Q.Surface tension is due to ..............

Water has: high specific heat capacity (resists rapid temperature change), high latent heat of vaporisation (cooling effect during transpiration), high surface tension and cohesive/adhesive properties (enables ascent...

Water's unique physical and chemical properties — high specific heat, cohesion-adhesion, solvent action and more — make it essential to plant physiology.

Water possesses several distinctive properties that underlie its central role in plants. Its high specific heat capacity means it absorbs or releases a large amount of heat with only a small change in temperature, helping buffer plant tissues against rapid temperature fluctuations. Its high latent heat of vaporisation means a large amount of energy is required to evaporate it, so transpiration produces a significant cooling effect on the plant. Water molecules show strong cohesion (attraction between water molecules, via hydrogen bonding) and adhesion (attraction to the walls of conducting vessels), together with high surface tension, which together enable the continuous ascent of sap up narrow xylem vessels against gravity and drive capillary movement in fine soil pores and cell walls. Water is also an excellent (near-universal) solvent for polar and ionic substances, allowing it to dissolve and transport minerals, sugars and other solutes throughout the plant. It is virtually incompre …

Cohesion (water-to-water attraction) and adhesion (water-to-surface attraction) are properties of water molecules, due to hydrogen bonding, that together explain how a continuous, unbroken column of water can be pulled up through narrow xylem vessels — a topic conventionally taught under 'Transport in Plants', which is not part of the current chapter set.

Water is a polar molecule, so individual water molecules form hydrogen bonds with each other and with other polar surfaces:

• Cohesion: the mutual attractive force between molecules of the SAME substance — here, between water molecules themselves. This keeps water molecules 'stuck together', forming a continuous, unbroken thread/column, and gives water a high tensile strength (resistance to being pulled apart).
• Adhesion: the attractive force between molecules of DIFFERENT substances — here, between water molecules and the polar walls of the xylem vessel (largely composed of cellulose). This attraction helps water cling to the vessel walls, resisting the pull of gravity. …