A student says: 'DNA is a polymer made from monomers called nucleotides.' Explain what this statement means, and explain why it is important for cells to be able to break polymers down into their monomers.
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 is the repeating unit of a polymer.
A polymer is a large molecule made from many monomers joined together.
In DNA the monomers are nucleotides, linked by phosphodiester bonds.
When a polymer is broken down, the monomers are released as free molecules.
These monomers can then be reused by the cell to build new polymers or to fuel other processes such as respiration.
A polymer is a large molecule made from many monomers joined together.
In DNA the monomers are nucleotides, linked by phosphodiester bonds.
When a polymer is broken down, the monomers are released as free molecules.
These monomers can then be reused by the cell to build new polymers or to fuel other processes such as respiration.
Examiner tips
- Use the exact terms ‘monomer’, ‘polymer’, ‘nucleotides’, and ‘phosphodiester bonds’.
- Show the logical sequence: definition → structure → bond type → cellular use.
- Keep the answer concise – one sentence per point.
- Mention that monomers are reused for new polymers or other cellular processes.
Common mistakes
- Confusing monomer with polymer or vice versa.
- Omitting the type of bond that links nucleotides.
- Failing to state why monomers are useful after breakdown.
Mark scheme (5 marks)
- A monomer is a small / single molecule that is the repeating unit (of a polymer)
- A polymer is a large molecule made from many monomers joined together
- The monomers are joined by chemical bonds (to form the polymer)
- Breaking polymers into monomers releases the smaller molecules so they can be used / reused by the cell
- Monomers released can be used to build new / different polymers (or for respiration / other cellular processes)
Key terms in this question
monomer · polymer · nucleotide
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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