Q.Given that the average duplication time of E.coli is 20 minutes, how much time will two E.coli cells take to become 32 cells?

Since the population doubles with every duplication cycle, the number of cycles needed can be worked out by counting how many times the starting number must double to reach the target.

• Starting count: 2 cells.
• After 1 cycle (20 minutes): 2 doubles to 4 cells.
• After 2 cycles (40 minutes): 4 doubles to 8 cells.
• After 3 cycles (60 minutes): 8 doubles to 16 cells.
• After 4 cycles (80 minutes): 16 doubles to 32 cells. …

Bacterial duplication (binary fission) works by simple doubling: every cell splits into two identical cells once per duplication cycle, so the total cell count doubles with each cycle that passes. Given a duplication time of 20 minutes, the calculation is a matter of counting how many doublings are needed to get from the starting count to the target count.

Working through it step by step, starting from 2 cells:

• After the 1st cycle (20 minutes): 2 cells become 4 cells.
• After the 2nd cycle (40 minutes): 4 cells become 8 cells.
• After the 3rd cycle (60 minutes): 8 cells become 16 cells.
• After the 4th cycle (80 minutes): 16 cells become 32 cells. …

Method: Count doublings needed, then multiply by cycle time

1. Start = 2 cells, target = 32 cells. Ratio = 32/2 = 16 = 2^4, so 4 doublings are needed.
2. Track it stepwise: 2→4 (1 cycle)→8 (2)→16 (3)→32 (4). …