Do living organisms defy the second law of thermodynamics?
No. No known phenomena violates the second law of thermodynamics.
The second law of thermodynamics postulates that the entropy of a closed system will always increase with time (and never be a negative value).
The only known closed system that exists is the entire universe and thus the law applies to the universe as a whole. The notion centres around the idea that when energy is transferred from one form to another, entropy increases as a result.
Human organisms are not a closed system and thus the energy input and output of an the organism is not relevant to the second law of thermodynamics directly.
No The Second Law of thermodynamics applies in the truest sense to closed systems. Living systems can not be closed systems or they are not living.
The second law says that everything goes from order to disorder, that is an increase in entropy. Living things die when the disorder in the system of the living organisms increases to the point where the system can no longer function.
A living organism contains information in the DNA that allows the system to obtain energy from outside the system. This makes a living organism an open system. The energy from outside the system is used to overcome entropy, the spontaneous breakdown of organization within the cells and systems within the living organism.
Shannon's Laws of information show that information transfer is subject to the second law of thermodynamics. That is information is lost whenever information is transferred. Over time the information in the cell's and organism's DNA is damaged and lost. When the information is damaged to the point that the organism can not longer overcome the forces of entropy the organism dies.
All closed systems are subject to the second law of thermodynamics that everything goes from order to disorder. While living things have the informational capability to maintain an open system the living things are not subject to law of entropy.