Ch. 36 Warm-Up

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. 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) Plasmolysis Turgid Plant Cell

10. A watered impatiens plant regains its turgor.

11. Vascular Tissues: conduct molecules

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 • Symplastentry 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