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transport processes (diffusion, osmosis, and active transport (3 kinds of…
transport processes
diffusion, osmosis, and active transport
diffusion
high to low concentration
osmosis
diffusion of water across a membrane
3 kinds of membranes
completely impermeable
isolation barrier
doesn't allow passage of anything
freely permeable
allows all solutes to diffuse
selectively permeable
allows only certain substances to pass through
aquaporins
protein channel for water
intracellular transport
vesicles
migrate through cytoplasm
vesicle contents transferred into organelle
fuse w/ other organelles
long distance transport: Xylem
pokilohydry
body water content that changes with habitat moisture
liverwort
water transport through xylem
cohesion-tension hypothesis
open stomatal pores
unavoidably allow water loss
water diffuses from intercellular space to atmosphere
transstomatal transpiration
transcuticular transport
some water loss directly through cuticle
control of water transport with guard cells
when water supply in soil is inadequate
water loss is advantageous
water movement
transpiration prevents heat stress in leaves
primary means of carrying nutrients upwards
properties of water
adhesive
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interacts with many other molecules
cohesive
H2O molecules interact with other H2O molecules
cavitation
embolism (air bubble)
space between water molecules drawn up from cavitation point
and molecules drawn down from cavitation point
cohesion overcome
water column breaks
air dry
soil dry
short distance intercellular transport
guard cell
potassium ions transported into guard cells
water diffuses into guard cells
guard cells open
motor cell
similar to guard cells
flexing/ folding in response to stimuli
location of flex
point petiole attaches to lamina or stem
midrib
accumulate or expel K+
apoplast
allows easy passage of small molecules
wall and intercellular space
transfer cell
ridge like outgrowths on inner surface
large surface area
high volume transport
found in:
glands that secrete salt
areas that pass nutrients to embryos
regions sugar loaded into/out of phloem
room for molecular pumps
walls smooth on outer surface
syplast
considered one continuous mass
all the protoplasm of one plant
water potential
symbol ψ
3 components
ψ=ψπ+ψp+ψm
pressure potential (ψπ)
measured in megapascal (MPa)
water under pressure = pressure potential ^ = water potential ^
pressure down = pressure potential down = water potential down
when compressed pressure is positive
when stretched pressure is negative
effects that pressure has on water potential
osmotic potential (ψp)
water interacts w solutes
water interacts w solutes
osmotic potential always neg
effects that solutes have on water potential
matric potential (ψm)
waters adhesion to non dissolved substances
cell walls
membranes
soil particles
adhesion decreases waters free energy
matric potential always neg
+ψ to -ψ
cells and water movement
lysis
absorbing water until cell bursts
cell walls strong enough to resist breakage
cells grow rather than burst
plant cells can never burst
plasmolysis
incipient plasmolysis
protoplast lost enough water to pull from cell wall
plasomlyzed
protoplast pulls completely from cell wall
cell shrinks
cell loses water and shrinks
more negative = more solutes
water available in water
eutrophication
bodies sink
decomposed by bacteria
algae die
bacteria use up available O2 to suffocate fis
free water
water not bound by solutes
water available in air
air also pulls water out of plants
motive force for transpiration
air supplies water to land plants
dew
frost
fog
snow
rain
hail
humidity
long distance transport: phloem
pressure flow hypothesis
postulated to be important drive force
active transport
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sugars
sieve cells
sieve tube members
polymer trap mechanism
phloem loaded by diffusing into conducting cells
polymerized into polysaccharides
cannot diffuse back out
STM/CC complex
functional unit
conducting cell
one or several companion cells
mass transfer
sugars/ nutrients transported per hour
excludes water
specific mass transfer
mass transfer divided by cross sectional area of phloem
sinks
extremely divers
p-protein
seals phloem rupture
protein plug
too large to pass sieve area and forms a plug
becomes tangled mass
sits that receive transported phloem sap
callose
injury causes pressure loss
callose precipitates into fflocculent mass
stays in solution under pressure
membrane bound molecular pumps
sources
sites water/ nutrients are transported
before new leaves
sources are storage sites
corms
wood/bark parenchyma
tubers
fleshy taproot
spring/ summer
leaves are dominant sources
steps:
uses active transport
H2O to other molecules
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ex: ER to dicytosomes
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