# Explain why DNA is described as a polymer and outline the role of complementary base pairing in holding the two strands of DNA together.

> Edexcel GCSE Biology (1BI0) — 3.3 DNA structure · Explain · 4 marks

## Mark scheme (4 marks)

1. DNA is a polymer because it is made up of monomers called nucleotides
2. Each nucleotide contains a sugar, a phosphate group and one of four bases (A, T, C or G)
3. Complementary base pairing means A pairs with T and C pairs with G
4. Weak hydrogen bonds form between the complementary base pairs, linking the two strands together

## Key terms

- [polymer](https://www.gradenine.co.uk/glossary/polymer)
- [complementary base pairing](https://www.gradenine.co.uk/glossary/complementary-base-pairing)

## Related

- [Revision notes for Edexcel GCSE Biology (1BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-dna-is-described-as-a49b9c43) · Published by Druglandscape Ltd.