Life
Life on a rocky peak in the Waitakere Ranges
Scientific classification
(unranked) Life (Biota)
Domains and Kingdoms
Life on Earth (Gaeabionta) Nanobes ? Nanobacterium ? Acytota **? Cytota Bacteria * Neomura Archaea Eukaryota Bikonta Apusozoa Rhizaria Excavata Archaeplastida Rhodophyta Glaucophyta Plantae Heterokontophyta Haptophyta Cryptophyta Alveolata Unikonta Amoebozoa Opisthokonta Choanozoa Fungi Animalia Extraterrestrial life (hypothetical)

Life is a condition that distinguishes organisms from non-living objects, such as non-life, and dead organisms, being manifested by growth through metabolism and reproduction. The Waitakere Ranges are a chain of hills generally running approximately 25 km (15 In some systems of Scientific classification, Biota or Vitae is the Superdomain that contains all Life. In biological Taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest Taxonomic rank of Organisms In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system Nanobes are tiny filamental Structures first found in some rocks and Sediments Some hypothesize that they are the smallest form of Life Nanobacteria is the name of a possible class of living organisms specifically cell-walled Microorganisms with a size much smaller than the generally accepted Non-cellular life is Life that exists without cells This term usually is applied to earth-based life and presumes the Phylogenetic classification In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different Cellular life is Life with cells The usual meaning of life as we know it expects that an organism have either Unicellular or Multicellular The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all Neomura is a speculative Clade composed of the two domains of life of Archaea and Eukarya. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex A Bikont ("two flagella" is a eukaryotic cell with two Flagella, as its name suggests The Apusozoa comprise several genera of Flagellate protozoa They are usually around 5-20 μm in size and occur in soils and aquatic habitats where they feed on bacteria The Rhizaria are a species-rich supergroup of Protists They vary considerably in form but for the most part they are Amoeboids with filose reticulose or microtubule-supported The excavates are a major assemblage of Protists often known as Excavata. The Archaeplastida or Primoplantae are a major line of Eukaryotes comprising the land plants green and Red algae and a small The red algae (Rhodophyta ˌroʊdəˈfaɪtə roʊˈdɒfɨtə from Greek: ῥόδον (rhodon = rose + φυτόν (phyton = plant thus red plant are The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater microscopic Algae. Plants are living Organisms belonging to the kingdom Plantae. The heterokonts or stramenopiles are a major line of Eukaryotes presently containing about 10500 known species The haptophytes, classed either as the Prymnesiophyta or Haptophyta are a Phylum of Algae The Chloroplasts are pigmented similarly to those of the The cryptomonads are a small group of Flagellates most of which have Chloroplasts They are common in freshwater and also occur in marine and brackish habitats The alveolates ("with cavities" are a major line of Protists There are three phyla, which are very divergent in form but are now known to be close relatives Unikonts are members of the Unikonta a taxonomic group proposed by Thomas Cavalier-Smith. The Amoebozoa are a major group of Amoeboid protozoa including the majority that move by means of internal Cytoplasmic flow The opisthokonts ( Greek: (opisthō- = "rear posterior" + (kontos = "pole" i Choanozoa ( Greek: (choanos = "funnel" + (zōon = "animal" is the name of a Phylum of protists that belongs A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Extraterrestrial life is Life originating outside of the Earth. Death is the termination of the biological functions that define living Organisms It refers both to a specific Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Reproduction is the Biological process by which new individual Organisms are produced Some living things can communicate and many can adapt to their environment through changes originating internally. Communication is the process of conveying information from a sender to a receiver with the use of a medium in which the communicated information is understood the same way An adaptation is a characteristic of an Organism that has been favored by Natural selection and A physical characteristic of life is that it feeds on negative entropy. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Negative Entropy or negentropy or syntropy of a living system is the entropy that it exports to maintain its own entropy low (see Entropy and life ^[1][2] 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 able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form (see: entropy and life). John Desmond Bernal FRS (born 10 May 1901 died 15 September 1971 was an Irish-born scientist known for pioneering X-ray crystallography. Eugene Paul "EP" Wigner ( Hungarian Wigner Pál Jenő) ( November 17, 1902 &ndash January 1, 1995) was a John Scales Avery, born in 1933 in Lebanon to American parents is a theoretical chemist noted for his research publications in Evolution, Thermodynamics, and In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering Much writing has been devoted to Entropy and life. Research concerning the relationship between the thermodynamic quantity Entropy and the Evolution of Life ^[3][4]

