"Malcolm"  wrote in message
news:c8mdpf$2550$1{at}darwin.ediacara.org...
>  wrote in message
> >
> > It is well known that an organism has requirements for health.
> > But my topic is: How did these requirements come to be?
> >
> Every organism needs a source of energy, and access to the basic
> constitutents of biochemicals (carbon, oxygen, hydrogen, and then
nitrogen,
> phosphorous and sulphur, and then minor constituents like potassium,
> calcium, zinc, and then traces of a lot more elements).
>
> Plants are autotrophs, and pretty much synthesise everything for
themselves.
> The only significant thing they can't do is to fix atmospheric nitrogen -
> they have to get it from the soil in the form of salts.

My Vegan friends also tell me that typical plants can't make their own
vitamin B12 and, as with nitrogen, are dependent on symbionts for this.

On a semi-related note, I wonder if anyone has argued that these sorts of
differences and dependencies are why most animals are motile and most plants
are not?  Hello all you budding genetic engineers -- if I could fix my own
carbon, I'd never leave the house!
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