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AP Biology Chapter 36 – Resource Acquisition and Transport in Vascular Plants Physical Forces in Plant Transport • Transport Occurs on 3 Levels 1. Uptake & Loss by Individual Cells 2. Short-Distance Transport from Cell to Cell • Tissues and Organs 3. Long-Distance Transport of Sap by Xylem and Phloem • Whole Plant Apoplast and Symplast • Inter-Cell Transport • Transmembrane Route • Crosses Plasma Membrane • Controls Transfer In and Out of Protoplast • Symplastic Route • Through Plasmodesmata • Protoplast to Protoplast • Apoplastic Route • Through Cell Walls • Extracellular Spaces (Tonoplast) Apoplast and Symplast (Tonoplast) Short Distance Transport of Solutes • Passive vs. Active Transport • Active Transport Required to Move Solutes Against an Electrochemical Gradient • Transport Proteins • Selectively Allow Ions and Polar Molecules to Cross the Lipid Bilayer • Proton Pump • ATP Used to Move Protons Outside the Cell • PE x2 Short Distance Transport of Solutes • Cation Transport • Driven by Potential Difference • Anion Co-transport • Coupled with Proton Gradient • Neutral Co-transport • Coupled with Proton Gradient Short Distance Transport of Water • Water Potential y = psi • Solute Potential + Pressure Potential • Osmosis (Passive Transport of Water) • Lower Solute Concentration to Higher • Higher Water Potential to Lower Short Distance Transport of Water • Turgor Pressure • Plasmolysis – Flaccidity – Turgidity • Aquaporins • Transport Proteins for Water Across Vacuole and Plasma Membranes (Increase Transport Rate) Transport in Root System 1. Sap Enters Hydrophilic Epidermal Cells to Apoplast and into Cortex 2. Sap Crosses Plasma Membranes to the Symplast 3. Some Sap Transported into Epidermis & Cortex and Inward via the Symplast 4. Sap in the Apoplastic Route Blocked by Casparian Strip at Endoderm 5. Endodermal & Parenchyma Cells Discharge Sap into Xylem Transport in Root System Transport of Xylem Sap • Xylem Sap Rises to Heights >100m Against Gravity • Pushed Upward by Root Pressure • At Night Roots Still Accumulate Ions Which Pushes Sap Upward • Guttation • Root Pressure > Transpiration/Evaporation • Water Pushed Out Stomata • Pulled Upward by Transpiration Transport of Xylem Sap • Transpiration • Difference in Water Potential • Root Pressure Stomata • Regulate Transpiration vs. Photosynthesis • Sap Transported Up Xylem @ 75 cm/min • Guard Cells • Water Intake (Turgidity) – Open • K+ Intake – Open • Microfibrils • Radial Orientation Shapes Guard Cells Stomata • Xerophytes • Arid Climate Plants • Evaporative Cooling • Reduce Surface Temp Up to 15oC • Reduced Leaf Surface Area • Limits Water Loss • Stomata on Underside of Leaf • Located in Depressions • Depressions Protected by Trichomes Transport of Phloem Sap • Sugar Up to 30% in Phloem Sap • Sugar Source to Sugar Sink • Source • Produces Sugar (Leaves) • Sink • Stores or Uses Sugar (Roots, Buds, Fruits) Transport of Phloem Sap • Sugar Produced in Leaf Translocated to Sieve Tube Cells /w Water from Xylem • Positive Pressure Forces Sap Downward • Sugar Unloaded to Sink • Excess Water Returned to Xylem
