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 first need to calculate how many doubling periods fit in 60 minutes.

Each doubling period is 20 minutes, so in 60 minutes:

$\frac{60}{20} = 3$

a doubling occurs 3 times.

We can calculate the final number of bacteria using the formula:

$N = N_0 \times 2^n$

where:

• $N_0$ is the initial number of bacteria (200),
• $n$ is the number of doubling periods (3).

Thus, we have:

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

So, the number of bacteria after 1 hour is 1600.