Another site with many links relating to the problem. Incidently, is this your child’s homework ? This site seems to be one that proposes science experiments for students.
http://www.gallaudet.edu/~tsapsoar/tsanov.html
So, padeyed, what was the basic formula for amount of plant life to produce enough oxygen for a human? Surely y’all had a good idea before the concrete started eating all the oxygen.
I believe they work by using a chemical (lithium oxide?) that absorbs CO2 out of the atmosphere. I don’t know if once the chemical is saturated the scrubbers have to be chucked, or if they have ones that can be cycled to drive off the CO2 for expulsion. I wonder what system is used onboard nuclear submarines?
In any event, while scrubbers keep the atmosphere breathable they don’t address the problem that a consumptable- oxygen- is being used up. Unfortunately there currently isn’t any practical way to reduce CO2 into carbon and oxygen. If there was, it would be great to have aboard a spacecraft where dumping the carbon would be an acceptable medium-term solution.
I believe they work by using a chemical (lithium oxide?) that absorbs CO2 out of the atmosphere. I don’t know if once the chemical is saturated the scrubbers have to be chucked, or if they have ones that can be cycled to drive off the CO2 for expulsion. I wonder what system is used onboard nuclear submarines?
In any event, while scrubbers keep the atmosphere breathable they don’t address the problem that a consumptable- oxygen- is being used up. Unfortunately there currently isn’t any practical way to reduce CO2 into carbon and oxygen. If there was, it would be great to have aboard a spacecraft where dumping the carbon would be an acceptable medium-term solution.
Come on y’all. The question isn’t “how to build Bioshere 3.” And not how much microbes in cow shit or in decaying plants or absorbed by the concrete effect the Bioshere (earth). I think Soup wanted to know, you got one “X” human being here, you got “Y” plant there. The Oxygen from “Y” minus the Oxygen used by “X” equals Zero. “X” is a half human,… no wait, a half-sized human, … ok, “X” is a human. What is “Y”?
Or, in other words, can a kid plant a christmas tree. And he and his tree equal each other (oxygenwise) and therefore are not taking oxygen from the environment. Or does he need a whole greenhouse to equal out.
Soup, if I’m off track, just tell me to shut up. I’m tough, I can take it.
No, JimB, you’re pretty much on track. And thanks to the website funeefarmer provided, it appears that a normal human at rest needs about 360,000 ml of oxygen a day delivered to the tissues in his body. The trick now is to find out what plant (or plants) can pump out that much oxygen in a day.
So, are there any botanists or biologists out there who can tell us how much oxygen plants produce in a day?
Hey, Soup, I’m going to push this to the top one more time. I can’t believe that no one in this vast expanse of knowledge wants to answer your question. I would if I could, but I haven’t found an answer. I’m really interested myself in the answer.
Thanks, Jim. We’ll crack this one yet. C’mon people! There’s an little eight-year-old counting on us!
Let’s see if I understand it correctly. Plants convert CO2 and H2O into, well, big organic molecules. (They do the opposite as well, but this is the net effect.) Animals convert big organic molecules into CO2 and H2O. The two makes a closed loop. So if there was a single plant and a single animal in a closed system, if the animal eats enough of the plant so that the plant doesn’t get bigger or smaller, the plant is also releasing just enough oxygen to support the animal.
Then the original question is equivalent to “How big a plant is needed to feed a man on a long-term basis?” So we just need to figure out how big a farm is needed to support a single person. A human needs, what, 2000 Calories per day? According to one on-line reference (which is in Japanese so I won’t bother to mention it), that’s equivalent of 600 grams of wheat a day, or 200 kilograms (400 pounds) per year. (Does that sound right?)
So how big a field is needed to grow 200 kg per year? Apparently the maximum yield of a wheat farm is about 80 Bushels per acre, or 3 cubic meters per acre. I have no idea what the density of wheat is, but as a wild guess I’d say about 0.5 grams per cm^3. So 3 cubic meters weighs 1500 kg. To produce 200 kg/year you need about 1/7 of an acre, or
600 square meters. That’s an area 20x30 meters, or 60x100 feet.
But this area of wheat farm doesn’t just feed people, it also feeds - and thus supplies oxygen for - other animals such as microbes and maybe cows. So the fraction of oxygen we use from this farm is the fraction of the plants we eat. Not a lot in terms of weight, but much of the energy is probably in the parts we do eat, so I’d guess about half. So, the answer to the original question is that we need a 50x50 feet area of some type of fast-growing crop to produce enough oxygen to keep a man alive.
Now, I have no feel about if this answer is correct, so it may be way off. Let us know if someone finds any big mistakes.
