Ch 25 - The history of life on earth (1 slide per page)-2

3 campbell 9th ed 34 2 origin of life how did life

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Unformatted text preview: Figure 25.3 (Campbell 9th ed) 34 2. Origin of life How did life begin? **Heredity is essential to life** - pass on beneficial characteristics for survival/reproduction DNA allows us to pass on our traits? - But DNA is a complex molecule - Likely preceded by a less complex molecule 35 Why RNA is believed to be the original unit of heredity RNA monomers spontaneously assemble into short RNA polymers (i.e. a simple gene). Certain RNA sequences act as catalysts (ribozymes) e.g. with some catalyzing copying of other RNA Tomas Cech 1982 40 Key Events: 3. Atmospheric O2 • 1st aquatic photosynthetic bacteria ~2.1 - 2.7 bya How do we know? • O2 is a byproduct of photosynthesis • O2 reacted w/ dissolved iron in H2O forming iron oxide sediments Figure 25.8 (Campbell 8th ed) • depleted dissolved iron and then saturated the H2O • then released into atmosphere rusting terrestrial rocks (2.7 bya) 41 Key Events: 3. Atmospheric O2 ~2 bya atmospheric [O2] began to increase rapidly…WHY? Hypothesis: > atmospheric [O2] made aerobic respiration possible → larger cells & organisms w/ > energy demands (i.e. eukaryotes) → > atmospheric [O2] Anerobic vs aerobic respiration 42 Key Events: 3. Atmospheric O2 Higher [O2]: • Killed many prokaryotes • (O2 still toxic to many bacteria) • Formed ozone layer → terrestrial life possible! 43 Key Events: 4. Eukaryotes • Oldest fossil eukaryotic cell ~1.6- 2.1 bya • but steroids, a constituent of euk cell membranes, found in sediments from 2.7 bya • Evolved from prokaryotes in several hypothesized steps: 44 Evolution of eukaryote morphology A. Nuclear Envelope Origin: infoldings of prok plasma membranes Evidence: - Extant bacteria w/ infoldings - Nuclear membrane &a...
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