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Investigation to find the lowest temperature that kills all the yeast cells in suspension of fresh bakers yeast

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Introduction

Investigation to find the lowest temperature that kills all the yeast cells in suspension of fresh bakers yeast Yeast has the ability to convert sugar to alcohol (ethanol) during anaerobic respiration. This process is known as fermentation and is caused by enzymes in yeast. They are temperature sensitive and as temperature increases, rate of reaction increases. This is due to both the enzyme and substrate having greater kinetic energy, therefore moving faster, having more frequent collisions and meaning that the substrate molecules enter the active site more often. However, above a certain temperature, the enzymes molecule becomes denatured. This is due to the enzymes vibrating so energetically that bonds holding the molecule together begin to break and the enzymes molecule starts to lose it shape and activity. The enzyme does not denature as temperature decreases but takes place slower and slower. (Bibliography (1)) The following investigation is going to be to try and find the lowest temperature at which all the yeast cells die. ...read more.

Middle

pH Enzymes are pH specific. Therefore, varying ranges of pH would affect the rate of reaction. Buffer - this maintains the same pH in all the test tubes. This is necessary because, as yeast respires; CO2 is given off which would make the conditions more acidic. Eg. At 35�C production of CO2 will be greater than at 60�C. Concentration of enzyme Change rate of reaction (400 words) This is a systematic problem and is unchangeable: Yeast cells are living things and therefore multiply when reacting. ? enzyme concentration ? uncontrollable ? unreliable ? results will vary. This is not helped by the fact that the actual concentration of the enzyme is unknown. Volume of substrate Change rate of reaction Add same amount of glucose/sucrose to each boiling tube. Fair test Make sure you: This will ensure it is a fairer test as: Repeat each test at least twice you can attain an average and/or helps to rule out any anomalies that may occur Keep the dependant variables the same all the reactions have been carried out under the same conditions to the best of your ability. ...read more.

Conclusion

o Remove boiling tubes after time for analysis by placing a sample into the colorimeter. Record transmitting % o Repeat the above 7 steps for other temperatures- ensuring that the appropriate temperatures are reached before the experiment is carried out. o Carry out complete experiment 2 more times, giving you 3 sets of results. Results table Temperature /�C Transmitting % Mean Transmitting % Test 1 Test 2 Test 3 40 45 50 55 60 65 70 75 80 Pot results on a graph- e.g. Safety/Risk Assessment Use standard laboratory conditions. Hazard Precautions Methylene blue Important to keep away from mouth and to wash hands after use because if swallowed can cause Nausea, headaches and/or diarrhoea. Hot water Use tongs to place and remove boiling tubes in and out of water baths Evaluation Despite following the method exactly every time, you are extremely unlikely ever to attain the same results as the time before as the conditions of the experiment can never be made constant. This is because yeast cells are living things, and therefore will multiply when reacting with the sugar. As they multiply the enzyme concentration increases, causing an uncontrollable and unreliable experiment with results that will vary. ...read more.

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