Subject: Re: plants' respiratory system

From: thorburn@.xyplex.com (Gary Thorburn)
Date: 4 Oct 1995 17:11:29 GMT

Yes indeed, when a plant is not photosynthesizing, (and even when it
is), it is respiring Oxygen into CO2 just like everybody else.  But I
doubt that the oxygen depletion at night is enough to warrant removing
plants, although I have heard that its sometimes done.

More interesting is the dubious assertion that Forests Produce Oxygen.  Not 
only do they produce it, but they consume it.  And the fauna consuming the
plant material as food -- including the soil fungi, bacteria and insects
consuming the litter, will consume ALL the net oxygen produced by the forest
UNLESS there is biomass accumulating.  So, a mature forest typically 
produces no oxygen, but a young forest, such as an abandoned field, or a 
forest recovering from a harvest, is accumulating biomass (wood) and is 
producing a net positive amount of oxygen.

So, if at one time our planet had less oxygen than it does now, perhaps 
some of that is related to the presence of extant biomass, including fossil 
fuels.  That is, fossil fuels in the ground, wood in buildings, and standing
biomass in forests may be related directly to just how much oxygen we have
to burn.

/****
*  Gary W. Thorburn
*  reply address:  [email-masked]
****/

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From: [email-masked] (Stefan van der Bijl)
Date: Tue, 03 Oct 1995 21:09:39 -0700

Can someone please tell me if I am correct or not? I have always been
under the impression that plants use the CO2 that animals exhale to
perform photosynthesis.  One of the major by-products is O2 that humans
inhale.  At night, what happens?  I would think that they slow down in
their production of O2.  Someone has recently informed me that plants
reverse the process at night and take in the very same O2 that we breathe,
and emit CO2. And that is why many hospitals in France and all over the
rest of the world remove the plants from patients rooms at night. 
HEELLLLPPPP!!!!

-- 
Stefan van der Bijl
Altura Software, Inc
[email-masked]

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From: [email-masked] (Nancy Harrison)
Date: Wed, 4 Oct 1995 18:44:03

>rest of the world remove the plants from patients rooms at night. 

Yes, that is correct...plants emit CO2 at night when they respire the energy 
they created during the day.

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From: [email-masked] (Ray Baxter)
Date: 5 Oct 1995 17:54:21 GMT

In article <[email-masked]>, [email-masked]
(Stefan van der Bijl) wrote:

> inhale.  

In photosynthesis, plants convert CO2, water, and the energy of sunlight 
into carbohydrates and O2. The O2 can come from any source.

At the same time, and at all other times, plants respire, using O2 to produce
energy from carbon compounds. These are the same reactions that are performed
by humans and all other aerobic organisms.

> At night, what happens?  I would think that they slow down in
> their production of O2.  

That is correct.

> Someone has recently informed me that plants
> and emit CO2. 

No, this is wrong. They continue to respire and they stop photosynthesizing.
There are two separate processes that work in opposite directions, not one
process that goes in reverse. If nothing else, photosynthesis and respiration
occur in different sub-cellular organelles (chloroplasts and mitochondria, 
respectively).

> And that is why many hospitals in France and all over the

Who can explain the French? 

Or doctors?

-- 
Ray Baxter                                Department of Plant Biology
[email-masked]                   University of California
(510) 642-8064                            Berkeley CA 94720

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From: [email-masked] (Adrian Lund)
Date: 6 Oct 1995 16:41:18 GMT

Stefan van der Bijl ([email-masked]) wrote:
: Can someone please tell me if I am correct or not? I have always been
: under the impression that plants use the CO2 that animals exhale to
: perform photosynthesis.  One of the major by-products is O2 that humans
: inhale.  At night, what happens?  I would think that they slow down in
: their production of O2.  
You are correct.  There is a specific light intensity required for plants 
to balance their O2 consumption and O2 production.  this is Called the 
light compensation point.

: Someone has recently informed me that plants
: reverse the process at night and take in the very same O2 that we breathe,
: and emit CO2. 
Surprise, Like the bad little eukaryotic cells that they are, plants do 
contain mitochondria.  The are customized to do some interesting things 
that only plants need, they oxidize glycolate formed from 
photo-respiration, and they can also produce heat through a 
cyanide-resitant oxidase in the electron transport chain.  They can also 
oxidise cytosolic NAD(P)H produced by the chloroplast and glycolysis.

: And that is why many hospitals in France and all over the
: rest of the world remove the plants from patients rooms at night. 
: HEELLLLPPPP!!!!

I doubt this is the real reason.  Air is 20% O2, to consume any more than 
a miniscule amount of the oxygen (assuming a hermetically sealed room) 
imagine th amount of plant material (sugars and starches) that would have 
to be consumed by the plant.  Not to mention the heat produced.
Maybe the nurses take them out to water them?

: -- : Stefan 
van der Bijl : Altura Software, Inc : [email-masked]
--
Adrian Lund   (I know my .sig is a piece of shit, but it's short.)

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From: [email-masked]
Date: 8 Oct 1995 02:28:38 GMT

In article <[email-masked]>, thorburn@.xyplex.com (Gary Thorburn) writes:
>only do they produce it, but they consume it.  

>And the fauna consuming the
I thought people were fauna too

>UNLESS there is biomass accumulating.  

Could you post a reference for this please.

So, a mature forest typically 
>*  reply address:  [email-masked]
 
[email-masked]

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From: [email-masked] (Jari Oksanen)
Date: Mon, 9 Oct 1995 15:45:02

>Maybe the nurses take them out to water them?

I think that is the real reason, since I have heard that claim from several 
sources, e.g., warnings that you should not have pot plants in your bedroom. 
Naturally, this is non-sense like Adrian Lund explains, but that does not 
prevent people from believing so. One of the myths, partly based on reality, 
but non-sense if you think about mass balance of gas exchange in plants. 
--- Jari Oksanen, Tromssa, Ruija / Romsa, Norga / Tromsø, Norge