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The Proterozoic eon is the longest epoch in the history of the Earth. It began 2.5 billion years ago. e. and ended 541 million years BC. During this time, the Earth has turned from an oxygen-free planet of microbes, prokaryotes into an oxygen planet of multicellular organisms.
1. Great Oxygen Event
Biologist Alexander Markov on the oxygen crisis, greenhouse gases and the emergence of eukaryotes
In the Early Proterozoic, a fairly rapid increase in the amount of free oxygen in the atmosphere and hydrosphere occurred over several hundred million years. The prerequisites for this were formed at the end of the Archean era. Approximately 2.45 billion years ago, the so-called great oxygen event began, when oxygen levels rose from almost 0% to about 1% of the current oxygen content.
Why do geologists believe that oxygen increased during this period? This is indicated by a number of signs, for example, the ratio of sulfur isotopes in sedimentary rocks. Apparently, volcanic gases that enter the atmosphere, if there is no oxygen in this atmosphere, participate in certain photochemical reactions, during which sulfur isotope fractionation occurs and an altered isotopic composition is obtained. But when oxygen appears in the atmosphere, these processes stop. And at the beginning of the Proterozoic, these processes just stopped.
A. Markov. 2010. The Birth of Complexity. Evolutionary biology today: unexpected discoveries and new questions. Moscow: Astrel: CORPUS.
2. Crisis in microbial communities
There are also a number of minerals in sedimentary rocks that can only form under anoxic conditions - in the presence of oxygen they oxidize. And such unoxidized minerals are also found in rocks before the beginning of the Proterozoic, and then they are no longer formed.
In those days, all microbes were adapted to life in oxygen-free conditions, and oxygen is a strong oxidizing agent, it is actually a strong poison, from which you need to protect yourself in some special way. The increase in the oxygen content in the atmosphere was supposed to cause a certain crisis in microbial communities, which then actually constituted the only form life on earth.
E. Kunin. 2014. The logic of the case. On the nature and origin of biological evolution. M.: Tsentrpoligraf.
3. Causes of the Huron glaciation
At the same time, the first major glaciation on Earth occurs - it is called the Huron.
The reasons for the onset of warm or cold epochs in the history of the Earth, apparently, were quite diverse. But one of the important reasons for their onset is the amount of such greenhouse gases in the atmosphere as CO2, methane, water vapor. However, the development of life affects the content carbon dioxide and then methane.
7 facts about the stages of abiogenesis and the problem of the origin of life on Earth
Why does glaciation occur when the oxygen content rises? First, in order for the oxygen content to increase, carbon must be removed from the cycle. During the biogenic carbon cycle, photosynthetic organisms remove carbon dioxide from the atmosphere and turn it into organic matter. Then heterotrophic organisms that feed on ready-made organic matter oxidize this organic matter with the help of oxygen released by photosynthetics and turn it back into CO2. Thus, photosynthetics release oxygen and take carbon from the atmosphere, while heterotrophic organisms, on the contrary, take oxygen and release carbon.
If the activity of photosynthetics is not fully balanced by the activity of heterotrophs, that is, the consumption of organic matter lags behind the production of organic matter, then this excess organic matter will be buried in the earth's crust. This leads to the fact that carbon is gradually removed from the atmosphere, the CO2 content in the atmosphere falls, the greenhouse effect weakens, and it becomes colder.
At the time of the rapid increase in oxygen content, glaciation occurred. In addition, the released oxygen could oxidize methane, which, apparently, was still present in significant quantities in the atmosphere at that time. And methane is also a very strong greenhouse gas.
K. Eskov. 2000. History of the Earth and life on it. M.: MIROS - MAIK "Science-Interperiodika".
4. The appearance of the first eukaryotic cell
By the end of the first glaciation and the end of the period of rapid oxygen growth, the most important event in the evolution of terrestrial life occurs - the first eukaryotic cell appears.
Until now, only prokaryotes lived on Earth - these are bacteria that do not have a cell nucleus and other membrane structures, organelles. In the cell, they do not have mitochondria, plastids, and any other complexities. Even at the dawn of cellular life, prokaryotes were divided into two large groups: bacteria and archaea (earlier they were called archaebacteria).
