7-3 Cell Boundaries - Weebly

7-3 Cell BoundariesSlide1 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell MembraneAll cells are surrounded by a thin, flexible barrierknown as the cell membrane.Many cells also produce a strong supporting layeraround the membrane known as a cell wall.Slide2 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell MembraneWhat is the main function of the cellmembrane?Slide3 of 47Copyright Pearson Prentice Hall1

7-3 Cell BoundariesCell MembraneCell MembraneThe cell membrane regulates what entersand leaves the cell and also providesprotection and support.Slide4 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell MembraneCell MembraneOutside ofcellCarbohydratechainsProteinsCellmembraneInside of cell(cytoplasm)ProteinchannelLipid bilayerSlide5 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell MembraneThe composition of nearly all cell membranes is adouble-layered sheet called a lipid bilayer.Lipid bilayerSlide6 of 47Copyright Pearson Prentice Hall2

7-3 Cell BoundariesCell MembraneThe lipid bilayer gives cell membranes a flexiblestructure that forms a barrier between the cell and itssurroundings.Slide7 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell MembraneMost cell membranes contain protein moleculesembedded in the lipid bilayer, some of which havecarbohydrate molecules attached to 8 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell WallsWhat is the main function of the cell wall?Slide9 of 47Copyright Pearson Prentice Hall3

7-3 Cell BoundariesCell WallsThe main function of the cell wall is toprovide support and protection for thecell.Slide10 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesCell WallsCell WallsCell walls are found in plants, algae, fungi, andmany prokaryotes.The cell wall lies outside the cell membrane.Most cell walls are porous enough to allow water,oxygen, carbon dioxide, and certain othersubstances to pass through easily.Slide11 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesDiffusion Through Cell BoundariesDiffusion Through Cell BoundariesEvery living cell exists in a liquid environment.The cell membrane regulates movement ofdissolved molecules from the liquid on one side ofthe membrane to the liquid on the other side.Slide12 of 47Copyright Pearson Prentice Hall4

7-3 Cell BoundariesDiffusion Through Cell BoundariesMeasuring ConcentrationA solution is a mixture of two or more substances.The substances dissolved in the solution are calledsolutes.The concentration of a solution is the mass ofsolute in a given volume of solution, ormass/volume.Slide13 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesDiffusion Through Cell BoundariesWhat happens during diffusion?Slide14 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesDiffusion Through Cell BoundariesDiffusionParticles in a solution tend to move from an areawhere they are more concentrated to an areawhere they are less concentrated.This process is called diffusion.When the concentration of the solute is the samethroughout a system, the system has reachedequilibrium.Slide15 of 47Copyright Pearson Prentice Hall5

7-3 Cell BoundariesDiffusion Through Cell BoundariesSlide16 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesDiffusion Through Cell BoundariesThere is a higher concentrationof solute on one side of themembrane as compared to theother side of the membrane.Slide17 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesDiffusion Through Cell BoundariesSolute particles move from theside of the membrane with ahigher concentration of soluteto the side of the membranewith a lower concentration ofsolute. The solute particles willcontinue to diffuse across themembrane until equilibrium isreached.Slide18 of 47Copyright Pearson Prentice Hall6

7-3 Cell BoundariesDiffusion Through Cell BoundariesWhen equilibrium is reached,solute particles continue todiffuse across the membranein both directions.Slide19 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesDiffusion Through Cell BoundariesDiffusion depends upon random particlemovements. Therefore, substances diffuse acrossmembranes without requiring the cell to useenergy.Slide20 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesOsmosisWhat is osmosis?OsmosisOsmosis is the diffusion of water through aselectively permeable membrane.Slide21 of 47Copyright Pearson Prentice Hall7

7-3 Cell BoundariesOsmosisHow Osmosis WorksDilute sugarsolution(Water moreconcentrated)Concentratedsugar solution(Water lessconcentrated)SugarmoleculesMovement ofwaterSelectivelypermeablemembraneSlide22 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesOsmosisWater tends to diffuse from a highly concentratedregion to a less concentrated region.If you compare two solutions, the more concentratedsolution is hypertonic (“above strength”).The more dilute solution is hypotonic (“belowstrength”).Slide23 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesOsmosisWhen concentrations of solutions are the same onboth sides of a membrane, the solutions are isotonic(“same strength”).Slide24 of 47Copyright Pearson Prentice Hall8

