To the best of my knowledge, all animal life needs oxygen to survive (save for some kind of bacteria, perhaps…?). Fire also needs oxygen.
Why?
Why can’t we breathe nitrogen, or neon?
What do we use the oxygen for, anyway?
Would it be possible for any kind of advanced life to exist that DIDN’T need oxygen?
/Etum
We’re basically internal combustion engines. We turn sugar into carbon dioxide and water, getting energy in the process. That’s what keeps us warm, enables us to move, and allows us to stick amino acids and proteins together to rebuild ourselves. (Entropy would very much rather we turned into something less complex, and to counter entropy’s natural tendencies you have to input energy. At bottom we’re all solar powered, but we use solar power by way of useful plants that can convert it directly into stored energy, turning water and carbon dioxide into sugar; and animals that feed on the plants.)
There are not many reactions involving nitrogen that liberate energy, still less neon which is as near chemically inert as makes no difference for all we care. Some primitive lifeforms can get their energy some other way - gangrene is caused by anaerobic microorganisms, for instance - but we’ve no evidence that higher lifeforms can possibly work that way, though we’re free to speculate.
Larry Niven’s short story The Green Plague postulated a pre-Cambrian civilization built by anaerobic life, which was rapidly driven to extinction as soon as photosynthetic plants made free oxygen available.
One cliche of 1940s science fiction is the Aliens who Live in Chlorine Atmosphere. There are some dramatic science demonstrations you can show of candles burining in pure chlorine (if you go to YouTube you won’t find these, but you’ll find sodium and other things buring in chlorine). Aha! think the pulpsters – if chlorine can support combustion, it can support life!
But it’s not so easy – Oxygen is more common, and early life produced lots of free oxygen as a waste product that eventually allowed oxygen-using creatures to evolve and take over. Polluted their own environment, they did. No similar scenario for producing and using a chlorine atmosphere is known.
The idea could still work, and Hard SF-master Hal Clement worked for a while on the science and background of a chlorine world he called “Bleachworld”, but he never wrote a story set in it (at least not one that was published). In principle, you’d think that other halogens could perform the same office – bromine or iodine, if the temperature were high enough for them to be gaseous.
Ever tried breathing Cool Whip?
We can and do breathe in Nitrogen, it’s got quite a presence in the ambient air that we breathe.
Our blood contains hemoglobin, which is iron-based (hence the hem-) and it binds to the oxygen to taxi it around our bodies through our blood stream.
Not sure if you’ve heard of cellular respiration, glycolosis or the kreb’s cycle, but basically, we need all these processes to go on in order to live. And in order for some of these reactions to occur, we need oxygen!
Glycolysis converts our food into pyruvate or ATP. We need the pyruvate for:
Respiration, which continues to help convert our yum-yums into ATP.
This are are contributors to the Kreb’s Cycle. When these steps are all said and done, we end up with ATP, which we need for energy transfer…like moving a muscle.
Not too sure about your last question!
What is cool whip?
Thanks for all the answers, everybody!
I can’t say that I understand it all in detail, but I’ll read those links later SharkB8, maybe that’ll help. 
Cool Whip is a dessert topping; basically artificial whipped cream.
Long ago, I was in the men’s room at college, and I saw the the following bit of graffiti on the stall wall.
Someone wrote, Why is there air?
Someone else answered, Ever try breathing Cool Whip?
Cool Whip is an American convenience food that tries to emulate whipped cream. It comes in a tub, but I think the poster meant a different form of whipped cream substitute, or nitrous-charged whipping cream. The component that the poster was probably referring to is the gas that keeps the cream in a … a … oh, I don’t know the word. Not emulsion. Suspension? Fluffy? Whatever – if you’ve had whipped cream, you know how it differs from regular cream.
Anyway, the gas that keeps it like that is also known as “laughing gas,” an anesthetic commonly associated with dentists. It’s also used as a recreational drug (in small, relatively controlled situations—like Dead shows), but I don’t want to skirt board rules about describing it. Since it’s largely nitrogen based (I believe the formula is N[sub]2[/sub]O), if you’ve ever breathed it, you know the effect it can have on the noggin.
Could someone touch on the mechanics (quantum or otherwise) that makes oxygen such a good reactant? Why it has such an affinity for releasing molecular energy? IIRC it has to do with the number of electrons it has in its shell and atom’s general ‘preference’ for settling into noble-like states. That is, why is oxygen’s number of (valence?) electrons jut right for this sort of thing, but another atom with similar proportions of its outer shell filled is not? Or am I completely off track as to why oxygen is so special?
ETA: Or the poster could have been referring to men’s room graphitti. 
It’s Reddi-Wip that comes in the spray can, not Cool Whip.
Plants use solar energy to split water into oxygen and hydrogen. The hydrogen, separated into protons and electrons, is used to drive the ATP synthase, the protein that produces ATP. ATP is the “gasoline” on which most cellular processes run. The plants release Oxygen as waste product, and use any excess energy to synthesize sugar, starch and fat from CO2 and water. These compounds release energy when metabolically “burned” to CO2 and water. When we eat the plants, we take up this stored chemical energy, “burn” it ourself to produce hydrogen (NADH+H+), which is used to drive our own ATP synthase to produce the ATP needed to power our own cellular processes.
I did breathe it a few times as a teen, it was quite fun, though the rush was over in about 30 secs or something. Not really worth risking brain damage over.