Is there a difference in the chemical composition of the planets? What is a substance? What are the classes of substances? Difference between organic and inorganic substances. What is the difference between inorganic and organic substances
Test No. 2.
Explore Chapter 2 "The Origin of Life on Earth"" pp. 30-80 of the textbook "General Biology. Grade 10" author, etc.
I. Answer the 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 L. Pasteur’s experiments proving the impossibility of spontaneous generation of life under 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, are star systems formed from gas-dust matter?
7. Are there differences in the chemical composition of planets of the same star system?
8. List the cosmic and planetary prerequisites for the emergence of life abiogenically on our planet.
9.What was the significance of the reducing nature of the primary atmosphere for the emergence of organic molecules from inorganic substances on Earth?
10.Describe the apparatus and methods of conducting experiments by S. Miller and P. Ury.
11. What is coacervation, coacervate?
12. What model systems can be used to demonstrate the formation of coacervate droplets in solution?
13.What opportunities existed for overcoming low concentrations of organic substances in the waters of the primary ocean?
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 dividing a solution into phases with high and low concentrations of molecules. ?
17. What are coacervate drops?
18. How does the selection of coacervates occur 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 obtain the energy necessary for vital processes?
21. Which organisms developed the sexual process 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:
Origin of life and development of the organic world
1. Proponents of biogenesis argue that
· All living things are from living things
· All living things are created by God
· All living things come from non-living things
· Living organisms were brought to Earth from the Universe
2. Proponents of abiogenesis argue that everything is living
· Comes from non-living
·Arises from living things
· Created by God
·Brought from 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 was provided by
· L. Pasteur
· A. Van Leeuwenhoek
· Aristotle
5. Aristotle believed that
· Living only from living
· Life arises from four elements
· Living things come from non-living things
· Living things can come from non-living things if they have an “active principle”
6. Hypothesis
· Strengthens the position of supporters of biogenesis
· Strengthens the position of supporters of abiogenesis
· Emphasizes the inconsistency of the position of biogenesis
· Emphasizes the inconsistency of the position of abiogenesis
7. According to the hypothesis, coacervates are the first
Organisms
"Organizations" of molecules
· Protein complexes
Accumulations of inorganic substances
8. At the stage of chemical evolution, they are formed
· 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 to appear 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 amount of carbon dioxide
· Ozone screen appeared
12. The amount of organic compounds in the primordial ocean decreased due to
Increase in the number of autotrophs
Increase in the number of heterotrophs
Reducing the number of autotrophs
· Decrease in the number of heterotrophs
13. The accumulation of oxygen in the atmosphere occurred due to
· The appearance of the ozone screen
· Photosynthesis
· Fermentation
· The cycle of substances in nature
14. The process of Photosynthesis led to
· Formation of large amounts of oxygen
· The appearance of the ozone screen
The emergence of multicellularity
The emergence of sexual reproduction
15. Check the correct statements:
Heterotrophs - organisms capable of independently synthesizing organic substances from inorganic ones
· The first organisms on Earth were heterotrophic
Cyanobacteria – the first photosynthetic organisms
· The mechanism of photosynthesis was formed gradually
16. Breakdown of organic compounds under oxygen-free conditions:
· Fermentation
· Photosynthesis
Oxidation
Biosynthesis
17. With the appearance of autotrophs on Earth:
Irreversible changes in the conditions of life have begun
A large amount of oxygen was formed in the atmosphere
· There was an accumulation of solar energy in the chemical bonds of organic substances
· All heterotrophs 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
· Emergence of eukaryotes
The appearance of flowering plants
The emergence of the first chordates
21. The process of soil formation on Earth occurred thanks to
· The water cycle in nature
· Colonization of the upper layer of the lithosphere by organisms
The death of organisms
· Destruction of hard rocks with the formation of sand and clay
22. They were widespread in Archean
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
· First land plants
· Dominance of reptiles
In life we are surrounded by various bodies and objects. For example, indoors this is a window, door, table, light bulb, cup, outdoors - a car, traffic light, asphalt. Any body or object consists 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 aqueous environment is favorable for the occurrence of basic chemical reactions. It is characterized by transparency and is 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, so 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 nonmetals (silicon), hydroxides, binary compounds, salts.
