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by jdblair 3060 days ago
Correction: https://en.wikipedia.org/wiki/Respiration_(physiology)
1 comments
thope 3060 days ago
Ok thank you, I also found a short answer[0]. It seems the carbon comes from the conversion of glucose; that is, from food.

[0] http://www.smh.com.au/news/big-questions/we-breath-in-oxygen...

link