PUBLIC LESSON
"ORIGIN OF LIFE ON EARTH
Goals: 1. To give knowledge about the origin of life on Earth.
2. Formation of a scientific outlook and a sense of patriotism among students.
3. Develop skills independent work and responsibility.
Testing for the lesson: "The origin of life on Earth"
1. Where did the first inorganic compounds originate?
a) in the bowels of the Earth;
b) in the primary ocean;
c) in the primary atmosphere.
2. What was the prerequisite for the emergence of the primary ocean?
a) cooling of the atmosphere;
b) sinking land;
c) the appearance of underground sources.
3. What were the first organic substances that arose in the waters of the ocean?
a) proteins;
b) fats;
c) carbohydrates;
d) nucleic reactions.
4. What properties did coacervates have?
a) growth;
b) metabolism;
c) reproduction.
5. Louis Pasteur proved with his experiments:
a) spontaneous generation of life is possible;
b) the impossibility of spontaneous generation of life.
Lesson topic: Evolutionary doctrine
Lesson Objectives:
1. Acquaintance of students with the principles of historicism in the development of evolutionary ideas.
2. Formation of knowledge about evolution
3. Formation of a scientific worldview among students
Lesson plan
Introducing students to the history of the evolutionary process
Evolutionary hypotheses J.B. Lamarck
Presentation of the evolutionary teachings of Ch. Darwin
Equipment: portraits of J.B. Lamarck, C. Darwin.
During the classes
1. Repetition of what has been learned:
– What levels of organization of life did you learn in the last lesson?
– What does the subject study? General biology»?
2. Study new topic:
At present, about 3.5 million species of animals and 600 thousand plants, 100 thousand fungi, 8 thousand bacteria and 800 types of viruses are known to science. And together with the extinct ones, in the entire history of the Earth, at least 1 billion species of living organisms lived on it.
–I just told you the word "species" - what does it mean?
– You studied plants and animals, name 5 types of each?
– How did such a variety of species come about?
– Can someone say that they are created by God? Others find the answer in scientific theory
evolution of living nature.
When studying the evolutionary doctrine, there is a need to consider it in development.
How did this doctrine develop?
Let's analyze the very concept of "Evolution" - (latevolution - deployment ). It was first used in biology by the Swiss naturalist C. Bonnet. Close to this word in sound isrevolution.
You know this word. What does it mean?
Revolution - a radical change, an abrupt transition from one state to another.
Evolution - gradual continuous adaptation of living things to constant changes in conditions environment.
Evolution is a process historical development organic world.
In the Middle Ages, with the establishment of the Christian Church in Europe, an official point of view based on biblical texts spread: all living things were created by God and remain unchanged. He created them in pairs, so they live expediently from the very beginning. That is, they were created for a purpose. Cats are made to catch mice, and mice are made to be eaten by cats. Despite the dominance of views on the immutability of species, interest in biology increased already in the 17th century. The ideas of evolution begin to be traced in the works of G.V. Leibniz. The development of evolutionary views arises in the 18th century, which are developed by J. Buffon, D. Diderot. Then there are doubts about the immutability of species, which lead to the emergence of the theorytransformism - proof of the natural transformation of wildlife. Adherents are: M.V. Lomonosov, K.F. Wolf, E.J. Saint Hilaire.
By the end of the 18th century. In biology, a huge amount of material has accumulated, where you can see:
Even outwardly distant species show certain similarities in their internal structure.
Modern views different from fossils that have long lived on Earth.
The appearance, structure and productivity of agricultural plants and animals change significantly with changes in their growing conditions.
The ideas of transformism were developed by J.B. Lamarck created the evolutionary concept of the development of nature. His evolutionary idea is carefully developed, supported by facts and therefore turns into a theory. It is based on the idea of development, gradual and slow, from simple to complex, and of the role of the external environment in the transformation of organisms.
J.B. Lamarck (1744-1829) - the creator of the first evolutionary doctrine, also, as you already know, introduced the term "biology". He published his views on the development of the organic world in the book Philosophy of Zoology.
1. In his opinion, evolution proceeds on the basis of the internal desire of organisms for progress and perfection, which is the main driving force. This mechanism is inherent in every living organism.
2. The law of direct adaptation. Lamarck recognizes that the external environment has an impact on living organisms. Lamarck believed that the reaction to changes in the external environment is an adaptive adaptive response to changes in the external environment (temperature, moisture, light, nutrition). He, like all his contemporaries, believed that changes arising under the influence of the environment can be inherited. As an example, we give the plant Arrowleaf. At the arrowhead in the water, the leaves form a ribbon-like leaf, on the surface of the water - a floating rounded one, and in the air - an arrow-shaped one.
3. "The law of exercise and non-exercise of the organs." The emergence of new signs in evolution, Lamarck imagined as follows, after a change in conditions, a change in habits immediately follows. As a result, organisms develop useful habits and begin to exercise some organs that they did not use before. He believed that increased exercise of the organs leads to their increase, and non-exercise leads to degeneration. On this basis, Lamarck formulates the law of exercise and non-exercise. For example, the giraffe's long legs and neck are a hereditarily fixed change associated with the constant use of these body parts when obtaining food. Thus, coastal birds (heron, crane, stork), reluctant to swim, but forced to live near water in search of food, are constantly in danger of sinking into silt. To avoid this, they make every effort to stretch and lengthen their legs as much as possible. The constant exercise of the organs by force of habit, directed by the will of the animal, leads to its evolution. In a similar way, in his opinion, all special adaptations in animals develop: this is the appearance of horns in animals, the lengthening of the tongue of an anteater.
4. "The law of inheritance of acquired characteristics." According to this “law”, beneficial changes are passed on to offspring. But most examples from the life of living organisms cannot be explained from the standpoint of Lamarck's theory.
Conclusion: Thus, Zh.B. Lamarck was the first to offer a detailed concept of transformism - the variability of species.
The evolutionary doctrine of Lamarck was not sufficiently demonstrative and did not receive wide recognition among his contemporaries.
The greatest evolutionary scientist is Charles Robert Darwin (1809-1882).
3. Report - information about Ch. Darwin
In the first half of the 19th century England became the most advanced capitalist country, with high level industrial development and Agriculture. Livestock breeders have achieved exceptional success in breeding new breeds of sheep, pigs, cattle, horses, dogs, and chickens. Plant breeders obtained new varieties of grain, vegetable, ornamental, berry and fruit crops. These achievements clearly showed that animals and plants change under the influence of man.
Great geographical discoveries, enriching the world with information about new species of plants and animals, special people from overseas countries.
The sciences are developing: astronomy, geology, chemistry, botany and zoology have been significantly enriched with knowledge about plant and animal species.
Darwin was born at such a historic moment.
