1. Endosymbiosis

2. The eukaryotic cell probably originated as a community of prokaryotes
Fossil record indicates that eukaryotes evolved from prokaryotes 2 billion years ago.
Endosymbiosis refers to one species taking up permanent residence in another, and evolving into a single lineage

3. Endosymbiosis
Chloroplasts and mitochondria seem to have evolved from small prokaryotes that established residence within other, larger prokaryotes.
Ancestral host cell
Ancestors of mitochondria were small heterotrophic prokaryotes that were able to use oxygen to release energy.
Ancestors of chloroplasts were small, photosynthetic prokaryotes.
Endosymbiosis Animation

4. How do we know this is true?
Mitochondria and chloroplasts are similar to prokaryotic cells
All contain small amounts of DNA, RNA
These organelles can transcribe their DNA creating their own enzymes
They also replicate their own DNA and reproduce within the cell

5. Also explains the double membrane…
Chloroplasts and mitochondria are enclosed by two membranes
Inner membrane is derived from the plasma membrane of the engulfed prokaryote.
Outer membrane comes from the infolded plasma membrane of host cell.
outer
inner
outer
inner