# Explain how the structural and physiological adaptations of a xerophyte, such as marram grass (Ammophila arenaria), reduce the rate of transpiration.

> IB DP Biology Higher Level (2023 syllabus) — B4.1 Adaptation to environment · Explain · 4 marks

## Mark scheme (4 marks)

1. Leaves are rolled/inrolled, trapping humid air and reducing the water vapour concentration gradient between the leaf interior and the atmosphere
2. Stomata are sunken into pits or located on the inner (adaxial) surface of the rolled leaf, reducing air movement over them and maintaining a localised high-humidity zone
3. A thick waxy cuticle on the outer (abaxial) epidermis reduces cuticular transpiration by being largely impermeable to water
4. Epidermal hairs (trichomes) on the inner leaf surface reflect radiation and/or further trap humid air, reducing leaf temperature and the vapour pressure deficit

## Key terms

- [xerophyte](https://www.gradenine.co.uk/glossary/xerophyte)
- [transpiration](https://www.gradenine.co.uk/glossary/transpiration)

## 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)
- [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-structural-and-physiological-9f8e9f26) · Published by Druglandscape Ltd.