In life, we are surrounded by various bodies and objects. For example, indoors it is a window, a door, a table, a light bulb, a cup, on the street - a car, a traffic light, asphalt. Any body or object is made up of matter. This article will discuss what a substance is.
What is chemistry?
Water is an essential solvent and stabilizer. It has strong heat capacity and thermal conductivity. The aquatic environment is favorable for the flow of the main chemical reactions. It is transparent and practically resistant to compression.
What is the difference between inorganic and organic substances?
There are no particularly strong external differences between these two groups of substances. The main difference lies in the structure, where inorganic substances have a non-molecular structure, and organic substances have a molecular structure.
Inorganic substances have a non-molecular structure, therefore, they are characterized by high melting and boiling points. They do not contain carbon. These include noble gases (neon, argon), metals (calcium, calcium, sodium), amphoteric substances (iron, aluminum) and non-metals (silicon), hydroxides, binary compounds, salts.
organic matter molecular structure. They have fairly low melting points and decompose rapidly when heated. Mostly composed of carbon. Exceptions: carbides, carbonates, oxides of carbon and cyanides. Carbon allows the formation of a huge number of complex compounds (more than 10 million are known in nature).
Most of their classes belong to biological origin (carbohydrates, proteins, lipids, nucleic acids). These compounds include nitrogen, hydrogen, oxygen, phosphorus and sulfur.
To understand what a substance is, it is necessary to imagine what role it plays in our life. Interacting with other substances, it forms new ones. Without them, the vital activity of the surrounding world is inseparable and unthinkable. All objects are made up of certain substances, so they play an important role in our lives.
Offset number 2.
Explore Chapter 2 "The Origin of Life on Earth""pages 30-80 of the textbook" General biology. Grade 10 "author, etc.
I. Answer the following questions in writing:
1. What are the foundations and essence of life according to ancient Greek philosophers?
2. What is the meaning of F. Redi's experiments?
3. Describe the experiments of L. Pasteur, proving the impossibility of spontaneous generation of life in modern conditions.
4. What are theories of the eternity of life?
5. What materialistic theories of the origin of life do you know?
What are nuclear fusion reactions? Give examples.
6. How, in accordance with the Kant-Laplace hypothesis, star systems are formed from gas-dust matter?
7. Are there differences in the chemical composition of the planets of the same star system?
8. List the cosmic and planetary prerequisites for the emergence of life in an abiogenic way on our planet.
9. What is the significance for the emergence of organic molecules from non organic matter on Earth had the restorative nature of the primary atmosphere?
10. Describe the apparatus and methodology for conducting the experiments of S. Miller and P. Urey.
11. What is coacervation, coacervate?
12. What model systems can be used to demonstrate the formation of coacervate drops in solution?
13. What opportunities existed in the waters of the primary ocean to overcome low concentrations of organic matter?
14. What are the advantages for the interaction of organic molecules in areas of high concentrations of substances?
15. How could organic molecules with hydrophilic and hydrophobic properties be distributed in the waters of the primary ocean?
16. Name the principle of separating a solution into phases with a high and low concentration of molecules. ?
17. What are coacervate drops?
18. How is the selection of coacervates in the "primary broth"?
19. What is the essence of the hypothesis of the emergence of eukaryotes through symbiogenesis?
20. In what ways did the first eukaryotic cells receive the energy necessary for life processes?
21. In which organisms did the sexual process appear for the first time in the process of evolution?
22. Describe the essence of the hypothesis about the emergence of multicellular organisms?
23. Define the following terms: protobionts, biological catalysts, genetic code, self-reproduction, prokaryotes, photosynthesis, sexual process, eukaryotes.
