How Does Water Move Through Plants Chapter 30.3 How Does Water Move Through Plants AP Biology Spring 2011

Transpiration Water moves from roots to stems and then to leaves Movement is driven by evaporation of water from the leaves (transpiration) and a chemical property of water which causes water molecules to be attracted to each other (cohesion)

Cohesion-Tension Theory Xylem: water moves through these in plants Composed of cells (dead at maturity) called tracheids and vessel members

Cohesion-Tension Theory Cohesion-Tension Theory of water transport: explains water movement in plants Water lost from the leaves due to transpiration is replaced from the roots by osmosis Creates a continuous negative pressure (tension) in the plant

Cohesion-Tension Theory Due to cohesion, unbroken columns of water in the xylem resist rupturing as they are pulled upward under tension The constant loss of water by transpiration causes tension inside xylem allowing more water and solutes to be pulled into the roots from the soil and then up from roots to leaves