Antibiotics and painkillers: Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics.

The idea

Antibiotics such as penicillin cure bacterial disease by killing infective bacteria inside the body. Penicillin interferes with bacterial cell wall formation, so the bacteria burst and die, while human cells are unaffected because they lack a cell wall. Because bacterial species differ in structure and metabolism, a medicine that works on one species may not work on another; for example, penicillin is effective against many Streptococcus infections but not against Mycobacterium tuberculosis. Doctors therefore identify the pathogen, often by laboratory culture or a rapid test, before prescribing. Using the wrong antibiotic wastes time, allows the infection to worsen and increases the chance of resistant bacteria surviving and multiplying.

What earns the marks

• Antibiotics are medicines that cure bacterial disease by killing infective bacteria inside the body.
• Penicillin is an example of an antibiotic and works by disrupting bacterial cell wall formation, causing the bacteria to burst.
• Antibiotics are selective: a specific antibiotic is effective against particular bacteria, not against all bacteria.
• Identifying the pathogen, for example by laboratory culture or a rapid test, allows the correct antibiotic to be prescribed.
• Using an ineffective antibiotic allows the infection to continue and can allow resistant bacteria to survive and multiply.
• Antibiotics do not work on viruses, so they should not be prescribed for viral infections.

Common mistakes and how to put them right

• Saying one antibiotic treats every bacterial infection.

  Put it right: Different antibiotics target different bacteria, so the pathogen must be identified first.

• Claiming penicillin kills viruses as well as bacteria.

  Put it right: Penicillin acts on bacterial cell walls, which viruses do not have.

• Describing antibiotics as painkillers.

  Put it right: Antibiotics kill bacteria, whereas painkillers only relieve symptoms such as pain or fever.

Exam tips

• Link the antibiotic to its mechanism, for example 'penicillin prevents cell wall formation so bacteria burst', to show understanding rather than recall.
• When explaining specificity, give a named example such as penicillin for a Streptococcus infection and state why it would not treat a viral infection.
• Use the term 'specific' explicitly when describing how the correct antibiotic is chosen for a particular bacterium.