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Transport Processes (12) (Water Potential psi (How to Increase (Heat…
Transport Processes (12)
Water Potential
Free energy of water
Botany's chemical potential
How to Increase
Heat water
Put the water under pressure
Elevate the water
How to decrease
Cool the water
Reduce the pressure
Lower it
Short-Distance Intercellular Transport
Symplast
One continuous mass of protoplasm in one plant
Apoplast
Cell wall and intercellular spaces
Long Distance Transport
Phloem
Pressure Flow Hypothesis
Theory to explain movement of sap through phloem
Sources
sites from which water & nutrients are transported
Sugars are actively transported
Polymer trap mechanism
Conducting-cell plasma membranes
Permeable to monosaccharides & disaccharides
Impermeable to polysaccharides
Sinks
Sites that receive transported phloem sap
Xylem
Properties of water
Cohesive
Water is attracted to water
Adhesive
Water is attracted to other substances
Water Transport through Xylem
cohesion-tension hypothesis
Explains the ascent of water from roots to leaves
Most widely accepted model of the process
Transstomatal transpiration
Loss of water through the stoma
More significant than transcuticular
Transcuticular Transpiration
Loss of water through cuticle
Control of water transport by Guard Cells
Water movement is primary means of carrying minerals upwards
Water moves from roots to shoots
Evaporative cooling
Prevents heat stress in leaves and young stems
Material moves through a solution and across a membrane
Diffusion
High to low concentration
Osmosis
Diffusion of water through a membrane
Active Transport
The use of ATP to pass through membrane
Types of membranes
Freely
Permeable
Have little biological significance
all solutes can diffuse through
Completely impermeable
Nothing can pass through
Act as isolation barriers
Selectively Permeable
only allow certain substance to pass through
All lipid/protein membranes
Pressure Potential
Psi w/ subscript p
the effect pressure has on water potential
Osmotic Potential
Psi w/ subscript pi
the effect solutes have on water potential
Matric potential
Psi w/ subscript m
water's adhesion to nondisolved structures
Cell walls
Short distance Transport
Guard Cells
Curved cells around a stoma
Motor Cells
Located at "joints" in lamina or stem
Accumulate/expel K
Adjusting their water potential
Transfer Cells
Specialized parenchyma cells
Have increased surface area
