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Chapter 16- Origin and Evolution of Microbial Life: Prokaryotes and Protists • Earth formed 4.6 billion years ago – Early atmosphere: CO, CO2, N2, H2O, CH4, NH3 – Very different from atmosphere today – Lightening, volcanic activity, UV- much more intense • Prokaryotes- fossils date 3.5bil yrs ago – Prevalent in mats – Photosynthesis produces O2 in atmosphere – Organic chemicals- 3.9bil yrs ago- possibly from energized inorganic material (from UV or lightening) • Hypotheses of life’s origin – 1- spontaneous generation- didn’t explain how life arose in the first place (Pasteur- maggots on meat) – 2- comets and meteorites brought organic compounds to Earth – 3- (broken up into stages) 1st- synthesis of organic molecules. 2nd- formation of polymers from organic molecules 3rd- polymers replicate (primitive heredity). 4thpolymers aggregate having different characteristics – Heterotroph Hypothesis- conditions of primitive Earth produced organic substances (which could then give rise to organisms) • • • • These organisms absorbed organic nutrients Miller and Urey experiment produced amino acids Now disproved due to change in primitive atmosphere Now, underwater volcanoes and vents may have provided chemical resources • Stages in chemical evolution – Organic molecules polymerized on hot rocks/clay • Due to binding sites and metals that clay contained – 1st genetic material was RNA • Replicated itself w/o assistance • Ribozymes- RNA that acts as enzyme, aids in splicing and polymerization • RNA World- hypothetical period or evolution when RNA served as genes and catalyst molecule – RNA could translate into protein (w/o ribosomes or tRNA) • Protein produced helped RNA replicate • Lipid/protein spheres held RNA/polypeptide co-op’s – Co-op’s grew and replicated • Evolved a single metabolism • Prokaryotes- bacteria – Smaller than eukaryotes, can live in extreme environments, live inside of us (digestive tract), are very important. – Come in sphere, rod and spiral shapes – 2 groups Bacteria and Achaea – Bacteria- found in air, land and water, everywhere • Covers skin, lining nose and mouth, fill digestive tract • Many bacteria are pathogens- disease-causing agent – Lyme disease, staph, meningitis, syphilis • Koch’s postulate* – Archaea- thrive in extreme conditions (heat, salt, areas high in methane) – Ways of nourishment• Photoautotroph- sun and CO2 • Chemoautotroph- inorganic compounds and CO2 • Most prokaryotes are heterotrophs** • Photoheterotroph- sun and organic compounds (obtain carbon from organic molecules, E from sun) • Chemoheterotroph- Most abundant*- get everything from organic compounds – Uses of bacteria • Biological weapons • Recycle chemicals, clean up environment (oil spills) • Bioremediation- use of prokaryotes to clean up pollution • Eukaryotes originated from communities of prokaryotes – Lived symbiotically (endosymbiosis)- gave rise to mitochondria and chloroplasts • Protists- unicellular and some multicellular eukaryotes – Some are photosynthetic – Heterotrophs are called protozoa – More complicated than prokaryotes- have membrane bound nucleus and organelles – 4 types: • Protozoa- ingest food “animal like” Ex:amoeba • Slime molds- have uni- and multi-cellular stages of life, heterotrophs • Unicellular algae-photosynthetic • Multicellular algae- “seaweed”- photosynthetic – Multicellular life probably evolved by specialization of protist colonies – Multicellular life- arose about 1bil yrs ago and was aquatic until 500mil yrs ago