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Transport Processes (Diffusion, Osmosis, and Active Transport (3 Types of…
Transport Processes
Diffusion, Osmosis, and Active Transport
Diffusion
high concentration to low concentration
Osmosis
diffusion through a membrane
3 Types of Membranes
freely permeable
allow all solutes to diffuse
completely impermeable
isolation barrier
do not allow anything to pass through
selectively permeable
differentially
allow only certain substances to pass through
Aquaporins
protein channel for water
Active Transport
memrane-bound molecular pumps
requires ATP (energy)
often used to pump molecules against concentration gradient
example: proton pumps in photosynthesis/ respiration
Intracellular Transport
vesicles
migrate through cytoplasm
fuse with other organelles
vesicle contents transferred into organelle
example:ER to dictyosomes
Short-Distance Intercellular Transport
symplast
all the protoplasm of one plant
considered one continuous mass
apoplast
wall and intercellular space
allows easy passage of small molecules
Guard Cells
potassium ions actively transported into guard cells
water diffuses into guard cells
guard cells open
Motor Cells
similar to guard cells
flexing/folding in response to stimuli
location of flexure
midrib
point petiole attaches to lamina or stem
accumulate or expel K+
Transfer Cells
walls smooth on outer surface
numerous finger-like/ ridge-like outgrowths on the inner surface
larger surface area
room for many molecular pumps
high volume transport
found in:
glands that secrete salt
areas that pass nutrients to embryos
regions of sugar loaded into/ out of phloem
Long-Distance Transport: Xylem
Properties of Water
cohesive
water molecules interact with other water molecules
adhesive
water interacts with many other molecules
Water Transport Through Xylem
cohesion-tension hypothesis
open stomatal pores
unavoidably allow water loss
water diffuses from intercellular space to atmosphere
transstomatal transpiration
transcuticular transpiration
some water loss directly through cuticle
pokilohydry
body water content that changes with habitat moisture
liverwort
cavitation
cohesion overcome
water column breaks
soil dry
air dry
embolism (air bubble)
space between water molecules drawn up from cavitation point
and molecules drawn down from cavitation point
Control of Water Transport by Guard Cells
#
when water supply in soil is adequate
water loss is advantageous
water movement
primary means of carrying nutrients upward
transpiration prevents heat stress in leaves
#
Water Potential
symbol Ψ
pronounced "sigh"
3 components: Ψ=Ψπ + Ψp + Ψm
pressure potential (Ψp)
effect that pressure has on water potential
water under pressure = pressure potential ^ = water potential ^
pressure ˅ = pressure potential ˅ = water potential ˅
when something is compressed pressure is positive
when something is stretched pressure is negative
measured in megapascals (MPa) or bars
1 megapascal=10 bars or 10 atmospheres
osmotic potential (Ψπ)
effects that solutes have on water potential
water interacts with solutes
osmotic potential always negative
cannot diffuse easily
matric potential (Ψm)
water's adhesion to non-dissolved structures
cell walls
membranes
soil particles
adhesion decreases water's free energy
matric potential always negative
water moves from regions of +Ψ to -Ψ
Cells and Water Movement
more negative=more solutes
lysis
absorbing water until the cell bursts
plant cells can never burst
cell walls strong enough to resist breakage
cells grow rather than burst
plasmolysis
cell loses water and shrinks
incipient plasmolysis
protoplast lost enough water to pull from cell wall
plasmolyzed
protoplast pulls completely from cell wall
cell shrinks
The Water Available in Water
free water
water not bound to solutes
eutrophication
1) algae die
2) bodies sink
3) decomposed by bacteria
4) bacteria use up available O₂ and suffocate fish
The Water Available in Air
air supplies water to land plants
rain
fog
dew
frost
snow
hail
humidity
air also pulls water out of plants
motive force for transpiration
Long-Distance Transport: Phloem
pressure flow hypothesis
membrane-bound molecular pumps
active transport
sugars
sieve tube members
sieve cells
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
amount sugars/ nutrients (excluding water) transported per hour
specific mass transfer
mass transfer divided by cross-sectional area of phloem
sinks
sites that receive transported phloem sap
extremely diverse
P-protein
becomes tangled mass
seals phloem rupture
P-protein plug
too large to pass sieve area & forms a plug
callose
stays in solution under pressure
injury causes pressure loss
callose precipitates into flocculent mass
postulated to be important driving force
sources
sites water and nutrients are transported
spring/ summer
leaves are dominant sources
before new leaves
sources are storage sites
tubers
corms
wood/bark parenchyma
fleshy taproots
