chapter 36 - plant transport
TRANSCRIPT
AP Biology 2006-2007
Transport in Plants
AP Biology
Review: Transport proteins Facilitate diffusion via carrier or selective
channel formation Carrier proteins
Selective to solute molecule Produces conformational change of protein Releases molecule to opposite side
Selective channel Passageways for certain solutes May be gated - open/close
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Transport in plants H2O & minerals
transport in xylem transpiration
evaporation, adhesion & cohesion negative pressure
Sugars transport in phloem bulk flow
Calvin cycle in leaves loads sucrose into phloem positive pressure
Gas exchange photosynthesis
CO2 in; O2 out stomates
respiration O2 in; CO2 out roots exchange gases within air spaces in soil
Why doesover-wateringkill a plant?
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Ascent of xylem fluid
Transpiration pull generated by leaf
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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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Mineral absorption Proton pumps
active transport of H+ ions out of cell chemiosmosis H+ gradient
creates membranepotential difference in charge drives cation uptake
creates gradient cotransport of other
solutes against theirgradient
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Water flow through root Porous cell wall
water can flow through cell wall route & not enter cells
plant needs to force water into cellsCasparian strip
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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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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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Mycorrhizae
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Chloroplasts
Epidermal cell
NucleusGuard cell
Thickened innercell 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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Water potential and osmosis Osmosis
Net absorption or loss of water Water potential ()
Combined effects of solute concentration and pressure
Determines direction of water movement
Water moves from areas of high water potential to areas of low water potential
0 Mpa = pure water open at sea level & room temp
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Water potential () Solute potential (s)
Proportional to number of dissolved solutes Osmotic potential s = 0 in pure water s = -0.23 in 0.1M solution of sugar Addition of solutes lowers the
Pressure Potential (P) Physical pressure on a solution Can be + or – Water in xylem is often negative Water in cell is often positive Additional pressure raises the
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= p + s
p - pressure potential
s - solute potential = osmotic potential
Flaccid cell (P = 0) placed in hypertonic solution will lose water via osmosis
Plasmolysis - protoplast pulls away from cell walls
Same cell placed within a hypotonic solution will gain water via osmosis = turgid
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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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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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Experimentation Testing pressure flow
hypothesis using aphids to measure sap
flow & sugar concentration along plant stem