Water Uptake and Movement

(h) explain, in terms of water potential, the movement of water between plant cells, and between plant cells and their environment. (No calculations involving water potential will

be set);(i) describe, with the aid of diagrams, the pathway by which water is transported from the

root cortex to the air surrounding the leaves, with reference to the Casparian strip, apoplast pathway, symplast pathway, xylem and the stomata;

(j) explain the mechanism by which water is transported from the root cortex to the air surrounding the leaves, with reference to adhesion, cohesion and the transpiration

stream;

http://www.egs.ie/files/cohesion-tension_animation.swf

Water uptake and movement...

Water movement up the xylem...

• Hydrogen bonds hold water molecules together in a column (cohesion)

• Water attracted to walls of xylem vessels (adhesion)• Water evaporates from the leaves (transpiration)• Generates negative pressure (tension)at the top of

the xylem that draws water upwards (transpiration pull)

• This movement of water is called the COHESION-TENSION THEORY

Cohesion

Notes pgs 74-75…

• Explain the role of the Casparian strip in movement of water into the xylem

• Explain the importance of root pressure, cohesion and tension of water molecules, and capillary action for water movement up the xylem

• How stomata control water loss from the leaf

8 Mark Question

• Describe the pathways and mechanisms by which water passes from the soil to the xylem vessels in the roots