Refer to the following graph to answer questions 1-5 1. What is the generation t

Question

Refer to the following graph to answer questions 1-5

1. What is the generation time (g) of this culture?

2. What is the growth rate constant (?) of this culture?

3. A sample of this culture taken at 10h is diluted by a factor of 106X, after which 0.1 ml are spread on a plate. How many CFUs are predicted?

4. A 0.1ml sample taken at 1h is applied to the counting chamber of a hemacytometer. What would be the average number of cells expected in a square with the following dimensions: 1.0mm X 0.2mm X 0.01mm?

5. A sample taken at 6h had an optical density 0.4. What would be the predicted optical density at 8h?

Explanation / Answer

1. The mean generation time or doubling time is 5 hrs. Since doubling time is time required to double the population size in graph it has taken from 2 hrs to 7 hrs Hence 7-2 = 5 hrs.

2. Rate constant K = 1/g = 1/5 = 0.2

3. A sample of this culture taken at 10h is diluted by a factor of 106X, after which 0.1 ml are spread on a plate. How many CFUs are predicted?

The CFU at 10 h in graph is 1.2 X 107/ml. Since it is diluted by 106 X and only 0.1 ml is taken 106 X 10 = 1060 times.

Hence CFU will be 1.2 X 10 7/ 1060 = 7.5 X 105

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