Explain how monoclonal antibodies can be used to deliver a drug directly to cancer cells, and why this method is more effective than giving the drug on its own.

AQA A-Level Biology (7402) — 3.2.4 Cell Recognition and the Immune System · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Monoclonal antibodies are produced to recognise a specific antigen on the surface of cancer cells. The drug is chemically linked to the antibody or carried in a conjugate. When the antibody binds to the cancer cell, the drug is delivered directly to that cell, where it can act. Normal cells lack the target antigen, so they are not bound or damaged. Consequently, the drug’s action is confined to tumour cells, reducing the systemic side‑effects that occur when the drug is given alone.

Examiner tips

  • Use the word ‘specific’ to describe the antibody–antigen interaction.
  • Show the sequence: antibody binds → drug delivered → normal cells spared.
  • Mention reduced side‑effects as the key advantage.

Common mistakes

  • Confusing monoclonal antibodies with polyclonal antibodies.
  • Failing to state that normal cells are not targeted.
  • Omitting the reduction in side‑effects as the benefit.

Mark scheme (5 marks)

  1. Monoclonal antibodies are specific to / complementary to antigens on the cancer cell surface
  2. The drug is attached to / carried by the monoclonal antibody
  3. The monoclonal antibody binds to the cancer cell (so delivers the drug directly to the cancer cell)
  4. Healthy / normal cells are not targeted / damaged
  5. This reduces side effects compared to giving the drug alone (which would affect the whole body / non-specific)

Key terms in this question

monoclonal antibodies · cancer cells

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