I recently had an eye-opening look at the differences between standard biology theory in the west versus the east. One of the teachers I know here recently had some inpatient surgery, and told all of us that she was going to “demand that the nurses don’t take my plants out of my hospital room at night!” Everyone who had lived in Jordan for awhile chuckled at this, but we new teachers were confused. Why would Jordanian nurses take plants out of the rooms of sick people?

Our elders explained that it was a common theory in the Arab world that at night, plants start taking in and using oxygen and compete with humans for it. Because of this theory, many people here make sure that they remove all the plants from their bedroom at night and put them outside in the hall. I confirmed this with a friend of mine here who has a bachelor’s degree in nursing. “Of course you put the plants outside of the room, especially in a hospital,” he said. “Otherwise, they might suck up all of the oxygen in the room.”

I was completely dumbfounded by this. Now, I can’t speak for all of the countries in the west, or other states besides Wisconsin, or even other school systems besides the ones I went to. However, I’m pretty sure that it’s a standard part of middle school biology classes that we learn that plants = good for oxygen, regardless of the time of day. On that same topic, I learned that there are old superstitions here that walking through a forest at night can be harmful to your health, for the same reasons.

I had to find out where this completely contradictory idea came from.

In my completely scientific research process of “searching The Google” I came across some pretty interesting articles, the most credible of these being from “Yahoo! Health Expert” Doctor Maoshing Ni. I checked his credentials – he’s a specialist in Chinese medicine and anti-aging research.

To get through the night, most plants reverse the process of photosynthesis and breathe, like you and I, by burning carbohydrates and oxygen while producing carbon dioxide and water. So surround yourself with plants during the day but remove them from your bedroom at night when you sleep.

On this Yahoo! Answers question thread, I found the back-and-forth between people to be particularly interesting. The reactions of most of the question answers that you can see if you scroll down the page (that the asker did not select to be “best answer”) were the same as mine – incredulous that someone would even ask the question (also note the citation on the “best answer” selection is Dr. Maoshing’s article).

Finally, the page that I found to be the most helpful was this one from the Aroid Forum. After establishing that yes, plants do shut down photosynthetic reactions at night, I learned that yes, that does mean that they need to carry out simple respiration at night, same as humans. Maybe it was just my school, but strike one against me: I was wrong. I don’t recall ever learning that plants carry out human-like respiration in the absence of light.

But is the Eastern World right? Let’s look at the math from Aroid Forum. (Bold emphasis added by me)

I asked a friend who did his doctoral work on plant respiration and got the approximation that the emission of CO2 in the dark is unlikely to exceed 4 micro moles per square meter of leaf surface per second. This is the same as the O2 taken up. Say our plants have a leaf area of one meter. Let’s say for the sake of argument that both upper and lower leaf surfaces emit at that rate, so our plants use up 8 micro moles PER SECOND (please excuse the upper case, but when we think of a whole night the seconds really add up).

In an 8-hour night, we have the 8 micro moles/s x 3600 s/h x 8 h = 230400 micro moles of oxygen the plants take up. That is only millionths of moles, so it amounts to 0.23 mole. That got the number back down in a hurry.

How much oxygen was in the room to start with?
A room 4 m x 4 m x 2.4 m has 38.4 cubic meters of air. That is 38400 liters.
At room temperature, a mole of gas is about 25 liters, so the room has 1536 moles of air.
If we say the air in the room is 20 % oxygen, we have 307 moles of oxygen to start with.

How much of the total oxygen in the room did the plant use? It is 0.23/307 = 0.075 %.

What about our oxygen-starved sleeper?
A person breathes out about 900 g CO2 per day or about 300 g in an 8-hour night.
CO2 has a mole weight of 44.
300/44 = 6.8 moles CO2 emitted = moles O2 taken up by a person in the night.

The 6.8 moles of oxygen used by the sleeping person amounts to only about 6.8/307 = 2.2 % of that available.

How do the plant and the sleeper compare? The plant uses 0.23/6.8 = 3.4 % as much.

With all the guessing (“approximation” in science-speak), none of the numbers has any meaning unless it’s rounded off to only one digit. You can insist that a sleeping person uses less oxygen than an active one, the room is smaller and the plant larger, but that doesn’t change anything. A good-sized plant surface won’t reduce the oxygen content of the room by much more than a tenth of a percent, and that is only about three percent of what the inhabitant uses up.

So, that takes care of that. To summarize, no one has been getting the complete picture so everyone’s a little bit wrong. My American school never taught me that plants consume any oxygen at all, and Eastern schools don’t mention exactly how ridiculously small the amount of consumed oxygen is.

And bottom line: how many of us sleep in completely air-tight sealed rooms, anyway? Eastern science really needs to take that into their considerations, otherwise they’re ignoring the question of how humans don’t just kill themselves off with the amount of CO2 we use up in one night. Or, for that matter, why a husband and wife who sleep in the same bed don’t suffer from oxygen deprivation. Unless you sleep with your head in a plastic bag (in which case you probably have bigger problems, my friend) that plant next to your bed, or even an entire roomful of them, isn’t going harm you a single bit.