There's a fairly common trope in SF series where you have a space station of some kind, and the lives of the people on board are maintained by having green vegetation around to exchange carbon dioxide with oxygen. I was just wondering about this, and I ask the Playground if anyone knows: has anyone ever worked out just how large an area of green plants would be needed to maintain the oxygen levels for a single person? Just curiosity, mainly, because I was wondering how much of the interior of a station would have to be given over to vegetation and how much could be used for people.