# Describe how the human immune system responds when a pathogen enters the body for the first time, and explain why the response is faster if the same pathogen enters the body a second time.

> Eduqas A-Level Biology — 3.4 Population size and ecosystems · Describe · 5 marks

## Mark scheme (5 marks)

1. White blood cells detect the pathogen using antigens on its surface
2. Lymphocytes release antibodies that are complementary / specific to the antigen
3. Phagocytes ingest and digest the pathogen (phagocytosis)
4. After the infection, memory cells remain in the body
5. On second exposure, memory cells rapidly divide and produce antibodies more quickly, destroying the pathogen before symptoms appear

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