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Re: Plants cause oxygen deprivation at night???????

  • Subject: Re: Plants cause oxygen deprivation at night???????
  • From: ExoticRainforest <Steve@ExoticRainforest.com>
  • Date: Tue, 16 Feb 2010 03:14:28 -0600

Thank you Walter! 

That is the kind of info I need to make a good explanation! 

I hope to be able to post a page on my website in the next few weeks explaining all of this since my little site receives a lot of hits from people around the globe looking for answers.  Almost one half million hits popped up last year so if none of you object I would like to be able to use selected quotes from your responses in that piece.


Walter Turner wrote:

I can’t add to the ideas Steve Marak presented, but I can try some numbers. I hope the readers of Aroid-L will work through my numbers here. It would be bad enough for me to look like an idiot because I overlooked something that changes the results by a factor of a hundred or so, but it would be worse for the wrong results to stand without correction.


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.


If the sleeper is oxygen-starved, he or she probably isn’t breathing right. It can’t be blamed on the plant. I’ve known people who slept with their heads under the covers. That does scare me.

Walter Turner

fn:Steve  Lucas

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