Transcript Warm-Up
Ch. 36 Warm-Up 1. Describe the process of how H2O gets into the plant and up to the leaves. 2. Compare and contrast apoplastic flow to symplastic flow. 3. Explain the mass flow of materials in the phloem (source to sink). Ch. 36 Warm-Up 1. What is transpiration? 2. What are mycorrhizae? 3. What is the function of the Casparian strip? Chapter 36 Resource Acquisition and Transport in Vascular Plants 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. What does a plant need? 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 Solute transport across plant cell plasma membranes 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 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 A watered impatiens plant regains its turgor. 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) Transport of H2O and minerals into xylem: Root epidermis cortex [Casparian Strip] vascular cylinder xylem tissue shoot system 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. Transport pathways across Cortex: Apoplast = materials travel between cells Symplast = materials cross cell membrane, move through cytosol & plasmodesmata 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! How does material move vertically (against gravity)? Transpiration: loss of H2O via evaporation from leaves into air Root pressure (least important) 1. Diffusion into root pushes sap up Cohesion-tension hypothesis 2. ◦ ◦ Transpiration provides pull Cohesion of H2O transmits pull from rootsshoots Guttation: exudation of water droplets seen in morning (not dew), caused by root pressure 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 Cells stimulated open by: light, loss of CO2 in leaf, circadian rhythms Stomata closure: drought, high temperature, wind BIOFLIX: WATER TRANSPORT IN PLANTS 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 Bulk flow in a sieve tube 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