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Transport Processes (Diffusion, Osmosis, and Active Transport (3 types of…
Transport Processes
Diffusion, Osmosis, and Active Transport
Diffusion
random movement of particles in solution moving from high to low concentration
Osmosis
diffusion through a membrane
3 types of membranes:
Selectively permeable
allow only certain substances to pass through
Completely impermeable
do not allow anything to pass through
Freely permeable
allow all solutes to move through them
little biological significance
aquaporins
protein channels that allow rapid diffusion of water molecules
molecular pumps
use ATP to force molecules across the membrance
this is active transport
Intracelluar transport
vesicles migrate through the cytoplasm and fuse with another organelle
Water Potential
defined as the free energy of water
pressure potential
the effect that pressure has on water potential
osmotic potential
the effect that solutes have on water potential
matric potential
waters adhesion to nondissolved structures
Cell and Water Movement
incipient plasmolysis
the point at which the protoplast has lost just enough water to pull slightly away from the wall
plasmolyzed
when the protoplast pulls completely away from the wall and shrinks
Long-Distance Transport: Phloem
sources
sites from which water and nutrients are transported
within sources, sugars are actively transported
mass transfer
the actual amount of sugars and other nutrients transported by phloem per hour
specific mass transfer
mass transfer divided by the cross-sectional area of phloem
sinks
sites that receive transported phloem sap
extremely diverse
2 mechanisms seal broken sieve elements
P-protein
a fine network adjacent to the plasma membrane inner surface of uninjured sieve elements
callose
Short-Distance Intracellular Transport
Motor Cells
similar to guard cells
can either accumulate or expel potassium
adjusts their water potential and turgidity
Transfer Cells
found in areas where rapid short-distance transport is expected
Guard Cells
when stomata are closed, they are somewhat shrunken and have little internal pressure
when they must open, K+ are actively transported from surrounding cells inside the guard cells
potassium cannot leave
in hydraulic equilibrium with surrounding cells
Long-Distance Transport: Xylem
Water Transport Through Xylem
transcuticular transpiration
water loss directly through the cuticle
transstomatal transpiration
diffusion from intracellular spaces to the atmosphere
Properties of Water
liquid water is said to be cohesive
any force acting on one molecule acts on all neighboring ones as well
adhesive
waters molecules interact with many other substances
Concepts
basic types of transport processes:
short-distance transport
distances of a few cell diameters or less
long-distance transport
between cells that are not close neighbors
isolation mechanisms
inhibit the movement of substances
