Intro to Lab #9 / Chpt. 36 Plant Structure and Transport pg. 744 - 753

Intro to Lab #9 / Chpt. 36

Plant Structure and Plant Structure and

Transport Transport pg. 744 - 753

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Transport in Transport in PlantsPlantsDid you know, an

average size maple tree looses 200 L of water per hour during the summer via. transpiration.

What would happen if this water were

not replaced by the roots???

Question ?

• How do plants move materials from one organ to

the other ?

TRANSPIRATIONTRANSPIRATIONTRANSPIRATIONTRANSPIRATION - -

when a plant looses water vapor from the inside of the leaf, to the outside environment -via. stomata

COHESIONCOHESION - - TENSIONTENSION THEORYTHEORY - - water is water is pulled up pulled up from roots to from roots to leaves via. leaves via. higher higher in in the leaf to a the leaf to a lower lower in the air in the air

Water & mineral absorption to Xylem:• Water absorption from soil

- osmosis

- aquaporins

ROOT HAIRS = increase surface area for the absorption of water &

minerals



Water & mineral absorption to Xylem: Mineral absorption

–active transport–proton pumps•active transport of H+

proton pumps

Water & mineral absorption to Xylem: proton pumps

• Proton pumps– active transport of H+ ions out of cell•chemiosmosis•H+ gradient

– creates membranepotential•difference in charge•drives cation uptake

– creates gradient•cotransport of othersolutes against theirgradient

Transport in Transport in PlantsPlantsuptake and loss by uptake and loss by

individual individual cellscells::

The survival of plant The survival of plant cells depends on the cells depends on the

ability to balance ability to balance the the uptakeuptake & & lossloss of of

HH22OO

Remember this?Remember this?*Presence of the *Presence of the cell cell

wallwall adds adds physical physical pressurepressure, this affects , this affects movement into the cell movement into the cell

negatively!negatively!

Remember this?Remember this?

**Solute Solute concentrationconcentration also also affects movement:affects movement:

Transport in Transport in PlantsPlantsHow can we predict the How can we predict the

direction of osmosis direction of osmosis when a plant cell is when a plant cell is

surrounded by a surrounded by a solution???solution???

Transport in Transport in PlantsPlants


Water moves from the Water moves from the solution of solution of higherhigher waterwater potentialpotential, to a , to a solution of solution of lowerlower waterwater potentialpotential..For plants, it is not just For plants, it is not just

enough to know if the enough to know if the extracellular solution is extracellular solution is hypotonic or hypertonic.hypotonic or hypertonic.


*Measured in *Measured in MEGAPASCALSMEGAPASCALS

•Has two components:–Pressure potential:

–Solute potential:


Pressure potential: Solute potential:

You have to know these two numbers first, when determining water potential.

You must know water potential in order to know which direction water will move!



any any solutionsolution will have will have a a negative negative w.p.w.p.

adding adding solutesolutes, s, lowers lowers w.p.w.p.


*Solute *Solute concentration concentration

affects affects movementmovement

Transport in Transport in PlantsPlants*External pressure on *External pressure on

a solution counters a solution counters its tendencyits tendencyto take up to take up

water due to water due to the presence of the presence of

solutessolutes


==

PP ++

SS


== the force the force that moves that moves water across water across the the membranes of membranes of plant cellsplant cells

COHESIONCOHESION - - TENSIONTENSION THEORYTHEORY - -

water is water is “pulled” b/c “pulled” b/c of it’s of it’s cohesivecohesive propertyproperty

EvolutionarEvolutionary advantage y advantage

of ROOT of ROOT HAIRS: add HAIRS: add surface surface area - area -

thus thus increasing increasing amount of amount of HH220/mineral 0/mineral solution solution

coming into coming into the plant!!the plant!!

Mycorrhizae increase absorption• Symbiotic relationship between fungi & plant

–symbiotic fungi greatly increases surface area for absorption of water & minerals

–increases volume of soil reached to plant–increases transport to host plant

Mycorrhizae


Because higher water

potential outside

COHESIONCOHESION - - TENSIONTENSION THEORYTHEORY - - minerals minerals absorbed from absorbed from soil into soil into root~ creates root~ creates ““rootroot pressurepressure”” that that pushes Hpushes H22O/soil O/soil solution into solution into xylemxylem


•uptake of uptake of soil solution soil solution by root hairs by root hairs to to apoplasticapoplastic routeroute --through the through the cell wallscell walls



Transport routes in plant cells




• uptake of uptake of minerals & minerals & water by root water by root hairs to hairs to symplasticsymplastic routeroute - - through through plasmodesmataplasmodesmata



Transport routes in plant cells



Controlling the route of water in root• Endodermis

– cell layer surrounding vascular cylinder of root

– lined with impermeable Casparian strip– forces fluid through selective cell membrane

• filtered & forced into xylem cells



• some soil some soil solution from solution from apoplast apoplast route, route, diffuses into diffuses into the the symplastic symplastic routeroute -through -through the plasma the plasma membranemembrane



Controlling the route of water in root

COHESIONCOHESION - - TENSIONTENSION THEORYTHEORY - - Water then Water then travels thru travels thru the root the root where the where the Casparian Casparian stripstrip forces forces HH22O into the O into the xylemxylem

REMEMBER: the casparian strip blocks water from entering via. The apoplastic route


• only minerals only minerals in the in the symplastic symplastic route can route can detour around detour around the Casparian the Casparian Strip AND Strip AND PASS PASS INTO THE INTO THE VASCULAR VASCULAR XYLEM!!XYLEM!!



Root anatomy

eudicot monocot


XYLEM XYLEM vessels vessels transport transport water and water and minerals minerals upward into upward into the shoot the shoot system (stem system (stem and veins)and veins)




problem… this problem… this can only take can only take the water “so the water “so far”far”


At the leaf At the leaf of the of the plant, water plant, water loss due to loss due to evaporation evaporation is taking is taking place.place.

Evaporating H2O decreases the water potential of the leaf.

Since water flows from higher water potential to lower, the water is pulled up the xylem with the minerals.

Transport of sugars in phloem• Loading of sucrose into phloem

–flow through cells via plasmodesmata–proton pumps create energy potential/proton gradient• cotransport of sucrose into cells down proton gradient

can flow 1m/hr

Pressure flow in phloem• Mass flow hypothesis

– “source to sink” flow• direction of transport in phloem is dependent on plant’s needs

– phloem loadingphloem loading• active transport of sucrose into phloem

• increased sucrose concentration decreases H2O potential

– water flows in from xylem cells• increase in pressure due to increase in H2O causes flow

Maple Maple sugarinsugarin

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Transport in Transport in PlantsPlants CO2O2

H2O

Transport in Transport in PlantsPlants CO2O2

H2O

How do How do environmental environmental influences influences effect?effect?

Transport in Transport in PlantsPlantsflacidflacid turgidturgid

Environmental factors influence this rate…

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Intro to Lab #9 / Chpt. 36 Plant Structure and Transport pg. 744 - 753