I think it's funny that there is a common misconception about the air that we breath is Oxygen. Generally, people believe that what we breath and what the atmosphere is made of is all oxygen. But in reality, what you may think is far from the truth.
True, we do breath in oxygen. Plant's produce it as a byproduct of photosynthesis. But we're actually breathing in a lot more of that. The "air" that we breath is about 21% Oxygen, and 78% Nitrogen by volume. The Oxygen enters our bloodstream and through the whole process, we exhale Carbon Dioxide, which, in turn, goes right back to the plants in their process of photosynthesis.
So yea we do need oxygen to survive, that was never my argument, I just think it's interesting that most of the Earth's atmosphere is Nitrogen and not what we think it is, Oxygen.