Starting from a single individual, what is the size of a population of bacteria that reproduce by binary fission every 20 minutes at the end of a 2-hour time period? (Assume unlimited resources and no mortality.)
A) 6
B) 18
C) 128
D) 512
E) 1,024

Question

Quizplus · Accepted Answer

The bacteria population doubles every 20 minutes. In 2 hours, or 120 minutes, there are 6 intervals of 20 minutes. Thus, the population would double 6 times. 
Starting with 1 bacterium and doubling the population every 20 minutes for 6 intervals: 
1 → 2 → 4 → 8 → 16 → 32 → 64 → 128 → 256 → 512 
Therefore, the population size at the end of a 2-hour time period is 512. So, the answer is D.

Starting from a Single Individual, What Is the Size of a Population