The theory of open systems in physics and biology

[L. von Bertalanffy](, 'The theory of open systems in physics and biology', _Science_, vol. 111 (1950), pp. 23-9. [[on JSTOR](] Snippets of text (from the beginning, maybe the middle, and the end) appear below, to give a sense of the content for the chapter. For more depth, the original source is cited, above. ---

From the physical point of view, the characteristic state of the living organism is that of an open system. * A system is closed if no material enters or leaves it; * it is open if there is import and export and, therefore, change of the components. Living systems are open systems, maintaining themselves in exchange of materials with environment, and in continuous building up and breaking down of their components. [p. 70, editoral paragraphing added]

So far, physics and physical chemistry have been concerned almost exclusively with processes in closed reaction systems, leading to chemical equilibria. * Chemical equilibria are found also in partial systems of the living organism -- for example, the equilibrium between hemoglobin, oxyhemoglobin, and oxygen upon which oxygen transport by blood is based. * The cell and the organism as a whole, however, do not comprise a closed system, and are never in true equilibrium, but in a steady state. We need, therefore, an extension and generalization of the principles of physics and physical chemistry, complementing the usual theory of reactions and equilibria in closed systems, and dealing with open systems, their steady states, and the principles governing them. [p. 70, editoral paragraphing added]

Though it is usual to speak of the organism as a "dynamic equilibrium", only in recent years has theoretical and experimental investigation of open systems and steady states begun. The conception of the organism as an open system has been advanced by von Bertalanffy since 1932, and general kinetic principles and their biological implications have been developed .... [p. 70] [....]

In physics, the theory of open systems leads to fundamentally new principles. It is indeed the more general theory, the restriction of kinetics and thermodynamics to closed systems concerning only a rather special case. * In biology, it first of all accounts for many characteristics of living systems that have appeared to be in contradiction to the laws of physics, and have been considered hitherto as vitalistic features. * Second, the consideration of organisms as open systems yields quantitative laws of important biological phenomena. So far, the consequences of the theory have been developed especially in respect to biological problems, but the concept will be important for other fields too, such as industrial chemistry and meteorology. [p. 71, editoral paragraphing added]

## General Characteristics of Open Systems Some peculiarities of open reaction systems are obvious. * A closed system _must_, according to the second law of thermodynamics, eventually attain a time-independent equilibrium state, with maximum entropy and minimum free energy, where the ratio between its phases remains constant. * An open system _may_ attain (certain conditions presupposed) a time-independent state where the system remains constant as a whole and in its phases, though there is a continuous flow of the component materials. This is called a steady state. [1] > [1] In German, the term _Filessgleichgewicht_ was introduced by von Bertalanffy. * Chemical equilibria are based upon reversible reactions. * Steady states are irreversible as a whole, and individual reactions concerned may be irreversible as well. * A closed system in equilibrium does not need energy for its preservation, nor can energy be obtained from it. * To perform work, however, the system must be, not in equilibrium, but tending to attain it. And to go on this way, the system must maintain a steady state. * Therefore, the character of an open system is the necessary condition for the continuous working capacity of the organism. [pp. 71-72, editorial paragraphing added] [....]

The energy need for synthesis is demonstrated by numerous facts showing the coupling of anabolic and oxidative processes (6, p. 218 ff.). * On the other hand, the efficiency of the 'living machine' appears to be rather low. Since the organism works as a chemodynamic system, theoretically an efficiency of 100 per cent, i.e. complete transformation of free energy into effective work, would be possible in isothermic and reversible processes, the condition of isothermy being almost ideally realized in the living organism. * But the efficiency of the organic system in performing effective work, except in photosynthesis, does not much surpass that of man-made thermic machines. It appears that we have to take into account, in the balance of cell work, not only effective work but also conservation energy, i.e. the energy needed for the maintenance of the steady state. [pp. 75, editorial paragraphing added] [....]

## Equifinality A profound difference between most inanimate and living systems can be expressed by the concept of _equifinality_. * In most physical systems, the final state is determined by the initial conditions. Take, for instance, the motion in a planetary system where the positions at a time _t_ are determined by those of a time _t_<sub>0</sub> or a chemical equilibrium where the final concentrations depend on the initial ones. If there is a change in either the initial conditions or the process, the final state is changed. * Vital phenomena show a different behavior. Here, to a wide extent, the final state may be reached from different initial conditions and in different ways. Such behavior we call equifinal. It is well known that equifinahty has been considered the main proof of vitalism. [p. 76, editoral paragraphing added] [....]

Analysis shows that closed systems cannot behave equifinally. * This is the reason why equifinality is, in general, not found in inanimate systems. * But in open systems which are exchanging materials with the environment, in so far as they attain a steady state, the latter is independent of the initial conditions; it is equifinal. [p. 76, editoral paragraphing added] [....]

