Transcript Chapter 36
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 - overview Transpiration: loss of water vapor from leaves pulls water from roots (transpirational pull); cohesion and adhesion of water Root pressure: at night (low transpiration), roots cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; guttation AP Biology Ascent of xylem fluid Transpiration pull generated by leaf AP Biology 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 Root anatomy - Water Flow dicot AP Biology monocot Endodermis & Casparian strip AP Biology Two Routes Symplast route (lateral) cytoplasmic continuum Apoplast route (lateral) AP Biology continuum of cell walls 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 lined with impermeable Casparian strip forces fluid through selective cell membrane filtered & forced into xylem cells AP Biology 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 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 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 Ghosts of Lectures Past (storage) AP Biology 2006-2007 Control of Stomates Guard cell Epidermal cell Uptake of K+ ions by guard cells proton pumps water enters by osmosis guard cells become turgid H2O K+ H2O K+ Loss of K+ ions Nucleus Chloroplasts H2O K+ H2O K+ K+ H2O K+ H2O K+ H2O K+ H2O Thickened inner cell wall (rigid) by guard cells AP Biology water leaves by osmosis H2O K+ guard cells become flaccid H2O K+ H2O K+ H2O K+ Stoma open Stoma closed water moves into guard cells 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 CO2 for photosynthesis AP Biology