Life is a characteristic that distinguishes individuals who have biological processes such as signaling and self-sustaining processes from those that do not, either because these functions have ceased, or because they never had such functions and are inanimate. There are various forms of life, such as plants, animals, fungi, Protista, archaea, and bacteria. Biology is the science concerned with the study of life.
Currently there is no consensus on the definition of life. One of the most popular definitions is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to the environment, respond to stimuli, reproduce and develop. Other definitions sometimes include such cell-free viruses and viroid.
Abiogenesis is the natural process of life arising from nonliving matter such as simple organic compounds. The prevailing scientific hypothesis is that the transition from inanimate to living beings not an isolated event, but a process of gradual increase of difficulty. Life on Earth first appeared to 4.28 billion years ago, soon after the formation of the ocean 4.41 billion years ago, soon after the formation of the Earth 4.54 billion years ago. The earliest known life forms are microorganisms bacteria. Researchers generally believe that the current life on Earth descends from an RNA world, RNA although life may not be the first life on earth. Classic 1952 the experiment the Miller–Urey and similar studies have shown that most amino acids, the chemical components of proteins in all living organisms, can be synthesized from inorganic compounds under conditions designed to replicate those of the early Earth. Complex organic molecules occur in the Solar system and in interstellar space, and these molecules can be provided source material for the development of life on Earth.
Since its original inception, life on Earth has changed the environment on a geological time scale, but it is also adapted to survive in the ecosystems and conditions. Some microorganisms, called extremophiles, can thrive in physical or geochemical extreme conditions that are detrimental to most other life forms on Earth. Cell is structural and functional unit of life. There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed in a membrane and contain many biomolecules, such as proteins and nucleic acids. Cells reproduce by cell division in which parent cell divides into two or more daughter cells.
In the past there have been many attempts to define what is meant by "life" through outdated concepts such as odic force, hylomorphism, spontaneous generation and vitalism, which is already refuted by biological discoveries. Aristotle was the first person to classify organisms. Later, Carl Linnaeus introduced his binomial nomenclature for the classification of species. The result was a new groups and categories of life detected, such as cells and microorganisms, causing dramatic changes in the structure of relationships between living organisms. Although currently known only on Earth, life can not be limited, and many scientists suggest the existence of extraterrestrial life. Artificial life is a computer simulation or human-made reconstruction of any aspect of life, which is often used to study systems associated with natural life.
Death is the cessation of all biological functions that maintain the organism, and as such, it is the end of his life. Extinction is a term that describes the dying out of a group or taxon, usually species. Fossils are the preserved remains or traces of living organisms.
1. Definition. (Определение)
The definition of life has long been a challenge for scientists and philosophers, with many different definitions put forward. This is partly because life is a process, not a substance. This is compounded due to the lack of knowledge of the characteristics of living beings, if any, which may be developed outside of the Earth. Philosophical definitions of life were also made, similar difficulties on how to distinguish the living from the dead. The legal definition of life was also discussed, although they usually focus on the decision to declare a person dead and the legal consequences of this decision.
1.1. Definition. Biology. (Биология)
Because there is no unequivocal definition of life, most of the existing definitions in biology is descriptive. Life is a characteristic of something that maintains, strengthens and enhances its existence in the environment. This feature shows all or most of the following:
- Reproduction: the ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.
- Adaptation: the ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organisms heredity, diet and external factors.
- Growth: maintenance of a high level of anabolism than catabolism. A growing organism increases in size in all its parts, not just the accumulation of matter.
- Homeostasis: regulation of internal environment to maintain a steady state, for example, sweating to reduce temperature.
- Response to stimuli: a response can take many forms, from the contraction of a unicellular organism to external chemicals, complex reactions involving all the senses of multicellular organisms. The answer is often expressed by motion, for example, the leaves of the plant turns to the Sun phototropism, and chemotaxis.
- Organization: being structurally composed of one or more cells – the basic units of life.
- Metabolism the transformation of energy by converting chemicals and energy anabolism cellular components and decomposition of organic matter catabolism. Living beings need energy to maintain internal organization homeostasis and to produce the other phenomena associated with life.
These complex processes, called physiological functions, the underlying physical and chemical bases, as well as signaling and control mechanisms required to sustain life.
1.2. Definition. Alternative definitions. (Альтернативные определения)
From the point of view of physics, living beings are thermodynamic systems with an organized molecular structure that can reproduce itself and evolve as survival dictates. Thermodynamically, life was described as an open system that allows the use of gradients in its vicinity to create imperfect copies of itself. Hence, life is self-sustained chemical system capable of undergoing Darwinian evolution. The main advantage of this definition is that it distinguishes the life of an evolutionary process, not its chemical composition.
Others take a systemic viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living beings are self-organizing and automoatically own production. Variations of this definition include definition of Stuart Kauffmans as an independent agent or multi-agent system capable of reproducing itself or themselves, and complete at least one thermodynamic work cycle. This definition also new functions over time.
