Multicellularity 1 Why be multicellular 2 First multicellular organism 575 mya 3 Complex Multicellular Organisms CMO a Specialized cells b Evolved from SMO s c Requirements for complex multicellular life i ii iii cells molecular signals from surrounding cells g Evolved at least 6 separate times 4 Simple Multicellular Organisms SMO Filaments hollow balls sheets a b Little differentiation or specialization c How do the cells stick together d What are the limitations of SMO s e What are the advantages of SMO s that are parasitic 5 Coenocytic a Results in large cells with nuclei b What are the advantages c What are the disadvantages 6 Diffusion a What is its function b What is the main disadvantage d e Small subset of tissue reserved for reproduction It s a three dimensional organism so not every cell is exposed to the external environment i Some cells are buried w in tissues and are relatively far from direct access to nutrients ii Interior cells don t receive signals from the environment but cells still need to grow reproduce and survive iii Therefore they require mechanisms for environmental signals received by external f Development increasing or decreasing in response to f Retain many functions including reproduction i How does cell death in SMO s compare to CMO s g Every cell is in direct close contact with the h Commonly cells that eat other microorganisms ingest small organism parts live suspended in water columns or c Some organisms have adapted ways to circumvent the limitations posed by diffusion i Ex sponges have canals in their bodies to ensure that all cells are in close contact w the environment 7 Bulk Transport a An requires E process that allows multicellular organisms to 8 Adhesion a In animals cells are organized into sheets of epithelia that line the inside and outside cover of the body i Cells adhere to one another by means of ii Integrins cadherins and provide molecular mechanisms for adhesion b In plants the cells synthesize adhesive molecules i Pectins