Porifera2

Porifera2 - primary This is why most cells are spherical...

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Archaeocyathids Early – Middle Cambrian, marine. Shallow current- washed water, high tolerance to turbidity. Passive filterer? Cambrian reef builders, symbiotic algae?
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D’Arcy Wentworth Thompson 1860-1948 Scottish naturalist, mathematician and classicist. Wrote “ On Growth and Form” (1917) pointing out that the morphology of organisms was related to the mechanisms of growth required to achieve the form and the physical forces acting on the organism. Initially viewed his approach as an alternative to Darwinian selection. Now seen as aspects of Darwinian fitness.
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Of Size and Small Things Physical forces do not scale linearly. Surface area and strength usually scale as the square of size increase, mass and metabolic demand increase as the cube of size. Small, single-celled organisms exist at a scale where gravity is relatively unimportant, but surface forces and viscosity are
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Unformatted text preview: primary This is why most cells are spherical surface tension This is why most simple aggregations of cells are like chains of beads Shells, tests, etc. can be viewed as responses to the dominant forces at these scales, operating over the organisms life span. Sponge Spicules Complex morphology often viewed as indicating phylogeny DArcy Thompson saw them as defined by boundaries between geometric packing of spherical bodies. Suggests that spicule morphology may be a secondary effect of colonial growth and not as closely tied to heredity as thought Holistic approach and Transform Grids DArcy Thompson also became famous for suggesting studying the whole form using transform grids an approach not really feasible until the latter 20 th century...
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This note was uploaded on 10/23/2011 for the course GLY 1000 taught by Professor Parker during the Spring '11 term at FSU.

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Porifera2 - primary This is why most cells are spherical...

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