1.3. Definition. Viruses. (Вирусы)
Whether or not viruses should be considered alive is debatable. They are most often considered as simple replicators, not life forms. They have been described as "organisms at the edge of life and death," because they possess genes, evolutionary by natural selection, and replicate by creating multiple copies of themselves through self-Assembly. However, viruses are not metaboliziruet, and they require a host cell to make new products. Virus self-Assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic molecules.
1.4. Definition. Biophysics. (Биофизика)
To reflect the minimum phenomena required, other biological definitions of life have been proposed, many of which are based on chemical systems. The researchers noted that the living function on negative entropy. In other words, living processes can be viewed as a delay of the spontaneous diffusion or dispersion of the internal energy of biological molecules towards more potential microstates. In more detail, according to physicists such as John Bernal, Erwin schrödinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena which are open or continuous systems enables to decrease their internal entropy at the expense of matter and energy from the environment and then rejected in a degraded form.
1.5. Definition. Living systems theory. (Живет Теория систем)
Living systems are open self-organizing living things that interact with their environment. These systems are supported by flows of information, energy and matter.
Some scientists have proposed in the last few decades, in the General theory of living systems needs to explain the nature of life. Such a General theory may arise from environmental and biological Sciences, attempts to map General principles for how all living systems. Instead of studying the phenomena, trying to break into components, a General living systems theory explores phenomena from the point of view of dynamic patterns of the relationships of organisms with their environment.
1.6. Definition. The Gaia Hypothesis. (Гипотеза Гайи)
The idea that the Earth is alive is found in philosophy and religion, but the first scientific discussion was by the Scottish scientist James Hutton. In 1785 he argued that the Earth is a superorganism and that its proper study should be physiology. Hutton is considered the father of Geology, but his idea of a living Earth was forgotten in the intense reductionism of the 19th century. The Gaia hypothesis, proposed in the 1960-ies of the scientist James Lovelock, means that life on Earth as a single organism that defines and maintains environmental conditions necessary for its survival. This hypothesis has served as one of the foundations of the modern system of Sciences about the Earth.
1.7. Definition. Nonfractionability
The first attempt of a General theory of living systems to explain the nature of life was in 1978, by American biologist James Grier Miller. Robert Rosen 1991 built on this by defining a system component as "a unit of organization in the composition function, i.e., a definite relation between part and whole." From this and other starting concepts, he developed a "relational theory of systems" that attempts to explain the special properties of life. In particular, he identified "nonfractionability components in an organism" as the fundamental difference between living systems and "biological machines."
1.8. Definition. Life as a property of ecosystems. (Жизнь как свойство экосистем)
The purpose of life treats environmental fluxes and biological fluxes together as a "reciprocity of influence", and the relationship with environment is arguably as important for understanding life as it is for understanding ecosystems. As Harold J. The morowitz 1992 explains it, life is a property of the ecosystem, not the individual organism or species. He argues that the definition of the ecosystem of life is preferable to a strictly biochemical or physical. Robert Ulanowicz 2009 mutualism as the key to understanding the systemic, order-generating behavior of life and ecosystems.
1.9. Definition. Complex system biology. (Комплексная система биологии)
Integrated system CSB biology-the science that studies the emergence of complexity in functional organisms from the viewpoint of dynamical systems theory. The latter is often called also systems biology and aims to understand the most fundamental aspects of life. A closely related approach to CSB and systems biology, called relational biology is mainly concerned with understanding life processes from the point of view of the most important relations, and categories of such relations among the essential functional components of organisms, to multicellular organisms, this has been defined as "categorical biology", or a model representation of organisms as a category theory of biological relations, and algebraic topology of the functional organization of living organisms from the point of view of their dynamic, complex networks of metabolic, genetic, and epigenetic processes and signaling pathways. An alternative, but closely related approaches focus on the interdependance of constraints, where constraints can be either molecules, such as enzymes, or macroscopic, such as the geometry of the bone or the vascular system.
1.10. Definition. Darwinian dynamic. (Дарвиновская динамические)
It was also argued that the evolution of order in living systems and certain physical systems obey a common fundamental principle called the Darwinian dynamic. The Darwinian dynamic was formulated by first considering how macroscopic order is generated in a simple air-biological system far from thermodynamic equilibrium, and continuing with consideration of short, replicating RNA molecules. The main goal of the generation process has been completed to be basically the same for both types of systems.
1.11. Definition. The theory of operator. (Теория оператора)
Another systemic definition, called the operator theory suggests that "life is a General term for the presence of typical closure in organisms, a typical circuit of a membrane and an autocatalytic set in the cell" and that the organism is any system of organization that corresponds to the type of operator that is at least as complicated as cells. Life can also be modeled as a network of inferior negative feedbacks of regulatory mechanisms subordinated to a higher positive feedback formed by the potential of expansion and reproduction.
