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

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

## Mark scheme (4 marks)

1. Saturated fatty acids have no carbon–carbon double bonds, so the hydrocarbon chain is straight/unbranched.
2. Unsaturated fatty acids have one or more C=C double bonds, which introduce a kink/bend in the hydrocarbon chain.
3. Straight chains in saturated fatty acids allow close packing / stronger van der Waals forces between adjacent molecules, so saturated fats are solid at room temperature.
4. Kinks in unsaturated fatty acids prevent close packing / reduce van der Waals forces, so unsaturated fats (oils) are liquid at room temperature / have a lower melting point.

## 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 Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structural-differences-between-d0e910a7) · Published by Druglandscape Ltd.