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Prokaryotic cells have differing oxygen requirements.
OBLIGATE AEROBES
Use O2 for
respiration;
cannot grow
without it
FACULTATIVE ANAEROBES
Use O2 when
available;
ferment when
O2 isn’t
available
OBLIGATE ANAEROBES
Poisoned by O2; use
fermentation or live
by anaerobic
respiration. In
anaerobic respiration,
inorganic molecules
like SO4, NO3, and
Fe3+ are used instead
of oxygen.
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A B C
BILL: For each sample, determine the oxygen requirements for the bacteria living within the bracketed area.
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VITAL ROLES IN ECOSYSTEMS: Producers
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VITAL ROLES IN ECOSYSTEMS: Decomposers
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VITAL ROLES IN ECOSYSTEMS: Nitrogen Fixers in the Nitrogen Cycle
Nitrogen (N 2) in the atmosphere is converted into ammonia (NH3), making the nitrogen available to plants
and animals.
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Go back…
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The poisonous gas …Oxygen • The amount of free oxygen
in the atmosphere increased after the evolution of photosynthesis in prokaryotes
• O2 appeared from about 2 billion years ago and reached about 21% 1 billion years ago
• Obligate anaerobes either became extinct or found niches where oxygen is absent
Stromatolites, Shark Bay Australia
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Oxygen atmosphere • Oxygen begins to accumulate 2.7 bya
• evidence in banded iron in rocks (rusting)
• makes aerobic respiration possible
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Stromatolites Fossilized mats of prokaryotes resemble modern microbial colonies