part_of identification 
___MASK54___ is a characteristic distinguishing physical entities having 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 ___MASK54___ exist , such as plants , ___MASK99___ , fungi , protists , archaea , and bacteria . The criteria can at times be ambiguous and ___MASK91___ or ___MASK91___ not define viruses , viroids , or potential artificial ___MASK54___ as " living ". Biology is the primary ___MASK30___ concerned with the study of ___MASK54___ , although many other sciences are involved . In ___MASK42___ , a ___MASK87___ ( abbreviated sp ., with the plural form ___MASK87___ abbreviated spp .) is the basic unit of ___MASK10___ and a taxonomic rank . A ___MASK87___ is often defined as the largest group of organisms in which two individuals can produce fertile offspring , typically by sexual reproduction . While this definition is often adequate , looked at more closely it is often problematic . For example , in a ___MASK87___ complex , the boundaries between closely related ___MASK87___ become unclear or disappear altogether . Other ways of defining ___MASK87___ include similarity of DNA , morphology , or ecological niche . The presence of locally adaptive traits may further subdivide ___MASK87___ into infraspecific taxa such as subspecies . An ___MASK48___ is a community of living organisms in conjunction with the nonliving components of their environment ( things like air , water and mineral soil ), interacting as a ___MASK77___ . These biotic and abiotic components are regarded as linked together through nutrient cycles and energy flows . As ecosystems are defined by the network of interactions among organisms , and between organisms and their environment , they can be of any size but usually encompass specific , limited spaces ( although some scientists say that the entire planet is an ___MASK48___ ). Reproduction ( or procreation or breeding ) is the biological ___MASK69___ by which new individual organisms  " offspring "  are produced from their " parents ". Reproduction is a fundamental feature of all known ___MASK54___ ; each individual ___MASK58___ exists as the result of reproduction . There are two forms of reproduction : asexual and sexual . ___MASK73___ traditionally refers to undomesticated animal ___MASK87___ , but has come to include all plants , fungi , and other organisms that grow or live wild in an area without being introduced by humans . ___MASK37___ ( from , " house ", or " environment "; -  , " study of ") is the scientific analysis and study of interactions among organisms and their environment . It is an interdisciplinary field that includes biology , ___MASK27___ , and Earth science . ___MASK37___ includes the study of interactions organisms have with each other , other organisms , and with abiotic components of their environment . Topics of interest to ecologists include the diversity , distribution , amount ( biomass ), and number ( population ) of particular organisms , as well as cooperation and competition between organisms , both within and among ecosystems . Ecosystems are composed of dynamically interacting parts including organisms , the communities they make up , and the non - living components of their environment . ___MASK48___ processes , such as primary production , pedogenesis , nutrient cycling , and various niche construction activities , regulate the flux of energy and matter through an environment . These processes are sustained by organisms with specific life ___MASK67___ traits , and the variety of organisms is called biodiversity . Biodiversity , which refers to the varieties of species , genes , and ecosystems , enhances certain ecosystem services . A ___MASK53___ is the number of all the organisms of the same group or species , which live in a particular geographical area , and have the capability of interbreeding . In ___MASK37___ , primary ___MASK90___ is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide . It principally occurs through the process of ___MASK33___ , which uses light as its source of energy , but it also occurs through chemosynthesis , which uses the oxidation or reduction of inorganic chemical compounds as its source of energy . Almost all life on Earth relies directly or indirectly on primary ___MASK90___ . The organisms responsible for primary ___MASK90___ are known as " primary producers " or autotrophs , and form the base of the food chain . In terrestrial ecoregions , these are mainly plants , while in aquatic ecoregions algae predominate in this role . Ecologists distinguish primary ___MASK90___ as either " net " or " gross ", the former accounting for losses to processes such as cellular respiration , the latter not . ___MASK73___ management attempts to balance the needs of ___MASK73___ with the needs of people using the best available ___MASK30___ . ___MASK73___ management can include game keeping , ___MASK73___ conservation and pest control . ___MASK73___ management draws on disciplines such as ___MASK4___ , ___MASK88___ , biology , ecology , climatology and ___MASK27___ to gain the best results . Pest control refers to the regulation or management of a ___MASK87___ defined as a pest , and can be perceived to be detrimental to a person ' s health , the ecology or the ___MASK15___ . A practitioner of pest control is called an exterminator . A unicellular ___MASK58___ , also known as a single - celled ___MASK58___ , is an ___MASK58___ that consists of only one cell , unlike a multicellular ___MASK58___ that consists of more than one cell . Historically , simple unicellular organisms have been referred to as monads , though this term is also used more specifically to describe organisms of the genus " Monas " and similar flagellate ameboids . The main groups of unicellular organisms are bacteria , archaea , protozoa , unicellular algae , and unicellular fungi . Unicellular organisms fall into two general categories : prokaryotic organisms and eukaryotic organisms . Unicellular organisms are thought to be the oldest form of life , with early protocells possibly emerging 3 . 