Transpiration Water Uptake in Plants

Plants Need Water Photosynthesis Keep cells turgid

Easy For Moss

But taller plants must move water long distances

Transpiration! Evaporation of water from leaves Creates a suction, or pull of water up the plant

Transpiration-Cohesion-Tension There is a pull on the water Water forms H- bonds with itself, and sides of walls Like water through a straw

Cost-Benefit Analysis Costs Benefits Plant can lose a lot of water and become dehydrated Plant can get water to leaves for photosynthesis

Control Mechanism – Guard Cells Open and close stomata/stoma (pores) Allows plants to control gas/water exchange Closed stomata conserve water, but no photosynthesis is possible

What Controls Stomata? Circadian rhythm Light Dehydration

Stomata and Evolution Plants have evolved to have different amounts Some have stomata only on underside of leaf, some on both, some only on top Some open stomata at night only and fix carbon dioxide into an organic compound Stomata open Stomata closed

Factors that Can Affect Transpiration Rates Temperature Humidity Sunlight Presence of water Wind # and location of stomata Leaf surface (waxiness)