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Passive Transport
Goals
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Relate concentration gradient, diffusion and
equilibrium
Predict direction of water movement in and out
of cells
Describe the importance of ion channels in
passive transport
Identify carrier proteins in facilitated diffusion
Passive Transport
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Random movement across a cell
membrane that does not require any
sort of energy
Passive Transport
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How does this happen?----Imagine
what happens when we place
bouncing balls into one room and
then open the door to another room?
Passive Transport
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Step 1: Imagine many balls bouncing around a
single room.
Step 2: Open a door to the adjoining room,
letting balls out of the room and into the other
Step 3: Eventually the amount of balls per
room will even out
Passive Transport
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Concentration gradient-A
difference in the concentration of a
substance from one spot to another
Passive Transport
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Equilibrium-When each side of the
concentration gradient is equal in
amounts of substances
Passive Transport
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In all solutions, the particles will
move randomly like the balls in the
model.
Passive Transport
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Once equilibrium is reached,
particles still move around
consistently, however we do not see
the movement
Movement
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Cell membrane (Phospholipid
Bilayer)
Selectively Permeable
 Membrane allows materials to dissolve
through
 Nonpolar material repels ions, but
small molecules can filter through
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Cell Membrane
Help organisms maintain
homeostasis by controlling the exit
and entrance of materials
 Passive transport-when organisms
cross the membrane without any
input of energy
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1. The activities of a
cell depend on the
materials that enter
and leave the cell.
2. To stay alive, a
CELL MUST
EXCHANGE Materials
such as Food and
Waste With Its
ENVIRONMENT.
3. These materials
must cross the Cell
Membrane.
4. Small molecules like WATER,
OXYGEN, AND CARBON DIOXIDE can
move in and out freely.
5. Large molecules like PROTEINS AND
CARBOHYDRATES CANNOT.
6. The Cell Membrane is
SEMIPERMEABLE.
7. A SEMIPERMEABLE MEMBRANE OR
SELECTIVELY PERMMEABLE ONLY
ALLOWS CERTAIN MOLECULES TO
PASS THROUGH.
Movement
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Diffusion-Movement of particles
from an area of high concentration to
an area of lower concentration
Diffusion
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Simplest type of passive transport
Driven by kinetic energy-energy of motion
Rate depends on
 Temperature
 Diffusion is quicker at high temperatures
 Type of molecule
 Smaller molecules diffuse faster
Diffusion
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When molecules are dispersed EVENLY, there
is no longer any Diffusion because there is no
longer a Concentration Gradient.
Diffusion will Eventually cause the
Concentration of molecules to be the SAME
Throughout the Space the Molecules Occupy.
Osmosis
Osmosis
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Osmosis-The Diffusion of water
from an area of high concentration
to low concentration across the cell
membrane
Osmosis
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Like any other Diffusing Molecule,
Water moves DOWN its
Concentration Gradient
Osmosis
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OSMOSIS OCCURS IN RESPONSE TO
THE CONCENTRATION OF SOLUTES
DISSOLVED IN WATER.
Osmosis
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SOLUTES-DISSOLVED SUBSTANCES IN
A SOLUTION.
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Cytoplasm is Mostly Water containing many
dissolved solutes.
Osmosis
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No two molecules can occupy the same space
at the same time, so if there are more solutes
there is less water
Water Moves from AREAS of LOW Solute
Concentration to AREAS of HIGH Solute
Concentration.
Osmosis
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HYPERTONIC SOLUTIONMore Solute then solution
Concentration of solute is higher outside the
cell then it is inside the cell
Water Moves out of the cell
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the cell loses too
much water, the
cell will shrivel
and shrink, it
will die
Osmosis
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IN A HYPOTONIC SOLUTIONLess Solute and more solution
concentration of solute inside the cell is higher
then the fluid out of the cell
water will diffuse into the cell
In Hypotonic
Solutions, WATER
DIFFUSES INTO
THE CELL until
Equilibrium is
established.
Osmosis
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Animal cells placed in distilled water
(Hypotonic Solution) will swell and often burst
because of Osmosis.
Cytolysis-bursting of cells due to increased
amounts of water
Osmosis
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Plant Cells do not burst because of their Rigid
Cell Wall.