Organic substances of molecular structure. They have fairly low melting points and decompose quickly when heated. Mainly composed of carbon. Exceptions: carbides, carbonates, carbon oxides and cyanides. Carbon allows the formation of a huge number of complex compounds (more than 10 million of them 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 lives. By interacting with other substances, it forms new ones. Without them, the life of the surrounding world is inseparable and unthinkable. All objects consist of certain substances, so they play an important role in our lives.
About atoms and chemical elements
There is nothing else in nature
neither here nor there, in the depths of space:
everything - from small grains of sand to planets -
consists of unified elements.
S. P. Shchipachev, “Reading Mendeleev.”
In chemistry, except for terms "atom" And "molecule" the concept is often used "element". What do these concepts have in common and how do they differ?
Chemical element – these are atoms of the same type . So, for example, all hydrogen atoms are the element hydrogen; all oxygen and mercury atoms are the elements oxygen and mercury, respectively.
Currently, more than 107 types of atoms are known, that is, more than 107 chemical elements. It is necessary to distinguish between the concepts of “chemical element”, “atom” and “simple substance”
Simple and complex substances
According to their elemental composition they are distinguished simple substances, consisting of atoms of one element (H 2, O 2, Cl 2, P 4, Na, Cu, Au), and complex substances, consisting of atoms of different elements (H 2 O, NH 3, OF 2, H 2 SO 4, MgCl 2, K 2 SO 4).
Currently, 115 chemical elements are known, which form about 500 simple substances.
Native gold is a simple substance.
The ability of one element to exist in the form of various simple substances differing in properties is called allotropy For example, the element oxygen O has two allotropic forms - dioxygen O 2 and ozone O 3 with different numbers of atoms in the molecules.
Allotropic forms of the element carbon C - diamond and graphite - differ in the structure of their crystals. There are other reasons for allotropy.
chemical compounds, for example, mercury(II) oxide HgO (obtained by combining atoms of simple substances - mercury Hg and oxygen O 2), sodium bromide (obtained by combining atoms of simple substances - sodium Na and bromine Br 2).
So, let's summarize the above. There are two types of molecules of matter:
1. Simple– the molecules of such substances consist of atoms of the same type. In chemical reactions they cannot decompose to form several simpler substances.
2. Complex– the molecules of such substances consist of atoms of different types. In chemical reactions they can decompose to form simpler substances.
The difference between the concepts of “chemical element” and “simple substance”
Distinguish between concepts "chemical element" And “simple substance” possible by comparing the properties of simple and complex substances. For example, a simple substance - oxygen– a colorless gas necessary for breathing and supporting combustion. The smallest particle of the simple substance oxygen is a molecule that consists of two atoms. Oxygen is also included in carbon monoxide (carbon monoxide) and water. However, water and carbon monoxide contain chemically bound oxygen, which does not have the properties of a simple substance; in particular, it cannot be used for respiration. Fish, for example, do not breathe chemically bound oxygen, which is part of the water molecule, but free oxygen dissolved in it. Therefore, when we talk about the composition of any chemical compounds, it should be understood that these compounds do not contain simple substances, but atoms of a certain type, that is, the corresponding elements.
When complex substances decompose, atoms can be released in a free state and combine to form simple substances. Simple substances consist of atoms of one element. The difference between the concepts of “chemical element” and “simple substance” is also confirmed by the fact that the same element can form several simple substances. For example, atoms of the element oxygen can form diatomic oxygen molecules and triatomic ozone molecules. Oxygen and ozone are completely different simple substances. This explains the fact that much more simple substances are known than chemical elements.
Using the concept of “chemical element”, we can give the following definition to simple and complex substances:
Simple substances are those that consist of atoms of one chemical element.
Complex substances are those that consist of atoms of different chemical elements.
The difference between the concepts of “mixture” and “chemical compound”
Complex substances are often called chemical compounds.
