transport in plants - seattlecentral.edu 36 - transport... · 1 transport in plants figure 36.1 an...

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Transport in plantsTransport in plants

Figure 36.1 An overview of transport in whole plants (Layer 1)Figure 36.1 An overview of transport in whole plants (Layer 1)

1) Roots

absorb water and dissolved

minerals from soil

2) Water and

minerals transported

upward form roots to

shoots in xylem

3) Transpiration

creates a force that pulls water

upward in xylem


4. Gas exchange occurs through the

stomata

5. Sugar is produced in the leaves


6. Sugar is

transported to other

parts of plant in

phloem


7. Respiration in the roots

leads to gas exchange

There are three levels of transport in There are three levels of transport in

plants:plants:

►►the individual cell level (membrane the individual cell level (membrane

transport)transport)

�� uptake and export of materials in root cellsuptake and export of materials in root cells

►►short distance short distance -- cell to cell cell to cell

�� sugar loading from mesophyll to phloemsugar loading from mesophyll to phloem

►► long distance transport long distance transport –– tissue to tissue or tissue to tissue or

organ to organorgan to organ

�� xylem and phloemxylem and phloem

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UniportUniport UniportUniport

COTRANSPORTCOTRANSPORTWater movement in plants is driven Water movement in plants is driven

by three processesby three processes

►►DiffusionDiffusion

►►OsmosisOsmosis

►►Bulk FlowBulk Flow

Water potential Water potential ((ΨΨ))

►►term used to characterize the energy state term used to characterize the energy state

of waterof water

►►free energy of water (that which is available free energy of water (that which is available

to do work~ potential energy of water). to do work~ potential energy of water).

►►differences in water potential drive water differences in water potential drive water

transport in plantstransport in plants

►►water potential is measure in water potential is measure in MPaMPa

Water potentialWater potential

►►In plants water potential has two partsIn plants water potential has two parts

�� ΨΨ SS = osmotic potential= osmotic potential

�� ΨΨ p p = hydrostatic potential (pressure potential)= hydrostatic potential (pressure potential)

►►Ψ= ΨΨ= Ψss + + ΨΨpp

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Water potentialWater potential

►►Water moves from regions where the water Water moves from regions where the water potential is relatively positive to areas where potential is relatively positive to areas where it is relatively negative. it is relatively negative.

►►The addition of solutes will lower the water The addition of solutes will lower the water potential (water will form a shell around a potential (water will form a shell around a solute and will move less freely than if only solute and will move less freely than if only in water). in water).

►►There are three assumptions of these There are three assumptions of these statements:statements:

►► water moves whenever there is a difference in water moves whenever there is a difference in water potential within the mass of water.water potential within the mass of water.

►► if water potentials of two regions are equal, the if water potentials of two regions are equal, the regions are in equilibrium and there will be no net regions are in equilibrium and there will be no net movement of water. movement of water.

►► water potentials must always be considered in water potentials must always be considered in pairs or groups because the movement of water is pairs or groups because the movement of water is due to the relative differences between areas.due to the relative differences between areas.

Figure 36.3 Water potential and water movement: a mechanical moFigure 36.3 Water potential and water movement: a mechanical modeldel

Water potential is

higher on the left side and lower on

the left side.

0 MPa vs. -.023MPa

The application of

pressure increases the water potential

on the right side so that now the two

sides are equal

When the

application of pressure is more

than the osmotic potential, water will

move in the opposite direction

(to the left)

When the

application of pressure is negative

relative to the right side, water will

move to the left

Q: Which way will the water move?Q: Which way will the water move?

-100-1000B (outside cell)

- 353-100-253A (inside cell)

Location Ψ s + Ψ p = Ψ

A: from B to A (to inside the cell)A: from B to A (to inside the cell)

Turgor PressureTurgor Pressure

►►fully supplied with water, plant cells exhibit fully supplied with water, plant cells exhibit

a a positivepositive hydrostatic pressure hydrostatic pressure

►►caused by the flow of water into the plant caused by the flow of water into the plant

cell and its pushing back onto the cell wall cell and its pushing back onto the cell wall

Figure 36.4 Water relations of plant cellsFigure 36.4 Water relations of plant cells

