What is life? It is difficult to give an exact definition of life, but everyone can accurately distinguish where the living and the inanimate are. That is to say, a different price is given for a live and a dead horse.
In fact, intuitively we understand what is alive and what is dead, but as a rule we find it difficult to accurately formulate the difference. There are many known attempts to give a definition, a definition of the concept of "life", but they all turn out to be imperfect. Therefore, an intelligent person generally refuses to define, replacing it with a tautology. Living is living, that in which there is life, that is arranged as living.
For example, life is what makes us related to small bacteria, plants and giant whales. Life is a constant and unpredictable movement. Life is something that can be born and die….
All living organisms are made up of molecules. Moreover, each of the molecules is not alive by itself. So, the water molecule that is inside the muscle cell is the same as the water molecule in a glass of tea. But, coming together, molecules of a wide variety of substances can form, for example, a muscle cell, which has the ability to contract and respond to changes in the environment, in a word, to live.
We call a miracle what we cannot explain. Therefore, the seemingly imperceptible transition from non-living molecules to a living organism is often called the miracle of life. On the other hand, perhaps we ourselves mystify what we see, but everything is much simpler …
"Life is a way of existence of protein bodies, the essential moment of which is a constant exchange of substances with the external nature surrounding them, and with the termination of this metabolism, life also stops, which leads to the decomposition of protein." This definition was given by Friedrich Engels - and relatively recently it was very popular with us. Well, not such a bad definition. But is it enough?
Engels himself did not think so. For him, metabolism is only an essential, but not the only criterion of life. It can also be inherent in an inanimate object. Suppose we have two opaque boxes that have holes "at the entrance" and "at the exit". What is inside - we do not know. However, we can measure the state of the air at the inlet and outlet. Measurements have shown that in both cases we have an oxygen deficiency, an increased concentration of carbon dioxide and water vapor.
We measure the temperature and see that the air at the outlet is warmer than at the inlet. We have the right to conclude that each box contains a system capable of exchanging substances with the environment. We open the boxes and what we see … in one of them there is a live mouse, and in the other - a burning candle. The criterion of metabolism does not work here, it does not make it possible to distinguish living from non-living, to distinguish the process of combustion from the process of respiration.
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If we cut off the air supply, the mouse dies. But even a dead organism can exchange substances with the environment. This, in particular, is the basis for the formation of fossils: the remains of animals and plants in the rock layer give the environment organic matter, and minerals take its place. In particular, petrified trees are amazing: outwardly they preserve the structure of wood to the smallest detail, but it was replaced by silica and iron oxides millions of years ago.
What conclusion can be drawn here? Metabolism is a necessary condition if we are talking about a living state. However, metabolism alone is not enough to define life! Something else is needed.
Let's try again. First, life is active. Life works. Even if it is “in passive”, adapts to the conditions (that is, “suffers”: “suffering” in Aristotle is a category of submission, a category opposite to action: actio - passio), the active component is still preserved, an independent act, as it were, “from myself and for myself. Such activity necessarily occurs with the expenditure of energy in the system: in order to live, energy is spent! Secondly, life is the maintenance and reproduction of an always concrete order, a definite, specific structure. Specifically specific. This is what energy is spent and energy is spent on!
What is active playback? This is a process when the system reproduces itself and maintains its integrity, using elements of the environment with a lower order. A passive process of this kind is by no means a sign of life. The bird reproduces its nests every year, the beaver builds a dam, but neither the nest nor the dam can be considered as living objects, unlike their builders. In general, it is unlikely that a bird can be obtained, reproduced by a nest, a beaver - by a dam, and a Bigfoot - by his trail …
Further on the expenditure of energy. For what reason is this a necessary condition in defining life? Because it makes it possible to distinguish living beings from other self-reproducing structures, for example, a crystal.
As early as the 18th century, analogies were drawn between the growth of organisms and the growth of crystals. In fact, each crystal has its own specific structure, which arises spontaneously. Sodium chloride crystallizes in the form of a cube, carbon (diamond) - in the form of an octahedron. Clusters, intergrowths of crystals are sometimes surprisingly similar to the structures of living nature. Let us recall the frosty patterns on the window panes. They sometimes resemble the leaves of ferns and other strange plants to such an extent that they seem more real than the real ones. Even metals form such structures. Metallurgists all over the world are well aware of the so-called Chernov tree. During the casting of metal products, gaps, shells, as experts call them, can form. And sometimes iron crystals grow together in such shells - this is very similar to a well-known plant.
