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Ch.12 Transport Processes (Moving material through a membrane (Completely…
Ch.12 Transport Processes
Moving material through a membrane
Diffusion
Particles move from low concentration to high concentration
Freely permeable membrane
Allows all solutes to pass through
Completely impermeable membrane
barriers
allow nothing to pass through
Selective permeable membranes
allow certain substances to pass through
aquaporins
rapid water exchange through a membrane
Active transport
burns ATP
uses a molecular pump to force molecules through the membrane
Intracellular transport
vacuoles transport materials from cell to cell
Water Potential
Water has free energy
Can be reduced
by cooling
By lowering the water
by reducing pressure
Can be increased
by heating
increase elevation
increasing pressure
osmotic potential
The effect solutes have on water potential
More solutes=less free energy
is always negative
decreases diffusion potential
Matric potential
the adhesion of water to non dissolved particles
Much less important in living cells
Water movement
Cells move from +Water potential to - water potential
equilibrium
equal water potential
Water can move through most plant regions
plants collect water from water based on solutes in the water
Rivers
streams
Lakes
Plants collect water from the air
Rain
fog
Dew
Air also pulls water from plants
Plasmolyzed cell
protoplasts pulls away from cell wall
cell shrinks
Short distance cellular Intercellular transport
Transferring materials:
Waters
Sugars
minerals
Hormones
Modes of transports
Plasmodesmata
Cytoplasmic channels
Pass through primary cell walls
Makes the protoplasm one continuous mass
Referrd to as Symplast
Across the plasma membrane
osmosis
transport vesicles
transport vesicles
Guard cells
Open and close to release/conserve water
Activated by potassium
Motor Cells
Trigger flexture in plants
Transfer Cells
Specialized to hold many molecular pumps
Long distance transport:Xylem
Based on the properties of water
water is very cohesive
interacts strongly within itself
water is adhesive
Interacts with many other substances
Water transport through xylem
Cohesion-tension hypothesis
open stoma cause water loss
referred to as transstomatal transpiration
Spongy mesophyll + Palisade parenchyma quickly lose water
Transcuticular Transpiration
Not typical
Water loss through cuticle
Immobile water layer forms on cell walls
Dry soil
Causes cavitation
Hyrdrogen bond breakdown over a large area
Kills the tracheid
Causes embolism
air bubble
guard cells
Water loss can be advantageous
Only when soil water is plenty
Provides cooling
often controlled by light