Test your knowledge on the topic:
The origin of life and the development of the organic world
1. Proponents of biogenesis argue that
All living things - from living
All living things are created by God
All living things - from non-living
Living organisms brought to Earth from the universe
2. Proponents of abiogenesis argue that all living things
Comes from inanimate
Arises from living
・Created by God
Brought in from outer space
3. Experiments by L. Pasteur using flasks with an elongated neck
Proved the inconsistency of the position of abiogenesis
Affirmed the position of abiogenesis
Affirmed the position of biogenesis
Proved the inconsistency of the position of biogenesis
4. Proof that life does not arise spontaneously
L. Pasteur
A. Van Leeuwenhoek
Aristotle
5. Aristotle believed that
Alive only from living
Life comes from the four elements
The living comes from the non-living
The living can come from the inanimate if it has an "active principle"
6. Hypothesis
Strengthens the position of supporters of biogenesis
Strengthens the position of supporters of abiogenesis
Emphasizes the failure of the position of biogenesis
Emphasizes the failure of the position of abiogenesis
7. According to the hypothesis, coacervates are the first
· Organisms
"Organization" of molecules
Protein complexes
Accumulations of inorganic substances
8. At the stage of chemical evolution,
Bacteria
Protobionts
Biopolymers
Low molecular weight organic compounds
9. At the stage of biological evolution,
Biopolymers
· Organisms
low molecular weight organic substances
Inorganic substances
1. According to modern ideas, life on Earth developed as a result of
· Chemical evolution
Biological evolution
Chemical and then biological evolution
· Chemical and biological evolution
Biological and then chemical evolution
10. The first organisms that appeared on Earth ate
Autotrophs
Heterotrophs
Saprophytes
11. As a result of the appearance of autotrophs in the Earth's atmosphere
Increased amount of oxygen
Decreased amount of oxygen
・Increased quantity carbon dioxide
The ozone screen appeared
12. The amount of organic compounds in the primordial ocean was decreasing due to
Increase in the number of autotrophs
An increase in the number of heterotrophs
Reducing the number of autotrophs
Reducing the number of heterotrophs
13. The accumulation of oxygen in the atmosphere is due to
The appearance of the ozone layer
Photosynthesis
fermentation
Circulation of substances in nature
14. The process of photosynthesis led to
Formation of a large amount of oxygen
The appearance of the ozone layer
The emergence of multicellularity
The emergence of sexual reproduction
15. Check the correct statements:
Heterotrophs - organisms capable of independently synthesizing organic substances from inorganic
The first organisms on Earth were heterotrophic
Cyanobacteria - the first photosynthetic organisms
The mechanism of photosynthesis was formed gradually
16. Cleavage of organic compounds in anoxic conditions:
fermentation
Photosynthesis
· Oxidation
Biosynthesis
17. With the advent of autotrophs on Earth:
Irreversible changes in the conditions of existence of life began
· Formed a large number of oxygen in the atmosphere
There has been an accumulation solar energy in chemical bonds of organic substances
All heterotrophs have disappeared
18. Man appeared on earth in
Proterozoic era
Mesozoic era
Cenozoic era
Proterozoic
Mesozoic
Paleozoic
Cenozoic
20. The largest events of the Proterozoic are considered
The emergence of eukaryotes
Emergence of flowering plants
The emergence of the first chordates
21. The process of soil formation on Earth was due to
The water cycle in nature
Settlement by organisms of the upper layer of the lithosphere
The death of organisms
Destruction of hard rocks with the formation of sand and clay
22. were widespread in Archaea.
Reptiles and ferns
Bacteria and cyanobacteria
23. Plants, animals and fungi came to land in
Proterozoic
Paleozoic
Mesozoic
24. Proterozoic era
Mammals and insects
Algae and coelenterates
The first land plants
Dominance of reptiles
Nature develops in dynamics, living and inert matter continuously undergoes transformation processes. The most important transformations are those that affect the composition of a substance. The formation of rocks, chemical erosion, the birth of a planet or the respiration of mammals are all observable processes that entail changes in other substances. Despite their differences, they all share something in common: changes at the molecular level.
- In the course of chemical reactions, elements do not lose their identity. Only the electrons of the outer shell of atoms participate in these reactions, while the nuclei of atoms remain unchanged.
- The reactivity of an element to a chemical reaction depends on the degree of oxidation of the element. In ordinary chemical reactions, Ra and Ra 2+ behave completely differently.
- Different isotopes of an element have almost the same chemical reactivity.
- The rate of a chemical reaction is highly dependent on temperature and pressure.
- The chemical reaction can be reversed.
- Chemical reactions are accompanied by relatively small changes in energy.
Nuclear reactions
- During nuclear reactions, the nuclei of atoms undergo changes and, therefore, new elements are formed as a result.
- The reactivity of an element to a nuclear reaction is practically independent of the degree of oxidation of the element. For example, Ra or Ra 2+ ions in Ka C 2 behave similarly in nuclear reactions.
- In nuclear reactions, isotopes behave quite differently. For example, U-235 undergoes division quietly and easily, but U-238 does not.
- The rate of a nuclear reaction does not depend on temperature and pressure.
- A nuclear reaction cannot be undone.
- Nuclear reactions are accompanied by large changes in energy.
Difference between chemical and nuclear energy
- Potential energy that can be converted to other forms primarily of heat and light when bonds are formed.
- The stronger the bond, the greater the converted chemical energy.
- Nuclear energy is not associated with the formation of chemical bonds (which are due to the interaction of electrons)
- Can be converted to other forms when there is a change in the nucleus of an atom.
Nuclear change occurs in all three major processes:
- Nuclear fission
- Joining two nuclei to form a new nucleus.
- The release of high energy electromagnetic radiation (gamma rays), creating a more stable version of the same nucleus.
Energy Conversion Comparison
The amount of chemical energy released (or converted) in a chemical explosion is:
- 5kJ for each gram of TNT
- The amount of nuclear energy released atomic bomb: 100 million kJ for every gram of uranium or plutonium
One of the main differences between nuclear and chemical reactions related to how the reaction occurs in the atom. While a nuclear reaction takes place in the nucleus of an atom, the electrons in the atom are responsible for the chemical reaction that takes place.
Chemical reactions include:
- Transfers
- Losses
- Gain
- Separation of electrons
According to the atom theory, matter is explained as a result of rearrangement to give new molecules. Substances involved in a chemical reaction and the proportions in which they are formed are expressed in the corresponding chemical equations underlying to perform various types of chemical calculations.