A diverse array of living organisms can be found in the biosphere on Earth. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. Properties common to these organisms—plants, animals, fungi, protists, archaea and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information. Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Carbon forms the backbone of Biology for all Life on Earth. Complex Molecules are made up of carbon bonded with other elements Water is a common Chemical substance that is essential for the survival of all known forms of Life. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called An organization (or organisation &mdash see spelling differences) is a social arrangement which pursues collective goals which controls its own performance and History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance They undergo metabolism, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Reproduction is the Biological process by which new individual Organisms are produced Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of

An entity with the above properties is considered to be a living organism, that is an organism that is alive hence can be called a life form. However, not every definition of life considers all of these properties to be essential. For example, the capacity for descent with modification is often taken as the only essential property of life. This definition notably includes viruses, which do not qualify under narrower definitions as they are acellular and do not metabolize. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable Non-cellular life is Life that exists without cells This term usually is applied to earth-based life and presumes the Phylogenetic classification

Definitions

There is no universal definition of life; there are a variety of definitions proposed by different scientists. To define life in unequivocal terms is still a challenge for scientists. ^[5][6]

Conventional definition: Often scientists say that life is a characteristic of organisms that exhibit the following phenomena:

1. Homeostasis: Regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature. Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit
2. Organization: Being composed of one or more cells, which are the basic units of life. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called
3. Metabolism: Consumption of energy by converting nonliving material into cellular components (anabolism) and decomposing organic matter (catabolism). In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Anabolism is the set of Metabolic pathways that construct molecules from smaller units For the related metabolic process see Anabolism. Catabolism is the set of Metabolic pathways which break down molecules into Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
4. Growth: Maintenance of a higher rate of synthesis than catalysis. The term cell growth is used in two different ways in Biology. A growing organism increases in size in all of its parts, rather than simply accumulating matter. The particular species begins to multiply and expand as the evolution continues to flourish.
5. Adaptation: The ability to change over a period of time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present. eVolution is the third Album by eLDee, it was due to be released in 2008
6. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. A response is often expressed by motion, for example, the leaves of a plant turning toward the sun or an animal chasing its prey.
7. Reproduction: The ability to produce new organisms. Reproduction can be the division of one cell to form two new cells. Usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from at least two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian

Plant life. Plants are living Organisms belonging to the kingdom Plantae.

Herds of zebra and impala gathering on the Masai Mara plain

Marine life around a coral reef. The Masai Mara (also spelled Maasai Mara) is a large Park reserve in south-western Kenya, which is effectively the northern continuation of the Serengeti Coral reefs are Aragonite structures produced by living organisms found in marine waters with little to no nutrients in the water

However, others cite several limitations of this definition. Thus, many members of several species do not reproduce, possibly because they belong to specialized sterile castes (such as ant workers), these are still considered forms of life. One could say that the property of life is inherited; hence, sterile or hybrid organisms such as mules, ligers, and eunuchs are alive although they are not capable of self-reproduction. In its common modern meaning a mule is the offspring of a male Donkey and a female Horse, which is classified as a kind of F1 hybrid. The liger, is a hybrid cross between a male Lion and a female Tiger (i A eunuch (ˈjuːnək is a Castrated man in particular one castrated early enough to have major hormonal consequences the term usually refers to those castrated in order to However, (a) The species as a whole does reproduce, (b) There are no cases of species where 100% of the individuals reproduce, and (c) specialized non-reproducing individuals of the species may still partially propagate their DNA or other master pattern through mechanisms such as kin selection. From the time of antiquity field biologists have observed that some organisms tend to exhibit strategies that favor the reproductive success of their relatives even at a cost to their own survival

Viruses and aberrant prion proteins are often considered replicators rather than forms of life, a distinction warranted because they cannot reproduce without very specialized substrates such as host cells or proteins, respectively. A prion (ˈpriːɒn is thought to be an infectious agent that according to current scientific consensus is comprised entirely of a propagated, mis-folded Also, the Rickettsia and Chlamydia are examples of bacteria that cannot independently fulfill many vital biochemical processes, and depend on entry, growth, and replication within the cytoplasm of eukaryotic host cells. Rickettsia is a Genus of motile, Gram-negative, non-sporeforming, highly Pleomorphic bacteria that can present The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex However, most forms of life rely on foods produced by other species, or at least the specific chemistry of Earth's environment.

The systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Systems theory is an Interdisciplinary field of Science and the study of the nature of Complex systems in Nature, Society, and Autopoiesis literally means "auto (self-creation" (from the Greek: auto αυτό for self- and poiesis ποίησις for creation or production These objects are not to be confused with dissipative structures (e. Another meaning of "dissipative system" is one that dissipates heat see heat dissipation. g. fire).

Variations of this definition include Stuart Kauffman's definition of life as an autonomous agent or a multi-agent system capable of reproducing itself or themselves, and of completing at least one thermodynamic work cycle. Stuart Alan A Kauffman ( 28 September, 1939) is an American theoretical Biologist and Complex systems researcher concerning the Origin of An autonomous agent is a system situated in and part of an environment, which senses that environment and acts on it over time in pursuit of its own agenda A multi-agent system ( MAS) is a system composed of multiple interacting Intelligent agents Multi-agent systems can be used to solve problems which are difficult or A thermodynamic cycle is a series of Thermodynamic processes which returns a system to its initial state

Proposed definitions of life include:

1. Living things are systems that tend to respond to changes in their environment, and inside themselves, in such a way as to promote their own continuation. ^[7]
2. Life (a living individual) is defined as a network of inferior negative feedbacks (regulatory mechanisms) subordinated to a superior positive feedback (potential of expansion, reproduction)^[8]
3. Life is a characteristic of self-organizing, self-recycling systems consisting of populations of replicators that are capable of mutation, around most of which homeostatic, metabolizing organisms evolve. Self-organization is a process of Attraction and repulsion in which the internal organization of a System, normally an open system, increases System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract In Biology a population is the collection of inter-breeding organisms of a particular Species; in Sociology In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life.
4. Type of organization of matter producing various interacting forms of variable complexity, whose main property is to replicate almost perfectly by using matter and energy available in their environment to which they may adapt. In this definition "almost perfectly" relates to mutations happening during replication of organisms that may have adaptive benefits.
5. Life is a potentially self-perpetuating open system of linked organic reactions, catalyzed simultaneously and almost isothermally by complex chemicals (enzymes) that are themselves produced by the open system.

Origin of life

Main article: Origin of life

An aerial photo of microbial mats around the Grand Prismatic Spring of Yellowstone National Park. In the Natural sciences, Abiogenesis, or origin of life, is the study of how Life on Earth emerged from Inanimate Organic The Grand Prismatic Spring in Yellowstone National Park is the largest Hot spring in the United States, and the third largest in the world next to

Although it cannot be pinpointed exactly, evidence suggests that life on Earth has existed for about 3. 7 billion years. ^[9]

There is no truly "standard" model for the origin of life, but most currently accepted scientific models build in one way or another on the following discoveries, which are listed roughly in order of postulated emergence:

1. Plausible pre-biotic conditions result in the creation of the basic small molecules of life. This was demonstrated in the Miller-Urey experiment, and in the work of Sidney Fox. The Miller-Urey experiment (or Urey-Miller experiment) was an Experiment that simulated hypothetical conditions present on the Early Earth and tested Sidney Walter Fox ( 24 March 1912 - 10 August 1998) was a Los Angeles -born biochemist responsible for unique discoveries
2. Phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane. Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate A lipid bilayer or bilayer lipid membrane ( BLM) is a membrane composed of Lipid molecules (usually Phospholipids. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer
3. Procedures for producing random RNA molecules can produce ribozymes, which are able to produce more of themselves under very specific conditions. Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes
4. The Panspermia hypothesis proposes that life originated elsewhere in the universe and was subsequently transferred to Earth perhaps via meteorites, comets or cosmic dust. Panspermia ( Gk. πάς/πάν (pas/pan all and σπέρμα ( sperma, seed is the Hypothesis that "seeds" of Life exist already A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail —

There are many different hypotheses regarding the path that might have been taken from simple organic molecules via pre-cellular life to protocells and metabolism. An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Many models fall into the "genes-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid models that do not fit into either of these categories. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. ^[10]

Classification of life

Main article: Biological classification

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The hierarchy of biological classification's major eight taxonomic ranks. Taxonomic rank ( rank, category, taxonomic category is an abstract term used in the Scientific classification, or Taxonomy, of organisms Life is divided into domains, which are subdivided into further groups. Intermediate minor rankings are not shown.

