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Cell Transport Mechanisms
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Moving molecules across the Cell Membrane
Two methods:
Passive Transport
Active Transport
Does not expend energy
Does expend energy
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Passive TransportAllows molecules to move on their own according to natural laws of physics
Everything tends towards disorder/chaos
Three types of passive transport mechanisms:Diffusion
OsmosisFacilitated diffusion
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Passive Transport – Diffusion
This forces molecules to move from areas of high concentration to areas of low concentration
Down a concentration gradient“Down the hill”
High Concentration
Low Concentration
Movement of molecules is randomWhen they bump into each other, they push each other awayWhen they are highly concentrated, they bump into each other more often
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Passive Transport – Diffusion
When molecules have reached equal concentrations in both locations, diffusion ends.
Molecules continue moving, but they move in both directions equally. NO NET CHANGE.
= Equilibrium
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Diffusion across a Membrane
Examples:small molecules (CO2,O2)small lipidsalcohol
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Quick Quiz!! In the situation below, what direction will the net movement of solutes be?
0% 0% 0%0%
A. To the left
B. Into the cell
C. Out of the cell
D. In circles
Inside cell
Outside cell
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Passive Transport – Osmosis
Moves water molecules across cell membrane (into or out of cells)Molecules still move down the concentration gradient
Purple dots are solutes, not water molecules
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Quick Quiz!! What direction do you think the water molecules will go?
0% 0%0%
A. NowhereB. From the Right to
the LeftC. From the Left to the
Right
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21 22 23 24 25 26 27 28 29 30
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Passive Transport – Osmosis
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Passive Transport – Osmosis
Osmotic Pressure – Pressure created by the presence of water
in the cell…cell shrinks or expands
Example: Blood cell in low/high salt solutions
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Passive Transport – Osmosis
Animal Cell
Plant Cell
Hypertonic Hypertonic Solution:Solution:Conc. of solutes outside cell is higher
5% salt
2% salt
Water leaves cell
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Passive Transport – Osmosis
Isotonic Isotonic Solution:Solution:Conc. of solutes outside cell is equal to inside cell
Animal Cell
Plant Cell
5% salt
5% salt
Water leaves and enters cell at the same rateNO NET MOVEMENT
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Passive Transport – Osmosis
Hypotonic Hypotonic Solution:Solution:Conc. of solutes outside cell is lower
Animal Cell
Plant Cell
2% salt
5% salt
Water enters cell
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Quick Quiz!! This cell is most likely to…
0.05% glucose
0.1% glucose
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0% 0%0%0%
A. Explode
B. Shrink
C. Lose Water
D. Change Color
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Passive Transport – Facilitated Diffusion
Molecules still move down the concentration gradient, but cannot pass phospholipids on their own.
Rely on proteins imbedded in membrane to “help” them acrossProteins are specific to the type of molecule that uses them
Protein Channels Transport Proteins
Examples: watersaltionsglucose
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Quick Quiz!! What kind of cell transport is illustrated below?
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0% 0%0%
A. Diffusion
B. Osmosis
C. Facilitated Diffusion
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Active TransportMoves molecules against the concentration gradient from areas of low concentration to areas of high concentration.
Restores order
Takes energy to “go uphill”
Protein pumps move molecules into or out of cell against gradient.
ATP
Outside Cell Inside Cell
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Active Transport
ExocytosisMoving molecules out of cells
EndocytosisMoving molecules into cellsPhagocytosis: “cellular eating”Pinocytosis: “cellular drinking”
Both processes involve moving large quantities of materials with the use of vesicles (wrap materials in membranes).
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Endocytosis
Molecules move into a “pocket” of the cell membrane
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Endocytosis“Pocket” pinches off the membrane into cytoplasm
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Endocytosis
Vesicle has now formed and can move around inside cell
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Exocytosis
Vesicle pinches off Golgi Apparatus
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Exocytosis
Free vesicle migrates towards cell membrane
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Exocytosis
Vesicle contacts cell membrane and begins to fuse with it
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Exocytosis
As vesicle becomes part of plasma membrane, contents spill out of cell
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Endocytosis and Exocytosis
These two processes occur at roughly the same rate
=No overall change in cell’s size