## Thermodynamics of Open Systems It has sometimes been maintained that the second law of thermodynamics does not hold in living nature. * Remember the sorting demon, invented by Maxwell, and Auerbach's doctrine of ectropy, stating that life is an organization created to avert the menacing entropy-death of the universe. * Ectropy does not exist. However, thermodynamics was concerned only with closed systems, and its extension to open systems leads to very unexpected results.[p. 77, editoral paragraphing added]

It has been emphasized by von Bertalanffy (4, 6) that, * 'according to definition, the second law of thermodynamics applies only to closed systems, it does not define the steady state'. * The extension and generalization of thermodynamical theory has been carried through by Prigogine (11, 25, 26, 30). * As Prigogine states, > 'classical thermodynamics is an admirable but fragmentary doctrine. This fragmentary character results from the fact that it is applicable only to states of equilibrium in closed systems. _It is necessary, therefore, to establish a broader theory, comprising states of non-equilibrium as well as those of equilibrium._ ' Thermodynamics of irreversible processes and open systems leads to the solution of many problems where, as in electrochemistry, osmotic pressure, thermodiffusion, Thomson and Peltier effects, etc., classical theory proved to be insufficient. We are indicating only a few, in part revolutionary, consequences. [p. 77, editoral paragraphing added]

Entropy must increase in all irreversible processes. * Therefore, the change in entropy in a closed system must always be positive. * But in an open system, and especially in a living organism, not only is there entropy production owing to irreversible processes, but the organism feeds, to use an expression of Schrodinger's, from negative entropy, importing complex organic molecules, using their energy, and rendering back the simpler end products to the environment. Thus, living systems, maintaining themselves in a steady state by the importation of materials rich in free energy, can avoid the increase of entropy which cannot be averted in closed systems. [p. 77-78, editoral paragraphing added] [....]

## Biological Applications Generally speaking, the basic fundamental physiological phenomena can be considered to be consequences of the fact that organisms are quasi-stationary open systems. * Metabolism is maintenance in a steady state. * Irritability and autonomous activities are smaller waves of processes superimposed on the continuous flux of the system, irritability consisting in reversible disturbances, after which the system comes back to its steady state, and autonomous activities in periodic fluctuations. * Finally, growth, development, senescence, and death represent the approach to, and slow changes of, the steady state. The theories of many physiological phenomena are, therefore, special cases of the general theory of open systems, and, conversely, this conception is an important step in the development of biology as an exact science. Only a few examples can be briefly mentioned. [p. 77-78, editoral paragraphing added]

Rashevsky's theoretical cell model (27), representing a metabolizing drop into which substances flow from outside and undergo chemical reactions, from which the reaction products flow out, is a simple case of an open system. * From this highly simplified abstract model, consequences can be derived which correspond to essential characteristics of the living cell, such as growth and periodic division, the impossibility of a 'spontaneous generation', an order of magnitude similar to average cell size, and the possibility of nonspherical shapes. [p. 80, editoral paragraphing added] [....]

To apply the conception of open systems quantitatively to phenomena in the organism-as-a- whole, we have to use a sort of generalized kinetics. * Since it is impossible to take into account the inextricable and largely unknown processes of intermediary metabolism, we use balance values for their statistical result. This procedure is in no way unusual. * Already in chemistry, gross formulas -- for example, those for photosynthesis or oxidation -- indicate the net result of long chains of many partly unknown reaction steps. * The same procedure is applied on a higher level in physiology when total metabolism is measured by oxygen consumption and carbon dioxide and calorie production, and bulk expressions, like Rubner's surface rule, are formulated; or when in clinical routine the diagnosis of, say, hyperthyroidism is based upon determination of basal metabolism. * A similar procedure leads to exact theories of important biological phenomena. [p. 82, editoral paragraphing added]

Thus, a quantitative theory of growth has been developed. * Growth is considered to be the result of the counteraction of anabolism and catabolism of the building materials. * By quantitative expressions, using the physiological values of anabolism and catabolism and their size dependence, an explanation of growth in its general course, as well as in its details, and quantitative growth laws have been established. This theory is almost unique in physiology, for it permits precise quantitative predictions which have been verified, often in a very surprising way, by later experiments. [p. 82, editoral paragraphing added] [....]

Also the theory of feedback mechanisms (36), much discussed in the last few years, is related to the theory of open systems. Feedbacks, in man-made machines as well as in organisms, are based upon structural arrangements. Such mechanisms are present in the adult organism, and are responsible for homeostasis. However, the primary regulability, as manifested, for example, in embryonic regulations, and also in the nervous system after injuries, etc., is based upon direct dynamic interactions (9, 10). [p. 83] [....]

The formal correspondence of general principles, irrespective of the kind of relations or forces between the components, leads to the conception of a 'General System Theory' as a new scientific doctrine, concerned with the principles which apply to systems in general. Thus, the theory of open systems opens a new field in physics, and this development is even more remarkable because thermodynamics seemed to be a consummate doctrine within classical physics. In biology, the nature of the open system is at the basis of fundamental life phenomena, and this conception seems to point the direction and pave the way for biology to become an exact science. [p. 84]