2.1. History of the study. Materialism. (Материализм)
Some of the earliest theories of life were materialist, believing that all that exists is matter and that life is merely a complex form or arrangement of matter. 430 BC Empedocles argued that everything in the Universe consists of a combination of four eternal "elements" or "roots": earth, water, air and fire. All changes are explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements.
Democritus 460 BC believed that the essential characteristic of life is the presence of the psyche of the soul. Like other ancient writers, he tries to explain what makes something alive. His explanation was that fiery atoms of the soul in exactly the same atoms and void account for any other thing. He elaborates on fire because of the apparent connection between life and heat, and because fire moves.
Platos the world of eternal and unchanging forms, are underrepresented in the divine artisan, contrasts sharply with the various mechanistic Weltanschauungen, of which atomism was, by the fourth century, at least the most famous. This dispute continued throughout the ancient world. Atomistic mechanism got a shot in the arm from Epicurus. while the Stoics adopted a divine teleology. The choice seems simple: either show how a structured, regular world could arise out of undirected processes, or enter data into the system.
The mechanistic materialism that originated in Ancient Greece was revived and revised by the French philosopher Rene Descartes who held that animals and humans was a complex of parts that together functioned as a machine. In the 19th century, advances in cell theory in biological science encouraged this view. The theory of evolution Charles Darwin 1859-this is the mechanistic explanation of the origin of species by means of natural selection.
2.2. History of the study. Hylomorphism
Hylomorphism is the theory, first expressed by the Greek philosopher Aristotle 322 BC. The application of hylomorphism to biology was important for Aristotle, and biology is widely discussed in his extant writings. From this point of view, everything in the Universe consists of matter and form, and the form of the living being is its soul, the Greek psyche, Latin Anima. There are three kinds of souls: the vegetative soul of plants, which causes them to grow and decay and nourish, but not cause motion and sensation, the animal soul, which causes animals to move and feel, and a reasonable soul, which is the source of consciousness and thought, which Aristotle believed, is only human. Each Higher Soul has all the attributes of the lower one. Aristotle believed that while matter can exist without form cannot exist without matter, and that therefore the soul cannot exist without body.
This score corresponds to the teleological explanation of life that make up the phenomenon from the point of view of purpose or goal-orientation. Thus, white polar bear fur to explain its camouflage function. A causal link from future to the past is in conflict with the scientific evidence for natural selection, which explains the result in the preliminary cause. Biological features are explained not by looking at future optimal results, but looking at the past evolutionary history that has led to the natural selection of the objects in question.
2.3. History of the study. Spontaneous generation. (Самозарождения)
Spontaneous generation was the belief that living organisms can be formed without descent from similar organisms. As a rule, the idea was that certain forms such as fleas could arise from inanimate matter such as dust or the supposed seasonal generation of mice and insects from dirt or debris.
The theory of spontaneous generation was proposed by Aristotle, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms, it dominated for two millennia. He finally dispelled the experiments of Louis Pasteur in 1859, who expanded on the studies of predecessors, such as Francesco Redi. A refutation of traditional notions of procreation is already not a matter of controversy among biologists.
2.4. History of the study. Vitalism. (Витализма)
Vitalism is the belief that the life-principle is non-material. This is due to Georg Ernst Stahl 17th century, and remained popular until the mid-19th century. He urged philosophers as Henri Bergson, Friedrich Nietzsche and Wilhelm Dilthey, anatomists like Marie françois Xavier Bichat, and chemists like Justus von Liebig. Vitalism suggested that there is a fundamental difference between organic and inorganic material, and the belief that organic material can only be derived from living things. This was disproved in 1828 when Friedrich Wohler prepared urea from inorganic materials. The Wohler synthesis is the starting point of modern organic chemistry. It has historical significance because it was the first organic compounds produced by inorganic reactions.
During the 1850s, Hermann von Helmholtz envisaged by Julius Robert von Mayer, demonstrated that no energy is lost in muscle movement, suggesting that no "vital forces" necessary to move. These results led to the abandonment of scientific interest in vitalistic theories, although the Belief lingered in pseudoscientific theories such as homeopathy, which interpreterpath diseases and diseases caused by disturbances in a hypothetical vital force or life force.
The age of the Earth-about 4.54 billion years. Evidence suggests that life on Earth at least 3.5 billion years with the oldest physical evidence of life is 3.7 billion years, however, some theories, such as the Late heavy bombardment theory suggest that life on Earth could have started even earlier, back in 4.1–4.4 billion years ago, and chemistry leading to life may have begun shortly after the Big Bang 13.8 billion years ago, in the era when the Universe was only 10-17 million years old.
More than 99% of all species of living organisms, of more than five million species living on Earth, estimated to have disappeared.
