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Ch.12 Transport Processes (Short-Distance Intercellular Transport…
Ch.12 Transport Processes
Diffusion, Osmosis, and Active Transport
Active Transport
molecular pumps
protein
ATP splits into ADP & phosphate
membrane extremely impermeable
energy transported to pump
binds to molecule & ATP
use ATP to force molecules across membrane
examples
respiration
proton pumping photosynthesis
Diffusion
particles move high to low
through a membranne
intracellular transport
vesicles migrate through cytoplasm and fuse with organelle
vesicle contents transferred
membranes merge
hydrophobic molecules
diffuse easily through any membrane
hydrophyilic molecules
polar
differentially permeable membranes
only if has aqauporins
protein channels
Osmosis
completely impermeable
isolation barriers
nothing passes through
freely permeable
all solutes
little biological significance
differentially/selectively permeable
only certain substances
lipid/protein membrane
Short-Distance Intercellular Transport
Transfer Cells
plasma membrane
finger-like/ ridge-like outgrowths inner surface
pressed firmly against all convolutions
much larger surface area than flat
outer surface area of walls smooth
larger membrane
more molecular pumps
found in areas w/rapid short-distance transport
Motor Cells
similar to guard cells
can accumulate or expel K+
adjust water potential & turgidity
examples
Prayer Plant
Venus Flytrap
move slowly and reorient themselves
location of flexture
where petiole attaches to lamina or stem
cells @ joints
entire midrib
flex and fold in response to stimulus
Guard Cells
night
little internal pressure
shrunken
hydraulic equilibrium w/surrounding cells
no net change occurs
water enters & leaves same rate
exception in CAM plants
day
guard cells close
process reversed
K+ pumped from guard cells -> surrounding cells
water follows
equilibrium
guard cells open
K+ ions actively transported
K+ cannot leave once inside
impermeable plasma membrane
diffusion not possible
surrounding cells -> guard cells
Material transferred from cell to cell across membrane
osmosis
molecular pumps
fusion between transport vesicles & plasma membrane
apoplast
small molecules move through wall and intercellular spaces
glandular regions
intercellular space
mc move easily
nonglandular regions
mostly cell wall :
mc absorbed
symplast
all of the protoplasm of one plant
one continuous mass
cells interconnected by plasmodesmata
fine cytoplasmic channels
pass through primary cell walls
The Water Available in Water
variety of forms
fresh
salty
brackish
eutrophication
algae die
bodies decomposed by bacteria
uses up so much oxygen
kills fish
can't grow w/out phosphate
water starts out as rain
less pure as it collects
very pure
distelled
ocean water
too much salt
cannot use to hydrate
water at top mountains pure
algae can't live here
Long-Distance Transport: Xylem
Water Transport Through Xylem
water heavy
tension on mc (pull)
pressure potential neg #
water mc must lift weight of entire water column
cohesion tension hypothesis
open stomatal pores allow water loss
transstomatal transpiration
hydrophobic
little water passes through
epidermal & mesophyll cells lose water
potentials more neg
some water lost through cuticle
transcuticular transpiration
apoplastic space
palisade parenchyma
filled w/ moisture saturated air
spongy mesophyll
cavitation
breaks hydrogen bonds
doesn't break cells
tracheid or vessel can never conduct water again
cohesion overcome
water column breaks
acts as broken cable
mc above cavitation point
drawn rapidly upward
free of water weight below them
mc below cavitation point
rush downward
no support
between points
embolism
air bubble
expands till surface encounters solid barrier
1 more item...
hydrogen bonding broken
Properties of Water
heavy
lifting to top of tree requires a lot of energy
movement based on simple properties & solutions
water molecules interact w/ other substances
adhesive
water adheres firmly to soil particles
dry soil
water not absorbed easily
moist soil
roots absorb free liquid H2O
almost all substances
lipids don't interact w/water
water molecules interact strongly w/one another
cohesive
Control of Water Transport by Guard Cells
movement influenced by powered by water loss in atmosphere
water loss through cuticle
significant when stomatal pores open
open means trade off
CO2 absorption
H2O water loss
advantageous in wet soil
water carries mineral from roots to shoots
transpiration occurs
2 more items...
most powerful mechanism
triggered by water stress
leaves dehydrate
release abscisic acid
hormone
guard cells close stomatal pore
often occurs in early afternoon
warm, dry days
light most often controls guard cells water relations
blue light
triggerswavelength
photosynthetic fixing of CO2
decrease in internal carbon may lead to openings
Water Potential
three components
pressure potential
effect of pressure on water potential
water under pressure decreases
water potetial decreasses
pressure potential decreases
water under pressure increases
water potential increases
pressure potential increases
osmotic potential
effect solutes have on water potential
pure water
no solutes
osmotic potential 0.0MPa
adding soultes
decreases water free energy
osmotic potential negative
sigh pie
number of particles present in solution
matric potential
water's adhesion to dissolved structures
soil particles
only decreases water's free energy
matric potential always negative
cell walls
membranes
free energy of water
decreased
cool
lowering it
decrease pressure
capacity to do work decreased
adheres to substance
increased
heat
elevation
increase pressure
Cells and Water Movement
osmotic potential
does not increase or decrease more than a few megapascals
pressure potential
change enormously
cells grow not burst
water loss still problem
incipient plasmolysis
not reached equilibrium
protoplast pulls away completely & shrinks
cell plasmolyzed
quite important
protoplast loses just enough water to pull slightly from walls
water moves from positive to negative regions
moves when diff in water potential in cell
potentials always in pairs/groups
equal in two regions
equalibrium
no net movement of water
measured in megapascals
MPa
= 10 bars
bars
pressure
negative
something stretched
positive
something compressed
Long-Distance Transport: Phloem
sources
sugars actively transported
sieve elements
sugar accumulation causes concentration
hydraulic disequalibrium
protoplasm squeezed
presure builds,
membrane disintegrates
vacuolar creates phloem sap
osmotic potential more neg
water potential more neg
sieve cells
plants other than angiosperms
other plants
phloem loaded by polymer trap mechanism
STM/CC complex
membranes permeable to mono & disaccharides
simple sugars diffuse into conducting cells
polymerized into polysaccharides
sites where nutrients are transported
storage sites
early spring
leaves dominant
spring
summer
phloem loading
along numerous vascular bundles
pressure builds
mass transfer
nutrients/sugars transported by phloem per hour
specific mass transfer
large volume of material flows from source
inner bark in storage roots & stems
network bundles in tublers & corms
massive loading
fine veins in leaves
sinks
sugars actively unloaded from sieve elements into surrounding cells
osmotic potential less neg
water potential less neg
water diffuses outward
end cells do not swell
phloem sap flow rapidly into sink
phloem sap under pressure
danger uncontrolled bleeding
two mechanisms seal sieve elements
2 more items...
if cut
loss of sugar
phloem sap more dilute
receive transported phloem sap
not all active simultaneously
plants don't all produce organs @ same time
fruits can only develop after flowers
extremely diverse
pressure flow hypothesis
active transport
membrane bound molecular pumps
The Water Available in Air
diff regions get diff amounts water
desert none/little precipitation
fog & cloud regions
water always in air
air pulls water out of plants
motive force for transpiration
air supplies water to land plants
frost
rain
snow
dew
fog
hail
humidity
timing & regularity of precipitation important
rate water lost