Eukaryotes are the third largest group of living organisms, which first appeared in the early Proterozoic, most likely in connection with an increase in oxygen. Eukaryotes are organisms that have a nucleus in the cell, mitochondria, and they are initially adapted precisely to an oxygen environment. Mitochondria are the organelles of a eukaryotic cell that are just needed for oxygen respiration, since they use oxygen to oxidize organic matter and produce energy. It was the eukaryotic cell that became the basis for the development of all complex forms of multicellular life on our planet: animals, plants, fungi.
Prokaryotes have tried several times and continue to sometimes try to move to multicellularity, but these attempts do not go far for a number of technical reasons. For example, in a multicellular organism, different cells perform different functions, respectively, different genes work in different tissues. The genome of a eukaryotic organism contains all the genes necessary for the formation of all the tissues of a multicellular organism, but only a part of them works in each tissue - the one that is needed. In order for this to work, we need a very complex and effective system for regulating the work of genes. And for this, it is just very important to have a cell nucleus in which genes are isolated from the turbulent biochemical processes occurring in the cytoplasm. There you can develop effective systems for regulating the work of genes, which prokaryotes do not have, since they have simpler regulatory systems.
5. The structure of a eukaryotic cell
Some researchers believe that the appearance of the eukaryotic cell is the most key event in the evolution of life on Earth. And maybe it happened only once, since all modern eukaryotes obviously come from the same ancestor. Perhaps there were some other attempts at such evolutionary experiments, but they did not survive to this day.
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The eukaryotic cell has a chimeric nature. It appeared as a natural result of the evolution of the Precambrian microbial communities, which constituted the main form of life in the Archean era and continued to dominate in the Proterozoic. If you look at what proteins a eukaryotic cell is made of, you get a very interesting thing. The central system of a eukaryotic cell, associated with DNA replication, work with genetic information, protein synthesis, is served by proteins similar to those of archaea. But on the periphery - metabolism, receptors, interaction with the external environment, signal transmission - proteins similar to bacterial proteins dominate. That is, a eukaryotic cell has an archaeal core and a bacterial periphery. In other words, in the process of evolution, there was a kind of merger, a combination of the genomes of representatives of the two great branches of prokaryotes.
N. Lane. 2014. Ladder of life. Ten Greatest Inventions of Evolution. M.: AST: CORPUS.
6. Adaptation of ancient microbes to oxygen
During the oxygen crisis, when ancient microbes had to adapt to a new poison that appeared - to free oxygen, some archaea, apparently, actively borrowed foreign genes, including bacterial ones, and as a result acquired a number of bacterial properties. The result was a kind of chimeric unicellular organism, capable, for example, of swallowing other prokaryotes. Perhaps they turned to predation, perhaps they merged with other cells in order to exchange genetic material. Most likely, sexual reproduction was formed at this stage. Another key feature of eukaryotes is true sexual reproduction associated with the fusion of germ cells and with reduction division (meiosis).
This chimeric organism at some point swallowed bacteria, representatives of the alpha-proteobacteria group, which became the ancestors of mitochondria - organelles for oxygen respiration. Thus, this organism, having acquired such a symbiont, protected itself from the toxic effect of oxygen. After that, oxygen was already utilized by these symbiotic mitochondria. The free-living ancestors of mitochondria learned how to deal with oxygen and invented a system of oxygen respiration. Probably, at first they simply burned organic matter to neutralize oxygen, and then they learned to extract benefit from it in the form of energy.
7. Development of the fauna of unicellular eukaryotes in the ocean
Biologist Evgeny Kunin on the view of genes from the point of view of statistical physics, the change in the evolutionary paradigm and the connection of cosmology with the origin of life
During the adaptation of ancient organisms to oxygen, microbes turned into a proto-eukaryotic cell with mitochondria. At some point, a nucleus appeared in the cell. There is a theory that the nucleus appeared as a result of symbiosis with viruses. Scientists have discovered very large viruses that resemble the cell nucleus in a number of properties, from which it can be concluded that, perhaps, the cell nucleus was also acquired during evolution through symbiosis.
At the beginning of the Proterozoic, two billion years ago, the eukaryotic cell appeared. The first eukaryotes were single-celled, heterotrophs, that is, they consumed ready-made organic matter. Somewhat later, some eukaryotes entered into symbiosis with cyanobacteria and swallowed them. Thus, these cyanobacteria gave rise to plastids, which led to the emergence of plants.
