Ch. 36 Warm-UpCh. 36 Warm-Up1. 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-UpCh. 36 Warm-Up1. What is transpiration?

2. What are mycorrhizae?

3. What is the function of the Casparian strip?

Chapter 36Chapter 36Resource Acquisition and Transport in Vascular Plants

What you need to know: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 What does a plant a plant need?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 Solute transport across plant cell across plant cell

plasma plasma membranesmembranes

OsmosisOsmosis****Water potential (Water potential (ψψ)): : 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 flowBulk flow: move H2O in plant from regions of high low pressure

** Review AP Bio Investigation 4** 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 A watered impatiensimpatiens plant regains its turgor. plant regains its turgor.

Vascular TissuesVascular Tissues: conduct molecules: conduct molecules

Xylem Phloem

Nonliving functional Living functional

Xylem sap = H2O & minerals

Phloem sap = sucrose, minerals, amino acids,

hormones

Source to sinkSource to sink(sugar made) to (sugar

consumed/stored)

Transport of HTransport of H22O and minerals into O and minerals into xylem:xylem:

Root epidermis cortex [Casparian Strip] vascular cylinder xylem tissue shoot system

At Root EpidermisAt 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:Transport pathways across Cortex:

ApoplastApoplast = materials travel between cellsSymplastSymplast = materials cross cell membrane, move

through cytosol & plasmodesmata

Entry into Vascular Cylinder: 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

◦ SymplastSymplast entry only!

How does material move vertically (against How does material move vertically (against gravity)?gravity)?

TranspirationTranspiration: loss of H2O via evaporation from leaves into air

1. Root pressure (least (least important)important)

Diffusion into root pushes sap up

2. Cohesion-tension hypothesis◦ 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 transpirationStomata regulate rate of transpirationStomata – pores in epidermis of leaves/stems,

allow gas exchange and transpirationGuard 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 openopen by: light, loss of CO2 in leaf, circadian rhythms

Stomata closureclosure: drought, high temperature, wind

BIOFLIX: WATER BIOFLIX: WATER TRANSPORT IN PLANTSTRANSPORT IN PLANTS

Sugar TransportSugar TransportTranslocation: transport of sugars into

phloem by pressure flowSource Sink

◦Source = produce sugar (photosynthesis)

◦Sink = consume/store sugar (fruit, roots)

Via sieve-tube elementsActive transport of sucrose

Bulk flow Bulk flow in a sieve in a sieve

tubetube

Symplast is dynamicSymplast is dynamicPlasmodesmata allows movement of

RNA & proteins between cellsPhloem can carry rapid, long-distance

electrical signaling◦Nerve-like function◦Swift communication◦Changes in gene expression,

respiration, photosynthesis