Please enable JavaScript.
Coggle requires JavaScript to display documents.
CHAPTER 12: TRANSPORT PROCESSES, stoma - open, stoma - closed, adhesion…
CHAPTER 12: TRANSPORT PROCESSES
Long-Distance Transport: Phloem
Pressure Flow Hypothesis
sources
types of sources
leaves
photosynthesis
storage sites
tubers
corms
wood and bark parenchyma
fleshy taproots
loading into sieve elements
polymer trap mechanism
STM/CC complex
active transport
protoplasm becomes more concentrated
phloem sap is squeezed through sieve pores
mass transfer
amount of sugars and nutrients transported by phloem per hour
divided by cross-sectional area
specific mass transfer
sinks
types of sinks
storage organs
meristems
root tips
leaf primordia
growing flowers
growing fruits
growing seeds
sugars are actively unloaded
water diffuses outward into surrounding cells
sealing broken sieve elements
P-protein
P-protein plug at sieve plate
callose
precipitates after pressure drop
contributes to plug
after sieve elements cease to function
callose permanently seals them
plants control direction and rate of flow of phloem sap
Water Potential
water potential ψ
changes
increased
heated
put under pressure
elevated
decreased
cooling
reducing pressure
lowering
hydrogen bonds
decreases ψ
water potential equation
ψ = ψπ + ψp + ψm
ψp
pressure potential
effect pressure has on water potential
positive when compressed
negative when stretched or under tension
ψπ
osmotic potential
effect that solutes have on water potential
always negative
ψm
matric potential
water's adhesion to nondissovled structures
always negative
usually insignificant and ignored
for living cells
ψ = ψπ + ψp
measured in megapascals (MPa) or bars
water moves form areas of
relatively +ψ to areas of relatively -ψ
#
mater moves due to difference in ψ within mass of water
if ψ is same, equilibrium
no net movement
ψ must be considered in pairs or groups
Cells and Water Movement
absorbing too much water
animal cells
lysis (rupture)
plant cells
never burst
cell wall exerts enough pressure
new cells
grow
water loss
protoplast shrinks
cell wilts
incipient plasmolysis
the point where protoplast loses just enough water to pull slightly away from the wall
ψp = 0
plasmolyzed
protoplast pulls completely away from the wall and shrinks
Long-Distance Transport: Xylem
Water Transport Through Xylem
Cohesion-Tension Hypothesis
water loss through stomata
transstomatal transpiration
water loss through the cuticle
transcuticular transpiration
loss of water causes gradient of ψ
pulls water through xylem all the way from roots
only a large difference in ψ is strong enough to pull water all the way up a tree
water adheres to sides of tracheids and vessels
layer of immobile water
adds friction
less so in wider cells
dependent on sufficiently moist soil
if too dry
water column breaks
cavitation
less likely in narrower cells
#
creates air bubble
embolism
cannot expand past tracheid
uses perforations to expand through vessel elements
very rarely fixed
climates
hotter and drier
mainly tracheids (narrow)
wetter
lots of wide vessels
temperate
early wood with large vessels
late wood with narrow tracheids
after area cavitates
becomes part of heartwood
Control of Water Transport by Guard Cells
when water supply is adequate
stomata open and lose water
generates water movement
carries minerals from roots to shoots
evaporative cooling
guard cell controls
CO2
light
water
overrides others
Properties of Water
cohesion
sticky to itself
adhsion
sticky to other things
heavy
takes more energy to get to top of tree
Diffusion, Osmosis, and Active Transport
diffusion
high to low concentration
through a membrane
osmosis
membrane types
completely impermeable
no solutes can diffuse
isolation barriers
selectively permeable
some solutes can diffuse
all lipid/protein cell membranes
hydrophobic molecules diffuse easily
polar. hydrophilic molecules must use channels
water passes through all membranes
faster with aquaporins
freely permeable
all solutes can diffuse
little biological significance
active transport
molecular pumps
force molecules across membrane
uses energy from ATP
intracellular transport
vesicles
Short-Distance Intercellular Transport
Guard Cells
#
stomatal pores
closed
guard cells slightly shrunken
hydraulic equilibrium with surrounding cells
open
potassium ions actively transported into guard cells
water potential in guard cells becomes more negative
water enters guard cells
guard cells swell and push apart
stomatal pore opens
hydraulic equilibrium with surrounding cells
Motor Cells
leaves in some plants flex and fold
similar guard cells
pumping of potassium ions controls movement
symplast
all protoplasm of one plant
interconnected through plasmodesmata
apoplast
the wall and intercellular spaces
Transfer Cells
plasma membrane has many outgrowths
increases surface area
increases # of pumps
increases potential for transport
Concepts
diffusion
high concentration to low concentration
types of transport
short-distance
cell to cell
necessary for internal cells
long-distance
between organs
evolved for land plants
roots can reach lower
shoots can stretch higher
vascular tissues
nutrients channeled to specific sites
isolation mechanisms
epidermis
cuticle
endodermis
Casparian strips
