Môn Sinh học - Chapter 36: Resource acquisition and transport in vascular plants

Ch. 36 Warm-UpDescribe the process of how H2O gets into the plant and up to the leaves.Compare and contrast apoplastic flow to symplastic flow.Explain the mass flow of materials in the phloem (source to sink).Ch. 36 Warm-UpWhat is transpiration?What are mycorrhizae?What is the function of the Casparian strip?Chapter 36Resource Acquisition and Transport in Vascular PlantsWhat you need to know:The role of passive transport, active transport, and cotransport in plant transport.The role of diffusion, active transport, and bulk flow in the movement of water and nutrients in plants.How the transpiration cohesion-tension mechanism explain water movement in plants.How pressure flow explains translocation.What does a plant need?Review:Selectively permeable membrane: osmosis, transport proteins, selective channelsProton pump: active transport; uses E to pump H+ out of cell  proton gradientCotransport: couple H+ diffusion with sucrose transportAquaporin: transport protein which controls H2O uptake/lossSolute transport across plant cell plasma membranesOsmosis**Water potential (ψ): H2O moves from high ψ  low ψ potential, solute conc. & pressureWater potential equation: ψ = ψS + ψPSolute potential (ψS) – osmotic potentialPressure potential (ψP) – physical pressure on solutionPure water: ψS = 0 MpaΨ is always negative!Turgor pressure = force on cell wallBulk flow: move H2O in plant from regions of high  low pressure** Review AP Bio Investigation 4Flaccid: limp (wilting)Plasmolyze: shrink, pull away from cell wall (kills most plant cells) due to H2O lossTurgid: firm (healthy plant)Turgid Plant CellPlasmolysisA watered impatiens plant regains its turgor.Vascular Tissues: conduct moleculesXylemPhloemNonliving functionalLiving functionalXylem sap = H2O & mineralsPhloem sap = sucrose, minerals, amino acids, hormonesSource to sink(sugar made) to (sugar consumed/stored)Transport of H2O and minerals into xylem:Root epidermis  cortex  [Casparian Strip]  vascular cylinder  xylem tissue  shoot systemAt Root EpidermisRoot hairs: increase surface area of absorption at root tipsMycorrhizae: symbiotic relationship between fungus + rootsIncrease H2O/mineral absorptionThe white mycelium of the fungus ensheathes these roots of a pine tree. Transport pathways across Cortex:Apoplast = materials travel between cellsSymplast = materials cross cell membrane, move through cytosol & plasmodesmataEntry into Vascular Cylinder: Endodermis (inner layer of cortex) sealed by Casparian strip (waxy material)Blocks passage of H2O and mineralsAll materials absorbed from roots enter xylem through selectively permeable membraneSymplast entry only!How does material move vertically (against gravity)?Transpiration: loss of H2O via evaporation from leaves into airRoot pressure (least important)Diffusion into root pushes sap upCohesion-tension hypothesisTranspiration provides pullCohesion of H2O transmits pull from rootsshootsGuttation: exudation of water droplets seen in morning (not dew), caused by root pressureStomata regulate rate of transpirationStomata – pores in epidermis of leaves/stems, allow gas exchange and transpirationGuard cells – open/close stoma by changing shapeTake up K+  lower ψ  take up H2O  pore opensLose K+  lose H2O  cells less bowed  pore closesCells stimulated open by: light, loss of CO2 in leaf, circadian rhythmsStomata closure: drought, high temperature, windBIOFLIX: WATER TRANSPORT IN PLANTSSugar TransportTranslocation: transport of sugars into phloem by pressure flowSource  SinkSource = produce sugar (photosynthesis)Sink = consume/store sugar (fruit, roots)Via sieve-tube elementsActive transport of sucroseBulk flow in a sieve tubeSymplast is dynamicPlasmodesmata allows movement of RNA & proteins between cellsPhloem can carry rapid, long-distance electrical signalingNerve-like functionSwift communicationChanges in gene expression, respiration, photosynthesis