Тереклек: юрамалар арасында аерма

** [[Хайваннар]]

 

{{Main|Биологик классификация}}

<!--Traditionally, people have divided organisms into the classes of [[plant]]s and [[animal]]s, based mainly on their ability of movement. The first known attempt to classify organisms was conducted by the Greek philosopher Aristotle (384–322 BC). 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 [[vertebrate]]s and [[invertebrate]]s respectively. He divided the blooded animals into five groups: viviparous quadrupeds ([[mammal]]s), [[bird]]s, oviparous quadrupeds ([[reptile]]s and [[amphibian]]s), [[fish]]es and [[Cetacea|whales]]. The bloodless animals were divided into five groups: [[cephalopod]]s, [[crustacean]]s, [[insect]]s (which included the [[spider]]s, [[scorpion]]s, [[centipede]]s, and what we define as insects in the present day), shelled animals (such as most [[mollusc]]s and [[echinoderm]]s) and "[[zoophyte]]s." 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.<ref>{{Cite news |title=Aristotle -biography |publisher=University of California Museum of Paleontology |url=http://www.ucmp.berkeley.edu/history/aristotle.html |accessdate=2008-10-20}}</ref>

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<!--[[Hylomorphism]] is the theory (originating with [[Aristotle]] (322 BC)) that all things are a combination of matter and form. Aristotle was one of the first ancient writers to approach the subject of life in a scientific way. Biology was one of his main interests, and there is extensive biological material in his extant writings. According to him, all things in the material universe have both matter and form. The form of a living thing is its [[Soul (spirit)|soul]] (Greek ''psyche'', Latin ''anima''). There are three kinds of souls: the "vegetative soul" of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation; the "animal soul" which causes animals to move and feel; and the rational soul which is the source of consciousness and reasoning which (Aristotle believed) is found only in man.<ref>Aristotle, ''[[On the Soul|De Anima]]'', Book II</ref> Each higher soul has all the attributes of the lower one. Aristotle believed that while matter can exist without form, form cannot exist without matter, and therefore the soul cannot exist without the body.<ref>{{cite book | first1=Don | last1=Marietta | page=104 | title=Introduction to ancient philosophy | publisher=M. E. Sharpe | year=1998 | isbn=0765602164 | url=http://books.google.com/books/about/Introduction_to_Ancient_Philosophy.html?id=Gz-8PsrT32AC }}</ref>

 

Consistent with this account is a [[teleological]] explanation of life. A teleological explanation accounts for phenomena in terms of their purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its ''purpose'' of camouflage. The direction of causality is the other way round from materialistic science, which explains the consequence in terms of a prior cause. Modern biologists reject this functional view in terms of a material and causal one: biological features are to be explained not by looking ''forward'' to future optimal results, but by looking ''backwards'' to the past evolutionary history of a species, which led to the natural selection of the features in question.<ref name=stewert_williams2010>{{citation | first1=Steve | last1=Stewart-Williams | year=2010 | title=Darwin, God and the meaning of life: how evolutionary theory undermines everything you thought you knew of life | publisher=Cambridge University Press | isbn=0521762782 | pages=193–194 | url=http://books.google.com/books?id=KBp69los_-oC&pg=PA193 }}</ref>

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<!--[[Vitalism]] is the belief that the life-principle is essentially immaterial. This originated with [[Georg Ernst Stahl|Stahl]] (17th century), and held sway until the middle of the 19th century. It appealed to philosophers such as [[Henri Bergson]], [[Nietzsche]], [[Wilhelm Dilthey]],<ref>{{cite book | first1=Sanford | last1=Schwartz | title=C. S. Lewis on the Final Frontier: Science and the Supernatural in the Space Trilogy | publisher=Oxford University Press | year=2009 | isbn=0199888396 | page=56 | url=http://books.google.com/books?id=4hQLdPtJe9EC&pg=PA56 }}</ref> anatomists like [[Marie François Xavier Bichat|Bichat]], and chemists like [[Justus von Liebig|Liebig]].<ref name=wilkinson>{{cite journal | first1=Ian | last1=Wilkinson | title=History of Clinical Chemistry – Wöhler & the Birth of Clinical Chemistry | journal=The Journal of the International Federation of Clinical Chemistry and Laboratory Medicine | volume=13 | issue=4 | year=1998 | url=http://ifcc.nassaro.com/index.asp?cat=Publications&scat=eJIFCC_&suba=Vol_13_No_4&subx=History_of_Clinical_Chemistry_W%C3%B6hler_and_the_Birth_of_Clinical_Chemistry_&zip=1&dove=1&zona=full&numero=&aq=1 | accessdate=0212-06-12 }}</ref>

