Transport Processes
Concepts
Short-distance Transport
involves distances of a few cell diameters or less
Long-distance Transport
between cells that are not close neighbors
involve transfer of basic nutrients
occurred due to xylem phloem evolving
isolation mechanisms
inhibit movement of substances
Diffusion, Osmosis, & Active Transport 
diffusion
diffusion=random movement of particles in a solution causes them to move from areas of high concentration to low concentration
osmosis
osmosis=diffusion through a membrane
membranes
freely permeable=allows all solutes to diffuse through them (have little biological significance)
competely impermeable=do not allow anything to pass through and occur as isolation barriers
differentially/selectively permeable=allow only certain substances to pass through
aquaporins=protein channels in the membrane that allows water to move faster
molecular pumps=in membranes that use ATP to force molecules across the membrane=active transport
active transport
active transport=forcing molecules across the membrane using ATP
intracellular transport=vesicles migrate through the cytoplasm and fuse with another organelle
Water Potential
water potential=free energy of water
pressure potential=effect that pressure has on water potential
measured in megapascals
osmotic potential=effect that solutes have on water potential
matric potential=water's adhesion to nondissolved structures like cell walls, membranes, and soil particles
important water points #
water moves whenever there is a difference in water potential
if two water potentials are the same in two areas they are in equilibrium; there is net diffusion across the membranes
water potentials must be considered in pairs or groups; knowing one potential will not allow you to predict will it will flow
Cells and Water Movement
lysis=cells bursting;plant cells never burst ⭐
The Water Available in Water
eutrophication=algae growing abundantly and then die causing oxygen depletions, killing off fish etc
land plants & animals can't survive on seawater due to its high salt concentration
Water Available in Air :
rain, fog,dew, frost, snow, hail, and humidity
too much water stunts plants' growth
Seattle & Austin receive that same amount of rainfall (35 inches)
but since Seattle is cool and cloudy the plants don't transpire quickly
since Austin will get rainfall in spurts with hot days in between, the plants transpire rapidly
incipient plasmolysis=point where protoplast has lost just enough water to pull slightly away from the wall
plasmolyzed=when a cell's protoplast pulls away from the wall and shrinks up
Short-Distance Intercellular Transport
apoplast
plasmodesmata=cells are connected by these fine cytoplasmic channels that pass through primary cell walls
symplast=all the protoplasm of one plant considered one mass
apoplast=cell wall and intercellular spaces
osmosis :
molecular pumps
fusion between transport vesicles and plasma membrane
guard cells
when stomata are closed=guard cells are shrunken & have little internal pressure
K ions leave guard cell and water follows them
water enters and exits the cells at the same rate
when stomata are open=K ions transported into guard cells
water flows into guard cells from surrounding ones
guard cells swell, bend, & push apart=open stomata
go back to water equilibrium
Motor Cells
move slowly and reorient themselves by flexing and folding in response to stimuli
motor cells=cells at entire midrib or point at which the petiole attaches to the lamina or stem
similar to guard cells=gain or lose K ions to swell or shrink
venus flytrap-closes in a second but takes hours to reopen
Transfer Cells
larger membrane=more molecular pumps it can hold
transfer cell walls are smooth on outer surface but have numerous finger-like ridges on the inner surface
found in areas
where rapid short-distance transport is expected to occur
where nutrients are passed to embryos
where sugar is loaded into or out of phloem
Long-Distance Transport: Phloem
pressure flow hypothesis
molecular pumps & active transport believed to be main driving forces
sources=sites where water & nutrients are transported
spring & summer sources=leaves
early spring sources=storage sites like tubers, corms, wood & bark parenchyma, and fleshy taproots
sources for embryos=cotyledons & endosperm
sugars actively transported into sieve elements
phloem is loaded by the polymer trap mechanism
conducting-cell plasma membranes are permeable to monosaccharides and disaccharides but not to polysaccharides
mass transfer=actual amount of sugars & nutrients transported by phloem per hour
specific mass transfer=mass transfer divided by the cross-sectional area of phloem
sinks=sites that receive transported phloem sap (extremely diverse)
To seal a broken sieve element 💥
P-protein=(P for phloem)gets swept into cell center to become tangled mass
P-protein plug= formed by P-protein mass when it's too large to pass through
callose=polymer in uninjured phloem that precipitates into a flocculent mass and is carried with P-protein to nearest sieve areas when injured
callose contributes to the plug, and leaking is prevented #
Long-Distance Transport: Xylem
Properties of Water
water molecules interact strongly with other ones, behaving as if weakly bound together
when frozen, molecules become strongly bound to each other
liquid water is cohesive=any force acting on one molecule acts on all neighboring ones as well
water molecules interact with many other substances
adhesive=firmly attached to a water molecule
makes attached water molecules less free to move around than other molecules
water adheres firmly to soil particles
Water Transport Through Xylem
governed by the properties of water
cohesion-tension hypothesis
apoplastic space of spongy mesophyll & palisade parenchyma is filled with moisture-saturated air, so water molcules have strong tendency to diffuse from intercellular spaces to the atmosphere
transstomatal transpiration=water loss from high humidity
transcuticular transpiration=water lost directly through the cuticle on epidermal surfaces
poikilohydry=a body water content that changes with habitat moisture
cavitaion=hydrogen bonding is broken over a large region, and the water column breaks
⚠
embolism=space between the two portions of cavitaion (above & below cavitaion point) #
often means that that tracheid or vessel can never conduct water again
occasionally healed where water can seep in and fill it
dry summer conditions cause them
eventually all tracheids & vessels cavitate
freezing in winter causes them
vibration by wind causes them
burrowing insects cause them
Control of Water Transport by Guard Cells
when water supply in soil is adequate, water loss is advantageous
if soil supply of water is too dry, transpiration represents an immediate, potentially lethal threat due to desiccation
healthy, turgid plants=light usually controls guard cell water relations
abscisic acid=produced by leaves when stressed causing guard cells to close right away
often occurs in the early afternoon on a warm, dry day
stops photosynthesis