GCSE Biology (AQA)

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Bacterial Population Size

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Cell Biology Cell Structure

Bacterial Population Size

2:20 Microorganisms and Measurements
Spec 4.1.1.6
Previous Measuring Zones of Inhibition Next Population Size in Standard Form
  • Bacterial populations double with each reproduction cycle.
  • The final number of bacteria is calculated as the initial number multiplied by two raised to the power of the number of divisions.
  • Example given over a 60-minute period starting with one bacterium:
  • At 0 minutes: 1 bacterium
  • At 20 minutes: 2 bacteria
  • At 40 minutes: 4 bacteria
  • At 60 minutes: 8 bacteria
  • The formula used for calculation is: final bacteria count = initial count * (2 ^ number of divisions).
  • Mean division time for the example bacteria is 20 minutes.
  • To find out how many bacteria are present after five hours:
  • Calculate divisions per hour: 60 minutes / 20 minutes = 3 divisions per hour.
  • Multiply by total hours: 3 divisions/hour * 5 hours = 15 divisions.
  • Apply the formula: 1 * (2 ^ 15) = 32,768 bacteria.
  • Students are expected to memorize this formula and perform such calculations in exams.

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