Water relations of plant cells –

cellular Ψ > Ψ > environmentalΨ

Cell plasmolyzes

Water relations of plant cells –

cellular Ψ < Ψ < environmentalΨ

−0.7 MPa vs O MPa

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Figure 36.5 A watered tomato plant regains its turgorFigure 36.5 A watered tomato plant regains its turgor


plants:plants:









Figure 36.6 Compartments of plant cells and tissues and routes Figure 36.6 Compartments of plant cells and tissues and routes for lateral transportfor lateral transport Figure 36.7 Lateral transport of minerals and water in rootsFigure 36.7 Lateral transport of minerals and water in roots


plants:plants:









Figure 36.8 Mycorrhizae, symbiotic associations of fungi and roFigure 36.8 Mycorrhizae, symbiotic associations of fungi and rootsots

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TRANSPIRATIONTRANSPIRATION►► is driving force for movement of water in is driving force for movement of water in the plantthe plant

►►Defined as the loss of water vapor from Defined as the loss of water vapor from leaves, which must be replaced continuously leaves, which must be replaced continuously

►►Q. What three forces are working to move Q. What three forces are working to move water up the stems? water up the stems?

►►A. Partially driven by cohesion, adhesion, A. Partially driven by cohesion, adhesion, surface tension surface tension

(hydrogen bonding OH MY (hydrogen bonding OH MY ☺☺!)!)

S S –– soilsoil

P P –– plantplant

A A –– airair

CC-- continuumcontinuum

The SPACThe SPAC

►►driving force in the SPAC is the continuously driving force in the SPAC is the continuously

decreasing value of decreasing value of Ψ.Ψ.►►No one point in space is isolated, movement No one point in space is isolated, movement

always depends on what is behind it and always depends on what is behind it and

ahead of it.ahead of it.

►►Atmosphere has a very low Atmosphere has a very low ΨΨ

GuttationGuttation

Figure 36.10 The generation of Figure 36.10 The generation of transpirationaltranspirational pull in a leafpull in a leaf Figure 36.11 Ascent of water in a treeFigure 36.11 Ascent of water in a tree

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Figure 36.13a The mechanism of Figure 36.13a The mechanism of stomatalstomatal opening and closingopening and closing

NIGHTΨ guard cell = Ψ adjacent cell

DAYΨ guard cell ≠ Ψ adjacent cellΨ is lower than adjacent cellSo water moves into the cell

►DAWN: Ψ guard cell ≠ Ψ adjacent cell

� Ψ in guard cell is < than adjacent cell

� Guard cells pump in K+, osmotic potential � (Ψs); water � the guard cell

►DAY Ψ guard cell = Ψ adjacent cell

� as Ψs � so does the Ψp until cell is in equilibrium with adjacent cells (net water movement stops)

� cell is turgid, stomata are open

►NIGHT Ψ guard cell ≠ Ψ adjacent cell

� K+ is pumped back into adjacent cells

� Equilibrium is reached and the guard cells are flaccid and the stoma is closed.

Figure 36.13b The mechanism of Figure 36.13b The mechanism of stomatalstomatal opening and closingopening and closing Figure 36.12 An open (left) and closed (right) stoma of a spideFigure 36.12 An open (left) and closed (right) stoma of a spider plant r plant ((ChlorophytumChlorophytumcolosumcolosum)) leafleaf

►► Transpiration rates are affected by environmental Transpiration rates are affected by environmental

factorsfactors

�� Wind, humidity, temperature, soil moisture, brightness Wind, humidity, temperature, soil moisture, brightness

of lightof light

Which of the following conditions Which of the following conditions

would increase transpiration? Which would increase transpiration? Which

would decrease transpiration?would decrease transpiration?

►►A windy day? A windy day?

►►A rainy day?A rainy day?

►►A hot day?A hot day?

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Figure 36.16 Loading of sucrose into phloemFigure 36.16 Loading of sucrose into phloem

Figure 36.17 Pressure flow in a sieve tubeFigure 36.17 Pressure flow in a sieve tube

Figure 36.18 Tapping phloem sap with the help of an aphidFigure 36.18 Tapping phloem sap with the help of an aphid

transport in plants - seattlecentral.edu 36 - transport... · 1 transport in plants figure 36.1 an...

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