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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.php7/28/2019 Bio f4_Root Transport 1011
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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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Water Transport into the Roots
Cells are usuallyinterconnected via
plasmodesmata.
Their plasma forms a
continuum (a
symplast).
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Water Transport into the Roots
The transport of substances from cell to cell via
plasmodesmata is called symplastic
transport.
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Water Transport into the Roots
Apoplastic transportis when water is transported between
cells through the extra-cellular space.
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Water Transport into the Roots
The endodermis
functions as a last
checkpoint forthe passage of
dissolved minerals
into the vasculartissue
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Water Transport into the Roots
Minerals already in the symplast when they reach the
endodermis continue through the endodermis and
pass into the xylem
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Water Transport into the Roots
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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Water Transport into the Roots
The only way to get through the endodermis is
through the symplastic route.
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Water Transport into the Roots
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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Water Transport into the Roots
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