Explain how a vaccine protects a person from becoming seriously ill if they are later exposed to a pathogen.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Vaccines contain weakened or inactive forms of a pathogen, or antigens from a pathogen. They are given to individuals to provide protection against communicable diseases.
Model answer (5 marks)
Vaccines introduce antigens into the body, so the immune system recognises them as foreign.
Lymphocytes (B‑cells) respond by producing antibodies that are specific to the antigen.
During this primary response, memory B‑cells and T‑cells are formed.
If the person is later exposed to the same pathogen, the memory cells recognise the antigen immediately and trigger a rapid secondary response, producing large amounts of antibodies.
The pathogen is neutralised or destroyed before it can replicate to a level that causes serious illness, so symptoms do not develop.
Lymphocytes (B‑cells) respond by producing antibodies that are specific to the antigen.
During this primary response, memory B‑cells and T‑cells are formed.
If the person is later exposed to the same pathogen, the memory cells recognise the antigen immediately and trigger a rapid secondary response, producing large amounts of antibodies.
The pathogen is neutralised or destroyed before it can replicate to a level that causes serious illness, so symptoms do not develop.
Examiner tips
- Use the term ‘antigen’ and ‘antibody’ explicitly. Show the sequence: antigen → lymphocyte activation → antibody production → memory cell formation → rapid secondary response. Mention that the secondary response is faster and stronger, preventing disease.
- common_mistakes
- :
- Confusing the primary and secondary immune responses. Not stating that memory cells are formed. Using vague phrases like ‘immune system’ without specifying lymphocytes or antibodies.
Mark scheme (5 marks)
- The vaccine introduces antigens into the body / the immune system detects the antigens from the vaccine
- Lymphocytes produce antibodies that are specific / complementary to the antigen
- Memory cells are formed after the initial immune response
- When the same pathogen enters the body again, memory cells recognise the antigen and respond more quickly / rapidly produce large quantities of antibodies
- The pathogen is destroyed before it can cause serious illness / symptoms do not develop because the pathogen is neutralised rapidly
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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