Explain why bacteria and viruses are both described as pathogens, and state ONE difference between the way bacteria and viruses cause disease.

WJEC GCSE Biology (Wales) — 2.6.1 Pathogens and disease · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

A pathogen is a microorganism that causes disease or infection. Both bacteria and viruses are pathogens because they can invade or enter the body and cause illness.

The main difference is that bacteria produce toxins or release harmful chemicals that damage tissues, whereas viruses must replicate inside host cells, causing cell damage or destruction.

Examiner tips

  • Use the term ‘pathogen’ and explain both invade the body; give one clear difference – toxins vs. intracellular replication.
  • Show the difference in a single sentence to use the full 4 marks.

Common mistakes

  • Confusing bacteria with viruses as the same type of organism; not mentioning the toxin/replication distinction.
  • Giving a vague answer such as ‘they both cause disease’ without explaining why they are pathogens.

Mark scheme (4 marks)

  1. A pathogen is a microorganism that causes disease / infection
  2. Both bacteria and viruses can invade / enter the body and cause disease / illness
  3. Bacteria produce toxins / release harmful chemicals that damage tissues / cause symptoms
  4. Viruses reproduce / replicate inside host cells, causing cell damage / destruction

Key terms in this question

pathogen · bacteria · viruses

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