# Explain why lipids are used as waterproofing agents on the surfaces of leaves and in the waxy cuticle of insects, and outline the elements that make up a lipid molecule.

> AQA A-Level Biology (7402) — 3.1.3 Lipids · Explain · 5 marks

> Plants and insects both produce lipid-based waxy coatings on their outer surfaces. These coatings reduce water loss and provide protection.

## Mark scheme (5 marks)

1. Lipids are insoluble in water (hydrophobic / do not dissolve in water)
2. Because lipids are insoluble/hydrophobic, water cannot pass through the waxy layer, reducing water loss by evaporation
3. This is an advantage for the plant / insect because it helps prevent dehydration (conserves water)
4. Lipids contain carbon (C) and hydrogen (H)
5. Lipids also contain oxygen (O) — accept: carbon, hydrogen, and oxygen

## Key terms

- [lipid](https://www.gradenine.co.uk/glossary/lipid)
- [waxy cuticle](https://www.gradenine.co.uk/glossary/waxy-cuticle)
- [elements](https://www.gradenine.co.uk/glossary/elements)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-lipids-are-used-as-ce92fbee) · Published by Druglandscape Ltd.