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Chapter 12: Transport Processes (Water Potential (pressure potential (the…
Chapter 12: Transport Processes
Diffusion, Osmosis, and Active Transport
diffusion
random movement of particles from high concentration to low concentration areas
technically known as osmosis
three types of membranes
freely permeable
allow all solutions to diffuse through them and have little biological significance
completely impermeable
do not allow all solutes to diffuse through them and occur as isolation barriers
selectively permeable (differentially)
allow only certain substances to pass through, all lipid and protein cell membranes are differentially permeable
Water Potential
free energy of water
water can be heated, put under pressure, or elevated
pressure potential
the effect that pressure has on water potential
osmotic potential
the effect that solutes have on water potential
metric potential
waters adhesion to non-dissolved structures
Short Distance Intercellular Transport
symplast
all of the protoplasm of one plant can be considered one continuous mass
apoplast
most small molecules can move easily through both the wall and their intercellular spaces
guard cells
opening and closing of stomatal pores are based on short distance intercellular transport
motor cells
similar to guard cells
accumulate or expel potassium adjusting their water potential and turgidity
transfer cells
walls are smooth on the outer surface but have finger-like outgrowths on the inner surface
Long Distance Transport
Phloem
pressure flow hypothesis
membrane bound molecular pumps and active transport are postulated to be the important driving forces
actively transported
spices and sugars are transported into sieve elements
ploymer trap mechanism
conducting cell plasma membranes are permeable to monosaccharides but not to polysaccharides
mass transfer
amount of sugars and other nutrients transported by phloem per hour
sinks
sites that receive transported phloem sap and they are extremely diverse
Xylem
cohesion tension hypothesis
most widely accepted model of the process
transstomatal transpiration
water loss
transcuticular transpiration
water lost through the cuticle
