BIOL 1108 Lecture 7: Chapter 28 - Multicellularity
Document Summary
Complex multicellularity arose several times in evolution. 83 of the 119 major groups of eukaryotes present within the 7 superkingdoms contain only single celled organisms. 36 remaining groups have at least simple multicellularity. Form is filaments, hollow balls, or flat sheets. Most cells retain a full range of functions. All cells are still in contact with environment. Complex multicellular organisms can be just a few or as many as a trillion or more cells that work in close coordination. The biological gulf between microbes and complex multicellular organisms is enormous, but complex multicellularity has evolved at least a dozen times. Most prokaryotic organisms are composed of a single cell, although some will form simple filaments (plaque) or live in colonies. No bacteria develop macroscopic bodies with functionally differential tissues. This is because bacteria are single celled organisms - they do one job, but tissues have more than one. An increased surface area to volume ratio increases exposure to the environment.
