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Chapter 12: Transport Processes (Long-Distance Transport: Phloem (sources,…
Chapter 12: Transport Processes
Concepts
specific transport occurs
enzymes transport electrons
protons
acetyl groups
entire organisms transport
water
carbohydrates
minerals
other nutrients from one organ to another
roots
leaves
flowers
fruits
basic type of processes
short-distance transport
involves distances of few cell diameter or less
long-distance transport
between cells not close
isolation mechanisms
inhibit movement of substances
essential if transport
Diffusion, Osmosis, and Active Transport
duffusion
simplest
random movement of particles
through a membrane
osmosis
three types of membranes
freely permeable
allow solutes pass through
completely impermeable
not allow anything pass through
selectively permeable
allow only certain substances pass
aquaporins
protein channel
molecular pumps
active transport
molecule extremely concentrated on receiving side
intracellular transport
long periods time
relatively permanent
Water Potential
Cell and Water Movement
lysis
animal cells often burst in pure water
plant cells never burst
water potential
chemical potential
symbol Ψ
free energy
can heat
put under pressure
elevated
pressure potential
Ψp
megapascals (MPa)/ bars
measured units of pressure
osmotic potential
Ψπ
effect solutes have on water Ψ
related # of particles in solution
matric potential
Ψm
water adhesion to nondissolved structures
cell walls
membranes
soil particles
Shorts-Distance Intercellular Transport
Motor Cells
#
sensitive plant
Mimosa pudica
prayer plant
Oxalis
many other species move slowly
reorient themselves by flexing & floding
joints cells
similar to guard cells
Transfer Cells
larger membrane
smooth walls
outgrowths
friger-like
ridge-like
symplast
all protoplasm of one plant
apoplast
small molecules move easily through both wall
intercellular spaces
Guard Cells
#
potassium ions(K+)
Long-Distance Transport: Phloem
pressure flow hypothesis
sources
water
nutrients
actively transported
polymer trap mechanism
conducting cell plasma membranes
permeable to monosaccharides
disaccharides but not to polysaccharides
STM/CC complex
conducting cells
several companion cells
sinks
transport phloem sap
extremely diverse
P-protein
P for phloem
callose
within uninjured phloem
Long-Distance Transport: Xylem
Properties of Water
cohesive
liquid water
adhesive
molecule interact with many substances
adheres firmly to soil particles
Water Transport Through Xylem
cohesion-tension hypothesis
widely accepted model of process
transstomatal transpiration
water loss
transcuticular transpiration
water lost directly through the cuticle
cavitation
H+ broken over large region
water column breaks
broken cable
embolism
between two portions
air bubble
Control of Water Transport by Guard Cells