Nuclear reactions are responsible for the decay of the nucleus and have nothing to do with electrons. When the nucleus decays, it can go to another atom, due to the loss of neutrons or protons. In a nuclear reaction, protons and neutrons interact inside the nucleus. In chemical reactions, electrons react outside the nucleus.
Any fission or fusion can be called the result of a nuclear reaction. A new element is formed due to the action of a proton or neutron. As a result of a chemical reaction, a substance changes into one or more substances due to the action of electrons. A new element is formed due to the action of a proton or neutron.
When comparing energy, a chemical reaction only involves a low energy change, whereas a nuclear reaction has a very high energy change. In a nuclear reaction, the energy changes in magnitude are 10^8 kJ. It is 10 - 10^3 kJ/mol in chemical reactions.
While some elements are converted into others in the nuclear, the number of atoms remains the same in the chemical. In a nuclear reaction, isotopes react differently. But as a result of a chemical reaction, isotopes also react.
Although a nuclear reaction does not depend on chemical compounds, a chemical reaction is highly dependent on chemical compounds.
Summary
- A nuclear reaction occurs in the nucleus of an atom, the electrons in the atom are responsible for chemical compounds.
- Chemical reactions cover the transfer, loss, amplification and separation of electrons without involving the nucleus in the process. Nuclear reactions involve the decay of the nucleus and have nothing to do with electrons.
- In a nuclear reaction, protons and neutrons react inside the nucleus; in chemical reactions, electrons interact outside the nucleus.
- When comparing energies, a chemical reaction uses only a low energy change, whereas a nuclear reaction has a very high energy change.
During chemical reactions, other substances are obtained from one substance (not to be confused with nuclear reactions, in which one chemical element turns into another).
Any chemical reaction is described by a chemical equation:
Reagents → Reaction products
The arrow indicates the direction of the reaction.
For example:
In this reaction, methane (CH 4) reacts with oxygen (O 2), resulting in the formation of carbon dioxide (CO 2) and water (H 2 O), or rather, water vapor. This is exactly the reaction that happens in your kitchen when you light a gas burner. The equation should be read like this: one molecule of methane gas reacts with two molecules of oxygen gas, resulting in one molecule of carbon dioxide and two molecules of water (steam).
The numbers in front of the components of a chemical reaction are called reaction coefficients.
Chemical reactions are endothermic(with energy absorption) and exothermic(with energy release). The combustion of methane is a typical example of an exothermic reaction.
There are several types of chemical reactions. The most common:
- compound reactions;
- decomposition reactions;
- single substitution reactions;
- double substitution reactions;
- oxidation reactions;
- redox reactions.
Connection reactions
In a compound reaction, at least two elements form one product:
2Na (t) + Cl 2 (g) → 2NaCl (t)- the formation of salt.
Attention should be paid to an essential nuance of compound reactions: depending on the conditions of the reaction or the proportions of the reactants involved in the reaction, different products can be its result. For example, under normal conditions of combustion of coal, carbon dioxide is obtained:
C (t) + O 2 (g) → CO 2 (g)
If there is not enough oxygen, then deadly carbon monoxide is formed:
2C (t) + O 2 (g) → 2CO (g)
Decomposition reactions
These reactions are, as it were, opposite in essence to the reactions of the compound. As a result of the decomposition reaction, the substance breaks up into two (3, 4...) more simple element(connections):
- 2H 2 O (g) → 2H 2 (g) + O 2 (g)- water decomposition
- 2H 2 O 2 (g) → 2H 2 (g) O + O 2 (g)- decomposition of hydrogen peroxide
Single substitution reactions
As a result of single substitution reactions, the more active element replaces the less active element in the compound:
Zn (t) + CuSO 4 (solution) → ZnSO 4 (solution) + Cu (t)
The zinc in the copper sulfate solution displaces the less active copper, resulting in a zinc sulfate solution.
The degree of activity of metals in ascending order of activity:
- The most active are alkali and alkaline earth metals.
The ionic equation for the above reaction will be:
Zn (t) + Cu 2+ + SO 4 2- → Zn 2+ + SO 4 2- + Cu (t)
The ionic bond CuSO 4, when dissolved in water, decomposes into a copper cation (charge 2+) and an anion sulfate (charge 2-). As a result of the substitution reaction, a zinc cation is formed (which has the same charge as the copper cation: 2-). Note that the sulfate anion is present on both sides of the equation, i.e., by all the rules of mathematics, it can be reduced. The result is an ion-molecular equation:
Zn (t) + Cu 2+ → Zn 2+ + Cu (t)
Double substitution reactions
In double substitution reactions, two electrons are already replaced. Such reactions are also called exchange reactions. These reactions take place in solution to form:
- insoluble solid(precipitation reactions);
- water (neutralization reactions).