Although the amount of land catalogued species of microorganisms, is between 1.2 million and 2 million, the Total number of species on the planet is uncertain. Estimates range from 8 million to 100 million, With a narrower range between 10 and 14 million, but it could be 1 trillion, only one-thousandth of one percent of the species are described according to the researches, implemented in may 2016. The total number of associated base pairs of DNA on the Earth is estimated at 5.0 x 10 37 and weigh 50 billion tons. For comparison, the total mass of the biosphere is the TTC as much as 4 trillion tonnes of carbon. In July 2016, scientists reported the identification of a set of 355 genes from the last common ancestor Luca all organisms living on Earth.
All known life forms share fundamental molecular mechanisms, reflecting their common origin, on the basis of these observations, hypotheses on the origin of life trying to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life protocells and metabolism. The model was divided into "genes-first" and "metabolism-first" category, but a recent trend is the emergence of hybrid models that combine both categories.
There is no current scientific consensus about how life originated. However, most accepted scientific models build in the course of the experiment the Miller–Urey and the work of Sidney Fox, show that conditions on primitive Earth favored chemical reactions that synthesize amino acids and other organic substances from inorganic precursors and phospholipids spontaneously form lipid bilayers, the basic structure of the cell membrane.
Living organisms synthesize proteins, which are polymers of amino acids using instructions encoded in DNA-deoxyribonucleic acid. Protein synthesis involves the intermediary ribonucleic acid RNA polymers. One possibility for how life began is that genes originated first, followed by proteins, in the otherness that proteins came first and then genes.
However, since genes and proteins are required for getting the other problem, given that it was before-its like the chicken or the egg. Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently.
So perhaps first proposed by Francis Crick that life based on RNA, which carries DNA as properties of information storage and the catalytic properties of some proteins. This is called the RNA world hypothesis, which is confirmed by the observation that many of the most important components of cells, those that develop more slowly are composed mainly or exclusively of RNA. In addition, many important co-factors, obtaining substances closely related to them. The catalytic properties of RNA had not yet been demonstrated when the hypothesis was first proposed, but they were confirmed by Thomas Cech in 1986.
One problem with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA. However, for the successful synthesis of certain RNA molecules under the conditions that existed before life on Earth has been achieved by adding alternative precursors in the prescribed manner with the phosphate is the precursor to the whole reaction. This study makes the RNA world hypothesis more plausible.
Geological results in 2013 showed that reactive phosphorus as phosphite were abundant prior to 3.5 GA, and that Schreibersite easily reacts with aqueous glycerol to generate phosphite and glycerol 3-phosphate. It is assumed that Schreibersite-containing meteorites from the Late heavy bombardment, could early reduced phosphorus, which could react with prebiotic organic molecules to form phosphorylated molecules, such as RNA.
In 2009, experiments demonstrated Darwinian evolution of a two-component system of RNA enzymes, ribozymes, in vitro. The work was performed in the laboratory of Gerald Joyce, who stated that "this is the first example, outside of biology, of evolutionary adaptation in a molecular genetic system."
Prebiotic compounds may occur extraterrestrially. The findings of the NASA in 2011, based on studies with meteorites found on Earth, suggest DNA and RNA components adenine, guanine and related organic molecules can form in outer space.
In March 2015, NASA scientists reported that, for the first time, the complex of DNA and RNA organic substances of life, including uracil, cytosine and thymine, were created in the laboratory in open space, using chemicals such as a pyrimidine, found in meteorites. Pyrimidine, such as polycyclic aromatic hydrocarbons PAHs, the most carbon-rich chemical substance contained in the Universe may have been formed in red giants or in interstellar dust and gas clouds, according to scientists.
According to the panspermia hypothesis, microscopic life-distributed by meteoroids, asteroids and other small Solar system bodies - may exist throughout the Universe.
4. Environmental conditions. (Условия окружающей среды)
The diversity of life on Earth is the result of a dynamic interaction between genetic opportunity, metabolic, and environmental challenges, and symbiosis. The greater part of its existence, Earths habitable environment is dominated by microorganisms and subjected to their metabolism and evolution. As a consequence of these microbial activities, the physical and chemical conditions on Earth changed on the geological time scale, thereby affecting the path of evolution of subsequent life. For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the environment of the Earth. Because oxygen was toxic to all life on Earth at the time, this creates a novel evolutionary problems, and eventually led to the formation of large land animals and plants. This interaction between organisms and their environment is an inherent property of living systems.
4.1. Environmental conditions. Biosphere. (Биосфера)
The biosphere is the global sum of all ecosystems. It can also be described as the zone of life on Earth, a closed system apart from solar and cosmic radiation and heat from the Earth, and is largely self-regulating. The most General biophysiological definition, the biosphere is the global ecological system integrating all living beings and their relationships, including interactions with elements of the lithosphere, Geosphere, hydrosphere and atmosphere.
