Transport in Plants 2006-2007
Water & mineral absorption Water absorption from soil osmosis aquaporins Mineral absorption active transport proton pumps active transport of H + aquaporin root hair proton pumps H 2 O
Mineral absorption Proton pumps active transport of H + ions out of cell chemiosmosis H + gradient creates membrane potential difference in charge drives cation uptake creates gradient cotransport of other solutes against their gradient
Vascular Tissue: Xylem Xylem: carries water and minerals Made up of tracheids and vessel elements Dead at maturity One-way transport only Walls of cells reinforced with lignin
Lateral transport in plants Transmembrane: substances cross cell walls and plasma membranes to move cell to cell Symplast: substances travel through cells via plasmodesmata Apoplast: substances travel between cell walls
Lateral transport in roots Minerals & water in symplast can pass into vascular cylinder (stele) Those in apoplast hit Casparian strip and must cross through membrane of endodermal cells and enter via symplast
Controlling the route of water in root Endodermis cell layer surrounding vascular cylinder of root lined with impermeable Casparian strip forces fluid through selective cell membrane filtered & forced into xylem cells Aaaah Structure Function yet again!
Root anatomy dicot monocot
Mycorrhizae increase absorption Symbiotic relationship between fungi & plant symbiotic fungi greatly increases surface area for absorption of water & minerals increases volume of soil reached by plant increases transport to host plant
Mycorrhizae
Long Distance Transport How does water get from roots up to the leaves? 1) Root pressure Guttation Minor mechanism can t keep up with transpiration after sunrise 2) **Transpiration-Cohesion-Tension Mechanism
Fluid Movement in Xylem Root pressure forces water into xylem while transpiration pulls it up: cohesiontension theory Adhesion: water sticks to cellulose walls Cohesion: water sticks to itself due to Hydrogen bonding
Transport of sugars in phloem Loading of sucrose into phloem flow through cells via plasmodesmata proton pumps cotransport of sucrose into cells down proton gradient
Pressure flow in phloem Mass flow hypothesis source to sink flow direction of transport in phloem is dependent on plant s needs phloem loading active transport of sucrose into phloem increased sucrose concentration decreases H 2 O potential water flows in from xylem cells increase in pressure due to increase in H 2 O causes flow can flow 1m/hr On a plant What s a source What s a sink?
Experimentation Testing pressure flow hypothesis using aphids to measure sap flow & sugar concentration along plant stem
Maple sugaring
Don t get mad Get answers!! Ask Questions! 2006-2007
Ghosts of Lectures Past (storage) 2006-2007
Endodermis & Casparian strip
Control of Stomates Uptake of K + ions by guard cells proton pumps water enters by osmosis guard cells become turgid Loss of K + ions by guard cells water leaves by osmosis guard cells become flaccid Guard cell H 2 O K + Chloroplasts H 2 O Thickened inner cell wall (rigid) Epidermal cell Nucleus K + K + H 2 O H 2 O H 2 O H 2 O K + K + K + H 2 O H 2 O H 2 O H 2 O K + K + K + K + Stoma open Stoma closed water moves into guard cells K + K + H 2 O H 2 O water moves out of guard cells
Control of transpiration Balancing stomate function always a compromise between photosynthesis & transpiration leaf may transpire more than its weight in water in a day this loss must be balanced with plant s need for CO 2 for photosynthesis