Try to answer the questions:
1. How do mixtures differ in composition from chemical compounds?
2. Compare the properties of mixtures and chemical compounds?
3. In what ways can you separate the components of a mixture and a chemical compound?
4. Is it possible to judge by external signs the formation of a mixture and a chemical compound?
Comparative characteristics of mixtures and chemicals
|
Questions to match mixtures to chemical compounds |
Comparison |
|
|
Mixtures |
Chemical compounds |
|
|
How do mixtures differ in composition from chemical compounds? |
Substances can be mixed in any ratio, i.e. variable composition of mixtures |
The composition of chemical compounds is constant. |
|
Compare the properties of mixtures and chemical compounds? |
Substances in mixtures retain their properties |
Substances that form compounds do not retain their properties, since chemical compounds with other properties are formed |
|
In what ways can a mixture and a chemical compound be separated into its constituent components? |
Substances can be separated by physical means |
Chemical compounds can only be broken down through chemical reactions |
|
Is it possible to judge by external signs the formation of a mixture and a chemical compound? |
Mechanical mixing is not accompanied by the release of heat or other signs of chemical reactions |
The formation of a chemical compound can be judged by the signs of chemical reactions |
Tasks for consolidation
I. Work with simulators
II. Solve the problem
NaCl, H 2 SO 4, K, S 8, CO 2, O 3, H 3 PO 4, N 2, Fe.
Explain your choice in each case.
III. Answer the questions
№1
How many simple substances are written in a series of formulas:
H 2 O, N 2, O 3, HNO 3, P 2 O 5, S, Fe, CO 2, KOH.
№2
Both substances are complex:
A) C (coal) and S (sulfur);
B) CO 2 (carbon dioxide) and H 2 O (water);
B) Fe (iron) and CH 4 (methane);
D) H 2 SO 4 (sulfuric acid) and H 2 (hydrogen).
№3
Choose the correct statement:
Simple substances consist of atoms of the same type.
A) Correct
B) Incorrect
№4
What is typical for mixtures is that
A) They have a constant composition;
B) Substances in the “mixture” do not retain their individual properties;
C) Substances in “mixtures” can be separated by physical properties;
D) Substances in “mixtures” can be separated using a chemical reaction.
№5
The following are typical for “chemical compounds”:
A) Variable composition;
B) Substances contained in a “chemical compound” can be separated by physical means;
C) The formation of a chemical compound can be judged by the signs of chemical reactions;
D) Permanent composition.
№6
In what case are we talking about gland how about chemical element?
A) Iron is a metal that is attracted by a magnet;
B) Iron is part of rust;
C) Iron is characterized by a metallic luster;
D) Iron sulfide contains one iron atom.
№7
In what case are we talking about oxygen as a simple substance?
A) Oxygen is a gas that supports respiration and combustion;
B) Fish breathe oxygen dissolved in water;
C) The oxygen atom is part of the water molecule;
D) Oxygen is part of air.
During chemical reactions, one substance turns into another (not to be confused with nuclear reactions, in which one chemical element is converted into another).
Any chemical reaction is described by a chemical equation:
Reactants → 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 more precisely, 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 to produce one molecule of carbon dioxide and two molecules of water (water vapor).
The numbers placed before the components of a chemical reaction are called reaction coefficients.
Chemical reactions happen endothermic(with energy absorption) and exothermic(with energy release). Methane combustion is a typical example of an exothermic reaction.
There are several types of chemical reactions. The most common:
- connection reactions;
- decomposition reactions;
- single replacement reactions;
- double displacement reactions;
- oxidation reactions;
- redox reactions.
Compound reactions
In compound reactions, at least two elements form one product:
2Na (t) + Cl 2 (g) → 2NaCl (t)- formation of table salt.
Attention should be paid to an essential nuance of compound reactions: depending on the conditions of the reaction or the proportions of the reagents entering the reaction, its result may be different products. For example, under normal combustion conditions of coal, carbon dioxide is produced:
C (t) + O 2 (g) → CO 2 (g)
If the amount of oxygen is insufficient, then deadly carbon monoxide is formed:
2C (t) + O 2 (g) → 2CO (g)
Decomposition reactions
These reactions are, as it were, essentially opposite to the reactions of the compound. As a result of the decomposition reaction, the substance breaks down into two (3, 4...) simpler elements (compounds):
- 2H 2 O (l) → 2H 2 (g) + O 2 (g)- water decomposition
- 2H 2 O 2 (l) → 2H 2 (g) O + O 2 (g)- decomposition of hydrogen peroxide
Single displacement reactions
As a result of single substitution reactions, a more active element replaces a less active one in a compound:
Zn (s) + CuSO 4 (solution) → ZnSO 4 (solution) + Cu (s)
Zinc in a copper sulfate solution displaces the less active copper, resulting in the formation of a zinc sulfate solution.
The degree of activity of metals in increasing 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, breaks down into a copper cation (charge 2+) and a sulfate anion (charge 2-). As a result of the substitution reaction, a zinc cation is formed (which has the same charge as the copper cation: 2-). Please note that the sulfate anion is present on both sides of the equation, i.e., according to 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 displacement reactions
In double substitution reactions, two electrons are already replaced. Such reactions are also called exchange reactions. Such reactions take place in solution with the formation of:
- insoluble solid (precipitation reaction);
- water (neutralization reaction).
Precipitation reactions
When a solution of silver nitrate (salt) is mixed with a solution of sodium chloride, silver chloride is formed:
Molecular equation: KCl (solution) + AgNO 3 (p-p) → AgCl (s) + KNO 3 (p-p)
Ionic equation: K + + Cl - + Ag + + NO 3 - → AgCl (t) + K + + NO 3 -
Molecular ionic equation: Cl - + Ag + → AgCl (s)
If a compound is soluble, it will be present in solution in ionic form. If the compound is insoluble, it will precipitate to form a solid.
Neutralization reactions
These are reactions between acids and bases that result in the formation of water molecules.
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 (l) or H + + OH - → H 2 O (l)
Oxidation reactions
These are reactions of interaction of substances with gaseous oxygen in the air, during 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 is the reaction between methane and oxygen:
CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O (g)
Methane belongs to hydrocarbons (compounds of carbon and hydrogen). When a hydrocarbon reacts with oxygen, a lot of thermal energy is released.
Redox reactions
These are reactions in which electrons are exchanged between reactant atoms. 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
Redox reactions with a large number of examples of solving equations using the electron balance method and the half-reaction method are described in as much detail as possible in the section
Current page: 3 (book has 18 pages total) [available reading passage: 12 pages]
Scientists believe that nebulae are a stage in the formation of galaxies or large star systems. In models of these types of theories, planets are a by-product of star formation. This point of view, first expressed in the 18th century. I. Kant and later developed by P. Laplace, D. Kuiper, D. Alfven 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; Stars and associated planetary systems are believed to form within these enormous clouds of matter.
Using spectroscopy, it was shown that interstellar matter consists of gases - hydrogen, helium and neon - and dust particles, measuring on the order of several microns and consisting of metals and other elements. Since the temperature is very low (10–20 K), all matter, except for the gases mentioned, is frozen on dust particles. Heavier elements and some hydrogen come 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 gas concentration in interstellar space is only 0.1 atom N/cm 3, while the gas concentration in nebulae is approximately 1000 atoms N/cm 3, i.e. 10,000 times more. (1 cm 3 of air contains approximately 2.7 × 10 19 molecules.)
When a cloud of gas and dust becomes large enough as a result of the slow settling and adhesion (accretion) of interstellar gas and dust under the influence of gravity, it becomes unstable - the close-to-equilibrium relationship between pressure and gravitational forces is disrupted. Gravitational forces prevail and therefore the cloud contracts. During the early phases of compression, the heat released when gravitational energy is converted into radiation energy easily leaves the cloud because the relative density of the material is low. As the density of matter increases, new important changes begin. Due to gravitational and other fluctuations, a large cloud is fragmented into smaller clouds, which in turn form fragments that ultimately have a mass and size several times greater than our Solar System (Fig. 2.2; 1–5). Such clouds are called protostars. Of course, some protostars are more massive than our Solar System and form larger, hotter stars, while less massive protostars form smaller, cooler stars that evolve more slowly than the former. The size of protostars is limited by an upper limit, above which further fragmentation would occur, and a lower limit, determined by the minimum mass required to support nuclear reactions.
Rice. 2.2. Evolution of a gas-dust nebula and the formation of a protoplanetary disk
First, the potential gravitational energy, converted into heat (radiative energy), is simply radiated outward during gravitational compression. But as the density of a substance increases, more and more radiation energy is absorbed and, as a result, the temperature increases. Volatile compounds that were initially frozen onto the dust particles begin to evaporate. Now gases such as NH 3, CH 4, H 2 O (vapor) and HCN are mixed with H 2, He and Ne. These gases absorb subsequent portions of radiation energy, dissociate and undergo ionization.