C. Darwin was born on February 12, 1809 in English city Shrewsbury in the family of a doctor. WITH early years he developed an interest in communicating with nature, in observing plants and animals in their natural habitat. Deep observation, passion for collecting and systematizing material, ability for comparisons and broad generalizations, philosophical thinking were natural properties personalities of Ch. Darwin. After graduating from high school, he studied at Edinburgh and Cambridge Universities. During that period, he met famous scientists: geologist A. Sedgwick and botanist J. Genslow, who contributed to the development of his natural abilities, introduced him to the methodology of field research.
Darwin was with the evolutionary ideas of Lamarck, Erasmus Darwin and other evolutionists, but they did not seem convincing to him.
The turning point in Darwin's biography was his journey (1831-1836) as a naturalist on the Beagle. During the trip, he collected a lot of factual material, the generalization of which led to conclusions that led to preparations for a sharp revolution in his worldview. Darwin returns to England a convinced evolutionist.
Upon returning to his homeland, Darwin settled in the countryside, where he spent his entire life. For 20 years. A long period of development of a coherent theory of evolution based on an autopsy beginsmechanism of the evolutionary process .
Finally 1859. Darwin's book "The Origin of Species by Means of Natural Selection" was published
Its edition (1250 copies) was sold out in one day, a case surprising in the book trade of that time.
In 1871 saw the light of the third fundamental work - "The Origin of Man and Sexual Selection", which completed the trilogy of Darwin's main works on the theory of evolution.
Darwin's whole life was devoted to science and was crowned with achievements that were included in the fund of the largest generalizations of natural science.
The great scientist died on April 19, 1882, and was buried next to poison with Newton's grave.
TEACHER CONTINUED
Darwin's discovery of the theory of evolution took society by surprise. One of his friends, very offended by the fact that he was equated with monkeys, sent him a message: "Your former friend, now a descendant of a monkey."
In his work, Darwin showed that the species that exist today naturally evolved from other more ancient species.
Expediency - observed in wildlife, it is the result of natural selection of features useful for the body.
MAIN PROVISIONS OF THE THEORY OF EVOLUTION
All types Living creaturesnever been created by anyone
Species having arisen , naturallygradually transformed and improved
At the heart of the transformation speciesvariability, heredity, natural selection
The result of evolution is the adaptability of organisms to living conditions (environment) and the diversity of species in nature.
4 . FIXING :
Work on cards - tasks and their verification.
I appoint one responsible student in each row who distributes task cards. Students complete assignments. Responsible collects and checks on answers and marks. Which we will discuss in the next lesson.
Conclusion :
The driving forces (factors) of evolution (according to Darwin) are the struggle for existence and natural selection based on hereditary variability.
C. Darwin created the theory of evolution, which was capable of answering the most important questions: about the factors of the evolutionary process and the reasons for the adaptation of living beings to the conditions of existence. Darwin had time to see the victory of his theory; his popularity during his lifetime was enormous.
Testing for the lesson: Evolutionary doctrine.
1. The result of evolution were:
A - artificial and natural selection;
B - hereditary variability;
B - adaptation of organisms to the environment;
G - variety of species.
2. Who created a holistic theory of evolution:
A - Ruler;
B - Lamarck;
B - Darwin
3 . main factor, main driving force evolution process:
A - mutational variability;
B - struggle for existence;
B - natural selection;
G - modification variability.
4. Modern species of animals and plants are not created by God, they originated from the ancestors of animals and plants through evolution. Species are not eternal, they have changed and are changing. What scientist was able to prove this?
A-Lamarck;
B - Darwin,
V-Linnaeus;
G-Timiryazev;
D-Rulie.
5. The driving and guiding force of evolution is:
A - divergence of signs;
B - variety of environmental conditions;
B - adaptability to environmental conditions;
D - natural selection of hereditary changes.
The situation was different on the surface of the Earth.
Here, the initially formed hydrocarbons must necessarily enter into chemical interaction with the substances surrounding them, primarily with the water vapor of the earth's atmosphere. Hydrocarbons are fraught with enormous chemical possibilities. Numerous studies by a number of chemists, in particular the work of the Russian academician A. Favorsky and his school, show the exceptional ability of hydrocarbons to various chemical transformations. Of particular interest to us is the ability of hydrocarbons to relatively easily attach water to themselves. There is no doubt that those hydrocarbons that originally arose on the earth's surface, in their main mass, should have combined with water. As a result of this, in earth's atmosphere new substances were formed. Previously, hydrocarbon molecules were built from only two elements: carbon and hydrogen. But in addition to hydrogen, water also contains oxygen. Therefore, the molecules of newly emerged substances already contained atoms of three different elements - carbon, hydrogen and oxygen. Soon they were joined by another fourth element - nitrogen.
In the atmosphere of large planets (Jupiter and Saturn), we, along with hydrocarbons, can always detect another gas - ammonia. This gas is well known to us, since its solution in water forms what we call ammonia. Ammonia is a compound of nitrogen and hydrogen. This gas was also found in significant quantities in the Earth's atmosphere during the period of its existence, which we are now describing. Therefore, hydrocarbons entered into combination not only with water vapor, but also with ammonia. In this case, substances arose, the molecules of which were already built from four different elements - carbon, hydrogen, oxygen and nitrogen.
Thus, at the time we are describing, the Earth was a bare rocky ball, enveloped from the surface with an atmosphere of water vapor. In this atmosphere, in the form of gases, there were also those various substances that were obtained from hydrocarbons. We can rightfully call these substances organic substances, although they arose long before the first living beings appeared. In their structure and composition, they were similar to some of the chemical compounds that can be isolated from the bodies of animals and plants.
The earth was gradually cooling down, giving off its heat to the cold interplanetary space. Finally, the temperature of its surface approached 100 degrees, and then the water vapor of the atmosphere began to condense into drops and rushed in the form of rain onto the hot desert surface of the Earth. Powerful showers poured onto the Earth and flooded it, forming a primary boiling ocean. The organic substances in the atmosphere were also carried away by these showers and passed into the waters of this ocean.
What was to happen to them next? Can we reasonably answer this question? Yes, at the present time we can easily prepare these or similar substances, artificially obtain them in our laboratories from the simplest hydrocarbons. Let us take an aqueous solution of these substances and let it stand at a more or less high temperature. Will these substances then remain unchanged, or will they undergo various kinds of chemical transformations? It turns out that even in those short periods during which we can conduct our observations in laboratories, organic substances do not remain unchanged, but are converted into other chemical compounds. Direct experience shows us that in this kind of aqueous solutions organic matter there are so numerous and varied transformations that it is even difficult to describe them briefly. But the main general direction of these transformations is that relatively simple small molecules of primary organic substances are combined with each other in a thousand ways and thus form more and more large and complex molecules.
To clarify, I will give here only two examples. Back in 1861, our famous compatriot, chemist A. Butlerov, showed that if you dissolve formalin in lime water and leave this solution to stand in a warm place, then after a while it will acquire a sweet taste. It turns out that under these conditions, six formalin molecules combine to form one larger, more complex sugar molecule.
