[arvin555]

Thanks guys, I am a bit lost with the technical aspect, though some I understood a bit.

I would like to point out that I am not really asking if my plant will die if put in 100% CO2 environment for 4 hours, I think that answer basically is no... Right?

I was just wondering if it is true that plants (or some plants) do need to inspire O2 during the day, which means they do use O2 as well.... unless what Khoas said can be taken as a general rule that O2 is really needed but is taken from the water that is absorbed.

The post is really to update my (most) general concept of plants, that they take in CO2 and expell O2. Would it still be accurate? At least the CO2 intake is higher than the O2 intake and that the O2 expired will be higher in concetrantion than what was inspired or absorbed?

Still scratching my head, but will search for C3 and C4 later.

TTFN
Arvin