Gravitational compression continues until the released radiation energy is dissipated during the evaporation and ionization of molecules in dust particles. When the molecules are completely ionized, the temperature rises rapidly until compression almost stops as the pressure of the gas begins to balance the gravitational forces. Thus, the phase of rapid gravitational compression (collapse) ends.
At this point in 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 the orbit of Jupiter. Such a protostellar disk continues to evolve: restructuring occurs in it, and it slowly contracts. The protostar itself gradually becomes more compact, more massive and hotter, since heat can now only radiate from its surface. Heat is transferred from the depths of the protostar to its surface using 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 required about 10 million years, the angular momentum of the system should be conserved. The entire galaxy rotates, making 1 revolution every 100 million years. As dust clouds compress, their angular momentum cannot change—the more they compress, the faster they rotate. Due to the conservation of angular momentum, the shape of the collapsing dust cloud changes from spherical to disk-shaped.
As the remaining matter of the protostar contracted, its temperature became high enough for the fusion reaction of hydrogen atoms to begin. With the influx of more energy from this reaction, the temperature became high enough to balance the forces of further gravitational compression.
Planets formed from the remaining gases and dust on the periphery of the protostellar disk (Fig. 2.3). Agglomeration of interstellar dust under the influence of gravitational attraction leads to the formation of stars and planets in about 10 million years (1–4). The star enters the main sequence (4) and remains in a stationary (stable) state for approximately 8000 million years, gradually processing hydrogen. The star then leaves the main sequence, expands to become a red giant (5 and 6), and “consumes” its planets over the next 100 million years. After pulsating as a variable star for several thousand years (7), it explodes as a supernova (8) and finally collapses into a white dwarf (9). Although planets are usually considered massive objects, the total mass of all planets is only 0.135% of the mass of the Solar System.
Rice. 2.3. Formation of a planetary system
Our planets, and presumably the planets formed in any protostellar disk, are located in two main zones. The inner zone, which in the 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 coated with frozen volatiles such as H 2 O, NH 3 and CH 4. This outer zone with Jupiter-type planets contains much more matter than the inner one because it is large and because much of the volatile material originally found in the inner zone is pushed outward 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 a star are known, then its absolute magnitude can be calculated, since the visible brightness of a star is inversely proportional to its distance. The absolute magnitude of the star 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 represents very hot stars, white represents hot stars, and red represents relatively cool stars.
Figure 2.4 shows the Hertzsprung-Russell diagram, familiar to you from your astronomy course, reflecting the relationship between absolute magnitude and color for a large number of stars. Because 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 stars are located on the straight 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 higher temperatures; In them, the reaction of fusion of hydrogen atoms proceeds faster, and their life expectancy is shorter. Stars with a mass less than the Sun have a lower temperature, the fusion of hydrogen atoms in them occurs more slowly, and their life expectancy is longer. Once a main sequence star has used up about 10% of its initial supply of hydrogen, its temperature will drop and expansion will occur. Red giants are believed to be “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 taking them into account show that not a single star in our galaxy is older than 11,000 million years. Some small stars are of this age; many of the bigger stars are much younger. The most massive stars can remain on the main sequence for no more than 1 million years. The Sun and stars of similar sizes spend about 10,000 million years on the main sequence before reaching the red giant stage.
Anchor points
1. Matter is in continuous movement 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 speed.
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 differences in the chemical composition of planets of the same star system?
Adhering to the above point of view on the origin of planetary systems, it is possible to make fairly reasonable estimates of the elemental composition of the Earth's primary atmosphere. Part of the modern view is, of course, based on the enormous 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 primordial Earth, which had a high average temperature, was something like this: before gravitational loss, hydrogen made up most of it, and the main molecular components were methane, water and ammonia. It is interesting to compare the elemental composition of stellar matter with the composition of modern Earth and living matter on Earth.
The most common elements in inanimate nature are hydrogen and helium; followed by carbon, nitrogen, silicon and magnesium. Let us note that the living matter of the biosphere on the surface of the Earth consists predominantly 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 made up 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 the giant planets. Much of the Earth's initial atmosphere must have been lost in a very 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 composed 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, during the gravitational heating of the earth's interior, hydrogen, methane, carbon monoxide, ammonia, water, etc. probably also appeared. These are the substances with which most experiments were carried out to simulate the primary atmosphere.
