How is the 2nd Law of Thermodynamic related to Biology?

Question

anonymous · Answer

The entropy of a closed system is constantly increasing or staying the same. Or, put another way, you can't do useful work without a supply of free energy. 

So think about this: What happens to biological systems when you take their energy supply (food, sunlight, whatever) away? In not very much time, they stop doing anything interesting. 

In any cell and in any organism, there are constantly all sorts of chemical processes going on. Some of these are spontaneous and don't require any energy input, but a lot of them (including a great many that are essential to the thing's continued survival) need constant inputs of energy-rich molecules to operate. 

Now, parts of the organism can become more complex as time passes. This is okay, since on the whole the entropy of the total system (organism + environment, including all energy sources) is increasing. This is no more mysterious than is the fact that water forms molecularly ordered crystals when you put it in a freezer. Unplug the freezer, and after a while it loses it ability to do that! 

That's the basic idea. The rest is details.

paki · Answer

The second law of thermodynamics states that the degree of disorder is always increasing in the universe. The amount of disorder in a system can be quantified, and this measurement is called entropy.