Homeostasis & Transport Homeostasis Passive Transport Active Transport.

Homeostasis & Homeostasis & TransportTransport

HomeostasisHomeostasis

Passive TransportPassive Transport

Active TransportActive Transport

HomeostasisHomeostasis

Plasma Membrane Plasma Membrane StructureStructure

Membrane Protein Membrane Protein FunctionsFunctions

Passive TransportPassive Transport

• DiffusionDiffusion EquilibriumEquilibrium Diffusion across membranesDiffusion across membranes

• OsmosisOsmosis:: Direction of osmosisDirection of osmosis How cells deal with osmosisHow cells deal with osmosis

• Facilitated DiffusionFacilitated Diffusion• Ion ChannelsIon Channels

Learning Learning ObjectivesObjectives

1.1. Explain how an equilibrium is established Explain how an equilibrium is established as a result of diffusionas a result of diffusion

2.2. Distinguish btw/ diffusion & osmosisDistinguish btw/ diffusion & osmosis

3.3. Explain how substances cross the cell Explain how substances cross the cell membrane through facilitated diffusionmembrane through facilitated diffusion

4.4. Explain how ion channels assist the Explain how ion channels assist the diffusion of ions across the cell diffusion of ions across the cell membranemembrane

DiffusionDiffusion

• DiffusionDiffusion The The movementmovement of moleculesof molecules from an from an

area of area of higher concentrationhigher concentration to an to an area of area of lower concentrationlower concentration until until equilibrium is reachedequilibrium is reached

• Concentration GradientConcentration Gradient The The difference in concentrationdifference in concentration of of

molecules across spacemolecules across space Molecules diffuse Molecules diffuse downdown their their

concentration gradientsconcentration gradients

DiffusionDiffusion

• The movement of substances from a The movement of substances from a region of high concentration to a region region of high concentration to a region of low concentration until equilibrium is of low concentration until equilibrium is reachedreached

Simple DiffusionSimple Diffusion

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EquilibriumEquilibrium

• EquilibriumEquilibrium The The equal concentrationequal concentration of molecules of molecules

throughout the spacethroughout the space they occupy they occupy Random movementRandom movement of molecules of molecules

continues at equilibrium but there is continues at equilibrium but there is no concentration gradientno concentration gradient

Molecules are just as likely to move in Molecules are just as likely to move in one direction as in any otherone direction as in any other

Diffusion Across Diffusion Across A MembraneA Membrane

DiffusionDiffusion

OsmosisOsmosis

• OsmosisOsmosis The process by which The process by which water molecules water molecules

diffuse across a cell membranediffuse across a cell membrane from from an area of higher concentration to an an area of higher concentration to an area of lower concentrationarea of lower concentration

• Direction of OsmosisDirection of Osmosis Depends on the relative concentration Depends on the relative concentration

of solutes on the two sides of the cell of solutes on the two sides of the cell membranemembrane

Direction of OsmosisDirection of Osmosis

• If [solute] in cytosol If [solute] in cytosol >> [solute] [solute] outside celloutside cell water diffuses INTO the cellwater diffuses INTO the cell A solution w/ A solution w/ higherhigher [ [solutesolute] is said to ] is said to

be be hypertonichypertonic• If [solute] outside cell If [solute] outside cell >> [solute] in [solute] in

cytosolcytosol water diffuses OUT OF the cellwater diffuses OUT OF the cell A solution w/ A solution w/ lowerlower [ [solutesolute] is said to ] is said to

be be hypotonichypotonic

Direction of OsmosisDirection of Osmosis

• If [solute] in cytosol If [solute] in cytosol == [solute] [solute] outside celloutside cell water diffuses equally in both water diffuses equally in both

directionsdirections there is no net gain or loss of water there is no net gain or loss of water

by the cellby the cell Solutions w/ Solutions w/ equalequal [ [solutesolute] are said to ] are said to

be be isotonicisotonic

OsmosisOsmosis



Tonicity &Tonicity &Water ConcentrationWater Concentration

• Hypotonic SolutionHypotonic Solution:: ↓ ↓ [[solutesolute] ↑ [] ↑ [HH22OO]]

• Hypertonic SolutionHypertonic Solution:: ↑ ↑ [[solutesolute] ↓ [] ↓ [HH22OO]]

• Isotonic SolutionsIsotonic Solutions:: solutesolute concentrations equal concentrations equal waterwater concentrations equal concentrations equal

How Cells How Cells Deal With OsmosisDeal With Osmosis

• Cells in isotonic conditions have no Cells in isotonic conditions have no trouble maintaining water balance trouble maintaining water balance (homeostasis)(homeostasis) Land vertebratesLand vertebrates Most marine organismsMost marine organisms

• Many cells function in hypotonic Many cells function in hypotonic environmentsenvironments Unicellular freshwater organismsUnicellular freshwater organisms

