Lecture Notes4

Leaves excessive leaf water loss is deadly cuticle

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Unformatted text preview: . Excessive leaf water loss is deadly: Cuticle seals epidermis. Most loss through stomata. H20 Opening & Closing of Stomata (p.710-711; 668) 668 Would loose too much water if stomata always open. Need open stomata for CO2 intake. intake. Stomatal regulation: a balancing act. Open H20 CO2 O2 Closed Regulation of Water Loss Regulation Factors causing stomatal opening (p.710-11; 670): Light. Low CO2. Factors causing stomatal closing Darkness. High CO2. High temperature (above 30-35o C.) Water stress. External Environmental Factors Affecting Transpiration Rates Affecting Temperature: (p. 711-712; 670) 670 Rates double for each 10o C increase. Humidity: Humidity: Higher evaporation rates at lower humidity Wind: Wind: Strips off moist boundary layer. Steepens diffusion gradient. Increases evaporation rates. Movement of Substances Through Phloem (P. 720-725; 680-685) 680-685 Contents of phloem sap: (after water) Chiefly disaccharide sucrose (90%). llow concentrations of amino acids. ow Inorganic minerals (like in xylem). Sucrose Phloem Flow Patterns: Phloem “From source to sink” Growing Season From leaves to storage From organs & meristems organs After Dormancy From storage organs to meristems Phloem Transport: Phloem Osmotically Generated Flow p. 722-724; 683 p. 683 Active transport of sugars at sources. Active Water follows by osmosis: High pressure. Continuous pipeline of Phloem cells. Transport of sugars out at sinks Transport (storage organs, metabolically active areas, etc). areas, Lower pressure. Result: Resu...
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