# Explain how rising atmospheric carbon dioxide concentrations contribute to ocean acidification and outline one consequence of ocean acidification for marine organisms.

> IB DP Biology Standard Level (2023 syllabus) — D4.3 Climate change · Explain · 4 marks

## Mark scheme (4 marks)

1. CO₂ dissolves in seawater to form carbonic acid (H₂CO₃)
2. Carbonic acid dissociates, releasing hydrogen ions (H⁺), lowering the pH of seawater
3. Increased H⁺ ions react with carbonate ions (CO₃²⁻), reducing carbonate ion availability
4. One consequence for marine organisms: reduced carbonate availability impairs the ability of organisms such as corals, molluscs, or echinoderms to form/maintain calcium carbonate shells or skeletons, leading to weakened or dissolving structures

## Key terms

- [ocean acidification](https://www.gradenine.co.uk/glossary/ocean-acidification)
- [pH](https://www.gradenine.co.uk/glossary/ph)

## 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)
- [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-rising-atmospheric-carbon-dioxide-ac2379ac) · Published by Druglandscape Ltd.