TURGOR PRESSURE- pressure that Water
molecules exert against the cell wall
Osmosis
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In Isotonic solutions the inside and outside of
the cells are equal
How does this relate to cells
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Single cell organisms and sea faring
vertebrates have no problems in an isotonic
solution
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Many cells function in a Hypotonic
environment, such as Unicellular Freshwater
Organisms. Water Constantly Diffuses into
these Organisms
Facilitated Diffusion
Facilitated Diffusion
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ReviewPassive Transport involves no energy
 Occurs down the gradient
 Diffusion and Osmosis are passive
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Facilitated Diffusion
Molecules that cannot cross by
passive transport are CARRIED
across by CARRIER PROTEINS
EMBEDDED IN the Cell Membrane.
Facilitated Diffusion
1. Carrier Proteins CHANGE SHAPE when
Molecules ATTACH to them.
2. The Carrier Protein then releases the molecule
and returns to its original shape
Facilitated Diffusion
Facilitated Diffusion-THE USE OF
CARRIER PROTEINS
 Facilitated Diffusion can help
substances move Either INTO or
OUT of a Cell
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Facilitated Diffusion
Example- When cells transport
Glucose into the Cell.
 Cells depend on Glucose for much of
their Energy Needs.
 Passive
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Facilitated Diffusion
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Ion Channels-Small passageways across the
membrane which ions can diffuse
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Sodium (Na+) and Potassium (K+)
Facilitated Diffusion
Some ION CHANNELS are always
open.
 Others have "Gates" that open to
allow ions to pass or close to stop
their passage.
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Facilitated Diffusion
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Gates are dependant upon the environment of
the cell
Three kinds of Stimuli that may open or close
the Gates:
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Stretching of the Cell Membrane
Electrical Signals
Chemicals in the Cytosol or External Environment
Active Transport
Goals
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Compare active transport with passive
transport
Describe the importance of the sodiumpotassium pump
Distinguish between endocytosis and
exocytosis
Identify three ways that receptor proteins can
change the activity of the cell
Active Transport
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ACTIVE TRANSPORT-When cells use
energy to move materials from an area of low
concentration to high concentration
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Active Transport
often involves
CARRIER
PROTEINS like
those in Facilitated
Diffusion
Cell Membrane Pumps
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Cell Membrane Pumps-Carrier
proteins that act to move ions across
the membrane during active transport
Cell Membrane Pumps
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IMPORTANT in MAINTAINING ION
CONCENTRATION IN CELLS AND
BETWEEN CELLS.
Cell Membrane Pumps
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SODIUM-POTASSIUM PUMPSIMPORTANT FOR MUSCLE
CONTRACTIONS,
TRANSMISSION OF NERVE IMPULSES
THE ABSORPTION OF NUTRIENTS
Cell Membrane Pumps
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SODIUM-POTASSIUM PUMPS -ANIMAL
CELLS PUMP SODIUM IONS OUT, AND
POTASSIUM IN
Cell Membrane Pumps
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In Plants, ACTIVE TRANSPORT enables
roots to absorb nutrients from the soil
Plant Nutrients are more concentrated inside
the roots than in the surrounding soil
WITHOUT ACTIVE TRANSPORT,
NUTRIENTS would DIFFUSE OUT OF THE
ROOTS
Why does this happen
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Takes away toxic sodium ions from the cell
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Maintains concentration gradient
Bulk Transport-Endocytosis and
Exocytosis
Transport
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Bulk Transport-COMPLEX PROTEINS,that
are too LARGE to cross the Cell Membrane,
travel through the membrane via bulk transport
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4 Types of bulk transport
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Endocytosis
Exocytosis
Pinocytosis
Phagocytosis
Endocytosis
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During ENDOCYTOSIS the Cell
Membrane Folds into a POUCH that Encloses
the Particles
The Pouch pinches off INSIDE the Cell to
form a VESICLE The VESICLE can then fuse
with other Organelles (LYSOSOMES) or
Release its contents into the Cytoplasm.
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PINOCYTOSIS AND PHAGOCYTOSIS
ARE TWO TYPES ON ENDOCYTOSIS
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PINOCYTOSIS IS SOMETIMES CALLED
"CELL DRINKING
PHAGOCYTOSIS -"CELL EATING"
Exocytosis
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EXOCYTOSIS IS THE OPPOSITE OR
REVERSE OF ENDOCYTOSIS
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Exocytosis is when waste and cell products
leave the cell