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September 13.doc

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McGill University
Biology (Sci)
BIOL 111

Bio 111 Alanna Houston September 13, 2007 ORGANIZING DIVERSITY - Classic approach is based on latin binomial and hierarchy - Modern terms have largely replaced hierarchy with more nuanced phylogeny - Phylogeny o Show common ancestors, time since branching o There isn’t just one way to make a phylogeny o Can be rearranged without changing info o Analogy – convergent evolution – same but not found in a common ancestor  Mess up phylogenies o Monophyletic groups – trace back to common ancestor then trace forward to all descendants (same set →monophyletic) Eukaryotes - Eu (good) + karyote (nucleus) - Most life we are familiar with and can see with the naked eye are eukaryotes (animals, plants, fungi, algae) - Between 1-2 billion years old - Eukaryotes are opposite of prokaryotes o They have no cell wall or cell wall not composed of peptidoglycans o They have internal organelles such as golgi apparatus, mitochondria (energy processors), and sometimes chloroplasts (photosynthesis) Prokaryote to Eukaryote - Lose the cell wall - Infolding of the membrane (increased surface area) - DNA and ribosomes are already attached to membrane, keep folding until they’re surrounded (nucleus / golgi apparatus) - Build cytoskeleton - Extend cytoskeleton to flagellum and develop motion - Develop phagocytosis - Swallow a purple sulfur bacteria and over time have it lose most of its genome to make a mitochondria Bio 111 Alanna Houston - Write out the labels for the diagram above* - Every cell has something living in it that isn’t part of the cell (bacteria) Endosymbiosis - In + together + live - Chloroplasts (photosynthesis) too - One cell ‘swallows’ a prokaryote but ends up living together instead of being digested - Evidence: o Double cell membrane around mitochondria o Genes in mitochondria that match bacterial genes o The target sequence DNA (tells protein sorting apparatus which compartment to send proteins to) of nuclear genes targeted for the chloroplast match a protein on the membrane of bacteria o Mitochondria and chloroplasts reproduce by binary fission – not by creation from nuclear proteins  Inherit 100% of mitochondria (and chloroplasts) from mother’s egg - Over long time living together o Genome of endosymbiont becomes very reduced, may move to the nuclear genome - Suggested for over 100 years but one bright, stubborn lady brought it to near universal acceptance (Lyn Margulis in 1960s 1970s) o Her now landmark paper was rejected for over 15 journals o She has suggested that the mostly male scientists are over obsessed with competition and consumption – cooperation is important biologically Protists - Eukaryotes - Not animal, plant, fungi - ‘Trash can’ – groups not interesting to us (not scientific) - Really 15 – 40 groups = animal, plant - Cause many diseases - Provide most energy in ocean and many freshwater systems - Extremely diverse in meeting the 3 challenges Slime Molds Acellular Cellular - Spend most of life as slime then produce fruiting bodies - At least two types: o Acellular slime o Cellular slime - live apart and come together to make fruiting bodies - Used as a model of evolution of multicellularity o Only a few cells / nuclei at top
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