Describe the role of lymphocytes and phagocytes in destroying a pathogen that has entered the body.

WJEC A-Level Biology (Wales) — 3.4 Population size and ecosystems · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

When a pathogen enters the body, the immune system responds by using two types of white blood cell to destroy it.

Model answer (5 marks)

Lymphocytes recognise antigens on the surface of the pathogen and release antibodies that are complementary to the antigen.
Antibodies then clump pathogens together (agglutination) or neutralise them, making it easier for the immune system to destroy the pathogen.
Phagocytes engulf or ingest the pathogen.
Inside the phagocyte the pathogen is digested by enzymes in a process called phagocytosis.

Examiner tips

Use the exact terms ‘lymphocytes’, ‘antigens’, ‘antibodies’, ‘agglutination’, ‘phagocytes’, ‘phagocytosis’. Show the sequence: detection → antibody production → clumping/neutralisation → phagocyte ingestion → digestion.

Common mistakes

Mixing up the roles of lymphocytes and phagocytes; e.g. saying phagocytes produce antibodies. Omitting the step that antibodies make the pathogen easier to destroy. Using vague words like ‘fight’ instead of ‘engulf’ or ‘digest’.

Mark scheme (5 marks)

Lymphocytes detect antigens on the surface of the pathogen
Lymphocytes release / produce antibodies complementary to the antigen
Antibodies clump pathogens together (agglutination) / neutralise the pathogen, making it easier for the immune system to destroy
Phagocytes engulf / ingest the pathogen
Phagocytes digest the pathogen using enzymes (phagocytosis)

Key terms in this question

lymphocyte · phagocyte