Precipitation reactions
When mixing a solution of silver nitrate (salt) with a solution of sodium chloride, silver chloride is formed:
Molecular equation: KCl (solution) + AgNO 3 (p-p) → AgCl (t) + KNO 3 (p-p)
Ionic equation: K + + Cl - + Ag + + NO 3 - → AgCl (t) + K + + NO 3 -
Molecular-ionic equation: Cl - + Ag + → AgCl (t)
If the compound is soluble, it will be in solution in ionic form. If the compound is insoluble, it will precipitate, forming a solid.
Neutralization reactions
These are reactions between acids and bases, as a result of which water molecules are formed.
For example, the reaction of mixing a solution of sulfuric acid and a solution of sodium hydroxide (lye):
Molecular equation: H 2 SO 4 (p-p) + 2NaOH (p-p) → Na 2 SO 4 (p-p) + 2H 2 O (l)
Ionic equation: 2H + + SO 4 2- + 2Na + + 2OH - → 2Na + + SO 4 2- + 2H 2 O (l)
Molecular-ionic equation: 2H + + 2OH - → 2H 2 O (g) or H + + OH - → H 2 O (g)
Oxidation reactions
These are reactions of interaction of substances with gaseous oxygen in the air, in which, as a rule, a large amount of energy is released in the form of heat and light. A typical oxidation reaction is combustion. At the very beginning of this page, the reaction of the interaction of methane with oxygen is given:
CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O (g)
Methane refers to hydrocarbons (compounds of carbon and hydrogen). When a hydrocarbon reacts with oxygen, a lot of heat energy is released.
Redox reactions
These are reactions in which electrons are exchanged between the atoms of the reactants. The reactions discussed above are also redox reactions:
- 2Na + Cl 2 → 2NaCl - compound reaction
- CH 4 + 2O 2 → CO 2 + 2H 2 O - oxidation reaction
- Zn + CuSO 4 → ZnSO 4 + Cu - single substitution reaction
The most detailed redox reactions with a large number of examples of solving equations by the electron balance method and the half-reaction method are described in the section
Current page: 3 (the book has a total of 18 pages) [available reading excerpt: 12 pages]
Scientists believe that nebulae are a stage in the formation of galaxies or large star systems. In models of this type of theory, planets are a by-product of star formation. This point of view, first expressed in the XVIII century. I. Kant and later developed by P. Laplace, D. Kuiper, D. Alven and R. Cameron, is confirmed by a number of evidence.
Young stars are found inside nebulae, regions of relatively concentrated interstellar gas and dust that are light-years across. Nebulae are found throughout our galaxy; it is believed that stars and their associated planetary systems form within these vast clouds of matter.
Using spectroscopy, it was shown that interstellar matter consists of gases - hydrogen, helium and neon - and dust particles that have dimensions of the order of several microns and consist of metals and other elements. Since the temperature is very low (10–20 K), all matter, except for the mentioned gases, is in a frozen state on dust particles. More heavy elements and some hydrogen is derived from stars of previous generations; some of these stars exploded as supernovae, returning the remaining hydrogen to the interstellar medium and enriching it with heavier elements formed in their depths.
The average concentration of gas in interstellar space is only 0.1 atoms N/cm 3 , while the concentration of gas in nebulae is about 1000 atoms N/cm 3 , i.e. 10,000 times greater. (1 cm 3 of air contains approximately 2.7 × 10 19 molecules.)
When a gas-dust cloud becomes large enough as a result of slow settling and sticking together (accretion) of interstellar gas and dust under the influence of gravity, it becomes unstable - the relationship between pressure and gravitational forces close to equilibrium is violated in it. Gravitational forces predominate, and so the cloud contracts. During the early phases of compression, the heat released by the conversion of gravitational energy into radiant energy easily leaves the cloud, since the relative density of matter is low. As the density of matter increases, new important changes begin. Due to gravitational and other fluctuations, a large cloud breaks up into smaller clouds, which, in turn, form fragments that ultimately exceed our solar system by several times in mass and size (Fig. 2.2; 1–5). Such clouds are called protostars. Of course, some protostars are more massive than our solar system, they form larger and hotter stars, while less massive protostars form smaller and cooler stars that evolve more slowly than the former. The sizes of protostars are limited by an upper limit above which further fragmentation would occur, and a lower limit by the minimum mass required to sustain nuclear reactions.
Rice. 2.2. Evolution of a gas-dust nebula and the formation of a protoplanetary disk
First, the potential gravitational energy, which turns into heat (radiant energy), is simply radiated outward during gravitational contraction. But as the density of matter increases, more and more radiation energy is absorbed and, as a result, the temperature rises. Volatile compounds, initially frozen on dust particles, begin to evaporate. Now gases such as NH 3 , CH 4 , H 2 O (vapours) and HCN are mixed with H 2, He and Ne. These gases absorb subsequent portions of radiation energy, dissociate and undergo ionization.
Gravitational contraction proceeds until the emitted radiation energy is dissipated during the evaporation and ionization of molecules in dust particles. When the molecules are fully ionized, the temperature rises rapidly until the compression almost stops as the pressure of the gas begins to balance the forces of gravity. Thus ends the phase of rapid gravitational contraction (collapse).