 

During the 1850s, [[Hermann von Helmholtz|Helmholtz]], anticipated by [[Julius Robert von Mayer|Mayer]], demonstrated that no energy is lost in muscle movement, suggesting that there were no ''vital forces'' necessary to move a muscle.<ref>{{cite book | first1=Anson | last1=Rabinbach | title=The Human Motor: Energy, Fatigue, and the Origins of Modernity | publisher=University of California Press | year=1992 | isbn=0520078276 | pages=124–125 | url=http://books.google.com/books?id=e5ZBNv-zTlQC&pg=PA124&lpg=PA124 }}</ref> These empirical results led to the abandonment of scientific interest in vitalistic theories, although the belief lingered on in non-scientific theories such as [[homeopathy]], which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force.<ref>{{cite web | title=NCAHF position paper on Homeopathy | month=February | year=1994 | publisher=National Council Against Health Fraud | url=http://www.ncahf.org/pp/homeop.html | accessdate=2012-06-12 }}</ref>

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<!--It is a challenge for scientists and philosophers to define life in unequivocal terms.<ref>{{cite web

| first1=Leslie | last1=Mullen | date=June 19, 2002

| url=http://www.nbi.dk/~emmeche/cePubl/97e.defLife.v3f.html | accessdate=2012-05-25 }}</ref><ref>{{cite web |url= http://artsandsciences.colorado.edu/magazine/2009/03/can-we-define-life/ |title=Can We Define Life |accessdate=2009-06-22 |year=2009 |publisher=Colorado Arts & Sciences}}</ref> Defining life is difficult—in part—because life is a process, not a pure substance.<ref name=McKay>{{Cite journal |title=What Is Life—and How Do We Search for It in Other Worlds? |journal=Public Library of Science – Biology |date=September 14, 2004 |first=Chris P. |last=McKay |pmid=15367939 |volume=2 |issue=2(9) |pmc=516796 |page=302 |doi=10.1371/journal.pbio.0020302}}</ref> Any definition must be sufficiently broad to encompass all life with which we are familiar, and it should be sufficiently general that, with it, scientists would not miss life that may be fundamentally different from life on Earth.<ref>{{Cite journal |last1=Nealson |first1=K. H. |last2=Conrad |first2=P. G. |title=Life: past, present and future |journal=Philosophical Transactions of the Royal Society of London B Biological Sciences |volume=354 |issue=1392 |pages=1923–39 |date= December 1999 |pmid=10670014 |pmc=1692713 |doi=10.1098/rstb.1999.0532 |url=http://journals.royalsociety.org/content/7r10hqn3rp1g1vag/fulltext.pdf}}</ref>

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<!--Since there is no unequivocal definition of life, the current understanding is descriptive, where life is a characteristic of organisms that exhibit all or most of the following [[phenomena]]:<ref name=McKay/><ref>{{cite web |url=http://www2.una.edu/pdavis/BI%20101/Overview%20Fall%202004.htm |title=How to Define Life |accessdate=2008-10-17 |last=Davison |first=Paul G. |publisher=The University of North Alabama }}</ref>

# '''[[Homeostasis]]''': Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature.

# '''[[Reproduction]]''': The ability to produce new individual organisms, either [[asexual reproduction|asexually]] from a single parent organism, or [[sexual reproduction|sexually]] from two parent organisms.

