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Chapter 36 Transport in Vascular Plants. A. Physical Forces H2OH2O CO 2 O2O2 light sugar H2OH2O CO 2 O2O2 minerals.

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Presentation on theme: "Chapter 36 Transport in Vascular Plants. A. Physical Forces H2OH2O CO 2 O2O2 light sugar H2OH2O CO 2 O2O2 minerals."— Presentation transcript:

1 Chapter 36 Transport in Vascular Plants

2 A. Physical Forces H2OH2O CO 2 O2O2 light sugar H2OH2O CO 2 O2O2 minerals

3 A. Physical Forces H2O and minerals transport in sugars transport in gas exchange xylem moves water because oftranspiration evaporation, cohesion and adhesion phloem bulk flow major substances transported are:

4 transport occurs on cellular from transport of into root hairs short-distance transport from loading of from photosynthetic leaves into phloem sieve tubes long-distance transport transport in throughout whole plant three scales environment into plant cells H 2 O and solutes cell to cell sugar xylem and phloem

5 membranes selective permeability diffusion, passive transport, active transport phospholipid bilayer, protein channels

6 solutes are moved into plant cells by active transport protein in cell membrane mechanism that uses the energy stored in a concentration gradient to drive cellular work Cellular Transport proton pumps use to pump against the concentration gradient the cell sets up a separation of across a membrane active transport chemiosmosis – ATPH + (hydrogen) ions out of membrane potential – opposite charge

7 The Proton Pump

8 both the proton pump and membrane potential have which is used to drive the transport of many different solutes stored energy


10 water uptake and loss must be Water Potential water moves by add which affects osmosis water potential,, takes both and into account measured in balanced osmosis cell wallsphysical pressure Ψ solute (dissolved substances) concentration physical pressure megapascals, MPa (or bars)

11 Ψ = Ψ S + Ψ P where: Ψ = water potential Ψ S = solute potential (osmotic potential) Ψ P = pressure potential the Ψ S of pure water is Pure water = 0 MPa zero

12 adding solute the water potential (because there is less free water molecules less capacity to do work) and Ψ S is Addition of solutes 0.1 M solution Pure water = 0 MPa = –0.23 MPa P = 0 S = –0.23 H2OH2O lowers negative

13 Ψ P can be relative to atmospheric pressure Applying physical pressure = 0 MPa P = 0.23 S = –0.23 Applying physical pressure = 0 MPa = 0.07 MPa P = 0.30 S = –0.23 H 2 O Pure water Pure water positive or negative

14 water under (pulling) gives pressure eg) water in xylem Negative pressure = –0.23 MPa P = 0 S = –0.23 = –0.30 MPa P = –0.30 S = 0 H 2 O Pure water tensionnegative

15 water gives pressure eg) turgor pressure water always moves from areas of to areas of water moves through the phospholipids bilayer and through transport proteins called cells will be or depending on the environment plasmolyzedturgid pushing outpositive high Ψ low Ψ aquaporins plasmolyzedturgid

16 loss of turgor causes wilting

17 plant cells are compartmentalized Short-Distance Transport cell wall cell membrane – cytosol vacuole Plasmodesma Plasma membrane Cell wall Cytosol Vacuole Vacuolar membrane (tonoplast)

18 transport routes for water and solutes transmembrane route repeated of plasma membrane Transmembrane route crossing

19 symplast route Key Symplast Symplastic route Symplast Transmembrane route movement within plasmodesmata junctions connect cytosol of neighboring cells cytosol

20 Key Symplast Apoplast Apoplastic route Apoplast Symplast Transmembrane route Symplastic route apoplast route movement through the continuum of from cell to cell no cell membranes are crossed cell walls

21 which is the movement of fluid driven by Long-Distance Transport lack of some organelles in phloem cells and the complete lack of cytoplasm in xylem cells makes them very efficient tubes for transport flow in xylem tracheids and vessels creates which xylem sap upwards from roots loading of sugar from photosynthetic leaf cells generates high positive pressure which pushes phloem sap through sieve tubes bulk flow pressure transpiration negative pressure pulls

22 much of the absorption of takes place at the root tips B. Roots root hairs extensions of walls are huge amount of water and minerals epidermal cells hydrophilic surface area

23 soil solution moves into flows through solution moves into of root cells water moves from Ψ in soil to Ψ in root active transport concentrates certain molecules in the root cells eg) K + ions apoplast walls into cortex symplast high low

24 mycorrhizae symbiotic structures plant roots with fungus greatly increases surface area for water and mineral absorption greatly increases volume of soil reached by plant

