Explain the role of memory cells in the secondary immune response.

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)

Memory cells are long‑lived lymphocytes that are produced during the primary immune response after the first exposure to an antigen.
They persist in the body for many years, so that when the same antigen is encountered again they can recognise it rapidly.
On re‑exposure the memory cells proliferate quickly and differentiate into large numbers of effector cells – plasma cells that produce antibodies or cytotoxic T cells that kill infected cells.
This gives a faster and larger antibody titre or immune response than the primary response, allowing the pathogen to be eliminated before symptoms develop.

Examiner tips

Use the term "memory cells" and explain they are long‑lived lymphocytes. Mention rapid proliferation and differentiation into effector cells. Show that the response is faster and larger than the primary response. Include the outcome – elimination of the pathogen before symptoms.

Common mistakes

Confusing memory cells with effector cells; forgetting to state they are long‑lived. Failing to mention the rapid proliferation or the larger antibody titre. Using vague phrases like "quick response" without linking to memory cells.

Mark scheme (4 marks)

Memory cells are long-lived lymphocytes produced during the primary immune response (after first exposure to an antigen).
Memory cells persist in the body for many years, allowing rapid recognition of the same antigen upon re-exposure.
On re-exposure to the same antigen, memory cells proliferate rapidly and differentiate into large numbers of effector cells (plasma cells / cytotoxic T cells).
This produces a faster and larger antibody titre / immune response compared with the primary response, eliminating the pathogen before symptoms develop.

Key terms in this question

memory cells · secondary immune response