Water supports life because its polarity and resulting hydrogen bonds give it unusual solvent, thermal, cohesive and density properties. These properties enable biochemical reactions, stabilize habitats and transport substances through organisms and ecosystems.
This content is HL only in IB ESS subtopic 4.1 Water systems.
Water molecules are polar because oxygen attracts shared electrons more strongly than hydrogen. The oxygen region therefore has a partial negative charge, while the hydrogen regions have partial positive charges. Attractions between these regions form hydrogen bonds, which explain many of water's life-supporting properties.
| Property | How it supports life |
|---|---|
| Solvent action | Water dissolves many ions and polar substances, allowing nutrients, gases and wastes to be transported in blood, plant sap and aquatic systems. It also provides the medium for many metabolic reactions. |
| High specific heat capacity | Large energy inputs are required to change water's temperature because hydrogen bonds must be disrupted. Oceans and lakes therefore reduce temperature fluctuations, producing relatively stable habitats and climates. |
| High latent heat of vaporization | Evaporation removes substantial thermal energy, enabling cooling through sweating and transpiration. |
| Cohesion and surface tension | Hydrogen bonds hold water molecules together. This supports continuous water columns in plant xylem and allows some organisms to live on the water surface. |
| Adhesion | Attraction between water and other polar surfaces contributes to capillary movement through soil and plant tissues. |
| Ice is less dense than liquid water | Ice floats and forms an insulating surface layer, preventing entire water bodies from freezing and allowing aquatic organisms to survive below. |
| Transparency |