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Green People

Ingrid Jakobsen ingrid at helios.anu.edu.au
Wed Jan 18 00:11:56 EST 1995

In article <bsheaff-1701951859460001 at lwbyppp6.epix.net>, bsheaff at epix.net (Braxton) writes:
> How about another possibility-that photosynthesis really stinks as far as
> making energy. If you are going to become an animal and 'specialize in
> transportation' photosynthesis of your own produces so little energy that
> abandoning it is of little or no consequence?
> I don't know the answer, that's why I posed the question.

I'm not actually a "plant" person, so I could on the wrong track here,
but if you look at a generic "plant cell" and "animal cell" there are 
two differences that stand out:

the plant cell has chloroplasts
the plant cell has a rigid cell wall.

Now if I remember correctly, the cell wall is neccessary because the plant
manipulates water concentration inside the cell. An animal cell that 
attempted to change its water concentration would just shrink or expand 
accordingly. I also seem to remember that it was neccessary for 
photosynthesis to occur.
(does anyone know of a multicellular photosynthetic organism without 
cell walls?)

Anyway, I think the cell wall prevents the development of mobility beyond
the kind of small light movements, that for example Venus fly traps are
capable of. Muscle cells need to be able to change size.

Another possibility is the fact that plant cells have connections between
them, allowing water and small ions to move freely between cells. That 
would be a direct clash with the general requirements for neurons each
maintaining and constantly changing their ion concentrations.

I don't think a mobile plant (or a photosynthetic animal, you decide)
is totally impossible, just that it would either photosynthesise or move
around according to completely different principles than are currently
used. In other words, plants and animals have each made certain sacrifices
in order to pursue their strategy.


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