During the Middle Proterozoic, we already see the remains of unicellular eukaryotes in the fossil record. Phytoplankton gradually developed from already eukaryotic unicellular algae. And at the same time, apparently, the first multicellular algae begin to appear.
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The role of green plants in providing energy to living
Organisms on our planet
As you know, the main source of energy on earth is the sun. But people and animals are not able to directly use solar energy, because their bodies do not have systems by which energy would be consumed in such a form as it is. Therefore, solar energy enters the human or animal body as useful energy only through substances produced by plants.
Plants are able to create organic substances from inorganic substances using light energy. This process is called photosynthesis (from the Greek words "photos" - light, "synthesis" - connection). The ability to photosynthesis is the most important property of green plants. This is the only process on our planet associated with the conversion of sunlight energy into energy. chemical bonds contained in organic matter. Therefore, photosynthesis is the most important process by which life on Earth is possible.
An outstanding Russian scientist of the late XIX - early XX century. Kliment Arkadyevich Timiryazev (1843-1920) called the role of green plants on Earth cosmic. K.A. Timiryazev wrote: “All organic substances, no matter how diverse they may be, wherever they are found, whether in a plant, animal or person, passed through the leaf, originated from substances produced by the leaf. Outside the leaf, or rather outside the chlorophyll grain, there is no laboratory in nature where organic matter is isolated. In all other organs and organisms, it is transformed, transformed, only here it is formed again from inorganic matter.
In addition, plants saturate the Earth's atmosphere with oxygen, which serves to oxidize organic substances and extract the chemical energy stored in them by aerobic cells in this way.
Every year, green plants synthesize a large amount of organic matter, absorb about 600 billion tons of carbon dioxide, and release 400 billion tons of free oxygen into the atmosphere. Thanks to photosynthesis, a huge amount of converted solar energy is stored annually.
The accumulation of energy is a very important phenomenon for wildlife, due to the photosynthesis of green plants. Organic matter is an excellent energy carrier.
Carbohydrates created with the participation of chlorophyll and sunlight, as well as proteins and fats formed in plants, contain a lot of energy. Especially a lot of it in starch and various sugars.
Many plants, such as sugar cane, sugar beets, onions, peas, corn, grapes, dates, store sugar in stems, roots, bulbs, fruits, and seeds. It is sugars that serve as the main source of energy for all living beings, since they can easily become one of the most active compounds in any living cell. By constantly absorbing energy in the form of solar radiation, plants accumulate it. Due to the huge number of green plants on Earth, there is more and more energy in the biosphere. A person widely uses gas, oil, coal, firewood - all these are organic substances that release energy during combustion, which was once stored in green plants.
It can be concluded that the existence of plants plays a very important and necessary role for the survival of living beings on earth. The energy of the sun's rays received from space, stored by green plants in carbohydrates, fats and proteins, ensures the vital activity of the entire living world - from bacteria to humans.
Corliss suggested that hydrothermal vents could create cocktails of chemicals. Each source, he said, was a kind of atomizer of the primordial soup.
As hot water flowed over the rocks, heat and pressure caused simple organic compounds to fuse into more complex ones, such as amino acids, nucleotides and sugars. Closer to the border with the ocean, where the water was not so hot, they began to bind in chains - to form carbohydrates, proteins and nucleotides like DNA. Then, as the water approached the ocean and cooled even further, these molecules would assemble into simple cells.
It was interesting, the theory got people's attention. But Stanley Miller, whose experiment we discussed in the first part, did not believe it. In 1988, he wrote that the deep sea vents were too hot.
While intense heat can produce chemicals like amino acids, Miller's experiments showed that it could also destroy them. Basic compounds like sugars “could survive for a couple of seconds, no more.” What's more, these simple molecules would be unlikely to chain together, as the surrounding water would break them instantly.
At this stage geologist Mike Russell joined the battle. He considered that the theory of hydrothermal vents could be quite correct. Moreover, it seemed to him that these sources would be an ideal home for the precursors of the Wachtershauser organism. This inspiration led him to create one of the most widely accepted theories on the origins of life.
Geologist Michael Russell
Russell had a lot of interesting things in his career - he made aspirin, looking for valuable minerals - and in one remarkable incident of the 1960s, he coordinated the response to a possible volcanic eruption, despite the lack of preparation. But he was more interested in how the surface of the Earth changed over the ages. This geological perspective allowed his ideas about the origin of life to take shape.