The oldest member of our Academy of Sciences, Alexei Nikolaevich Bakh, left an aqueous solution of formalin and potassium cyanide standing for a long time. In this case, even more complex substances were formed than those of Butlerov. They possessed huge molecules and in their structure approached proteins, the main constituent substances of any living organism.
There are dozens and hundreds of such examples. They undoubtedly prove that the simplest organic substances in the aquatic environment can easily be converted into much more complex compounds such as sugars, proteins and other substances from which the bodies of animals and plants are built.
The conditions that were created in the waters of the primordial hot ocean differed little from the conditions reproduced in our laboratories. Therefore, at any point in the ocean of that time, in any drying puddle, the same complex organic substances that were obtained by Butlerov, Bach and in the experiments of other scientists should have been formed.
So, as a result of the interaction between water and the simplest derivatives of hydrocarbons, through a series of successive chemical transformations, the waters of the primordial ocean formed the material from which all living beings are currently built. However, this was only construction material. In order for living beings - organisms to arise, this material had to acquire the necessary structure, a certain organization. So to speak, it was only brick and cement with which to build a building, but it is not the building itself.
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Option 1
Part A
1.
b) the presence of catalysts;
d) metabolic processes.
2.
a) anaerobic heterotrophs;
b) aerobic heterotrophs;
c) autotrophs;
d) symbiont organisms.
3. To such common property alive, as self-regulation, refers to:
a) heredity;
b) variability;
c) irritability;
d) ontogeny.
4. The essence of the theory of abiogenesis is:
c) the creation of the world by God;
5. The crystal is not a living system, because:
a) he is incapable of growth;
c) he is not characterized by irritability;
6. The experiments of Louis Pasteur proved the possibility:
a) spontaneous generation of life;
d) biochemical evolution.
7.
a) radioactivity;
b) presence liquid water;
c) the presence of gaseous oxygen;
d) the mass of the planet.
8. Carbon is the basis of life on Earth, because He:
9. Eliminate excess:
a) 1668;
b) F. Redi;
c) meat;
d) bacteria.
10.
a) L. Pasteur;
b) A. Levenguk;
c) L. Spallanzani;
d) F. Redi.
Part B
Complete the sentences.
1. The theory postulating the creation of the world by God (Creator) - ... .
2. Pre-nuclear organisms that do not have a nucleus limited by a shell and organelles capable of self-reproduction - ....
3. A phase-separated system interacting with the external environment by type open system, – … .
4. The Soviet scientist who proposed the coacervate theory of the origin of life, - ... .
5. The process by which an organism acquires a new combination of genes is ....
Part B
Give short answers to the following questions.
1. What are the common features of living and non-living matter?
2. Why, when the first living organisms appeared in the Earth's atmosphere, there had to be no oxygen?
3. What was Stanley Miller's experience? What corresponded to the "primary ocean" in this experience?
4. What is the main problem of the transition from chemical to biological evolution?
5. List the main provisions of the theory of A.I. Oparin.
Option 2
Part A
Write down the numbers of the questions, next to them write down the letters of the correct answers.
1. Living differs from non-living:
a) composition inorganic compounds;
c) interaction of molecules with each other;
d) metabolic processes.
2. The first living organisms on our planet were:
a) anaerobic heterotrophs;
b) aerobic heterotrophs;
c) autotrophs;
d) symbiont organisms.
3.
a) metabolism;
b) reproduction;
c) irritability;
d) ontogeny.
4. The essence of the theory of biogenesis is:
a) the origin of the living from the non-living;
b) the origin of the living from the living;
c) the creation of the world by God;
d) bringing life from space.
5. A star is not a living system, because:
a) it is not capable of growth;
c) she does not have irritability;
6.
a) spontaneous generation of life;
b) the appearance of the living only from the living;
c) bringing "seeds of life" from the Cosmos;
d) biochemical evolution.
7. Of these conditions, the most important for the emergence of life is:
a) radioactivity;
b) the presence of water;
c) the presence of an energy source;
d) the mass of the planet.
8. Water is the basis of life, because:
a) is a good solvent;
d) has all of the above properties.
9. Eliminate excess:
a) 1924;
b) L. Pasteur;
c) meat broth;
d) bacteria.
10. Arrange the following names in logical order:
a) L. Pasteur;
b) S. Miller;
c) J. Haldane;
d) A.I. Oparin.
Part B
Complete the sentences.
1. The process of formation by living organisms of organic molecules from inorganic ones due to energy sunlight – … .
2. Precellular formations that possessed some properties of cells (the ability to metabolism, self-reproduction, etc.) - ....
3. Separation of a protein solution containing other organic substances into phases with a greater or lesser concentration of molecules - ....
4. English physicist, who suggested that adsorption was one of the stages of concentration of organic substances in the course of prebiological evolution - ... .
5. The system of recording hereditary information in DNA molecules in the form of a sequence of nucleotides, characteristic of all living organisms, is ....
Part B
1. What was Stanley Miller's experience? What corresponded to "lightning" in this experiment?
2. Why should the mass of a planet on which life can arise be no more than 1/20 of the mass of the Sun?
3. To what stage of the development of life on Earth can the words of the Gogol hero be attributed: “I don’t remember the number. There was no month either. What the hell was that?”
4. What conditions are necessary for the origin of life?
5. What is panspermia? Which scientists you know adhered to this theory?
Option 3
Part A
Write down the numbers of the questions, next to them write down the letters of the correct answers.
1. Living differs from non-living:
a) the composition of inorganic compounds;
b) the ability to self-reproduce;
c) interaction of molecules with each other;
d) metabolic processes.
2. The first living organisms on our planet were:
a) anaerobic heterotrophs;
b) aerobic heterotrophs;
c) autotrophs;
d) symbiont organisms.
3. Such a general property of the living as self-renewal includes:
a) metabolism;
b) reproduction;
c) irritability;
d) ontogeny.
4. The essence of creationism is:
a) the origin of the living from the non-living;
b) the origin of the living from the living;
c) the creation of the world by God;
d) bringing life from space.
5. The river is not a living system because:
a) it is not capable of growth;
b) it is not capable of reproduction;
c) she is not capable of irritability;
d) not all properties of the living are inherent in it.
6. The experience of Francesco Redi proved the impossibility:
a) spontaneous generation of life;
b) the appearance of the living only from the living;
c) bringing "seeds of life" from outer space;
d) biochemical evolution.
7. Of these conditions, the most important for the emergence of life is:
a) radioactivity;
b) the presence of water;
c) an infinitely long time of evolution;
8. During the emergence of life in the Earth's atmosphere, there should have been no oxygen, because:
a) it is an active oxidizing agent;
b) has a high heat capacity;
c) increases its volume when it freezes;
d) all of the above combined.
9. Eliminate excess:
a) 1953;
b) bacteria;
c) S. Miller;
d) abiogenic synthesis.
10.
a) L. Pasteur;
b) F. Redi;
c) L. Spallanzani;
d) A.I. Oparin.
Part B
Complete the sentences.
