# Describe how the human body responds to a pathogen that has entered the bloodstream. Include in your answer the roles of lymphocytes and phagocytes.

> Eduqas A-Level Biology — 3.2 Respiration · Describe · 5 marks

> When a pathogen such as the influenza virus enters the bloodstream, the immune system is activated to destroy it.

## 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. Antibodies bind to the antigens on the pathogen to neutralise it / cause agglutination (clumping together of pathogens)
4. Phagocytes engulf (ingest) and digest the pathogen using enzymes in a process called phagocytosis
5. Memory cells are produced so that if the same pathogen enters the body again, antibodies are produced more quickly

## Key terms

- [pathogen](https://www.gradenine.co.uk/glossary/pathogen)
- [lymphocyte](https://www.gradenine.co.uk/glossary/lymphocyte)
- [phagocyte](https://www.gradenine.co.uk/glossary/phagocyte)

## Related

- [Revision notes for Eduqas A-Level Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-the-human-body-responds-c9521291) · Published by Druglandscape Ltd.