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Ch 12 Transport Processes (Long-Distance Transport: Phloem (STM/CC complex…
Ch 12 Transport Processes
Diffusion, Osmosis, and Active Transport
diffusion
random movement of particles in solution causes them to move from areas where they are in lower concentration
osmosis
diffusion through a membrane
3 Membrane Types
Freely Permeable
membranes allow all solutes to diffuse through them and have little biological significance
Completely Permeable
membranes do not allow anything to pass through as occur as isolation barriers
Selectively Permeable
allow certain substances to pass through
aquaporins
membrane protein that permits water to cross membrane rapidly
molecular pumps
use ATP to forces molecules across membrane
ACTIVE TRANSPORT
Intracellular transport
vesicles migrate through the cytoplasm and fuse with another organelle
Water Potential
Cells and Water Movement
lysis
animal cells explodes in places in pure water
Plant cell NEVER bursts :red_cross: :forbidden:
incipient plasmolysis
protoplast has lost just enough water to pull away from wall
plasmolyzed
cell constantly losses water
water potential
free energy of water
increased by:
heat
under pressure
elevated
pressure potential
effect pressure has on water potential
can be positive
measure in megapascals (MPa)
osmotic potential
effect that solutes have on water potential
number of particles present in solution
matric potential
water's adhesion to nondisolved structures
decrease water's free energy
Water Movement
Water moves whenever there is a difference in water potential within the mass of water
If water potentials are at equilibrium there is no movement of water
Water Potentials must always be considered in pairs or groups
Short-Distance Intercellular Transport
Guard Cells
opening and closing of stomatal pores
at night = shrunken
cat eye when open
water enters and leaves cells at same rate
& adjacent cells are in equilibrium when stomata are fully opened and closed
when open= high negative osmotic potential
abundant K+
Motor Cells
cells at joints
similar to guard cells
accumulate or expend K+
Transfer Cells
walls are smooth on outer surface
ridge-like growths on inner surface
found where rapid, short distance transport occurs
glands that secrete salt
passing nutrients to embryos
sugar is load in or out of phloem
symplast
protoplasm of one plant, one continuous mass
apoplast
intercellular spaces and cell walls of plant
volume of plant not occupied by protoplast
Long-Distance Transport: Phloem
pressure flow hypothesis
flow in phloem is due to active loading in sources and active unloading in sinks
sources
sites from which water and nutrients are stored
polymer trap mechanism
conducting cell plasma membranes are permeable to monosaccharides and disaccharides but not polysaccharides
STM/CC complex
sieve tube members and guard cells work together
in phloem loading and conduction
mass transfer
sugars and nutrients transported by phloem by the hour
specific mass transfer
mass transfer/cross sectional area of phloem
sinks
sites that receive transported phloem sap
P-protein
phloem
fine network adjacent to plasma membrane
callose
seals certain regions
damaged sieve elements
growing pollen tubes
Long-Distance Transport: Xylem
Properties of Water
adhesive
water molecules interact with many other substances
cohesive
acts on neighboring cells
frozen
molecules become strongly bound together
behaves weakly when bound together
Water Transport Through Xylem
cohesion-tension hypothesis
most widely accepted
water is pulled upward by transpiration
molecules cohere sufficiently to withstand tension
transstomatal
water loss through stomata
transcuticular transpiration
water loss through cuticle
poikilohydry
body water content that changes with habitat moisture
cavitation
hydrogen bonding broken over large region and water column breaks
embolism
space between two portions
sometimes called air bubble
expands until surface encounters a solid barrier
Control of Water Transport by Guard Cells
primarily powered by water loss in atmosphere
light and CO2are normal controlling factors
if moisture content is adequate
