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Investigating the Effect of Temperature on the Fermentation of Yeast

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Introduction

Investigating the Effect of Temperature on the Fermentation of Yeast Planning Aim To fully investigate the effect of temperature on the rate of fermentation of yeast Background Information Yeast is a single-cell fungus, occurring in the soil and on plants, commonly used in the baking and alcohol industries. Every living thing requires energy to survive and through respiration, glucose is converted into energy. There are two types of respiration available to living cells are: 1. Aerobic requires oxygen and takes place inside the mitochondria of iving cells. The energy is stored as adenosine triphosphate (ATP) Aerobic respiration produces 2890KJ/Mole or 38ATP. This is much more than anaerobic. The by-products are carbon dioxide and water. Glucose + Oxygen � Carbon Dioxide + Water + Energy C6H12O6 + 6O2 � 6CO2 + 6H2O + 2890KJ/Mole 2. Anaerobic occurs in the absence of oxygen. Creates a smaller amount of energy than aerobic: 210KJ/Mole or 2ATP. The by-products are carbon dioxide and ethanol which is toxic and eventually kills the cells unless it is broken down. Glucose � Ethanol + Carbon Dioxide + Energy C6H12O6 � 2C2H5OH + 2CO2 + 210 KJ/mole Yeast can perform both aerobic and anaerobic respiration. In the absence of oxygen, fermentative yeasts produce their energy by converting sugars into carbon dioxide and ethanol (an alcohol). In brewing, the ethanol is bottled, while in baking the carbon dioxide raises the bread, and the ethanol evaporates. Anaerobic respiration of yeast is often referred to as fermentation. Fermentation was first discovered by Louis Pasteur in 1854. He noticed that yeast ferments sugars into alcohols and also that fermentation is an anaerobic reaction. In order for the yeast to ferment enzymes are needed. Enzymes are organic substances, composed of polymers of amino acids, which act as catalysts to regulate the speed of the many chemical reactions involved in the metabolism of living organisms. In their globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. ...read more.

Middle

from heat energy. The Kinetic Theory works on another theory, the Collision Theory, which states that if two particles collide with sufficient energy (called the activation energy) bonds will be broken and a reaction will take place. Therefore, I predict that the greater the temperature, the greater the amount of CO2 produced by fermentation, as the particles will move more quickly, therefore there will be a greater number of collisions, between substrate and enzymes, with more force, and therefore a greater rate of. In the same way I predict that at lower temperatures there will be less carbon dioxide produced, as the particles will have less energy and fewer collisions would occur. Consequently there will be a slower rate of reaction. However, despite the above predictions, from my research and knowledge, I know that at the highest temperatures the active sites of enzymes deform, becoming denatured and unproductive. I also know that most enzymes in the human body work effectively at about 37�C as the body constantly attempting to maintain this internal temperature by homeostasis. I can safely assume from this fact, from my preliminary work and from research and knowledge that body temperature is about the optimum temperature for enzyme activity. I think this is backed up by As a result, I predict that there will be little products at room temperature, that there will be a constant increase, following the 'Q10 by 2 theory' (see background info), until about 37�C, body temperature, and then that the enzymes will begin to denature and the amount of gas produced will decrease as the active sites can no longer bind to their specific substrate. See prediction graph Experimental Plan Modification to method I decided to get a new yeast suspension for every reading. This is because the glucose was getting more and more used up every time and consequently the accuracy and the reliability of the investigation was not at its best. ...read more.

Conclusion

Another would obviously be to take more readings at different ranges. I would also increase the amount of re-agent and collection time, as by doing the latter I increase the amount of carbon dioxide collected. This means that with increased values, the percentage errors are less (�0.25ml is a smaller fraction of 40ml, for example, than 20ml). I would have also liked to have used a buffer, which keeps the pH constant, educing the effect of it. As the yeast cells respire CO2 is produced, which is acidic. This means that the pH drops rapidly and this can cause the enzymes to denature. Using a buffer will stop the pH dropping as donates hydrogen ions into solution and therefore it fluctuates around a certain pH. Extension work Perhaps an alternative method could have been to measure the time taken to collect a certain amount of CO2 gas at certain temperatures. The great disadvantage of this would be the time required for the ends of the range of temperatures to create the amount of gas, especially difficult if the yeast has already denatured. Therefore, given the circumstances, especially due to the time limit, the method used was more effective. For other experiments based on the same principle I would have used more types of yeast to see if they contain different enzymes, which might be more or less resistant to temperature. I would use a water bath, to keep the temperature constant. I would use a buffer to keep the pH constant. I would probably like to change the concentration of the yeast to see if the rate increases with the amount of glucose present. Another good piece of further work would be to investigate the gas; one cannot be certain that it is carbon dioxide, which is being produced. For example, the glucose could be reacting to form carbon monoxide or even a non carbon-compound gas, such as hydrogen. A simple way to investigate this would be to use the carbon dioxide test: "Carbon dioxide turns limewater milky". ...read more.

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