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<!--{{See also|Entropy and life}}

 

Others take a [[Living systems theory|systemic]] viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living things are [[self-organization|self-organizing]] and [[autopoiesis|autopoietic]] (self-producing). Variations of this definition include [[Stuart Kauffman]]'s definition as an [[autonomous agent]] or a [[multi-agent system]] capable of reproducing itself or themselves, and of completing at least one [[thermodynamic cycle|thermodynamic work cycle]].<ref>{{cite journal | first1=Stuart | last1=Kaufmann | year=2004 | title=Autonomous agents | editor1-first=John D. | editor1-last=Barrow | editor2-first1=P. C. W. | editor2-last=Davies | editor3-first=C. L. | editor3-last=Harper Jr. | work=Science and Ultimate Reality: Quantum Theory, Cosmology, and Complexity | publisher=Cambridge University Press | pages=654–666 | isbn=052183113X | url=http://books.google.com/books?id=K_OfC0Pte_8C&pg=PA654 }}</ref> Life can be modeled as a network of inferior [[negative feedback]]s of regulatory mechanisms subordinated to a superior [[positive feedback]] formed by the potential of expansion and reproduction.<ref>{{cite journal | last1=Korzeniewski | first1=Bernard | year=2001 | title=Cybernetic formulation of the definition of life | journal=Journal of Theoretical Biology | date=April 7, 2001 | volume=209 | issue=3 | pages=275–86 | pmid=11312589 | doi=10.1006/jtbi.2001.2262 }}</ref> From a simplified perspective, life can be said to consist of things with the capacity for metabolism and motion,<ref name=McKay/> or that life is self-reproduction "with variations"<ref name="JBS-2012Feb">{{cite journal |last=Trifonov |first=Edward N. |title=Definition of Life: Navigation through Uncertainties |url=http://www.jbsdonline.com/mc_images/category/4317/21-trifonov-jbsd_29_4_2012.pdf |journal=Journal of Biomolecular Structure & Dynamics |volume=29 |issue=4 |pages=647–650 |issn=0739-1102 |publisher=Adenine Press |accessdate=2012-01-12 }}</ref><ref name="MSN-20120111">{{cite web |last=Zimmer |first=Carl |title=Can scientists define 'life' ... using just three words? |url=http://www.msnbc.msn.com/id/45963181/ns/technology_and_science/ |date=January 11, 2012 |publisher=[[MSN]] |accessdate=2012-01-12 }}</ref> or "with an error rate below the sustainability threshold."<ref name="MSN-20120111" />

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<!--[[Virus]]es are most often considered [[DNA replication|replicator]]s rather than forms of life. They have been described as "organisms at the edge of life,"<ref>{{Cite journal |last=Rybicki |first=EP |year=1990 |title=The classification of organisms at the edge of life, or problems with virus systematics |journal=S Aft J Sci |volume=86 |pages=182–186}}</ref> since they possess [[gene]]s, evolve by natural selection,<ref name="pmid17914905">{{Cite journal |last1=Holmes | first1=E. C. |title=Viral evolution in the genomic age |journal=PLoS Biol. |volume=5 |issue=10 |pages=e278 |date=October 2007 |pmid=17914905 |pmc=1994994 |doi=10.1371/journal.pbio.0050278 |url=http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050278 |accessdate=2008-09-13}}</ref> and replicate by creating multiple copies of themselves through self-assembly. However, viruses do not metabolize 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.<ref name="pmid16984643">{{Cite journal |last1=Koonin | first1=E. V. | last2=Senkevich | first2=T. G. | last3=Dolja | first3=V. V. |title=The ancient Virus World and evolution of cells |journal=Biology Direct |volume=1 |page=29 |year=2006 |pmid=16984643 |pmc=1594570 |doi=10.1186/1745-6150-1-29 |url=http://www.biology-direct.com/content/1//29 |accessdate=2008-09-14}}</ref><ref>{{cite web |url=http://www.mcb.uct.ac.za/tutorial/virorig.html#Virus%20Origins |title=Origins of Viruses |accessdate=2009-04-12 |last=Rybicki |first=Ed |date=November 1997}}</ref>

