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Unformatted text preview: 1 Vascular system: water and mineral movement Site of movement (xylem) Driving force for movement = water potential gradient Path of water movement through plant Control of stomatal aperture Key concepts: apoplast vs. symplast water potential Xylem is major site of water and mineral movement 2 major cell types: tracheids and vessel elements Cells dead at maturity -> apoplastic movement tracheids vessel elements How does water move to tops of trees or other plants? Xylem = major site of fluid movement No macroscopic pumps Plant acts like drinking straw Driving force for water movement = water potential ( ) gradients = tendency of solution to take up water from pure water, across a membrane Total = s + p Pure water has = 0 Dissolved solutes s < 0 p may be positive or negative Water always moves to region of lower Measured in units of pressure (1 MPa=~10 atm) 2 Water movement depends on evaporation, cohesion and tension of water Xylem connects water in soil ( near 0) and air surrounding leaves ( <<<0) Evaporation draws water out of leaf mesophyll Cohesion of water via H- bonding maintains continuous column of water through plant: transpiration stream Water moves under tension Movement is unidirectional When humidity is high, root pressure results in guttation Xylem sap is under tension...
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- Winter '08