7748156 plant transport

8/12/2019 7748156 Plant Transport

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Nutrient Transport inNutrient Transport in

PlantsPlants


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Three Levels of TransportThree Levels of Transport

Transport in vascular plants occurs onTransport in vascular plants occurs on

three scalesthree scales Transport of water and solutes by individualTransport of water and solutes by individual

cells, such as root hairscells, such as root hairs

Short-distance transport of substances fromShort-distance transport of substances from

cell to cell at the levels of tissues andcell to cell at the levels of tissues and

organsorgans Long-distance transport (bulk flow withinLong-distance transport (bulk flow within

!ylem and phloem at the level of the whole!ylem and phloem at the level of the whole

plantplant


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"inerals

#$% &%$

%$

&%$ %$

#$% Sugar

Light

' variety of physical processes' variety of physical processes're involved in the different types of transport're involved in the different types of transport

Sugars are produced by

photosynthesis in the leaves.

5

Sugars are transported as

phloem sap to roots and other

parts of the plant.

6

Through stomata, leaves

take in CO2and epel O2.

The CO2provides carbon for

photosynthesis. Some O2

produced by photosynthesis

is used in cellular respiration.

!

Transpiration, the loss of "ater

from leaves #mostly through

stomata$, creates a force "ithin

leaves that pulls ylem sap up"ard.

%

&ater and minerals are

transported up"ard from

roots to shoots as ylem sap.

2

'oots absorb "ater

and dissolved minerals

from the soil.

( 'oots echange gases

"ith the air spaces of soil,

taking in O2and discharging

CO2. )n cellular respiration,

O2supports the breakdo"n

of sugars.

*


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ffects of )ifferences in *aterffects of )ifferences in *ater

PotentialPotential To surviveTo survive Plants must balance water uptake and lossPlants must balance water uptake and loss

%smosis%smosis +s the movement of water from low solute+s the movement of water from low solute

concentration to areas of high soluteconcentration to areas of high soluteconcentrationconcentration

)etermines the net uptake or water loss by a)etermines the net uptake or water loss by acellcell

+s affected by solute concentration and pressure+s affected by solute concentration and pressure


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*ater potential*ater potential +s a measurement that combines the effects of+s a measurement that combines the effects of

solute concentration and pressuresolute concentration and pressure

)etermines the direction of movement of water)etermines the direction of movement of water

*ater*ater lows from regions of high water potential tolows from regions of high water potential to

regions of low water potentialregions of low water potential


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Solutes and PressureSolutes and Pressure

The solute potential of a solutionThe solute potential of a solution +s proportional to the number of dissolved+s proportional to the number of dissolved

moleculesmolecules

Pressure potentialPressure potential +s the physical pressure on a solution+s the physical pressure on a solution


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Quantitative Analysis of WaterQuantitative Analysis of Water

PotentialPotential The addition of solutesThe addition of solutes

educes water potentialeduces water potential

+.( M

solution

2O

-ure

"ater

- +S +.2% +.2% /-a + /-a

#a$


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'pplication of physical pressure'pplication of physical pressure +ncreases water potential+ncreases water potential

2O

- +.2%S +.2% + /-a + /-a

#b$

2O

- +.%+S +.2% +.+* /-a + /-a

#c$


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*ater potential*ater potential

'ffects uptake and loss of water by plant cells'ffects uptake and loss of water by plant cells +f a flaccid cell is placed in an environment+f a flaccid cell is placed in an environment

with a higher solute concentration twith a higher solute concentration the cell willhe cell willlose water and become plasmoly.edlose water and become plasmoly.ed

+.! Msucrose solution0

)nitial flaccid cell0

-lasmoly1ed cell

at osmotic e/uilibrium

with its surroundings

P0 1

S0 123

P0 1

S0 124

P0 1

S0 124

+. /-a

+.* /-a

+. /-a


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+f the same flaccid cell is placed in a+f the same flaccid cell is placed in a

solution with a lower solute concentrationsolution with a lower solute concentration The cell will gain water and become turgidThe cell will gain water and become turgid

3istilled "ater0

)nitial flaccid cell0

Turgid cell

at osmotic e/uilibrium

with its surroundings

P0 1

S0 123

P0 1

S0 1

P0 123

S0 123

+.* /-a

+ /-a

+ /-a


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Turgor loss in plants causes wiltingTurgor loss in plants causes wilting *hich can be reversed when the plant is*hich can be reversed when the plant is

wateredwatered


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Three "a5or &ompartments ofThree "a5or &ompartments of

6acuolated Plant &ells6acuolated Plant &ells

Transport is also regulatedTransport is also regulated 7y the compartmental structure of plant cells7y the compartmental structure of plant cells