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<!--In 1978, American biologist [[James Grier Miller]] first formulated a general [[living systems]] theory to explain the nature of life.<ref>{{Cite book |last=Woodruff |first=T. Sullivan |coauthor=John Baross |title=Planets and Life: The Emerging Science of Astrobiology |publisher=Cambridge University Press | isbn=0521824214 |date=October 8, 2007}} Cleland and Chyba wrote a chapter in Planets and Life: "In the absence of such a theory, we are in a position analogous to that of a 16th-century investigator trying to define 'water' in the absence of molecular theory." [...] "Without access to living things having a different historical origin, it is difficult and perhaps ultimately impossible to formulate an adequately general theory of the nature of living systems".</ref> Such a general theory, arising out of the [[ecology|ecological]] and [[biology|biological sciences]], attempts to map general principles for how all living systems work. Instead of examining phenomena by attempting to break things down into component parts, a general living systems theory explores phenomena in terms of dynamic patterns of the relationships of organisms with their environment.<ref>{{cite web

| first1=Molly Young | last1=Brown | year=2002

A systems view of life treats environmental [[flux]]es and biological fluxes together as a "reciprocity of influence",<ref>{{cite web |url=http://www.calresco.org/fiscus/esl.htm |title=The Ecosystemic Life Hypothesis |accessdate=2009-08-28 |first=Daniel A. Fiscus |date=April 2002 |publisher=Bulletin of the Ecological Society of America}}</ref> and a reciprocal relation with environment is arguably as important for understanding life as it is for understanding ecosystems. As [[Harold J. Morowitz]] (1992) explains it, life is a property of an [[ecosystem|ecological system]] rather than a single organism or species.<ref>{{cite book | last1=Morowitz | first1=Harold J. | year=1992 | title=Beginnings of cellular life: metabolism recapitulates biogenesis | publisher=Yale University Press | isbn=0-300-05483-1 | url=http://books.google.com/books?id=CmQDSHN_UrIC }}</ref> He argues that an ecosystemic definition of life is preferable to a strictly biochemical or physical one. [[Robert Ulanowicz]] (2009) highlights mutualism as the key to understand the systemic, order-generating behavior of life and ecosystems.<ref>{{cite book | first1=Robert W. | last1=Ulanowicz | first2=Robert E. | last2=Ulanowicz | title=A third window: natural life beyond Newton and Darwin | publisher=Templeton Foundation Press | year=2009 | isbn=1-59947-154-X | url=http://books.google.com/books?id=gAQKAQAAMAAJ }}</ref>

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<!--{{Main|Abiogenesis}}

Evidence suggests that [[life on Earth]] has existed for about 3.7 [[1000000000 (number)|billion]] years,<ref>{{cite book | first1=Clare | last1=Milsom | first2=Sue | last2=Rigby | title=Fossils at a Glance | edition=2nd | publisher=John Wiley & Sons | year=2009 | isbn=1405193360 | page=134 | url=http://books.google.com/books?id=OdrCdxr7QdgC&pg=PA134 }}</ref> with the oldest traces of life found in fossils dating back 3.4 billion years.<ref>{{cite web | last1=Dean | first1=Tim | url=http://www.lifescientist.com.au/article/398092/world_oldest_fossils_reveal_earliest_life_earth | title=World’s oldest fossils reveal earliest life on Earth | work=Australian Life Scientist | publisher=IDG Communications | date=August 23, 2011 | accessdate=2012-05-26 }}</ref> All known life forms share fundamental molecular mechanisms, and based on these observations, theories on the origin of life attempt to find a mechanism explaining the formation of a [[common descent|primordial single cell organism]] from which all life originates. There are many different hypotheses regarding the path that might have been taken from simple [[organic molecule]]s via pre-cellular life to protocells and metabolism. Many models fall into the "genes-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid models that combine both categories.<ref>{{cite journal | last1=Coveney | first1=Peter V. | first2=Philip W. | last2=Fowler | title=Modelling biological complexity: a physical scientist's perspective | journal=Journal of the Royal Society Interface | year=2005 | volume=2 | issue=4 | pages=267–280 | doi=10.1098/rsif.2005.0045 }}</ref>