1. The formation of organic molecules from inorganic outside living organisms - ....
2. Bubbles of liquid surrounded by protein films, arising from the shaking of aqueous solutions of proteins, - ....
3. The ability to reproduce biological systems similar to itself, which manifests itself at all levels of the organization of living matter, is ... .
4. An American scientist who proposed a thermal theory of the origin of protobiopolymers, - ... .
5. Protein molecules that accelerate the course of biochemical transformations in aqueous solutions at atmospheric pressure, – … .
Part B
Give a short answer to the question.
1. What is the main difference between burning wood and "burning" glucose in cells?
2. What are the three modern points of view on the problem of the origin of life?
3. Why is carbon the basis of life?
4. What was Stanley Miller's experience?
5. What are the main stages of chemical evolution?
Option 4
Part A
Write down the numbers of the questions, next to them write down the letters of the correct answers.
1. Living differs from non-living:
a) the composition of inorganic compounds;
b) the ability to self-regulate;
c) interaction of molecules with each other;
d) metabolic processes.
2. The first living organisms on our planet were:
a) anaerobic heterotrophs;
b) aerobic heterotrophs;
c) autotrophs;
d) symbiont organisms.
3. Such a general property of the living as self-reproduction includes:
a) metabolism;
b) reproduction;
c) irritability;
d) ontogeny.
4. The essence of the theory of panspermia is:
a) the origin of the living from the non-living;
b) the origin of the living from the living;
c) the creation of the world by God;
d) bringing to Earth the "seeds of life" from the Cosmos.
5. The glacier is not a living system because:
a) he is incapable of growth;
b) he is not capable of reproduction;
c) he is not capable of irritability;
d) not all the properties of a living thing are inherent in it.
6. The experience of L. Spallanzani proved the impossibility:
a) spontaneous generation of life;
b) the appearance of the living only from the living;
c) bringing "seeds of life" from the Cosmos;
d) biochemical evolution.
7. Of these conditions, the most important for the emergence of life is:
a) radioactivity;
b) the presence of water;
c) the presence of certain substances;
d) a certain mass of the planet.
8. Carbon is the basis of life, because He:
a) is the most common element on Earth;
b) the first of the chemical elements began to interact with water;
c) has a small atomic weight;
d) is able to form stable compounds with double and triple bonds.
To be continued
The process of formation by living organisms of organic molecules from inorganic ones due to energy
The initial substances of photosynthesis - carbon dioxide and water on the earth's surface are neither oxidizing agents nor reducing agents. In the course of photosynthesis, this “neutral environment” splits into opposites: a strong oxidizing agent arises - free oxygen and strong reducing agents - organic compounds (outside plant organisms, the decomposition of carbon dioxide and water is possible only at high temperatures, for example, in magma or in blast furnaces, etc.). d.).
Carbon and hydrogen of organic compounds, as well as free oxygen released during photosynthesis, were “charged” with solar energy, rose to a higher energy level, and became “geochemical accumulators”.
Carbohydrates and other products of photosynthesis, moving from leaves to stems and roots, enter into complex reactions, during which the whole variety of organic compounds of plants is created.
However, plants are composed not only of carbon, hydrogen and oxygen, but also of nitrogen, phosphorus, potassium, calcium, iron and other chemical elements, which they receive in the form of relatively simple mineral compounds from the soil or water bodies.
Absorbed by plants, these elements are incorporated into complex energy-rich organic compounds (nitrogen and sulfur into proteins, phosphorus into nucleoproteins, etc.) and also become geochemical accumulators.
This process is called biogenic accumulation of mineral compounds. Thanks to biogenic accumulation, elements from water and air pass into a less mobile state, i.e., their migration ability decreases. All other organisms - animals, the vast majority of microorganisms and chlorophyll-free plants (for example, fungi) are heterotrophs, i.e. they are not able to create organic substances from minerals.
Organic compounds necessary for building their body and as a source of energy, they receive from green plants.
The process of photosynthesis proceeds in unity with the work of the root system, which supplies water and nutrients to the leaf.
There are a number of hypotheses that explain the mechanism of ion entry through the root system: by diffusion, adsorption, metabolic transport of substances against electrochemical gradient. All hypotheses are based on the statement about the exchange of ions between the root system and the soil. In this case, the root system, like the leaf, is a synthesis laboratory. Plants through the root system primarily absorb those chemical elements that perform essential functions in the body.
Other elements penetrate mechanically according to their concentration gradient. Simultaneously with the release of nutrients, various metabolic products are released into the soil by the root system. Among them, organic acids (citric, malic, oxalic, etc.) perform an important function.
As a result of dissociation, hydrogen ions are released, which acidify the reaction of the soil, thereby accelerating the dissolution of minerals, and chemical elements are released for plant nutrition.
Other metabolic products are used during the life of certain types of microorganisms, which are also involved in the destruction of minerals.
Cations and anions that enter plants through the root system are distributed in organs and tissues, enter organic and mineral compounds, perform various physiological functions: maintain osmotic pressure, alkaline-acid balance, are used as a plastic material, an integral part of enzymes, chlorophyll and etc. During the metabolic process continuing education acid compounds.
During the breakdown of carbohydrates, pyruvic and lactic acids are formed, with the breakdown of fatty acids - butyric, acetoacetic, and with the breakdown of proteins - sulfuric and phosphoric. Excessive accumulation of acids is neutralized by buffer compounds, which convert them into compounds that are easily removed from the body.
The synthesis of organic matter proceeds not only through the use of the radiant energy of the sun by green plants.
Bacteria are known that use for this purpose the energy released during the oxidation of certain inorganic compounds (In 1890
S.P. Vinogradsky discovered microorganisms capable of oxidizing ammonia to salts of nitrous and then nitric acids). This process of creating organic substances is called chemosynthesis. Chemosynthetic bacteria are typical autotrophs; independently synthesize the necessary organic compounds (carbohydrates, proteins, lipids, etc.) from inorganic substances. The most important group of chemosynthetic microorganisms is nitrifying bacteria.
They oxidize the ammonia formed during the decay of organic residues to nitric acid. Chemosynthetic bacteria include sulfur-, iron-, methane-, carbon-bacteria, etc. For example, swamp iron ore is often found in floodplain soils in the form of solid nodules of various shapes and sizes; it is formed with the participation of iron bacteria.
Under the action of iron bacteria, ferrous iron is converted into oxide. The resulting iron hydroxide precipitates and forms bog iron ore.
V.G. SMELOVA,
biology teacher
MOU secondary school No. 7, Noyabrsk
Ending. See No. 9/2006
Control work on the topic:
"The Origin of Life on Earth"
9. Eliminate excess:
a) DNA;
b) genetic code;
c) chromosome;
d) cell membrane.
Test on the topic: Hypotheses of the origin of life on Earth
Arrange the following names in logical order:
a) A.I. Oparin;
b) L. Pasteur;
c) S. Miller;
d) J. Haldane.
Part B
Complete the sentences.
1. Organisms with a limited shell of the nucleus, having self-reproducing organelles, internal membranes and cytoskeleton, - ....
