Explain how the inflammatory response acts as a non-specific defence mechanism following tissue damage or infection.

IB DP Biology Higher 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)

Mast cells and damaged cells release histamine when tissue is damaged or infected. Histamine causes vasodilation and increased blood flow, producing redness and heat. It also increases capillary permeability, allowing fluid and plasma proteins to leak into the tissue, giving swelling or oedema. Chemokines attract phagocytes such as neutrophils to the site, where they phagocytose the invading pathogens.

Examiner tips

Use the word ‘release’ for mast cells, ‘cause’ for vasodilation and permeability, and ‘attract’ for chemokines. Include the four key effects in the correct order. Keep the answer concise and use the exact terminology: histamine, vasodilation, capillary permeability, swelling, chemokines, phagocytes, neutrophils, phagocytosis.

Common mistakes

Confusing the order of the events or omitting one of the four points; writing ‘inflammation’ instead of ‘histamine’.
Using vague terms such as ‘increased blood flow’ without linking it to redness and heat, or saying ‘immune cells move in’ without specifying chemokines and phagocytosis.

Mark scheme (4 marks)

Mast cells / damaged cells release histamine in response to tissue damage or infection
Histamine causes vasodilation / increased blood flow to the infected area, resulting in redness and heat
Histamine increases capillary permeability, allowing fluid / plasma proteins to move into the tissue, causing swelling / oedema
Phagocytes / neutrophils are attracted to the site by chemokines / chemical signals and carry out phagocytosis of pathogens

Key terms in this question

inflammatory response · non-specific defence