The mitochondria is only part of the story.
Before that, there's glucose activation => glycolysis =>
fermentation => cellular respiration => Krebs Cycle before
the mitochondria finally gets into the picture.
And even the process in the mitochondria seems pretty complicated
to me... there's the electron transport chain process and
chemiosmosis (where the bulk of the energy finally gets harvested)
.
At times like this I get reminded of why I'm doing mechanical
engineering instead of the life sciences. 
