Chapter 25

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Author:
kamrunsreno
ID:
171992
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Chapter 25
Updated:
2012-09-19 18:53:20
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Biology
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Exam 1
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  1. Hypothetical Steps in the origin of simple cells
    • Abiotic synthesis of small organic molecules 
    • • Amino acids, nucleotides 
    • 2. Joining small molecules into macromolecules 
    • • Proteins, nucleic acids 
    • 3. Packaging of molecules into protobionts (25.3) 
    • • Droplets of macromolecules within membranes 
    • 4. Origin of self-replicating molecules
  2. Miller and Urey Experiments
    • Early atmosphere contained ingredients for organic molecules 
    • •Water vapor, nitrogen compounds, carbon dioxide, sulfur compounds 
    • –Produced amino acids, sugars, lipids 
    • • Volcanoes and deep-sea vents also a possible source of energy 
  3. Proposed role of RNA in early life
    • RNA can act as enzyme-like catalysts 
    • –Called ribozymes 
    • • Some ribozymes can copy RNA 
    • –Create complementary molecules and/or 
    • –Capable of self-replication 
    • –If nucleotide building blocks are present 
  4. Radiometric dating the fossil record
    • Based on decay of isotopes (ex. C14->C12) 
    • –Fossils contains unstable isotope from the organism when it was alive 
    • –Over time the unstable isotope decays 
    • –The amount of isotope remaining gives age
  5. Single celled prokaryotic organisms
    • First evidence: fossilized stromatolites 
    • –Layered rocks that form when prokaryotes bind sediment together 
    • • Prokaryotes are single celled organisms that lack a nucleus and other membrane bounded organelles 
    • –3.5 billion years ago 
    • • Simpler organisms probably existed earlier 
    • • Still produced today by similar organisms
  6. Photosynthetic Oxygen Production
    • Early atmosphere had little oxygen gas 
    • • Photosynthesis produces oxygen 
    • –Likely evolved in Cyanobacteria (> 2.7 bya) 
    • • Gradually oxygen gas levels build up 
    • –Allowed the evolution of aerobic respiration 
    • • Evidence: banded iron formations 
    • –Created by iron oxide 
    • –Some cyclical variation (seasonal etc.)
  7. Endosymbiotic hypothesis
    Larger cells engulf smaller prokaryotes
  8. Multicellularity
    • First multicellular organisms were likely small algae 
    • –Ex. Forming filaments or sheets of cells 
    • • Benefits of being multicellular 
    • –Larger, more complex organisms 
    • –Specialization of cells 
    • • Leads to formation of tissues and organs 
  9. Cambrian Explosion
    • period of rapid species diversification 
    • –~525 mya 
    • • Prior to this period most animals were: 
    • –Soft bodied 
    • –Herbivorous, filter feeders, scavengers 
    • • Origin of larger predators 
    • • Simultaneously, defensive features arose 
    • –Spines, body armor etc. 
  10. Colinization on Land
    • Cyanobacteria > 1 bya 
    • • Larger life forms ~ 500 mya 
    • –Plants and fungi first, then animals 
    • • Required adaptations for dehydration 
    • –Ex. Plant adaptations: 
    • • Waterproof exterior coating 
    • • Internal vascular system 
  11. Continental Drift
    • Continents move over time 
    • –Plates of Earth’s crust float over hot mantle 
    • –Drift a few cm / year 
    • • Slowly rearrange geography 
    • • Alters the habitat of organisms 
    • –Ex. Cold --> warm, wet --> dry 
    • • Leads to adaptation, speciation, extinction 
    • –Ex. Allopatric speciation 
  12. Mass Extinctions
    • Most species that ever lived are extinct 
    • • Extinctions caused by: 
    • –Ex. Habitat destruction 
    • –Ex. Environmental change 
    • • Five mass extinctions in fossil record 
    • –Best observed in hard-bodied sea animals 
    • –In each event, 50% of marine species extinct
  13. Adaptive Radiations
    • Periods in which many new species form 
    • • Can occur after mass extinctions 
    • –Adaptations to new open ecological niches 
    • • Occur with colonization of “vacant” areas 
    • –Less natural selection, more variation persists 
    • –Less competition between species 
    • • Periods often include major innovations 
    • –Ex. plants producing seeds

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