The mitochondria are organelles in cells that produce ATP a usable energy source for the cell from glucose.
They have 70s ribosomes like bacteria.They all have circular DNA.
Contain their own DNA is the most pertinent answer.
Eukaryotic cells, found in animals, plants, and insects, have a nucleus, however they do not have cell walls unless they are in plants. Prokaryotic cells (in bacteria, etc.) have no nucleus, but always has a cell wall (this is part of what makes it hard to get rid of the bacteria that makes us sick)