[extropy-chat] Singularity heat waste

[Robert Bradbury]

On 7/17/06, BillK <pharos at gmail.com> wrote:
>
> Thus, if the cell grows beyond a certain limit, not enough material
> will be able to cross the membrane fast enough to accommodate the
> increased cellular volume. When this happens, the cell must divide
> into smaller cells with favorable surface area/volume ratios, or cease
> to function.
>
> That is why cells are so small.
>

I'm not buying it.  This was pointed out to me by Prof. Skulachev at MSU who
is an expert on mitochondrial bioenergetics.  There are multiple cell layers
between the capillaries where O2 is released and CO2 absorbed.  The gases
have to diffuse across multiple cell layers to enter or exit from the cells
most distant from the capillaries (I think he cited at least 3 cell layers
as being typical).  So there is going to be a concentration gradient of the
gases and the complication of largely flat cells vs. cubic cells. vs.
spherical cells.  If the cells had wanted they could have evolved ways of
storing resources (e.g. glycogen or gas vacuoles) that would mitigate the
surface area problem.  In cells with large volumes one has active transport
systems to take up materials and expel wastes.  Genome sizes range *all*
over the place so it isn't a requirement for a certain amount of DNA.

So I tend to lean in the direction that nature has developed solutions to
many of these problems in specific situations but hasn't been clever enough
to structure them into optimal organisms.

Robert
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