[littlestymaar]

I stand corrected, I had somehow built-up a wrong understanding of it (looks like those high school classes are long lost).

But where does all that excess oxygen go then? (the O/C ratio is 2 in C but ~1 in carbohydrates).

[jedimastert]

It gets released into the air through the leaves. It's the animal respiration cycle in reverse

[littlestymaar]

No. It was my first understanding as well, but it's not what happens. See this link from a sibling comment: http://www-plb.ucdavis.edu/courses/bis/2A/bis2A-F11/Photosyn...