Equipment needed:
Calorimeter Sterile pipettes Bunsen Burner Nutrient broth Yeast pellets Sterile work surface Conical flask (cotton wool instead of bung) Method: Firstly, sterilise your work station. To do this, firstly, wipe down the area and trays you may be using with ethanol, Then, light a bunsen burner and keep it on a blue flame. this creates a vacuum of air which keeps microbes in the air away from your work area. Once you have done this, you're ready to begin. Ensure you sterilise your instruments before and after use by passing them through the tip of the flame. Now, in order to create a yeast solution, place a set amount of yeast pellets in distilled water and mix until you can no longer see the pellets. Then, extract a small amount of this solution using a pipette in your sterile work surface, ensuring you keep it near the flame at all times. Once you have extracted it, mix it into your nutrient broth and swill it until there is no sediment visible. Place it in a water bath at 30-40 degrees (optimal temperature for yeast replication) and leave for a few hours so that the yeast can replicate. At set intervals of time (for my group, we measured at 8AM, 1PM and 6PM), you should revisit your broth and take a small sample from it and test it to see how much the yeast has replicated, using the method below: Firstly, create a sterile work surface using the aforementioned method. Then, remove the yeast solution from the bath and swill until there is no sediment at the bottom. Then, keeping it near the flame, remove the cotton bung. Run the neck of the flask through the flame, and remove 1cm cubed of the broth with a pipette. Place this in a test tube of 9cm cubed distilled water, ensuring you replace the bung on the conical flask as well. Mix the water and yeast solution well and place it to one side in a test tube rack. Now, use a cuvette full of sample solution (some of the original broth without the yeast) and use this to calibrate the calorimeter. Then, test your new solution 3 times using the calorimeter and record your results. repeat this at your set time intervals for about a week and plot your results onto a graph. You should see a lag phase, a period of exponential growth, a stationary phase and then finally, a declining (death) phase. This post will be updated with pictures once I get them.
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