[brendan_dj]

Ok, It depends on the size of the plant!

We've all be taught that plants absorb carbon dioxide and emits oxygen during the process of photosynthisis. But my question is, How much?

In other words, if I was enclosed in a sealed room with a plant, how big must it be so that both me and the plant support each other's needs?

I ask this because we have a large plant in our living-room. It is almost touching the ceiling and resembles a small tree.

If the room is air-tight, would I eventually die of lack of oxygen? How big must this tree be to insure my survival? (please assume that I have a supply of food/water and other essential life requirments)

[avinitski]

not only the size but the type of plant matters too apparently.

[brendan_dj]

I think its a Ficus tree. It looks like this and is about 2 metres or 7 feet high.

http://www.theficus.com

[krish]

interesting question Brendan

sorry I can't help at all
- but I like that inventive thinking ... sounds like you're the type that could come up with concepts for inventions

[danmc_82]

I wouldnt of thought that a plant even of that size would be able to support your life. Maybe as the room filled up with more carbon dioxide, the plant would respond and produce more oxygen

[njp]

Originally Posted by brendan_dj

If the room is air-tight, would I eventually die of lack of oxygen? How big must this tree be to insure my survival? (please assume that I have a supply of food/water and other essential life requirments)

Either that, or the CO2 would get you (in the suffocation sense, rather than the global warming sense!).

Small closed ecosystems are very hard to get right, and yours would be very small indeed. You would need a lot (yes, I know that's a cop-out but I'm too lazy to do the research!) of rapidly-growing foliage, with plenty of light getting to the leaves. Those requirements are somewhat contradictory in a small enclosed space. In fact, I doubt any normal domestic living space would be large enough, even in principle.

In the rather larger Biosphere 2 experiment, the CO2 levels fluctuated wildly, and the oxygen levels dropped to the point where more had to be introduced from outside. They never succeeded in getting the system balanced.

[danmc_82]

Originally Posted by brendan_dj

Of course! It is indeed a hypothetical question.

Let me phrase it a different way....

How big must a typical indoor plant be (eg: Ficus) so that my breathing and the plant's process of photosynthisis reaches equalibrium?

I think what njp was getting at is theres no def answer as there can be so many variables. Consider the amount of plantage compared to humans and animals on the planet and you'll see to get an equal system, there is so much more plantage. Sorry not very scientific

[njp]

Originally Posted by danmc_82

Maybe as the room filled up with more carbon dioxide, the plant would respond and produce more oxygen

It can only do that by fixing more CO2 (i.e by getting bigger) and by releasing more oxygen from the water it takes in. And of course there are other limits that kick in - plants don't just grow faster and faster as the CO2 levels rise.

[Sporran]

looking at things in real life

Im a chronic asthmatic since i was a kiddie.

If there is enuff oxcy for me there is certainly enuff for you

Breath and enjoy

Btw bar a caccy i have no plants but do live in west wales (literally the devil)

[njp]

According to this site, NASA think that 25 square metres of leaf cover ("about 2 average sized trees") exposed to 12 hours of light per day is sufficient to provide enough oxygen for one person.

Of course, how much oxygen you use depends on how hard you are exercising, and they neglect to say anything about that.

[Miyazaki]

I would postulate that about 2/3 of the carbon dioxide that the plant takes in, (as long as photosynthesis is constant, and the plant has enough water and heat etc) is released as oxygen.

We would need to get into avogadro's constant and work out the mass of one mole of carbon and two moles of oxygen, as carbon dioxide contains twice as much oxygen as it does carbon.

[njp]

Originally Posted by Games Guru

I would postulate that about 2/3 of the carbon dioxide that the plant takes in, (as long as photosynthesis is constant, and the plant has enough water and heat etc) is released as oxygen.

You could postulate that, but you'd be wrong. The oxygen released during photosynthesis comes from the water molecules.

[Miyazaki]

Originally Posted by njp

You could postulate that, but you'd be wrong. The oxygen released during photosynthesis comes from the water molecules.

Ah,

thanks for that. I always assumed it came from the carbon dioxide.

I wondered where the electrons came from for the transport chain.

[njp]

Wikipedia has a pretty good article on photosynthesis.

[Miyazaki]

To attempt to answer the original question, (and if we discount dissolved oxygen in the water given to the plant) one mole of oxygen weighs slightly less than 16 grammes. A mole of hydrogen weighs slightly more than 1 gramme.

For simplicity, if we said one molecule of water weighed 18 grammes, then 2 of those grammes would be hydrogen as there are 2 atoms of hydrogen and one of oxygen, the remaining 16 grammes would be oxygen.

If the average adult human has a lung capacity of 6 litres and a gramme is equivilent to 0.001 litres, then a molecule of water is equivilent to 0.018 litres.

0.018 x 333.333 = ~ 6 litres.

of that 88.89% is oxygen

so 5.34 litres of oxygen theoretically should be released by the plant for every 6 litres of water it takes in.

We use about 5% of the 21% of atmospheric oxygen for respiration per breath, so if we use that as an example then 5.34 litres of oxygen if mixed with nitrogren so it simulates the atmosphere should last:

So, at sea level, in this purely hypothetical example, for every 6 litres of water a plant is fed you should get 20 breaths before you run out of oxygen.

I'm going to get shot down now aren't I

[Miyazaki]

I also forgot to mention that carbon dioxide is toxic, so the above hypothetical example would only work if you were able to remove the carbon dioxide from every exhaled breath.

[njp]

Originally Posted by Games Guru

I'm going to get shot down now aren't I

I'm afraid so. Partly because I thought of answering the question in a similar way, until I realised I didn't know how much of the water was lost to the air through transpiration (but then again, it's a sealed room, so that imposes an upper bound!).

But mostly, because we don't breath liquid oxygen. I think you've missed a factor of about 800, somewhere along the line...

[brendan_dj]

Originally Posted by njp

You could postulate that, but you'd be wrong. The oxygen released during photosynthesis comes from the water molecules.

Interesting.....
So what happens to the hydrogen from the water after the oxygen has been extracted?

[njp]

Originally Posted by brendan_dj

Interesting.....
So what happens to the hydrogen from the water after the oxygen has been extracted?

It becomes part of the carbohydrates created by the process... Oxygen is just a waste product (luckily for us!).

[Miyazaki]

Hydrogen is made up of an electron and a proton.

The electron becomes part of a transport chain which is involved in photosynthesis and the proton becomes involved in the krebs cycle (i think?)

[apul]

Its been a while, but as far as I remember the H is used to turn NADP to NADPH and the energy from the electron is used to fix an extra phosphate (i think) to ADP to create ATP. Both of these are used to fix carbon. A small amount of water is also created. This is a very simplified version of events.

Alot of energy is also used by the plants for, well, living. This produced CO2 as we would. Overall though there is a net consumption of carbon and emission of oxygen.

As stated previously, you would need alot of plant and the amount of oxygen produced and CO2 fixed fluctuates greatly from time of day to time of year. All limiting factors will need to be addressed, such as light, water, temperature, nutrients, humidity.

Maybe using algae would be better? Spread it over your carpet and walls? Well worth it for abit of extra oxygen.

[Girthvader]

Haha.....
what a read.

[njp]

Are you inspired to construct a human terrarium?

Carpet and wallpaper algae has to be the way to go, perhaps with a pond full of phytoplankton in the middle.

It's the future for conservatories, you mark my word.