Cell Structure & Function

Foothill High School Science Department

Cell Structure & Function

Structure & Movement Through Membranes

(There and Back Again)


The Cell Membrane

Key Concept:Key Concept:

The cell membrane regulates The cell membrane regulates what enters and leaves the what enters and leaves the cell and also provides cell and also provides protection and supportprotection and support


The Cell Membrane

• The cell takes in nutrients and expels The cell takes in nutrients and expels wastes plus cell products through the wastes plus cell products through the cell membranecell membrane

• The Basic Structure Of Nearly All Cell The Basic Structure Of Nearly All Cell Membranes Is The Membranes Is The LIPID BILAYERLIPID BILAYER


LIPID BILAYERS

• Form Automatically When Certain Form Automatically When Certain Lipids Are Dissolved In WaterLipids Are Dissolved In Water

• Tough Flexible StructureTough Flexible Structure• Strong Barrier Between Cell Contents Strong Barrier Between Cell Contents

And Its SurroundingsAnd Its Surroundings


LIPID BILAYERS


Fluid Mosaic Model

In Addition To The Bilayer,In Addition To The Bilayer,The Cell Membrane Contains:The Cell Membrane Contains:

• Proteins That FormProteins That Form– Channels & PumpsChannels & Pumps

• Proteins with Carbohydrates That FormProteins with Carbohydrates That Form– Antigenic SitesAntigenic Sites– Communication SitesCommunication Sites


Diffusion

All Living Cells Contain And Are All Living Cells Contain And Are Surrounded By Liquid.Surrounded By Liquid.

• THE CELL MEMBRANE REGULATES THE CELL MEMBRANE REGULATES THE MOVEMENT OF MOLECULES THE MOVEMENT OF MOLECULES FROM ONE SIDE OF THE MEMBRANE FROM ONE SIDE OF THE MEMBRANE TO THE OTHERTO THE OTHER


Cytoplasm

Is A Is A SolutionSolutionOf Many Different Substances Of Many Different Substances

In WaterIn Water


Solution

A liquid mixture of 2 or more A liquid mixture of 2 or more substances evenly mixed.substances evenly mixed.

• SolventSolvent– The liquid in which the substances are The liquid in which the substances are

mixedmixed• SoluteSolute

– Substances dissolved in the SolventSubstances dissolved in the Solvent


Concentration Of Solution

Concentration = Mass of the solute Concentration = Mass of the solute in a given volume of solvent.in a given volume of solvent.

Mass/VolumeMass/Volume e.g.e.g.

12g of NaCl dissolved in 3L H2Oequalsequals

12g/3L12g/3L or 4.0 g/L4.0 g/L


In A Solution

Molecules Are Moving ConstantlyMolecules Are Moving Constantly They Collide and Bounce off each otherThey Collide and Bounce off each other

This causes them to spread out randomlyThis causes them to spread out randomly

Resulting In:Resulting In:Movement from:Movement from:

an area of higher concentration to an an area of higher concentration to an area of lower concentrationarea of lower concentrationThis process is called: DiffusionThis process is called: Diffusion


DIFFUSION

• Molecules move awayMolecules move awayfrom an area of Higher Concentrationfrom an area of Higher Concentrationto area’s of Lower Concentrationto area’s of Lower Concentration

• EquilibriumEquilibrium– Concentration of a solute is the same Concentration of a solute is the same

throughout the solutionthroughout the solution• The concentration is the same EVERYWHEREThe concentration is the same EVERYWHERE


Diffusion

diffusion_osmosis.mov


DIFFUSION

Key ConceptKey Concept::Diffusion Causes Many Substances To Diffusion Causes Many Substances To Move Across A Cell Membrane But:Move Across A Cell Membrane But:

Diffusion Does Diffusion Does NOTNOT Require The CellRequire The CellTo Use EnergyTo Use Energy

It just happens naturally!It just happens naturally!


Diffusion & Cells

• Substances that can diffuse across cell Substances that can diffuse across cell membranes will do so until equilibrium membranes will do so until equilibrium is reachedis reached

DiffusionDiffusioncontinuescontinues afterafter equilibriumequilibrium

but the rates are equalbut the rates are equalin ALL Directionsin ALL Directions

Atoms & Molecules Never Stop MovingAtoms & Molecules Never Stop Moving


OSMOSIS

Osmosis.mov


Osmosis Requires A MembraneOsmosis Requires A Membrane

• Permeable MembranePermeable Membrane– Substance Can Easily CrossSubstance Can Easily Cross

• Impermeable MembraneImpermeable Membrane– Substance Can NOT CrossSubstance Can NOT Cross

• Selectively Permeable MembraneSelectively Permeable Membraneaka = Semipermeable Membraneaka = Semipermeable Membrane– Some Substances Can Cross, Others Can NotSome Substances Can Cross, Others Can Not– Cell Membranes are SemipermeableCell Membranes are Semipermeable


OSMOSIS

Key ConceptKey Concept::

OsmosisOsmosis = = The Diffusion Of The Diffusion Of WaterWater ThroughThrough A A Selectively Permeable MembraneSelectively Permeable Membrane


The Tonics

• HypotonicHypotonic– Less concentrated solutionLess concentrated solution

• IsotonicIsotonic– Equally concentrated solutionEqually concentrated solution

• HypertonicHypertonic– More Highly concentrated solutionMore Highly concentrated solution


The Tonics


How Osmosis Works

• Overhead – Sugar & WaterOverhead – Sugar & Water• Membrane Impermeable To SugarMembrane Impermeable To Sugar• WaterWater moves moves fromfrom

a higher concentration of a higher concentration of WATERWATERto ato a

lower concentration of lower concentration of WATERWATER((NOTNOT Sugar) Sugar)


Osmotic Pressure• Pressure exerted on the hypertonic side of a Pressure exerted on the hypertonic side of a

selectively permeable membraneselectively permeable membrane• May cause cells to shrink or burstMay cause cells to shrink or burst


Osmotic PressureCell Membrane

Contractile Vacuoles


Facilitated Diffusion

• Molecules that can easily diffuse across the cell membrane:–Alcohol–Water–Small Lipids



• Other molecules can not pass through the cell membrane but still get into the cell.

HOW?



• Thru Protein Channels in the Cell Membrane that allow a substance to cross.–Allows Diffusion In Both DirectionsAllows Diffusion In Both Directions–Each Channel Substance SpecificEach Channel Substance Specific–DOES NOTNOT REQUIRE ENERGY



Protein Channel Is Substrate Specific

Substrate Can Move Either Direction Depending On Concentration. Substrate Can Move Either Direction Depending On Concentration. Always from area of Higher Concentration to area of Lower Always from area of Higher Concentration to area of Lower

Concentration!Concentration!


Active Transport

• Moves Material Across A Cell Moves Material Across A Cell MembraneMembrane

• AgainstAgainst A Concentration Gradient A Concentration Gradient(from area of Lower concentration into an area of (from area of Lower concentration into an area of

Higher concentration)Higher concentration)


Active Transport

Requires EnergyRequires Energy


Energy Molecule


Active Transport


Active Transport

• EndocytosisEndocytosis– Used to bring in large molecules, food, and Used to bring in large molecules, food, and

whole cellswhole cells• ExocytosisExocytosis

– Membrane surrounded material from inside Membrane surrounded material from inside the cell fuses with the cell membrane, the cell fuses with the cell membrane, releasing the contents.releasing the contents.

Cell Structure & Function

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