General Population Growth

Exercise 1- General Population Growth

1. Describe the appearance of the graph on the linear paper and on semi-log paper. Explain why the appearance of the two graphs differs.

3. Fill in the table below. Note that the doubling time is not specified in this case. Graph these data on linear and semi-log paper in the same manner as before, except that the x-axis is now "number of doublings", rather than a specific time.

4. What is the shape of the growth curve if the doubling time is one week? One month? Twenty years?

Exercise 2- Cell Division and Population Growth in Escherichia coli

1. Note the shape of the curve plotted from Table 5 on the semi-log paper. This curve is S-shaped and is called sigmoid (from the Greek letter for "S"; sigmoid means "like sigma"). Why might this curve look like this? Hint: Prior to inoculation, the bacteria in their stock culture were in a semi-dormant condition.

3. What was the doubling time of your bacterial culture (Table 3)? Show your computations. Why is it different (if it is) from the model data (from a previous class), when the experiment producing it was run the same way?

4 How would you explain the increase in doubling time (decrease in slope) towards the end of the experimental period in the model data from Table 5? Did you see this change in your growth curve today (Table 3)? If not, why not?

6 Does the doubling time of your culture change throughout the course of the experiment? Compare the time required to double at the beginning and the end of class to answer this question.

7 What factors could cause the doubling time of a population of E. coli to change? Would these factors affect a population of multicellular plants in the same way? A human population?

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