Cell Structure & Function
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Cell Structure & FunctionStructure & Movement Through Membranes(There and Back Again)
The Cell MembraneKey Concept:The cell membrane regulates what enters and leaves the cell and also provides protection and support
The Cell MembraneThe cell takes in nutrients and expels wastes plus cell products through the cell membraneThe Basic Structure Of Nearly All Cell Membranes Is The LIPID BILAYER
LIPID BILAYERSForm Automatically When Certain Lipids Are Dissolved In WaterTough Flexible StructureStrong Barrier Between Cell Contents And Its Surroundings
Fluid Mosaic ModelIn Addition To The Bilayer, The Cell Membrane Contains:
Proteins That FormChannels & Pumps
Proteins with Carbohydrates That FormAntigenic SitesCommunication Sites
DiffusionAll Living Cells Contain And Are Surrounded By Liquid.THE CELL MEMBRANE REGULATES THE MOVEMENT OF MOLECULES FROM ONE SIDE OF THE MEMBRANE TO THE OTHER
CytoplasmIs A Solution Of Many Different Substances In Water
SolutionA liquid mixture of 2 or more substances evenly mixed.SolventThe liquid in which the substances are mixedSoluteSubstances dissolved in the Solvent
Concentration Of SolutionConcentration = Mass of the solute in a given volume of solvent.Mass/Volume e.g.
12g of NaCl dissolved in 3L H2Oequals12g/3L or 4.0 g/L
In A SolutionMolecules Are Moving Constantly They Collide and Bounce off each otherThis causes them to spread out randomly
Resulting In:Movement from: an area of higher concentration to an area of lower concentration This process is called: Diffusion
DIFFUSIONMolecules move away from an area of Higher Concentration to areas of Lower ConcentrationEquilibriumConcentration of a solute is the same throughout the solutionThe concentration is the same EVERYWHERE
DIFFUSIONKey Concept: Diffusion Causes Many Substances To Move Across A Cell Membrane But:Diffusion Does NOT Require The CellTo Use Energy It just happens naturally!
Diffusion & CellsSubstances that can diffuse across cell membranes will do so until equilibrium is reachedDiffusioncontinues after equilibrium but the rates are equal in ALL Directions Atoms & Molecules Never Stop Moving
Osmosis Requires A MembranePermeable MembraneSubstance Can Easily CrossImpermeable MembraneSubstance Can NOT CrossSelectively Permeable Membrane aka = Semipermeable MembraneSome Substances Can Cross, Others Can NotCell Membranes are Semipermeable
OSMOSISKey Concept:Osmosis = The Diffusion Of Water Through A Selectively Permeable Membrane
The TonicsHypotonicLess concentrated solutionIsotonicEqually concentrated solutionHypertonicMore Highly concentrated solution
How Osmosis WorksOverhead Sugar & WaterMembrane Impermeable To SugarWater moves from a higher concentration of WATER to a lower concentration of WATER (NOT Sugar)
Osmotic PressurePressure exerted on the hypertonic side of a selectively permeable membraneMay cause cells to shrink or burst
Osmotic PressureCell MembraneContractile Vacuoles
Facilitated DiffusionMolecules that can easily diffuse across the cell membrane:AlcoholWaterSmall Lipids
Facilitated DiffusionOther molecules can not pass through the cell membrane but still get into the cell.
Facilitated DiffusionThru Protein Channels in the Cell Membrane that allow a substance to cross.Allows Diffusion In Both DirectionsEach Channel Substance SpecificDOES NOT REQUIRE ENERGY
Facilitated DiffusionProtein Channel Is Substrate SpecificSubstrate Can Move Either Direction Depending On Concentration. Always from area of Higher Concentration to area of Lower Concentration!
Active TransportMoves Material Across A Cell Membrane
Against A Concentration Gradient
(from area of Lower concentration into an area of Higher concentration)
Active TransportRequires Energy
Active TransportEndocytosisUsed to bring in large molecules, food, and whole cellsExocytosisMembrane surrounded material from inside the cell fuses with the cell membrane, releasing the contents.