Life forms in all parts of the Earths biosphere including soil, hot springs, inside rocks, at least 19 km, 12 miles deep in the earth, in the deepest parts of the ocean, and at least 64 km 40 Mi high in the atmosphere. Under certain test conditions, life forms observed to thrive in almost zero gravity and survive in the vacuum of outer space. Life forms appear to thrive in the Mariana trench, the deepest place on Earths oceans. Other researchers reported related studies that forms of life thrive inside rocks up to a height of 580 m 1.900 m, 0.36 miles below the sea floor under 2.590 m 8.500 ft, 1.61 Mi ocean off the coast of North-Western part of the United States, and 7.900 m 2.400 m, 1.5 mi under the seabed in the waters of Japan. In August 2014, scientists confirmed the existence of life forms 800 m 2.600 feet, 0.50 Mi under the ice of Antarctica. According to one researcher, "you can find microbes everywhere - theyre extremely adaptable to conditions, and survive wherever they are."
The biosphere is postulated to have evolved, beginning with a process of biopoesis life created naturally from non-living matter such as simple organic compounds, biogenesis, or life created from living matter, at least some 3.5 billion years ago. The earliest evidence of life on Earth includes found biogenic graphite in 3.7 billion-year-old recommendations of the rocks from Western Greenland and microbial fossils found in 3.48 billion-year-old Sandstone from Western Australia. Recently, in 2015, remains "the biotic life" was discovered in the 4.1 billion year old rocks in Western Australia. In 2017, the putative fossilized microorganisms or microorganisms were announced discovered in hydrothermal vent precipitates in the Nuvvuagittuq belt, Quebec, Canada, which was as old as 4.28 billion years, the oldest record of life on earth, offering "an almost instantaneous appearance of life" after the ocean forming 4.4 billion years ago, soon after the formation of the Earth 4.54 billion years ago. According to biologist Stephen Blair hedges, "if life arose relatively quickly on the Ground. then this may be common in the Universe."
In a General sense, biospheres, or closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as Biosphere 2 and BIOS-3, and possibly on other planets or moons.
4.2. Environmental conditions. The range of tolerance. (Диапазон толерантности)
The inert components of an ecosystem are physical and chemical factors necessary for life - energy from sunlight or chemical energy, water, heat, atmosphere, gravity, nutrients and ultraviolet solar radiation protection. In most ecosystems the conditions vary during the day and from one season to the next. To live in most ecosystems, then, organisms must be able to survive in various conditions, called "range of tolerance". Outside the "zones of physiological stress" where the survival and reproduction are possible but not optimal. Outside these zones the "zones of intolerance", where survival and reproduction of this organism is unlikely or impossible. Organisms with a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance.
4.3. Environmental conditions. Extremophiles. (Экстремофилы)
To survive, some microorganisms can assume forms that enable them to withstand freezing, complete desiccation, starvation, high levels of radiation exposure and other physical or chemical problems. These microorganisms may survive exposure to such conditions for weeks, months, years, or even centuries. Extremophiles are microbial life forms that thrive outside the ranges where life is commonly found. They differ in harnessing unusual energy sources. While all organisms are composed of nearly identical molecules, evolution has enabled such microbes to cope with this wide range of physical and chemical conditions. Characterization of the structure and metabolic diversity of microbial communities in such extreme environments is ongoing.
Microbial life forms thrive even in the Mariana trench, the deepest place on Earths oceans. Also microbes thrive inside rocks up to 580 ft 1.900 m below the sea floor under 8.500 2.600 m feet from the ocean.
Investigation of the strength and versatility of life on Earth, as well as understanding the molecular systems that some organisms utilize to survive such extremes, is important to search for life beyond Earth. For example, the lichen could survive for a month in a simulated Martian environment.
4.4. Environmental conditions. Chemical elements. (Химические элементы)
All life forms require certain core chemical elements needed for biochemical functioning. They include carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur - the elemental macronutrients for all organisms, often represented by the acronym CHNOPS. Together, these components of nucleic acids, proteins and lipids, the bulk of living matter. Five of these six elements comprise the chemical components of DNA, with the exception of sulfur. The latter is a component of amino acids cysteine and methionine. The most biologically abundant of these elements is carbon, which has the desirable attribute of forming multiple, stable covalent bonds. This allows organic molecules based on carbon in the form of a huge diversity of chemical events. Alternative hypothetical types of biochemistry was invited to address one or more of these items, a replacement item to one not included in the list, or change required chiralities or other chemical properties.