[[NASA]] findings in 2011, based on studies with [[meteorites]] found on [[Earth]], suggest [[DNA]] and RNA components ([[adenine]], [[guanine]] and related organic molecules) may be formed extraterrestrially in [[outer space]].<ref name="Callahan">{{cite web |last1=Callahan |last2=Smith |first2=K.E. |last3=Cleaves |first3=H.J. |last4=Ruzica |first4=J. |last5=Stern |first5=J.C. |last6=Glavin |first6=D.P. |last7=House |first7=C.H. |last8=Dworkin |first8=J.P. |date=August 11, 2011 |title=Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases |url=http://www.pnas.org/content/early/2011/08/10/1106493108 |publisher=[[PNAS]] |doi=10.1073/pnas.1106493108 |accessdate=2011-08-15 |unused_data=M.P. }}</ref><ref name="Steigerwald">{{cite web |last=Steigerwald |first=John |title=NASA Researchers: DNA Building Blocks Can Be Made in Space |url=http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |publisher=[[NASA]] |date=August 8, 2011 |accessdate=2011-08-10}}</ref><ref name="DNA">{{cite web |author=ScienceDaily Staff |title=DNA Building Blocks Can Be Made in Space, NASA Evidence Suggests|url=http://www.sciencedaily.com/releases/2011/08/110808220659.htm |date=August 9, 2011 |publisher=[[ScienceDaily]] |accessdate=2011-08-09}}</ref><ref name=Lincei>{{cite journal |last=Gallori |first=Enzo |title=Astrochemistry and the origin of genetic material |journal=Rendiconti Lincei|date=November 2010 |volume=22 |issue=2 |pages=113–118 |id=|url=http://www.springerlink.com/content/x332837483630g24/|accessdate=2011-08-11 |doi=10.1007/s12210-011-0118-4}}</ref>

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<!--The diversity of life on Earth is a result of the dynamic interplay between [[genetic opportunity]], metabolic capability, [[environment (biophysical)|environmental]] challenges,<ref name=astrobiology>{{cite web |url=http://astrobiology.arc.nasa.gov/roadmap/g5.html |title=Understand the evolutionary mechanisms and environmental limits of life |accessdate=2009-07-13 |last= Rothschild |first=Lynn |date=September, 2003 |publisher=NASA}}</ref> and [[symbiosis]].<ref>{{Cite journal |title=Symbiosis and the origin of life |journal=Origins of Life and Evolution of Biospheres |date= April, 1977 |first=G.A.M. |last=King |volume=8 |issue=1 |pages=39–53 |doi=10.1007/BF00930938 |url=http://www.springerlink.com/content/n10p775113175l67/ |accessdate=2010-02-22 |bibcode=1977OrLi....8...39K}}</ref><ref>{{Cite book |last= Margulis |first=Lynn |title=The Symbiotic Planet: A New Look at Evolution |publisher=Orion Books Ltd. |year=2001 |location=London, England |isbn=0-7538-0785-8}}</ref><ref>{{Cite book |author=Douglas J. Futuyma |coauthor=Janis Antonovics |title=Oxford surveys in evolutionary biology: Symbiosis in evolution |publisher=Oxford University Press |year=1992 |volume=8 |location=London, England |pages=347–374 |isbn= 0-19-507623-0}}</ref> For most of its existence, Earth's habitable environment has been dominated by [[microorganism]]s and subjected to their metabolism and evolution. As a consequence of such microbial activities on a [[geologic time scale]], the physical-chemical environment on Earth has been changing, thereby determining the path of evolution of subsequent life.<ref name=astrobiology/> For example, the release of molecular [[oxygen]] by [[cyanobacteria]] as a by-product of [[photosynthesis]] induced fundamental, global changes in the Earth's environment. The altered environment, in turn, posed novel evolutionary challenges to the organisms present, which ultimately resulted in the formation of our planet's major animal and plant species. Therefore this "co-evolution" between organisms and their environment is apparently an inherent feature of living systems.<ref name=astrobiology/>

 

