1114 Chapter 16

  1. Geologic Timescales
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  2. What does changes over time indicate?
    Adaptations to novel environmental pressures
  3. Ediacarion Biota
    Large group of eukaryotes, exclusively soft-bodied
  4. Why did the burgess shale group evolve from the ediacarion biota?
    They are organisms with large spikes covering bodies for protection predators
  5. Why did tiktaalik evolve from burgess shale group?
    Front appendages (better for land) for pushing, upward facing eyes (alligator)
  6. Extinction
    The loss of all individuals of a species
  7. Background extinction rate
    Happens constantly
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    What is the background extinction rate?



    B) ~ 3 families/million yr.
  9. Mass extinction
    • A rapid decline in a large number of species, much higher than background extinction rate
    • 5 mass extinctions so far
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    Which of the following best describes changes in diversity following mass extinctions?



    B) Mass extinctions are followed by periods of rapid increased in diversity

    There is adapted radiation. Species fill the niches that used to be filled
  11. How do you test if we are in the 6th mass extinction?
    Look at background extinction rates and current extinction rates
  12. Estimated background extinction rate
    • 2 extinctions/10,000 species/100 years
    • Every 100 years, 2 of every 10,000 species are expected to go extinct
    • This estimate higher than any background rate previously used to compare with modern extinction rates
  13. Why is the very high estimated background extinction rate a good thing?
    • If background extinction rate estimate is too low, modern extinction rates may seem much higher just because background rate was so low
    • This would incorrectly indicate a 6th mass extinction
  14. What determines modern extinction rates?
    International Union for the Conservation of Nature
  15. How are species classified?
    • Extinct (none remaining)
    • Extinct in the wild (exist only in captivity)
    • Presumed extinct (very likely extinct, but not confirmed)
  16. 2 estimates of modern extinction rate:
    • High conservative estimate
    • Conservative estimate
  17. Highly conservative estimate
    Includes only species classified as extinct
  18. Conservative estimate
    Includes species classified as extinct, extinct in the wild, and presumed extinct
  19. Which do you think is a better estimate of species persistence and why?
    • Conservative, better reflects what happens in nature
    • Highly conservative>background then we are in another mass extinction
  20. Are we in a 6th mass extinction?
    Yes
  21. Prokaryotes
    • Organisms with cells that lack membrane-bound organelles and a membrane-bound nucleus
    • Include domains Bacteria and Archaea
  22. Eukaryotes
    • Organisms with cells that have membrane-bound organelles and a membrane-bound nucleus (domain Eukarya)
    • Include protists, plants, fungi, and animals
  23. Prokaryotic genetic information
    • Have smaller genomes than eukaryotes
    • Chromosomes are circular rather than linear
    • Have plasmids: small, independently replicating, circular DNA molecules -> often carry alleles for antibiotic resistance
    • Ribosomes are small for gene translation
  24. How do prokaryotic cells reproduce?
    Binary fission: splitting one cell into two after replicating genetic information
  25. Pathogenic bacteria
    • Bacteria associated with disease
    • MRSA, Lyme disease, cholera, etc
  26. Antibiotic
    • "against life"
    • Kill pathogenic and beneficial bacteria
    • Can result in irritable bowel syndrome and secondary infections
  27. How do we kill bacterial cells without killing our own cells?
    • Prevent cell walls from forming
    • Disrupt ribosomes that make protein needed for life
  28. Beneficial bacteria
    Gut flora: allow proper digestion of food and protect your bowels from pathogenic bacteria (~1-3% of of your body weight is bacteria)
  29. Which best describes the relationship between humans and gut floral species?



    D) Mutualism
  30. Clostriduim difficile infections
    Beneficial bacteria no longer check growth of C. difficile, results in severe diarrhea
  31. Treatment for gut flora loss?
    Fecal transplants
  32. WHich of the following best describes the interaction between C. difficile and beneficial gut bacterial species?



    D) Competition

    Limitation on a shared resource
  33. Archaea
    • Single celled prokaryotes
    • Often extremophiles: "lovers" of extreme conditions
  34. Extreme thermophiles
    Thrive in extreme heat (e.g. hot springs of Yellowstone)
  35. Extreme halophiles
    Live in extremely salty environments (e.g. the Dead Sea in Israel
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    Which is the best hypothesis for the relationship among bacteria, archaea, and eukarya?
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  37. Eukaryotes
    • Organisms with cells that have a membrane-bound nucleus and organelles
    • Most are protists
  38. Similarities between mitochondria and chloroplasts?
    • Both have their own lipid bilayers
    • Both have circular DNA molecules that can replicate independently
    • Both have their own ribosomes that are smaller than the ribosomes of the cell in which they live
    • Both reproduce by a splitting process similar to fission
  39. Endysymbiont theory
    • Mitochondria and chloroplasts derived from ancestral prokaryotes that were engulfed by another cell -> relationship became symbiotic
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  40. Protists
    A group of mostly unicellular eukaryotic organisms that are not fungi, plants, or animals
  41. Are protists a valid evolutionary group?
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    • No. Not a monophyletic group
    • Some protists are more closely related to plants, animals, or fungi
    • We still don't know how protists should be classified
  42. What is the vast majority of the diversity of life?
    Unicellular
  43. Brown algae
    Large, multicellular photosynthetic algae
  44. Carotenoids
    • Orange-ish brown photosynthetic pigment 
    • Contained in plasmids of kelp cells (plastids=broader group that includes chloroplasts)
  45. Adaptations for aquatic life and photosynthesis
    • Holdfast
    • Blade
    • Stipe
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  46. Holdfast
    Anchors to seafloor
  47. Blade
    Leaf-like structures increase photosynthetic surface areas
  48. Stipe
    Stalk-like structure brings blade closer to the ocean surface and therefore light
  49. Holdfast, blade, and stipe are very similar to root, stalk, and leaf, but DNA analysis shows that they came from different evolutionary lineages. What kind of evolution is this?
    Convergent evolution
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    What type of evolutionary group is green algae?
    • Paraphyletic group
    • Green algae are photosynthetic protists
    • Green algae=protists=closest relatives of land plants
  51. Green Algae
    Charophytes=closest relative of land plants
  52. How are green algae related to environmental pressures of life on land?
    • Often live in intertidal zones: sometimes submerged, sometimes not 
    • Zygotes coated with sporopollenin: tough polymer that prevents desiccation
    • Flagellated gametes: gametes "swim" to each other through water
    • No internal structural support -> supported by water
  53. Challenges for movement onto land?
    • Must be able to avoid desiccation
    • Must develop supportive tissue to remain upright (and compete for sunlight)
    • Need to have gametes that don't require water to swim in to meet each other and achieve fertilization
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1114 Chapter 16
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