Question: How can medicines such as penicillin kill the bacteria?

Rosie Coates answered on 10 Mar 2014:

Different medicines work in different ways to stop bacteria from reproducing. Penicillin does this by disrupting the bacteria’s cell wall.

Think about the cell wall like a car tyre. The tyre has to be strong enough to resist the pressure from the air inside it. The same is true of the bacterial cell wall; it has to be strong enough to help the bacteria hold its shape. Penicillin stops the bacteria from being able to make it’s cell wall properly so it loses its strength. Imagine what would happen to a car tyre if it started to get weaker and weaker- it would eventually burst. This is what happens to bacteria when they try to grow where there is penicillin. Their cell walls get too weak to stand the pressure from inside the growing cell and the cell eventually bursts.