2.4.2—Properties and roles in living organisms

Water is useful in living organisms because its polarity and hydrogen-bond network create distinct properties. Each property should be linked to the biological job it makes possible, rather than memorised as an isolated list.

• Solvent → reactions and transport: Water’s polarity allows many ionic and polar substances, such as salts and glucose, to dissolve. Dissolved particles can move freely enough for metabolic reactions and transport; non-polar substances do not dissolve readily.
• High specific heat capacity → temperature buffering: Many hydrogen bonds absorb energy before water’s temperature rises substantially, helping cells and bodies resist rapid temperature change and keep enzyme conditions more stable.
• High latent heat of vaporisation → cooling: A large energy input is needed for water molecules to escape during evaporation. Water leaving sweat or a transpiring leaf therefore removes thermal energy and produces cooling.
• Cohesion/surface tension → a connected water surface: Hydrogen bonds attract neighbouring water molecules, giving cohesion and surface tension. This helps water remain together rather than separating at a surface.

The common cause is intermolecular hydrogen bonding, but the applications differ: polarity supports dissolution and movement of solutes; many hydrogen bonds buffer temperature; and breaking hydrogen-bond attractions during evaporation removes heat. Keep these mechanisms separate so “specific heat capacity” is not confused with “latent heat of vaporisation.”

Water is not a solvent for every substance, and “high specific heat capacity” describes resistance to temperature change, not the energy required for a phase change. “High latent heat of vaporisation” describes evaporation and cooling. These properties explain biological usefulness without adding unsupported ecological or physiological claims.