Robert Koch (1843–1910) discovered that bacteria cause some diseases - Edexcel - GCSE Biology - Question 5 - 2016 - Paper 1

To find the number of bacteria after 1 hour, we need to determine how many times the bacteria double in that period.

An hour is equal to 60 minutes. Since the bacteria double every 20 minutes, we can divide the total time by the doubling time:

$ext{Number of doublings} = \frac{60 ext{ minutes}}{20 ext{ minutes}} = 3$

Starting with 200 bacteria and applying the formula for exponential growth:

$N = N_0 \times 2^n$

where:

• $N_0$ is the initial quantity (200),
• $n$ is the number of doublings (3).

Thus:

$N = 200 \times 2^3 = 200 \times 8 = 1600$

So, after 1 hour, there will be 1600 bacteria in the broth.