In the 1980s, he discovered fossil evidence of a less turbulent type of hydrothermal vent, in which temperatures did not exceed 150 degrees Celsius. These mild temperatures, he said, could allow the molecules of life to live longer than Miller believed.
Moreover, the fossil remains of these "cool" vents contained something strange: the mineral pyrite, composed of iron and sulfur, formed in tubes with a diameter of 1 mm. While working in the lab, Russell discovered that pyrite can also form spherical droplets. And he suggested that the first complex organic molecules could form inside these simple pyrite structures. 
iron pyrite
Around this time, Wachtershauser began to publish his ideas, which were based on the flow of hot chemically enriched water flowing through minerals. He even suggested that pyrite was involved in this process.
Russell put two plus two together. He hypothesized that hydrothermal vents deep in the sea, cold enough to allow pyrite structures to form, harbored the precursors of Wachtershauser's organisms. If Russell was right, life began at the bottom of the sea - and metabolism came first.
Russell put it all together in a paper published in 1993, 40 years after Miller's classic experiment. It didn't generate the same media frenzy, but it was perhaps more important. Russell combined two seemingly separate ideas - the Wachtershauser metabolic cycles and the Corliss hydrothermal vents - into something truly compelling.
Russell even offered an explanation for how the first organisms got their energy. That is, he understood how their metabolism could work. His idea was based on the work of one of the forgotten geniuses modern science.
Peter Mitchell, Nobel laureate
In the 1960s, biochemist Peter Mitchell fell ill and was forced to retire from the University of Edinburgh. Instead, he set up a private laboratory on a remote estate in Cornwall. isolated from scientific society, he funded his work with a herd of dairy cows. Many biochemists, including Leslie Orgel, whose work on RNA we discussed in part two, thought Mitchell's ideas were completely ridiculous.
A few decades later, Mitchell was waiting for an absolute victory: in chemistry in 1978. He did not become famous, but his ideas are in every biology textbook today. Mitchell spent his career figuring out what organisms do with the energy they get from food. Basically, he wondered how we all manage to stay alive every second.
He knew that all cells store their energy in one molecule: adenosine triphosphate (ATP). A chain of three phosphates is attached to adenosine. Adding a third phosphate requires a lot of energy, which is then locked into ATP.
When a cell needs energy—for example, when a muscle contracts—it breaks down a third phosphate into ATP. This converts ATP to adenoside diphosphate (ADP) and releases stored energy. Mitchell wanted to know how the cell generally creates ATP. How does it store enough energy in ADP to attach a third phosphate?
Mitchell knew that the enzyme that makes ATP is in the membrane. Therefore, he suggested that the cell pumps charged particles (protons) through the membrane, so many protons are on one side, but not on the other.
The protons then try to leak back across the membrane to balance the number of protons on each side - but the only place they can get through is the enzyme. The flow of flowing protons thus provided the enzyme with the energy needed to create ATP.
Mitchell first presented his idea in 1961. He spent the next 15 years defending her from every angle until the evidence became irrefutable. We now know that the Mitchell process is used by every living thing on Earth. Right now it's leaking in your cells. Like DNA, it underlies life as we know it.
Russell borrowed the idea of the proton gradient from Mitchell: having a large number of protons on one side of the membrane and few on the other. All cells need a proton gradient to store energy.
Modern cells create gradients by pumping protons through membranes, but this requires a complex molecular mechanism that simply could not appear on its own. So Russell took another logical step: life had to form somewhere with a natural proton gradient.
For example, somewhere near hydrothermal springs. But it must be a special type of source. When the Earth was young, the seas were acidic, and acidic water has a lot of protons. To create a proton gradient, the source water must be low in protons: it must be alkaline.
Corliss' sources were not suitable. They were not only too hot, but also sour. But in 2000, Deborah Kelly of the University of Washington discovered the first alkaline springs. 
Kelly had to work hard to become a scientist. Her father died while she was finishing high school and she had to work to stay in college. But she coped and chose underwater volcanoes and scalding hot hydrothermal springs as the subject of her interest. This couple brought her to the center of the Atlantic Ocean. In this place, the earth's crust cracked and a range of mountains rose from the seabed.
