Embedded Files
Resource Acquisition and Transport in Vascular Plants What a Plant Needs:Water, minerals, oxygen, carbon dioxide, light Review:-selectively permeable membrane – osmosis, transport proteins, selective channels-proton pump – active transport; uses E to pump H+ out of cell à proton gradient-cotransport – couple H+ diffusion with sucrose transport-aquaporin – transport protein which controls water uptake/loss Osmosis-Water potential (w): water moves from high (w) à low (w) and pressure --water potential equation: (w) = (ws)+ (wp) --solute potential (ws) – osmotic potential --pressure potential (wp) – physical pressure on solution --pure water: (ws) = 0 Mpa --(w) is always negative --TURGOR PRESSURE = force on cell wall-Bulk flow: move water in plant from regions of high à low pressure-Flaccid: limp/wilting-Plasmolyze: shrink, pull away from cell wall (kills most plant cells) b/c of water loss-Turgid: firm/healthy plant --a wilting plant regains its turgor after being sufficiently watered Vascular tissues: conduct molecules-Xylem: nonliving functional. Xylem sap = water and minerals-Phloem: living functional. Phloem sap = sucrose, minerals, amino acids, hormones source to sink – sugar made to sugar consumed/stored Transport of water and minerals into xylem:Root epidermis à cortex à Casparian Strip à vascular cylinder à xylem tissue à shoot system-at root epidermis: root hairs increase surface area of absorption at root tips. Mycorrhizae (symbiotic relationship between fungus and roots) increase water and mineral absorption. Transport pathways across Cortex:-Apoplast = materials travel between cells (apoplastic route)-Symplast = materials cross cell membrane, move through cytosol and plasmodesmata (symplastic route) Entry into vascular cylinder:-Endodermis (inner layer of cortex) sealed by Casparian Strip (waxy material) --blocks passage of water and minerals--all materials absorbed from roots enter xylem through selectively permeable membrame --symplastic How material Moves Vertically (against gravity)Transpiration = loss of water via evaporation from leaves into air1. root pressure (least important) – diffusion into roots pushes sap up2. cohesion-tension hypothesis – transpiration provides pull, cohesion of water transmits pullGuttation: exudation of water droplets seen in morning (not dew), caused by root pressure Stomata regulate rate of transpiration-stomata – pores in epidermis of leaves/stems, allow gas exchange and transpiration-guard cells – open/close stomata by changing shape --take up K+ à lower (w) à cells take up water à pore opens --lose K+ à lose water à cells less bowed à pore closes-cells stimulated open by: light, loss of CO2 in leaf, circadian rythms-stomata closure: drought, high temperature, wind Sugar Transport-Translocation: transport of sugars into phloem by pressure flow-source à sink: source = produce sugar (photosynthesis). Sink = consume/store sugar (fruit, roots)-via sieve-tube elements-active transport of sucrose-bulk flow in a sieve tube: loading of sugar à uptake of water à unloading of sugar à water recycled Symplast is Dynamic-plasmodesmata allows movement of RNA and proteins between cells-phloem can carry rapid, long-distance electrical signaling--nerve-like function, swift communication, changes in gene expression, respiration, photosynthesis
Google Sites
Report abuse