8  4 billion years ago . ___MASK79___ is change in the heritable characteristics of biological populations over successive generations . Evolutionary processes give rise to biodiversity at every level of biological organisation , including the levels of ___MASK87___ , individual organisms , and molecules . A fungus ( plural : fungi or funguses ) is any member of the group of eukaryotic organisms that includes unicellular microorganisms such as yeasts and molds , as well as multicellular fungi that produce familiar fruiting forms such as mushrooms and bracket fungi . These organisms are classified as a kingdom , Fungi , which is separate from the other eukaryotic ___MASK54___ kingdoms of plants and ___MASK99___ . A ___MASK77___ is a set of interacting or interdependent component parts forming a complex or intricate whole . Every ___MASK77___ is delineated by its spatial and temporal boundaries , surrounded and influenced by its environment , described by its structure and purpose and expressed in its functioning . Identification in ___MASK42___ is the process of assigning a pre - existing taxon ___MASK96___ to an individual ___MASK58___ . Identification of organisms to individual scientific names ( or codes ) may be based on individualistic natural body features ( e . g . ) , experimentally created individual markers ( e . g . , color dot patterns ) , or natural individualistic molecular markers ( similar to those used in maternity or paternity identification tests ) . Individual identification is used , e . g . , in ecology , wildlife management or conservation ___MASK42___ . The more common form of identification is the identification of organisms to common names ( e . g . , `` lion '' ) or scientific ___MASK96___ ( e . g . , `` Panthera leo '' ) . By necessity this is based on inherited features ( `` characters '' ) of the sexual organisms , the inheritance forming the basis of defining a class . The features may , e . g . , be morphological , anatomical , physiological , behavioral , or molecular . The term `` determination '' may occasionally be used as a synonym for identification ( e . g . ) , or as in `` determination slips '' . Identification methods may be manual or computerized and may involve using identification keys , browsing through fields guide that contain ( often illustrated ) species accounts , or comparing the ___MASK58___ with specimens from natural history collections . ___MASK27___ ( from Greek , " geographia ", literally " earth description ") is a field of science devoted to the study of the lands , the features , the inhabitants , and the phenomena of Earth . The first person to use the word "  " was Eratosthenes ( 276  194 BC ). ___MASK27___ is an all - encompassing discipline that seeks an understanding of the Earth and its human and natural complexities  not merely where objects are , but how they have changed and come to be . It is often defined in terms of the two branches of human ___MASK27___ and physical ___MASK27___ . The four historical traditions in geographical research are : spatial analyses of natural and the human phenomena , area studies of places and regions , studies of human - land relationships , and the Earth sciences . ___MASK27___ has been called " the world discipline " and " the ___MASK24___ between the human and the physical sciences ". In ___MASK42___ and ___MASK37___ , abiotic components or abiotic factors are non - living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems . Abiotic factors and phenomena associated with them underpin all ___MASK42___ . Natural ___MASK30___ is a branch of ___MASK30___ concerned with the description , prediction , and understanding of natural phenomena , based on observational and empirical evidence . Mechanisms such as peer review and repeatability of findings are used to try to ensure the validity of scientific advances . Biomass is organic matter derived from living , or recently living organisms . Biomass can be used as a source of energy and it most often refers to plants or ___MASK80___ - based materials that are not used for food or feed , and are specifically called lignocellulosic biomass . As an energy source , biomass can either be used directly via combustion to produce heat , or indirectly after converting it to various forms of biofuel . Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into : " thermal ", " chemical ", and " biochemical " methods . ___MASK30___ is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe . Heredity is the genetic information passing for traits from parents to their offspring , either through asexual reproduction or ___MASK61___ . This is the process by which an offspring cell or ___MASK58___ acquires or becomes predisposed to the characteristics of its parent cell or ___MASK58___ . