We breathe in air, not straight oxygen. Attached is a pie chart showing roughly what percentage of what is in the air we breathe
Nitrogen,<span>The atmosphere is composed of ~78% nitrogen and ~21% oxygen, with small amounts of other gases. The bulk composition of the earth by weight is mostly, iron, oxygen, silicon and magnesium, in that order, with all the other elements making up only about 5% of the earth's weight.</span>
Light, carbon dioxide, and water are the materials necessary for photosynthesis. Glucose (sugar), water, and oxygen are produced.