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Cell Transport
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The molecules can move freely in the membrane.
They are constantly renewed during a cell's life span.
Grow with the growth of cell and its organelles.
Regenerate to some extent in cases of minor
disruptions.
Contract and expand during cell movements.
Allow interactions of cells such as recognition of self
and fusion of cell.
Regulate the flow of materials passing through them.
These properties indicate that
biomembranes are fluid and dynamic.
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Fluid - highly viscous fluid
Mosaic = matrix of…
 Bilayer of phospholipids
 Globular proteins embedded
▪ Channel proteins (doorways)
▪ Marker proteins (name badge)
▪ Receptor proteins (on/off switch)
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The membrane is only as good as its parts
 Phospho-
portion is polar and attracts
 -lipid portion is nonpolar and repels
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Jobs:
 Acts as a barrier
 Transports materials
 Transfers materials
 Processes materials
Inside the cell membrane
 The amount of a substance per volume is the
concentration
 The concentration of molecules ranges from
high to low, hence gradient.
 But molecules
 are in constant motion
 collide into & bounce off of one another
 eventually spread out evenly = equilibrium
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maintain a constant internal conditions
(homeostasis)
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respond to their environment (the
concentration gradient)
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balance between inside and outside
concentrations occurs to create equilibrium
 molecules are transported into the cell if there’s
more outside the cell
 molecules are transported out of the cell if there’s
more inside the cell
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Passive Transport
 Simple diffusion (solute)
 Facilitated diffusion (with help)
 Osmosis (water)
Molecules move with the concentration
gradient (from high to low)
 Requires no energy
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Carrier or
channel
proteins help
large
molecules to
diffuse from
high to low
 Water movement from high to low
concentrations
 Osmotic pressure is the force exerted on
the cell membrane from the water found on
either side of the cell membrane
 Osmotic (water) pressure gives plant cells
turgidity (crisp veggies vs. soggy)
When is equilibrium reached in a
solution?
 When equal concentrations of
molecules are found throughout the
solution or on either side of a semipermeable membrane, like that of a
cell.
 Active transport – move against
gradient (from low to high )
 Sodium-potassium pump
 Endocytosis (cell eating – think
PacMan) to form vacuoles
 Exocytosis (cell pooping) to rid
cells of waste
The [concentration] of dissolved solutes
inside/outside of the cell.
 Start by determining the concentration of
solutes found inside the cell.
 Then determine the concentration of
solutes found outside the cell.
 Compare the two.
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concentration of dissolved solutes is
equal to cell contents
 Cell is in equilibrium with its
environment
 No net movement of solutes or water in
either direction
 Molecules are still moving but equally in
BOTH directions
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Concentration of dissolved solutes is
greater than cell contents
 Water moves out
 Cell size shrinks = “skinny” cell
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concentration of dissolved solutes is less
than cell contents
 Water moves in and solute moves out
 Cell size swell/increase = “hippo-fat” cell
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