4.5. Environmental conditions. DNA. (ДНК)
Deoxyribonucleic acid is the molecule which carries most of the genetic instructions used in the process of growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA nucleic acids along with proteins and complex carbohydrates, they are one of the three main types of macromolecules that are essential for all known forms of life. Most DNA molecules consist of two biopolymer strands being twisted around each other, forming a double helix. Two DNA strands are known as polynucleotides since they are composed of simple units called nucleotides. Each nucleotide consists of a nitrogen containing nitrogen or with a cytosine, g-guanine, adenine and thymine t, and deoxiribose sugar and a phosphate group. The nucleotides are connected to each other in a chain by covalent bonds between sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. According to base pairing rules with t and g hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. The total amount of the adjacent base pairs of DNA on the Earth is estimated at 5.0 x 10 37, and weigh 50 billion tons. For comparison, the total mass of the biosphere is the TTC as much as 4 trillion tonnes of carbon.
DNA stores biological information. The DNA backbone is resistant to cleavage and both strands of the double-stranded structure retains the same biological information. Biological information is replicated as the two strands are separated. A substantial part of the DNA of more than 98% for humans is not coding, meaning that these sections do not serve as models for protein sequences.
The two strands of DNA run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of the four informal types of nitrogenous bases, bases. This sequence of the four nucleobases along the backbone that encodes biological information. Genetic code, RNA Strands are translated to specify the sequence of amino acids in proteins. These RNA Strands are initially created using DNA as a template in a process called transcription.
Within cells, DNA is organized into structures called chromosomes. During cell division chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. Unlike prokaryotes bacteria and archaea store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of DNA are transcribed.
DNA was first isolated by Friedrich Miescher in 1869. Its molecular structure was determined by James Watson and Francis Crick in 1953, the model-building whose efforts have been guided by x-ray diffraction data acquired by Rosalind Franklin.
5.1. Classification. Antiquity. (Древности)
The first known attempt to classify organisms was conducted by the Greek philosopher Aristotle 384-322 BC, who classified all living organisms as plant or animal, based mainly on their ability to move. He also distinguished animals with blood from animals without blood, or at least without red blood, which can be compared with the concepts of vertebrates and invertebrates respectively, and divided the animals into five groups: viviparous quadrupeds mammals, oviparous quadrupeds reptiles and amphibians, birds, fish and whales. The bloodless animals were also divided into five groups: cephalopods, crustaceans, insects, shelled animals such as molluscs and echinoderms, and "zoophytes" animals that resemble plants. Although Aristotles work in Zoology was not without errors, it was the greatest biological synthesis and remained the ultimate authority for many centuries after his death.
5.2. Classification. Linnaeus. (Линней)
The study of South America discovered many new plants and animals that needed descriptions and classification. In the second half of the 16th century and beginning of the 17th, careful study of animals commenced and was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification.
In the late 1740s, Carolus Linnaeus introduced his binomial nomenclature for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new terms, and accurately determine their meaning. The classification of Linnaeus has eight levels: Domain, Kingdom, class, order, family, genus and species.
Fungi were originally considered as plants. For a short period Linnaeus had classified them in the taxon vermes in the world, but then put them back in the soles. Copeland classified the fungi in his Protoctista, thus partially avoiding the problem but to recognize their special status. The problem was eventually solved by Whittaker, when he gave them their own Kingdom in his five-Kingdom system. Evolutionary history shows that the fungi are closer to animals than to plants.
As new discoveries enabled detailed study of cells and microorganisms, have been identified and new groups of life were created in the field of cell biology and Microbiology. These new organisms were originally described separately in protozoa as animals and protophyta / div as plants, but were United Haeckel in the Kingdom Protista, later the prokaryotes were divided into kingdoms, the prokaryotes, which ultimately will be divided into two distinct groups, bacteria and archaea. This led to the six-Kingdom, and eventually to the current three-domain system, which is based on evolutionary relationships. However, the classification of eukaryotes, especially of protists, is still controversial.
As Microbiology, molecular biology and Virology developed, non-cellular reproducing agents were discovered, such as viruses and viroid. Will this be working, was a subject of debate viruses lack characteristics of life such as cell membranes, metabolism and ability to grow and respond to their environment. The virus can still be classified into "types" based on their biology and genetics but many aspects of such a classification remain controversial.
In may 2016, scientists reported that 1 billion species are estimated at the present time on Earth was only one-thousandth described by one percent.
The original system of Linnaeus has been changed over time as follows:
5.3. Classification. Cladistic. (Кладистический)
In the 1960-ies appeared cladistics: a system of organization of taxa based on clades in an evolutionary or phylogenetic tree.
6. Cells. (Клетки)
Cells are the basic unit of structure in every living thing, and all cells arise from existing cells by division. Cell theory was formulated by Henri Dutrochet, Theodor Schwann, Rudolf Virchow and others in the early nineteenth century and then became widely accepted. The activity of an organism depends on total activity of its cells, with energy flow occurring within and between them. Cells contain hereditary information which is passed on as a genetic code during cell division.
