A-Level Biology May/June 2024 Q1(d)(i): Explain how giving this vaccine to a person can lead to the development of long-term im…

1 answer

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  The vaccine contains proteins that are recognised by the immune system as foreign antigens [1]. These antigens stimulate a primary immune response [2]. During this response, specific T-lymphocytes and B-lymphocytes are selected and activated. This leads to the production of antibodies and, crucially, the formation of long-lived memory B-lymphocytes and memory T-lymphocytes [3]. If the individual is later infected with the actual Zika virus, these memory cells initiate a secondary immune response which is much faster and stronger than the primary response [4]. A high concentration of specific antibodies is produced rapidly, destroying the virus before the person can develop symptoms of the disease.

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  How the marks are awarded

  • B1 — The model answer correctly identifies the proteins in the vaccine as 'foreign antigens', which is the trigger for the immune response (Marking Point 1).
  • B1 — The answer states that the antigens stimulate a 'primary immune response', correctly naming the initial process (Marking Point 2).
  • B1 — The answer explains that the key to long-term immunity is the 'formation of... memory B-lymphocytes and memory T-lymphocytes' (Marking Point 5).
  • B1 — The answer describes the effect of memory cells, stating that a subsequent secondary immune response is 'faster and stronger', preventing disease (Marking Point 7).

  Common mistakes

  • Confusing active and passive immunity by suggesting the vaccine contains antibodies rather than antigens.
  • Failing to mention memory cells, which is essential for explaining 'long-term' immunity. Simply describing antibody production in the primary response is not enough.
  • Using vague terms like 'fights the disease' or 'prepares the body' instead of specific terminology like 'primary/secondary response', 'clonal selection', and 'memory cells'.
  • Not distinguishing between the primary and secondary responses, for example, by incorrectly stating the primary response is fast and strong.

  Examiner tip: For process-explanation questions, structure your answer as a logical sequence, ensuring you use precise scientific terminology for each step (e.g., antigen, primary response, memory cells, secondary response).

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