Everything Else . My friend says it is common knowledge in Europe that it is dangerous to sleep with a live plant in the room because it uses up oxygen. There is a grain of truth in the idea, as green plants do absorb some oxygen for use in respiration, the mirror image of photosynthesis.
Photosynthesis can occur only when there is light, so at night plants are net absorbers of oxygen.
However, true danger would result only from an extremely large body of plants in a very tightly closed sleeping chamber with a very limited supply of oxygen. Another breathing person in the room would be a much heavier burden on the oxygen content of the atmosphere than the slow respiratory oxidation of ordinary houseplants. These principles of gas exchange in photosynthesis and respiration were explored in the late 18th century by Jan Ingenhousz, a Dutch botanist who also worked in England. Ingenhousz was skeptical about the benefits and decided to check them out. In photosynthesis, carbon dioxide and water react in the presence of light energy to produce sugar and oxygen.