How many plants would you need to generate oxygen for yourself in an airlock? | Hacker News Reader

How many plants would you need to generate oxygen for yourself in an airlock?

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30 pointscpeterso12 comments

I am not a biologist but my recollection of high school biology is that photosynthesis is basically carbon dioxide + water + light energy = oxygen + glucose. So saying, "About 300 to 500 plants would produce the right amount of oxygen, but it's much harder to estimate the amount of carbon dioxide the plants absorb" is wrong - the quantity of oxygen produced will be exactly proportionate to the amount of carbon dioxide consumed. (There is also an issue of how much oxygen the plants' respiration would consume but let's not get into that).

And finally, some plants only "breathe," at night in order to save water - I also remember this (many if not most plants control water loss through transpiration by shutting down their stomata during , but I'm pretty much sure that no plants are able to photosynthesise at night! That would be an interesting species...

Overall, seems like some relatively serious misunderstandings of the basic science if even I (not a great GCSE mark in biology...) find myself wringing my hands...

> but I'm pretty much sure that no plants are able to photosynthesise at night! That would be an interesting species...

There are three types of plants, and instead of explaining them, let me just provide links.

The type of plant that breathes at night are the CAM ones.

* http://en.wikipedia.org/wiki/C3_carbon_fixation - most common, almost all plants are like this

* http://en.wikipedia.org/wiki/C4_carbon_fixation - very efficient, corn is the most common example

* http://en.wikipedia.org/wiki/CAM_photosynthesis - night breathing, pineapple is the example

Very interesting! Although as the other reply points out only some of the photosynthetic reactions take place at night. However I assume (but it's not exactly clear from scanning the article linked) that the actual emission of oxygen is likely also happening at night as this would require stomata to be open, although the actual production of oxygen is one of the light-dependent reactions in the photosynthetic chain. Is this correct?

> the quantity of oxygen produced will be exactly proportionate to the amount of carbon dioxide consumed

Not necessarily. Consider photorespiration -- under certain conditions, some plants will use oxygen instead of carbon dioxide.

> I'm pretty much sure that no plants are able to photosynthesise at night

Some reactions in photosynthesis are light independent, and many plants (especially ones in hot and arid environments) will perform these reactions at night in order to conserve water.

The effect of photorespiration is that some of the oxygen is transformed back to carbon dioxide. It reduces the efficiency of the photosynthesis, so you would need more light. But it doesn't change the global amount of oxygen produced form the carbon dioxide.

"[...] but it's much harder to estimate the amount of carbon dioxide the plants absorb, especially if every time a person breathes out, they inhibit oxygen production."

Not having scrolled down far enough to see the end, this is the moment where i hoped this article would burst into a wild jungle of different scenarios and scientific data analysis. But it ended... :(

Still nice thing to ponder about though...

Algae, would prove a much better oxygen producer than plants.

There are many studies being done, and done previously, on the viability of algae oxygenating artificial atmospheres.

http://www.ecology.com/2011/09/12/important-organism/

I read through the article a couple times, but couldn't find any pointers regarding the efficiency of algae as an oxygen producer - only that there is a lot of it out in the ocean. Do you have any citations that would suggest algae would be better in an airlock than a potted plant? (starts off on his 90 minute google/wikipedia distraction of the day)

[15 minutes later - this is the best link I've been able to find - from a Navy research paper in 1963, no less: http://torpedo.nrl.navy.mil/tu/ps/doc.html?dsn=7590785&h...

-- snip --

The results obtained with a small pilot plant containing 6200 ml of algal suspension have been evalu- ated; the effects of light intensity, rate of stirring, rate of carbon dioxide supply, and other variables were part of this study. Light energy was supplied by six 1500-watt incandescent lamps which extended through the suspension and were encased in 50-mm O.D. cooling jackets. When the light intensity at the surface of these jackets was 34,000 foot-candles (the limit with the equipment at hand), the oxygen production was 4500 cc per hour. Oxygen production increases with light intensity, but the oxygen produced per watt of electrical en- ergy expended is constant over a wide range of light intensities. The amount of electrical energy re- quired to provide enough oxygen for one man is between 30 and 50 kw, depending on the design of the gas exchanger. This high requirement makes the process prohibitive at present; but the development of more efficient high-intensity light sources could change the outlook. The dependability of the algal system in providing a constant supply of oxygen has been assured by this study; also, the volume requirements of the algal system are competitive with existing systems for carbon dioxide removal and oxygen production.

-- snip --

That's nice, because it pays some attention to alternative means to use energy to sink CO2, which is one way to look at the plant example.

One simple rule of thumb -- get enough plants to produce 100% of the food you consume. Your body converts food into co2, and plants convert co2 into food (yeah, a bunch of details are left out, but that is the simple version).

Photosynthesis really seems to be this weeks "what if" scenario: http://what-if.xkcd.com/17/

I wonder if you can scale this down to be scientifically accurate for Sandy from Spongebob, one tree per squirrel seems like it would be alright.

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