25 endodermis layer surrounding vascular cylinder of root lined with impervious forces solution through selective cell membrane and into symplast also prevents leakage of xylem sap back into soil solution in endodermis and parenchyma cells is discharged into cell walls (apoplast) by this allows the solution to then move to the xylem cells Casparian strip active and passive transport

26 Casparian strip Endodermal cell Pathway along apoplast Pathway through symplast Casparian strip Plasma membrane Apoplastic route Symplastic route Root hair Vessels (xylem) Cortex EndodermisEpidermisVascular cylinder

27 root pressure C. Ascent of Xylem Sap in xylem of roots the Ψ water flows causing pressure of xylem sap accounts for of ascent of sap mineral ionslowers in root pressure positive upward push very small part

28 generated by powered Ψ in leaf is than Ψ in water vapour leaves the leaf through the stomata (transpiration) water transpiration pull Ψ is in roots and in leaves, moves water plant adhesion, cohesion, hydrogen bonding leaf solar higher atmosphere pulled up highlow up

29 Xylem sap Mesophyll cells Stoma Water molecule Atmosphere Transpiration Xylem cells Adhesion Cell wall Cohesion, by hydrogen bonding Cohesion and adhesion in the xylem Water molecule Water potential gradient Root hair Soil particle Water Water uptake from soil Trunk xylem Ψ = –0.8 Mpa Root xylem Ψ = –0.6 MPa Leaf Ψ (air spaces) = –7.0 MPa Outside air Ψ = –100.0 MPa Leaf Ψ (cell walls) = –1.0 MPa Soil Ψ = –0.3 MPa

30 photosynthesis and transpiration D. Stomata compromise in and out but also out leaf transpires more than its weight in a day xylem sap can flow at 75 cm/min O2,H2OO2,H2O CO 2 O2O2 H2OH2O

31 H 2 O evaporation takes place even with drought will cause wilting transpiration causes of the leaves closed stomata evaporative cooling

32 regulation of stomata microfibril mechanism guard cells attached at tips contain microfibrils in cell walls guard cells elongate and bow out when turgid guard cells shorten and become less bowed when flaccid Cells turgid/Stoma open Radially oriented cellulose microfibrils Vacuole Cell wall Guard cell Cells flaccid/Stoma closed

33 ion mechanism proton pumps are used to move into guard cells (stored in vacuoles) Ψ in cells than surrounding cells H 2 O moves of K + ions causes H 2 O to move of guard cells become and Cells turgid/Stoma open Cells flaccid/Stoma closed H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O K+K+ guard cells become and K + ions lower in turgidopen loss out flaccid close

34 other cues light blue-light receptors in plasma membrane triggers ATP-powered proton pumps causing K + uptake stomata open depletion of CO 2 CO 2 in air spaces in mesophyll is used for photosynthesis depletion causes stomata to open

35 circadian rhythm automatic 24-hour cycle stomata open in day, close at night

36 xerophytes plants adapted for small, thick leaves adapted to water loss reflective leaves hairy leaves stomata in pores on underside of leaves alternative photosynthetic pathway (CAM) arid regions reduce

37 is the transport of organic nutrients E. Organic Nutrients water phloem contains: sugar (sucrose) (30% by weight) minerals amino acids hormones translocation sap

38 sieve tubes carry sap from to sap flow rate can be as high as 1 m/hr sugars are loaded into the flow through via active of sucrose into phloem cells with H + ions in proton pump sugar source (leaves) sugar sink (growing roots, buds, stems and fruit) variable direction of flow phloem symplastplasmodesmata cotransport

39 Mesophyll cell Cell walls (apoplast) Plasma membrane Plasmodesmata Companion (transfer) cell Mesophyll cell Bundle- sheath cell Phloem parenchyma cell Sieve-tube member Proton pump Low H + concentration Sucrose High H + concentration Cotransporter Key Apoplast Symplast

40 pressure flow Ψ in is than in the xylem at because of the that takes place H 2 O diffuses from xylem is generated which causes the through phloem sieve tubes Ψ in is than in the xylem at because of the from the phloem H 2 O diffuses from phloem phloemlower sugar sourcesugar loading into phloem positive pressure sap to move phloemhigher sugar sinks back into xylem sugar being removed

41 Vessel (xylem) Sieve tube (phloem) Sucrose Source cell (leaf) H2OH2O H2OH2O Sucrose Sink cell (storage root) H2OH2O Pressure flow Transpiration stream low Ψ high Ψ low Ψ high Ψ

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