RecallTransport Mechanism

Passive vs. ActivePlant Transport Tissues

XylemPhloem

Transport MechanismsPassive transport

Passive DiffusionFacilitated DiffusionOsmosis

Active transportBulk transport

Plant Transport TissuesXylem

Vessel elementsTracheids

PhloemSieve tube memberCompanion cells

Problem of Terrestrial PlantsAncestral plants: transport is through

diffusionModern plants: transport from roots to shoots

Long distance transport

Figure 36.1

Transport in PlantsThree scales of plant transport

Intracellular Epidermal cells

Short distance: cell-to-cell At the levels of tissues and organs

Long distance: xylem and phloem

MineralsH2O CO2

O2

CO2 O2

H2O Sugar

Light

A variety of physical processesAre involved in the different types of transport

Sugars are produced byphotosynthesis in the leaves.

5

Sugars are transported asphloem sap to roots and otherparts of the plant.

6

Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon forphotosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.

4

Transpiration, the loss of waterfrom leaves (mostly through

stomata), creates a force withinleaves that pulls xylem sap upward.

3

Water and minerals aretransported upward from

roots to shoots as xylem sap.

2

Roots absorb waterand dissolved minerals

from the soil.

1

Figure 36.2

Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars.

7

Effects of Differences in Water Potential

To survivePlants must balance water uptake and loss

OsmosisDetermines the net uptake or water loss by a cellIs affected by solute concentration and pressure

Water potentialIs a measurement that combines the effects of

solute concentration and pressureDetermines the direction of movement of water

WaterFlows from regions of high water potential to

regions of low water potentialBoth pressure and solute concentrations affect

water potential

Water potentialAffects uptake and loss of water by plant

cellsIf a flaccid cell is placed in an environment

with a higher solute concentrationThe cell will lose water and become

plasmolyzed

Figure 36.6a

0.4 M sucrose solution:

Initial flaccid cell:

Plasmolyzed cellat osmotic equilibriumwith its surroundings

P = 0

S = 0.7

P = 0

S = 0.9

P = 0

S = 0.9

= 0.9 MPa

= 0.7 MPa

= 0.9 MPa

If the same flaccid cell is placed in a solution with a lower solute concentrationThe cell will gain water and become turgid

Distilled water:

Initial flaccid cell:

Turgid cellat osmotic equilibriumwith its surroundings

P = 0

S = 0.7

P = 0

S = 0

P = 0.7

S = 0.7

Figure 36.6b

= 0.7 MPa

= 0 MPa

= 0 MPa

How water movesPlasmodesmataSymplastapoplast

Bulk Flow in Long-Distance TransportIn bulk flow

Movement of fluid in the xylem and phloem is driven by pressure differences at opposite ends of the xylem vessels and sieve tubes

The xylem sap and phloem sapXylem sap

Root pressureTranspiration-cohesion-tension mechanism

Phloem sapPressure Flow Theory

Translocation