And yet, the analogies between frosty patterns and fern leaves are misleading. Although these structures are outwardly similar, the processes of their formation are diametrically opposite energetically. A crystal is a system with a minimum of free energy. What does it mean? This means that during crystallization, energy is released in the form of heat. For example, when one kilogram of "frosty patterns" occurs, 619 kcal of heat should be released.
The same amount of energy must be spent on the destruction of this structure. Fern leaves, on the other hand, absorb the energy of the sun's rays when they arise and grow. By destroying this structure, we can get energy back. We, in fact, do this, for example, by burning coal, which was formed from the remains of giant ferns of the Paleozoic era, or simply basking around an ordinary fire. And the point here is not in the leaf-like pattern itself, which outwardly unites the forest fern and the pattern on the glass.
A shapeless ice floe of the same mass will require the same amount of energy to melt and evaporate. And for the formation of the external complexity of a plant leaf, energy is expended, negligible in comparison with that which is conserved in organic matter.
But what about external resemblance? The point is this. Both fern leaves and frosty patterns have the maximum surface area for a given volume. For a fern (and any other plant) this is necessary, because respiration and assimilation of carbon dioxide goes through the surface of the leaves. In cases where it is necessary to reduce the consumption of water for evaporation, plants, such as cacti, take on a spherical shape with a minimum surface area. But this has to be paid for by a decrease in the rate of CO2 assimilation and, as a consequence, a slowdown in growth.
Water vapor, crystallizing on cold glass, also forms a structure with a maximum surface, because the rate of free energy loss is maximum in this case (crystals grow from the surface). So the analogies between crystals and living organisms have no essential meaning, so to speak. The liquid, which is thrown out of the vessel under zero gravity, takes the shape of a ball (minimum surface tension energy). But this can hardly mean that the laws of the cosmos are similar to the rules of the game with balls at the pool table!
In fairness, it should be noted that crystalline forms are not alien to life. Many people know large and completely harmless centipede mosquitoes with long fragile limbs. Their larvae live in moist soil, feeding on decaying plant debris. Among them there are individuals painted in blue with an iridescent tint. They seem lethargic, and they are actually sick - infected with the so-called rainbow virus. In the hemolymph of such larvae under a microscope, crystals of amazing beauty can be found, iridescent like sapphires.
These crystals are composed of virus particles - virions. When the larva dies, they will enter the soil to be swallowed by the larvae of a new generation of mosquitoes. By the way, such crystals are formed by many viruses, and not only insect viruses. But it is essential that this is precisely the inactive form of the existence of the virus, in contrast to the active, living one. In the form of a crystal, the virus does not multiply, but only goes through its "hard times" in this way. The famous physicist Erwin Schrödinger called the chromosome "aperiodic crystal." In fact, the nuclear substance of the cell during the period of division is ordered, and formally it can be called a crystal. But when a nuclear substance (chromatin) is “packed” into a chromosome, it is, again, inactive, and the chromosome itself is only a way of transferring chromatin from cell to cell.
So, no external energy is needed for crystallization. But to maintain and reproduce its own order of life in the next generation, the body needs to absorb energy (in the form of light quanta or unoxidized organic compounds, simple substances, and release oxidized waste products, etc.). This is metabolism.
However, why, what is this exchange for? “Everything flows,” said Heraclitus of Ephesus. If this is the case, then most of all the living organism "flows". He is a stream along which energy and substances continuously move - elements for the reconstruction of structures. Throughout life, there is a continuous replacement of old cellular structures with newly formed ones. So, blood cells are completely replaced after 4 months. Ultimately, this is also repair work, but the body replaces not only cells that have received defects, but everything.
They say that nerve cells are not restored. This means that the body does not generate new nerve cells, they do not multiply - there is as much as there was. Yes, absolutely new cells are not formed. But throughout their lives, they are constantly being rebuilt. It's like a deep overhaul and redevelopment of a house. The house is old, but renovated and in excellent condition! We can only formally consider the neurons with which we end our life, the same cells with which we started it.
