02.Growth Curve

# Now do you really think we ʼ ll get enough growth to

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Now... Do you really think we ʼ ll get enough Growth to produce 100% Absorbance (which would be 0% Transmission)? No Way. You ʼ re probably going to need a Range of about 0.01 to 1.0. 4. Use a Pencil to graph your OD Readings • Read “up” the Vertical Scale to the Value that matches a particular OD Reading - The Vertical Scale is Logarithmic. Take your Time. This can get a bit Tedious and the Logarithmic Markings can get really Small. • Read “across” the Horizontal Arithmetic Scale to the Value that matches the Timepoint of this particular OD Reading - The Horizontal Scale is Arithmetic. Again, take your Time. But this is a lot Easier. • Make a Dot where these Coordinates meet 5. Repeat Step 4 (above) for all of your OD Readings and Timepoints 6. Draw a Theoretical Best-Fit Straight Line You may need to ignore one or two of your OD Readings to get this to work. Actually, your Lab Partner says you ʼ ll definitely need to ignore some of your dodgy OD Readings to get semi-lucid Results.

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Lab 2 Page 11 Using your Graph to Determine Generation Time 1. Pick any two Points along your Theoretical Best Fit Line that represent a Doubling of the Optical Density 0.1 and 0.2 tend to be Favorites, but any Doubling of Optical Density will work just as well. We ʼ re making the (Valid) Assumption that a Doubling of the Optical Density represents a Doubling in the Number of Bacteria. 2. Plot directly down from each of these Points. This will take you down to the Arithmetic Time Scale. Let ʼ s assume you get an OD of 0.1 at 20 Minutes and an OD of 0.2 at 50 Minutes. 3. Subtract the Time between these two Points. In our Example: 50 Minutes - 20 Minutes = 30 Minutes So the Generation Time (Doubling Time) for our Example would be 30 Minutes. There really isn ʼ t a “Right” or “Wrong” Generation Time, but since everyone was using the same Bacterium grown under the same Conditions, your Generation Time should be similar to everyone else ʼ s Generation Time (although your Lab Partner says the Operative Word here is “should”). _______________________________ “Hey, Your Worship, I'm only trying to help.” Would you please stop calling me that?’ Sure, Leia.“ You make it so difficult sometimes.’ I do, I really do. You could be a little nicer, though. Come on, admit it. Sometimes you think I'm all right.” Occasionally, maybe... when you aren't acting like a scoundrel.’ Scoundrel? Scoundrel? I like the sound of that.” Stop that.’ Stop what?” Stop that. My hands are dirty.’ My hands are dirty, too. What are you afraid of?” Afraid?’ You're trembling.” I'm not trembling.’ You like me because I'm a scoundrel. There aren't enough scoundrels in your life.” I happen to like nice men.’ I'm a nice man.” No, you're not. You're...’ Sir. Sir, I've isolated the reverse, power flux coupling.
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• Winter '09
• MANN
• Bacteria, Agar plate, Bacterial growth, semi-log graph paper, Microtiter Pipettes

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