water movement ...awais

7/25/2019 Water Movement ...Awais

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There are two ways for water to enter into theplant roots Active Transport

Passive TransportActive Transport:

Water is absorbed due to activities going on inroots. Absorption of water occurs with the

help of energy in the form of ATP. Absorptiontakes

How Water Enters TheRoot


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place against concentration gradient - evenwhen the concentration of cell sap is lowerthan that of soil water.

Passive Transport:Passive absorption is by osmosis. Passiveabsorption takes place along theconcentration gradient - when the

concentration of cell sap is higher than that ofsoil water. Water is absorbed

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when transpiration rate is high or soil is dry.Due to high transpiration rate, water decit iscreated in transpiring cells. !apidtranspiration removes water and reducesturgor pressure in living cells of root. Thesuction force thus developed is transmitted toroot "ylem. #t pulls water from surroundingroot cells to make up water decit.

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Difusion:

Di$usion is the movement of molecules froma region of high concentration to a region of

low concentration by means of randommolecular motion.

Di$usion re&uires kinetic energy from theenvironment but does not re&uire cellular

energy. 'ence di$usion is a form of passivetransport.

Cont


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Osmosis:

(mosis is di$usion of water across asemipermeable membrane. Again (smosis

like di$usion in general does not re&uire anycellular energy but )ust the kinetic energyrelated to the heat on either side of themembrane. 'ence its also a passive transport.

Aquaporins:Are transport proteins in the cell membrane

that allow the passage of water.

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*ost of the water absorbed by plants comes inthrough root hairs

-+ollectively provide enormous surface area

Water ovement in Roots

-Almost alwaysturgid becausetheir waterpotential is greaterthan that of soil


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An e"penditure of energy is re&uired for ions toaccumulate in root cells

-(nce in the roots, the ions are transported

via the "ylem throughout the plant

urface area for water and mineral absorptionis further increased by mycorrhial fungi

-Particularly helpful in phosphorus uptake

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Cont


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Three transport routes e"ist through cells

-Apop!ast route1 *ovement through thecell walls and the space between cells

-"#mp!ast route1 A cytoplasm continuumbetween cells connected by plasmodesmata

-Transmem$rane route1 *embranetransport between cells and across the

membranes of vacuoles within cells-Permits the greatest control

//

Cont


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Ce!! wa!! P!asmo%esmaP!asma mem$rane

Apop!ast route

"#mp!ast route

Transmem$rane route

&acuo!e

+ont3


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4ventually on their )ourney inward, moleculesreach the endodermis

-Any further passage through the cell walls is

blocked by the +asparian strips-*olecules must pass through the cell

membranes and protoplasts of theendodermal cells to reach the "ylem

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Cont

C i ht * Th + Hi!! C i P i i i % /


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H'O an%

minera!s

En%o%ermis

(#!em

Ph!oem

Casparian strip

Ce!! mem$rane

En%o%erma! ce!!

apop!astic routes#mp!astic route

H'O an%

minera!s

H'O an%

minera!s

H'O an%

minera!s

Cop#ri)ht * The c+raw,Hi!! Companies- nc. Permission require% /orrepro%uction or %isp!a#.


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7ateral transport of water in roots

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8ptake of soil solution by thehydrophilic walls of root hairsprovides access to the apoplast.Water and minerals can then

soak into the corte" alongthis matri" of walls.

*inerals and water that crossthe plasma membranes of roothairs enter the symplast.

As soil solution moves alongthe apoplast, some water andminerals are transported intothe protoplasts of cells of theepidermis and corte" and thenmove inward via the symplast.

Within the transverse and radial walls of each endodermal cell is the+asparian strip, a belt of wa"y material 9purple band: that blocks thepassage of water and dissolved minerals. (nly minerals already inthe symplast or entering that pathway by crossing the plasmamembrane of an endodermal cell can detour around the +asparianstrip and pass into the vascular cylinder.

