# Explain how the adaptations of a mangrove tree allow it to survive in a saline, waterlogged environment.

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

> Mangrove trees grow in coastal intertidal zones where sediment is frequently anaerobic and soil water has a salt concentration that would be lethal to most terrestrial plants.

## Mark scheme (4 marks)

1. Mangroves possess aerial roots (pneumatophores / prop roots / knee roots) that project above the anaerobic sediment, allowing oxygen to diffuse into the root tissues for aerobic respiration.
2. Ultrafiltration at the root endodermis / Casparian strip excludes most salt ions from entering the xylem, preventing toxic salt concentrations from reaching the shoot.
3. Salt glands on leaves actively secrete excess sodium chloride / salt ions to the leaf surface, which are then washed or blown away, preventing toxic ion accumulation in cells.
4. Thick, succulent / waxy leaves with low surface-area-to-volume ratio and reduced stomatal aperture / sunken stomata limit water loss by osmosis / transpiration, counteracting the tendency to lose water to the hypertonic soil solution.

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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