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Transport in Plants AP Biology 2006-2007 Transport in plants H2O & minerals transport in xylem transpiration evaporation, adhesion & cohesion negative pressure Sugars transport in phloem bulk flow Calvin cycle in leaves loads sucrose into phloem positive pressure Gas exchange photosynthesis CO2 in; O2 out stomates AP Biology respiration O2 in; CO2 out roots exchange gases within air spaces in soil Why does over-watering kill a plant? Ascent of xylem fluid Transpiration pull generated by leaf AP Biology Control of Stomates Epidermal cell -non photosynthetic Guard cell Nucleus Chloroplasts -photosynthetic Uptake of K+ ions by guard cells proton pumps water enters by osmosis guard cells become turgid Loss of K+ ions H+ H+ H2O H2O K+ H+ K+ K+ H2O K+ H2O K+ H2O K+ H+ H2O K+ H2O K+ H2O H+ Thickened inner cell wall (rigid) by guard cells AP Biology water leaves by K+ K+ osmosis H2O H2O + H+ H guard cells Stoma open become flaccid water moves into guard cells H2O K+ H2O K+ Stoma closed water moves out of guard cells The guard cells control the opening and closing of the stomata Guard cells flaccid Guard cells turgid Thin outer wall Thick inner wall Stoma closed AP Biology Stoma open Regulating Stomatal Opening:-the potassium ion pump hypothesis Guard cells flaccid K+ K+ ions have the same concentration in guard cells and epidermal cells K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Stoma closed AP Biology Light activates or decreased CO2 activates proton pumps moving H+ ion our of Guard Cells and allowing K+ to transport from the epidermal cells into the guard cells Regulating Stomatal Opening H2O H2O K+ H2O K+ K+ K+ H2O AP Biology K+ K+ Increased concentration of K+ in guard cells K+ K+ H2O K+ K+ K+ K+ Lowers the in the guard cells Water moves in by osmosis, down gradient Guard cells turgid H2O K+ K+ H2O K+ K+ H2O K+ K+ H2O K+ K+ H2O K+ K+ H2O K+ Stoma open AP Biology Increased concentration of K+ in guard cells K+ Lowers the in the guard cells Water moves in by osmosis, down gradient Water & mineral absorption Water absorption from soil osmosis aquaporins Mineral absorption active transport proton pumps active transport of H+ aquaporin root hair AP Biology proton pumps H2O 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 AP Biology Fig. 36-11 Cell wall Cytosol Vacuole Plasmodesma Vacuolar membrane Plasma membrane (a) Cell compartments Key Transmembrane route Apoplast Symplast Apoplast Symplast Symplastic route (b) Transport routes between cells AP Biology Apoplastic route Absorption of Water and Minerals by Root Cells • Most water and mineral absorption occurs near root tips, where the epidermis is permeable to water and root hairs are located • Root hairs account for much of the surface area of roots • After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals AP Biology Water flow through root Porous cell wall water can flow through cell wall route & not enter cells plant needs to force water into cells Casparian strip AP Biology Controlling the route of water in root Endodermis cell layer surrounding vascular cylinder of root • The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder • forces fluid through selective cell membrane filtered & forced into xylem cells Animation: Transport in Roots AP Biology Root anatomy Phloem dicot AP Biology Phloem Casparian strip Xylem Xylem monocot Mycorrhizae increase absorption Symbiotic relationship between fungi & plant AP Biology symbiotic fungi greatly increases surface area for absorption of water & minerals increases volume of soil reached by plant increases transport to host plant Mycorrhizae AP Biology Endomycorrhizae Cell Wall AP Biology From: http://shachar-hill.plantbiology.msu.edu/?page_id=44 Cohesion and Adhesion in the Ascent of Xylem Sap • The transpirational pull on xylem sap is • transmitted all the way from the leaves to the root tips and even into the soil solution Transpirational pull is facilitated by cohesion of water molecules to each other and adhesion of water molecules to cell walls Animation: Transpiration AP Biology Fig. 36-15 Xylem sap Outside air ψ = −100.0 Mpa Mesophyll cells Stoma Leaf ψ (air spaces) = −7.0 Mpa Water molecule Transpiration Leaf ψ (cell walls) = −1.0 Mpa Trunk xylem ψ = −0.8 Mpa Water potential gradient Xylem cells Atmosphere Adhesion by hydrogen bonding Cell wall Cohesion Cohesion and by hydrogen adhesion in bonding the xylem Water molecule Root hair Trunk xylem ψ = −0.6 Mpa Soil particle Soil ψ = −0.3 Mpa Water Water uptake from soil AP Biology 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 AP Biology 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 H2O potential water flows in from xylem cells increase in pressure due to increase in H2O causes flow AP Biology On a plant… What’s a source…What’s a sink? can flow 1m/hr Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms In studying angiosperms, researchers have concluded that sap moves through a sieve tube by bulk flow driven by positive pressure Animation: Translocation of Phloem Sap in Summer Animation: Translocation of Phloem Sap in Spring AP Biology Experimentation Testing pressure flow hypothesis using aphids to measure sap flow & sugar concentration along plant stem AP Biology Maple sugaring AP Biology Don’t get mad… Get answers!! Ask Questions! AP Biology 2006-2007