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17-3 Modern Classification Biologists are always revising taxonomies THE TREE OF LIFE - When looking under a microscope, biologists split all cells into 2 fundamental types, the basis for life into 2 groups: o Eukaryotes -membraned-nucleus, organelles People, pangolins o Prokaryotes – no membraned- nucleus, no organelles – smaller! Bacteria Revising the Tree - Systematists can’t assume that the organisms within the groups of cells are equally related o Evolutionary relationships are based on homologous features o Euks and proks do have homologous macromolecules – used to store&translate genetic info – when these can be compared, biologists use the proteins&RNAs for phylogenetic analyses - Carl Woese o o Proposed revision of system of classification for life on earth into 6 kingdoms He compared rRNA sequences of diff organism – grouped to similarities (all organisms have ribosomes) The sequences changed little over time So rRNA is unique and useful for finding evolutionary relationships between earth’s organisms THREE DOMAINS OF LIFE After phylogenetic analyses of rRNa, scientists found new relationships between big groups – suggesting new tree of life 1. last universal common ancestor – data showed that all organisms got their rRNA genes from one ancient form of life 2. all living things related to one of three lineages ; domains: a. Bacteria, Archaea, Eukarya most things we know like plants & animals 3. Archaea – more recently found, more surprising findings -at first thought as bacteria, but it’s been found that it’s VERY diff from bacteria, and that this must have descended from unique proks early in time DOMAIN BACTERIA - Single celled proks w/ cell wall o Reproduce through cellular fission All have: cell wall, plasma membrane, cytoplasm with No complex organelles, at least 1 circular chromosome No membrane bound DNA – no nucleus Very small – 2 um vs. human cell is 6 um Oldest found cell fossils! DOMAIN ARCHAEA - - Proks with cell membranes and other unique properties o Some are autotrophic – produce their own food by chemosynthesis o Some produce waste products – like methane (flammable!) Mainly in harsh environments o Hot springs, deep sea thermal vents, salty lakes, intestines of animals Because archaea is so unique, scientists think it may be the earliest organisms on earth o Some think the cells closely interacted with bacteria- coevolved o Led to theory of endosymbiosis - saying euks arose when ancient proks began living as one cell DOMAIN EUKARYA - Eukaryotic organisms –large cells, true nucleus , complex organelles Includes plants, animals, fungi, etc SIX KINGDOMS 1st kingdom aligns with domain Bacteria 2nd kingdom aligns with domain Archaea Last 4 kingdoms align with domain Eukarya Kingdom Eubacteria (UNDER BACTERIA DOMAIN) - Means “true bacteria”, meant to distinguish from archaea (not bacteria!!) Kingdom Archaebacteria (UNDER DOMAIN ARCHAEA) - Means “ancient bacteria” – but now it’s considered so diff from bacteria scientists just say archaea Kingdom Protista (EUKARYA) - Called protists - Basically euks that aren’t plants, animals or fungi – bad because it defines based on what it’s not - Unicellular – hard to make generalizations, for protists are not similar to one another o Biologists consider getting riid of taxon protista, - Examples of unicellular protists: amoebas and paramecia Multicellular: seaweed and mold Kingdom Fungi - Heterotrophic, eukaryotic; both uni and multicellular o Unique: Absorb their nutrients, not ingest Include mushrooms, rusts, smuts, mildews, molds Kingdom Plantae - - Eukaryotic, multicellular plants o Mostly autotrophic, using photosynthesis as energy o Develop from embryos Most live on land; moss, ferns, conifers, flowering plants Kingdom Animalia - Eukaryotic, multicellular, heterotrophic Devlop from embryos Most have symmetrical body organization & move in environment to find food FUTURE TAXONOMIC SYSTEMS - Just scientific models- subject to change! Some Modern biologists – proposed new ways for 6-kingdom and 3-domain systems o Kingdoms to replace protista*** Some want subkingdom or superorder to adapt Linnaean ways Some just want cladistics over Linnaean categories