Practice Question

1.State the name of the process that bacteria use to divide.

Binary fission

2. Under ideal conditions what would be the mean division time?

Suitable temperature and plenty nutrients will produce a mean division time of 20 minutes.

3. State the formula used to:

3a. Calculate new population size

N= N₀ x 2ⁿ

3b. Calculate number of divisions

n = total time/mean division time

4.A bacterial culture starts with 2 bacteria. The mean division time is 30 minutes. How many bacteria will there be after 3 hours?

3 hours = 3 × 60 = 180 minutes

n = total time/mean division time

n = 180/30 = 6 divisions

N = 2 x 2⁶ = 128

5.A bacterial culture starts with 1 bacterium. The mean division time is 15 minutes. How many bacteria will there be after 6 hours? Express your answer in standard form.

6 hours = 6 × 60 = 360 minutes

n = 360/15 = 24 divisions

N = 1 x 2²⁴ = 16777216

N = 1.7 x 10⁷

Rounded up as the number after the 1st  6 is greater than 5.

6.A bacterial culture has a mean division time of 20 minutes. If the population grows to 512 cells after 2 hours, how many bacteria were there at the start?

2 hours = 2 × 60 = 120 minutes

n = total time/mean division time

n = 120/20 = 6 divisions

N= N₀ x 2ⁿ

512 = N₀ x 2⁶ 

512 = N₀ x 64

N₀ = 512/64 = 8