Download Cellular transport

6.3-Active & Passive Transport
Across Cell Membranes
*Connect diffusion to equilibrium.
*Describe how and why passive transport occurs.
*Relate osmosis to solute concentration.
*Explain how active transport differs from passive
transport.
*Describe how large and/or charged molecules move
through a cell’s membrane.
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Passive Transport
No energy expended by the
cell
Goes “downhill” with the
concentration gradient
Substances move from
[HI]
[LOW]
Examples: diffusion, osmosis,
facilitated diffusion
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Active Transport
Requires cell to expend energy
Goes “uphill” or against the
concentration gradient
Involves embedded proteins
(transport proteins) acting like
pumps
Other examples: Exocytosis,
endocytosis, pinocytosis,
phagocytosis
Diffusion
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Solution = solute + solvent
Solute- substance that is dissolved
Solvent- substance that does the dissolving (fluid)
Solute particles dissolved in a solvent are constantly
in motion.
Temperature
motion
This constant motion causes DIFFUSION
Diffusion- movement of particles from areas of
high concentration to areas of low concentration
[HI]
[LOW]
Diffusion
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The net flow of solute continues until equilibrium is reached.
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Solute continue to move across the membrane, but for every one that
moves in one direction, another moves in the opposite direction, so
there is no net movement.
[HI]
[MED]
[LOW]
[MED]
Diffusion
not all substances can pass thru a cell membrane.
Diffusion
not all substances can pass thru a cell membrane.
Facilitated Diffusion
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Diffusion “made easy”
No energy required, goes with the concentration gradient
Embedded proteins (channels) provide a convenient pathway
for LARGE and/or charged substances to pass thru cell
membrane.
Also called “passive diffusion”
Another type of embedded protein, a carrier/transport
protein, grabs hold and carries the substance thru a cell
membrane.
Still, no energy required
Ions, sugars, etc… now can enter and leave cells
Facilitated Diffusion
Protein Channel
Facilitated
Diffusion
Can involve embedded protein channels
OR
Embedded protein carrier/transport
molecules
NO ENERGY REQUIRED
IT IS A PASSIVE PROCESS
Facilitated Diffusion
Substances move from
areas of high
concentration to areas of
low concentration
NO ENERGY REQUIRED
IT IS A PASSIVE PROCESS
OSMOSIS
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Diffusion of water
Passive process, does
not require energy
The membrane is
permeable to water,
the solvent.
The membrane is not
permeable
(impermeable) to the
solute.
Osmosis
Osmosis and Tonicity
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Hypertonic- the solution that has
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Hypotonic- the solution that has
[solute]
Water flows toward the hypertonic environment
[solute]
Water flows away from a hypotonic environment
Isotonic- the solutions have
equal concentrations of solute
(no net osmosis)
Osmosis and Tonicity
Water Balance in Animal Cells
Compared to the solute-free cup
of water, the cell is hypertonic
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If the animal cell is in a
hypotonic environment…
…the cell gains water,
swells, and may even pop
like an overfilled balloon!
Osmosis can kill cells
Water Balance in Animal Cells
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If the cell is in a
hypertonic environment…
The environment has
higher [solute] than the
cell…
The cell loses water
(osmosis) and shrivels
and may die
Osmosis kills
Water Balance in Plant Cells
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Plant cells like a hypotonic environment (water flows in)
Their strong cell walls withstand the osmotic pressure
that can cause animal cells to burst or shrivel
Active Transport
Cells use energy (ATP) to move large molecules or ions thru a cell
membrane
Usually, these substances are moved “uphill” or against the
concentration gradient. In other words, the substances are moved in
the opposite direction of diffusion (passive transport)
The embedded proteins involved are often called PUMPS
Examples: pumps, exocytosis, endocytosis, phagocytosis,
pinocytosis.
Active Transport: Pumps
Active Transport: Exocytosis
For really LARGE molecules, vesicles form and fuse
to the plasma membrane & spills its contents out
Active Transport: Exocytosis
Active Transport: Endocytosis
1. Vesicles bud inward
2. Opposite ends of the cell
membrane meet & connect
3. Vesicle pinches off & brings
LARGE substances into cell
Active Transport: Endocytosis
An Amoeba feeding
via the process of
endocytosis.
Active Transport: Pinocytosis
Cells actively engulf large
quantities of fluid (water)
Vesicles/vacuoles
Active Transport: Phagocytosis
6.3: Passive & Active Transport Online Review
Diffusion & Osmosis Animation 1, 2, 3, 4, 5
Osmosis Tutorial 1, 2
Cellular Transport Animation 1, 2,
Cellular Transport Tutorial 1
Diffusion/Osmosis Quiz 1, 2, 3, 4, 5, 6, 7, 8
Cell Transport Quiz 1, 2, 3, 4, 5, 6
Active Transport by Group Translocation
Animation
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