Thanks scr4.
I’d still like to know the actual daily oxygen output of a plant. I suppose this is usually measured in milliliters? Then we can try to match it up with a person’s daily oxygen requirement (the number I’m working with right now is 360,000 ml).
JimB sez:
They never bothered with stuff like that. It was all based on the so-called Gaia (sp?) hypothesis that the earth is a self-regulating entity. They did some work with a single person in a house size test module but AFAIK a lot of was wild ass guesses.
They overlooked a lot of simple things. The glass cut out all UV light but it never occurred to them that it would effect the primary pollinators like bees. They all died. The bats died. The hummingbirds died. One of the galagos (bush babies) crawled into an electric bus, was electrocuted and died. They took the rest out. The cockroaches and ants thrived. You did not want to be the first one to turn on the light in the kitchen in that place.
A lot of it was apparently done just to be exotic. They developed a hybrid of a Japanese silky chicken and jungle fowl for eggs but it didn’t work out. After much research and analysis they determined that common leghorns would be better. Any farmer in America could have told them that.
“Popeye? Hm? He’s not much of a judge of women!” King Blozo
Since O2 concentration in normal air is about 21%, and in exhaled breath is about 19% (depending on how much you’re working, etc.), about 2% of the 3500 gallons you breathe in is used. This gives about 270,000 ml, which is pretty close to your 360,000 ml (close for this kind of “back of the napkin” calculation).
My WAG is about 100 square feet of leaves per human, or maybe 10 trees.
Arjuna34
Everyday we creep closer to The Answer! Thanks Arjuna34. I’m stll looking for the actual oxygen output of a plant. It may be different for different species. I’ve yet to see hard numbers for this.
Just to recap. Our educated guesses as to how much plant is needed to supply a man with enough oxygen to live are: 1/3 acre of shrubs and monkey grass, 1/2 acre of rainforest, a 50x50 plot of fast-growing crops, and 10 trees (I’m dropping my guess of a billion Chia Pets). We’re getting there!
The calculation issues are much more complex than anyone generally accounts for. If you use a single figure for human’s oxygen uptake what happens when they all have to do strenuous labor to farm enough food to eat? What happens when the leaf material dies out? the rotting leaves release carbon back into the system. How about the glass and steel structure that blocks out a large percentage of sunlight?
One of the biggest problems with a small sealed system is that variations in O2 and CO2 don’t have much of a buffer. On biosphere 1 (the earth) CO2 is rising but it isn’t a big problem right this second though it will be in the future. When CO2 starts rising in a small system people can be dead in a very short time.
“Popeye? Hm? He’s not much of a judge of women!” King Blozo
Padeye-
While I’ll admit our eight-year-old is bright, I don’t think the original question went much beyond “How much oxygen does a plant produce?” How did you figure out how much plant life was needed in Biosphere 2?
Remember, this is a hypothetical man and a hypothetical plant locked in a hypothetical box. Ballpark figures are gladly accepted.
Padeye-
While I’ll admit our eight-year-old is bright, I don’t think the original question went much beyond “How much oxygen does a plant produce?” How did you figure out how much plant life was needed in Biosphere 2?
Remember, this is a hypothetical man and a hypothetical plant locked in a hypothetical box. Ballpark figures are gladly accepted.
Looks like I found some hard numbers! According to the website below, 1kg of organic matter will release 1.5 kg of oxygen.
http://www.infodienst-mlr.bwl.de/la/lap/ergebnisse/agraroekologie/allgemeine_oekologie/CO2-Bindung_E.htm
This guy even goes into what plants produce how much oxygen. I’m not sure what unit of measurement he’s using in that chart, but as soon as I figure out how to convert kg into ml, we may have something to work with! Feel free to crunch some numbers!
Soup-
Sounds like you have a very bright child asking good questions. I was just trying to point out that in a tiny closed system the fluctuations of Oxygen and CO2 become critical long before the long term averages do.
I wondered the same thing a a child, if you could seal a terrarium with a few mice and plants and it would sustain itself. I was told by more than one teacher that it couldn’t be done, no reason, just that it could not be done. I was also told we would never see an atom but thanks to electron microscopes we have pictures of individual atoms. I found Bio2 to be fascinating because of this and it’s one of the reasons I took the job they offered me. That plusx the fact that they offered me more money than Computerland was paying.
“Popeye? Hm? He’s not much of a judge of women!” King Blozo
Padeye-
She’s a very bright kid, and has more questions like this. Thank goodness for The Straight Dope! We’re having alot of fun watching the thought process involved in answering this question.