Transpiration Evaporation of water from mostly leaves (could also be stems). Transpiration You Tube
How does the water get from the roots to the leaves? 1. Root pressure – water absorbed in roots 2. Mass flow of liquid water from the roots to the leaves is driven in part by capillary action up the xylem tubes. 3. Transpiration evaporation pulls the water up.
Capillary Action in Xylem Adhesion of water to sides of xylem tubes (hydrophilic cellulose molecules via H-bonds) and cohesion of water to water molecules (H-bonds) to make a column.
Transpiration Pulling force of water by evaporation Guard cells control transpiration.
How Guard Cells Work A stoma opens when its guard cells gain K + ions and water by osmosis The water vacuoles become turgid and the guard cells become bowed (inner membrane is thicker) as they fill and open the stoma
How the Guard Cells Work (2) When the guard cells lose K+, they also lose water by osmosis The water vacuoles become flaccid and less bowed The stomata close
Usually Guard cells keep stomata open during the day CO 2 enters for photosynthesis Guard cells keep stomata closed at night No sunlight-no photosynthesis-save water
3 clues to stomatal opening at dawn 1. SUNLIGHT-stimulates guard cells to accumulate K+ 2. LOW LEVEL OF CO 2 in the leaf 3. BIOLOGICAL CLOCK of some sort (even if put in a dark closet, they will still open)
If it is a drought, WHAT HAPPENS? The stomata will close to reduce water loss and prevent wilting. This also slows down CO 2 intake and photosynthesis.
Root Pressure Pushes water up xylem a few meters