Rob Halgren wrote in message ...
J. Del Col wrote:

"Wendy" wrote in message news:sB23b.69617$kP.25605@fed1read03...


Just another thought on algae..........It is alive & growing, so it's using
up the oxygen
that the plants need? Yes?
Cheers Wendy




No. Plants use CO2 and give off oxygen as a waste product. Most of
the
oxygen presently on earth is the product of plant metabolism. (mostly
by marine plankton) Before oxygenating organisms evolved, Earth's
atmosphere was probably devoid of free oxygen.



Well... A bit of an oversimplification, but close enough for
government work. Plants need oxygen too. Depending on the type of
metabolism (Oh yes, there are several types... nothing is simple), a
plant may fix carbon during the day (bringing in CO2 and turning it into
sugars and whatnot) and utilize that fixed carbon (respiration,
requiring oxygen just like animals do) at night. So, plants can
literally suck the oxygen _out_ of the air at night...

All that said, CO2 is always more limiting than O2. In fact, many
growers of numerous indoor crops (including peppers, tomatos, and
various illegal substances...) supplement their atmospheres with CO2,
either from a compressed gas tank or special propane burners.

The websites for somefirms that supply this stuff are amusingly vague
about
the applications.


For your reading pleasure... The composition of dry air at sea level is

78.084 Mol% N2 (nitrogen)
20.948 Mol% O2 (oxygen)
0.0314 Mol% CO2 (carbon dioxide - and a scary coincidence with PI....)

And the rest a bunch of other stuff, including argon, krypton, neon,
helium, methane, and hydrogen. Needless to say, we don't need to be too
worried about plants sucking all the oxygen out of the air, and it
becomes obvious why a little extra CO2 can't hurt...

Rob

Yes, I know I over-simplified.


Any plant growing set-up---greenhouse, basement, etc. should have
enough air exchange, even through the cracks,that lack of CO2, O2, or
any other gas isn't going to be a problem, no matter how many plants
are in it--something I should have said in my first post.


J. Del Col