On this ridge, Kelly discovered a field of hydrothermal vents, which she called the "Lost City". They were not like those found by Corliss. Water flowed out of them at a temperature of 40-75 degrees Celsius and was slightly alkalized. The carbonate minerals from this water clung together into steep white "columns of smoke" that rose from the seafloor like organ pipes. In appearance, they are creepy and ghostly, but this is not so: they are inhabited by many microorganisms.
These alkaline vents fit Russell's ideas perfectly. He firmly believed that life appeared in such "lost cities". But there was one problem. Being a geologist, he knew little about biological cells to present your theory convincingly. 
Pillar of smoke "black smoking room"
So Russell teamed up with biologist William Martin. In 2003 they presented an improved version of Russell's earlier ideas. And this is probably the best theory of the origin of life at the moment.
Thanks to Kelly, they now knew that alkali spring rocks were porous: they were littered with tiny holes filled with water. These tiny pockets, they suggested, acted as "cages". Each pocket contained the main chemical substances including pyrite. Combined with the natural proton gradient from the sources, they were the perfect place to start metabolism.
Once life learned to harness the energy of spring waters, Russell and Martin say, it began to create molecules like RNA. In the end, she created a membrane for herself and became a real cell, escaping from the porous rock into open water.
Such a plot is currently considered as one of the leading hypotheses about the origin of life. 
Cells escape from a hydrothermal vent
In July 2016, he received support when Martin published a study reconstructing some of the details of "" (LUCA). This is an organism that lived billions of years ago and from which all existing life.
It is unlikely that we will ever find direct fossilized evidence of the existence of this organism, but nevertheless we can well make educated guesses about what it looked like and what it did by studying the microorganisms of our day. This is what Martin did.
He examined the DNA of 1930 modern microorganisms and identified 355 genes that almost everyone had. This strongly suggests the transmission of these 355 genes, through generations and generations, from a common ancestor - about the time when the last universal common ancestor lived.
These 355 genes include some to use the proton gradient, but not to generate one, as the theories of Russell and Martin predicted. What's more, LUCA seems to have adapted to the presence of chemicals like methane, suggesting that it inhabited a volcanically active environment - like a vent.
Proponents of the "RNA world" hypothesis point to two problems with this theory. One can be fixed; the other can be fatal. 
hydrothermal vents
The first problem is that there is no experimental evidence for the processes described by Russell and Martin. They have step by step story, but none of these steps have been observed in the laboratory.
“People who believe that it all started with reproduction are constantly finding new experimental data,” says Armen Mulkidzhanyan. "People who stand for metabolism don't."
But that could change, thanks to Martin's colleague Nick Lane of University College London. He built an "origin of life reactor" that mimics the conditions inside an alkaline spring. He hopes to see metabolic cycles, and maybe even molecules like RNA. But it's still early.
The second problem is the location of the sources in the deep sea. As Miller noted in 1988, long-chain molecules like RNA and proteins cannot form in water without help from enzymes.
For many scientists, this is a fatal argument. “If you're good at chemistry, you won't be bribed with the idea of deep sea sources because you know that the chemistry of all these molecules is incompatible with water,” Mulkidjanian says.
Yet Russell and his allies remain optimistic.
It was only in the last decade that a third approach came to the fore, supported by a series of unusual experiments. It promises something that neither the "RNA world" nor the hydrothermal vents have been able to achieve: a way to create an entire cell from scratch. More on this in the next section.
Transformation of sunlight energy and organisms using it
Today we will talk about organisms that use solar energy in their life. To do this, you need to touch upon such a science as bioenergetics. It studies the methods of energy conversion by living organisms and its use in the process of life. Bioenergy is based on thermodynamics. This science describes the mechanisms for converting different types of energy into each other. Including the use and transformation of solar energy by various organisms. With the help of thermodynamics, it is possible to fully describe the energy mechanism of the processes occurring around us. But with the help of thermodynamics it is impossible to understand the nature of this or that process. In this article we will try to explain the mechanism of using solar energy by living organisms.
To describe the transformation of energy in living organisms or other objects of our planet, one should consider them from the point of view of thermodynamics. That is, a system that exchanges energy with environment and objects. They can be divided into the following systems:
- closed;
- isolated;
- Open.
After a while, these substances break down and provide the body with energy. Their decay products are removed from the body. Their place in the body is filled by other molecules. In this case, the integrity of the structure of the body is not violated. Such assimilation and processing of energy in the body ensures the renewal of the body. Energy metabolism is necessary for the existence of all living organisms. When the energy conversion processes in the body stop, it dies.
