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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.
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Sugars are transported asphloem sap to roots and otherparts of the plant.
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Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon forphotosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.
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Transpiration, the loss of waterfrom leaves (mostly through
stomata), creates a force withinleaves that pulls xylem sap upward.
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Water and minerals aretransported upward from
roots to shoots as xylem sap.
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Roots absorb waterand dissolved minerals
from the soil.
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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.
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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
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