There are two main types of cells. Prokaryotes no nucleus and other membrane-bound organelles, although they do have circular DNA and ribosomes. Bacteria and archaea are the two domains of prokaryotes. The other major type of cells are the eukaryotes, have a certain nuclei are associated with nuclear membrane and membrane-bound organelles, including mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, and vacuoles. In addition, they possess organized chromosomes that store genetic material. All species of large complex organisms are eukaryotes, including animals, plants and fungi, although most species of eukaryotic protists are microorganisms. The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through endosymbiosis between bacteria and the progenitor eukaryotic cell.
Molecular mechanisms of cell biology protein-based. Most of them are synthesized by the ribosomes through an enzyme-catalyzed process is called protein biosynthesis. The sequence of amino acids is assembled and joined on the basis of gene expression in cells of nucleic acids. In eukaryotic cells, these proteins can be transported and processed through the Golgi apparatus in preparation for dispatch to their destination.
Cells reproduce by cell division in which parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of division in which DNA is replicated, the two copies are attached to parts of the cell membrane. In eukaryotes, then a more complex process of mitosis is. However, the end result is the same, resulting cell copies are identical to each other and to the original cell, except for mutations, and both are capable of further division following an interphase period.
Multicellular organisms may have first appeared through the formation of colonies of identical cells. These cells can form group organisms based on cell adhesion. Individual members of the colony, able to survive on their own, while the members of the true multi-cellular organism has developed a specialization that makes them dependent on the rest of the body for survival. Such organisms are formed clonal and relative or from a single embryonic cell, which is capable of forming the various specialized cells that form the adult organism. This specialization allows multicellular organisms to use resources more efficiently than single cells. In January 2016, scientists reported that about 800 million years ago, minor genetic changes in a molecule called GK-PID may have allowed organisms to move from one cell body to one of the many cells.
Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their processability. Cell signaling coordinates cellular activities, and hence determines the basic functions of multicellular organisms. Signaling between cells can occur via direct contact of cells using juxtacrine signalling, or indirectly through metabolism in the endocrine system. In more complex organisms, coordination of activities can occur through a dedicated nervous system.
7. Extraterrestrial. (Внеземной)
Though life is confirmed only on the Earth, many think that extraterrestrial life is not only plausible, but probable or inevitable. Other planets and their satellites in the Solar system and other planetary systems studied proof that once supported simple life, and projects such as SETI are trying to detect radio signals from possible extraterrestrial civilizations. Other places in the Solar system that can make microbial life included in the composition of the Martian surface, in the upper layers of Venuss atmosphere, and subsurface oceans on some moons of the giant planets. Beyond the Solar system, around other main sequence stars that could support life like the earth, the planet earth type is called the habitable zone. Inner and outer radii of this zone depends on the luminosity of the star, as well as the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone but remain on the Sun-as the "main sequence" of stellar evolution for a short period of time. Small red dwarfs have the opposite problem, with a smaller habitable zone that is prone to higher levels of magnetic activity and the influence of tidal lock with the close orbit. Consequently, stars in the intermediate mass range such as the Sun may have a greater likelihood for Earth-like life to develop. The location of the stars inside the galaxy, can also affect the probability of the formation of life. Stars in regions with a high abundance of heavy elements that can form planets, in combination with low levels of potentially habitat-destructive phenomena supernovae presumably have a higher probability of such planets with complex life. The variables in the Drake equation are used to discuss the conditions on the planets where civilization is likely to exist. Use the equation to predict the number of extraterrestrial life, however, is difficult because many variables are unknown, the equation functions as a mirror of what the user already thinks. As a result, the number of civilizations in the galaxy may be estimated as a minimum of 9.1 x 10 -11 level 156 million, for the calculations, see the Drake equation.
8. Artificial. (Искусственный)
Artificial life is a simulation of some aspect of life, as through computers, robotics, or biochemistry. The study of artificial life imitates traditional biology by recreating some aspects of biological phenomena. Scientists study the logic of living systems by creating artificial environments, seeking to understand the complex information processing that defines such systems. But life, by definition, alive, artificial life is generally referred to as data confined to a digital environment and existence.
Synthetic biology-a new area of biotechnology that combines biological science and engineering. The overall goal is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes a major revision and expansion of biotechnology, with the ultimate goal to be able to design and build engineered biological systems that process information, manipulate chemicals, manufacture of materials and structures, produce energy, obtain food, and maintain and enhance human health and the environment.
9. Death. (Смерть)
Death is the cessation of all vital functions or life processes in an organism or a cell. This can occur as a result of accident, disease, biological interaction, malnutrition, poisoning, senescence, or suicide. After death, the remains of an organism re-enter the biogeochemical cycle. The organisms can be eaten by a predator or scavenger, and then the remaining organic material can be further decomposed by detritivores, organisms which recycle detritus, returning it to the environment for reuse in the food chain.
