text: Inside the body oxygen is delivered to cells and in the cells to mitochondria, where it is consumed in the process generating most of the energy required by the organism.
  Mitochondrial respirometry measures the consumption of oxygen by the mitochondria without involving an entire living animal and is the main tool to study mitochondrial function. Three different types of samples may be subjected to such respirometric studies:
  isolated mitochondria (from cell cultures, animals or plants); permeabilized cells (from cell cultures); and permeabilized fibers or tissues (from animals). In the latter two cases the cellular membrane is made permeable by the addition of chemicals leaving selectively the mitochondrial membrane intact. Therefore, chemicals that usually would not be able to cross the cell membrane can directly influence the mitochondria. By the permeabilization of the cellular membrane, the cell stops to exist as a living, defined organism, leaving only the mitochondria as still functional structures.
  Unlike whole-animal respirometry, mitochondrial respirometry takes place in solution, i.e. the sample is suspended in a medium. Today mitochondrial respirometry is mainly performed with a closed-chamber approach.