Explain how the inflammatory response acts as a defence against infection at a site of tissue damage.

IB DP Biology Standard Level (2023 syllabus) — C3.2 Defence against 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)

Damaged cells and mast cells release histamine and other cytokines.
Histamine causes vasodilation and increased blood flow, bringing more immune cells and plasma to the site.
Phagocytes such as neutrophils and macrophages are attracted by chemotaxis and engulf pathogens by phagocytosis.
This limits the spread of infection, containing pathogens locally and preventing systemic spread.

Examiner tips

Use the exact terms (histamine, vasodilation, chemotaxis, phagocytosis).
Show the sequence: release → vasodilation → recruitment → phagocytosis → containment.

Common mistakes

Confusing inflammation with the immune response as a whole; forgetting to mention vasodilation or chemotaxis.

Mark scheme (4 marks)

Damaged cells / mast cells release histamine (or other signalling chemicals / cytokines)
Histamine causes vasodilation / increased blood flow to the affected area, bringing more immune cells and plasma to the site
Phagocytes (neutrophils / macrophages) are attracted to the site by chemotaxis and engulf pathogens by phagocytosis
The response limits the spread of infection / contains pathogens locally, preventing systemic spread

Key terms in this question

inflammatory response