Assertions re plant "cellularity"

Tony Travis ajt at uk.ac.sari.rri
Wed Jul 8 06:29:11 EST 1992


In article <Wed.8Jul92.0204.bionet-news at uk.ac.daresbury> you write:
: In article <1992Jul7.165609.2115 at gserv1.dl.ac.uk>, ajt at uk.ac.sari.rri (Tony Travis) writes:
: > In article <Mon.6Jul92.2232.bionet-news at uk.ac.daresbury> you write:
: > : 
: > : [...]
: > : What are the fundamental characters common to all things we
: > : categorize as plants, whether unicellular or multicellular?
: > 
: > A plant is an organism that has the ability to use sunlight to feed on
: > C02 from the air using water and minerals from the soil.
: 
: Someone else has already pointed out this excludes rare 
: saprophytic/parasitic forms, but it also _includes_ a large group of 
: prokaryotes.  I've never objected to the term 'blue green _algae_', as 
: these organisms do very similar things to eukaryotic algae, but now you've 
: got the plant kingdom stradling the divide between eu- and prokaryotes.
: 
: I think I'll stick with a definition I heard a while ago -
: 
: "If it's green, it's a plant" :-)

Read Una's question carefully - she did not say what are higher plants.

It has been suggested that chloroplasts originate from ancient
endosymbionts and retain some degree of genetic autonomy.  My 
definition was intended to include *any* organism capable of 'feeding'
itself by fixing CO2 photosynthetically.

I accept that saprophytic/parasitic plants do this indirectly but are
they _incapable_ of photosynthesis, or do they not just invest more
resources in reproduction than they are capable of acquiring
independently and supplement their energy balance from elsewhere ??

My definition might also be:

A plant is an organism that has the ability to decrease its own entropy
by storing the energy from sunlight as carbohydrate.

Ultimately, the ability of all organisms to organise themselves against
the thermodynamically favourable slide into chaos depends on the
capture of energy by photosynthetic organisms.  This, in turn, depends
on the entropy of the rest of the universe increasing.  In particular,
the entropy of the Sun increases as a consequence of the nuclear
reactions that yield (amongs other things) the energy of sunlight.

The decrease in entropy of cyber-space also depends on plants ;-)

	Tony

--
Dr. A.J.Travis,                       |  Tony Travis
Rowett Research Institute,            |  JANET: <ajt at uk.ac.sari.rri>
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