1. Chapter 36: Resource Acquisition and Transport in Plants
36.1
Admit Slip
3. List 3 words you think of when you look at the picture/diagram
2. Write 2 ideas you have based on the picture and your words. If possible, use your words as you write your ideas.
1. Write 1 question you have.

3. Transport
Begins with the movement of water and solutes across a cell membrane
Solutes diffuse down electrochemical gradients
Passive Transport: No energy required to move materials across the membrane
Diffusion, Osmosis
Active Transport: energy is required to move materials across the membrane
Usually requires a transport protein in membrane
Proton pump=most important transport protein

4. Transport
Proton Pump
Creates electrochemical gradient by using ATP to pump H+ ions across a membrane. This changes the electrochemical gradient of the membrane and powers transport

5. Transport of Water
Osmosis is the passive transport of water across a membrane
Water moves from high water potential to low water potential

6. Movement of water in plants
cells are flaccid
plant is wilting
Water relations in plant cells is based on water potential
osmosis through aquaporins
transport proteins
water flows from high potential to low potential
Water potential is the force that moves water across the membranes of plant cells, but how do the water molecules actually cross the membranes? Because water molecules are so small, they move relatively freely across the lipid bilayer, even though the middle zone is hydrophobic. Water transport across biological membranes, however, is too specific and too rapid to be explained entirely by diffusion through the lipid bilayer. Indeed, water typically crosses vacuolar and plasma membranes through transport proteins called aquaporins These selective channels do not affect the water potential gradient or the direction of water flow, but rather the rate at which water diffuses down its water potential gradient. Evidence is accumulating that the rate of water movement through these proteins is regulated by phosphorylation of the aquaporin proteins induced by changes in second messengers such as calcium ions (Ca2+).
cells are turgid
2009

7. Transport in Water Potential water equation: Ѱ= Ѱs+ Ѱp
Ѱ=water potential, Ѱs=solute potential, Ѱp= pressure potential
The Ѱs of pure water=0. Adding solutes lowers the potential (always negative)
Pressure Potential refers to the cell contents pressing on the plasma membrane, (turgor Pressure). If the cell loses water, the pressure potential becomes more negative (wilting of plant)

9. Practice Calculation
Potential water equation: Ѱ= Ѱs+ Ѱp
Ѱ=water potential, Ѱs=solute potential, Ѱp= pressure potential
1. If a cell’s ΨP = 3 bars and its ΨS = -4.5 bars, what is the resulting Ψ?
2. The cell from question #1 is placed in a beaker of sugar water with ΨS = -4.0 bars. In which direction will the net flow of water be?

10. Transport in Water
Aquaporins: transport proteins (channels) in the membrane that allow the passage of water through the hydrophobic region of the lipid bilayer.
Bulk Flow: movement of water through the plant
Moves from regions of high pressure to regions of low pressure
Xylem and Phloem move materials through bulk flow

11. Chapter 36: Resource Acquisition and Transport in Plants
36.2

12. Absorption of Water and Minerals from the Soil
Most absorption happens near the root tips through the root hairs
Pathway of water/minerals: root epidermiscortexvascular cylindertracheidsshoot system
Roots and fungi have a symbiotic relationship called mycorrhizae. Increases absorption and uptake of water/minerals by plants

14. Chapter 36: Resource Acquisition and Transport in Plants
36.3

15. Lateral Transport from Roots to Shoots
Apoplastic Route: movement of water and minerals between cells
Symplastic Route: occurs after the solution crosses a plasma membrane
Casparian Strip: waxy material that blocks passage of materials, control point for passage of materials (passing the casparian strip the solution passes the plasma membrane

16. Lateral Transport

17. Transport
Once water and minerals get to the xylem, they are transported through the plant by bulk flow. Eventually they exit the plant through the leaves
Transpiration: loss of water vapor primarily from the leaves or other parts in contact with air.
This plays an important part in the movement of water through the plant

18. Water Movement in Plants
2 mechanisms:
Root Pressure: water entering the cortex creates positive pressure. This pushes water up the xylem.
Does not have the force to push water up to the top of trees
Transpiration-cohesion-tension Mechanism: water is lost through transpiration due to lower water potential of air. Cohesion and adhesion of water (from hydrogen bonding) enables it to create a column and be drawn up through the xylem

19. Rise of water in a tree by bulk flow
Transpiration pull
adhesion & cohesion
H bonding
brings water & minerals to shoot
Water potential
high in soil  low in leaves
Root pressure push
due to flow of H2O from soil to root cells
upward push of xylem sap
The transpiration–cohesion–tension mechanism that transports xylem sap against gravity is an excellent example of how physical principles apply to biological processes. In the long–distance transport of water from roots to leaves by bulk flow, the movement of fluid is driven by a water potential difference at opposite ends of a conduit. In a plant, the conduits are vessels or chains of tracheids. The water potential difference is generated at the leaf end by transpirational pull, which lowers the water potential (increases tension) at the “upstream” end of the xylem.
On a smaller scale, water potential gradients drive the osmotic movement of water from cell to cell within root and leaf tissue. Differences in both solute concentration and turgor pressure contribute to this short–distance transport. In contrast, bulk flow depends only on pressure. Another contrast with osmosis, which moves only water, is that bulk flow moves the whole solution, water plus minerals and any other solutes dissolved in the water.
The plant expends no energy to lift xylem sap by bulk flow. Instead, the absorption of sunlight drives transpiration by causing water to evaporate from the moist walls of mesophyll cells and by lowering the water potential in the air spaces within a leaf. Thus, the ascent of xylem sap is ultimately solar powered.

20. Chapter 36: Resource Acquisition and Transport in Plants
36.4

21. Stomata Help regulate the rate of transcription
Large surface area increases photosynthesis (gas into plant cell)/increases water loss
Guard cells open and close the stomata
Control gases coming in and water moving out

22. Guard Cells Control the size of stomata by changing shape
When guard cells take up K+ from surrounding cells, water potential decreases in guard cells=take up water. Cells swell and buckle=open pore
Guard cells lose K+, cells lose water, become less bowed=pore closes
Guard Cells

23. Guard Cells Stimulated to open by: Light
Loss of carbon dioxide in leaf
Normal circadian rhythms
Circadian rhythms=part of plants internal clock mechanism. Cycle with intervals for 24 hours.