One of the challenges in defining death is in distinguishing it from life. Death seems to refer to the moment life ends, or when the state that the next life starts. However, to determine when death has occurred is difficult, as the cessation of vital functions are often not at the same time multiple organ systems. Therefore, this solution requires the development of a conceptual line between life and death. This is problematic, however, because there is no consensus about how to define life. The nature of death for millennia, is in the spotlight of the worlds religious traditions and of philosophical inquiry. Many religions maintain faith in some sort of afterlife or reincarnation of the soul, and the resurrection of the body at a later date.
9.1. Death. Extinction. (Вымирание)
Extinction is the process by which a group of taxa and species dies out, reducing biodiversity. At the moment of extinction is generally regarded the death of the last representative of this species. Because the species potential range may be very large, determining this moment is difficult and is usually done retrospectively after a period of apparent absence. Species become extinct when they are no longer able to survive in a changing environment or against superior competition. In the history of the Earth, more than 99% of all species that ever lived are extinct, however, mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.
9.2. Death. Fossils. (Окаменелости)
Fossils are the preserved remains or traces of animals, plants and other organisms from the distant past. The totality of fossils, discovered and undiscovered, and their placement in fossil-containing rock formations and sedimentary layers called strata the fossil record. A preserved specimen is called a fossil if it is older than the arbitrary date of 10.000 years ago. Thus, fossils range in age from the youngest at the beginning of the Holocene, the oldest from the Archaean EON, up to 3.4 billion years.
- Life is the characteristic that distinguishes organisms from inorganic substances and dead objects. Life or The Life may also refer to: Human life disambiguation
- there are significant differences. LFP chemistry offers a longer cycle life than other lithium - ion approaches. Like nickel - based rechargeable batteries
- Life insurance or life assurance, especially in the Commonwealth of Nations is a contract between an insurance policy holder and an insurer or assurer
- Life imprisonment also known as imprisonment for life life in prison, whole - life order, a life sentence, a life term, lifelong incarceration, life incarceration
- A still life plural: still lifes is a work of art depicting mostly inanimate subject matter, typically commonplace objects which are either natural
- The life sciences or biological sciences comprise the branches of science that involve the scientific study of life and organisms such as microorganisms
- Extraterrestrial life is hypothetical life which may occur outside of Earth and which did not originate on Earth. Such life might range from simple prokaryotes
- Kingdom, life peers are appointed members of the peerage whose titles cannot be inherited, in contrast to hereditary peers. In modern times, life peerages
- Life was an American magazine published weekly until 1972, as an intermittent special until 1978, and as a monthly from 1978 until 2000. During its golden
- The meaning of life or the answer to the question: What is the meaning of life pertains to the significance of living or existence in general. Many
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- Half - Life is a series of first - person shooter games developed and published by Valve. In most installments, players control Gordon Freeman, a physicist
- Half - life is a mathematical and scientific description of exponential or gradual decay. Half - life half life or halflife may also refer to: Half - Life film
- The monthly Chess Life and bi - monthly Chess Life Kids formerly School Mates and Chess Life for Kids are the official magazines published by the United
- Slice of life describes the depiction of mundane experiences in art and entertainment. In theater, slice - of - life refers to naturalism, while in literary
- Life cycle, life - cycle, or lifecycle may refer to: Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction
- In England and Wales, life imprisonment is a sentence which lasts until the death of the prisoner, although in most cases the prisoner will be eligible
- A person s life stance, or lifestance, is their relation with what they accept as being of ultimate importance. It involves the presuppositions and theories
- Life After Life may refer to: Life After Life 1975 book a 1975 book about near - death experiences by Raymond Moody Life After Life a 2006 book about
- Fox Life is an international pay television network, launched by the Fox Broadcasting Company in 2004, which airs across Latin America, Europe also available
- Life simulation games form a subgenre of simulation video games in which the player lives or controls one or more virtual characters human or otherwise
- Artificial life often abbreviated ALife or A - Life is a field of study wherein researchers examine systems related to natural life its processes, and
- Life Savers is an American brand of ring - shaped hard and soft candy. Its range of mints and fruit - flavored candies is known for its distinctive packaging
- Standard Life Aberdeen plc, formerly Standard Life plc, is a United Kingdom - based global investment company with headquarters in Edinburgh. In March 2017
- common law and statutory law, a life estate or life tenancy is the ownership of land for the duration of a person s life In legal terms, it is an estate
- The Congregation for Institutes of Consecrated Life and Societies of Apostolic Life CICLSAL Latin: Congregatio pro Institutis Vitae Consecratae et
- The Good Life or Good Life may refer to: Eudaimonia, a philosophical term for the life that one would like to live, originally associated with Aristotle
- Everyday life daily life or routine life comprises the ways in which people typically act, think, and feel on a daily basis. Everyday life may be described
- The Great - West Life Assurance Company also Great - West Life French: La Great - West, compagnie d assurance - vie is a life insurance company. Its headquarters
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