Traditionally, people have divided organisms into the classes of plants and animals, based mainly on their ability of movement. Plants are living Organisms belonging to the kingdom Plantae. The first known attempt to classify organisms, as per personal observations, was conducted by the Greek philosopher Aristotle. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great.

He classified all living organisms known at that time as either a plant or an animal. Aristotle 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. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate He divided the blooded animals into five groups: viviparous quadrupeds (mammals), birds, oviparous quadrupeds (reptiles and amphibians), fishes and whales. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is The bloodless animals were also divided into five groups: cephalopods, crustaceans, insects (which also included the spiders, scorpions, and centipedes, in addition to what we now define as insects), shelled animals (such as most molluscs and echinoderms) and "zoophytes". The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Structure of crustaceans As Arthropods crustaceans have a stiff Exoskeleton, which must be shed to allow the animal to grow ( Ecdysis or molting Spiders are Predatory Invertebrate Animals that have two body segments, eight legs no chewing mouth parts and no wings Scorpions are eight-legged Carnivorous Arthropods They are members of the order Scorpiones within the class Arachnida. Centipedes (from Latin prefix centi-, "hundred" and Greek ποδός podos, " Foot " are Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) A zoophyte is an Animal that visually resembles a Plant. An example is a Sea anemone. Though Aristotle's work in zoology was not without errors, it was the grandest biological synthesis of the time, and remained the ultimate authority for many centuries after his death. His observations on the anatomy of octopus, cuttlefish, crustaceans, and many other marine invertebrates are remarkably accurate, and could only have been made from first-hand experience with dissection. ^[11]

The exploration of parts of the New World produced large numbers of new plants and animals that needed descriptions and classification. The New World is one of the names used for the non-Eurasian/non-African parts of the Earth specifically the Americas and Australia. The old systems made it difficult to study and locate all these new specimens within a collection and often the same plants or animals were given different names because the number of specimens were too large to memorize. A system was needed that could group these specimens together so they could be found, the binomial system was developed based on morphology with groups having similar appearances. The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism In the latter part of the 16th century and the beginning of the 17th, careful study of animals commenced, which, directed first to familiar kinds, was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification.

Carolus Linnaeus is best known for his introduction of the method still used to formulate the scientific name of every species. Carl Linnaeus (Latinized as Carolus Linnaeus, also known after his ennoblement as, May 23 new style (13 May old style 1707 who laid the foundations for Before Linnaeus, long many-worded names (composed of a generic name and a differentia specifica) had been used, but as these names gave a description of the species, they were not fixed. In his Philosophia Botanica (1751) Linnaeus took every effort to improve the composition and reduce the length of the many-worded names by abolishing unnecessary rhetorics, introducing new descriptive terms and defining their meaning with an unprecedented precision. In the late 1740s Linnaeus began to use a parallel system of naming species with nomina trivialia. Nomen triviale, a trivial name, was a single- or two-word epithet placed on the margin of the page next to the many-worded "scientific" name. The only rules Linnaeus applied to them was that the trivial names should be short, unique within a given genus, and that they should not be changed. Linnaeus consistently applied nomina trivialia to the species of plants in Species Plantarum (1st edn. Species Plantarum ("The Species of Plants" was first published in 1753, as a two-volume work by Carl Linnaeus. 1753) and to the species of animals in the 10th edition of Systema Naturae (1758). The book Systema Naturae was one of the major works of the Swedish doctor of medicine Carolus Linnaeus. By consistently using these specific epithets, Linnaeus separated nomenclature from taxonomy. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos Even though the parallel use of nomina trivialia and many-worded descriptive names continued until late in the eighteenth century, it was gradually replaced by the practice of using shorter proper names combined of the generic name and the trivial name of the species. In the nineteenth century, this new practice was codified in the first Rules and Laws of Nomenclature, and the 1st edn. of Species Plantarum and the 10th edn. Species Plantarum ("The Species of Plants" was first published in 1753, as a two-volume work by Carl Linnaeus. of Systema Naturae were chosen as starting points for the Botanical and Zoological Nomenclature respectively. The book Systema Naturae was one of the major works of the Swedish doctor of medicine Carolus Linnaeus. The International Code of Botanical Nomenclature ( ICBN) is the set of rules and recommendations dealing with the formal Botanical names that are given to The International Code of Zoological Nomenclature is a set of rules in Zoology that have one fundamental aim to provide the maximum universality and continuity in the naming This convention for naming species is referred to as binomial nomenclature. Today, nomenclature is regulated by Nomenclature Codes, which allows names divided into ranks; separately for botany and for zoology. The Nomenclature Codes (or the " Codes of nomenclature") are the rulebooks that govern biological nomenclature Taxonomic rank ( rank, category, taxonomic category is an abstract term used in the Scientific classification, or Taxonomy, of organisms Taxonomic rank ( rank, category, taxonomic category is an abstract term used in the Scientific classification, or Taxonomy, of organisms Whereas Linnaeus classified for ease of identification, it is now generally accepted that classification should reflect the Darwinian principle of common descent. A group of organisms is said to have common descent if they have a common Ancestor.