Sunlight is the source of biological energy on Earth. The nuclear energy of the Sun provides the generation of radiant energy. Hydrogen atoms in our star are converted into He atoms as a result of the reaction. The energy released during the reaction is released in the form of gamma radiation. The reaction itself looks like this:
4H ⇒ He4 + 2e + hv, where
v ─ wavelength of gamma rays;
h is Planck's constant.
Later, after the interaction of gamma radiation and electrons, energy is released in the form of photons. This light energy is emitted by the celestial body.
When solar energy reaches the surface of our planet, it is captured and converted by plants. In them, the energy of the sun is converted into chemical energy, which is stored in the form of chemical bonds. These are bonds that connect atoms in molecules. An example is the synthesis of glucose in plants. The first stage of this energy conversion is photosynthesis. Plants provide it with the help of chlorophyll. This pigment ensures the conversion of radiant energy into chemical energy. There is a synthesis of carbohydrates from H 2 O and CO 2. This ensures the growth of plants and the transfer of energy to the next stage.
The next stage of energy transfer occurs from plants to animals or bacteria. At this stage, the energy of carbohydrates in plants is converted into biological energy. This occurs in the process of oxidation of plant molecules. The amount of energy received corresponds to the amount that was spent on synthesis. Some of this energy is converted into heat. As a result, energy is stored in macroergic bonds of adenosine triphosphate. So solar energy, passing through a series of transformations, appears in living organisms in a different form.
Here it is worth answering the frequently asked question: “What organelle uses the energy of sunlight?”. These are chloroplasts involved in the process of photosynthesis. They use it for the synthesis of organic substances from inorganic substances.
The continuous flow of energy is the essence of all life. It constantly moves between cells and organisms. At the cellular level, there are effective mechanisms for energy conversion. There are 2 main structures where energy conversion takes place:
- Chloroplasts;
- Mitochondria.
Man, like other living organisms on the planet, replenishes his energy supply from food. Moreover, part of the consumed products of plant origin (apples, potatoes, cucumbers, tomatoes), and part of the animal (meat, fish and other seafood). The animals we eat also get their energy from plants. Therefore, all the energy received by our body is converted from plants. And they get it as a result of the conversion of solar energy.
According to the type of energy production, all organisms can be divided into two groups:
- Phototrophs. Draw energy from sunlight;
- Chemotrophs. They receive energy during a redox reaction.
That is, solar energy is used by plants, and animals receive energy that is in organic molecules while eating plants.
How is energy converted in living organisms?
There are 3 main types of energy converted by organisms:
- Conversion of radiant energy. This type of energy carries sunlight. In plants, radiant energy is captured by the pigment chlorophyll. As a result of photosynthesis, it turns into chemical energy. That, in turn, is used in the process of oxygen synthesis and other reactions. Sunlight carries kinetic energy, and in plants it turns into potential energy. The resulting energy reserve is stored in nutrients. For example, in carbohydrates;
- Conversion of chemical energy. From carbohydrates and other molecules, it turns into the energy of high-energy phosphate bonds. These transformations take place in the mitochondria.
- Energy conversion of macroergic phosphate bonds. It is consumed by the cells of a living organism to perform various types of work (mechanical, electrical, osmotic, etc.).
During these transformations, part of the energy reserve is lost and dissipated in the form of heat.
The use of stored energy by organisms
In the process of metabolism, the body receives an energy reserve that is spent on biological work. It can be light, mechanical, electrical, chemical work. And a very large part of the energy the body spends in the form of heat.
The main types of energy in the body are briefly described below:
- Mechanical. It characterizes the movement of macrobodies, as well as the mechanical work of their movement. It can be divided into kinetic and potential. The first is determined by the speed of movement of macro-bodies, and the second is determined by their location in relation to each other;
- Chemical. It is determined by the interaction of atoms in a molecule. It is the energy of electrons that move along the orbits of molecules and atoms;
- Electric. This is the interaction of charged particles, which causes them to move in an electric field;
- Osmotic. It is consumed when moving against the gradient of concentrations of substance molecules;
- regulatory energy.
- Thermal. It is determined by the chaotic movement of atoms and molecules. The main characteristic of this movement is temperature. This type of energy is the most devalued of all those listed above.
