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Chapter 12: Transport Processes (Diffusion, Osmosis, and Active Transport,…
Chapter 12: Transport Processes
Long-distance Transport: Xylem
Water Transport Through Xylem
Transstomatal transpiration
water loss
-50.0 MPa
Cohesion-tension hypothesis
most accepted model
Transcuticular transpiration
water loss through cuticle
Control of Water Transport by Guard Cells
influenced by water loss
#
dry atmosphere
determines guard cells opening
Properties of Water
Cohesive
liquid water
Soil adhesion
soil dries
water unusable
Adhesive
molecular interaction
Long-Distance Transport: Phloem
#
actively transported
sugars go into sieve elements
sources
sites
#
transport of water and nutrients
polymer trap mechanism
mechanism that loads phloem
pressure flow hypothesis
water and nutrients moved through phloem
most supported theory
Diffusion, Osmosis, and Active Transport
membrane types
completely impermeable
nothing is allowed passage
differentially or selectively permeable
only certain substances pass
freely permeable
all solutes diffuse
osmosis
less conc. to more conc. solution
aquaporins
protein channels
diffusion
random movement of particles
molecular pumps
ATP used for movement across membrane
active transport
extremely concentrated on the receiving side
intracellular transport
vesicles migrate through cytoplasm
fuses with another organelle
Short-Distance Intercellular Transport
Motor Cells
stimulus
midrib or at petiole attachment
flexing
folding
venus fly trap
motor cells virtually collapse
Transfer Cells
found in many areas
nutrient passage to embryos
loading of sugar in or out phloem
#
glands that secrete salt
smooth walls
Guard Cells
#
opening and closing of stomata
usage of potassium ions
impermeable membrane
potassium cannot leave
Water Potential
Cells and Water Movement
lysis
animal cells
burst in pure water
equal movement of molecules
in each direction
Water available in Water
Eutrophication
abundant algae growth
suffocates fish
Water available in Air
incipient plasmolysis
protoplast moves away from wall
plasmolyzed
moves completely away from wall
Long-distance transport: phloem cont'd
Specific mass
cross-sectional area of phloem
STM/CC complex
functional unit
conducting cells
companion cells
Sinks
sites
receive transported phloem sap
Mass transfer
phloem
sugars and nutrients (not water) transported
measured per hour
P-protein
phloem protein
fine network adjacent to plasma membrane
in all eudicots
not in all monocots
P-protein plug
mass is too large to pass
forms plug
Callose
uninjured phloem