The system of recording hereditary information in DNA molecules in the form of a sequence of nucleotides, characteristic of all organisms, is ....
3. The ability to reproduce biologically similar systems, which manifests itself at all levels of the organization of living matter, is ... .
The creators of the low-temperature theory of the origin of protobiopolymers - ... .
5. Pre-cellular formations that possessed some properties of cells: the ability to metabolism, self-reproduction, etc., - ....
Part B
Give a short answer to the question.
1. What role did the study of meteorites play in the development of the theory of the origin of life?
2. What is racemization and chirality?
Why was water in the liquid phase a necessary condition for the origin of life?
4. What was Stanley Miller's experience? What was the gas composition of the "atmosphere"?
5. What are the main stages of studying the question of the origin of life on Earth?
Answers
Option 1
Part A: 1d, 2a, 3c, 4a, 5d, 6b, 7b, 8d, 9d, 10d,b,c,a.
Part B: 1 - creationism; 2 - prokaryotes; 3 - coacervate; 4 - A.I.
Oparin; 5 - sexual process.
Part B.
1. Living and non-living matter consist of the same chemical elements, physical and chemical processes with their participation proceed according to general laws.
Oxygen is a strong oxidizing agent and all newly formed organic molecules would be immediately oxidized.
3.
The "primary ocean" in this experiment corresponded to a flask with boiling water.
4. The main problem of the transition from chemical to biological evolution is to explain the emergence of self-reproducing biological systems (cells) in general and the genetic code in particular.
The main provisions of Oparin's theory:
– life is one of the stages of the evolution of the Universe;
– the emergence of life is a natural result of the chemical evolution of carbon compounds;
- for the transition from chemical to biological evolution, the formation and natural selection of integral, isolated from the environment, but constantly interacting with it, multimolecular systems are necessary.
Option 2
Part A: 1b,d, 2a, 3b, 4b, 5d, 6a, 7b, 8d, 9a, 10a,d,c,b.
Part B: 1 - photosynthesis; 2 - protobionts; 3 - coacervation; 4 - J. Bernal; 5 - genetic code.
Part B.
1. In 1953, S. Miller created an experimental setup in which the conditions of the primary Earth were simulated and molecules of biologically important organic compounds were obtained by abiogenic synthesis. "Lightning" in this experiment was imitated by high-voltage electric discharges.
2. If the mass of the planet is more than 1/20 of the mass of the Sun, intense nuclear reactions begin on it, which raises its temperature, and it begins to glow with its own light.
3. To the initial stage of the biochemical evolution of the Earth.
4. For the emergence of life, the following basic conditions are necessary:
- the presence of certain chemical substances(including water in the liquid phase);
– availability of energy sources;
- restorative atmosphere.
Additional conditions may be the mass of the planet and a certain level of radioactivity.
Panspermia - bringing the "seeds of life" to Earth from space. Supporters: J. Liebig, G. Helmholtz, S. Arrhenius, V.I. Vernadsky.
Option 3
Part A: 1 b, d, 2a, 3a, 4c, 5d, 6a, 7b, 8a, 9b, 10 b, c, a, d.
Part B: 1 - abiogenic synthesis; 2 - microspheres; 3 - self-reproduction; 4 - S. Fox; 5 - enzymes.
Part B.
1. When burning wood, all the energy released is dissipated in the form of light and heat. When glucose is oxidized in cells, energy is stored in macroergic bonds of ATP.
2. There are three main approaches to the problem of the origin of life:
– there is no problem, because
life was either created by God (creationism), or has existed in the universe since its inception and spreads randomly (panspermia);
- the problem is insoluble due to insufficient knowledge and the impossibility of reproducing the conditions in which life arose;
- the problem can be solved (A.I.
Oparin, J. Bernal, S. Fox and others).
3. Carbon is tetravalent, capable of forming stable compounds with double and triple bonds, which increases the reactivity of its compounds.
4. In 1953, S. Miller created an experimental setup in which the conditions of the primary Earth were simulated and molecules of biologically important organic compounds were obtained by abiogenic synthesis.
Atoms ––> simple chemical compounds ––> simple bioorganic compounds ––> macromolecules ––> organized systems.
Option 4
Part A: 1b,d, 2a, 3b, 4d, 5d, 6a, 7c, 8d, 9d, 10b,a,d,c.
Part B: 1 - eukaryotes; 2 - genetic code; 3 - self-reproduction; 4 - K.Simonescu, F.Denesh; 5 - protobionts.
Part B.
1. Analysis of the chemical composition of meteorites showed that some of them contain amino acids (glutamic acid, proline, glycine, etc.), fatty acids (17 types).
Thus, organic matter is not exclusively belonging to the Earth, but can also be found in space.
2. Racemization is the reaction of interconversion of D- and L-forms of any stereoisomer; chirality is the existence of two or more mirror asymmetric stereoisomers of a chemical compound.
3. Organisms are made up of 80% or more water.
4. In 1953, S. Miller created an experimental setup in which the conditions of the primary Earth were simulated and molecules of biologically important organic compounds were obtained by abiogenic synthesis.
The gas composition of the "atmosphere": methane, ammonia, water vapor, hydrogen.
5. From ancient times to the experiments of F. Redi - the period of universal faith in the possibility of spontaneous generation of living things; 1668–1862 (before the experiments of L. Pasteur) - experimental clarification of the impossibility of spontaneous generation; 1862–1922 (before AI Oparin's speech) – philosophical analysis of the problem; 1922–1953 – development of scientific hypotheses about the origin of life and their experimental verification; since 1953
up to the present time - experimental and theoretical studies of the ways of transition from chemical evolution to biological.
Note
Part A is worth 1 point, part B is worth 2 points, and part C is worth 3 points.
The maximum score for test – 35.
Score 5: 26-35 points;
score 4: 18–25 points;
score 3: 12–17 points;
score 2: less than 12 points.
Biology
Textbook for grades 10-11
Section I The cell is the unit of life
Chapter I. Chemical composition of the cell
Chapter I. Chemical composition of the cell
Living organisms contain a large number of chemical elements. They form two classes of compounds - organic and inorganic.
Chemistry48.Ru
Chemical compounds, the basis of the structure of which are carbon atoms, are hallmark alive. These compounds are called organic.
Organic compounds are extremely diverse, but only four classes of them are of general biological significance: proteins, nucleic acids, carbohydrates and lipids.
§ 1. Inorganic compounds
Biologically important chemical elements. Of the more than 100 chemical elements known to us, living organisms contain about 80, and only in relation to 24 it is known what functions they perform in the cell. The set of these elements is not accidental.
Life originated in the waters of the World Ocean, and living organisms consist mainly of those elements that form compounds that are easily soluble in water. Most of these elements are among the light, their feature is the ability to enter into strong (covalent) bonds and form many different complex molecules.
Oxygen (more than 60%), carbon (about 20%) and hydrogen (about 10%) predominate in the composition of the cells of the human body.