7-3 Cell BoundariesOsmosisOsmotic PressureOsmosis exerts a pressure known as osmoticpressure on the hypertonic side of a selectivelypermeable membrane.Slide25 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesOsmosisBecause the cell is filled with salts, sugars, proteins,and other molecules, it will almost always behypertonic to fresh water.If so, the osmotic pressure should produce a netmovement of water into the cell. As a result, thevolume of the cell will increase until the cell becomesswollen or bursts.Slide26 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesOsmosisCells in large organisms are not in danger of burstingbecause they are bathed in fluids, such as blood, thatare isotonic.Other cells are surrounded by tough cell walls thatprevent the cells from expanding even undertremendous osmotic pressure.Slide27 of 47Copyright Pearson Prentice Hall9

7-3 Cell BoundariesFacilitated DiffusionFacilitated DiffusionCell membranes have protein channels that act ascarriers, making it easy for certain molecules tocross.Slide28 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesFacilitated DiffusionThe movement of specific molecules across cellmembranes through protein channels is known asfacilitated diffusion.Hundreds of different protein channels have beenfound that allow particular substances to crossdifferent membranes.Slide29 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesFacilitated DiffusionGlucosemoleculesFacilitated DiffusionProteinchannelSlide30 of 47Copyright Pearson Prentice Hall10

7-3 Cell BoundariesFacilitated DiffusionAlthough facilitated diffusion is fast and specific, it isstill diffusion.Therefore, facilitated diffusion will only occur if thereis a higher concentration of the particular moleculeson one side of a cell membrane as compared to theother side.Slide31 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesActive TransportActive TransportSometimes cells move materials in the oppositedirection from which the materials would normallymove—that is against a concentration difference.This process is known as active transport.Active transport requires energy.Slide32 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesActive TransportMolecular TransportIn active transport, small molecules and ions arecarried across membranes by proteins in themembrane.Energy use in these systems enables cells toconcentrate substances in a particular location,even when diffusion might move them in theopposite direction.Slide33 of 47Copyright Pearson Prentice Hall11

7-3 Cell BoundariesActive TransportMolecule to be carriedActiveTransportSlide34 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesActive TransportEndocytosis and ExocytosisLarge molecules and even solid clumps of materialmay undergo active transport by means of the cellmembrane.Endocytosis is the process of taking material intothe cell by means of infoldings, or pockets, of thecell membrane.The pocket breaks loose from the outer portion ofthe cell membrane and forms a vacuole within thecytoplasm.Slide35 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesActive TransportTwo examples of endocytosis are: phagocytosis pinocytosisSlide36 of 47Copyright Pearson Prentice Hall12

7-3 Cell BoundariesActive TransportIn phagocytosis, extensions of cytoplasm surrounda particle and package it within a food vacuole. Thecell then engulfs it.Phagocytosis requires a considerable amount ofenergy.Slide37 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesActive TransportIn pinocytosis, tiny pockets form along the cellmembrane, fill with liquid, and pinch off to formvacuoles within the cell.Slide38 of 47Copyright Pearson Prentice Hall7-3 Cell BoundariesActive TransportExocytosisMany cells also release large amounts of materialfrom the cell, in a process called exocytosis.During exocytosis, the membrane of the vacuolesurrounding the material fuses with the cellmembrane, forcing the contents out of the cell.Slide39 of 47Copyright Pearson Prentice Hall13

7-3Click to Launch:Continue to:- or -Slide40 of 47Copyright Pearson Prentice Hall7-3Unlike a cell wall, a cell membranea.is composed of a lipid bilayer.b.provides rigid support for the surroundingcell.c.allows most small molecules and ions topass through easily.d.is found only in plants, fungi, algae, andmany prokaryotes.Slide41 of 47Copyright Pearson Prentice Hall7-3The concentration of a solution is defined as thea. volume of solute in a given mass of solution.b. mass of solute in a given volume of solution.c. mass of solution in a given volume of solute.d. volume of solution in a given mass of solute.Slide42 of 47Copyright Pearson Prentice Hall14

7-3If a substance is more highly concentratedoutside the cell than inside the cell and thesubstance can move through the cell membrane,the substance willa. move by diffusion from inside the cell tooutside.b. remain in high concentration outside the cell.c. move by diffusion from outside to inside thecell.d. cause water to enter the cell by osmosis.Slide43 of 47Copyright Pearson Prentice Hall7-3The movement of materials in a cell against aconcentration difference is calleda. facilitated diffusion.b. active transport.c. osmosis.d. diffusion.Slide44 of 47Copyright Pearson Prentice Hall7-3The process by which molecules diffuse acrossa membrane through protein channels is calleda. active transport.b. endocytosis.c. facilitated diffusion.d. osmosis.Slide45 of 47Copyright Pearson Prentice Hall15

7-3 Cell Boundaries Slide 31 of 47 Facilitated Diffusion Although facilitated diffusion is fast and specific, it is still diffusion. Therefore, facilitated diffusion will only occur if there is a higher concentration of the particular molecules on one side of a cell membrane as compared to the