Transcript Transport in Vascular Plants

Transport in
Vascular Plants
Chapter 36
Transport in Plants
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Occurs on three levels:
 the
uptake and loss of
water and solutes by
individual cells
 short-distance transport
of substances from cell
to cell at the level of
tissues or organs
 long-distance transport
of sap within xylem and
phloem at the level of
the whole plant
Cellular Transport
Most solutes have to be transported via
a transport proteinnad with the use of
energy active transport
 Proton pumps provide this energy
 Cotransport

proton pumps
Cotransport
Water Potential / Uptake of
Water
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Uptake of water
osmosis
Water moves from
high water potential
to low water potential
Ψ= Ψs+ Ψp
Movement of Water in Plants
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Water potential impacts the
uptake and loss of water in plant
cells
In a flaccid cell, Ψp=0 and the cell
is not firm
 the cell  lower water potential
(presence of solutes) than the
surrounding solution  water
will enter the cell.
 As the cell begins to swell, it
will push against the wall,
producing a turgor pressure
Aquaporins
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Transport proteins that facilitate the passive
movement of water across a membrane
Do not affect the water potential gradient or
the direction of water flow, but rather the
rate at which water diffuses down its water
potential gradient
Aquaporins are gated channels open and
close in response to variables, such as turgor
pressure, in the cell.
Routes from cell to cell
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Moving water & solutes between cells

transmembrane route
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symplast route
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repeated crossing of plasma membranes
slowest route but offers more control
move from cell to cell within cytosol
apoplast route
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move through connected cell wall without crossing cell membrane
fastest route but never enter cell
Roots Absorb Water and
Minerals
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Water and mineral salts from soil enter
the plant through the epidermis of
roots, cross the root cortex, pass into
the stele, and then flow up xylem
vessels to the shoot system
Fig. 36.7
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Water Route through the Root
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Water uptake by root hairs
a
lot of flow can be through cell wall route
 apoplasty
Controlling the route of water
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Endodermis
 cell
layer surrounding vascular cylinder of root
 lined with impervious Casparian strip
 forces fluid through
selective cell membrane
& into symplast
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filtered &
forced into
xylem vessels
Transpiration
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The loss of water vapor from leaves and
other aerial parts of the plant
 An
average-sized maple tree losses more
than 200 L of water per hour during the
summer
 The flow of water transported up from the
xylem replaces the water lost in
transpiration and also carries minerals to
the shoot system.
Mechanisms of Transpiration
Root Presssure
 Cohesion –Adhesion pull
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Fig. 36.11
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Control of Transpiration
Keeps leaf temperature lower
 Rate is affected by evaporation:
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 Sunny,
dry, warm, windy
Control of Transpiration
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Stomata:
 Open
when turgid
 Closed when flaccid
Figure 36.13a The mechanism of stomatal opening and closing
The role of potassium in stomatal opening
and closing
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K+ actively moved into guard cells
Water follows
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Triggers:
 Blue light receptors
 Low CO2 levels
 Circadian rhythms
Adaptations to Reduce
Transpiration
XEROPHYTES
1. small, thick leaves
2. Thick cuticle
3. Stomata in pits
4. Reduced surface area
5. CAM plants
Movement of Sugars
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Translocation process that transports the
organic products of photosynthesis
throughout the plant
In general, sieve tubes carry food from a
sugar source to a sugar sink
A sugar source (mature leaves) in which sugar
is being produced by either photosynthesis or
the breakdown of starch
A sugar sink (growing roots, shoots, or fruit)
that is a net consumer or storer of sugar