In the sentence, what does "it" mean? Oxygen is what it is all about. Ironically, the stuff that gives us life eventually kills it. The ultimate life force lies in tiny cellular factories of energy, called mitochondria, that burn nearly all the oxygen we breathe in. But breathing has a price. The combustion of oxygen that keeps us alive and active sends out by-products called oxygen free radicals. They have Dr. Jekyll and Mr. Hyde characteristics. On the one hand, they help guarantee our survival. For example, when the body mobilizes to fight off infectious agents, it generates a burst of free radicals to destroy the invaders very efficiently. Oxygen is what it is all about. In the sentence, what does "it" mean? Please help me! Thanks!