A student adds 5 bacterial cells to a test tube containing fresh medium and incubates it for 3 hours at 37°C. The bacterial population shows an initial lag phase of 20 minutes followed thereafter by a growth phase with a doubling time of 40 minutes. Given this, what is the approximate number of bacterial cells present at the end of the incubation period? (Note: Assume unrestricted growth during incubation.)A.20 cellsB.40 cellsC.80 cellsD.160 cells
Question
A student adds 5 bacterial cells to a test tube containing fresh medium and incubates it for 3 hours at 37°C. The bacterial population shows an initial lag phase of 20 minutes followed thereafter by a growth phase with a doubling time of 40 minutes. Given this, what is the approximate number of bacterial cells present at the end of the incubation period? (Note: Assume unrestricted growth during incubation.)A.20 cellsB.40 cellsC.80 cellsD.160 cells
Solution
First, let's understand the growth pattern of the bacteria. The bacteria have a lag phase of 20 minutes, during which they do not reproduce. After this, they enter a growth phase where they double every 40 minutes.
The total incubation time is 3 hours, or 180 minutes. Subtracting the 20 minute lag phase, we have 160 minutes of growth phase.
During the growth phase, the bacteria double every 40 minutes. So, we divide the 160 minutes of growth phase by the 40 minute doubling time to find the number of doubling periods. 160 / 40 = 4 doubling periods.
We start with 5 bacterial cells. After one doubling period, we have 5 * 2 = 10 cells. After two doubling periods, we have 10 * 2 = 20 cells. After three doubling periods, we have 20 * 2 = 40 cells. After four doubling periods, we have 40 * 2 = 80 cells.
So, the approximate number of bacterial cells present at the end of the incubation period is 80 cells. The answer is C. 80 cells.
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