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CELL TRANSPORT
TYPES OF TRANSPORT
Passive Transport: does not require energy to
move substances across the cell membrane
 Active Transport: requires energy to move
substances across the cell membrane
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PASSIVE TRANSPORT VOCABULARY
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Equilibrium: when there is an equal number of
molecules on both sides of the cell membrane
Concentration: the amount of a particular substance
in a given volume
Concentration Gradient: When there is a higher
concentration of a substance on one side than the
other
Diffusion: When a substance moves from an area of
higher concentration to an area of lower concentration
PASSIVE TRANSPORT
When substances enter or leave the cell by
diffusing across the cell membrane down their
concentration gradient
 The direction the substances move depends on
the concentration gradient
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TYPES OF PASSIVE TRANSPORT
Simple Diffusion
 Facilitated Diffusion
 Osmosis
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SIMPLE DIFFUSION
When small, nonpolar (uncharged) substances
pass directly through the lipid bilayer from an
area of higher concentration to an area of lower
concentration
 Ex: If there is more oxygen outside the cell than
inside the cell, it will diffuse across the lipid
bilayer and into the cell.
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FACILITATED DIFFUSION
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Substances that cannot pass directly through
the membrane are helped to diffuse through
the membrane using transport proteins
TRANSPORT PROTEINS
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Channel Proteins: Serve as a tunnel through
the lipid bilayer that allow ions, sugars, and
amino acids to pass through the membrane
 Each
channel only allows specific substances to
pass through
 Ex: The channel for sodium ions does not allow
sugars to pass through
TRANSPORT PROTEINS
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Carrier Proteins: Only transport substances that
fit within their binding site through the cell
membrane
 Carrier
protein binds to a specific substance on one
side of the cell membrane, changes shape and
allows the substance out on the other side of the
cell membrane
OSMOSIS
Facilitated diffusion of
water from an area of
higher concentration to
an area of lower
concentration
 Allows the cell to
maintain water balance
as their environment
changes
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WATER CHANNELS
Since water is a polar substance, it does not
directly diffuse across the cell membrane
 So the cell has specific protein channels that
only allow water to pass through
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PREDICTING WATER MOVEMENT
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The direction the water moves depends on the
concentration of the cell’s environment
HYPERTONIC
Water moves out of the cell
 There is more solute outside the cell than
inside the cell
 The cell loses water and shrinks
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HYPOTONIC
Water moves in
 There is more solute inside the cell than
outside the cell
 Cell gains water and expands
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ISOTONIC
There is the same concentration of water inside
the cell and outside the cell
 Equilibrium is reached
 Cell stays the same size
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ACTIVE TRANSPORT
Transport of substances against their
concentration gradients
 Requires energy usually in the form of ATP
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USE OF CARRIER PROTEINS AS PUMPS
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Carrier proteins require energy to pump
substances across their concentration gradient
SODIUM-POTASSIUM PUMP
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Sodium ions inside the cell bind to the carrier
protein which changes shape and releases sodium
ions outside the cell membrane
As a result a phosphate group is released from the
pump, returning the channel protein to its original
shape, and releasing potassium ions inside the cell
For every three sodium ions pumped out, two
potassium ions are brought inside
This prevents sodium from building up inside the
cell, which would cause the cell to burst due to
osmosis bringing in too much water
VESICLES
Large substances are too big to cross the
membrane in channel proteins so they use
vesicles
 Vesicle membranes are lipid bilayer, so they
can bud off from the cell membrane or fuse
with it to move large substances in or out of the
cell
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ENDOCYTOSIS
The movement of large substances into a cell
using a vesicle
 The cell membrane forms a pouch around the
substance that closes and then pinches off
inside the cell
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 Pinocytosis:
also known as cellular drinking,
engulfing liquid particles
 Phagocytosis: engulfing solid particles
EXOCYTOSIS
The movement of large substances out of a cell
using a vesicle
 Vesicles inside the cell fuse with the cell
membrane and are released outside the cell
 Used to transport proteins modified by the
Golgi apparatus, excrete wastes, or remove
bacteria
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