Metabolism and the Laws of Thermodynamics

The Three Laws of Thermodynamics and how they apply to metabolism are described below:

1. The Conservation of Energy. The amount of energy in the universe is constant. Energy cannot be created or destroyed but may be converted from one form to another. 

The First Law applies to metabolism in the sense that energy is not free. For example, if the body needs to do a certain amount of work - let's say 5 kJ - the body needs to consume 5 kJ of chemical energy in the form of food to do the 5 kJ of work required. Any energy that is released by an exergonic reaction is absorbed by the surroundings. Conversely, any energy that is stored by an endergonic reaction causes a commensurate decrease in energy of the surroundings.

2. The Law of Entropy. The entropy in an isolated system increases with any changes that occur. All spontaneous events act to increase total entropy.

Entropy is a measure of the randomness or disorder in a collection of objects or energy. Everything in the universe favours an increase in entropy. Therefore, reactions that produce an increase in entropy are favoured over reactions that produce a decrease in entropy, and the metabolic processes in living things are no exception. Living organisms obey the Second Law of Thermodynamics. When they use anabolic processes to make complex ordered structures like proteins and DNA, they are creating order out of chaos. However, these processes must be accompanied by an even greater disorder caused by energy-yielding catabolic processes. For example, a child lifting a potato chip to his mouth results in an increase in gravitational potential energy and a decrease in entropy. The child obtains the necessary free energy for this action through the entropy-producing catabolic reactions of digestion and cellular respiration. In the end, the entropy produced by the metabolic processes is greater than the decrease in entropy produced by moving the potato chip to the mouth, resulting in a net increase in the entropy of the universe. In conclusion, "living organisms create order out of chaos in a local area of the universe at the expense of creating a greater amount of disorder in the universe as a whole."

3. Absolute Zero. Absolute zero is the temperature (-273°C) at which all thermal kinetic energy ceases. Nothing can be colder than absolute zero. 

Metabolism is unable to proceed at extremely low temperatures close to absolute zero because of the fact that all molecular motion ceases, making chemical reaction unable to occur. Also, enzymes are unable to function at extremely high and extremely low temperatures.