1. Ch. 36 Warm-Up
Describe the process of how H2O gets into the plant and up to the leaves.
Compare and contrast apoplastic flow to symplastic flow.
Explain the mass flow of materials in the phloem (source to sink).

2. Ch. 36 Warm-Up What is transpiration? What are mycorrhizae?
What is the function of the Casparian strip?

3. Resource Acquisition and Transport in Vascular Plants
Chapter 36
Resource Acquisition and Transport in Vascular Plants

4. What you need to know:
The role of passive transport, active transport, and cotransport in plant transport.
The role of diffusion, active transport, and bulk flow in the movement of water and nutrients in plants.
How the transpiration cohesion-tension mechanism explain water movement in plants.
How pressure flow explains translocation.

5. What does a plant need?

6. Review:
Selectively permeable membrane: osmosis, transport proteins, selective channels
Proton pump: active transport; uses E to pump H+ out of cell  proton gradient
Cotransport: couple H+ diffusion with sucrose transport
Aquaporin: transport protein which controls H2O uptake/loss

7. Solute transport across plant cell plasma membranes

8. Osmosis
**Water potential (ψ): H2O moves from high ψ  low ψ potential, solute conc. & pressure
Water potential equation: ψ = ψS + ψP
Solute potential (ψS) – osmotic potential
Pressure potential (ψP) – physical pressure on solution
Pure water: ψS = 0 Mpa
Ψ is always negative!
Turgor pressure = force on cell wall
Bulk flow: move H2O in plant from regions of high  low pressure
** Review AP Bio Investigation 4

9. Flaccid: limp (wilting)
Plasmolyze: shrink, pull away from cell wall (kills most plant cells) due to H2O loss
Turgid: firm (healthy plant)
Turgid Plant Cell
Plasmolysis

10. A watered impatiens plant regains its turgor.

11. Vascular Tissues: conduct molecules
Xylem
Phloem
Nonliving functional
Living functional
Xylem sap = H2O & minerals
Phloem sap = sucrose, minerals, amino acids, hormones
Source to sink
(sugar made) to (sugar consumed/stored)

12. Transport of H2O and minerals into xylem:
Root epidermis  cortex  [Casparian Strip]  vascular cylinder  xylem tissue  shoot system

13. At Root Epidermis
Root hairs: increase surface area of absorption at root tips
Mycorrhizae: symbiotic relationship between fungus + roots
Increase H2O/mineral absorption
The white mycelium of the fungus ensheathes these roots of a pine tree.

14. Transport pathways across Cortex:
Apoplast = materials travel between cells
Symplast = materials cross cell membrane, move through cytosol & plasmodesmata

15. Entry into Vascular Cylinder:
Endodermis (inner layer of cortex) sealed by Casparian strip (waxy material)
Blocks passage of H2O and minerals
All materials absorbed from roots enter xylem through selectively permeable membrane
Symplast entry only!

16. How does material move vertically (against gravity)?
Transpiration: loss of H2O via evaporation from leaves into air
Root pressure (least important)
Diffusion into root pushes sap up
Cohesion-tension hypothesis
Transpiration provides pull
Cohesion of H2O transmits pull from rootsshoots

18. Guttation: exudation of water droplets seen in morning (not dew), caused by root pressure

19. Stomata regulate rate of transpiration
Stomata – pores in epidermis of leaves/stems, allow gas exchange and transpiration
Guard cells – open/close stoma by changing shape
Take up K+  lower ψ  take up H2O  pore opens
Lose K+  lose H2O  cells less bowed  pore closes

20. Cells stimulated open by: light, loss of CO2 in leaf, circadian rhythms
Stomata closure: drought, high temperature, wind

21. BioFlix: Water Transport in plants

22. Sugar Transport
Translocation: transport of sugars into phloem by pressure flow
Source  Sink
Source = produce sugar (photosynthesis)
Sink = consume/store sugar (fruit, roots)
Via sieve-tube elements
Active transport of sucrose

23. Bulk flow in a sieve tube

24. Symplast is dynamic
Plasmodesmata allows movement of RNA & proteins between cells
Phloem can carry rapid, long-distance electrical signaling
Nerve-like function
Swift communication
Changes in gene expression, respiration, photosynthesis