At this moment of its development, the protostar corresponding to our system is a disk with a thickening in the center and a temperature of approximately 1000 K at the level of Jupiter's orbit. Such a protostellar disk continues to evolve: a restructuring takes place in it, and it slowly shrinks. The protostar itself is gradually becoming more compact, more massive, and hotter, as now heat can only radiate from its surface. Heat is transferred from the depths of a protostar to its surface by means of convection currents. The region from the surface of the protostar to a distance equivalent to the orbit of Pluto is filled with gas and dust fog.
During this complex series of contractions, which is believed to have taken about 10 million years, the angular momentum of the system must be conserved. The entire galaxy rotates, making 1 revolution in 100 million years. As dust clouds compress, their angular momentum cannot change—the more they compress, the faster they spin. Due to the conservation of angular momentum, the shape of a collapsing dust cloud changes from spherical to disk-shaped.
As the remaining matter of the protostar compressed, its temperature became high enough to start the reaction of fusion of hydrogen atoms. With the influx of more energy, due to this reaction, the temperature became high enough to balance the forces of further gravitational contraction.
The planets formed from the remaining gases and dust at the periphery of the protostellar disk (Fig. 2.3). The agglomeration of interstellar dust under the influence of gravitational attraction leads to the formation of a star and planets in approximately 10 million years (1–4). The star enters the main sequence (4) and remains in a stationary (stable) state for about 8000 million years, gradually processing hydrogen. The star then leaves the main sequence, expands to a red giant (5 and 6) and "absorbs" its planets over the next 100 million years. After several thousand years of pulsing as a variable star (7), it explodes as a supernova (8) and finally collapses into a white dwarf (9). Although the planets are usually considered massive objects, the total mass of all the planets is only 0.135% of the mass of the solar system.
Rice. 2.3. Formation of the planetary system
Our planets, and presumably the planets that form in any protostellar disk, lie in two main zones. The inner zone, which solar system extends from Mercury to the asteroid belt, is a zone of small terrestrial planets. Here, in the phase of slow contraction of the protostar, temperatures are so high that metals evaporate. The outer cold zone contains gases such as H 2 O, He and Ne, and particles covered with frozen volatiles such as H 2 O, NH 3 and CH 4 . This outer zone, with planets like Jupiter, contains much more matter than the inner one, because it is large and because most of the volatile matter originally in the inner zone is pushed out by the activity of the protostar.
One way to build a picture of a star's evolution and calculate its age is to analyze a large random sample of stars. At the same time, the distances to the stars, their apparent brightness and the color of each star are measured.
If the apparent brightness and distance to the star are known, then its absolute magnitude can be calculated, since the apparent brightness of a star is inversely proportional to the distance to it. Absolute magnitude is a function of the rate of energy release, regardless of its distance from the observer.
The color of a star is determined by its temperature: blue is very hot, white is hot, and red is relatively cold.
Figure 2.4 shows the Hertzsprung-Russell diagram that you know from your astronomy course, showing the relationship between absolute magnitude and color for a large number of stars. Since this classic diagram includes stars of all sizes and ages, it corresponds to the "average" star at various stages of its evolution.
Rice. 2.4. Hertzsprung-Russell diagram
Most of the stars are located on the rectilinear part of the diagram; they experience only gradual changes in equilibrium as the hydrogen they contain burns out. In this part of the diagram, called the main sequence, stars with more mass have a higher temperature; in them, the reaction of fusion of hydrogen atoms proceeds faster, and their life span is shorter. Stars with less mass than the sun have more low temperature, the fusion of hydrogen atoms proceeds in them more slowly, and their life expectancy is longer. Ever a star main sequence will use up about 10% of its original hydrogen reserves, its temperature will decrease and expansion will occur. As suggested, red giants are "aged" stars of all sizes that previously belonged to the main sequence. When accurately determining the age of a star, these factors must be taken into account. Calculations based on them show that not a single star in our galaxy is older than 11,000 million years. Some small stars are of this age; many more big stars much younger. The most massive stars can be on the main sequence for no more than 1 million years. The sun and stars of similar sizes stay on the main sequence for about 10,000 million years before reaching the red giant stage.
Anchor points
1. Matter is in continuous motion and development.
2. Biological evolution is a certain qualitative stage in the evolution of matter as a whole.
3. Transformations of elements and molecules in outer space occur constantly at a very low rate.
1. What are nuclear fusion reactions? Give examples.
2. How, in accordance with the Kant-Laplace hypothesis, are star systems formed from gas-dust matter?
3. Are there any differences in the chemical composition of the planets of the same star system?
Adhering to the above point of view on the origin of planetary systems, one can make fairly reasonable estimates of the elemental composition of the Earth's primary atmosphere. Part of the modern view is based, of course, on the vast predominance of hydrogen in space; it is also found in the sun. Table 2.2 shows the elemental composition of stellar and solar matter.
Table 2.2. Elemental composition of stellar and solar matter
It is assumed that the atmosphere of the primary Earth, which had a high average temperature, was something like this: before gravitational loss, hydrogen made up most of it, and methane, water and ammonia were the main molecular constituents. It is interesting to compare the elementary composition of stellar matter with the composition of the modern Earth and living matter on Earth.
