TRANSPORT IN PLANTS

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2 types of transport tissue:XYLEM & PHLOEM

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Vascular Cambium

creates new xylem cells on the inside, and new phloem cells on the outside.

XYLEM & PHLOEM anatomy:

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companion cells

plasmodesmata

sieve cells

XYLEM~ moves water and minerals

• Acts like a bundle of straws

• functions via. negative pressure

• “sucking”• http://

www.youtube.com/watch?v=Ir9bm3fli90

XYLEM cells (transport water & dissolved minerals)

~2 kinds of cells:

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* Conifers, have only these

* Pits (holes) between and surrounding these~

* Dead & hollow at maturity

Tracheid = single cell, elongated, tapered ends (wall composed of cellulose)

XYLEM cells~ 2 kinds:

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Vessel Element = numerous elongated cells make up this tube. (typically smaller in length than tracheids, but wider in diameter)

* Conifers do not have these

* Have “pits” or openings on their ends and are stacked to create one long “pipe”

* Carry more water than tracheids

* Dead & hollow at maturity

XYLEM ~ water movement b/c of 2 forces:

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1) Transpirational pull

- via. negative pressure as water is evaporated out of the

stomatahttp://www.youtube.com/watch?v=EKyHbanzYnI&feature=related

XYLEM ~ water movement b/c of 2 forces:

1) Transpirational pull

- via. negative pressure

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2) Root Pressure - more negative water potential in the root as compared to the

outside soil

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2) Root Pressure - water moves from the soil… into

the root

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PHLOEM~ has 2 types of cells:

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companion cells

sieve tube cells

PHLOEM

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companion cells:

nucleus

sieve tube cells:

no nucleus

both types are alive

How do solutions move through the PHLOEM ~ Ernst Munch 1933

PRESSURE FLOW

HYPOTHESISQuickTime™ and a decompressor

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How do solutions move through the PHLOEM ~ Ernst Munch 1933

PRESSURE FLOW

HYPOTHESISQuickTime™ and a decompressor

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Solutes move through plants as a result of

pressure gradients, not negative pressure

(aka. pulling)

• SOURCE = area of excess sugar supply

aka. leaf in the summer

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• SINK = area of storage aka. roots in the summer & winter

• SINK = area of storage aka. leaf are

in the spring

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• SOURCE = area of excess sugar supply aka. roots in the spring.

TRANSPORT OF SAP

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source

1) @ SOURCE, sucrose moves from mesophyll cells into companion cells via. active transport

Phloem companion cell

sugar

(Photosynthesizing cell)

TRANSPORT OF SAP

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source

2) Companion cells move sap into SIEVE TUBE CELLS via. active transport

sugar

Photosynthesizing cellPhotosynthesizing cell

Phloem companion cell

Mineral absorption

• Proton pumps– active transport (ATP) of H+ ions out of cell

• chemiosmosis• H+ gradient

– creates membranepotential• difference in charge• drives cation uptake

– creates gradient• cotransport of other

solutes against theirgradient

H+

H+

H+

H+

H+

H+

H+

H+

H+

sugar

ATP

TRANSPORT OF SAP

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3) Sugar accumulates in SIEVE TUBES, thus decreasing (lowering) water potential (aka. making more negative)

sugar

Phloem companion cell

TRANSPORT OF SAP

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4) WATER then, moves in from the XYLEM (as a result)… thus increasing turgor pressure in SIEVE TUBES -->

H2Osugar

Phloem companion cell

Maple sugaring

TRANSPORT OF SAP

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5) thus moving sugar to areas of lower pressure (the sink).

sugar

Phloem companion cell

H2O

TRANSPORT OF SAP

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source

6) @ sink, sugar is unloaded from sieve tubes, thus INCREASING water potential...

sugar

Phloem companion cell

TRANSPORT OF SAP

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7) Water moved back into xylem… and UP via. negative pull

H2Osugar

Phloem companion cell

Pressure Flow Hypothesis

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Don’t get mad…

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