cell transport system

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Cell Physiology

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Passive Transport

• No energy expended by thecell

• Goes “downhill” with the

concentration gradient

• Substances move from• [HI] [LOW]

• Examples: diffusion, osmosis,

facilitated diffusion 

 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  

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DIFFUSION

• 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]

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•  The net flow of solute continues until equilibrium is reached.

• Solute continue to move across the membrane, but for every one thatmoves in one direction, another moves in the opposite direction, sothere is no net movement.

[HI]  [LOW]

[MED] [MED]

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DIFFUSION 

Not all substances can pass thru a cell membrane. 

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Diffusion

Not all substances can pass thru a cell membrane.

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Facilitated Diffusion

• 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 cellmembrane.  Also called “passive diffusion”  

•  Another type of embedded protein, a carrier/transport

 protein, grabs hold and carries the substance thru a cellmembrane. Still, no energy required  

• Ions, sugars, etc… now can enter and leave cells 

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Facilitated Diffusion

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Protein Channel

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Facilitated

Diffusion

Can involve embedded

protein channels

OR  

Embedded protein

carrier/transport molecules

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Facilitated DiffusionSubstances move from

areas of high

concentration to areas of 

low concentration

NO ENERGY REQUIRED

IT IS A PASSIVE PROCESS

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NO ENERGY REQUIRED

IT IS A PASSIVE PROCESS

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OSMOSIS

• Diffusion of water

• Passive process, does not

require energy 

•  The membrane is

permeable to water, the

solvent.

•  The membrane is notpermeable (impermeable)

to the solute.

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Osmosis

O i d T i it

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Osmosis and Tonicity• Hyper tonic- the solution that has [solute]

 Water flows toward the hypertonic environment

• Hypo tonic- the solution that has [solute]

 Water flows away from a hypotonic environmentIsotonic- the solutions haveequal concentrations ofsolute (no net osmosis)

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Osmosis and Tonicity

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Water Balance in Animal Cells

• 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

Compared to the solute-free

cup of water, the cell ishypertonic 

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Water Balance in Animal Cells

• If the cell is in a

hypertonic  environment…

•  The environment has

higher [solute] than thecell… 

•  The cell loses water

(osmosis) and shrivels

and may die

• Osmosis kills

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Cells use energy (ATP) to move large molecules or ions thru a cell

membrane

Usually, these substances are moved “uphill” or against theconcentration 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

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Active Transport: Pumps 

A ti T t E t i

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 Active Transport: Exocytosis 

For really LARGE molecules, vesicles form and fuse tothe plasma membrane & spills its contents out 

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Active Transport:

Exocytosis 

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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

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 An Amoeba feeding

 via the process of 

endocytosis. 

Active Transport: Endocytosis 

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 Active Transport: Pinocytosis 

Cells actively engulf largequantities of fluid (water)

 Vesicles/vacuoles

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Active Transport:Phagocytosis