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CH. 12 Transport Processes (Water Potential (Osmotic potential (pure water…
CH. 12 Transport Processes
Diffusion, Osmosis, Active Transport
Diffusion
High to low
Hydrophobic molecules
diffuse through easily
Polar, Hydrophilic molecules
cross differentially membrane
have special protein channels
water molecules
highly polar
pass through all membranes
membrane has protein channels
aquaporins
rapid movement
Osmosis
Diffusion through membrane
Freely permeable
allow all solutes
little biological significance
completely permeable
don't allow anything
isolation barriers
differentially (selectively permeable)
allow certain substances
lipid/protein cell membranes
Active Transport
Molecular Pumps
force molecules across membrane
a protein
binds to molecule & ATP
ATP splits into ADP/phospate
uses ATP
proton pumping
respiration
https://www.khanacademy.org/science/biology/membranes-and-transport/active-transport/a/active-transport
Short-Distance Intercellular Transport
Guard Cells
symplast
all the protoplasm
apoplast
wall & intercellular space
stomata closed
guard cells shrink
little internal pressure
in hydraulic equalibrium
must open
K ions transported into guard cells
cannot leave because plasma membrane
Guard Cells
potassium pumping is possible
diffusion is not
Motor Cells
cells where the petiole attaches
located along midrib
similar to guard cells
accumulate/expel potassium
adjust water potential & turgidity
when shrunken
pressure in midrib cells
causes blades to be appressed
trap is closed
trap opening
potassium accumulated by motor cells
water diffuses in
motor cell turn turgid
Transfer Cells
walls are smooth
outer surface
numerous finger-like outgrowths
inner surface
plasma membrane
pressed firmly against convultions
larger surface area
available room for molecular pumps
high-volume transport
rapid short-distance transport
glands secrete salt
pass nutrients to embyos
sugar loaded in/out phloem
Water Potential
Cells & Water Movement
free energy of water
can be increased
can be heated
put under pressure
elevated
can be decreased
cooling
reducing pressure
lowering elevation
Pressure potential
effect of pressure on water potential
if increases so does water potential
if decreases so does water potential
can be positive
something is compressed
can be negative
something is stretched
water is under tension
measured in megapascals
MPa or bars
1 MPa = 10 bars
Osmotic potential
effect that solutes have
pure water
osmotic potential = 0.0 MPa
adding solutes decreases
always negative
number of particles
Matric potential
adhesion to nondissolved structures
cell walls
membranes
soil particles
always negative
Long-Distance Transport: Phloem/Xylem
Phloem
pressure flow hypothesis
water & nutrients moved through phloem
sources
leaves dominant sources
during spring and summer
tubers, corms, wood
early spring
new leaves
bark, parenchyma, fleshy taproots
early spring
new leaves
cotyledons and endosperms
embryo source during germination
membrane-bound molecular pumps
active transport
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Xylem
Properties of Water
cohesive
water molecules strongly bound
one molecule acts on neighboring ones
adhesive
shell of water molecules
cellulose
enzymes
DNA
sugars
heavy
lifting to top of tree
great deal of energy
Water Transport Through Xylem
cohesion-tension hypothesis
water movement through xylem
widely accepted model
transstomatal transpiration
water loss
stomatal pores open
cuticle and waxes
transcuticular transpiration
water loss through cuticle
cuticle and waxes
cavitation
water column breaking
acts like broken cable
molecules above cavitation
draw rapidly upward
molecules below cavitation
rush downward
embolism
space between portions
air bubble
expands until encounters barrier
pit membrane
tracheid or vessel
can never conduct water
Control of Water Transport by Guard Cells
bulk water movement
through xylem
water loss
powered by atmosphere
CAM
https://biologydictionary.net/cam-plants/
driving force
