SECTION 13.4:
TRANSPORT IN PLANTS
How it works…
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Essentially a plant is a tube with its base
embedded in the ground (the roots), and leaves
are at the top of the tube
Materials like sugars which are made in the leaves
must get carried all over the plant
Water dissolves the carbohydrates (energy) and
moves up it and down the plant via the
_____________
Water and dissolved nutrients in the ground must
be taken up by the roots to the cells in the leaves
and other parts via the _____________
Water and Nutrients in and out of
Cells…
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Particles move according to concentration gradients the difference in concentration between two areas
______________________ - the movement of
particles from an area of high concentration to an
area of low concentration until a balance is achieved.
 “moving down the gradient”
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Diffusion of WATER across a membrane down its
concentration gradient is called _________________
Diffusion
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Diffusion and Osmosis occur naturally and
____________________ require energy to move
down the gradient
Sugars and other nutrients must move across cell
membranes and _________ require energy
This is called ACTIVE TRANSPORT
Transport in the Xylem
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Roots contain more dissolved nutrients than
surrounding soil so water moves into roots via
osmosis
Xylem transports water up from roots into the stem
and some water moves by diffusion to other tissues
Xylem branches into numerous veins as it enters
leaves. Water and minerals diffuses into the leave
at the end of each vein
Up to 90% of water that reaches the leaf is lost to
the atmosphere as it evaporates through the
___________________.
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This is called ________________________
What about Tall Trees?
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How can water travel through Xylem up to the top
of trees that are a hundred feet tall??
Long Distance Transport in Xylem
Root Pressure
1.
•
•
•
•
Pushes water and minerals up the plant, against
gravity
Water enters the roots and creates a positive pressure
that pushes water upward
Minerals are moved into the roots via active transport,
which increases the concentration in the xylem and
causes more water to move by osmosis
Root pressure can sometimes be seen as tiny droplets
on leaf edges – called _______________________
 (Figure, 13.21 on p.561)
Long Distance Transport in Xylem
2. Transpiration Pull
 Negative
pressure (pulling) from above is the strongest
force for long distance transport in plants
 ____________________________________ accounts
for the majority of water movement in plants
 The loss of water from leaves via transpiration creates
a pull, or negative pressure, that moves water up the
plant to replace the water that was lost
Three Factors of Cohesion-Tension Model
1.
•
•
Transpiration
Negative pressure created as water exits leaves through the
stomata.
Negative pressure exerts tension on the water confined in xylem’s
conducting tubes all the way to the roots
•
Cohesion
The force of attraction between water in each narrow xylem tube
provides a force that keeps the water column unbroken while it is
being pulled up under tension
•
Adhesion
Causes water molecules to adhere to xylem walls and keeps
water column from breaking
2.
3.
Factors Affecting Transpiration
1.
2.
3.
4.
5.
Temperature: high temp = ______________
transpiration rate
Light: stomata open during day = ____________
transpiration rate during day
Humidity: high humidity = ____________
transpiration rate in humid conditions
Wind: high wind = ___________ transpiration
rate
Number of Stomata per Leaf Surface Area: more
stomata = ____________ transpiration rate
Transport in Phloem
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Photosynthesis in leaves creates glucose (sugar)
Phloem transports sugar through the plant via
_______________________________.
 From
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“source to sink”
Moves sugar from where is is made to where it is
need for growth, metabolism and storage
Translocation
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Phloem transports substances in ____________
directions by ACTIVE TRANSPORT
The Pressure-flow model uses osmosis and pressure
dynamics to explain how sugars are pushed from
where they are made (source) to where they are
needed (sink)
Ex: Maple Syrup
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Summer - transport from leaves to roots
Spring - from roots to branches
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Collect sap  Syrup
Sugar is transported as ___________________, not glucose