The most common elements in inanimate nature are hydrogen and helium; they are followed by carbon, nitrogen, silicon and magnesium. notice, that living matter The biosphere on the Earth's surface consists mainly of hydrogen, oxygen, carbon and nitrogen, which, of course, was to be expected, judging by the very nature of these elements.
The initial atmosphere of the Earth could change as a result of a variety of processes, primarily as a result of the diffusion escape of hydrogen and helium, which constituted a significant part of it. These elements are the lightest, and they should have been lost from the atmosphere, because the gravitational field of our planet is small in comparison with the field of giant planets. Much of the Earth's initial atmosphere must have been lost in a very a short time; therefore, it is assumed that many of the primary gases of the earth's atmosphere are gases that were buried in the bowels of the earth and were released again as a result of the gradual heating of the earth's rocks. The Earth's primary atmosphere was probably made up of organic substances of the same kind that are observed in comets: molecules with carbon-hydrogen, carbon-nitrogen, nitrogen-hydrogen, and oxygen-hydrogen bonds. In addition to them, hydrogen, methane, carbon monoxide, ammonia, water, etc., probably also appeared during the gravitational heating of the earth's interior. These are the substances with which most experiments were carried out to model the primary atmosphere.
What could actually happen in the conditions of the primitive Earth? In order to determine this, it is necessary to know what types of energy were most likely to affect its atmosphere.
The development and transformation of matter without an influx of energy is impossible. Let us consider those sources of energy that determine the further evolution of substances no longer in space, but on our planet - on Earth.
Assessing the role of energy sources is not easy; in this case, it is necessary to take into account the non-equilibrium conditions, the cooling of the reaction products and the degree of their screening from energy sources.
Apparently, any energy sources (Table 2.3) had a significant impact on the transformation of substances on our planet. How did it happen? Of course, objective evidence simply does not exist. However, the processes that took place on our Earth in ancient times can be modeled. Firstly, it is necessary to determine the time limits, and secondly, to reproduce with possible accuracy the conditions in each of the discussed epochs of the planet's existence.
To discuss questions about the origin of life on Earth, in addition to knowing the energy sources necessary for the transformation of matter, one must also have a fairly clear idea of the time of these transformations.
Table 2.3. Possible Energy Sources for Primary Chemical Evolution
Table 2.4. Half-lives and other data on some elements used in determining the age of the Earth
Development physical sciences has now provided biologists with several effective methods for determining the age of certain breeds earth's crust. The essence of these methods is to analyze the ratio of various isotopes and end products of nuclear decay in samples and correlate the results of the study with the time of splitting of the initial elements (Table 2.4).
The use of such methods allowed scientists to build a time scale of the Earth's history from the moment of its cooling, 4500 million years ago, to the present (Table 2.5). Now our task is to establish, within this time scale, what were the conditions on the primitive Earth, what kind of atmosphere the Earth had, what was the temperature, pressure, when the oceans formed, and how the Earth itself was formed.
Table 2.5. Geological scale
Today, the reconstruction of the conditions in which the first "germs of life" arose is of fundamental importance for science. Great is the merit of A. I. Oparin, who in 1924 proposed the first concept of chemical evolution, according to which an oxygen-free atmosphere was proposed as a starting point in laboratory experiments to reproduce the conditions of the primary Earth.
In 1953, American scientists G. Urey and S. Miller subjected a mixture of methane, ammonia and water to the action of electrical discharges(Fig. 2.5). For the first time, using such an experiment, amino acids (glycine, alanine, aspartic and glutamic acids) were identified among the products obtained.
The experiments of Miller and Urey stimulated research into molecular evolution and the origin of life in many laboratories and led to a systematic study of the problem, during which biologically important compounds were synthesized. The main conditions on the primitive Earth, taken into account by the researchers, are shown in Table 2.6.
Pressure, like the quantitative composition of the atmosphere, is difficult to calculate. Estimates made taking into account the "greenhouse" effect are quite arbitrary.
Calculations that take into account the "greenhouse" effect, as well as the approximate intensity of solar radiation in the abiotic era, have led to values several tens of degrees above the freezing point. Almost all experiments to recreate the conditions of the primordial Earth were carried out at temperatures of 20–200°C. These limits were not established by calculations or extrapolation of some geological data, but rather by taking into account the temperature limits of the stability of organic compounds.
The use of gas mixtures similar to the gases of the primary atmosphere, various types of energy that were characteristic of our planet 4–4.5 × 10 9 years ago, and taking into account the climatic, geological and hydrographic conditions of that period, made it possible in many laboratories studying the origin of life , to find evidence of the ways of abiotic occurrence of such organic molecules as aldehydes, nitrites, amino acids, monosaccharides, purines, porphyrins, nucleotides, etc.
Rice. 2.5. Miller apparatus
Table 2.6. Conditions on primeval earth
The emergence of protobiopolymers is a more complex problem. The necessity of their existence in all living systems is obvious. They are responsible for protoenzymatic processes(for example, hydrolysis, decarboxylation, amination, deamination, peroxidation etc.), for some very simple processes, such as fermentation, and for other, more complex ones, such as photochemical reactions, photophosphorylation, photosynthesis and etc.
