Re: What is negative entropy of photosynthesis?

Entropy is a concept which can be confusing.  In short, entropy is 
disorder.  A chemical reaction which proceeds with a positive entropy 
change is one which produces a more disordered system than before the 
reaction occurred.  Negative entropy refers to reactions which produce less 
disorder; or, in other words, take disordered reactants and convert them 
into a more ordered product.  

Here are a couple of simple examples to make this idea clearer.  A brick 
wall has a high degree of order; the bricks are arranged in a specific 
pattern.  If the wall falls down, the individual bricks are now randomly 
scattered on the ground.  Clearly we have gone from a more ordered system 
to a less ordered one.  This is an example of a positive entropy change – 
we have more disorder than when we started,  Here is a chemical example.  
When a fuel like gasoline burns, the large hydrocarbon molecules are 
converted into many small molecules of carbon dioxide and water.  There is 
more order in the reactant; all of the carbon and hydrogen atoms are bonded 
into large molecules and the atoms are pretty restricted in their 
positions.  In the products, we now have a number of small molecules which 
are independent of one another, each with their own rotations, vibrations, 
and motions through space.  Thus we have gone to a system having more 
disorder.  

The term photosynthesis describes the light-dependent conversion of carbon 
dioxide into carbohydrate carried out by organisms which posses 
chlorophyll.  In this process multiple molecules of carbon dioxide are 
combined into single molecules of sugars, which are in turn connected to 
form larger molecules of carbohydrates.  Since this process involves taking 
several units and combining them into one, it proceeds with a loss of 
disorder or, in other words, negative entropy.