The plasma membraneThe plasma membrane )irectly controls the traffic of molecules into)irectly controls the traffic of molecules into

and out of the protoplastand out of the protoplast

+s a barrier between+s a barrier between two ma5or compartments,two ma5or compartments,

the cell wall and the cytosolthe cell wall and the cytosol


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The third ma5or compartment in most matureThe third ma5or compartment in most mature

plant cellsplant cells +s the vacuole, a large organelle that can occupy as+s the vacuole, a large organelle that can occupy as

much as 418 of more of the protoplast9s volumemuch as 418 of more of the protoplast9s volume

The vacuolar membraneThe vacuolar membrane egulates transport between the cytosol and theegulates transport between the cytosol and the

vacuolevacuoleTransport proteins in

the plasma membrane

regulate traffic of

molecules between

the cytosol and the

cell wall2

Transport proteins in

the vacuolar

membrane regulate

traffic of moleculesbetween the cytosol

and the vacuole2

Plasmodesma

6acuolar membrane

(tonoplastPlasma membrane

&ell wall

&ytosol

6acuole

Cell compartments.The cell wall, cytosol, and vacuole are the three main

compartments of most mature plant cells2

#a$


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4ey

Symplast

poplast

The symplast is the

continuum of

cytosol connected

by plasmodesmata.

The apoplast is

the continuum

of cell "alls and

etracellular

spaces.

poplast

Transmembrane route

Symplastic routepoplastic route

Symplast

Transport routes bet"een cells. t the tissue level, there are three passages0

the transmembrane, symplastic, and apoplastic routes. Substances may transfer

from one route to another.

#b$


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7ulk low in Long-)istance7ulk low in Long-)istance

TransportTransport +n bulk flow+n bulk flow

"ovement of fluid in the !ylem and phloem is"ovement of fluid in the !ylem and phloem is

driven by pressure differences at oppositedriven by pressure differences at oppositeends of the !ylem vessels and sieve tubesends of the !ylem vessels and sieve tubes


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oots absorb water and minerals from theoots absorb water and minerals from the

soilsoil*ater and mineral salts from the soil*ater and mineral salts from the soil

nter the plant through the epidermis of rootsnter the plant through the epidermis of rootsand ultimately flow to the shoot systemand ultimately flow to the shoot system

"uch of the absorption of water and minerals"uch of the absorption of water and mineralsoccurs near root tips, where the epidermis isoccurs near root tips, where the epidermis ispermeable to water and where root hairs arepermeable to water and where root hairs arelocatedlocated

oot hairs account for much of the surfaceoot hairs account for much of the surfacearea of rootsarea of roots


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(

2

%

ptake of soil solution by the

hydrophilic "alls of root hairs

provides access to the apoplast.

&ater and minerals can then

soak into the corte alongthis matri of "alls.

/inerals and "ater that cross

the plasma membranes of root

hairs enter the symplast.

s soil solution moves along

the apoplast, some "ater and

minerals are transported into

the protoplasts of cells of the

epidermis and corte and then

move in"ard via the symplast.

&ithin the transverse and radial "alls of each endodermal cell is the

Casparian strip, a belt of "ay material #purple band$ that blocks the

passage of "ater and dissolved minerals. Only minerals already in

the symplast or entering that path"ay by crossing the plasma

membrane of an endodermal cell can detour around the Casparian

strip and pass into the vascular cylinder.

7ndodermal cells and also parenchyma cells "ithin the

vascular cylinder discharge "ater and minerals into thei

"alls #apoplast$. The ylem vessels transport the "ater

and minerals up"ard into the shoot system.

Casparian strip

-ath"ay alongapoplast

-ath"ay

through

symplast

-lasma

membranepoplastic

route

Symplastic

route

'oot

hair

7pidermis Corte 7ndodermis 8ascular cylinder

8essels

#ylem$

Casparian strip

7ndodermal cell

! 5

2

(

Lateral transport of minerals and water in root hairs


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*ater and minerals ascend from roots to*ater and minerals ascend from roots toshoots through the !ylemshoots through the !ylem Plants lose an enormous amount of waterPlants lose an enormous amount of water

through transpiration, the loss of water vaporthrough transpiration, the loss of water vaporfrom leaves and other aerial parts of the plantfrom leaves and other aerial parts of the plant

The transpired water must be replaced by waterThe transpired water must be replaced by water

transported up from the rootstransported up from the roots


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Pushing Xylem Sap: RootPushing Xylem Sap: Root

PressurePressure't night, when transpiration is very low't night, when transpiration is very low

oot cells continue pumping mineral ions intooot cells continue pumping mineral ions into

the !ylem of the vascular cylinder, lowering thethe !ylem of the vascular cylinder, lowering thewater potentialwater potential

*ater flows in from the root corte!*ater flows in from the root corte!

