# Explain how the adaptations of a named deep-sea hydrothermal vent organism allow it to obtain energy in the absence of sunlight.

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

> Deep-sea hydrothermal vents are found at mid-ocean ridges where superheated, mineral-rich water is released from the ocean floor. No sunlight penetrates to these depths, yet diverse communities of organisms thrive around these vents.

## Mark scheme (4 marks)

1. Named organism correctly identified as one associated with hydrothermal vents (e.g. tube worm / Riftia pachyptila, vent mussel / Bathymodiolus, vent shrimp)
2. Chemosynthetic bacteria (or Archaea) oxidise inorganic compounds such as hydrogen sulfide to release energy, instead of using light energy
3. The named multicellular organism (e.g. tube worm) harbours chemosynthetic bacteria as endosymbionts, providing the host with organic carbon / nutrients in return for shelter and access to reactants
4. Structural adaptation of the named organism that facilitates access to vent chemicals or efficient uptake of nutrients from endosymbionts (e.g. tube worms lack a mouth and digestive tract; rely entirely on trophosome for nutrition / large surface area of gill filaments in vent mussels maximises uptake of dissolved sulfide and oxygen)

## Key terms

- [hydrothermal vent](https://www.gradenine.co.uk/glossary/hydrothermal-vent)

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-adaptations-of-a-dd744652) · Published by Druglandscape Ltd.