E h = 3/2rT, where
r ─ Boltzmann's constant (1.380*10 -16 erg/deg).
The universe is filled with energy, but only a few types of it are suitable for living organisms. The main source of energy for the vast majority of biological processes on our planet is sunlight. The radiation power of the Sun is estimated on average as 4 × 10 33 erg / s, which costs our star in the annual loss of 10 -15 -10 -14 mass. There are also much more powerful emitters. For example, 1-2 times a century in our galaxy there are bursts of supernovae, each of which is accompanied by a strong explosion with a power of more than 10 41 erg/s. And quasars (the nuclei of galaxies hundreds of millions of light years away from us) radiate even greater powers - 10 46 -10 47 erg / s.
The cell is the basic unit of life, it continuously works to maintain its structure, and therefore needs a constant supply of free energy. Technologically, it is not easy for her to solve such a problem, since a living cell must release and use energy at a constant (and, moreover, quite low) temperature in a dilute aqueous medium. In the course of evolution, over hundreds of millions of years, elegant and perfect molecular mechanisms have been formed that can operate with unusual efficiency in very mild conditions. As a result, the efficiency cellular energy is much higher than that of any engineering devices invented by man.
Cellular energy transformers are complexes of special proteins embedded in biological membranes. Regardless of whether it enters the cell from outside free energy directly with light quanta (during photosynthesis) or as a result of the oxidation of food products with atmospheric oxygen (during respiration), it starts the movement of electrons. As a result, adenosine triphosphate (ATP) molecules are produced and the difference in electrochemical potentials across biological membranes increases. ATP and membrane potential are two relatively stationary sources of energy for all kinds of intracellular work.
The movement of matter through cells and organisms is easily perceived by our consciousness as a need for food, water, air and waste removal. The movement of energy is almost imperceptible. At the cellular level, both of these streams interact in concert in that extremely complex network of chemical reactions that makes up cellular metabolism. Life processes at any level, from the biosphere to a single cell, essentially perform the same task: converting nutrients, energy and information into an increasing mass of cells, waste products and heat.
The ability to capture energy and adapt it to perform various types of work, apparently, is the very life force that has worried philosophers since time immemorial. In the middle of the XIX century. physics formulated the law of conservation of energy, according to which energy is conserved in an isolated system; as a result of certain processes, it can be transformed into other forms, but its quantity will always be constant. However, living organisms are not closed systems. Every living cell has been well aware of this for hundreds of millions of years and continuously replenishes its energy reserves.
During the year, land and ocean plants manipulate colossal amounts of matter and energy: they assimilate 1.5 × 10 11 tons of carbon dioxide, decompose 1.2 × 10 11 tons of water, release 2 × 10 11 tons of free oxygen and store 6 × 10 20 calories solar energy in the form of chemical energy of photosynthesis products. Many organisms, such as animals, fungi and most bacteria, are not capable of photosynthesis: their life activity is entirely dependent on organic matter and oxygen, which are produced by plants. Therefore, we can safely say that, in general, the biosphere exists due to solar energy, and the ancient sages were not at all mistaken when they proclaimed that the sun is the basis of life.
An exception to the heliocentric view of the global energy flow are certain types of bacteria that live by inorganic processes, such as the reduction of carbon dioxide to methane or the oxidation of hydrogen sulfide. Some of these "chemolithotrophic" creatures are well studied (for example, methanogenic bacteria living in the stomach of cows), but their vast number is unknown even to microbiologists. Most chemolithotrophs have chosen extremely uncomfortable habitats that are very difficult to explore - deprived of oxygen, too acidic or too hot. Many of these organisms cannot be grown in pure culture. Until recently, chemolithotrophs were commonly regarded as some kind of exotic, interesting from a biochemical point of view, but of little importance for the energy budget of the planet. In the future, this position may turn out to be erroneous for two reasons. First, bacteria are increasingly found in places that were previously considered sterile: in extremely deep and hot rocks of the earth's crust. In our time, so many habitats of organisms have been identified that can extract energy from geochemical processes that their population may be a significant proportion of the total biomass of the planet. Secondly, there is reason to believe that the very first living beings depended on inorganic sources of energy. If these assumptions are justified, our views on both the global flow of energy and its relationship to the origin of life could change significantly.