KEY TAKEAWAYS •
Prokaryotes can live in just about any habitat on earth.
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Prokaryotes are all unicellular but can form different arrangements.
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Gram-negative bacteria are divided into proteobacteria and non-proteobacteria.
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Gram-positive bacteria are divided into high GC bacteria and low GC bacteria.
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Archaea are unicellular. Many prefer very extreme environments.
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Deeply branching bacteria are considered a common ancestor to all other living things throughout evolution.
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