The Biophysical Modeling of the Living System

Main characteristics of living organisms are motion, excitability, reproduction, adaptation, inheritance, changeability, growth, and development. Living matter is a complex highly-structured system which can sustain the complex structure only by means of continuous work – through metabolism work done to prevent the increase in entropy. The two basic functions that make survival of the living matter are the energy-releasing processes and biosynthesis: metabolism. The functioning of the living systems without exception is based on the use of chemical energy, hence they must have chemical “motors” capable of a continuous use of energy through some chains of autocatalytic cyclic reactions.


Introduction
Of the 92 elements from Mendeleev's periodical table, over 60 of them have been found in living organisms. In terrestrial organisms: oxygen forms 70 % of their mass, carbon -18 %, hydrogen 10 %, calcium, nitrogen, potassium, and silicon a few tenths of percentage, phosphorus, magnesium, sulphur, chlorine, sodium, aluminium, iron a few hundredths of percentage.

Excitability
The concept of excitation was introduced in medicine by J. Brown in his book "Elementa medicinae" (1778), as a fundamental property of living matter. The modern biophysics concept constitutes a synthesis of molecular biology data and contemporary electrobiophysics. The excitation is in this concept a primary functional manifestation inside the cellular membrane. Secondary, there are cytoplasm processes taking place: contraction, secretion.
Due to this unequal repartition of ions, the cellular membrane is "polarized", with a potential difference of 70-80 mV for the nerve and muscular cell.
Generally, the excitation is correlated with a local modification of the membrane potential; but if the depolarization is intense, it "propagates" and the electric features of the membrane of the entire cell change. The action current appears with a quite complex aspect.
Through recordings of the action potentials -EKG, EEG, EMG, ERG in various conditions: today one can investigate successfully in the experimental research the excitation processes in the main living structures. The data supplied through these biophysical methods are used in the medical diagnostic.

Adaptation
The organisms must adapt their function and structures to the

Metabolism -Fundamental Criteria
The most important characteristic of living matter is represented by the exchange of substances between organism and the environment.

Modelling of the Living Structure
The functioning of the living systems without exception is based on the use of chemical energy, hence they must have chemical "motors" The concentration flows can be calculated from the following minimal system (n = 5) of differential equations: Next, we will show that the cycle of this regenerative autocatalytic reaction characterized by this system of differential equations In the case of the living organism the functioning of the system is assured by the chemical "engine" of the metabolism, whose premise is that the amount of the energetic content (free enthalpy) of the nutritive substances must be greater that the sum of the energetic content of the products. Some products resulted can have a higher energetic content that any of the exogene substances consumed, if compensated by the decreased energetic content of the other products.  ................................

Rn + An → 2R1 + Wn
This synthesis is possible during the cycle because there was no constraint for Wi. If the cycle repeats the second time, then it starts from 2R1 it auto reproduces again, doubling, reaching fourth times the initial value. It means that after k retakes the system will increase by doubling: where: pnumber of cells from the population; p0initial number of cells; ndivision number [9].
In tight connection with the growth process, we question how the ratio between surface and volume varies, with the growth of the cell (let us assume that it is a sphere of ray r). The ratio between the surface (S) and volume (V) is: If the ray grows to double, then the S/V volume drops to half. It seems to be an acceptable quantitative argument in favour of the conception when the surface cannot maintain cells, this moment the cell divides, the new cells increase at their turn, then they divide, and so on.
According to the biostructure model, the surface of the membrane (St) in the t moment is: where: τperiod of auto reproduction; S0initial surface.
Assuming that the cell is spherical, then from the growth of the surface it results that the volume variation in the t moment will be: where: r0is the initial ray from the moment t0. Thus, to the double cellular volume does not correspond a double surface, but a smaller one, since the volume varies proportionally with the cube of the ray and the surface only with the square of the ray [10]. The reproduction is the capacity of living systems to generate descendants like them. It ensures the perpetuation of the species dispite the individual life and at the same time it is the link between the following generations.

Epilogue
Biology is nowadays chiefly an experimental and descriptive science.