In selecting plants for indoor gardening, consider the oxygen generating potential of algae compared to the common potatoe plant. Algae is also an outstanding food source high in protein. One drawback of algae ponds - they can stink.
NASA Questions and Answers
QUESTION: How many potato plants does it take to supply one person with enough oxygen. - Canada
ANSWER is curtesy of Cheryl Mackowiak on July 30, 1997 at: http://atlas.ksc.nasa.gov/celss/STAFF/staff.htm
It has been reported that the average human needs 0.83 kg of oxygen each day.
Oxygen regeneration from plants is dependent on photosynthetic rate and this is dependent on various environmental factors. In our system (20/16 C light/dark, at a 12/12 hr. photoperiod and CO2 at 1200 ppm), it would take 171 potato plants or 26 m2 growing area. Wheat can be grown at a much greater density and so it would only take 19 m2 growing area (11,937 plants).
Encyclopaedia Britannica, on algae.
Ninety percent of all photosynthesis is carried out by algae, and it is believed that they played an important role in creating the Earths oxygen-rich atmosphere early in the planets history.