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Or the period during which the death rate equals the

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-- or -- The Period during which the Death Rate equals the Growth Rate (“Cryptic Growth”) Death Phase The Period during which the Death Rate exceeds the Growth Rate Don’t worry. We’re going to give you a Culture of E. coli that’s already in Logarithmic Phase and you’ll plot the Numbers on Semi-Log Graph Paper until the Culture makes the Transition from Logarithmic Phase to Stationary Phase. So how are we going to come up with these Numbers? In the Case of E. coli , the scattering of Light at 600 nm is directly proportional to the Number of Bacteria in the Suspension. So you’ll be using the Spectrophotometers to monitor the Scattering of Light or Optical Density (“Absorbance”) in your Culture of E. coli undergoing Exponential Growth. Let’s get to the Rationale of Today’s Exercise. We’re trying to maintain the Logarithmic Phase of a Bacterial Growth Curve. Each Lab will receive a Flask of E. coli in Logarithmic Phase. And we’ll give each Clan a Flask of Nutrient Broth (which happens to be a Rich Medium). You’ll inoculate your Medium with our Exponential E. coli and then monitor their (continued) Exponential Growth with a Spectrophotometer. You’ll plot your Data and generate the characteristic “Straight Curve” of Exponential Growth on Semi-Log Graph Paper. This will probably take 5 or 6 Spectrophotometer Readings (so about an Hour and a Half once you’ve set-up). Then you’ll want to use your Data from these Curves to determine the Generation Time of your Bacterium. There should be no Lag Phase. Bacteria growing in a Rich Medium like Nutrient Broth will have all the necessary Nutrients for Growth, plus they’ll have a Pantry full of Pre-Made Amino Acids, Carbohydrates, Lipids, Nucleotides, and Vitamins. Bacteria have learned from the School of Hard Knocks -- Natural Selection -- that when a Growth Component is already present, use it and don’t waste any Time or Energy synthesizing it for yourself. These lucky Bacteria will be growing at their Maximum Rate from your first Time Point and will have a short Generation Time.
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Lab 2 Page 20 Determining Generation Time Graphically (i.e. The Really Easy Way) Well, yes. It’s kind of like how after being molested by an Apple Tree, kidnapped by Flying Monkeys, and traumatized by The Wicked Witch of the West, Dorothy learns from The Witch of the North that she really didn’t have to experience any of these stressful Events. “You always had the Ruby Slippers.” If you were Dorothy wouldn’t you want to haul-off and punch Glinda’s Lights out? But I digress. Remember how an Arithmetic J-Shaped Curve was deemed Useless but the Logarithmic Straight Line was implied to be ever-so-Useful? That Straight Line represents your Ruby Slippers. All you have to do is pick two Points on the Linear Portion of your Logarithmic Straight Line that represent a Doubling of the Optical Density (say, 0.1 and 0.2).
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