Endosymbiant Theory

• Early ancestor of a eukaryotic cell engulfed an oxygen-using, non-photosynthetic prokaryotic cell → Engulfed cell became an endosymbiont (a cell living within another cell) • Over time, the two merged into one organism → Eukaryotic cell with a mitochondrion

• One of these eukaryotic cells with a mitochondrion took up a photosynthetic prokaryote → Became ancestor of eukaryotic cells with chloroplasts Support for ENDOSYMBIONT THEORY • Mitochondria and chloroplasts are bounded by 2 membranes (other organelles are not) – Ancestral prokaryotes had 2 membranes • Mitochondria and chloroplasts contain ribosomes and DNA • Mitochondria and chloroplasts are independent (Grow and reproduce inside cell on their own)