OsmosisBIOL160

LabMod5

Transport

•  Diffusion

•  Tendencyformoleculesto

spreadoutevenlyintothe

availablespace

•  DuetoBrownian

movement

•  Dynamicequilibrium

•  Asmanymoleculescross

onewayascrossinthe

otherdirecDon

Fig.7-11Molecules of dye Membrane (cross section)

WATER

Net diffusion Net diffusion Equilibrium

(a) Diffusion of one solute

Net diffusion

Net diffusion

Net diffusion

Net diffusion

Equilibrium

Equilibrium

(b) Diffusion of two solutes

•  SimpleDiffusion

•  Substancesmove(diffuse)down

theirconcentra/ongradient

•  differenceinconcentraDonof

asubstancefromoneareato

another

•  Passivetransport

•  Noenergyinputrequired

TypesofTransport:Passive–SimpleDiffusion

TypesofTransport:Passive-Osmosis

•  Osmosis

•  diffusionofwateracrossaselecDvely

permeablemembrane

•  fromtheregionoflowersolute

concentraDon(higherwater

concentraDon)

•  totheregionofhighersolute

concentraDon(lowerwater

concentraDon)

•  Waterwillfollowthesolutes

Lower concentration of solute (sugar)

Fig.7-12

H2O

Higher concentration of sugar

Selectively permeable membrane

Same concentration of sugar

Osmosis

WaterBalanceofCellsWithoutWalls•  Tonicity–describesthesolu/on

•  abilityofasoluDontocauseacelltogainorlosewater

•  IsotonicsoluDon

•  SoluteconcentraDonoutsideisthesameasthatinsidethecell

•  Nonetwatermovementacrosstheplasmamembrane

•  HypertonicsoluDon

•  SoluDonwithhighersoluteconcentraDon

•  HypotonicsoluDon

•  SoluDonwithlowersoluteconcentraDon

Hypotonic solution

(a) Animal cell

(b) Plant cell

H2O

Lysed

H2O

Turgid (normal)

H2O

H2O

H2O

H2O

Normal

Isotonic solution

Flaccid

H2O

H2O

Shriveled

Plasmolyzed

Hypertonic solution

•  HypertonicorhypotonicenvironmentscreateosmoDcproblemsfororganisms

•  Osmoregula/on

•  Controlofwaterbalance

•  NecessaryadaptaDonforlifeinsuchenvironments

•  TheproDstParamecium

•  Hypertonictoitspondwaterenvironment

•  HasacontracDlevacuolethatactsasapump

WaterBalanceofCellsWithoutWalls

Filling vacuole 50 µm

(a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm.

Contracting vacuole

(b) When full, the vacuole and canals contract, expelling fluid from the cell.

WaterBalanceofCellswithWalls

•  PlantcellinahypotonicsoluDon

•  SwellsunDlthewallopposes

uptake

•  Cellisnowturgid(firm)

•  Ifisotonic

•  Nonetmovementof

waterintothecell

•  thecellbecomes

flaccid(limp)

•  Plantmaywilt

•  Plasmolysis

•  Hypertonicenvironment

•  Plantcellslosewater

•  membranepulls

awayfromthe

wall

•  usually

lethal

WaterBalanceofCellswithWalls