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History and Diversity of Life (History of Earth dates (Earth is 4.5…
History and Diversity of Life
History of Earth dates
Earth is 4.5 billion years old
Life began 3.8 billion years ago
Cambrian mass extinction: 540 million years ago
Photosynthetic bacteria evolved 2.5 billion years ago (oxygen gradually becomes more abundant)
Aerobic metabolism evolved 2 billion years ago
Prokaryotes evolved into eukaryotes through endosymbiosis 1.5 billion years ago
Origin of multicellular organisms
Adaptive radiation
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The process by which organisms rapidly diversify (new species form quickly) after new trait or environment is introduced into a population
All listed dates of transitions are examples of adaptive radiation
Can selection alone explain the evolution of complex organisms?
Probably not; large genomes are slightly deleterious
Genetic drift and mutation likely played a role
Three domains of life
Eukaryotes, bacteria, and archaea
Similarities among them
Ability to conduct glycolysis
Replicate DNA semi-conservatively
Have cell membranes and ribosomes
DNA codes for proteins
Comparison of the domains (Prokaryotes typically more diverse in all categories)
Oxygen use
Obligate anaerobes: Will die in the presence of oxygen
Aerotolerant anaerobes: Can tolerate oxygen, but do not use it for cellular respiration
Facultative anaerobes: Can switch between aerobic and anaerobic respiration
Obligate aerobes: Cannot survive in the absence of oxygen
Energy and carbon use
Photoautotrophs: Use light as energy and get carbon from inorganic sources like carbon dioxide
Photoheterotrophs: Use light as an energy source but get carbon from other organisms
Chemolithotrophs: Get energy from oxidizing organic compounds, but can fix carbon from inorganic sources (also called chemoautotrophs)
Chemoheterotrophs: Obtain energy and carbon from oxidizing organic compounds
Other differences
Eukaryotes have membrane bound organelles (which prokaryotes do not)
Eukaryotes reproduce sexually and asexually (prokaryotes reproduce strictly asexually)