Nitrogen, calcium, phosphorus, chlorine, potassium, sulfur, sodium, magnesium, taken together, account for about 5%. The remaining 13 elements make up no more than 0.1%. The cells of most animals have a similar elemental composition; only the cells of plants and microorganisms differ. Even those elements that are contained in cells in negligible amounts cannot be replaced by anything and are absolutely necessary for life. Thus, the content of iodine in cells does not exceed 0.01%. However, with a lack of it in the soil (because of this and in food products), the growth and development of children is delayed.
The value for the cell of basic elements is given at the end of this paragraph.
Inorganic (mineral) compounds. The composition of living cells includes a number of relatively simple compounds that are also found in inanimate nature - in minerals, natural waters.
These are inorganic compounds.
Water is one of the most common substances on earth. It covers most of the earth's surface. Almost all living things are made up primarily of water. In humans, the water content in organs and tissues varies from 20% (in bone tissue) to 85% (in the brain). About 2/3 of the mass of a person is water, in the body of a jellyfish up to 95% of water, even in dry plant seeds, water is 10-12%.
Water has some unique properties.
These properties are so important for living organisms that it is impossible to imagine life without this combination of hydrogen and oxygen.
The unique properties of water are determined by the structure of its molecules. In a water molecule, one oxygen atom is covalently bonded to two hydrogen atoms (Fig. 1). The water molecule is polar (dipole). Positive charges are concentrated at hydrogen atoms, since oxygen is more electronegative than hydrogen.
Rice. 1. Formation of hydrogen bonds in water
The negatively charged oxygen atom of one water molecule is attracted to the positively charged hydrogen atom of another molecule to form a hydrogen bond (Fig.
The strength of the hydrogen bond is about 15-20 times weaker covalent bond. Therefore, the hydrogen bond is easily broken, which is observed, for example, during the evaporation of water. Due to the thermal motion of molecules in water, some hydrogen bonds are broken, others are formed.
Thus, molecules in liquid water are mobile, which is important for metabolic processes. Water molecules easily penetrate cell membranes.
Due to the high polarity of the molecules, water is a solvent for other polar compounds. More substances dissolve in water than in any other liquid. That is why many chemical reactions take place in the aquatic environment of the cell. Water dissolves metabolic products and removes them from the cell and the body as a whole.
Water has a high heat capacity, i.e., the ability to absorb heat with a minimum change in its own temperature. Due to this, it protects the cell from sudden changes in temperature. Since a lot of heat is spent on the evaporation of water, by evaporating water, organisms can protect themselves from overheating (for example, during sweating).
Water has a high thermal conductivity. This property creates the possibility of uniform distribution of heat between the tissues of the body.
Water serves as a solvent for the "lubricants" needed wherever there are rubbing surfaces (for example, in joints).
Water has a maximum density at 4°C.
Therefore, ice, which has a lower density, is lighter than water and floats on its surface, which protects the reservoir from freezing.
In relation to water, all cell substances are divided into two groups: hydrophilic - “loving water” and hydrophobic - “afraid of water” (from the Greek “hydro” - water, “phileo” - love and “phobos” - fear).
Hydrophilic substances are substances that are highly soluble in water. These are salts, sugars, amino acids. Hydrophobic substances, on the other hand, are practically insoluble in water.
These include, for example, fats.
The cell surfaces separating the cell from the external environment, and some other structures, consist of water-insoluble (hydrophobic) compounds. This maintains the structural integrity of the cell. Figuratively, a cell can be represented as a vessel with water, where bio chemical reactions providing life. The walls of this vessel are insoluble in water. However, they are able to selectively pass water-soluble compounds.
In addition to water, among the inorganic substances of the cell, salts, which are ionic compounds, should be mentioned. They are formed by cations of potassium, sodium, magnesium and other metals and anions of hydrochloric, carbonic, sulfuric, phosphoric acids. During the dissociation of such salts, cations (K+, Na+, Ca2+, Mg2+, etc.) and anions (CI-, HCO3-, HS04-, etc.) appear in solutions.
The concentration of ions on the outer surface of the cell differs from their concentration on the inner surface. different number potassium and sodium ions on the inner and outer surface of the cell creates a charge difference across the membrane.
On the outer surface of the cell membrane there is a very high concentration of sodium ions, and on the inner surface there is a very high concentration of potassium ions and a low concentration of sodium. As a result, a potential difference is formed between the inner and outer surface of the cell membrane, which causes the transmission of excitation along the nerve or muscle.
Calcium and magnesium ions are activators of many enzymes, and if they are deficient, vital processes in cells are disrupted. perform a number of important functions in living organisms inorganic acids and their salts. Hydrochloric acid creates an acidic environment in the stomach of animals and humans and in special organs of insectivorous plants, accelerating the digestion of food proteins.
Residues of phosphoric acid (H3PO4), joining a number of enzymatic and other cell proteins, change their physiological activity.
Residues of sulfuric acid, joining water-insoluble foreign substances, give them solubility and thus contribute to their removal from cells and organisms. Sodium and potassium salts of nitrous and phosphoric acids, calcium salt of sulfuric acid are important constituent parts mineral nutrition of plants, they are applied to the soil as fertilizers for plant nutrition. In more detail, the value for the cell of chemical elements is given below.
Biologically important chemical elements of the cell
- What is the biological role of water in a cell?
- What ions are found in the cell? What is their biological role?
- What role do the cations contained in the cell play?
The process of formation of the first organic compounds on Earth is called chemical evolution. It preceded biological evolution. The stages of chemical evolution were identified by A.I. Oparin.
Stage I - non-biological, or abiogenic (from the Greek. u, un - a negative particle, bios - life, genesis - origin). At this stage, chemical reactions took place in the Earth's atmosphere and in the waters of the primary ocean, saturated with various inorganic substances, under conditions of intense solar radiation. In the course of these reactions, simple organic substances could form from inorganic substances - amino acids, alcohols, fatty acids, nitrogenous bases.
The possibility of synthesizing organic substances from inorganic substances in the waters of the primary ocean was confirmed in the experiments of the American scientist S. Miller and domestic scientists A.G. Pasynsky and T.E. Pavlovskaya.
Miller designed an installation in which a mixture of gases was placed - methane, ammonia, hydrogen, water vapor. These gases could be part of the primary atmosphere. In another part of the apparatus was water, which was brought to a boil. Gases and water vapor circulating in the apparatus under high pressure were subjected to electrical discharges for a week. As a result, about 150 amino acids were formed in the mixture, some of which are part of proteins.
Subsequently, the possibility of synthesizing other organic substances, including nitrogenous bases, was experimentally confirmed.
Stage II - the synthesis of proteins - polypeptides that could be formed from amino acids in the waters of the primary ocean.
Stage III - the appearance of coacervates (from lat. coacervus - a clot, a bunch). Amphoteric protein molecules, under certain conditions, can spontaneously concentrate and form colloidal complexes, which are called coacervates.
