There are links with this practical to Antibiotics and painkillers.

The idea

The zones of inhibition you measure show how well an antibiotic stops bacterial growth. This connects to the topic of antibiotics and painkillers: antibiotics kill bacteria or stop their growth, while painkillers relieve symptoms but do not kill pathogens. Antibiotics are effective only against bacteria, not viruses, which is why viral infections such as colds are not treated with antibiotics. The practical also shows why the wrong antibiotic, or too low a dose, may fail, and why overuse contributes to antibiotic resistance. A clear, large zone around an antibiotic disc indicates that the bacterium is susceptible to that antibiotic. This evidence helps explain why doctors choose particular antibiotics and why completing a prescribed course matters.

What earns the marks

• States that antibiotics kill bacteria or inhibit their growth, whereas painkillers relieve symptoms without killing pathogens.
• Links a large zone of inhibition to greater susceptibility of the bacterium to that antibiotic.
• Explains that antibiotics are ineffective against viruses, so viral infections are not treated with them.
• Relates the practical to antibiotic resistance, including the idea that overuse or incomplete courses can allow resistant bacteria to survive.
• Uses zone measurements as evidence when discussing which antibiotic might be chosen for a bacterial infection.

Common mistakes and how to put them right

• Claiming painkillers kill bacteria.

  Put it right: Painkillers relieve symptoms but do not kill pathogens.

• Stating antibiotics treat viral infections.

  Put it right: Antibiotics act on bacteria and are ineffective against viruses.

• Saying resistance means the patient's body becomes resistant.

  Put it right: The bacteria become resistant, not the person.

Exam tips

• Use the phrase zone of inhibition when linking practical results to antibiotic effectiveness.
• Distinguish clearly between antibiotics and painkillers in any comparison question.
• When discussing resistance, refer to bacteria surviving and reproducing rather than to human immunity.