Cell TransportCell Transport

Diffusion & OsmosisDiffusion & Osmosis(aka Passive Transport)(aka Passive Transport)

Active TransportActive Transport

Cells are very busy doing Cells are very busy doing many things in order to many things in order to keep organisms alive.keep organisms alive.

One important thing that the One important thing that the cell cell membranemembrane does is to does is to control control cell cell

transporttransport-- what comes into and out -- what comes into and out of the cell through the cell membrane. of the cell through the cell membrane.

Picture the cell Picture the cell membrane as a membrane as a slice of Swiss slice of Swiss

cheese.cheese.It has many small It has many small openings called openings called porespores.. It is through these tiny It is through these tiny pores that many small pores that many small molecules like molecules like waterwater,, oxygenoxygen,, and and carbon carbon dioxidedioxide enter and leave enter and leave the cell.the cell.

The cell membrane is very The cell membrane is very ““choosy.choosy.”” It It allows some materials to pass through allows some materials to pass through

quickly, some slowly, and some materials quickly, some slowly, and some materials may not be allowed to pass through at all. may not be allowed to pass through at all.

Because of this Because of this ““choosiness,choosiness,”” the membrane the membrane is said to be is said to be selectively permeableselectively permeable; it ; it lets lets

some substances through, but not allsome substances through, but not all..

ConcentrationConcentration

ConcentrationConcentration = the number of = the number of molecules in a given spacemolecules in a given space

High concentrationHigh concentration = ______________ = ______________ number of molecules in a given spacenumber of molecules in a given space

Low concentrationLow concentration = ______________ = ______________ number of molecules in a given spacenumber of molecules in a given space

Examples of ConcentrationExamples of Concentration

If you use the example of If you use the example of peoplepeople, which living , which living area would be more highly concentrated, area would be more highly concentrated, New New York CityYork City or the or the Sahara desertSahara desert??

If you use the example ofIf you use the example of frogsfrogs, which area , which area would have a would have a lowlow concentration of frogs: the concentration of frogs: the Charles RiverCharles River in Needham, or the in Needham, or the top of top of Mount WashingtonMount Washington in New Hampshire? in New Hampshire?

Passive TransportPassive Transport

DiffusionDiffusion andand Osmosis Osmosis are calledare called Passive Passive TransportTransport, , because they because they do notdo not require require energy for them to take place. energy for them to take place.

A good analogy is A good analogy is that Diffusion and that Diffusion and Osmosis are Osmosis are like like riding a bicycle riding a bicycle downhilldownhill … you … you dondon’’t need to pedal!t need to pedal!

Definition of Diffusion:Definition of Diffusion:

DiffusionDiffusion is is the the movement of movement of

molecules from an molecules from an area of higher area of higher

concentrationconcentration (where (where therethere’’s more) s more) to an to an

area of lower area of lower concentrationconcentration (where (where

therethere’’s less.)s less.)

This movement of molecules also This movement of molecules also takes place across cell membranes.takes place across cell membranes.

Which way will these molecules move?Which way will these molecules move?

DiffusionDiffusion is the process is the process that allows certain that allows certain

materials to enter and materials to enter and leave the cell.leave the cell.

Animation of Diffusion across cell membrane

http://www.abpischools.org.uk/page/modules/homeostasis_kidneys/kidneys3.cfm?coSiteNavigation_allTopic=1

We can see (and smell) We can see (and smell) diffusion all around us.diffusion all around us.

HowHow does Diffusion occur? does Diffusion occur?

animation

• All molecules are in constant, random All molecules are in constant, random motion.motion.

• Molecules are constantly colliding Molecules are constantly colliding with each other.with each other.

• As molecules collide, they push each As molecules collide, they push each other around, until they reach other around, until they reach equilibrium.equilibrium.

animation

EquilibriumEquilibrium meansmeans ““balancedbalanced””-- -- the molecules are evenly the molecules are evenly distributed.distributed.

OsmosisOsmosisOsmosis is a special type of diffusion.Osmosis is a special type of diffusion.