:enerating root pressure:enerating root pressure


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Pulling Xylem Sap: ThePulling Xylem Sap: The

Transpiration-Cohesion-TensionTranspiration-Cohesion-TensionMechanismMechanism

*ater is pulled upward by negative*ater is pulled upward by negative

pressure in the !ylem of the leavespressure in the !ylem of the leaves


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Transpirational PullTranspirational Pull

*ater vapor in the airspaces of a leaf*ater vapor in the airspaces of a leaf

diffuses down its water potential gradientdiffuses down its water potential gradient

and e!its the leaf via stomataand e!its the leaf via stomata

Transpiration produces negative pressureTranspiration produces negative pressure

(tension in the leaf which e!erts a pulling(tension in the leaf which e!erts a pulling

force on water in the !ylem, pulling waterforce on water in the !ylem, pulling water

into the leafinto the leaf

%


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7vaporation causes the air9"ater interface to retreat farther into

the cell "all and become more curved as the rate of transpiration

increases. s the interface becomes more curved, the "ater fi lm:s

pressure becomes more negative. This negative pressure, or tension,

pulls "ater from the ylem, "here the pressure is greater.

Cuticle

pper

epidermis

/esophyll

;o"er

epidermis

Cuticle

&ater vapor

CO2 O2


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&ohesion and 'dhesion in the&ohesion and 'dhesion in the

'scent of ;ylem Sap'scent of ;ylem Sap The transpirational pull on !ylem sapThe transpirational pull on !ylem sap

+s transmitted all the way from the leaves to+s transmitted all the way from the leaves to

the root tips and even into the soil solutionthe root tips and even into the soil solution

+s facilitated by cohesion and adhesion+s facilitated by cohesion and adhesion


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'scent of'scent of

!ylem sap!ylem sap


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egulation of Transpirationegulation of Transpiration

Stomata help regulate the rate ofStomata help regulate the rate of

transpirationtranspiration

Leaves generally have broad surfaceLeaves generally have broad surface

areas and high surface-to-volume ratiosareas and high surface-to-volume ratios


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7oth of these characteristics7oth of these characteristics +ncrease photosynthesis+ncrease photosynthesis +ncrease water loss through stomata+ncrease water loss through stomata

$1


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Stomata= "a5or Pathways forStomata= "a5or Pathways for

*ater Loss*ater Loss'bout 418 of the water a plant loses'bout 418 of the water a plant loses

scapes through stomatascapes through stomata


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ach stoma is flanked by guard cellsach stoma is flanked by guard cells *hich control the diameter of the stoma by*hich control the diameter of the stoma by

changing shapechanging shape

Cells flaccid?Stoma closedCells turgid?Stoma open

'adially oriented

cellulose microfibrils

Cell

"all

8acuole

@uard cell

Changes in guard cell shape and stomatal opening

and closing #surface vie"$.:uard cells of a typicalangiosperm are illustrated in their turgid (stoma open

and flaccid (stoma closed states2 The pair of guard

cells buckle outward when turgid2 &ellulose microfibrils

in the walls resist stretching and compression in the

direction parallel to the microfibrils2 Thus, the radial

orientation of the microfibrils causes the cells to increase

in length more than width when turgor increases2

The two guard cells are attached at their tips, so the

increase in length causes buckling2


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&hanges in turgor pressure that open and&hanges in turgor pressure that open and

close stomataclose stomata esult primarily from the reversible uptakeesult primarily from the reversible uptake

and loss of potassium ions by the guard cellsand loss of potassium ions by the guard cells

'ole of potassium in stomatal opening and closing.

The transport of >?(potassium ions, symboli.ed

here as red dots across the plasma membrane and

vacuolar membrane causes the turgor changes of

guard cells2

#$%

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#$%#$%

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>?

#$% #$%

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Phloem TransportPhloem Transport

%rganic nutrients are translocated through%rganic nutrients are translocated through

the phloemthe phloem

TranslocationTranslocation +s the transport of organic nutrients in the+s the transport of organic nutrients in the

plantplant


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"ovement from Sugar Sources"ovement from Sugar Sources

to Sugar Sinksto Sugar Sinks Phloem sapPhloem sap

+s an a/ueous solution that is mostly sucrose+s an a/ueous solution that is mostly sucrose

Travels from a sugar source to a sugar sinkTravels from a sugar source to a sugar sink

' sugar source' sugar source +s a plant organ that is a net producer of+s a plant organ that is a net producer of

sugar, such as mature leavessugar, such as mature leaves

' sugar sink' sugar sink +s an organ that is a net consumer or storer of+s an organ that is a net consumer or storer of

sugar, such as a tuber or bulbsugar, such as a tuber or bulb

7748156 plant transport

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