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Lecture 6

BIO153 Lecture 6 .pdf

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Christoph Richter

2009 BIO153: Lecture 6 From 2 Kingdoms to 3 Domains January 26, 2009 Insights into life’s diversity: From Aristotle until recently, everything was either a plant or an animal (Note that even in modern biology departments, mycologists (people who study fungi) were often grouped in with the botanists!) Microscopy brought new insight (the ability to see unicellular organisms): van Leeuwenhoek (1632 – 1723): observed rainwater, his own stools (!) and saw “little animalicules” (protists); however, these were still classified with plants or animals (depending on “plantlike” or “animal-like” traits) Cell theory: arrived at independently by Schleiden (1804 – 1881) studying plants, and Schwann (1810 – 1882) studying animals: the observation that living things were constructed of cells The importance of cell structure to taxonomy was not immediately appreciated. Haeckel (1866): proposed a new kingdom: Protista: single-celled organisms Problem with “Protista”: “protista” included both nucleated & non-nucleated cells E.g. cyanobacteria (prokaryote) and green algae (eukaryote) were grouped together Next step: a distinction was made between nucleated and non-nucleated cells: Chatton: French marine biologist (1937): “procaryotique” = cells without a nucleus “eucaryotique” = cells with a nucleus karyon = kernel pro = before eu = true or good 1 Next step: Whittaker’s 5 kingdom system (1969): consumpption production absorpton ▯ groups were defined on the basis of Annimaalaa whether they had nucleated or non- Plantae Funggi nucleated cells; ▯ multicellular organisms with nuclei were grouped on the basis of function (plants eukaryootes are photosynthesizers; fungi absorb Prrotoctisaa nutrients directly from the environment; animals consume and digest to obtain nutrients) Moonnera prokaaryotes Problems with the 5 kingdom system: “Monera” and “Protoctista” are paraphyletic groups 2 ▯ do not include all descendents of a common ancestor ▯ members share more recent common ancestors with organisms outside their group Recent changes (1990’s): ▯ “Protoctista” abandoned; revert back to the old informal name of protists for the grade (paraphyletic group) of eukaryotes that are not plants, animals or fungi ▯ molecular evidence reveals profound differences among the prokaryotic organisms: Woese et al. (1990) defined 3 domains: Eubacteria, Archaea and Eukarya (Domain is a taxonomic level above Kingdom) ~2 bya prokaryotes ~3.5 bya prokaryotes are paraphyletic The Prokaryotic domains: Bacteria & Archaea Prokaryotes are everywhere: ▯ resting spores of Bacillus permians (last active 250 million years ago) was “resurrected” in 2000 ▯ 1 gram of soil has > 10,000 bacterial types; billions of cells ▯ divide rapidly: under ideal conditions. colicould outweigh the mass of the earth in 3 d 3 ▯ bacterial spores have been found 30 km above Earth’s surface; ~ 2 km deep in crust Prokaryotic cell structure is simple ▯ no cytoskeleton ▯ no membrane-bound organelles ▯ binary fission; no mitosis ▯ DNA in nucleoid (not nucleus) ▯ no chromosomes ▯ permanently haploid ▯ no sexual reproduction ▯ flagel
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