The Fungi have long been a problematic group in the biological classification: Originally, they were treated as plants. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ For a short period Linnaeus had placed them in the taxon Vermes in Animalia because he was misinformed: the hyphae were said to have been worms. Vermes (" Worms quot is an obsolete Taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non- Arthropod Invertebrate A hypha (plural hyphae) is a long branching filamentous cell of a Fungus, and also of unrelated Actinobacteria. A worm is a common name given to a diverse group of invertebrate animals that have a long soft body and no legs He later placed them back in Plantae. Copeland classified the Fungi in his Protoctista, thus partially avoiding the problem but acknowledging their special status. Herbert Faulkner Copeland (1902-1968 was an American Biologist who contributed to the theory of biological kingdoms His father was Edwin Copeland. The problem was eventually solved by Whittaker, when he gave them their own kingdom in his five-kingdom system. Robert Harding Whittaker (1920–1980 was an American Vegetation Ecologist, active in the 1950s to the 1970s In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system As it turned out, the fungi are more closely related to animals than to plants.

As new discoveries enabled us to study cells and microorganisms, new groups of life where revealed, and the fields of cell biology and microbiology were created. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually See also List of basic cell biology topics. Cell biology (also called cellular biology or formerly cytology, from the Microbiology (from Greek grc μῑκρος mīkros, "small" grc βίος bios, " Life " and grc -λογία These new organisms were originally described separately in Protozoa as animals and Protophyta/Thallophyta as plants, but were united by Haeckel in his kingdom Protista, later the group of prokaryotes were split of in the kingdom Monera, eventually this kingdom would be divided in two separate groups, the Bacteria and the Archaea, leading to the six-kingdom system and eventually to the three-domain system. Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular The thallophytes are a Polyphyletic group of non-mobile Organisms traditionally described as " relatively simple Plants " or " Ernst Heinrich Philipp August Haeckel ( February 16, 1834 — August 9, 1919)also written von Haeckel, was an eminent German Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system The three-domain system is a Biological classification introduced by Carl Woese in 1990 that divides cellular life forms into Archaea, The 'remaining' protists would later be divided into smaller groups in clades in relation to more complex organisms. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor Thomas Cavalier-Smith, who has published extensively on the classification of protists, has recently proposed that the Neomura, the clade which groups together the Archaea and Eukarya, would have evolved from Bacteria, more precisely from Actinobacteria. Professor Thomas (Tom Cavalier-Smith (born October 21 1942) FRS, FRSC, NERC Professorial Fellow is a Professor of Neomura is a speculative Clade composed of the two domains of life of Archaea and Eukarya. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Actinobacteria or actinomycetes are a group of Gram-positive bacteria with high G+C ratio.

