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

2. 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)

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

4. 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

5. 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