1.1—Water as a transport solvent

Water is polar: oxygen attracts the shared electrons more strongly than hydrogen, giving oxygen a partial negative charge and hydrogen a partial positive charge. This lets water molecules form hydrogen bonds with one another and with other polar substances.

Water dissolves ions and other polar molecules, so blood plasma and plant sap can carry solutes. Its cohesion helps maintain continuous water columns, while its high specific heat capacity makes temperature changes less abrupt.

Sodium ions do not travel as isolated crystals in plasma; they are surrounded by oriented water molecules. In xylem, hydrogen bonding between water molecules helps a transpiration stream remain continuous when evaporation pulls water upwards.

Water is not a universal solvent: non-polar lipids do not dissolve readily. Polarity explains both transport of charged solutes and why membranes can separate aqueous compartments.