The presence of water on our planet (primary ocean) has led to the possibility of the emergence of protobiopolymers in the process of a chemical reaction - condensation. So, for the formation of a peptide bond in aqueous solutions according to the reaction:
energy costs are required. These energy costs increase many times over when protein molecules are obtained in aqueous solutions. The synthesis of macromolecules from "biomonomers" requires the involvement of specific (enzymatic) methods of water removal.
General process of evolution of matter and energy in the Universe includes several consecutive stages. Among them are the formation of space nebulae, their development and structuring of planetary systems can be recognized. Transformations of substances that take place on the planets are determined by some general natural laws and depend on the position of the planet within the star system. Some of these planets, like the Earth, are characterized by the features that enable the development of inorganic matter towards the appearance of various complicated organic molecules.
Anchor points
1. The primary atmosphere of the Earth consisted mainly of hydrogen and its compounds.
2. The Earth is at the optimal distance from the Sun and receives enough energy to keep water in a liquid state.
3. In aqueous solutions, due to various energy sources, the simplest organic compounds arise in a non-biological way.
Review questions and assignments
1. List the cosmic and planetary prerequisites for the emergence of life abiogenically on our planet.
2. What is the significance for the emergence of organic molecules from inorganic substances on Earth was the reducing nature of the primary atmosphere?
3. Describe the apparatus and methodology for conducting experiments by S. Miller and P. Urey.
Using the vocabulary of the sections "Terminology" and "Summary", translate into English language reference points.
Terminology
For each term indicated in the left column, select the corresponding definition given in the right column in Russian and English.
Select the correct definition for every term in the left column from English and Russian variants listed in the right column.
2.3. Theories on the origin of protobiopolymersIssues for discussion
What, in your opinion, sources of energy prevailed on the ancient Earth? How can one explain the nonspecific influence of various energy sources on the processes of formation of organic molecules?
Various assessments of the nature of the environment on the primitive Earth led to the creation of different experimental conditions, which had fundamentally the same, but not always the same results in particular.
Let's consider some of the most important theories of the emergence of polymer structures on our planet, which lie at the origins of the formation of biopolymers - the basis of life.
Thermal theory. Condensation reactions that would lead to the formation of polymers from low molecular weight precursors can be carried out by heating. Compared with other components of living matter, the synthesis of polypeptides is the most well studied.
The author of the hypothesis of thermal synthesis of polypeptides is the American scientist S. Fox, who for a long time studied the possibilities of peptide formation under the conditions that existed on the primitive Earth. If a mixture of amino acids is heated to 180–200 °C under normal atmospheric conditions or in an inert environment, then polymerization products, small oligomers, in which the monomers are connected by peptide bonds, as well as small amounts of polypeptides, are formed. In cases where the initial mixtures of amino acids were enriched by experimenters with amino acids of the acidic or basic type, for example, aspartic and glutamic acids, the proportion of polypeptides increased significantly. The molecular weight of polymers obtained in this way can reach several thousand D. (D - Dalton, a mass unit numerically equal to the mass of 1/16 of an oxygen atom.)
Polymers obtained thermally from amino acids - proteinoids - exhibit many of the specific properties of protein-type biopolymers. However, in the case of thermal condensation of nucleotides and monosaccharides having a complex structure, the formation of currently known nucleic acids and polysaccharides seems unlikely.
Theory of adsorption. The main counterargument in disputes about the abiogenic occurrence of polymer structures is the low concentration of molecules and the lack of energy for the condensation of monomers in dilute solutions. Indeed, according to some estimates, the concentration of organic molecules in the "primordial soup" was about 1%. Such a concentration, due to the rarity and randomness of contacts of various molecules necessary for the condensation of substances, could not provide such a “rapid” formation of protobiopolymers, as was the case on Earth, according to some scientists. One of the solutions to this issue, related to overcoming such a concentration barrier, was proposed by the English physicist D. Bernal, who believed that the concentration of dilute solutions of organic substances occurs by "adsorption of them in aqueous clay deposits."
As a result of the interaction of substances in the process of adsorption, some bonds are weakened, which leads to the destruction of some and the formation of other chemical compounds.
Low temperature theory. The authors of this theory, the Romanian scientists C. Simonescu and F. Denesh, proceeded from somewhat different ideas about the conditions for the abiogenic occurrence of the simplest organic compounds and their condensation into polymeric structures. The authors attach the leading importance as a source of energy to the energy of cold plasma. Such an opinion is not unfounded.
Cold plasma is widely distributed in nature. Scientists believe that 99% of the universe is in a state of plasma. This state of matter also occurs on the modern Earth in the form of ball lightning, auroras, as well as a special type of plasma - the ionosphere.
Regardless of the nature of the energy on the abiotic Earth, any kind of energy transforms chemical compounds, especially organic molecules, into active particles, such as mono- and polyfunctional free radicals. However, their further evolution largely depends on the density of the energy flux, which is most pronounced in the case of using cold plasma.
