On Fri, May 02, 2014 at 08:44:37AM +0200, Knapp wrote:
> As stated the speed of reactions is important I I would guess that
> changing the solvent would change that speed but NOT uniformly
> resulting in messed up systems.

The main problem is that different reactions change in their rates
and/or equilibrium values in different ways, and biology involves huge
numbers of different, important, and interdependent reactions.  Mess
with any of them and you get widespread problems.

In humans a +/-2% internal temperature change is a life-threatening
emergency.  That's not fundamental to carbon/water based life, though.
Some organisms can multiply with cellular temperatures up to 390 K (at
higher pressure), and others down to 250 K.  In dormant form, or for
relatively short periods, the temperature ranges can be even wider.

Those wide temperature ranges come at quite a large biological cost:
such organisms generally only survive only because they occupy very
restricted niches.  If required to compete with other organisms in
more ordinary conditions they don't thrive so well.

I would expect all poikilothermic life forms - regardless of
biochemical solvent - to have tradeoffs against more homeothermic
organisms.  It won't be a simple matter of "this solvent stays liquid
in a wider range, therefore all life forms based on it will function
equally well at all temperatures".  That's far too simplistic and
ignores competition with other organisms based on the same solvent.

- Tim