Vaccines are used to protect individuals against communicable diseases. Explain how a vaccine causes the body to produce antibodies and describe the role of memory cells in providing long-term protection.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Measles is a communicable disease caused by a virus. A vaccine against measles contains weakened measles virus particles. Children are vaccinated against measles as part of a routine immunisation programme.
Model answer (5 marks)
The weakened measles virus in the vaccine provides antigens that are recognised by B‑lymphocytes. These B‑cells are activated and differentiate into plasma cells that secrete antibodies specific to the measles antigen.
During this primary response, some activated B‑cells become memory B‑cells. If the real measles virus is later encountered, these memory cells recognise the same antigen and react much faster.
They quickly proliferate and produce a large amount of specific antibodies, which neutralise the virus before it can cause disease, giving long‑term protection.
During this primary response, some activated B‑cells become memory B‑cells. If the real measles virus is later encountered, these memory cells recognise the same antigen and react much faster.
They quickly proliferate and produce a large amount of specific antibodies, which neutralise the virus before it can cause disease, giving long‑term protection.
Examiner tips
- Use the term ‘antigens’ and ‘B‑lymphocytes’ to show understanding of the mechanism.
- Explain that memory cells are formed during the primary response and enable a faster, stronger secondary response.
- Mention that the rapid antibody surge prevents symptoms.
- Keep the answer concise – 5 points can be covered in 3–4 short sentences.
Common mistakes
- Confusing T‑cells with B‑cells in antibody production.
- Failing to mention memory cells or their rapid response.
- Using vague phrases like ‘immune system’ without specifying antibodies or memory cells.
Mark scheme (5 marks)
- The vaccine contains antigens (from the weakened measles virus)
- The antigens stimulate B-lymphocytes to produce antibodies specific to the measles antigen
- Memory cells are produced during the initial immune response to the vaccine
- If the same measles antigen is encountered again, memory cells recognise it and respond more quickly
- A large amount of antibodies is produced rapidly, destroying the pathogen before symptoms develop / preventing disease
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Immune response questions
- Explain how the immune system responds when a pathogen enters the body for the f…
- A person is infected with influenza virus for the first time. Some B-lymphocytes…
- T-lymphocytes and B-lymphocytes both play important roles in the immune response…
- A patient is given a blood transfusion using blood from a donor whose antigens d…