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CELLULAR TRANSPORT
SBI 3C SEPTEMBER 2010
PASSIVE TRANSPORT:
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Transport that does not require energy.
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Important Terms:
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Dynamic equilibrium:
 A state of balance where particles move in all directions at equal rates.
Selectively Permeable:
 Allows only certain substances to pass through it.
Concentration gradient:
 A difference in concentration between two areas
Transmembrane Protein:
 A protein molecule in a membrane that spans the thickness of the
phospholipid bilayer (goes all the way across the membrane)
Carrier Protein:
 A transmembrane protein that facilitates the diffusion of certain
substances through the membrane.
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SIMPLE DIFFUSION
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A movement of particles from an area of high
concentration to low concentration
Process continues until dynamic equilibrium is reached
and particles are spread out evenly
Examples:
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Small, uncharged molecules, such as water, oxygen, carbon
dioxide
Ions (small, charged molecules) and large molecules
(amino acids, carbohydrates, nucleic acids, large lipids)
cannot pass through easily
SIMPLE DIFFUSION
FACILITATED DIFFUSION:
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Just like simple diffusion except particles are helped
across the membrane by a carrier protein
Used for larger molecules that can’t fit through the
membrane
Continues until dynamic equilibrium is reached
Examples:
 Ions (small, charged molecules)
 Large molecules (amino acids, carbohydrates, nucleic
acids, large lipids)
FACILITATED DIFFUSION:
OSMOSIS

Movement of water across a selectively permeable
membrane from high water concentration (low solute
concentration) to low water concentration (high solute
concentration)
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Note: only the water molecules (open circles) move not
the solute molecules (closed circles)
ISOTONIC SOLUTION
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Equal concentration of solute and water inside and
outside
Everything is balanced and nothing moves
HYPOTONIC SOLUTION
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Lower concentration of solute outside the cell
Higher concentration of water outside the cell
Water enters the cell
Cell swells and bursts
HYPERTONIC SOLUTION
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Higher concentration of solute outside of cell
Lower concentration of water outside of cell
Water leaves the cell
Cell shrivels up
ACTIVE TRANSPORT
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Special carriers use energy
(ATP) to move chemicals
across a membrane
Goes against the
concentration gradient
Keeps going even after
dynamic equilibrium is
reached
SODIUM-POTASSIUM PUMP
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An active transport mechanisms that pumps sodium and
potassium ions into and out of the cell
Required so that nerve and muscle cells function properly
BULK TRANSPORT
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The movement of large quantities of materials into or out
of a cell
Endocytosis:
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A form of bulk transport used to bring large amounts of
materials into the cell from the outside
Two forms:
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Phagocytosis
Pinocytosis
PHAGOCYTOSIS:
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Also known as cell eating
The bulk transport of solids into the cell
PINOCYTOSIS:
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Also known as cell drinking
The bulk transport of liquid into the cell
EXOCYTOSIS:
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The movement of large amounts of material out of a cell
FACTORS AFFECTING RATE OF DIFFUSION:
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Rate of diffusion depends on temperature and
concentration of solute molecules in solution