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Fermentation project - I am trying to find out what effects respiration in yeast.

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Fermentation project Aim I am trying to find out what effects respiration in yeast. Introduction Yeast is any of a number of microscopic one-celled fungi used for their ability to ferment carbohydrates in various substances. Yeasts are extensive in nature, occurring in the soil and in plants. Most cultivated yeasts belong to the species Saccharomyces; those known as brewers yeast are strains of S. cerevisiae. Yeasts have been used since the early years for the making of beer, wines and bread and today are used furthermore in industrial processes. Pure yeast cultures are grown in a medium of sugars, nitrogen sources, minerals and water. The final product may take the form of dried yeast cells. In the making of wines and beers, the fermented medium is the desired product and the yeast itself is discarded or used to feed animals. Anaerobic respiration Because yeast respires in anaerobic way fermentation can take place. Anaerobic respiration is respiration without the presence of oxygen. The first step consists of breaking down glucose into pyruvic acid and the end product (in yeast respiration) will be ethyl alcohol. Theory of fermentation Fermentation is the chemical changes in organic substances produced by the action of enzymes. In alcoholic fermentation, the action of zymase (the enzyme) secreted by yeast allows anaerobic respiration to take place, converts simple sugars such as glucose and fructose into ethyl alcohol (ethanol) ...read more.


Conversely enzymes will still allow respiration at low temperatures, as they are very efficient. Minute quantities of an enzyme can accomplish at low temperatures what would require violent reagents and high temperatures by ordinary chemical means. As a catalyst cannot be used up, the rate of bubbles will be released at a constant speed. The rate at which the bubbles carbon dioxide is produced (how fast the bubbles emerge) will not alter with time. However enzymes are proteins and become denatured if the temperature becomes too high. The active site changes shape and the substrate will no longer fit. Most enzymes stop working at around 45 C. This will mean that the rate of respiration will increase as the temperature gets higher until a certain temperature (around 45 C). I predict the enzyme will then become denatured and respiration will not occur. No CO will be produced. Method Before the experiment, a set of control results need to be obtained to compare against these will be carried out in the same way as the final experiment only using water in place of yeast. Firstly a yeast suspension needs to be prepared. This can be achieved by pouring a packet of yeast into around 500ml of water at 20 adding glucose and stirring until the granules are dispersed. The solution will become cloudy and frothing will occur. This is the carbon dioxide. ...read more.


It was quite hard to keep the temperature constant throughout each test. The tin foil helped but the temperature sometimes dropped 1 or 2 degrees. To solve this, better insulation methods could be used such as more tinfoil or a layer of polystyrene as well. Then there was the accuracy in the amount of carbon dioxide being released. It was quite simple to count the number of bubbles, however each bubble was not the same size making it impossible to know the actual volume of carbon dioxide being released. To solve this, a more complicated experiment would need to be carried out using a piece of apparatus called the Ganongs respirometer. This is a u shape monometer with a tap to equalize the pressure. The tap is then closed and co pushes a salt solution through the tube. Depending on how much the solution has moved, the amount of co can be recorded. This allows the quantity of co in cm to be recorded giving more accurate results. My results are reliable as for both tests, similar results were achieved and the conclusion fitted both sets of results. However my conclusion is only valid to the range of values I have investigated. To get more accurate results I would use smaller steps between each temperature. I only know that the temperature of denaturing is between 45 and 50 C plus the enzyme isn't full denatured at 50 . Some bubbles are still being produced. I would have to extend my range to see what happens when the temperature is increased further. ...read more.

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