# Explain how the polarity of water molecules enables water to act as a solvent for ionic compounds, and outline one consequence of this solvent property for living organisms.

> IB DP Biology Standard Level (2023 syllabus) — A1.1 Water · Explain · 4 marks

## Mark scheme (4 marks)

1. Water molecules are polar / have an uneven distribution of charge, with a partial negative charge (δ−) on the oxygen and partial positive charges (δ+) on the hydrogen atoms.
2. The partial charges on water molecules attract the oppositely charged ions of an ionic compound, surrounding / dissociating the ions and holding them in solution (hydration shells form around each ion).
3. One biological consequence: dissolved ions / minerals / nutrients can be transported in blood plasma, cytoplasm, or xylem sap (accept any specific example such as sodium ions in blood, mineral ions in xylem).
4. Further consequence or elaboration: because ions/polar solutes remain dissolved they are available for metabolic reactions / enzyme activity / maintaining osmotic balance / nerve impulse transmission (accept any one distinct, relevant biological function linked to solvent property).

## Key terms

- [ionic compound](https://www.gradenine.co.uk/glossary/ionic-compound)
- [solvent](https://www.gradenine.co.uk/glossary/solvent)

## 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-the-polarity-of-water-f2471947) · Published by Druglandscape Ltd.