4ndodermal cells and also parenchyma cells within thevascular cylinder discharge water and minerals into thewalls 9apoplast:. The "ylem vessels transport the waterand minerals upward into the shoot system.

+asparian strip

Pathway alongapoplast

Pathwaythroughsymplast

Plasmamembrane

Apoplasticroute

ymplasticroute

!oot

hair

4pidermis +orte" 4ndodermis;ascular cylinder

;essels9"ylem:

+asparian strip

4ndodermal cell

2 3

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Water rst enters the roots and then movesto the "ylem, the innermost vascular tissue.

Water rises through the "ylem because of acombination of factors.

There are to types of movement on the basis

of distance covered.

Water ovement in P!ant

4Root to "tomata5


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"hort,%istance movement:

*ovement of water at the cellular level playsa ma)or role in bulk water transport. Watercan di$use through cell membranes.9'erbaceous: 6on),%istance movement:

Water movement in most of the vascular

plants from roots to leaves. 9ometimes morethan /00m:

Cont..


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Potentials are a way to represent free energy

Water potentia!4w5is used to predict which

way water will move

-*easured in units of pressure calledme)apasca!s 4Pa5

/ 0 *Pa:The total potential energy of water in the cell

w 7 p 8 s

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Water Potentia!


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When a cell is placed in pure water, watermoves into the cell because the waterpotential of the cell is relatively negative

When a cell is placed in a solution with adi$erent s, water moves in the direction that

eventually result in e&uilibrium

-?oth cell and solution have the same w

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Water Potentia!

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p# ) p qrepro%uction or %isp!a#.

Tur)or pressure p7,9.3Pa

Pressure Potentia! p

Ce!! wa!!

Ce!!mem$rane

Pure water

Wa!!pressure

"o!ute Potentia! s

Water Potentia!

s7,9.'Pa

7 s8 p

watermovement

a.

b.

c.

8

s79.;Pa

"ucrosemo!ecu!es

ce!!7 9.; Pa 8 9.3 Pa 7 9.' Pa

so!ution 7 9.' Pa 4so!ution has no pressure potentia!5

Ce!! nitia!!# ntro%uce% into "o!ution


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Ce!! p7 9

9.; Pa 7

s8 9 Pa

s7 9.; Pa

.

.

Ce!! nitia!!# ntro%uce% into "o!ution

"o!utions7 9.;

Pap7 9 Pa

Ce!!s7 9.'

Pap7 9.3

Pa

Ce!! at Equi!i$rium s P!asmo!#


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A&uaporins are water channels that e"ist invacuole and cell membranes

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Water Potentia!

-They speed uposmosis, withoutchanging the

direction ofwater movement


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Water potential regulates movement of waterthrough the whole plant as well

-Water moves from the soil into the roots only

if the soil@s water potential is greater-#t then moves along gradients of

successively more negative waterpotentials in the stems, leaves and air

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Water Potentia!


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4vaporation of water in a leaf creates negativepressure or tension in the "ylem

-This Bnegative water potentialC literally pulls

water up the stem from the rootsThe driving force for transpiration is the

gradient in vapor pressure

-rom /00E relative humidity inside the leaf,

to much less than /00E outside the stomata

2F

Water Potentia!


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There are three main forces for watermovement trough "ylem

Transpiration Pull +ohesion Adhesion orces

9+ohesive Tension Theory: !oot Pressure

echanisms o/ Water

ovement Trou)h (#!em


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Transpiration Pu!!:#t is the pulling force responsible for lifting thewater column. As water is lost in form of watervapour to atmosphere from the mesophyllcells by transpiration, a negative hydrostaticpressure is created in the mesophyll cellswhich in turn draw water from veins of the

leaves.

