ensure a fair test because different PH values alter the active site structure on the yeast enzyme. This will produce inconsistent reaction rates. The mass and volumes will be taken accurately and kept constant by using an electronic weighing scale (for measuring mass) and graduated apparatus e.g. measuring cylinder, graduates pipette, syringe etc (for measuring volume). ...read more.


It is a long chain of molecules and branched molecules. This is a polysaccharide which has many units of glucose linked together. It is a very compact structure therefore hard to breakdown. It is difficult to break down all these glycosidic bonds and the structure is very compact. Therefore starch will have the lowest rate of respiration and will produce least amount of bubbles. Prediction I predict that when glucose reacts with yeast it will produce most amount of bubbling than sucrose and starch and therefore the rate of respiration of glucose with yeast will be higher than with sucrose and glucose. Null hypothesis: Increasing the substrate will not affect the rate at which yeast (Saccharomyces cerevisiae) is broken down (fermented) to alcohol. Method To be able to test the rate of respiration within the yeast I will need an straightforward but accurate way of monitoring the yeast and the best approach to do this is to measure the amount of carbon dioxide produced, as a result I am going to use a method that will enable me to unmistakably see how quickly the carbon dioxide is produced. ...read more.


Thermostatically controlled water bath at 40?C - for a constant temperature 6. Test-tube rack 7. Gloves 8. Measuring cylinder 9. Weighing scale 10. Labels for test tubes 11. weighing scale 12. weighing boat Substances 1. 5 grams of baking yeast (Saccharomyces cerevisiae) 2. Distilled water 3. Glucose, sucrose and starch solutions at 5% Safety measures My investigation will be conducted safely by wearing a laboratory coat and goggles when handling chemicals and yeast. I will make sure that the bench is sterilized before I start so that the yeast is not contaminated. I will have to take care when using calcium chloride, as it irritates when is in prolonged contact with the skin so I will be using gloves when handling this substance and be gentle when handling the glassware, I will be using Vaseline so I will have to make sure that I do not handle glass when there is Vaseline on my glove as I can drop the glassware and break it. Resources: 1. http://www.scientificpsychic.com/fitness/carbohydrates.html 2. http://en.wikipedia.org/wiki/Sucrose 3. http://www.scientificpsychic.com/fitness/carbohydrates1.html 4. Essential AS Biology for OCR, Glenn and Susan Toole, nelson thornes pages; 28, 30. ?? ?? ?? ?? 1 ...read more.

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