1. Chapter 36 Transport in Vascular Plants

2. Physical forces drive the transport of materials in plants over a range of distances Transport in vascular plants occurs on three scales: –Transport of water and solutes by individual cells, such as root hairs –Short-distance transport of substances from cell to cell at the levels of tissues and organs –Long-distance transport within xylem and phloem at the level of the whole plant

3. Minerals H2OH2O CO 2 O2O2 O2O2 H2OH2O Sugar Light A variety of physical processes –Are involved in the different types of transport Sugars are produced by photosynthesis in the leaves. 5 Sugars are transported as phloem sap to roots and other parts of the plant. 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 Figure 36.2 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

4. Selective Permeability of Membranes: A Review The selective permeability of a plant cell’s plasma membrane controls the movement of solutes into and out of the cell Specific transport proteins enable plant cells to maintain an internal environment different from their surroundings

5. The Central Role of Proton Pumps Proton pumps in plant cells: –Create a hydrogen ion gradient that is a form of potential energy that can be harnessed to do work –Contribute to a voltage known as a membrane potential Figure 36.3 CYTOPLASM EXTRACELLULAR FLUID ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Proton pump generates membrane potential and H + gradient. – – – – – + + + + +

6. In the mechanism called cotransport –A transport protein couples the passage of one solute to the passage of another Figure 36.4b H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ NO 3 – – – – + + + – – – + + + (b) Cotransport of anions H+H+ of through a cotransporter. Cell accumulates anions (, for example) by coupling their transport to the inward diffusion

7. H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ S S S S S Plant cells can also accumulate a neutral solute, such as sucrose ( ), by cotransporting down the steep proton gradient. S H+H+ – – – + + + – – + + – Figure 36.4c H+H+ H+H+ S + – (c) Contransport of a neutral solute The effect of cotransport is also responsible for the uptake of the sugar sucrose by plant cells

8. Water Potential –Is a measurement that combines the effects of solute potential and pressure potential –Determines the direction of movement of water Water flows from regions of high water potential to regions of low water potential

9. How Solutes and Pressure Affect Water Potential The solute potential of a solution: –Is proportional to the number of dissolved molecules Pressure Potential –Is the physical pressure on a solution

10. The addition of solutes reduces water potential Figure 36.5a 0.1 M solution H2OH2O Pure water  P = 0  S =  0.23  =  0.23 MPa  = 0 MPa (a)

11. Application of physical pressure increases water potential H2OH2O  P = 0.23  S =  0.23  = 0 MPa (b) H2OH2O  P = 0.30  S =  0.23  = 0.07 MPa  = 0 MPa (c) Figure 36.5b, c

12. Negative pressure –Decreases water potential H2OH2O  P = 0  S =  0.23  =  0.23 MPa (d)  P =  0.30  S = 0  =  0.30 MPa Figure 36.5d

13. 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

14. 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

15. Turgor loss in plants causes wilting which can be reversed when the plant is watered Figure 36.7

16. Compartments of Plant Cells and Tissues and Three Routes for Short-Distance Transport

17. Lateral Transport of Minerals and Water in Roots

18. The Fungal Hyphae of Mycorrhizae Increase the Absorption of Water and Minerals

19. Aquaporin Proteins and Water Transport Aquaporins –Are transport proteins in the cell membrane that allow the passage of water –Do not affect water potential

20. The plasma membrane –Directly controls the traffic of molecules into and out of the protoplast –Is a barrier between two major compartments, the cell wall and the cytosol

21. Water and Minerals Ascend From Roots to Shoots Through the Xylem Figure 36.1

22. Transpiration produces negative pressure (tension) in the leaf which draws water out of the xylem into the mesophyll Evaporation causes the air-water interface to retreat farther into the cell wall and become more curved as the rate of transpiration increases. As the interface becomes more curved, the water film’s pressure becomes more negative. This negative pressure, or tension, pulls water from the xylem, where the pressure is greater. Cuticle Upper epidermis Mesophyll Lower epidermis Cuticle Water vapor CO 2 O2O2 XylemCO 2 O2O2 Water vapor Stoma Evaporation At first, the water vapor lost by transpiration is replaced by evaporation from the water film that coats mesophyll cells. In transpiration, water vapor (shown as blue dots) diffuses from the moist air spaces of the leaf to the drier air outside via stomata. Airspace Cytoplasm Cell wall Vacuole Evaporation Water film Low rate of transpiration High rate of transpiration Air-water interface Cell wall Airspace  = –0.15 MPa  = –10.00 MPa 3 1 2 Figure 36.12 Air- space

23. The Generation of Transpirational Pull in a Leaf

24. Ascent of Water in a Tree

25. The Mechanism of Stomatal Opening and Closing

26. The Diffusion of K Ions Into and Out of the Guard Cells Opens and Closes the Stomata

27. An open (left) and closed (right) stoma of a spider plant (Chlorophytum colosum) leaf

28. Review 1)As water ascends up a tree water potential decreases/increases. 2) A beaker of pure water open to the atmosphere has a water potential of... A flaccid cell placed in this solution would become...

29. 3) A turgid cell is placed into a solution with a high solute concentration. The pres- sure remains unchanged. What happens to water potential inside the cell? 4) Discuss the movement of K ions in guard cells that would occur during a 24 hour period on a typical hot summer day.