Intro to Lab #9 / Chpt. 36
Plant Structure and Transport
pg. 744 - 753
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Transport in
Did you know,
an
Plants
average size maple tree
looses 200 L of water per
hour during the summer
via. transpiration.
What would happen if
this water were not
replaced by the
Question ?
• How do
plants move
materials
from one
organ to the
other ?
TRANSPIRATION
TRANSPIRATION -
when a plant looses water vapor
from
the inside of the leaf, to
the outside environment -via.
COHESION
- TENSION
THEORY water is
pulled up from
roots to leaves
via. higher  in
the leaf to a
Water & mineral absorption to Xylem:
• Water absorption from soil
- osmosis
- aquaporins
ROOT HAIRS = increase surface area
for the absorption of water & minerals
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Water & mineral absorption to Xylem:
 Mineral absorption
– active transport
– proton pumps
• active transport of H+
proton pumps
Water & mineral absorption to Xylem:
• Proton pumps
– active transport of H+ ions out of cell
• chemiosmosis
• H+ gradient
– creates membrane
potential
• difference in charge
• drives cation uptake
– creates gradient
• cotransport of other
solutes against their
gradient
proton pumps
Transport in
uptake and
loss by individual
Plants
cells:
The survival of plant cells
depends on the ability to
balance the uptake & loss
of H2O
Remember this?
*Presence of the cell wall
adds physical pressure, this
affects movement into the
cell negatively!
Remember this?
*Solute concentration
also affects movement:
Transport in
HowPlants
can we predict the
direction of osmosis when a
plant cell is surrounded by a
solution???
Transport in
Plants

Remember this?

Water moves from the
solution of higher water
potential, to a solution of
lower water potential.
For plants, it is not just enough
to know if the extracellular
solution
is
hypotonic
or
Remember this?

*Measured in MEGAPASCALS
• Has two components:
–Pressure potential: yr
–Solute potential: yp
y = yr + yp
Remember this?
You have to know these two numbers
first, when determining water potential.
You must know water potential in order
to know which direction water will move!

Pressure potential:
yr Solute potential:
yp
Remember this?

Remember this?

any
solution
will have a
negative
w.p. adding
solutes,
lowers
w.p.
Transport in
Plants
*Solute
concentration
affects movement
Transport in
*ExternalPlants
pressure on a
solution counters its
tendency to take up water
due to the presence
of solutes
Transport in
Plants



=
+
P
S
Transport in
Plants
the force that

=
moves water
across the
membranes of
plant cells
COHESION
- TENSION
THEORY water is “pulled”
b/c of it’s
cohesive
property
Evolutionary
advantage of
ROOT HAIRS:
add surface
area thus increasing
amount of
H20/mineral
solution coming
Mycorrhizae increase absorption
• Symbiotic relationship between fungi & plant
– symbiotic fungi greatly increases surface
area for absorption of water & minerals
– increases volume of soil reached to plant
– increases transport to host plant
Mycorrhizae
COHESION
- TENSION
THEORY Because
higher water
potential
outside
COHESION TENSION
THEORY minerals absorbed
from soil into root~
creates “root
pressure” that
pushes H2O/soil
solution into xylem
COHESION - TENSION
THEORY -
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• uptake of
soil solution
by root hairs
to apoplastic
route through the
cell walls
Transport routes in plant cells
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COHESION - TENSION
THEORY -
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
• uptake of
minerals &
water by root
hairs to
symplastic
route - through
plasmodesmata
Transport routes in plant cells
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Controlling the route of water in root
• Endodermis
– cell layer surrounding vascular cylinder of root
– lined with impermeable Casparian strip
– forces fluid through selective cell membrane
• filtered & forced into xylem cells
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Controlling the route of water in
root
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
• some soil
solution from
apoplast route,
diffuses into the
symplastic
route -through
the plasma
membrane
COHESIO
NTENSION
THEORY Water then
travels thru the
root where the
Casparian strip
forces H2O into
REMEMBER: the
casparian strip blocks
water from entering via.
The apoplastic route
COHESION - TENSION
THEORY -
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.

• only minerals in
the symplastic
route can
detour around
the Casparian
Strip AND
PASS INTO
THE
VASCULAR
Root anatomy
eudicot
monocot
COHESION - TENSION
THEORY -
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
•  XYLEM
vessels
transport
water and
minerals
upward into
the shoot
system (stem
and veins)
COHESION
- TENSION
THEORY problem… this can
only take the
water “so far”
COHESIO
NTENSION
THEORY At the leaf of the
plant, water loss
due to
Evaporating H2O decreases the
water potential of the leaf.
Since water flows from higher
water potential to lower, the water
is pulled up the xylem with the
minerals.
Transport of sugars in phloem
• Loading of sucrose into phloem
– flow through cells via plasmodesmata
– proton pumps create energy potential/proton gradient
• cotransport of sucrose into cells down proton gradient
Pressure flow in phloem
• Mass flow hypothesis
– “source to sink” flow
• direction of transport in phloem is
dependent on plant’s needs
– phloem loading
• active transport of sucrose
into phloem
• increased sucrose concentration
decreases H2O potential
– water flows in from xylem cells
• increase in pressure due to increase in
H2O causes flow
can flow
1m/hr
Maple
sugaring
Transport in
O
CO
Plants
2
H 2O
2
Transport in
O
CO
Plants
2
H 2O
2
How do
environmental
influences effect?
Transport in
turgid
flacidPlants
Environmental factors
influence this rate…