When I was a kid, my parents held the belief that if you keep lily flowers in a vase in a room with the windows closed overnight, and you sleep in that room, you will get a headache. The belief went on to state there is a small chance of death, for the presumed cause that the flowers somehow consume the oxygen in the room. As an adult, I never revisited this superstition; I don't buy flowers often, but my wife does.…
Well photosynthesis stops at night but metabolic activity doesn't, so presumably they consume oxygen. No idea how much though.
Plants consume CO2 and ‘exhale’ oxygen. They don’t consume it.