# Endosymbiotic theory of mitochondrial origin

Size The cell of mitochondria (${\displaystyle 0.5-1.0\mu m}$) is in the size range for the prokaryotic cells from which they are probably descended. The overall prokaryotic cell size range is ${\displaystyle 1-10\mu m}$, but the older ones from which mitochondria are believed to have descended have sizes at the lower end of the range.