Plant Transport

• Transport in Plants   * Water and minerals     * Transport in xylem     * Transpiration       * Evaporation, adhesion, and cohesion       * Negative pressure   * Sugars     * Transport in phloem     * Bulk flow       * Calvin cycle in leaves loads sucrose in phloem       * Positive pressure   * Gas Exchange     * Photosynthesis       * CO2 in; O2 out       * Stomates     * Respiration       * O2 in; CO2 out       * Roots exchange gases within air spaces in soil
• Water and Mineral Absorption   * Water absorption from soil     * Osmosis     * Aquaporins   * Mineral absorption     * Active transport     * Proton pumps       * Active transport of H+
• 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       * Co-transport of other solutes against their gradient
• Water Flow Through Root   * Porous cell wall     * Water can flow through cell wall route and not enter cells     * Plant needs to force water into cells
• 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 and forced through xylem cells
• Mycorrhizae Increase Absorption   * Symbiotic relationship between fungi and plant     * Symbiotic fungi greatly increase surface area for absorption of water and minerals     * Increases volume of soil reached by plant     * Increases transport to hist plant
• 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
• 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
• Experimentation   * Testing pressure flow hypothesis     * Using aphids to measure sap flow and sugar concentration along plant system

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