Active & Passive Active & Passive TransportTransport

Across Cell MembranesAcross Cell Membranes

Cells Need to Exchange Cells Need to Exchange Materials with the Materials with the Extracellular FluidExtracellular Fluid

Membrane PermeabilityMembrane Permeability

SizeSize

- the smaller the particle, the more - the smaller the particle, the more permeablepermeable

- small molecules (O- small molecules (O22, CO, CO22, H, H22O) canO) can

- large molecules (proteins, DNA) cannot- large molecules (proteins, DNA) cannot Lipid SolubilityLipid Solubility

- Yes: nonpolar molecules (O- Yes: nonpolar molecules (O22, cholesterol), cholesterol)

- No: charged ions, polar molecules (Na- No: charged ions, polar molecules (Na++, , ClCl--, ,

large molecules (glucose)large molecules (glucose)

Passive TransportPassive Transport No energy expended by No energy expended by

the cellthe cell Goes Goes ““downhilldownhill”” with with

the concentration the concentration gradientgradient

Substances move from Substances move from [HIGH][HIGH] [LOW][LOW] Examples: Examples: diffusion, diffusion,

osmosis, facilitated osmosis, facilitated diffusiondiffusion

Active TransportActive Transport Requires cell to expend Requires cell to expend

energy energy Goes Goes ““uphilluphill”” or against or against

the concentration the concentration gradientgradient

Involves embedded Involves embedded proteins (transport proteins (transport proteins) acting like proteins) acting like pumpspumps

Other examples: Other examples: Exocytosis, endocytosis, Exocytosis, endocytosis, pinocytosis, phagocytosispinocytosis, phagocytosis

DiffusionDiffusion Solution = solute + solventSolution = solute + solvent Solute-Solute- substance that is dissolved substance that is dissolved Solvent-Solvent- substance that does the dissolving substance that does the dissolving

(fluid)(fluid) Solute particles dissolved in a solvent are Solute particles dissolved in a solvent are

constantly in motion. constantly in motion. TemperatureTemperature motionmotion

This constant motion causes This constant motion causes DIFFUSIONDIFFUSION Diffusion-Diffusion- movement of particles from movement of particles from

areas of high concentration to areas of low areas of high concentration to areas of low concentrationconcentration

[HIGH] [LOW][HIGH] [LOW]

Solvent transport is from right to left.

The net flow of solute continues until The net flow of solute continues until equilibriumequilibrium is is reached.reached.

Solute continue to move across the membrane, but for Solute continue to move across the membrane, but for every one that moves in one direction, another moves every one that moves in one direction, another moves in the opposite direction, so there is no net movement.in the opposite direction, so there is no net movement.

[HI][HI] [LOW][LOW]

[MED] [MED][MED] [MED]

Diffusion

DiffusionDiffusionnot all substances can pass through a not all substances can pass through a

cell membrane.cell membrane.

Facilitated DiffusionFacilitated Diffusion Diffusion Diffusion ““made easymade easy”” No energy required, goes with the concentration No energy required, goes with the concentration

gradientgradient Embedded proteins (Embedded proteins (channelschannels) provide a convenient ) provide a convenient

pathway for pathway for LARGELARGE and/or and/or charged charged substances to pass substances to pass thru cell membrane. thru cell membrane. Also called Also called ““passive passive diffusiondiffusion””

Another type of embedded protein, a Another type of embedded protein, a carrier/transport carrier/transport proteinprotein, grabs hold and carries the substance thru a , grabs hold and carries the substance thru a cell membrane. cell membrane. Still, no energy requiredStill, no energy required

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

Facilitated Diffusion

Facilitated Diffusion

Can involve embedded protein channels

OR

Embedded protein carrier/transport molecules

Facilitated Diffusion

Substances move from areas of high concentration to

areas of low concentration

NO ENERGY REQUIRED

IT IS A PASSIVE PROCESS

Factors Affecting the Rate of Diffusion•Magnitude of the gradient gradient rate

•Permeability of the membrane permeability rate

•Temperature of the Solution temperature rate

•The surface area of the membrane through which diffusion is taking place SA rate

OSMOSISOSMOSIS Diffusion of Diffusion of waterwater PassivePassive process, process,

does not require does not require energyenergy

The membrane is The membrane is permeable to permeable to water, the solvent.water, the solvent.

