Explain how monoclonal antibodies can be used to target cancer cells without harming healthy cells.

AQA GCSE Biology (8461) — 4.3.2 Monoclonal antibodies (Bio only) · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Monoclonal antibodies are engineered to recognise a single, specific antigen that is expressed on the surface of cancer cells.

They can be conjugated to a cytotoxic drug, a radioactive isotope or a toxin.

When the antibody binds to its antigen on the cancer cell it delivers the attached toxic agent directly into or onto that cell.

Because healthy cells lack the target antigen, the antibody does not bind to them and the toxic agent is not released, sparing normal tissue.

Examiner tips

  • Use the phrase ‘specific antigen’ and mention conjugation to a drug or toxin.
  • Explain the delivery mechanism and why healthy cells are spared.
  • Keep each point brief and use exam‑style terminology.

Mark scheme (4 marks)

  1. Monoclonal antibodies are specific to one antigen / complementary to a specific antigen on cancer cells
  2. Monoclonal antibodies can be attached to a drug / toxic substance / radioactive substance
  3. The antibody binds to / attaches to the antigen on the cancer cell, delivering the drug / toxic substance directly to the cancer cell
  4. Healthy cells are unaffected because they do not have the same antigen / the antibody does not bind to healthy cells

Key terms in this question

monoclonal antibodies

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