What could actually happen under the conditions of the primordial Earth? In order to determine this, it is necessary to know what types of energy most likely affected its atmosphere.
The development and transformation of matter without an influx of energy is impossible. Let us consider those energy sources 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, cooling of the reaction products and the degree of their shielding from energy sources.
Apparently, any energy sources (Table 2.3) had a significant impact on the transformation of substances on our planet. How did this happen? Of course, objective evidence simply does not exist. However, the processes that took place on our Earth in ancient times can be simulated. Firstly, it is necessary to determine the time boundaries, and secondly, to reproduce as accurately as possible the conditions in each of the discussed eras of the planet’s existence.
To discuss questions about the origin of life on Earth, in addition to knowledge of 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 for some elements used in determining the age of the Earth
The development of physical sciences has now provided biologists with several effective methods for determining the age of certain rocks of the earth's crust. The essence of these methods is to analyze the ratio of various isotopes and final products of nuclear decay in samples and correlate the research results with the time of fission of the original elements (Table 2.4).
The use of such methods allowed scientists to construct a time scale of the history of the Earth from the moment of its cooling, 4500 million years ago, to the present (Table 2.5). Our task now is to establish, within this time scale, what conditions were like on the primitive Earth, what kind of atmosphere the Earth had, what the temperature and pressure were like, when the oceans formed, and how the Earth itself was formed.
Table 2.5. Geochronological scale
Today, recreating the conditions in which the first “embryos 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 primordial Earth.
In 1953, American scientists G. Urey and S. Miller exposed a mixture of methane, ammonia and water to 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 resulting products.
The experiments of Miller and Urey stimulated research into molecular evolution and the origin of life in many laboratories and led to systematic study of the problem, during which biologically important compounds were synthesized. The main conditions on the primitive Earth taken into account by 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 very arbitrary.
Calculations that take into account the greenhouse effect, as well as the approximate intensity of solar radiation in the abiotic era, 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 established not by calculation or extrapolation of certain geological data, but most likely by taking into account the temperature limits of stability of organic compounds.
The use of mixtures of gases 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 , find evidence for pathways of abiotic occurrence of organic molecules such as aldehydes, nitrites, amino acids, monosaccharides, purines, porphyrins, nucleotides, etc.
Rice. 2.5. Miller apparatus
Table 2.6. Conditions on primitive Earth
The emergence of protobiopolymers poses a more complex problem. The need for 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 others, more complex, for example photochemical reactions, photophosphorylation, photosynthesis and etc.
The presence of water on our planet (primary ocean) made it possible for protobiopolymers to arise in the process of a chemical reaction - condensation. Thus, for the formation of a peptide bond in aqueous solutions according to the reaction:
energy expenditure is required. These energy costs increase many times when producing protein molecules in aqueous solutions. The synthesis of macromolecules from “biomonomers” requires the use of specific (enzymatic) methods for removing water.
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 maintain liquid water.
3. In aqueous solutions, due to various energy sources, the simplest organic compounds arise non-biologically.
Review questions and assignments
1. List the cosmic and planetary prerequisites for the emergence of life abiogenically on our planet.
2. What significance did the reducing nature of the primary atmosphere have for the emergence of organic molecules from inorganic substances on Earth?
3. Describe the apparatus and methods of conducting experiments by S. Miller and P. Urey.
Using the vocabulary of the “Terminology” and “Summary” headings, translate the paragraphs of “Anchor Points” into English.
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 of the origin of protobiopolymersIssues for discussion
What do you think were the dominant energy sources on ancient Earth? How can we explain the nonspecific influence of various energy sources on the processes of formation of organic molecules?
Different assessments of the nature of the environment on the primitive Earth led to the creation of different experimental conditions that had fundamentally uniform, but not always identical 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 to other components of living matter, the synthesis of polypeptides is the most well studied.
The author of the hypothesis of the synthesis of polypeptides by thermal means is the American scientist S. Fox, who for a long time studied the possibilities of the formation of peptides 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 monomers are connected by peptide bonds, as well as small amounts of polypeptides are formed. In cases where experimenters enriched the initial mixtures of amino acids with acidic or basic amino acids, 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 is Dalton, a unit of mass measurement 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 with a complex structure, the formation of currently known nucleic acids and polysaccharides seems unlikely.
