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Transport Processes (Long-Distance Transport: Xylem (Properties of water…
Transport Processes
Long-Distance Transport: Xylem
Properties of water
Cohesive
Strong interaction between H2O
Adhesive
Interaction with other substances
Heavy
Lifting requires energy
Cohesion-tension hypothesis
Cohesion
Pulls water upward
Weight of water
Puts tension on molecules
Pressure potential negative
Adhesion
Hinders water movement
0.2 MPa difference
Leaf more negative
Root more positive
Cavitation
Breakage of water column
Embolism
Tracheids
Only one tracheid affected
Vessel elements
Entire vessel at risk
Spreads through perforations
Transpiration types
Transstomatal
Intercellular spaces to air
Transcuticular
Cuticle to air
Guard cells' role
Controls water loss
Factors that close/open stomata
Light and CO2
Abscisic acid
Mechanism of Movement
Membrane Types
Differentially Permeable
Selectively Permeable
Diffusion of certain substances
Lipid/protein cell membranes
Protein channels
Aquaporins
Completely impermeable
No diffusion/movement
Isolation barriers
Freely Permeable
Diffusion of all substances
Active Transport
Molecular pumps
Use ATP
Diffusion
Simplest method
High concentration to low
Osmosis
Intracellular Transport
Vesicles
Means of short-distance transport
Short-Distance Intercellular Transport
Guard Cells
Opening/closing stomata
Potassium pumping
Used to prevent water loss
K+ into guard cells
Water potential more negative
Water swells guard cells
Guard cells open
K+ out of guard cells
Water potential more positive
Water flows out
Guard cells close
Motor Cells
Potassium pumping
Controls flexing and folding
Transfer Cells
Larger membrane S.A.
Many outgrowths inner surface
More molecular pumps
High-volume transport
Communication with other cells
Plasmmodesmata
Plasma membrane
Apoplast
Plant Transport Processes
Long- distance Transport
Xylem and phloem
Allow shoot growth upright
Channels nutrients
Rapid growth of sites
Isolation mechanisms
Inhibits movement
Short-distance transport
Survival of internal cells
Distance <= few cell diameters
Water Potential
Chemical potential of water
Matric Potential
Effect of nondissolved structures
Always negative
Very small effect
Usually ignored
Pressure Potential
Effect of pressure
Measured in megapascals
Positive or negative
Increases with more pressure
Decreases with less pressure
Osmotic Potential
Solutes affect water ecosystems
Effect of solutes
Always negative
No solutes = 0.0 MPa
Number of particles
Movement of water
Positive potential to negative
Cause of upward water movement
Extreme cases
Incipient plasmolysis
Water loss
Protoplast pulls from wall
Water Availability
In Water
Many solutes "unpurify" water
Runoff/sewage
Algae growth and death
Decomposition by bacteria
Eutrophication
Salt
Oceans
Ratio of salt changes
Affects many ecosystems
In Air
Transpiration
Supplier of water
Rain
Hail
Dew
Frost/Snow
Fog
Humidity
Timing/regularity of precipitation
Affects shape/size of plant
Long-Distance Transport: Phloem
Pressure flow hypothesis
Sources
Mass Transfer
Sugars transported/hour
Specific mass transfer
Sites of transport (loading)
Actively transported
Sieve elements
Polymer trap mechanism
STM/CC complex
Phloem sap
Sieve element protoplasm
Transported through sieve pores
Sinks
Receiving (unloading) sites
Storage organs
Sugars actively unloaded
Water diffusion outward
Sealing broken sieve elements
P-protein
Near sieve inner membrane
Forms P-protein plug
Callose
Pressure drop
Callose joins P-protein
