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Transport Processes (Short-Distance Intercellular Transport (Guard Cells…
Transport Processes
Short-Distance Intercellular Transport
Symplast
all protoplasm
apoplast
intercellular space
Guard Cells
cells surrounding stomatal pores
K+ actively transported into
absorption of K+
H2O Pot
Negative
thrown out of hydraulic equilibrium
when closed
less K+
less positive pressure pot.
motor cells
"joints" of stem or lamina
similar to guard cells
#
K+
Can be expelled
or accumulated
adjusts water pot
example
venus flytrap
located on midrib
Transfer cells
smooth walls
on outer surface
many finger-like and ridge-like outgrowths
inner surface
occurs in
glands that secrete salt
passes nutrients to embryos
sugar goes in or out of phloem
Water Potential
#
free energy
measured in MPa or bars
increased
elevated
increasing pressure
heated
decreased
cooling
reducing pressure
lowering it
pressure pot
#
#
effect of pressure on pot.
h20 under pressure
pressure pot increases
water pot inreases
matric pot
h2o adesion
#
membranes
cell walls
soil particles
decrease free energy
always negative
Long-Distance Intercellular Transport: phloem
exact mech not known
pressure flow hypothesis
molecular pumps
active transport
sugars turned into sieve elements
becomes more concentrated
become more negative
water pot
hydraulic disequilibrium
osmotic pot
sources
tranport site of
water
#
nutrients
mass transfer
divided to make
specific mass transfer
polymer trap mech
conducting cell plasma membranes
permeable to
dissacharides
monosaccharides
NOT POLYSACCHARIDES
simple sugars diffuse into cc
companion cells
together make STM/CC complex
sinks
transported phloem sap
P-protein
P-protein plug
callose
polymer
diverse
storage organ
Long-Distance Intercellular Transport: Xylem
Water
adhesive
cohesive
water held in soil
breaking of
hydrogen bonding
water columns
cavitation
powered mainly by water-loss thru atm
cohesion-tension hypothesis
water-loss through stomatal pores
#
transstomatal transpiration
#
transcuticular transpiration
poikilohydry
h2o content changes with habitat moisture
methods
Diffusion
high to low movement
osmosis
3 types
completely impermeable
nothing passes
selectively permeable
certain substances
Freely permeable
all solutes
h2o
#
aquaporins
protein channels
molecular pumps
#
ATP
Active transport
#
protein
