The More the Merrier?
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Transcript of The More the Merrier?
All animals need to exchange substances with the environment
Diffusion› Surface area› Difference in
concentration› Distance
SURFACE AREA : VOLUME› Bacteria – 6 000
000/m› Whale – 0.06/m
Maximum size limit of single cell
All organisms larger than size limit are MULTICELLULAR
Surface area to volume ratio
gets smaller as the
cell gets larger!
AvoidanceGeometric solutions
Increase surface areaDecrease effective volume
Increase rate of supplyHigh concentration of nutrientsImprove nutrient transport within
Improve efficiency to reduce demandDivision of labor within the cellDivision of labor between cells
Evolved many times in eukaryotes Three theories
› Symbiotic Theory Like the endosymbiotic theory Different species are involved
› Syncytial Theory Ciliates and slime molds Commonly occur in multinucleated cells
› Colonial Theory (Haeckel, 1874) Same species are involved Green algae (Chlorophyta) > 7000 species Model: Volvocine series – Order Volvocales
Unicellular flagellate
Isogamy
Small colony (4, 8,16, or 32 cells) Flat plane, mucilage No differentiation Isogamy Intercellular communication
Colony (8, 16, or 32 cells) in 1 layer
Spherical Isogamy Anterior cells
larger eyespots Coordinate
flagellar movement
Colony dies when disrupted
16 or 32 cells 16 cells – no specialization 32 – 4 for motility, the rest for reproduction Heterogamy – female gametes not released Halves are more pronounced
32 to 128 cells Heterogamy –
female gametes not released, in some cases becoming truly non-motile
Division of labor› Anterior
vegetative cells› Larger posterior
reproductive cells
Spherical colonies (500-50000 cells) Hollow sphere – coenobium Cell differentiation:
somatic/vegetative cells and gonidia 2-50 scattered in the posterior
reproductive Female reproductive cells
daughter colonies Intercellular communication possible
Reproduction in the Volvox
Anisogamy
Anisogamy/Heterogamy
Unicellular colonial life Increase in # of cells in colonies Change in shape of colony Increase in interdependence among
vegetative cells Increase in division of labor:
vegetative and reproductive cells Isogamy anisogamy oogamy Fewer female gametes are
produced
Increase in size of the organism
Permits cell specialization Increase in surface area to
volume ratio
Interdependence Complexity
http://protist.i.hosei.ac.jp/pdb/images/Chlorophyta/Gonium/pectorale/sp_2b.jpg
http://www.rbgsyd.nsw.gov.au/__data/assets/image/48212/Gonium2.gif
http://www.ac-rennes.fr/pedagogie/svt/photo/microalg/pandorin.jpg
http://protist.i.hosei.ac.jp/PDB/images/Chlorophyta/Eudorina/elegans/sp_5.jpg
http://www.fytoplankton.cz/FytoAtlas/thm/0078.jpg