All life forms require certain core [[chemical element]]s needed for [[biochemistry|biochemical]] functioning. These include [[carbon]], [[hydrogen]], [[nitrogen]], oxygen, [[phosphorus]], and [[sulfur]]—the elemental [[nutrient|macronutrients]] for all organisms<ref name=wsj20101203>{{cite news | first1=Robert Lee | last1=Hotz | title=New link in chain of life | work=[[Wall Street Journal]] | date=December 3, 2010 | publisher=Dow Jones & Company, Inc | url=http://online.wsj.com/article/SB10001424052748703377504575650840897300342.html?mod=ITP_pageone_1#printMode | quote="Until now, however, they were all thought to share the same biochemistry, based on the Big Six, to build proteins, fats and DNA." }}</ref>—often represented by the acronym CHNOPS. Together these make up [[nucleic acid]]s, proteins and [[lipid]]s, the bulk of living matter. Five of these six elements comprise the chemical components of DNA; the exception being sulfur. The latter forms a component of the important amino acid [[methionine]]. The most essential of these elements is carbon, which has the desirable attribute of forming multiple, stable [[covalent bond]]s. This allows carbon-based (organic) molecules to form an immense variety of chemical arrangements.<ref name=neuhauss2005>{{citation | first1=Scott | last1=Neuhaus | title=Handbook for the Deep Ecologist: What Everyone Should Know About Self, the Environment, And the Planet | publisher=iUniverse | year=2005 | isbn=059535789X | pages=23–50 | url=http://books.google.com/books?id=uzBDQPxe6zsC&pg=PA23 }}</ref> Alternative [[hypothetical types of biochemistry]] have been proposed which eliminate one or more of these elements, swap out an element for one not on the list, or change required [[Chirality (chemistry)|chiralities]] or other chemical properties.<ref>{{cite book | author1=Committee on the Limits of Organic Life in Planetary Systems | author2=Committee on the Origins and Evolution of Life | author3=National Research Council | year=2007 | publisher=National Academy of Sciences | title=The Limits of Organic Life in Planetary Systems | isbn=0-309-66906-5 | url=http://www.nap.edu/catalog.php?record_id=11919 | accessdate=2012-06-03 }}</ref><ref>{{cite journal | first1=Steven A. | last1=Benner | first2=Alonso | last2=Ricardo | first3=Matthew A. | last3=Carrigan | journal=Current Opinion in Chemical Biology | title=Is there a common chemical model for life in the universe? | volume=8 | issue=6 | month=December | year=2004 | pages=672–689 | doi=10.1016/j.cbpa.2004.10.003 | url=http://www.fossildna.com/articles/benner_commonmodelforlife.pdf | accessdate=2012-06-03 }}</ref>

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<!--The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or [[biochemistry|chemical energy]]), water, temperature, [[Earth's atmosphere|atmosphere]], [[gravitational biology|gravity]], [[nutrient]]s, and [[ultraviolet]] [[ozone layer|solar radiation protection]].<ref>{{cite web |url=http://cmapsnasacmex.ihmc.us/servlet/SBReadResourceServlet?rid=1025200161109_2045745605_1714&partName=htmltext |title=Essential requirements for life |accessdate=2009-07-14 |publisher=CMEX-NASA}}</ref> In most ecosystems the conditions vary during the day and often shift from one season to the next. To live in most ecosystems, then, organisms must be able to survive a range of conditions, called the "range of tolerance."<ref name=tolerance>{{Cite book |last=Chiras |first=Daniel C. | edition=6th |title=Environmental Science – Creating a Sustainable Future |year=2009 | isbn=0763713163 | year=2001}}</ref> Outside that are the "zones of physiological stress," where the survival and reproduction are possible but not optimal. Beyond these zones are the "zones of intolerance," where life for that organism is implausible. Organisms that have a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance.<ref name=tolerance/>

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<!--To survive, selected microorganisms can assume forms that enable them to withstand [[psychrophile|freezing]], [[xerophile|complete desiccation]], [[oligotroph|starvation]], high-levels of [[radioresistance|radiation exposure]], and other physical or chemical challenges. These microorganisms may survive exposure to such conditions for weeks, months, years, or even centuries.<ref name= astrobiology/> [[Extremophiles]] are microbial life forms that thrive outside the ranges where life is commonly found. They excel at exploiting uncommon sources of energy. 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 [[morphology (biology)|structure]] and metabolic diversity of microbial communities in such [[extreme environment]]s is ongoing.<ref>{{cite journal | first1=Pabulo Henrique | last1=Rampelotto | year=2010 | volume=2 | issue=6 | pages=1602–1623 | title=Resistance of microorganisms to extreme environmental conditions and its contribution to astrobiology | doi=10.3390/su2061602 | bibcode=2010Sust....2.1602R }}</ref>

