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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 ( Ψ ) gradients • Ψ = tendency of solution to take up water from pure water, across a membrane •Total Ψ = Ψ s + Ψ p •Pure water has Ψ = 0 •Dissolved solutes Ψ s < 0 • Ψ p may be positive or negative •Water always moves to region of lower Ψ •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 ( Ψ near 0) and air surrounding leaves ( Ψ <<<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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This note was uploaded on 04/07/2008 for the course MCDB 1B taught by Professor Weimbs during the Winter '08 term at UCSB.
- Winter '08