Coacervate droplets are formed by mixing two different proteins. A solution of one protein in water is transparent. When mixing different proteins, the solution becomes cloudy; under a microscope, drops floating in water are visible in it. Such drops - coacervates could have arisen in the waters of the 1000 primary ocean, where there were various proteins.
Some properties of coacervates are outwardly similar to the properties of living organisms. For example, they "absorb" from the environment and selectively accumulate certain substances, increase in size. It can be assumed that substances entered into chemical reactions inside the coacervates.
Because the chemical composition The “broth” in different parts of the primary ocean varied, the chemical composition and properties of the coacervates were not the same. Relationships of competition for substances dissolved in the “broth” could form between coacervates. However, coacervates cannot be considered living organisms, since they lacked the ability to reproduce their own kind.
Stage IV - the emergence of nucleic acid molecules capable of self-reproduction.
Studies have shown that short chains of nucleic acids are able to double without any connection with living organisms - in a test tube. The question arises: how did the genetic code appear on Earth?
The American scientist J. Bernal (1901-1971) proved that minerals played an important role in the synthesis of organic polymers. It was shown that a number of rocks and minerals - basalt, clay, sand - have informational properties, for example, polypeptide synthesis can be carried out on clays.
Apparently, initially a “mineralogical code” arose on its own, in which the role of “letters” was played by cations of aluminum, iron, magnesium, alternating in various minerals in a certain sequence. In minerals, a three-, four- and five-letter code appears. This code determines the sequence of connecting amino acids in a protein chain. Then the role of the information matrix passed from minerals to RNA, and then to DNA, which turned out to be more reliable for the transmission of hereditary traits.
However, the processes of chemical evolution do not explain how living organisms arose. The processes that led to the transition from the inanimate to the living, J. Bernal called biopoiesis. Biopoiesis includes the stages that should have preceded the appearance of the first living organisms: the emergence of membranes in coacervates, metabolism, the ability to self-reproduce, photosynthesis, oxygen respiration.
The formation of cell membranes by lining up lipid molecules on the surface of coacervates could lead to the appearance of the first living organisms. This ensured the stability of their shape. The inclusion of nucleic acid molecules in coacervates ensured their ability to self-reproduce. In the process of self-reproduction of nucleic acid molecules, mutations arose that served as material for.
So, on the basis of coacervates, the first living beings could have arisen. They appear to have been heterotrophs and fed on energy-rich complex organic matter found in the waters of the primordial ocean.
As the number of organisms increased, competition between them intensified, as the supply of nutrients in the ocean waters decreased. Some organisms have the ability to synthesize organic substances from inorganic substances using solar energy or energy of chemical reactions. So there were autotrophs capable of photosynthesis or chemosynthesis.
The first organisms were anaerobes and obtained energy during oxygen-free oxidation reactions, such as fermentation. However, the advent of photosynthesis led to the accumulation of oxygen in the atmosphere. The result was respiration, an oxygenic, aerobic oxidation pathway that is about 20 times more efficient than glycolysis.
Initially, life developed in the waters of the ocean, as strong ultraviolet radiation had a detrimental effect on organisms on land. The appearance of the ozone layer as a result of the accumulation of oxygen in the atmosphere created the prerequisites for the emergence of living organisms on land.
For the first time, the American scientist Stanley Miller succeeded in obtaining organic molecules - amino acids - in laboratory conditions, simulating those that were on the primitive Earth, in 1952. Then these experiments became a sensation, and their author gained worldwide fame. He currently continues to do research in prebiotic (pre-life) chemistry at the University of California. The installation on which the first experiment was carried out was a system of flasks, in one of which it was possible to obtain a powerful electric discharge at a voltage of 100,000 V. Miller filled this flask with natural gases - methane, hydrogen and ammonia, which were present in the atmosphere of the primitive Earth. The flask below contained a small amount of water, simulating the ocean. An electric discharge was close to lightning in its strength, and Miller expected that under its action chemical compounds were formed, which, having then got into the water, would react with each other and form more complex molecules. The result exceeded all expectations. Turning off the installation in the evening and returning the next morning, Miller found that the water in the flask had acquired a yellowish color. What formed was a broth of amino acids, the building blocks of proteins. Thus, this experiment showed how easily the primary ingredients of the living could be formed. All that was needed was a mixture of gases, a small ocean and a small lightning bolt.
Other scientists tend to believe that the ancient atmosphere of the Earth is different from the one that Miller modeled, and most likely consisted of carbon dioxide and nitrogen. Using this gas mixture and Miller's experimental setup, chemists tried to make organic compounds. However, their concentration in the water was as negligible as if a drop of food coloring had been dissolved in a swimming pool. Naturally, it is difficult to imagine how life could have arisen in such a dilute solution. If indeed the contribution of terrestrial processes to the creation of reserves of primary organic matter was so insignificant, then where did it come from? Maybe from space? Asteroids, comets, meteorites, and even interplanetary dust particles could carry organic compounds, including amino acids. These extraterrestrial objects could provide enough organic compounds to enter the primary ocean or a small body of water for the origin of life. The sequence and time interval of events, starting from the formation of primary organic matter and ending with the appearance of life as such, remains and will probably forever remain a mystery that worries many researchers, as well as the question of what, in fact, is considered life.
The process of formation of the first organic compounds on Earth is called chemical evolution. It preceded biological evolution. The stages of chemical evolution were identified by A.I. Oparin.
I stage- non-biological, or abiogenic (from the Greek u, un - negative particle, bios - life, genesis - origin). At this stage, chemical reactions took place in the Earth's atmosphere and in the waters of the primary ocean, saturated with various inorganic substances, under conditions of intense solar radiation. In the course of these reactions, simple organic substances could form from inorganic substances - amino acids, simple carbohydrates, alcohols, fatty acids, nitrogenous bases.
The possibility of synthesizing organic substances from inorganic substances in the waters of the primary ocean was confirmed in the experiments of the American scientist S. Miller and domestic scientists A.G. Pasynsky and T.E. Pavlovskaya.
Miller designed an installation in which a mixture of gases was placed - methane, ammonia, hydrogen, water vapor. These gases could be part of the primary atmosphere. In another part of the apparatus was water, which was brought to a boil. Gases and water vapor circulating in the apparatus under high pressure were subjected to electrical discharges for a week. As a result, about 150 amino acids were formed in the mixture, some of which are part of proteins.
Subsequently, the possibility of synthesizing other organic substances, including nitrogenous bases, was experimentally confirmed.
II stage- the synthesis of proteins - polypeptides that could be formed from amino acids in the waters of the primary ocean.
Stage III- the appearance of coacervates (from lat. coacervus - a clot, a bunch). Amphoteric protein molecules, under certain conditions, can spontaneously concentrate and form colloidal complexes, which are called coacervates.
Coacervate droplets are formed by mixing two different proteins. A solution of one protein in water is transparent. When mixing different proteins, the solution becomes cloudy; under a microscope, drops floating in water are visible in it. Such drops - coacervates could have arisen in the waters of the 1000 primary ocean, where there were various proteins.