 

Investigation of the tenacity and versatility of life on Earth, as well as an understanding of the molecular systems that some organisms utilize to survive such extremes, will provide a critical foundation for the search for [[extraterrestrial life|life beyond Earth]].<ref name=astrobiology/> In this regard, on April 26, 2012, scientists reported that [[lichen]] survived and showed remarkable results on the [[adaptive capacity|adaptation capacity]] of photosynthetic activity within a simulated [[Life on Earth under Martian conditions|Martian environment]].<ref name="Skymania-20120426">{{cite web |last=Baldwin |first=Emily |title=Lichen survives harsh Mars environment |url=http://www.skymania.com/wp/2012/04/lichen-survives-harsh-martian-setting.html |date=April 26, 2012 |publisher=Skymania News |accessdate=27 April 2012 }}</ref><ref name="EGU-20120426">{{cite web |last1=de Vera |first1=J.-P. |last2=Kohler |first2=Ulrich |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |url=http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |date=April 26, 2012 |publisher=[[European Geosciences Union]] |accessdate=27 April 2012 }}</ref>

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[[Cell theory]] propounds the concept that cells are the basic unit of structure in every living thing. This idea was formulated by [[Henri Dutrochet]] and others during the early nineteenth century, and subsequently became widely accepted.<ref name=sapp2003>{{cite book | first1=Jan | last1=Sapp | title=Genesis: The Evolution of Biology | publisher=Oxford University Press | year=2003 | isbn=0195156196 | pages=75–78 | url=http://books.google.com/books?id=f4kXJv1XiFUC&pg=PA75 }}</ref> According to this theory, all cells arise from pre-existing cells by [[Cell division|division]]. The activity of an organism depends on the total activity of independent cells, with [[Cellular respiration|energy flow]] occurring within cells. Cells contain hereditary information that is carried forward as a [[genetic]] code during cell division.<ref>{{cite journal | last1=Lintilhac | first1=P. M. | title=Thinking of biology: toward a theory of cellularity--speculations on the nature of the living cell | journal=Bioscience | year=1999 | month=Jan | volume=49 | issue=1 | pages=59-68 | pmid=11543344 | url=https://www.rz.uni-karlsruhe.de/~db45/Studiendekanat/Lehre/Master/Module/Botanik_1/M1401/Evolution_Zellbiologie/Lintilhac%202003.pdf | accessdate=2012-06-02 }}</ref>

Cells have evolved methods to perceive and correctly respond to their microenvironment, thereby enhancing their adaptability. [[Cell signaling]] is a form of communication that is used to coordinate cell activities, and hence governs basic cellular activities in multicellular organisms. This can occur through direct cell contact using [[juxtacrine signalling]], or indirectly through the exchange of agents as in the [[endocrine system]]. In more complex organisms, coordination of activities can occur through a dedicated [[nervous system]].<ref name=alberts2002>{{cite book | display-authors=1 | first1=Bruce | last1=Alberts | first2=Alexander | last2=Johnson | first3=Julian | last3=Lewis | first4=Martin | last4=Raff | first5=Keith | last5=Roberts | first6=Peter | last6=Walter | chapter=General Principles of Cell Communication | title=Molecular Biology of the Cell | location=New York | publisher=Garland Science | year=2002 | url=http://www.ncbi.nlm.nih.gov/books/NBK26813/ | accessdate=2012-06-12 | isbn=0-8153-3218-1 }}</ref>

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<!-- {{Main|Extraterrestrial life|astrobiology}} -->

<!-- Earth is the only planet known to harbor life. The [[Drake equation]], which predicts the number of extraterrestrial civilizations in our galaxy with which we might come in contact, has been used to discuss the probability of life elsewhere, but scientists disagree on many of the values of variables in this equation.

