cell transport system

7/29/2019 Cell Transport System

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Cell Physiology



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



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]



• 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]



DIFFUSION

Not all substances can pass thru a cell membrane.



Diffusion

Not all substances can pass thru a cell membrane.



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



Facilitated Diffusion



Protein Channel



Facilitated

Diffusion

Can involve embedded

protein channels

OR

Embedded protein

carrier/transport molecules



Facilitated DiffusionSubstances move from

areas of high

concentration to areas of

low concentration

NO ENERGY REQUIRED

IT IS A PASSIVE PROCESS



NO ENERGY REQUIRED

IT IS A PASSIVE PROCESS



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.



Osmosis

O i d T i it



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)



Osmosis and Tonicity



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



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



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



Active Transport: Pumps

A ti T t E t i



Active Transport: Exocytosis

For really LARGE molecules, vesicles form and fuse tothe 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



An Amoeba feeding

via the process of

endocytosis.

Active Transport: Endocytosis



Active Transport: Pinocytosis

Cells actively engulf largequantities of fluid (water)

Vesicles/vacuoles



Active Transport:Phagocytosis

cell transport system

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