 Controlled by guard cells  Flaccid  Little water  Limp  Turgid  Fill with water  Bend  ions/0021.swf ions/0021.swf

 Triggered by blue light  Yellow pigments located in membrane (?)  Activates proton pump  H+ out, creates electrochemical gradient  K+ diffuses in through ion channels, Cl- follows  K+, Cl- accumulate in vacuoles, water moves in

 K+ concentration in guard cells decrease during day  Sucrose increases, maintains osmotic pressure  As sucrose concentration decreases, water leaves  Pores close

 Blue Light  Low CO 2 concentration  Water stress  Hormones  Abscisic acid

 Transpiration  99% of water plants take in is lost by evaporation  Open stomata  Rate of Transpiration affected by:  Humidity  Temperature  Wind  Guttation  Liquid water forced out when transpiration negligible

 Allows water to move from roots to leaves

 Shedding of leaves

 Conifers lose needles year- round  Deciduous trees  Survive low temp of winter  Water uptake inhibited  Prevents continuous water loss by transpiration  Controlled by hormones: Ethylene

 Essential organic compounds & minerals move to other parts of plant for storage  Chlorophyll breaks down, other pigments seen  Cork forms protective layer on stem side of abscission zone of petiole  Enzymes dissolve middle lamella in abscission zone of petiole  Leaf detaches in breeze