OsmoregulationOsmoregulation

Contractile Contractile vacuole - fullvacuole - full

RBCs & TonicityRBCs & Tonicity

Plant Cells & TonicityPlant Cells & Tonicity

Facilitated DiffusionFacilitated Diffusion

• Facilitated DiffusionFacilitated Diffusion The process by which a substance The process by which a substance

moves down its concentration moves down its concentration gradientgradient across a cell membrane with across a cell membrane with the assistance of a carrier proteinthe assistance of a carrier protein

• Carrier ProteinCarrier Protein A A membrane protein that transports membrane protein that transports

specific substancesspecific substances across a cell across a cell membranemembrane

Facilitated Facilitated DiffusionDiffusion

• Substances using Substances using facilitated facilitated diffusion:diffusion:– Large, water Large, water

soluble moleculessoluble molecules– Charged (+ or -) Charged (+ or -)

molecules or ionsmolecules or ions





Diffusion ThroughDiffusion ThroughIon ChannelsIon Channels

• Ion channelIon channel A membrane protein that provides a A membrane protein that provides a

passagewaypassageway across a cell membrane across a cell membrane through which an ion can diffusethrough which an ion can diffuse

• Channel TypesChannel Types Open channelsOpen channels – always remain open – always remain open Gated channelsGated channels – can open or close in – can open or close in

response to a stimulusresponse to a stimulus

Ion ChannelsIon Channels

ION CHANNELSION CHANNELS

Channel Protein FunctionChannel Protein Function



Passive Transport &Passive Transport &Membrane PermeabilityMembrane Permeability

Passive -v- Active Passive -v- Active TransportTransport

• PassivePassive TransportTransport:: Occurs Occurs w/out energy inputw/out energy input from ATP from ATP Ex: simple diffusion; osmosis; Ex: simple diffusion; osmosis;

facilitated diffusion; ion channelsfacilitated diffusion; ion channels

• ActiveActive TransportTransport:: Requires energy inputRequires energy input from ATP from ATP Ex: ion pumps; vesicular transportEx: ion pumps; vesicular transport

Active TransportActive Transport

• CellCell MembraneMembrane PumpsPumps Sodium-potassium PumpSodium-potassium Pump

• VesicularVesicular TransportTransport:: EndocytosisEndocytosis ExocytosisExocytosis

LearningLearningObjectivesObjectives

1.1. Distinguish btw/ passive Distinguish btw/ passive transport & active transporttransport & active transport

2.2. Explain how the sodium-Explain how the sodium-potassium pump operatespotassium pump operates

3.3. Compare & contrast endocytosis Compare & contrast endocytosis & exocytosis& exocytosis

Cell Membrane PumpsCell Membrane Pumps

• Sodium-potassium PumpSodium-potassium Pump Carrier proteinCarrier protein that that actively transportsactively transports Na Na

ionsions out of out of && K ionsK ions into the cell into the cell Pumps NaPumps Na++ & K & K++ againstagainst theirtheir concentration concentration

gradientsgradients Requires Requires energy fromenergy from ATP ATP

• Proton PumpProton Pump Carrier protein Carrier protein that that activelyactively transports Htransports H++

ions ions againstagainst their their concentration gradientconcentration gradient Important in photosynthesis & cellular Important in photosynthesis & cellular

respirationrespiration

Protein Pump FunctionProtein Pump Function



NaNa++ - K - K++ Exchange Pump Exchange Pump

Na-K Ion PumpNa-K Ion Pump


• MOV Video plays about 1 minMOV Video plays about 1 min

Proton PumpProton Pump

Endocytosis & ExocytosisEndocytosis & Exocytosis



Vesicular TransportVesicular Transport

• EndocytosisEndocytosis Process by which aProcess by which a cell surrounds & cell surrounds &

engulfs substancesengulfs substances RequiresRequires energy from ATP energy from ATP to form to form

vesiclevesicle• Types of EndocytosisTypes of Endocytosis::

PinocytosisPinocytosis – cell engulfs– cell engulfs fluids &/or fluids &/or solutes solutes

PhagocytosisPhagocytosis – cell engulfs – cell engulfs large large particles or whole cellsparticles or whole cells

PhagocytosisPhagocytosisof Paramecium by Amoebaof Paramecium by Amoeba

ParameciumParamecium in in foodfood vacuole vacuole

lysosomeslysosomesAmoebaAmoeba is a is a phagocytephagocyte


• ExocytosisExocytosis Process by which aProcess by which a vesicle inside a vesicle inside a

cell fuses w/ the cell membrane cell fuses w/ the cell membrane & & releases its contents to the external releases its contents to the external environmentenvironment

Requires Requires energy from ATPenergy from ATP to move to move vesiclevesicle to cell membrane to cell membrane




Endocytosis & Exocytosis Endocytosis & Exocytosis in a WBCin a WBC

Homeostasis & Transport Homeostasis Passive Transport Active Transport.

Documents

cell solute

cell water

water molecules

cytosol solute

hypertonicif solute

cytosol water

area of higher concentration

solute h2ohypertonic