The endosymbiotic theory proposes that modern eukaryotic cells evolved from prokaryotic cells living symbiotically with larger unicellular organisms. Chloroplasts and mitochondria were once free-living bacterial cells that benefited from living inside larger prokaryotes, which eventually took them inside their cells to form the first eukaryotic cells. Evidence for this includes chloroplasts and mitochondria having their own membranes, DNA, ability to replicate, and other cellular structures like ribosomes.

1. Unit 2 Notes:
Endosymbiotic
Theory

2. (1) Endosymbiotic Theory
• Modern eukaryotic cells evolved from free-living
prokaryotic cells living symbiotically
with larger unicellular organisms.
• Symbiotically??
– The cells lived and worked together because
they benefited from the relationship.

3. (2) Summarizing theTheory
• Chloroplasts + Mitochondria were once free-living
bacterial cells (prokaryotes).
• The chloroplasts + mitochondria benefited
from living with larger prokaryotes.
• The larger prokaryotes took the
chloroplasts + mitochondria inside their
cell.
• TA-DA!  The Modern Day Eukaryotic Cell

6. (3) Evidence for the Theory
• Chloroplasts, Mitochondria, ….
–Have their own fully developed cell
membranes.
–Have their own copy of DNA.
–Can replicate themselves, all on their own.
–They have their own ribosomes.
–They produce their own proteins.
–They can exist/survive on their own w/o a
larger cell.

7. (4) Other Examples Today…
• Bobtailed Squid + Glowing Bacteria
• Aphids + Digestive Bacteria
• Spotted Salamander + Algae