Actually, I think that a better way to say this would be that they intake both CO2 and O2 through the stoma. The oxygen is then used for cellular respiration (oxidation, crebs cycle, etc) and the CO2 is used in the grana of the cloroplasts to produce "food"(much more than just glucose is produced, including ammino acids, nucleotides and lipids). I think my problem is that I was looking primarily at the Photosynthetic side of plant respiration, and took the cellular or mitochondrial side (O2) to be supplied mostly by the Photosynthesis reation. I don't know if that is true, and I don't know where I could go to verify that statement.