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{{Main|Үлем}}

<!--[[File:Male Lion and Cub Chitwa South Africa Luca Galuzzi 2004.JPG|right|thumb|Animal corpses, like this [[African buffalo]], are recycled by the [[ecosystem]], providing energy and nutrients for living creatures]]

| accessdate=2012-05-25 }}</ref> Hence, fossils range in age from the youngest at the start of the [[Holocene]] Epoch to the oldest from the [[Archaean]] Eon, up to 3.4 [[1000000000 (number)|billion]] years old.<ref> {{cite news | first1 = Brian |last1=Vastag | title = Oldest 'microfossils' raise hopes for life on Mars | date =August 21, 2011 | url = http://www.washingtonpost.com/national/health-science/oldest-microfossils-hail-from-34-billion-years-ago-raise-hopes-for-life-on-mars/2011/08/19/gIQAHK8UUJ_story.html?hpid=z3 | work = The Washington Post | accessdate = 2011-08-21}}</ref><ref> {{cite news | first = Nicholas | last = Wade | title = Geological Team Lays Claim to Oldest Known Fossils | date = August 21, 2011 | url = http://www.nytimes.com/2011/08/22/science/earth/22fossil.html?_r=1&partner=rss&emc=rss&src=ig | work = The New York Times | accessdate = 2011-08-21}}</ref>

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*[[Тормыш]]

*[[Гомер]]

*[[Яшәү]]

 

{{Искәрмәләр}}

 

* Kauffman, Stuart. [http://www.edge.org/3rd_culture/kauffman03/kauffman_index.html The Adjacent Possible: A Talk with Stuart Kauffman]

* Walker, Martin G. [http://rationalphilosophy.net/index.php/the-book ''LIFE! Why We Exist...And What We Must Do to Survive''] Dog Ear Publishing, 2006, ISBN 1-59858-243-7

 

* [http://species.wikimedia.org/wiki/Main_Page Wikispecies] – a free directory of life

* [http://www.edge.org/3rd_culture/kauffman03/kauffman_index.html "The Adjacent Possible: A Talk with Stuart Kauffman"]

{{Link FA|id}}

 

[[af:Lewe]]

[[am:ህይወት]]

[[ar:حياة]]

[[ast:Vida]]

[[ay:Jakaña]]

[[az:Həyat]]

[[be:Жыццё]]

[[be-x-old:Жыцьцё]]

[[bg:Живот]]

[[bo:འཚོ་བ།]]

[[bs:Život]]

[[ca:Vida]]

[[cs:Život]]

[[da:Liv]]

[[de:Leben]]

[[el:Ζωή]]

[[en:Life]]

[[eo:Vivo]]

[[eu:Bizi]]

[[fa:زندگی]]

[[fr:Vie]]

[[gl:Vida]]

[[hi:जीवन]]

[[hr:Život]]

[[ia:Vita]]

[[is:Líf]]

[[it:Vita]]

[[jv:Urip]]

[[kn:ಜೀವನ]]

[[krc:Джашау]]

[[ku:Jiyan]]

[[la:Vita]]

[[li:Leve]]

[[ln:Bomɔi]]

[[mk:Живот]]

[[ml:ജീവൻ]]

[[mr:जीवन]]

[[ms:Hidupan]]

[[mwl:Bida]]

[[ne:जीवन]]

[[new:उयिर् (सन् २००६या संकिपा)]]

[[nn:Livet]]

[[oc:Vida]]

[[pa:ਜੀਵਨ]]

[[pap:Bida]]

[[pl:Życie]]

[[pt:Vida]]

[[qu:Kawsay]]

[[ru:Жизнь]]

[[sah:Олох]]

[[scn:Vita]]

[[si:ජීවය]]

[[simple:Life]]

[[sk:Život]]

[[sl:Življenje]]

[[sr:Живот]]

[[su:Hirup]]

[[sv:Liv]]

[[ta:உயிர்]]

[[te:జీవం]]

[[th:ชีวิต]]

[[tr:Yaşam]]

[[uk:Життя]]

[[ur:حیات]]

[[vec:Vita]]

[[vi:Sự sống]]

[[war:Kinabuhi]]

[[yi:לעבן]]

[[zh:生命]]