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
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