bio f4_root transport 1011

7/28/2019 Bio f4_Root Transport 1011

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Review: Root Anatomy

Three regions

Meristematic

Elongation

Maturation


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Root hairs and

branching greatly

increase the

surface through

which water and

dissolved minerals

can be absorbed.
http://botit.botany.wisc.edu/images/130/Root/Grass_Seedling_root/Root_hair.php


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Functions of Roots

Absorption

Anchorage

Storage

Conduction of water Hormone synthesis

TODAY

TOMORROW


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Uptake ofIons by the Roots WHAT?

Root hairs bring

nitrates,

phosphates,sulphates, and a

variety of other

essential inorganicnutrients into the

plant

Why are these

nutrientsneeded?


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Uptake of Ions by the Roots HOW? Root interception

Root grows and intercepts ions

Simple diffusion Ions move down their concentration gradient

No energy expense by plant

Example: K+

Mass flow Bulk flow of water into the root carries ions to root

Delivers N, Ca, Mg, S

Active transport Ions move against their concentration gradient

Requires a specific protein pump in the cell membrane

Energy expense by plant


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Water Transport into the Roots

Water flows from

SOIL

EpidermisRoot CortexEndodermisXylem

via osmosis


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Cells are usuallyinterconnected via

plasmodesmata.

Their plasma forms a

continuum (a

symplast).


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The transport of substances from cell to cell via

plasmodesmata is called symplastic

transport.


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Apoplastic transportis when water is transported between

cells through the extra-cellular space.


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The endodermis

functions as a last

checkpoint forthe passage of

dissolved minerals

into the vasculartissue


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Minerals already in the symplast when they reach the

endodermis continue through the endodermis and

pass into the xylem


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Minerals that reach the

endodermis via the

apoplast encounter a

waxy layer on the

endodermis that blocks

their entry into the

xylem called theCasparian strip.


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The only way to get through the endodermis is

through the symplastic route.


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Water and minerals

following the

apoplastic route

must first cross theplasma membrane

of the endodermis

cells and enter thesymplast system. This ensures that no minerals

can enter the vascular systemwith out first being checked by

the plasma membrane


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Once through

the endodermis

layer, the water

and minerals are

now free to

enter the xylem

tracheids and

vessels.


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Uptake of water through

root epidermis by osmosis

Water that crosses the

root hair plasma membrane

enters the symplast system

Water that does not cross the

root hair plasma membrane

enters the apoplast system

The Casparian Strip blocks

passage of water unless it

is moving via the symplast

Water moves into the

xylem for transportup the plant

bio f4_root transport 1011

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