Rubber is a natural polymer produced by some plants. A student claims that rubber must be built from repeating monomer units joined together. Explain what is meant by the terms monomer and polymer, and describe the type of chemical reaction that joins monomers together to form a polymer. Give one example of a monomer and its corresponding polymer found in the human body.

AQA A-Level Biology (7402) — 3.1.1 Monomers and Polymers · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

A monomer is a small, single molecule that acts as the repeating unit or building block of a polymer.
A polymer is a large molecule made from many monomers joined together.
Monomers are linked by condensation (dehydration) reactions, in which a water molecule is released.
Example: the amino‑acid glycine is a monomer; when many glycine units are joined by condensation reactions they form the polymer protein (e.g. collagen).

Examiner tips

  • Use the exact wording ‘monomer’ and ‘polymer’ as defined in the mark scheme.
  • Show that the linking reaction is a condensation reaction and mention water is released.
  • Give a correct human‑body example such as amino acid → protein.
  • Keep the answer brief – 5 marks, so one sentence per point is enough.

Common mistakes

  • Confusing ‘polymerisation’ with ‘polymerisation reaction’ – only the condensation step is required.
  • Giving an incorrect example such as ‘rubber → polymer’ without naming a specific monomer.
  • Omitting that water is released in the condensation reaction.

Mark scheme (5 marks)

  1. A monomer is a small / single molecule that is the repeating unit / building block of a polymer
  2. A polymer is a large molecule made from many monomers joined together
  3. Monomers are joined together by condensation reactions
  4. Water is released / produced during the condensation reaction
  5. Correct named example: amino acid (monomer) and protein (polymer) OR glucose (monomer) and glycogen / starch / cellulose (polymer) OR nucleotide (monomer) and DNA / RNA (polymer)

Key terms in this question

monomer · polymer

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