# Explain how the structures of saturated and unsaturated fatty acids differ, and how these structural differences affect the physical properties of the lipids that contain them.

> IB DP Biology Standard Level (2023 syllabus) — B1.1 Carbohydrates and lipids · Explain · 4 marks

## Mark scheme (4 marks)

1. Saturated fatty acids have no double bonds between carbon atoms / contain only single C–C bonds, whereas unsaturated fatty acids have one or more C=C double bonds in the hydrocarbon chain.
2. The C=C double bond(s) in unsaturated fatty acids introduce a bend / kink in the hydrocarbon chain.
3. Saturated fatty acid chains are straight, allowing close packing of molecules and strong van der Waals / London dispersion forces between chains, so lipids containing them are solid at room temperature (e.g. animal fats).
4. The kinks in unsaturated fatty acid chains prevent close packing, resulting in weaker intermolecular forces, so lipids containing them are liquid / oils at room temperature (e.g. plant oils).

## Key terms

- [saturated fatty acid](https://www.gradenine.co.uk/glossary/saturated-fatty-acid)
- [unsaturated fatty acid](https://www.gradenine.co.uk/glossary/unsaturated-fatty-acid)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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-how-the-structures-of-saturated-d505da9e) · Published by Druglandscape Ltd.