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Re: Nitrogen


Moontanman wrote:

> Your proof of that would be located where?

Pick up a biology text.  The closest one I have on hand is "Microbiology,
A Human Perspective" (Nester, Roberts and Nester, Wm. C Brown publisher,
1995). On page 128 they say:

"The overall reaction of photosynthesis carried out by green plants,
algae, and cyanobacteria is summarized in the equation
        
           Light Energy
    6CO2 + 6H2O --> C6H12O6 + 6O2

The cell gains energy from the light, which is uses to convert CO2 and
H20 into carbohydrate and other cellular material, and to release oxygen."

There's no nitrogen in the formula.  Photosynthesis does nothing to change
the state or concentration of nitrogen inside or outside the plant or
algae cell.

I figure you can find very similar statements in pretty much any biology
text, because that's the definition of photosynthesis.

Moon went on to say:

> Stephen Spotte in his book "Sea Water Aquariums' states that all plants use 
> nitrogen in some form, Higher plants are more likely to use nitrates algae 
> tend to use ammonia although some can use the nitrogen in urea. Nitrogen is 
> assimilated during phtosysnthisis to make the amino acids inside cells.

No one disputes that plants and algae use nitrogen, the question is
whether it's linked to the light cycle. Nor do I dispute that plants and
algae can take that nitrogen from the water.  They (and many other monera)
take it from the water and/or from the soil then use it to synthesize
amino acids which are then used to build proteins, nucleotides and so on.  
This process is part of what is called anabolism.  It isn't photosynthesis
and it isn't unique to photosynthesizing organisms.

Then Kevin Buckley wrote:
 
> I've seen a number of texts that re-iterate the following statements - 
>  
> "From the observed average ratios of the major elemental constituents of
> algal biomass we can use 'C106-H263-O110-N16-P' as the 'formula' for algae.
> Depending on whether the nitrogen is taken up as nitrate or ammonium ion, we
> can write the following two more complete stoichiometric descriptions of
> photosynthesis -
>  
> 106CO2 + 16NO3- + H2PO4- + 122H2O + 17H+  <==> algae + 138O2
>  
> or
>  
> 106CO2 + 16NH4+ + H2PO4- + 106H2O <==> algae + 106O2 + 15H+

These formulas don't express photosynthesis, they just say that algae have
a composition that can be expressed as a chemical formula.  They're fairly
meaningless formulae; if you were to dump CO2, NO3- (or NH4+), and H2PO4
into aqueous solution you would not get algae and oxygen.

If you look back at the beginning of this letter at the general formula
for what photosynthesis does you'll see that the 106 carbon dioxide
molecules and 106 water molecules on the left side, and the 106 oxygen
molecules on the right side of your equation *are* part of photosynthesis.  
The rest of the formula would be 17 2/3 molecules of glucose, which in
your equations is part of the algae.  Everything else going into and
coming out of your equations is something other than photosythesis; it's
nutrient uptake and anabolism.

Stoichiometry is a wonderous thing.  Using your two equations and
subtracting out photosynthesis, I get two equations that express the net
effect of nutrient uptake and anabolism:

 17 2/3 glucose  + 16NO3- + H2PO4- + 16H2O + 17H+  <==> algae + 32O2
  
 or
  
 17 2/3 glucose + 16NH4+ + H2PO4- <==> algae + 15H+

No wonder biochemists don't depend much on stoichiometry.
   
> Can anyone confirm if this is (or isn't) correct (or relevant!)?

There's a great (painfully detailed and complete) description of
photosynthesis that's been on the web for a few years.  The paper is
formally titled "The photosynthetic process" and is less formally known as
"the paper".  It's at

http://www-new.life.uiuc.edu/govindjee/paper/gov.html
 
Happy reading,

Roger Miller