And one more expression: specific structure. What it is? From generation to generation, organisms reproduce the ordering characteristic of the species to which they belong. This is done with almost perfect precision (the word "almost" is extremely important). Here the wolf ate a hare. Does he need the organs of a hare, its tissues, its proteins and nucleic acids - everything that is specific to the structure "hare", "hare ordering"? Of course no!
All this in the stomach of the wolf will turn into a mixture of low molecular weight organic substances - amino acids, carbohydrates, nucleotides, etc., common to all living nature, nonspecific. The wolf's body will oxidize some of them to carbon dioxide and water in order (using the received energy!) To build from the remaining nonspecific substances its own, specifically ordered structure "wolf" - its proteins, its cells and tissues. Feed the wolf a chemist's synthesized amino acid mix and it will do the same.
Is this so with regard to life as such, life in general? The question is open. But this is how things are on Earth. Terrestrial organisms do not need someone else's order. They are struggling, desperately fighting her. Everyone knows about numerous medical attempts to transplant various organs or tissues to animals and humans: heart, lungs, kidneys, pancreas, etc. Is it possible to call these attempts successful? The result was always similar: the transplanted organs had a persistent tendency to rejection.
The only exceptions were organs "of the same order" with the patient, taken from an identical twin - and this is a "structural" copy of the same organism. As for the tissues, doctors prefer to take them for transplantation from the same organism: for example, the skin from the victim's leg is transplanted to the place affected by the burn. It is possible to preserve a foreign transplanted organ only by suppressing the protective immune systems for the formation of antibodies. But then the patient will be defenseless against any infection! This is a huge, fatal risk, and, one way or another, in the end it is only about the continuation of life, but not about the extension of a normal full-fledged life.
Even hormones, so to speak, are simply bioactive substances (that is, not only complex biological formations) are species-specific. Here, of course, there is a gap, there is a difference in degree. For example, insulin, the only effective remedy against diabetes, has a relatively low species-specificity, so this protein, isolated from the pancreas of cattle, can be used to treat diabetics. But the growth hormone - somatotropin - is species-specific. For the treatment of dwarf growth in a person, it is precisely human growth hormone that is secreted from the pituitary gland of a deceased person (yes, yes, there is no other way yet).
Someone will notice: there are complex organisms, their structural identity is complex, and, naturally, their structural specificity is quite demanding. But there are simple organisms, there are even the simplest. How then? It would seem that lower organisms should have less aversion to "alien order". In fact, fish and amphibians succeed in organ transplants between different species, and bovine somatotropin can stimulate the growth of trout. But all of these are artificially created by the experimenter. This means that it is not a completely "normal", unnatural course of life. In the end, they say: if you beat a hare, he will learn to light matches. The only question is, will this unfortunate hunted creature still be a hare? Let's put it this way: a hare that dies in a wolf's teeth is much more a hare, more true, "correct" than a hare,who can light matches!
Animals, feeding on other animals or plants, begin by destroying someone else's order. Food in their stomachs and intestines is broken down into simple chemical compounds, and by the structure of, for example, the amino acids glycine or phenylalanine, it is impossible to tell whether they are obtained from proteins of bovine meat, peas, or synthesized by an artificially clever chemist wearing glasses. From these elementary building blocks of life, organisms build only their inherent structures. Each organism is characterized by a unique, inherent only combination of protein molecules. And already on this basis, a complex of all the characteristics of the organism appears - at the level of cells, tissues and organs.
In plants, this is even more pronounced. Water, a set of nutrient salts, carbon dioxide and light - with this set of the same factors a rose grows from one seed, a nettle grows from another, and a tree grows from the third (and not at all “Chernov's tree” - remember?). Each time - a certain plant with its own set of properties. With its orderliness.
So, the body does not take order from the outside, but energy. Due to this energy, he builds his specific ordering "according to their kind" - so, it seems, is said in the Scripture, neglecting someone else's. From a chicken egg - a homogeneous mass of yolk and protein - a chicken appears with a head, legs, wings. And this simple thing, this miracle is called life.
S. Minakov