Question

Explain how transpiration results in water moving through the plant (cohesion-tension theory).

Accepted Answer

Cohesion-tension theory:Water molecules evaporate from surface of mesophyll cells into air spaces in leaf and move out of stomata into surrounding air by diffusion down conc gradientLoss of water lowers water potential of mesophyll cell so water moves into it from an adjacent cell by osmosis along both pathwaysRepeated across leaf to xylem, water moves out of xylem by osmosis into cells of leafWater mols form hydrogen bonds with carbs in walls of xylem vessels - adhesion, they also form them with each other - cohesion resulting in combined effect - capillary action allowing water to move against force of gravityWater is drawn up xylem in continuous stream to replace water lost by evaporation - transpiration pullTranspiration pull results in tension in xylem helping to move water across roots from the soil

Water Xylem Transpiration Leaf Move Results Mesophyll Cells