The membrane is The membrane is not permeable not permeable (impermeable) to (impermeable) to the solute.the solute.

OsmosisOsmosis

Osmosis and TonicityOsmosis and Tonicity HyperHypertonictonic- the solution that has [solute and less - the solution that has [solute and less

water]water]

Water flows Water flows towardtoward the hypertonic environment the hypertonic environment

HypoHypotonictonic- the solution that has [solute and more - the solution that has [solute and more water]water]

Water flows Water flows awayaway from a hypotonic environment from a hypotonic environmentIsotonic- the solutions have equal concentrations of solute (no net osmosis)

Water Balance in Animal Water Balance in Animal CellsCells

If the animal cell is If the animal cell is in a in a hypotonichypotonic environment…environment…

……the cell gains the cell gains water, swells, and water, swells, and may even pop like may even pop like an overfilled an overfilled balloon!balloon!

Osmosis can kill Osmosis can kill cellscells

Hypo – more Hypo – more waterwater

Hyper – less Hyper – less waterwater

Water Balance in Animal Water Balance in Animal CellsCells

If the cell is in a If the cell is in a hypertonichypertonic environment… environment…

The environment The environment has higher [solute] has higher [solute] than the cell…than the cell…

The cell loses water The cell loses water (osmosis) and (osmosis) and shrivels and may dieshrivels and may die

Osmosis killsOsmosis kills

Water Balance in Plant Water Balance in Plant CellsCells

Plant cells like a Plant cells like a hypotonichypotonic environment (water flows environment (water flows in)in)

Their strong cell walls withstand the Their strong cell walls withstand the osmotic pressureosmotic pressure that can cause animal cells to burst or shrivelthat can cause animal cells to burst or shrivel

Cells use energy Cells use energy (ATP)(ATP) to move large molecules or to move large molecules or ions thru a cell membraneions thru a cell membraneUsually, these substances are moved Usually, these substances are moved ““uphilluphill”” or or against the concentration gradient. In other words, against the concentration gradient. In other words, the substances are moved in the opposite direction of the substances are moved in the opposite direction of diffusion diffusion (passive transport)(passive transport)The embedded proteins involved are often called The embedded proteins involved are often called PUMPSPUMPSExamples: Examples: pumps, exocytosis, endocytosis, pumps, exocytosis, endocytosis, phagocytosis, pinocytosisphagocytosis, pinocytosis..

Active Active TransportTransport

Active Transport: Active Transport: PumpsPumps

Facilitated DiffusionFacilitated Diffusion Facilitated Facilitated

Diffusion-Diffusion- molecules move molecules move down a down a concentration concentration gradient with the aid gradient with the aid of special proteins.of special proteins.

Active TransportActive Transport Requires Energy.Requires Energy. ATPATP (form of (form of

energy made by energy made by mitochondria).mitochondria).

Moves Moves againstagainst the concentration the concentration gradient.gradient.

Active Transport: Active Transport: ExocytosisExocytosis

For really LARGE molecules, vesicles For really LARGE molecules, vesicles form and fuse to the plasma membrane form and fuse to the plasma membrane

& spills its contents out& spills its contents out

Active Transport: Active Transport: ExocytosisExocytosis

Active Transport: Active Transport: EndocytosisEndocytosis

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: Active Transport: EndocytosisEndocytosis

Active Transport: Active Transport: PinocytosisPinocytosis

Cells actively engulf Cells actively engulf large quantities of fluid large quantities of fluid

(water)(water)

Vesicles/vacuoles

Active Transport: Active Transport: PhagocytosisPhagocytosis

Solid particlesSolid particles

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