This document discusses plant transport mechanisms including passive and active transport. It describes the key plant tissues involved - xylem and phloem. Xylem transports water and minerals from roots to shoots, while phloem transports sugars from leaves to other plant parts. Water potential, determined by solute concentration and pressure, drives the movement of water and solutes within plant cells and tissues.

2. Recall Transport Mechanism Passive vs. Active Plant Transport Tissues Xylem Phloem

3. Transport Mechanisms Passive transport Passive Diffusion Facilitated Diffusion Osmosis Active transport Bulk transport

4. Plant Transport Tissues Xylem Vessel elements Tracheids Phloem Sieve tube member Companion cells

5. Problem of Terrestrial Plants Ancestral plants: transport is through diffusion Modern plants: transport from roots to shoots Long distance transport Figure 36.1

6. Transport in Plants Three scales of plant transport Intracellular Epidermal cells Short distance: cell-to-cell At the levels of tissues and organs Long distance: xylem and phloem

7. A variety of physical processes Are involved in the different types of transport Minerals H 2 O CO 2 O 2 CO 2 O 2 H 2 O Sugar Light Sugars are transported as phloem sap to roots and other parts of the plant. Figure 36.2 Sugars are produced by photosynthesis in the leaves. 5 6 Through stomata, leaves take in CO 2 and expel O 2 . The CO 2 provides carbon for photosynthesis. Some O 2 produced by photosynthesis is used in cellular respiration. 4 Transpiration, the loss of water from leaves (mostly through stomata), creates a force within leaves that pulls xylem sap upward. 3 Water and minerals are transported upward from roots to shoots as xylem sap. 2 Roots absorb water and dissolved minerals from the soil. 1 Roots exchange gases with the air spaces of soil, taking in O 2 and discharging CO 2 . In cellular respiration, O 2 supports the breakdown of sugars. 7

8. Effects of Differences in Water Potential To survive Plants must balance water uptake and loss Osmosis Determines the net uptake or water loss by a cell Is affected by solute concentration and pressure

9. Water potential Is a measurement that combines the effects of solute concentration and pressure Determines the direction of movement of water Water Flows from regions of high water potential to regions of low water potential Both pressure and solute concentrations affect water potential

10. Water potential Affects uptake and loss of water by plant cells If a flaccid cell is placed in an environment with a higher solute concentration The cell will lose water and become plasmolyzed Figure 36.6a 0.4 M sucrose solution: Initial flaccid cell: Plasmolyzed cell at osmotic equilibrium with its surroundings  P = 0  S = 0.7  P = 0  S = 0.9  P = 0  S = 0.9  =  0.9 MPa  = 0.7 MPa  =  0.9 MPa

11. If the same flaccid cell is placed in a solution with a lower solute concentration The cell will gain water and become turgid Distilled water: Initial flaccid cell: Turgid cell at osmotic equilibrium with its surroundings  P = 0  S = 0.7  P = 0  S = 0  P = 0.7  S = 0.7 Figure 36.6b  = 0.7 MPa  = 0 MPa  = 0 MPa

12. How water moves Plasmodesmata Symplast apoplast

13. Bulk Flow in Long-Distance Transport In bulk flow Movement of fluid in the xylem and phloem is driven by pressure differences at opposite ends of the xylem vessels and sieve tubes

14. The xylem sap and phloem sap Xylem sap Root pressure Transpiration-cohesion-tension mechanism Phloem sap Pressure Flow Theory Translocation