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Transport Process :checkered_flag: (Long Distance Transport: Phloem…
Transport Process :checkered_flag:
Diffusion, Osmosis, and Active Transport
diffusion
random movement of particles
to move from
relatively high concentration to
relatively low concentration
diffusion through membrane is called
osmosis
Membranes
membranes are of three types:
differentially or selectively permeable membranes
allow only certain substances to pass through
freely permeable
allows all solutes to diffuse through
completely impermeable
allow anything to pass through
pass through all membranes
movement is rapid
aquaporins
most membranes have
molecular bumps
use ATP
to force molecules through the membrane
remaining in the cell for long periods of time
intercellular transport
water potential
effect that pressure has on water potential
pressure potential
is a negative number and is measured in units of pressure
megapascals or bars
effect that solutes have on water potential
osmotic potential
waters adhesion to nondisolved structures such as cells
matric potential
cells and water movement
cell wall is turgid
presses against the cell wall
cell wall presses back equally
pressure potential is positive
osmotic potential
#
plus pressure potential
equals -0.1MPa
animal cells burst with pure water
lysis
mature parenchyma cells
exert pressure to raise the pressure potential high
immature growing cells cannot generate enough pressure
in growing regions
cells keep osmotic pressure very negative
protoplast pulls away from wall
incipient plasmolysis
pulls away completely away from wall and it shrinks
plasmolyzed
Short Distance Intercellular Transport
protoplasm of one plant
symplast
wall and intercellular spaces
apoplast
Guard cells
at night stomata close
guard cells are shrunken
#
little internal pressure
after sunrise
cells must open potassium enters and cannot leave
motor cells
location of flexure
petiole attaches to lamina or stem
cells at these joints
motor cells
Venus flytraps
motor cells
when shrunken pressure in midrib
causes two halves
Transfer cells
the larger the membrane
the more molecular pumps it can hold
walls are smooth on the outer surface
inner surface
finger like and ridge like outgrowths
are found in
areas where rapid short distance transport is expected to occur
Long Distance Transport: Phloem
pressure flow hypothesis
flow in phloem
is due to
loading sources
active unloading
where water and nutrients
are transported
sources
sources for embryos during germination
cotyledons
endosperms
many species
sugars
are actively transported
into sieve elements
sieve tube members in angiosperms
sieve cells in plants other than angiosperms
in other species
phloem is loaded by
polymer trap mechanism
phloem loading occurs
long vascular bundles
such as fine veins in leaves
conducting cells plasma membranes are permeable to
disaccharides
but not poly saccharides
monosaccharides
consisting of a conducting cell
and one or several companion cells
is called
STM/CC complex
sugars and other nutrients transported
by phloem
mass transfer
mass transfer divided by the cross sectional are of phloem
specific mass
sites that receive transported
phloem sap
sinks
here storage cells do not accumulate sugar as sucrose but instead polymerize it into starch
is under a lot of pressure
if phloem is cut then there is “bleeding”
to seal broken sieve elements
P-Protein
it is carried to sieve area
P-Protein Plug
uninjured phloem
there is a polymer
callose
storage organs
important to
perennial plants
meristems
root tips
leaf primordia
growing flowers
fruits
seeds
plants control direction and flow of phloem
active
phloem transport increases rapidly
dormant
buds receive every little phloem sap
#
stem tip
leaves near stem tip
export upward to the shoot apical meristem
leaves further back
export towards the trunk and roots
Long Distance Transport: Xylem
properties of water
liquid water is cohesive
molecules interact with other substances
adhesive
water transport through xylem
cohesion tension hypothesis
water loss is called
transstomatal transpiration
water loss directly through the cuticle
transecular transpiration
water is held in soil by
cohesion
adhesion
hydrogen bonding is broken
water column breaks
cavitation
air bubble
embolism
control of water transport by Guard cells
if soil is dry to supply water
transpiration represents an immediate
potentially lethal threat due to desiccation
if leaf had adequate moisture content
light and carbon dioxide
are controlling factors
for most healthy plants
light controls guard cell
