body plans & develop

body plans & develop - Animal body plans and...

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Multicellular organisms have a new challenge: development . They have a life cycle with a unicellular stage (or stages). Typically: adult gametes zygote (multicellular) (unicellular) (unicellular) embryo (developmental processes) Sexual adult unicellular gametes unicellular zygote one or more multicellular one or more multicellular asexual “larval” stages “embryonic” stages A more complex life cycle: Animal body plans and developmental patterns Another characteristic of multicellular organisms: Senescence (aging) Unicellular forms divide without limit • Multicellular forms have limited life span (~115 years in humans) Zygote embryo juvenile adult senescence, death time age Survival (% still alive) Speed Disease resistance Fertility Animal body plans and developmental patterns Four basic developmental processes lead from unicellular zygote to adult: cell proliferation : more cells produced by cell divisions cell differentiation : cells change into various types (differing structurally, biochemically, etc.) for specialized functions -- but all have the same genetic information cell death (apoptosis): a programmed process that contributes to formation of body structures In animals, but not in plants: cell migration : embryonic cells move with respect to each other Animal body plans and developmental patterns These four processes create an enormous increase in complexity -- but no change in genetic information: Start as an undifferentiated single cell; finish as a very complex structure containing many types of cells arranged in precise ways. About 10 14 cells of 80-100 types in a human, for example. Developmental biology is key to understanding animal diversity and the overall body ‘plan’ of an organism. The body plan is specified by four fundamental properties established during development • these are also crucial traits that differentiate major phyla. Animal body plans and developmental patterns
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1. The degree of differentiation and specialization of cells and tissues. • One phylum, the sponges or Parazoa , is at a cellular grade of organization: few cell types; loosely organized into functional units. • Other animal phyla have more complex organization. Cells more specialized, more cell types, cells organized into distinct tissues (tissues are groups of specialized cells with integrated function, isolated from other tissues by membranous layers). These are Eumetazoans , or ‘true’ multicellular animals. Animal body plans and developmental patterns Animal body plans and developmental patterns • One group, the Radiata, has radial primary symmetry: the body can be 'cut' into identical halves (mirror images) along any plane around a major axis, as shown in this diagram: • The major axis is the heavy black arrow. The 'cutting plane' can be rotated to any
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body plans & develop - Animal body plans and...

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