# Explain how water acts as a metabolite in living organisms, giving two distinct examples of reactions in which water is either produced or consumed.

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

## Mark scheme (4 marks)

1. Water is a metabolite, meaning it participates directly as a reactant or product in metabolic reactions (not merely as a solvent).
2. Water is consumed (used as a reactant) in hydrolysis reactions, e.g. the breakdown of polymers such as polypeptides, polysaccharides, or triglycerides into their monomers.
3. Water is produced as a product in condensation reactions, e.g. formation of peptide bonds between amino acids, glycosidic bonds between monosaccharides, or ester bonds in lipid synthesis.
4. Water is also a reactant in photosynthesis (light-dependent reactions / photolysis), where it is split to release oxygen, electrons, and protons / hydrogen ions that are used in the light-dependent stage.

## Key terms

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

## 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-water-acts-as-a-bc30905a) · Published by Druglandscape Ltd.