Adsorption theory. The main counterargument in the debate about the abiogenic origin 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 “primary broth” 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 ensure 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 through “their adsorption in aqueous clay deposits.”
As a result of the interaction of substances during the adsorption process, 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, Romanian scientists C. Simonescu and F. Denes, proceeded from slightly different ideas about the conditions for the abiogenic occurrence of the simplest organic compounds and their condensation into polymer structures. The authors attach leading importance to the energy of cold plasma as an energy source. This opinion is not unfounded.
Cold plasma is widespread in nature. Scientists believe that 99% of the Universe is in a plasma state. This state of matter also occurs on modern Earth in the form of ball lightning, auroras, and also a special type of plasma - the ionosphere.
Regardless of the nature of energy on the abiotic Earth, any type of energy converts chemical compounds, especially organic molecules, into active species, such as mono- and polyfunctional free radicals. However, their further evolution largely depends on the energy flux density, 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 were able to obtain both individual monomers and peptide-type polymer structures and lipids.
Oparin believed that the transition from chemical evolution to biological required the obligatory emergence of individual phase-separated systems capable of interacting with the surrounding external environment, using its substances and energy, and on this basis capable of growing, multiplying and being subject to 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-lived in the presence of microbes that destroy all living things. Therefore, to understand this stage of the origin of life, it is necessary to artificially obtain phase-separated organic systems under strictly controlled laboratory conditions and, using the models thus formed, to establish both the paths of their possible evolution in the past and the patterns of this process. When working with high-molecular organic compounds in laboratory conditions, we constantly encounter the formation of this kind of phase-separated systems. Therefore, we can imagine the ways of their occurrence and experimentally obtain various systems in laboratory conditions, many of which could serve us as models of formations that once appeared on the earth’s surface. For example, we can name some of them: "bubbles" Goldacre, "microspheres" Fox, "jayvan" Bahadura, "probionts" Egami and many others.
Often, when working with such artificial systems that self-isolate from solution, special attention is paid to their external morphological similarity to 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 regard are coacervate drops.
Each molecule has a certain structural organization, that is, the atoms that make up its composition are regularly 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 a negative charge (-). In addition, some molecules (for example, salts) dissociate into ions in an aqueous environment. Due to these features of the chemical organization of molecules around them in water, water “shirts” are formed from water molecules oriented in a certain way. Using the example of the NaCl molecule, you can notice that the water dipoles surrounding the Na + ion have negative poles facing it (Fig. 2.6), and positive poles are facing the Cl − ion.
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 aqueous 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 drops also arise from simple mixing of various polymers, both natural and artificially obtained. In this case, self-assembly of polymer molecules occurs into multimolecular phase-separated formations - droplets visible under an optical microscope (Fig. 2.8). The majority of polymer molecules are concentrated in them, while the environment is almost completely devoid of them.
Drops are separated from the environment by a sharp interface, but they are capable of absorbing substances from outside like open systems.
Rice. 2.8. Coacervate drops obtained in the experiment
By incorporating various catalysts(including enzymes) can 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 split into daughter formations.
For example, the processes occurring in a coacervate drop are depicted in square brackets, and substances located in the external environment are placed outside them:
glucose-1-phosphate → [glucose-1-phosphate → starch → maltose] → maltose
A coacervate droplet 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 into starch in it under the action of a catalyst, phosphorylase. Due to the formed starch, the drop grows, which can be easily determined both by chemical analysis and by direct microscopic measurements. If another catalyst, b-amylase, is included in the drop, starch breaks down to maltose, which is released into the external environment.
Thus, the simplest metabolism. The substance enters the drop, polymerizes, causing height system, and when it decays, the products of this decay come out into the external environment, where they were not previously present.
Another diagram illustrates an experiment where the polymer is a polynucleotide. A droplet consisting of histone protein and gum arabic is surrounded by an ADP solution.
Entering the drop, ADP polymerizes 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 + F] → F
In this case, the drop more than doubles in volume within a short period of time.
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 droplets occurred. In another series of experiments by Academician A.I. Oparin and his colleagues, it was demonstrated that reactions associated with energy dissipation can also occur in the coacervate droplets themselves.
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