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Transport Processes (Long Distance Transport Phloem and Xylem (properties…
Transport Processes
Long Distance Transport Phloem and Xylem
supports pressure flow hypothesis
membrane-bound molecular pumps
active transport are postulated
the sites where water and nutrients are transferred are called sources
within sources of many species sugars are actively transported
turned into sieve elements
phloem is loaded by polymer trap mechanism
the actual amount of sugars and nutrients transported per hour is called specific mass transfer
sinks are sites that receive transported phloem sap
P-Protien
properties of water
cohesive
any force acting on one molecule acts on another
adhesive
molecules interacting with other substances
Cohesion-Tension hypothesis
Water from the roots is pulled up by this tension
At night, when stomata close and transpiration stops
the water is held in the stem and leaf by the cohesion of water molecules to each other
the adhesion of water to the cell walls of the xylem vessels and tracheids
Transstomatal transpiratons
When stomata are open, transpiration rates increase; when they are closed, transpiration rates decrease
Stomata are pores in the leaf that allow gas exchange
Transcuticular Transpiration
is the process of water movement through a plant and its evaporation from aerial parts especially from leaves
Water Potential
the potential energy of water per unit volume relative to pure water in reference conditions
can increase in several ways
be heated
under pressure
elevated pressure
cooling it
pressure potential effects water potential
when water is under pressurel is low
water potential increases
pressure potential increases
pressure can be positive or negative
when water is under tension
pressure potential is negative
measured in megapascals
osmotic potential is the effect a solute has on water
matric potential is waters adhesion to non dissolved structures
Short Distance Intercellular Transport
all living cells are connected by plasmodesmata
protoplasm of one plant is called the symplast
the space between the wall and intercellular space is called apoplast
Motor Cells
adjust their internal concentration of potassium ions
alter their turgidity, and hence the cell shape
can either accumulate or expel potassium ions
which adjusts water potential and turgidity
Guard Cells
opening and closing of stomatal pores
guard cells shrink at night
at hydraulic equilibrium with surrounding cells
water enters and leaves cell at same rate
no net change
guard cells are open
potassium ions are transported into guard cells
loss of potassium cause water potential to be negative
absorption of potassium causes it to be increasingly negative
Transfer Cells
specialized parenchyma cells that have an increased surface area
found where rapid short distance transport occurs
Diffusion, Osmosis and Active Transport
Diffusion
the random movement of particles
move from high concentration to low concentration
technically known as osmosis
Three different membranes
Freely Permeable
allows all molecules to move through
no biological significance
Completely Permeable
doesn't allow anything through
isolation barriers
Differentially/Selectively Permeable
allow only certain substances to move through
lipids & proteins are differentially permeable
hydrophobic molecules can pass through any
hydrophilic can cross differentially
only with special protein channels
known as aquaporins
Active Transport
molecular pumps
use ATP to force molecules across membrane
even if it's highly concentrated on receiving side
this is Active Transport
this is a protein
binds to molecule and ATP
ATP splits into ADP and phosphate
energy transferred to pump
Intercellular Transport
vesicle migrates through cytoplasm
fuses with another organelle
