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All animals need toAll animals need toexchange substances withexchange substances withthe environmentthe environment

DiffusionDiffusion

Surface areaSurface area Difference inDifference in

concentrationconcentration

SURFACE AREA : VOLUMESURFACE AREA : VOLUME

BacteriaBacteria 6 000 000/m6 000 000/m

WhaleWhale 0.06/m0.06/m

Maximum size limit ofMaximum size limit ofsingle cellsingle cell

All organisms larger thanAll organisms larger thansize limit aresize limit areMULTICELLULARMULTICELLULAR

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Surface area toSurface area tovolume ratiovolume ratio

getsgetssmallersmaller as theas the

cell getscell getslargerlarger!!

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AvoidanceAvoidance

Geometric solutionsGeometric solutions Increase surface areaIncrease surface area

Decrease effective volumeDecrease effective volume

Increase rate of supplyIncrease rate of supply High concentration of nutrientsHigh concentration of nutrients

Improve nutrient transport withinImprove nutrient transport within

Improve efficiency to reduceImprove efficiency to reducedemanddemand Division of labor within the cellDivision of labor within the cell

Division of labor between cellsDivision of labor between cells

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Evolved many times in eukaryotesEvolved many times in eukaryotes

Three theoriesThree theories Symbiotic TheorySymbiotic Theory

Like theLike the endosymbioticendosymbiotic theorytheory

SyncytialSyncytial TheoryTheory Ciliates and slime moldsCiliates and slime molds

Commonly occur in multinucleated cellsCommonly occur in multinucleated cells

Colonial Theory (Haeckel, 1874)Colonial Theory (Haeckel, 1874) Same species are involvedSame species are involved

Green algae (Green algae (ChlorophytaChlorophyta) > 7000 species) > 7000 species

Model:Model: VolvocineVolvocine seriesseries OrderOrder VolvocalesVolvocales

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UnicellularUnicellular

flagellateflagellate IsogamyIsogamy

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Small colony (4, 8,16, or 32 cells)Small colony (4, 8,16, or 32 cells) Flat plane, mucilageFlat plane, mucilage

No differentiationNo differentiation

IsogamyIsogamy

Intercellular communicationIntercellular communication

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Colony (8, 16, or 32Colony (8, 16, or 32cells) in 1 layercells) in 1 layer

SphericalSpherical IsogamyIsogamy

Anterior cellsAnterior cells

CoordinateCoordinate flagellarflagellarmovementmovement

Colony dies whenColony dies when

disrupteddisrupted

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16 or 32 cells16 or 32 cells 16 cells16 cells no specializationno specialization 3232 4 for motility, the rest for reproduction4 for motility, the rest for reproduction HeterogamyHeterogamy female gametes not releasedfemale gametes not released

Halves are more pronouncedHalves are more pronounced

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32 to 128 cells32 to 128 cells

HeterogamyHeterogamy female gametes notfemale gametes notreleased, in some casesreleased, in some casesbecoming truly nonbecoming truly non--motilemotile

Division of laborDivision of labor AnteriorAnterior

vegetative cellsvegetative cells

Larger posteriorLarger posteriorreproductivereproductivecellscells

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Spherical colonies (500Spherical colonies (500--50000 cells)50000 cells)

Hollow sphereHollow sphere coenobiumcoenobium

Cell differentiation:Cell differentiation:

somatic/vegetative cells andsomatic/vegetative cells and gonidiagonidia 22--50 scattered in the posterior50 scattered in the posterior

reproductivereproductive

Female reproductive cellsFemale reproductive cells daughterdaughtercoloniescolonies

Intercellular communication possibleIntercellular communication possible

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Reproduction

in the Volvox

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Anisogamy

Anisogamy/

Heterogamy

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UnicellularUnicellular colonial lifecolonial life

Increase in # of cells in coloniesIncrease in # of cells in colonies

Change in shape of colonyChange in shape of colony

Increase in interdependence amongIncrease in interdependence amongvegetative cellsvegetative cells

Increase in division of labor: vegetativeIncrease in division of labor: vegetative

and reproductive cellsand reproductive cells IsogamyIsogamy anisogamyanisogamy oogamyoogamy

Fewer female gametes are producedFewer female gametes are produced

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Increase in size of theIncrease in size of theorganismorganism

Permits cell specializationPermits cell specializationIncrease in surface area toIncrease in surface area to

volume ratiovolume ratio

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InterdependenceInterdependence

ComplexityComplexity

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http://protist.i.hosei.ac.jp/pdb/images/Chlo

rophyta/Gonium/pectorale/sp_2b.jpg http://www.rbgsyd.nsw.gov.au/__data/asse

ts/image/48212/Gonium2.gif

http://www.ac-rennes.fr/pedagogie/svt/photo/microalg/pandorin.jpg

http://protist.i.hosei.ac.jp/PDB/images/Chlo

rophyta/Eudorina/elegans/sp_5.jpg http://www.fytoplankton.cz/FytoAtlas/thm/

0078.jpg