As microbiology, molecular biology and virology developed, non-cellular reproducing agents were discovered, sometimes these are considered to be alive and are treated in the domain of non-cellular life named Acytota or Aphanobionta, which are virus. Microbiology (from Greek grc μῑκρος mīkros, "small" grc βίος bios, " Life " and grc -λογία Molecular biology is the study of Biology at a molecular level Virology is the study of viruses and virus-like agents: their structure classification and evolution their ways to infect and exploit cells for virus reproduction Non-cellular life is Life that exists without cells This term usually is applied to earth-based life and presumes the Phylogenetic classification A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable

And thus all the primary taxonomical ranks were established: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Since the 1960s a trend called cladistics has emerged, arranging taxa in an evolutionary or phylogenetic tree. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos RANK (Receptor Activator of Nuclear Factor κ B, also known as TRANCE Receptor is a type I membrane protein which is expressed on the surface of Osteoclasts and is involved In biological Taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest Taxonomic rank of Organisms In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. A class is the Taxonomic rank in the Biological classification of organisms in Biology below phylum and above order. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used In Biological classification, family ( Latin A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Cladistics is the hierarchical classification of Species based on evolutionary ancestry A phylogenetic tree, also called an evolutionary tree, is a tree showing the Evolutionary relationships among various biological Species or other If a taxon includes all the descendants of some ancestral form, it is called monophyletic, as opposed to paraphyletic, groups based on traits which have evolved separately and where the most recent common ancestor is not included are called polyphyletic. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all In Genetics, the most recent common ancestor ( MRCA) of any set of Organisms is the most recent individual from which all organisms in the group are directly In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different

A new formal code of nomenclature, the PhyloCode, to be renamed "International Code of Phylogenetic Nomenclature" (ICPN), is currently under development, intended to deal with clades, which do not have set ranks, unlike conventional Linnaean taxonomy. The International Code of Phylogenetic Nomenclature, known for short as the PhyloCode, is a developing draft for a formal set of rules governing Phylogenetic Phylogenetic nomenclature (PN is an alternative to rank-based nomenclature. Linnaean taxonomy is a method of classifying living things originally devised by (and named for Carolus Linnaeus, although it has changed considerably since his time It is unclear, should this be implemented, how the different codes will coexist.

Extraterrestrial life

Main articles: Extraterrestrial life and astrobiology

Earth is the only planet in the universe known to harbour life. The three-domain system is a Biological classification introduced by Carl Woese in 1990 that divides cellular life forms into Archaea, Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Plants are living Organisms belonging to the kingdom Plantae. Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Plants are living Organisms belonging to the kingdom Plantae. Plants are living Organisms belonging to the kingdom Plantae. Plants are living Organisms belonging to the kingdom Plantae. Extraterrestrial life is Life originating outside of the Earth. Astrobiology (from Greek grc ἄστρον astron, "constellation star" grc βίος bios, "life" and grc -λογία EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy The Drake equation has been used to estimate the probability of life elsewhere, but scientists disagree on many of the values of variables in this equation (although strictly speaking Drake equation estimates relate the number of extraterrestrial civilizations in our galaxy with which we might come in contact - not probability of life elsewhere). The Drake equation (also sometimes called the "Green Bank equation" the "Green Bank Formula" or often erroneously labeled the " Sagan equation" Depending on those values, the equation may either suggest that life arises frequently or infrequently. Drake himself estimated the number of civilizations in our galaxy with which we might expect to be able to communicate at any given time as equal to one.

Relating to the origin of life on Earth, panspermia and exogenesis are theories proposing that life originated elsewhere in the universe and was subsequently transferred to Earth perhaps via meteorites, comets or cosmic dust. Panspermia ( Gk. πάς/πάν (pas/pan all and σπέρμα ( sperma, seed is the Hypothesis that "seeds" of Life exist already A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — For example, there is the meteorite ALH84001. A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface ALH 84001 (full name Allan Hills 84001) is a Meteorite found in Allan Hills, Antarctica in December 1984 by a team of US meteorite hunters from However those theories do not help explain the origin of this extraterrestrial life.

See also

References

Further reading

• Kauffman, Stuart. The Adjacent Possible: A Talk with Stuart Kauffman. Retrieved Nov. 30, 2003 from [1]
• Walker, Martin G. LIFE! Why We Exist. . . And What We Must Do to Survive (Book Page) (Web Site), Dog Ear Publishing, 2006, ISBN 1-59858-243-7

External links

• Wikispecies - a free directory of life
• "The Adjacent Possible: A Talk with Stuart Kauffman"
• Stanford Encyclopedia of Philosophy entry
• Life under extreme conditions An in depth look at how life can form under the most extreme conditions.