Water Transport (Chap. 30)

Transpiration (Overview) • evaporation of water that occurs mainly

at leaves while stomata are open for the passage of CO2 and O2 during

photosynthesis.

• the resulting flow of water through the plant is called the transpiration stream

• less than 1% of the water reaching the leaves is used in photosynthesis and plant growth. Most of it is lost in transpiration.

• Important in order to:

• Environmental factors that affect the rate of transpiration

– Light – Temperature

– Humidity

– Wind – Soil water

Water (and dissolved mineral ions) Transport in Roots, Stems, and

Leaves

Roots (Root Pressure)

• then, it travels through the cortex in order to reach the xylem via two routes:

• Although root pressure plays a role in the transport of water in the xylem in some plants and in some seasons, it does not account for most water transport.

Stem (Transpiration Pull)

• water is pulled through the xylem (tracheid and vessel element cells) by three forces that create an incredible amount of tension: – transpiration – – adhesion – – cohesion

Leaves (Transpiration)

• opening of guard cells

The Big

Picture