Cellular Transport

‘07 Biology

2 Types:

PassiveNo energy!

ActiveEnergy!

Passive TransportSubstances are allowed to cross the cell

membrane without any input of energyRemember: The cell membrane is

“selectively permeable”

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Types of Passive TransportDiffusionFacilitated DiffusionOsmosis

DiffusionMovement of molecules from areas of

high concentration to lowHow does it work?“Kinetic energy” (energy in motion)Concentration gradient- caused by a

difference in concentrationDiffusion results in equilibrium (all

molecules occupy the same amount of space)

Facilitated DiffusionSome molecules are helped across the

cell membrane by carrier proteinsNo energy is required in this process

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OsmosisThe diffusion of water across the

cell membraneThe direction of osmosis depends

on the concentration of solutes inside and outside the cell

Osmosis (continued)Hypotonic- concentration of solutes

outside the cell is lower than the concentration inside

Hypertonic- concentration outside is higher than inside

Isotonic- concentrations inside and out are equal

Direction of Osmosis

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Active TransportSometimes cells must move molecules

against the concentration gradientThis process requires energy (ATP)

and special protein “pumps”

Sodium-Potassium PumpSpecial proteins within the membrane

that transport Na+ and K- ionsSome cells must have a higher

concentration of Na+ ions outside of the cell and a higher concentration of K- ions inside the cell

2 Potassiums are brought in for every 3 Sodiums removed

Sodium-Potassium Pump

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Movement In VesiclesSome molecules are too big to be

transported across the cell membrane by passive and active transport

Endocytosis- “cell eating”Exocytosis- “cell pooping”

EndocytosisProcess by which cells ingest

macromolecules, fluids, large particles and even other cells

These molecules are enclose in a bubble of membrane (vesicle) that pinches away from the cell membrane

Endocytosis (continued)Pinocytosis- ingestion of small

particles and fluidPhagocytosis- ingestion of large

molecules or other cells

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ExocytosisProcess by which waste and large

particles are released from the cellA vesicle will fuse with the membrane,

releasing its contents into the extra cellular environment

Endocytosis/Exocytosis

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