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Lecture 5

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Biological Sciences
BISC 110
Robin Barrow

Lecture 5- Cambrian Explosion Chapter 25, pp. 517-518: section on the origin of multicellularity Chapter 32, pp. 656-658 (657 in 8th edn) Concept 32.2: read to end of Paleozoic Era QUESTIONS TO ASK: -will we need to know the role of oxygen in metabolism (obligate aerobes, obligate anaerobes, anaerobic respiration, etc ) and about Nitrogen Metabolism (nitrogen fixation), both on pg 564? -also, will we need to study about the metabolic cooperation on page 565 of the textbook? Although these information were not mentioned in the lecture, will we still need to study them? Fossil record •includes: •partial/complete remains of bones, shells, etc •traces of footprints, shadows, etc •preservation is biased •hard vs soft parts •abundant vs rare species •long-lived vs short-lived species •size of geographical range Multicellularity •2 bya: unicellular eukaryotic organisms •1.2 bya: oldest known fossils of multicellular organisms (small algae) •Bangiomorpha pubescens How multicellularity began •Symbiosis: interaction between two different species living in the same environment •genomes/species are separate •Cellularisation: The formation of cells around each nucleus in a multinucleate cytoplasm, transforming it into a multicellular structure •starts with a cell and result in multiple neclei •Coloniality: there are many colonial protists; between same species Animals •Multicellular •Heterotrophic •Eukaryotic •Structural proteins (eg: collagen), nerve, and muscle cells •Unique sequence of development, regulated by Hox genes •small change in hox genes can have a big effect •they start unicellular, form stalk, produce spores, and cycle repeates •proves coloniality can form • Edicaran fauna •Earliest known complex multicellular organisms •lived 610-542 mya •discovered by Reg Sprigg in 1947, and is occurred around the world Ediacaran animals (no facial features, complicated animals) •Frond-like (eg: charnia) •Disk-like (eg: Cyclomed usa) •Segmented (eg: Spriggina) • What happened to these Edicaran animals? (Theory) •seem to just disappear; not certain •Preservation •bias, predation •competition •change in environmental conditions •Their Heritage: •died out without descendants •ancestral o modern animal phyla •not sure if they were really animals The Cambrian Explosion (535-5
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