Cell Transport Mechanisms

Moving molecules across the Cell Membrane

Two methods:

Passive Transport

Active Transport

Does not expend energy

Does expend energy

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

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

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

Diffusion across a Membrane

Examples:small molecules (CO2,O2)small lipidsalcohol

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

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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Passive Transport – Osmosis

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

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

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

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

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

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

Quick Quiz!! What kind of cell transport is illustrated below?

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0% 0%0%

A. Diffusion

B. Osmosis

C. Facilitated Diffusion

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

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).

Endocytosis

Molecules move into a “pocket” of the cell membrane

Endocytosis“Pocket” pinches off the membrane into cytoplasm

Endocytosis

Vesicle has now formed and can move around inside cell

Exocytosis

Vesicle pinches off Golgi Apparatus

Exocytosis

Free vesicle migrates towards cell membrane

Exocytosis

Vesicle contacts cell membrane and begins to fuse with it

Exocytosis

As vesicle becomes part of plasma membrane, contents spill out of cell

Endocytosis and Exocytosis

These two processes occur at roughly the same rate

=No overall change in cell’s size