Why Do Living Systems Have Such a High Level of Eco Exergy

A frog of 20 g will have an eco-exergy content of 20 x 18.7 x 688 kJ « 257 MJ, while a dead frog will have only an exergy content of 374 kJ, although they have the same chemical composition, at least a few seconds after the frog has died. The difference is rooted in the information or rather the difference in the useful information. The dead frog has the information a few seconds after its death (the amino acid composition of the proteins has not yet been decomposed), but the difference between a live frog and a dead one is the ability to utilize the enormous information stored in the genes and the proteomes of the frog.

The amount of information stored in a frog is really surprisingly high. The number of amino acids placed in the right sequence is about 200 000 000 and for each of these 200 000 000 amino acids there are 20 possibilities. This information is again repeated in billions of cells that are cooperating to make up the frog. This enormous amount of information is able to allow reproduction and is transferred from generation to generation which implies that the evolution can continue because what is already a favorable combination of properties is conserved through the genes.

The information in living organisms applies 'nano-technology' in the sense that the weight of 200 000 000 amino acids is for an average amino acid molecular weight of 125 g moles-1 2.5 x 1010g/A = 4 x 10~14g, where A is Avogadro's number (A = 6.2 x 1023). A book with the same amount of information would weigh several hundreds of kilograms.

Because of the very high number of amino acids, about 200 000 000, it is not surprising that there will always be a minor difference from frog to frog in the amino acid sequence. It may be a result of mutations or of a minor mistake in the copying process. These variations are important because they give possibilities to 'test' which amino acid sequence gives the best result with respect to survival and growth. The best - representing the most favorable combination of properties - will offer the highest probability of survival and give the most growth and the corresponding genes will therefore prevail. Survival and growth mean more exergy, resulting in a bigger distance from thermodynamic equilibrium. Exergy could therefore be used as a thermodynamic function which could be used to quantify Darwin's theory. In this context, it is interesting that it has been demonstrated that eco-exergy also represents the amount of energy needed to tear down the system. It means that the more exergy the system possesses the more difficult it becomes to degrade the system and the higher is therefore the probability of survival. Consequently, eco-exergy can be applied as a measure of sustainability. The crucial question is therefore: do we hand over the Earth to our children and grandchildren with the same distance from the thermo-dynamic equilibrium, that is, the same exergy, as we received it from our ancestors?

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