living systems and 2nd law of thermo??????

simon sbe at biochem.usyd.edu.au
Tue Sep 26 02:09:42 EST 1995


rray at ix.netcom.com (ROMAN RAY ) wrote:
>  Living sytems have order.  Why does this not violate the second law
>of thermodynamics?????

Because they are *open* systems (ie they can exchange both matter 
(nutrients, excreta) and heat with their surroundings). Any increase in 
the *order* (or decrease in entropy) of a living system is more than 
balanced by a decrease in order (or increase in entropy) of its 
surroundings. The second law of thermodynamics only applies to 
*isolated* systems (those which can nor exchange matter and heat with 
their surroundings. Thus, if you you consider a living system *and* its 
surroundings as an isolated system, then deltaS for this will be 
positive for any spontaneous change.  

Simon





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