Some properties of coacervates are outwardly similar to the properties of living organisms. For example, they "absorb" from the environment and selectively accumulate certain substances, increase in size. It can be assumed that substances entered into chemical reactions inside the coacervates.
Since the chemical composition of the "broth" in different parts of the primary ocean varied, the chemical composition and properties of the coacervates were not the same. Relationships of competition for substances dissolved in the “broth” could form between coacervates. However, coacervates cannot be considered living organisms, since they lacked the ability to reproduce their own kind.
IV stage- the emergence of nucleic acid molecules capable of self-reproduction.
Studies have shown that short chains of nucleic acids are able to double without any connection with living organisms - in a test tube. The question arises: how did the genetic code appear on Earth?
The American scientist J. Bernal (1901-1971) proved that minerals played an important role in the synthesis of organic polymers. It was shown that a number of rocks and minerals - basalt, clay, sand - have informational properties, for example, polypeptide synthesis can be carried out on clays.
Apparently, initially a “mineralogical code” arose on its own, in which the role of “letters” was played by cations of aluminum, iron, magnesium, alternating in various minerals in a certain sequence. In minerals, a three-, four- and five-letter code appears. This code determines the sequence of connecting amino acids in a protein chain. Then the role of the information matrix passed from minerals to RNA, and then to DNA, which turned out to be more reliable for the transmission of hereditary traits.
However, the processes of chemical evolution do not explain how living organisms arose. The processes that led to the transition from the inanimate to the living, J. Bernal called biopoiesis. Biopoiesis includes the stages that should have preceded the appearance of the first living organisms: the emergence of membranes in coacervates, metabolism, the ability to self-reproduce, photosynthesis, oxygen respiration.
The formation of cell membranes by lining up lipid molecules on the surface of coacervates could lead to the appearance of the first living organisms. This ensured the stability of their shape. The inclusion of nucleic acid molecules in coacervates ensured their ability to self-reproduce. In the process of self-reproduction of nucleic acid molecules, mutations arose that served as material for natural selection.
So, on the basis of coacervates, the first living beings could have arisen. They appear to have been heterotrophs and fed on energy-rich complex organic matter found in the waters of the primordial ocean.
As the number of organisms increased, competition between them intensified, as the supply of nutrients in the ocean waters decreased. Some organisms have acquired the ability to synthesize organic substances from inorganic substances using solar energy or the energy of chemical reactions. So there were autotrophs capable of photosynthesis or chemosynthesis.
The first organisms were anaerobes and obtained energy during oxygen-free oxidation reactions, such as fermentation. However, the advent of photosynthesis led to the accumulation of oxygen in the atmosphere. As a result, respiration arose - an oxygenic, aerobic oxidation pathway that is about 20 times more efficient than glycolysis.
Initially, life developed in the waters of the ocean, as strong ultraviolet radiation had a detrimental effect on organisms on land. The appearance of the ozone layer as a result of the accumulation of oxygen in the atmosphere created the prerequisites for the emergence of living organisms on land.
Currently, there are several scientific definitions of life, but they are not all accurate. Some of them are so wide that inanimate objects such as fire or mineral crystals fall under them. Others are too narrow, and according to them, mules that do not produce offspring are not considered alive.
One of the most successful defines life as a self-sustaining chemical system capable of behaving in accordance with the laws of Darwinian evolution. This means that, firstly, a group of living individuals must produce descendants similar to themselves, who inherit the characteristics of their parents. Secondly, in the generations of descendants, the consequences of mutations should appear - genetic changes that are inherited by subsequent generations and cause population variability. And, thirdly, it is necessary that a system of natural selection operate, as a result of which some individuals gain an advantage over others and survive in changed conditions, giving offspring.
What elements of the system were necessary for it to have the characteristics of a living organism? A large number of biochemists and molecular biologists it is believed that RNA molecules possessed the necessary properties. Ribonucleic acids are special molecules. Some of them can replicate, mutate, thus transmitting information, and, therefore, they could participate in natural selection. True, they are not able to catalyze the replication process themselves, although scientists hope that in the near future an RNA fragment with such a function will be found. Other RNA molecules are involved in "reading" genetic information and transferring it to ribosomes, where protein molecules are synthesized, in which third-type RNA molecules take part.
Thus, the most primitive living system could be represented by RNA molecules that doubled, mutated and were subject to natural selection. In the course of evolution, on the basis of RNA, specialized DNA molecules arose - the keepers of genetic information - and no less specialized protein molecules, which assumed the functions of catalysts for the synthesis of all currently known biological molecules.
At some point in time, a "living system" of DNA, RNA and protein found shelter inside the sac formed by the lipid membrane, and this structure, more protected from external influences, served as the prototype for the very first cells that gave rise to the three main branches of life, which are presented in modern world bacteria, archaea and eukaryotes. As for the date and sequence of the appearance of such primary cells, this remains a mystery. In addition, according to simple probabilistic estimates, there is not enough time for the evolutionary transition from organic molecules to the first organisms - the first simple organisms appeared too suddenly.
For many years, scientists believed that life could hardly have arisen and developed during the period when the Earth was constantly subjected to collisions with large comets and meteorites, and this period ended about 3.8 billion years ago. Recently, however, traces of complex cellular structures dating back at least 3.86 billion years have been found in the oldest sedimentary rocks on Earth, found in southwestern Greenland. This means that the first forms of life could have arisen millions of years before the bombardment of our planet by large cosmic bodies stopped. But then a completely different scenario is possible (Fig. 4). Organic matter has been brought to Earth from space along with meteorites and other extraterrestrial objects that have bombarded the planet for hundreds of millions of years since its formation. Today, a collision with a meteorite is a rather rare event, but even now from space, along with interplanetary material, exactly the same compounds continue to come to Earth as they did at the dawn of life.
Fallen to the ground space objects could have played a central role in the emergence of life on our planet, since, according to some researchers, cells like bacteria could originate on another planet and then get to Earth along with asteroids. One of the pieces of evidence in favor of the extraterrestrial origin of life was found inside a potato-shaped meteorite named ALH84001. This meteorite was originally a piece of the Martian crust, which was then ejected into space as a result of an explosion when a huge asteroid collided with the surface of Mars, which occurred about 16 million years ago. And 13 thousand years ago, after a long journey within solar system this fragment of Martian rock in the form of a meteorite landed in Antarctica, where it was recently discovered. A detailed study of the meteorite inside it revealed rod-shaped structures resembling fossilized bacteria in shape, which gave rise to heated scientific debate about the possibility of life in the depths of the Martian crust. It will not be possible to resolve these disputes until 2005, when the National Aeronautics and Space Administration of the United States of America will carry out an interplanetary mission to Mars to take samples of the Martian crust and deliver samples to Earth. And if scientists manage to prove that microorganisms once inhabited Mars, then it will be possible to speak with a greater degree of certainty about the extraterrestrial origin of life and the possibility of bringing life from space.
