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Biology AS Planning Exercise.

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AS Planning Exercise. Yeast cells anaerobically respire to produce CO2 and Ethanol. This process is referred to as fermentation. Thousands of enzymes catalyse this process. Yeast cells will die if their enzymes become denatured. High temperatures can bring about the denaturation of an enzyme. (Ref ?) Plan an investigation to find the lowest temperature that kills all the yeast cells in a suspension of either dried or fresh bakers yeast. ............................... To find the lowest temperature that will result in the yeast cells ceasing to respire I will mix glucose (C6H12O6) into a yeast suspension, add Methylene Blue and time how long it takes for the Methylene Blue to be reduced ie. go colourless (the longer it takes, the lesser respiratory activity occurring). Prediction. The temperature at which the yeast cells are killed will be 45�C. Explanation. Enzymes are globular proteins which denature (lose their tertiary structure) when exposed to a number of factors such as pH and high temperatures. ...read more.


Results. Volume of Yeast Suspension (cm3) Volume of Glucose Solution (cm3) Time taken for Methylene Blue to be reduced (s) 8 2 227 6 4 512 5 5 516 4 6 600+ I will use 8cm3 yeast suspension and 2cm3 glucose solution as my preliminary experiments showed these two volumes to be effective in achieving the shortest time in reducing the Methylene Blue. Factors Kept Constant. 1. Volume of glucose solution (2cm3) 2. Volume of yeast suspension (8cm3) 3. Concentration of glucose solution (10%) 4. Concentration of yeast suspension (10%) 5. Type of yeast Apparatus. Boiling Tubes Water Bath Thermometer Stop-Clock Yeast Suspension Glucose Solution Glass Rod Sticky Labels Tongs 5cm3 Syringe 10cm3 Syringe Methylene Blue Method. 1. Prepare the water bath at 30�C. 2. Place 8cm3 10% yeast suspension and 2cm3 10% glucose solution using a 10cm3 syringe (for the yeast suspension) and a 5cm3 syringe (for the glucose solution) into a boiling tube. 3. Add a drop of 1% Methylene Blue. 4. Stir with a glass rod. 5. ...read more.


2. Ensure that additional items of clothing & other obstructions are out of the way. 3. Take care to avoid spillage's by using tongs to place the test tubes into the water bath. After the experiment is finished leave 20 minutes before removing it. Wear gloves to protect your hands. Table of Results. Temperature (�C) Time Taken For Methylene Blue To Go Colourless (s). Average Value (s) Expt 1 Expt 2 Expt 3 30 35 40 45 50 55 60 Calculations. I will use the average time values to calculate the rate. Rate = 100/time Graph. 0 30 35 40 45 50 55 60 Temperature (�C) Interpretation of Results. After 45�C there will be a decline in the time taken for the Methylene Blue to go colourless. This will be shown on the graph by being the peak of the rate. Validity of Results. A fundamental part of this experiment is to time how long it takes for the Methylene Blue to lose its colour. However, this presents a problem as an individuals interpretation of when this occurs can vary, therefore affecting the results due to human error. ...read more.

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