 Controlled by guard cells  Flaccid  Little water  Limp  Turgid  Fill with water  Bend  http://academic.kellogg.edu/herbrandsonc/bio111/animat 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