• Scientists think that protists are the oldest eukaryotes.
  • If so, they must have evolved from prokaryotic cells.
  • How did this happen?
  • The endosymbiotic theory provides the most widely-accepted explanation.
  • This theory is well-supported by evidence.
  • The first eukarian cells evolved from a symbiotic relationship between two or more prokarian cells.
  • Some of the small cells were cyanobacteria.
  • They were specialized for photosynthesis.
  • They evolved into the chloroplasts of eukaries.
  • They also had DNA that is different from the DNA found in the cell nucleus.
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