As a result of painstaking and complex experiments with cold plasma as an energy source for the abiogenic synthesis of protobiopolymers, researchers managed to obtain both individual monomers and peptide-type polymer structures and lipids.
Oparin believed that the transition from chemical to biological evolution required the obligatory emergence of individual phase-separate systems capable of interacting with the external environment, using its substances and energy, and on this basis capable of growing, multiplying and undergoing natural selection.
The abiotic isolation of multimolecular systems from a homogeneous solution of organic substances, apparently, had to be carried out repeatedly. It is still very widespread in nature. But under the conditions of the modern biosphere, only the initial stages of the formation of such systems can be directly observed. Their evolution is usually very short-term in the presence of microbes that destroy all living things. Therefore, to understand this stage of the emergence of life, it is necessary to artificially obtain phase-separated organic systems in strictly controlled laboratory conditions and on the models formed in this way to establish both the ways of their possible evolution in the past, and the laws of this process. When working with high molecular weight organic compounds under laboratory conditions, they constantly meet with the formation of this kind of phase-separated systems. Therefore, one can imagine the ways of their occurrence and experimentally obtain various systems under laboratory conditions, many of which could serve us as models of formations that once appeared on the earth's surface. For example, here are some of them: "bubbles" Goldeicra, "microspheres" fox, "jeyvanu" Bahadur, "probionts" Egami and many others.
Often, when working with such artificial systems that are self-isolating from solution, special attention is paid to their external morphological similarity with living objects. But this is not the solution to the problem, but that the system can interact with the external environment, using its substances and energy like open systems, and on this basis grow and multiply, which is typical for all living beings.
The most promising models in this respect are coacervate drops.
Each molecule has a certain structural organization, i.e., the atoms that make up its composition are naturally located in space. As a result, poles with different charges are formed in the molecule. For example, a water molecule H 2 O forms a dipole, in which one part of the molecule carries a positive charge (+), and the other negative (-). In addition, some molecules (for example, salts) dissociate into ions in an aqueous medium. Due to such features of the chemical organization of molecules around them in water, water “shirts” are formed from certain oriented water molecules. Using the NaCl molecule as an example, one can notice that the water dipoles surrounding the Na + ion are turned to it by negative poles (Fig. 2.6), and to the Cl − ion by positive poles.
Rice. 2.6. Hydrated sodium cation
Rice. 2.7. Assembly of coacervates
Organic molecules have a large molecular weight and a complex spatial configuration, so they are also surrounded by a water shell, the thickness of which depends on the charge of the molecule, the concentration of salts in the solution, temperature, etc.
Under certain conditions, the water shell acquires clear boundaries and separates the molecule from the surrounding solution. Molecules surrounded by an aqueous shell can combine to form multimolecular complexes - coacervates(Fig. 2.7).
Coacervate droplets also arise from the simple mixing of various polymers, both natural and artificially obtained. In this case, self-assembly of polymer molecules into multimolecular phase-separate formations occurs - drops visible under an optical microscope (Fig. 2.8). Most of the polymer molecules are concentrated in them, while the environment is almost completely devoid of them.
The drops are separated from environment sharp interface, but they are able to absorb substances from the outside as open systems.
Rice. 2.8. Coacervate drops obtained in the experiment
By incorporating into coacervate drops various catalysts(including enzymes) it is possible to cause a number of reactions, in particular, the polymerization of monomers coming from the external environment. Due to this, drops can increase in volume and weight, and then break up into daughter formations.
For example, the processes occurring in a coacervate drop are shown in square brackets, and outside of them are substances that are in the external environment:
glucose-1-phosphate → [glucose-1-phosphate → starch → maltose] → maltose
A coacervate drop formed from protein and gum arabic is immersed in a solution of glucose-1-phosphate. Glucose-1-phosphate begins to enter the drop and polymerizes in it into starch under the action of a catalyst - phosphorylase. Due to the formed starch, the drop grows, which can be easily established both by chemical analysis and by direct microscopic measurements. If another catalyst, b-amylase, is included in the drop, the starch decomposes to maltose, which is released into the external environment.
Thus, the simplest metabolism. The substance enters the drop, polymerizes, causing growth system, and during its decay, the products of this decay go into the external environment, where they were not previously.
Another scheme illustrates an experiment where the polymer is a polynucleotide. A drop consisting of a histone protein and gum arabic is surrounded by an ADP solution.
Entering the drop, ADP is polymerized under the influence of polymerase into polyadenylic acid, due to which the drop grows, and inorganic phosphorus enters the external environment.
ADP → [ADP → Poly-A + P] → P
In this case, the drop over a short period of time increases in volume by more than two times.
Both in the case of starch synthesis and in the formation of polyadenylic acid, energy-rich (macroergic) connections. Due to the energy of these compounds coming from the external environment, the synthesis of polymers and the growth of coacervate drops took place. In another series of experiments by Academician A.I. Oparin and coworkers, it was demonstrated that reactions associated with energy dissipation can also occur in coacervate drops themselves.
