ⓘ Blog | Life - Life, Biological organisation, Carbon-based life, Chirality, Coleridges theory of life, extension ..

Life

Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased, or because they never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. Biology is the science concerned with the study of life. There is currently no consensus regarding the definition of life. One popular definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve. Other definitions sometimes include non-cellular life forms such as viruses and viroids. Abiogenesis is the natural process of life arising from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but a gradual process of increasing complexity. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. The earliest known life forms are microfossils of bacteria. Researchers generally think that current life on Earth descends from an RNA world, although RNA-based life may not have been the first life to have existed. The classic 1952 Miller–Urey experiment and similar research demonstrated that most amino acids, the chemical constituents of the proteins used in all living organisms, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. Complex organic molecules occur in the Solar System and in interstellar space, and these molecules may have provided starting material for the development of life on Earth. Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale, but it has also adapted to survive in most ecosystems and conditions. Some microorganisms, called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to most other life on Earth. The cell is considered the structural and functional unit of life. There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many biomolecules such as proteins and nucleic acids. Cells reproduce through a process of cell division, in which the 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 obsolete concepts such as odic force, hylomorphism, spontaneous generation and vitalism, that have now been disproved by biological discoveries. Aristotle is considered to be the first person to classify organisms. Later, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Eventually new groups and categories of life were discovered, such as cells and microorganisms, forcing dramatic revisions of the structure of relationships between living organisms. Though currently only known on Earth, life need not be restricted to it, and many scientists speculate in 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 examine systems related to natural life. Death is the permanent termination of all biological functions which sustain an organism, and as such, is the end of its life. Extinction is the term describing the dying out of a group or taxon, usually a species. Fossils are the preserved remains or traces of organisms.

Biological organisation

Biological organization is the hierarchy of complex biological structures and systems that define life using a reductionistic approach. The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of this scheme are often referred to as an ecological organization concept, or as the field, hierarchical ecology. Each level in the hierarchy represents an increase in organizational complexity, with each "object" being primarily composed of the previous levels basic unit. The basic principle behind the organization is the concept of emergence - the properties and functions found at a hierarchical level are not present and irrelevant at the lower levels. The biological organization of life is a fundamental premise for numerous areas of scientific research, particularly in the medical sciences. Without this necessary degree of organization, it would be much more difficult - and likely impossible - to apply the study of the effects of various physical and chemical phenomena to diseases and physiology body function. For example, fields such as cognitive and behavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts of pharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism. These applications extend into the ecological levels as well. For example, DDTs direct insecticidal effect occurs at the subcellular level, but affects higher levels up to and including multiple ecosystems. Theoretically, a change in one atom could change the entire biosphere.

Carbon-based life

Carbon is a primary component of all known life on Earth, representing approximately 45–50% of all dry biomass. Carbon compounds occur naturally in great abundance on Earth. Complex biological molecules almost always consist of carbon atoms bonded with other elements, especially oxygen and hydrogen and frequently also nitrogen, phosphorus, and sulfur. Because it is lightweight and relatively small in size, carbon molecules are easy for enzymes to manipulate. It is frequently assumed in astrobiology that if life exists elsewhere in the Universe, it will also be carbon-based. Critics refer to this assumption as carbon chauvinism.

Chirality

Chirality is a property of asymmetry important in several branches of science. The word chirality is derived from the Greek χειρ, "hand," a familiar chiral object. An object or a system is chiral if it is distinguishable from its mirror image; that is, it cannot be superposed onto it. Conversely, a mirror image of an achiral object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called enantiomorphs Greek, "opposite forms" or, when referring to molecules, enantiomers. A non-chiral object is called achiral sometimes also amphichiral and can be superposed on its mirror image. The term was first used by Lord Kelvin in 1893 in the second Robert Boyle Lecture at the Oxford University Junior Scientific Club which was published in 1894: I call any geometrical figure, or group of points, chiral, and say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself. Human hands are perhaps the most universally recognized example of chirality. The left hand is a non-superimposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide across all axes. This difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using their left hand, or if a left-handed glove is placed on a right hand. In mathematics, chirality is the property of a figure that is not identical to its mirror image.

Coleridge's theory of life

Romanticism grew largely out of an attempt to understand not just inert nature, but also vital nature. Romantic works in the realm of art and Romantic medicine were a response to the general failure of the application of method of inertial science to reveal the foundational laws and operant principles of vital nature. German romantic science and medicine sought to understand the nature of the life principle identified by John Hunter as distinct from matter itself via Johan Friedrich Blumenbachs Bildungstrieb and Romantic medicines Lebenskraft, as well as Roschlaubs development of the Brunonian system of medicine system of John Brown, in his excitation theory of life, working also with Schellings Naturphilosophie, the work of Goethe regarding morphology, and the first dynamic conception of physiology of Richard Saumarez. However, it is in Samuel Taylor Coleridge that we find the question of life and vital nature most intensely and comprehensively examined, particularly in his Hints towards the Formation of a more Comprehensive Theory of Life, providing the foundation for Romantic philosophy, science and medicine. The work is key to understanding the relationship of Romantic literature and science.

Life extension

Life extension is the idea of extending the human lifespan, either modestly – through improvements in medicine – or dramatically by increasing the maximum lifespan beyond its generally settled limit of 125 years. The ability to achieve such dramatic changes, however, does not currently exist. Some researchers in this area, and "life extensionists", "immortalists" or "longevists" those who wish to achieve longer lives themselves, believe that future breakthroughs in tissue rejuvenation, stem cells, regenerative medicine, molecular repair, gene therapy, pharmaceuticals, and organ replacement such as with artificial organs or xenotransplantations will eventually enable humans to have indefinite lifespans agerasia through complete rejuvenation to a healthy youthful condition. The ethical ramifications, if life extension becomes a possibility, are debated by bioethicists. The sale of purported anti-aging products such as supplements and hormone replacement is a lucrative global industry. For example, the industry that promotes the use of hormones as a treatment for consumers to slow or reverse the aging process in the US market generated about $50 billion of revenue a year in 2009. The use of such products has not been proven to be effective or safe.

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