Someone who knows this stuff better than I do, please clue me in. Does the water in the human body serve a purpose other than a fluid transport medium for dissolved solids and small colloids?
If not, could you have complex life on a planet like Titan where there is abundant liquid... just not water? What would the consequences of a -180°C temperature be on the properties of various candidate cellular structural materials?
A Titanian analog to a terrestrial cell might have liquid ethane inside for transport and... would probably not be a big fan of free oxygen. Non-oxygen reactions dominate? Who knows. Dad: this is your cue to tell me that my understanding of chemistry and materials science is pathetic.
There are a lot of problems building a life form around a solvent non=polar enough to be liquid at temperatures below 150K. The rates of reactions would be very slow. The level of interaction between molecules differs vastly, solubilities would be decreased for most things. If such a form existed it would have to be completely different, in many ways opposite from a water based system. There is also the problem of freeze/thaw relationships. Life is possible on Earth at least in part because of the fact that water expands on freezing. If water contracted on freezing, as most things do, the oceans would freeze solid and stay that way. All that said, I am not willing to rule out completely the possibility of life existing in a medium such as liquid hydrocarbon. You would need membranes that were reversed from what we have, polar on the inside and non-polar surfaces. You would also have macromolecules in which the polar components were interior. I think you would have to find some way to deal with a very slow rate of metabolic function, and temperature control would have to be very good because most things have a much narrower liquid range than water.
I'm assuming your comment about the oceans has to do with the bouyancy of ice vs. water, right? So surface water would freeze on account of the cold air temperature, then sink, freeing additional water for surface freezing, right? I could see this leading to a vastly increased ice shelf, but at some latitude the surface air would be warm enough to melt the surface ice, no? Also the continuous surface freezing would cause a lot of heat flow into the air leading to some bizzare climate conditions...
The lipids that currently handle cellular boundary transport could simply be reversed to keep their apolar ends on the outside, right?
I think the large amount of submerged ice would gradually drag the whole water body down to below freezing. It would act like a huge negative calorie sink. You also would not get the inversion that now stirs up the water and releases nutrients.
As for the membranes, I suppose you could get some sort of reversal except that you would have to have negative and positive lipids so that all the charges wouldn't repel each other in the middle. Still, I suppose that the membrane could work. There are phospholipids with both + and - charges.
There are also some interesting questions about how the metabolism would function. To be stable in a hydrocarbon medium, life would have to be based on a reducing rather than an oxidizing catabolism. Of course, the general opinion is that life on earth probbly started that way and only evolved to the oxidizing system as the hydrogen in the atmosphere excaped into space. There are still a few organisms that seem to exist on a reducing process. These mostly live in the deep sea thermal vents.