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Can you help me understand this Biology question?

Answer and do the following calculations:

1. Suppose your professor handed you a test tube with 2.0 mL of an E. coli broth culture in it and told you to make a 10–2 dilution of the entire culture. Explain how you would do this. Show your calculations.

2. How would you produce a 10–1 dilution of a 3 mL bacterial sample using the entire 3 mL volume?

3. You have 0.05 mL of an undiluted culture at a concentration of 3.6 X 106
CFU/mL. You then add 4.95 mL sterile diluent.
What is the dilution, and what is the final density of cells?

4. What is the purpose of serial dilutions?

5. Plating 1.0 mL of a sample diluted by a factor of 10–3 produced 43 colonies. What was the original cell
density in the sample?

Remember to use the following formulas for the above questions:

Calculate the original density in CFU/mL using the following formula:
OCD = CFU/ original sample volume

OCD = original cell density

CFU = colony forming units


V1D1 = V2D2

Note: unless told otherwise, the original dilution (D1) is always 1.

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