Describe why antibiotics cannot be used to treat viral infections, and explain why patients prescribed antibiotics should always complete the full course of treatment.

Cambridge International IGCSE Biology (0610) — 15.1 Drugs · Describe and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Antibiotics target structures or processes that are unique to bacteria, such as the peptidoglycan cell wall or bacterial ribosomes. Viruses lack a cell wall and have a very different replication cycle, so antibiotics cannot act on them.

When a patient finishes the full course, every bacterium that was present is killed. If the course is stopped early, some bacteria survive; these survivors can develop or possess resistance genes and then multiply, spreading resistant strains.

Examiner tips

  • Use the term ‘cell wall’ and ‘replication cycle’ to show understanding of why antibiotics fail against viruses.
  • Explain that completing the course removes all bacteria, preventing the survival of resistant mutants.

Common mistakes

  • Confusing antibiotics with antiviral drugs.
  • Failing to mention that incomplete treatment allows resistant bacteria to proliferate.

Mark scheme (4 marks)

  1. Antibiotics cannot kill viruses because viruses do not have a cell wall (that antibiotics can destroy)
  2. Viruses do not grow and reproduce in the same way as bacteria, so antibiotics cannot inhibit them
  3. Completing the full course ensures all bacteria are killed
  4. If the course is not completed, surviving bacteria may be antibiotic-resistant and reproduce, spreading resistance

Key terms in this question

antibiotic

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