The regenerative cycle

keeping material for exergy consumption


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To be efficient in the utilization of available exergy, you need material in order to maintain the process.
The most efficient way to secure this is to re-use the basic material that is not destroyed in the process -- recycling!

In biological systems a very general method is used for this process. It is called the regenerative cycle. I will give some examples of this type of cycling in nature.

Living systems are functionally ordered in holarchies. a 'hierarchy' of holons. The basic holons are the following:

 Cell (eucaryote)

Organism

Ecosystem

Ecosphere (Gaia)

The diffrent holarchic (holonic) levels follow the same general principles of life.

All living (=self-organizing, far from equilibrium) systems thrive by consuming exergy. They take energy with high exergy content (solar radiation, food etc.) use the exergy in their self-organizing processes and expel energy with low exergy content. This is the basic principle for all self-organizing systems.

A very efficient consumption of exergy is accomplished when exergy is used to put together simple compounds into complicated ones.
If the compounds produced are subsequently taken apart and the resulting available exergy is used in another process, the exergy consumption is nearly maximal.

But if there is a lack of material for the initial process, the exergy consumption will be hampered. A cyclic process, returning the basic material for new exergy consumption would therefore be more in line with the Second Law of Thermodynamics than a process that 'loses' its material.

Thus, evolution towards cyclic processes would be expected.

A well-known example of this is the Krebs, or Citric acid, cycle

The 'exergy source' of this process is the Acetyl Coenzyme A. This is combined with the end product of the cyclic reaction to provide the initial compound in the new reaction round. This compound is successively utilized in a series of reactions, until a new end product is produced.

Also, the normal respiration of a vertebrate body can be described in the same way.

Here, the blood system is the conductive substance. Blood is 'loaded' with exergy in the liver and the lungs (sugar from the liver and oxygen from the lungs to facilitate the process). The exergy rich blood is transported by the arteries to the capillary web in the body. Here, the exergy is consumed and the low-exergy blood is transported back through the veins together with the waste products from the process (low exergy, CO2 and water).

Subsequently, the waste is released from the blood, and it is reloaded with high-exergy products again.

In an ecosystem, the regenerative cycle is easiest to understand if the phosphorus cycle is followed.

Simple compounds, such as phosphates, CO2 and nitrogen compounds, are taken up by the plants leaves or roots, paid for with sugar from the plants. The compounds are put together using photosynthesis, with sunlight as exergy source. Most of the production is used up by the plants and micro-organisms by themselves, but the remaining substances are used by heterotrophic organisms (insects, squirrels, humans and the like).

The end products (faeces, urine, dead plants and animals) are utilized by the recyclers (a term that better describes ther function than the earlier used 'destruent'), such as bacteria and fungi and given back to the plant roots in return for sugar (with high exergy content, there is a lack of such things down under).

During the development (maturation) of the ecosystem, the efficiency of the regenerative cycle increases, and therefore also its exergy consumption capacity.

Naturally, this principle is also applicable to the entire ecosphere, or Gaia system. In this case, nutrients are not the only part of the regenerative cycle, but also other biologically active substances, like water and CO2. Even entire living systems, wheather systems and sea currents. (E.g., the salmon could in this connection be regarded as a phosphorus pump from sea to high altitudes)

Actually, the living Earth system is driven by the difference in exergy content of the sunlight and the Outgoing Longwave Radiation with much lower exergy content returning to space.

Also it is possible to organize societal systems according to the principles of the regenerative cycle if a balanced agriculture is connected to a community that recycles nutrients to the land which grows its food.

Of necessity, this was done in pre-industrial time. Today, it is normally not done.
A change toward ruralisation would improve ecological adaptation as well as decreasing the vulnerability to energy depletion.

 

On exergy consumption by living systems

An article by Günther and Folke

Back to phosphorus



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Updated:
2013-01-06