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The negative tension is then graduallytransmitted downwards via "ylem tissues ofthe leaf, stem and nally to the roots. As a

result there is a continuous upwardmovement of water column in the plant.Thus the transpiration pull acts as pull from

above on the-whole of water column of the

plant which pushes the water column of"ylem vessels of roots lowers leaves i.e. inan upward direction. This is how ascent ofsap is a$ected in plants.

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Cohesion A%hesion =orces:9+ohesive Tension Theory:

The water molecules in the chain are heldtogether by hydrogen bonds which e"ist

between neighboring water molecules.9cohesion:

The chain of molecules is prevented from beingpulled down because each water molecule in

the chain is attracted to the walls of the "ylemby hydrophilic attraction between water andthe cellulose in the cell walls. 9Adhesion:

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'ence the water column which is heldtogether by cohesion and prevented fromlowering by adhesion is pulled up by thetension generated from above by

transpiration.

#t is valuable both for herbaceous grasses as

well as vascular plant.

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Root Pressure:!oot pressure is caused by active transport ofmineral nutrient ions into the root "ylem. Withouttranspiration to carry the ions up the stem, they

accumulate in the root "ylem and lower the waterpotential. Water then di$uses from the soil into theroot "ylem due to osmosis. !oot pressure is causedby this accumulation of water in the "ylem pushingon the rigid cells. !oot pressure provides a force,which pushes water up the stem, but it is notenough to account for the movement of water toleaves at the top of the tallest trees.

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5F

Air

P!ant

99.30.9 099

wWater potentia! 4Pa5

D e c r e a s

i n )

w a

t e r

p o

t e n t

i a !

The water >!m thatcoats mesoph#!!ce!! wa!!s evaporates.Ripp!e% ce!! sur/acesresu!t in hi)her rate o/transpiration thansmooth ce!! sur/aces.

"moothsur/ace

Ripp!e%sur/ace

Cohesion $#h#%ro)en $on%in)$etween watermo!ecu!es

A%hesion %ue to po!arit#o/ water mo!ecu!es

Water e?its p!antthrou)h stomata.

Water moves up p!antthrou)h ?#!em.

Water

entersp!antthrou)hroots.

"oi!

Proton pumpscontri$ute to thew)ra%ient that

%etermines the%irectiona! @ow

o/ water.

C#toso!

"oi!

H8

inera!ions

Water

Protonpump

H'O

H'O

"oi!

Air

P!ant

9 9.30.9 099

wWater potentia! 4Pa5

D e c r e a s

i n )

w a

t e r

p o

t e n

t i a !

The water >!m thatcoats mesoph#!!ce!! wa!!s evaporates.Ripp!e% ce!! sur/acesresu!t in hi)her rate o/transpiration thansmooth ce!! sur/aces.

"moothsur/ace

Ripp!e%sur/ace

Cohesion $#h#%ro)en $on%in)$etween watermo!ecu!es

A%hesion %ue to po!arit#o/ water mo!ecu!es

Water e?its p!antthrou)h stomata.

Water moves up p!antthrou)h ?#!em.

Water

entersp!antthrou)hroots.

"oi!

Proton pumpscontri$ute to thew)ra%ient that

%etermines the%irectiona! @ow

o/ water.

C#toso!

"oi!

H8

inera!ions

Water

Protonpump

H'O

H'O

"oi!


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0. Ph#sica! =actors:a5 "oi! =actors

oil water contents

oil Temperatureoil Aeration

looding

Te"ture and tructure

peed of Water *ovement

4$ective !oot Gone

=actors Afectin) The WaterA$sorption in P!ants


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$5 Atmospheric =actors:Temperature

!elative 'umidity

;DPWind peed

tress 9chemical:

'. io!o)ica! =actors

Plant +lass 9'erbaceous or ;ascular :

!oot 7ength

Cont


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!oot ystemPlant 'ealth

?iological tresses

Tolerance to tresses 9alinity:Henetic *akeup

Hrowth !ate

Hrowth 'ormones

Cont


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water movement ...awais

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