# Describe the role of the immune system in defending the body against a pathogen that has entered the body for the first time.

> WJEC A-Level Biology (Wales) — 3.1 Photosynthesis · Describe · 5 marks

> When a pathogen enters the body for the first time, the immune system mounts a response to destroy it and provides protection against future infections by the same pathogen.

## Mark scheme (5 marks)

1. White blood cells detect the pathogen using receptors on their cell surface to identify antigens on the pathogen
2. Lymphocytes release antibodies that are complementary/specific to the antigen on the pathogen
3. Phagocytes ingest and digest the pathogen using enzymes (phagocytosis)
4. Antibodies neutralise the pathogen / clump pathogens together (agglutination) making them easier to destroy
5. Memory cells remain after the infection so that if the same pathogen enters the body again, antibodies are produced more quickly

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