Physical Principles of Life

According to J. S. Mill (1806-73), laws of life cannot be something other than laws of behavior of molecules, interacting as parts of a living organism. But, because of emergence of biological systems, it is not easy to reduce biological laws to physical ones. Such a way, called 'reductionism', does not always give practical results, but it is important as the theoretical basis for searching borders of the possible for living objects. It is not easy to predict fundamental consequences from fundamental laws; each forecast of possible effects is a discovery.

Biology is a continuation of physics and chemistry and chemistry is a continuation of physics. One can understand biology as 'new physics' and pose a problem to find its form, which corresponds to physical traditions. Particularly, physics of life is possible only under very special values of the world constants; traditional physics 'does not know' what life is, and cannot explain these values. It is necessary to use the 'anthropic principle': our existence as intellectual beings, studying the world, presupposes its features ensuring origin of man.

In biology, as well as in the other sciences, the problem of energetic balance is very essential. It gives a general estimation of the process of life functioning. As open systems, living objects need permanent energy income; they use it step by step and finally transform it to thermal energy of the environment. The main source of energy for life as a whole is the radiation of the Sun (and, insufficiently, energy of the Earth's interior: chemical, thermal, and, probably, radioactive). Plants ('phototrophs') use the solar energy for chemical synthesis of organic substances (the process of photosynthesis), supporting their own existence and providing chemical energy for all other forms of life: 'heterotrophs' (herbivores and carnivores) and 'saprotrophs'. Physically one can say that the solar energy in the course of photosynthesis raises energetic levels of electrons in some atoms of living matter; then the electrons gradually and purposefully descend, executing chemical and mechanical work.

Life directs energy flux to itself and uses it. According to the I. Prigogine theorem, an open system, in the case of linearity of the energy flux through it, produces minimum likely entropy. Life is an inconvertible process, going in a linear area of forces-flow rates; it endeavors to keep this linearity. But irreducible small nonlinearity produces stochastic noise, finally destroying each living organism.

Contrary to general physical tendency, postulated in the second thermodynamic law, life as a global process is characterized by gradual decrease of entropy. (Separate organisms also decrease its entropy during most periods of their life, but after their death the entropy 'gains revenge'.) The paradox was already pointed out by the father of statistical physics L. Boltzmann (1844-1906), and later was deeply analyzed by A.J. Lotka (1880-1949). In 1944, the Nobel Prize winner physicist E. Schrodinger (1887-1961) published his famous book What Is Life? devoted to this problem.

The general explanation why entropy can be decreased in living systems is evident; these systems are open; they use external energy to decrease their own entropy and, at the same time, increase entropy of the environment. In general, both first and second thermodynamic laws hold true. But the ways of converting the energy income to entropy reduction (or maintaining order) is not so clear. According to E. Schrodinger, organisms 'drink orderliness' from a suitable environment. He explains about flux of 'negative entropy' (negentropy) to organism, which compensates natural increasing entropy. He does not explain the process in detail, but stresses that life's tools for this aim are 'aperiodic solids' - the chromosome molecules. Schrodinger's book had an essential influence on molecular biology; particularly, it stimulated J. D. Watson and F. Crick to discover the DNA structure (1953) and explore in that way, the physical explanation of life.

It is not very clear yet what Schrodinger's negentropy is - free or stored energy, information, organization, or something else? Probably, a perspective conception is the idea about necessity for life of two coupled processes. The first (energetic) one accepts energy from environment and provides it to the second (information) process, which is responsible for the living system's development. A disproportion of entropy takes place; the second process presupposes decrease of entropy; the first one, correspondingly, increases it. Such processes are observed in inanimate nature; for example, explosion of an ultranew star transforms it into a primitive clot of neutrons, but, at the same time, heavy elements of the periodic system (prerequisites of life) are synthesized and spread in the universe. High-ordered entropy disproportion in living organisms presupposes very exact coordination of biological processes; in accordance with Schrodinger's opinion, information DNA molecules play the role of the coordination center.

Life is not contradictory to the second thermodynamic law, but uses it in a special way. Excluding from reproduction all the descendants of a couple except two of them, death of prey killed by predator, extinction of species in the course of evolution - all these events on the one hand increase entropy, but on the other hand they lead to general progress, to ordering matter in some local areas (from which, because of reproduction, the new forms spread as widely as possible).

As for inanimate nature, many scientists see in unidir-ectionality of the entropy change the basis of the time phenomenon; the tendency of entropy reduction in living systems can give a key to understanding of the general laws of living matter evolution. A. J. Lotka in the article 'Contribution to the energetics of evolution biology', published in 1922, proposed to consider energetic power of organisms as the main criterion maximized in the course of evolution. Later, he called this maximum power principle, the 'fourth thermodynamic law'. The approach is still under discussion; it was supported and developed by such prominent scientists as V. I. Vernadsky and H. T. Odum.

The law is based on the consideration of species' evolution, when in conditions of ''the struggle for existence, the advantage must go to those organisms whose energy-capturing devices are most efficient in directing available energy into channels favorable to the preservation of the species'' (A. J. Lotka). A capability of better assimilation of solar energy or energy collected by other organisms is a prior evolutional advantage.

It is quite right at the level of ecosystems, when stochastic fluctuations and individual peculiarities at the level of species are integrated and averaged out. More and more effective populations are involved into biological cycling, increasing its intensity. As a result, the ecosystem power (consumed energy per unit time) permanently grows. It is mainly the result of competition from plants (producers), which are forced to maximize production for keeping their place in the ecosystem. Another extremely important factor is the activity of animals (consumers). They withdraw producers' biomass and additionally intensify cycling. Probably, the global role of consumers in biosphere consists exactly in the spinning up of ecological cycles.

At the level of concrete species, classical power is not the only parameter determining its evolutionary perspectives. One should take into account, for example, the efficiency of the species in limitation of entropy growth. As a result, it is more reasonable to speak not about all the available energy, but about 'exergy' (entropy-free energy, see Exergy). The latter shows an ability of the organism to make the work relative to the surrounding; it is the 'co-property' of a system and a reservoir.

Another important aspect, influencing vitality of the species, is the integrated character of energetic abilities of living organisms. H. T. Odum proposed a concept of emergy (embodied energy) as ''a measure of energy used in the past'' and stored in the system's structure. The concept is being developed by S. E. J0rgensen and others. The maximum 'empower principle' is proposed by H. T. Odum as ''a unifying concept that explains why there are material cycles, autocatalytic feedbacks, succession stages, spatial concentrations in centers, and pulsing over time.'' Generalization of the approach is possible by way of taking into consideration 'population strategies' of species. For example, one can base on the r/K concept or its modification the r/ C model (in the context of which population preferences in division of its energetic recourses between the processes of growth and competition are considered).

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