What is it?
A giant bacteria colony! Stromatolites are some of the earliest forms of life found on earth...3.9 billion years old.
Shark Bay, Australia
The larger cell is a eukaryotic cell show up in the fossil record about 2.7 bya and the small is a prokaryotic cell (3.8 + bya)
Google images
Question to answer...how did eukaryotic cells develop over time?
Specifically, how did mitochondria and chloroplasts develop?
Lynn Margulis Endosymbiotic Theory
https://www.youtube.com/watch?v=lxWJsJetG10
Sciences “Unruly Earth Mother”
“Not just survival of the fittest...it’s also about cooperation.”
Endosymbiotic Theory is based on the following evidence:
Evidence #1: Mitochondria/Chloroplasts and Bacteria have similar sizes, shapes, and structures:
Endosymbiotic Theory is based on the following evidence:
Evidence #2: Mitochondria/Chloroplasts and Bacteria have similar circular DNA:
Eukaryotic nuclear DNA is in linear chromosomes.
Endosymbiotic Theory is based on the following evidence:
Evidence #3: Mitochondria/Chloroplasts and Bacteria divide using binary fission:
Eukaryotic cells use mitosis.
Evidence #4: Mitochondria, Chloroplasts, & Bacteria have 70S ribosomes
Evidence #4. Eukaryotic free floating and Rough ER ribosomes are 80S.
Evidence #5: Antibiotics meant for bacteria can harm mitochondria and chloroplasts too.
Evidence #6: Mitochondria and Chloroplasts have a double membrane.
Double membrane could come from endocytosis of a smaller bacteria cell by a larger cell.
Evidence Recap for Endosymbiotic Theory:
Bacteria, Chloroplasts, and Mitochondria have #1 through #6 below in common:
Endosymbiotic Theory
Mitochondria and chloroplasts were once bacteria that lived outside of a larger cell. The cell engulfed them by endocytosis and they developed a symbiotic relationship. Over time, the engulfed bacteria became mitochondria and/or chloroplasts!