Yes, if you have enough plants around they can convert enough CO2
to sugars to make up for the CO2
burned in a candle. Up to a point, thatís just how the world usually works, since many of us (people, yeast, mushrooms, etc.) are like candles, using up O2
and releasing CO2
. Plants and photosynthetic bacteria do the opposite.
Right now, unfortunately, people are burning up so much of the carbon materials stored up from previous photosynthesis that plants canít keep up with us, and the CO2
level is going up. That is the main source of global warming, which is going to be big trouble.
Well, the vacuum part will make both your candle and your plant stop functioning, but you should also provide some air. Air is about 70% nitrogen, and most of the rest is oxygen. There are ideas of spacecraft which can voyage for many years by using plants to recycle the CO2
of the crew back into oxygen. More practically, the experiment has been done in the Arizona desert in a laboratory called "Biosphere" and "Biosphere II". They were pretty close to getting it to work, but the Earthís ecosystem is very complicated and difficult to understand every last little bit of it. And a closed (except for sunlight input and heat output) ecosystem may be missing vital parts, or may introduce its own features which are not present in significant quantities in the Earthís ecosystem to matter.
The Earth itself is an example of a closed (well, except for energy input and output) system which has worked for billions of years. Weíre making a mess of the equilibrium, though.
(republished on 07/18/06)