The Cell The Cell Membrane Membrane

and and MovementMovement

s of s of MoleculesMolecules

The Plasma Membrane

The The Plasma MembranePlasma Membrane (aka cell membrane) (aka cell membrane) Boundary Boundary between the cell and its between the cell and its

environmentenvironment Controls what enters and leaves the cell--- Controls what enters and leaves the cell---

performing performing homeostasishomeostasis Has Has selective permeabilityselective permeability- the ability to - the ability to

allow some molecules through the allow some molecules through the membrane -but not others membrane -but not others (aka semi-permeability)(aka semi-permeability)

Water

Plasma Membrane

Plasma Membrane Structure

Fluid Mosaic ModelFluid Mosaic Model describes the structure of the plasma describes the structure of the plasma

membranemembrane FluidFluid: : PhospholipidsPhospholipids

Polar head- loves waterPolar head- loves water2 Fatty acid tails- avoid water2 Fatty acid tails- avoid water

Fluid Mosaic ModelFluid Mosaic ModelPhospholipids in water form a Phospholipids in water form a

doubledouble layer “sandwich” with layer “sandwich” with tails tails pointing inpointing in

Fluid Mosaic ModelFluid Mosaic ModelThe sandwich forms a hollow The sandwich forms a hollow

sphere with an sphere with an insideinside and an and an outsideoutside

Fluid Mosaic ModelFluid Mosaic ModelThe phospholipids are considered The phospholipids are considered

“fluid” because they can “fluid” because they can move move throughout the membrane.throughout the membrane.

Fluid Mosaic ModelFluid Mosaic Model MosaicMosaic: : ProteinsProteins

embedded in the phospholipid embedded in the phospholipid bilayerbilayer

Fluid Mosaic ModelFluid Mosaic Model3 types of proteins:3 types of proteins:

• Transport proteinsTransport proteins-allow molecules -allow molecules to enter or leaveto enter or leave

• Support proteinsSupport proteins• Recognition proteinsRecognition proteins

Other Membrane StructuresOther Membrane Structures CholesterolCholesterol- makes the membrane - makes the membrane

less permeableless permeable

Other Membrane StructuresOther Membrane Structures Carbohydrate ChainsCarbohydrate Chains-glycoproteins -glycoproteins

allow cells to allow cells to recognize recognize each other.each other.Immune systemImmune system

COLOR AND LABEL THE COLOR AND LABEL THE MEMBRANE STRUCTURESMEMBRANE STRUCTURES

Molecular MovementsMolecular Movements Molecules of liquids and gases are in Molecules of liquids and gases are in

constant random constant random motionmotion–Travel in a straight line pathTravel in a straight line path–Bump into another moleculeBump into another molecule–Bounce off on another straight Bounce off on another straight

line courseline course

Molecular MovementsMolecular Movements DiffusionDiffusion-net movement of the -net movement of the

same kind of molecule same kind of molecule From an area of From an area of highhigh

concentration to an area of concentration to an area of lowlow concentration- aka “down a concentration- aka “down a concentration gradient” concentration gradient”

Continues until the Continues until the molecules are molecules are equallyequally distributed distributed

Molecular MovementsMolecular Movements OsmosisOsmosis –the diffusion of –the diffusion of waterwater through through

a selectively permeable membrane a selectively permeable membrane From an area of From an area of highhigh concentration to concentration to

an area of an area of lowlow concentration- aka “down concentration- aka “down a concentration gradient”a concentration gradient”

OsmosisOsmosisThe concentration of water in solution The concentration of water in solution

increases as the concentration of increases as the concentration of solutes decreasessolutes decreases

• 5% salt solution means ?% water5% salt solution means ?% water

•5% salt solution means 95% water5% salt solution means 95% water

•10% salt solution means ?% water10% salt solution means ?% water

•10% salt solution means 90% water10% salt solution means 90% water

20% Solute

80% Solute

Which direction will the water flow?

-Towards side A

Or

-Towards side B

AA BB

Types of Solutions IsoIsotonic Solutiontonic Solution:: Concentration of Concentration of

solutessolutes is the is the samesame inside and outside inside and outside the cell.the cell. Some water moves in, some water Some water moves in, some water

moves out.moves out. No net movement of water.No net movement of water. Cell remains the same.Cell remains the same.

Types of Solutions IsoIsotonic Solutiontonic Solution::

HypoHypotonic Solutiontonic Solution: The : The concentration of concentration of solutessolutes is is lessless outside the cell than inside the cell.outside the cell than inside the cell. Net movement of water Net movement of water intointo the the

cell.cell. The cell will The cell will swellswell and may burst. and may burst. Ex: distilled water, pure water, Ex: distilled water, pure water,

pond waterpond water

Types of Solutions

HypoHypotonic Solutiontonic Solution::

Types of Solutions

Types of Solutions

HyperHypertonic Solutiontonic Solution: The : The concentration of solutes is concentration of solutes is moremore outside outside the cell than inside the cell. the cell than inside the cell. Net movement of water out of the Net movement of water out of the

cell.cell. Cell willCell will shrink shrink.. Ex: salt water, sea water, ocean Ex: salt water, sea water, ocean

waterwater

““Salt sucks!”Salt sucks!”

Types of Solutions HyperHypertonic Solutiontonic Solution: :

osmosis

Comparison of Hypo, Iso, and Hypertonic Solutions

88% H2O 99% H2O

Which direction will the water flow?

Water always flows from high to low

Water (H2O)

25% H2O10% NaCl

Which direction will the water flow?

Change % NaCl to % water –osmosis is the movement of water through the plasma membrane

90% H2OWater (H2O)

90% H2O 80% H2O

Which direction will the water flow?

Water always flows from high to low

Water (H2O)

Osmotic Pressure in Plant Cells

Turgor PressureTurgor Pressure: The pressure in a : The pressure in a plant cell that results from water flowing plant cell that results from water flowing into the cell- maintaining central into the cell- maintaining central vacuole.vacuole. Gives plants the ability to stand up.Gives plants the ability to stand up.

Osmotic Pressure in Plant Cells With loss of turgor pressure central With loss of turgor pressure central

vacuole shrinks--plants wilt!vacuole shrinks--plants wilt!Plant cells require hypotonic situation to Plant cells require hypotonic situation to maintain turgor pressuremaintain turgor pressure