Explain why monoclonal antibodies can be used to detect the presence of a specific antigen in a patient's blood sample.

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).

Monoclonal antibodies are widely used in medical diagnosis. They can be used to detect whether a particular antigen is present in a blood sample taken from a patient.

Model answer (4 marks)

Monoclonal antibodies are produced from a single clone of B‑cells, so they recognise only one specific epitope on a single antigen.

If that antigen is present in the blood sample, the antibody will bind to it.

The antibody is usually conjugated to a detectable label such as a fluorescent dye or a radioactive isotope.

Detection of the label shows that binding has occurred; if no label is seen, the antigen is absent.

Examiner tips

  • Use the word ‘specific’ to show understanding of monoclonal nature.
  • Mention the label (fluorescent or radioactive) to explain detection.
  • Explain that binding indicates presence, lack of binding indicates absence.

Common mistakes

  • Confusing monoclonal with polyclonal antibodies.
  • Forgetting to mention the label used for detection.
  • Saying the antibody binds to all antigens rather than a single one.

Mark scheme (4 marks)

  1. Monoclonal antibodies are specific to one antigen (complementary to one antigen)
  2. The antibody binds to / attaches to the target antigen if it is present in the sample
  3. The antibody can be labelled (e.g. with a fluorescent dye / radioactive marker) so that binding can be detected
  4. If no binding occurs / label is not detected, the antigen is absent from the sample

Key terms in this question

monoclonal antibodies · antigen · specific

Related

More Monoclonal antibodies (Bio only) questions

▶ Try answering this question with AI marking (free) →