Properties of Water

Water shows the following properties, which together give it its great biological importance:

• Liquid state and solvent power. Water stays liquid at ordinary room temperature and dissolves more substances, in greater quantity, than almost any other common solvent, which is why it is the medium in which nearly all of a cell's biochemistry happens.
• Chemical inertness and neutral pH. Pure water does not itself react chemically with most solutes and has a neutral pH, so it can carry dissolved minerals and food molecules around the plant without altering them, and it provides a stable medium for the many enzyme-catalysed reactions of metabolism.
• Raw material for photosynthesis. Water is one of the two raw materials (with carbon dioxide) that chloroplasts use to build sugars.
• Thermal buffering. Water has an unusually high specific heat, a high heat of vaporisation, and a high heat of fusion, so it resists sudden temperature swings and helps buffer plant tissues against overheating or chilling.
• Cohesion, adhesion and surface tension. Because water molecules form hydrogen bonds with one another, they attract each other strongly (cohesion) and also attract other polar surfaces strongly (adhesion). Combined with a high surface tension, these forces let water rise readily inside very narrow tubes (capillaries) — a property that becomes essential later in the chapter, when it helps explain the ascent of sap up the xylem. …