ch. 25 notes - General Biology II-Biology 102 Lecture...

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General Biology II-Biology 102 Spring 2010/gpd Lecture Notes/Objectives – Unit 1: Evolution Chapter 25: Notes I. Life in a year! II. Geologic timescale A. Precambrian Large animals were soft-bodied, no sign of predation, instead animals were herbivores, filter feeders, or scavengers B. Phanerozoic— Multicellular Ekaryotic Life (roughly the last half a billion years) “Cambrian Explosion” The “Cambrian Explosion” is when pyla of living animals appear suddenly in fossils. The three phyla were Cnidaria (sea anemone and their relatives), Profera (sponges), and Mollusca (mollusks). Predation was revealed from this era, features for prey capturing, like sharp spines and heavy body armor. The safe slow-moving world ceased to exist after this explosion. C. Extinctions The fossil record shows that the overwhelming majority of species that ever lived are now extinct. Mass extinction— results in which large numbers of species become extinct throughout Earth. Evolutionary history has been punctuated by five mass extinctions that radically altered the history of life. These extinctions could have been caused by changes in continent positions, volcanic activity, or impacts from meteorites or comets. III. Plate Tectonics Continental plates move gradually over time, altering the physical geography and climate of Earth; these changes lead to extinctions in some groups of organisms and burst of speciation in others. IV. Chronology of life on Earth A. Age of Earth & oldest fossils the approximate age of the Earth. 4.6 billion years the oldest fossils. 3.5 billion years ago B. Prokaryotic evolution First living organisms were some form of prokaryotes, which may have evolved out of Protobionts. C. Photosynthesis evolution Photosynthesis evolves: CO 2 + 2 H 2 X→ CH 2 O + H 2 O + 2X Purple & green bacteria Oxygenic photosynthesis evolves: CO 2 + H 2 O→ CH 2 O + O 2 Cyanobacteria D. Oxidation of atmosphere Ancient cyanobacteria responsible for oxygen in the atmosphere because they produced O 2 during the water-splitting step of photosynthesis. When this oxygenic photosynthesis first evolved it probably dissolved into the surrounding water until it reached a high enough concentration to react with dissolved iron. This would eventually cause the iron oxide to accumulate as sediments, dissolve in the water, which eventually lead to the release of O 2 out of water and into the atmosphere. The oxygen levels increased gradually but then shot up relatively rapidly (maybe caused by the evolution of eukaryotic cells containing chloroplasts) having an enormous impact on life. Doomed many of the anaerobic prokaryotes, many adaptations evolved including cellular respiration. E. Eukaryotic evolution 1. Endosymbiosis Theory
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This theory claims that mitochondria and plastids (chloroplasts and related organelles) were formally small prokaryotes that began living within larger cells, and overtime the host and endosymbionts would have become a single organism.
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