Respiration can be broken down into three metabolic stages:
In most eukaryotic cells, glycolysis (stage 1) occurs in the cytosol (the protein-rich, semi-fluid part of the cell in which the cell's organelles are immersed), whereas the Krebs cycle, electron transport, and oxidative phosphorylation (stages 2 and 3) occur in the mitochondria. While our discussion will focus on cellular respiration in the eukaryotic cell, you should note that this process also takes place in prokaryotes (even though they lack mitochondria).
Sometimes glycolysis is presented as a process separate from cellular respiration, so don't be confused if you hear someone mention "glycolysis and cellular respiration."