OsmosisOsmosis isis thethe movement ofmovement of waterwater molecules from an area of higher molecules from an area of higher concentration to an area of lower concentration to an area of lower concentration, across a membraneconcentration, across a membrane

Examples of OsmosisExamples of Osmosis

Mummification Putting salt on a slug

grapes turning into raisins

H2O

H2O

H2O

Sponge in a bucket of water

H2O

OsmosisOsmosisThe water molecules are small enough to fit through the pores, but the sugar molecules are too big to fit. The water molecules will move from the left (high concentration of water) to the right (low concentration of water), to try to reach equilibrium.

The water molecules are small enough to fit through the pores, but the sugar molecules are too big to fit. The water molecules will move from the left (high concentration of water) to the right (low concentration of water), to try to reach equilibrium. http://www.youtube.com/watch?v

=J-bAiJcLdxI&feature=youtu.be

OsmosisOsmosisOsmosis happens across cell membranes, Osmosis happens across cell membranes,

just as diffusion does.just as diffusion does.

swells

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Osmosis in red blood cellsOsmosis in red blood cells

Blood is slightly salty (3% salt). If red blood Blood is slightly salty (3% salt). If red blood cells are put in cells are put in salt watersalt water, they shrivel up (water , they shrivel up (water leaves the cells). If they are put in leaves the cells). If they are put in pure waterpure water, , they fill up with water and burst.they fill up with water and burst.

HH22OOHH22OO

HH22OO

pure water salty water Normal concentration

(in blood)

Advanced video on osmosis

Osmosis in red blood cellsOsmosis in red blood cells

HH22OOHH22OO

HH22OO

pure water salty water Normal concentration

(in blood)

http://www.abpischools.org.uk/page/modules/homeostasis_kidneys/kidneys4.cfm?coSiteNavigation_allTopic=1

Osmosis in red blood cells-- animation

Active TransportActive Transport

Animation of Active Transport

is theis the movement of molecules across a movement of molecules across a cell membrane using energycell membrane using energy, from an , from an area of area of lower concentrationlower concentration to an area to an area of of higher concentrationhigher concentration..

Active TransportActive Transport

A good analogy is that Active Transport A good analogy is that Active Transport is like is like riding a bicycle uphillriding a bicycle uphill … it takes … it takes energy!energy!

Two Types of Active TransportTwo Types of Active TransportTransport ProteinsTransport Proteins Endocytosis & Endocytosis &

ExocytosisExocytosisCell uses a vacuole or Cell uses a vacuole or vesicle to move vesicle to move substances in & out of substances in & out of the cell.the cell.

TransportTransport or or Carrier proteins Carrier proteins carry a large molecule across carry a large molecule across the cell membrane, going from the cell membrane, going from low to high concentration. This low to high concentration. This takes energy!takes energy!

EndocytosisEndocytosisEndo means “inside”. Cyto means “cell”.Endocytosis is the process of bringing process of bringing something inside a cell by enclosing it in a something inside a cell by enclosing it in a

vacuole or vesicle.vacuole or vesicle.

Endo means “inside”. Cyto means “cell”.Endocytosis is the process of bringing process of bringing something inside a cell by enclosing it in a something inside a cell by enclosing it in a

vacuole or vesicle.vacuole or vesicle.

EndocytosisEndocytosis

Amoeba eats 2 paramecia

ExocytosisExocytosisExo means “outside”. Cyto means “cell”.Exocytosis is the process of moving something outside a cell by means of a

vacuole or vesicle.

Exo means “outside”. Cyto means “cell”.Exocytosis is the process of moving something outside a cell by means of a

vacuole or vesicle.

Active Transport of Active Transport of Materials in & out of a cellMaterials in & out of a cell

http://www.teachersdomain.org/asset/tdc02_int_membraneweb/

Exocytosis in Paramecium video

http://www.phschool.com/science/biology_place/biocoach/biomembrane1/diffusion.html

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Facilitated Diffusion & Active Transport

Diffusion, Osmosis & Active Transport