transport in plants · lateral transport in plants transmembrane: substances cross cell walls and...
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AP Biology 2006-2007
Transport in
Plants
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AP Biology
Water & mineral absorption
Water absorption from soil
osmosis
aquaporins
Mineral absorption
active transport
proton pumps active transport of H+
H2O
root hair
aquaporin
proton pumps
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AP Biology
Mineral absorption
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
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AP Biology
Vascular Tissue: Xylem
Xylem: carries water and minerals
Made up of tracheids and vessel elements
Dead at maturity
One-way transport only
Walls of cells reinforced with lignin
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AP Biology
Lateral transport in plants
Transmembrane: substances cross cell walls and plasma membranes to move cell to cell
Symplast: substances travel through cells via plasmodesmata
Apoplast: substances travel between cell walls
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AP Biology
Lateral transport in roots
Minerals & water in symplast can pass into vascular cylinder (stele)
Those in apoplast hit Casparian strip and must cross through membrane of endodermal cells and enter via symplast
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AP Biology
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
Aaaah… Structure–Function
yet again!
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AP Biology
Root anatomy
dicot monocot
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AP Biology
Mycorrhizae increase absorption
Symbiotic relationship between fungi & plant
symbiotic fungi greatly increases surface area for
absorption of water & minerals
increases volume of soil reached by plant
increases transport to host plant
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AP Biology
Mycorrhizae
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AP Biology
Long Distance Transport
How does water get from roots up to the
leaves?
1) Root pressure
Guttation
Minor mechanism– can’t keep up with
transpiration after sunrise
2) **Transpiration-Cohesion-Tension
Mechanism
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AP Biology
Fluid Movement in Xylem
Root pressure forces water into xylem while transpiration pulls it up: cohesion-tension theory
Adhesion: water sticks to cellulose walls
Cohesion: water sticks to itself due to Hydrogen bonding
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AP Biology
Transport of sugars in phloem Loading of sucrose into phloem
flow through cells via plasmodesmata
proton pumps
cotransport of sucrose into cells down
proton gradient
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AP Biology
On a plant… What’s a source…What’s a sink?
can flow
1m/hr
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
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AP Biology
Experimentation
Testing pressure flow
hypothesis
using aphids to measure sap
flow & sugar concentration
along plant stem
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AP Biology
Maple
sugaring
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AP Biology 2006-2007
Don’t get mad…
Get answers!!
Ask Questions!
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AP Biology 2006-2007
Ghosts of Lectures Past
(storage)
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AP Biology
Endodermis &
Casparian strip
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AP Biology
Chloroplasts
Epidermal cell
Nucleus Guard cell
Thickened inner cell wall (rigid)
Stoma open Stoma closed
H2O
water moves into guard cells
H2O H2O H2O
H2O H2O
H2O
H2O
H2O H2O H2O H2O
Control of Stomates
K+
K+
K+
K+
K+ K+
K+ K+
K+ K+ K+ K+
water moves out of guard cells
Uptake of K+ ions
by guard cells
proton pumps
water enters by
osmosis
guard cells
become turgid
Loss of K+ ions
by guard cells
water leaves by
osmosis
guard cells
become flaccid
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AP Biology
Control of transpiration
Balancing stomate function
always a compromise between
photosynthesis & transpiration
leaf may transpire more than its weight in
water in a day…this loss must be balanced
with plant’s need for CO2 for photosynthesis