Explain why a second infection by the same pathogen is usually overcome much more quickly than the first infection.

WJEC GCSE Biology (Wales) — 2.6.2 The immune system · Explain · 4 marks · View as Markdown

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

When a person catches a disease for the first time, it can take the immune system up to two weeks to overcome the infection. If the same pathogen enters the body again at a later date, the person rarely becomes ill at all.

Model answer (4 marks)

Memory cells are produced after the first infection
Memory cells recognise the same antigen when the pathogen enters again
Antibodies are produced more rapidly / in greater quantities on second exposure
The pathogen is destroyed before it can multiply enough to cause symptoms / illness

Examiner tips

  • Use the term "memory cells" and "antibodies" explicitly
  • Show the sequence: first infection → memory cells → rapid antibody response
  • Mention that the rapid response prevents symptom development

Common mistakes

  • Confusing memory cells with regular lymphocytes
  • Failing to state that antibodies are produced more quickly
  • Omitting that the pathogen is destroyed before symptoms appear

Mark scheme (4 marks)

  1. Memory cells are produced after the first infection
  2. Memory cells recognise the same antigen when the pathogen enters again
  3. Antibodies are produced more rapidly / in greater quantities on second exposure
  4. The pathogen is destroyed before it can multiply enough to cause symptoms / illness

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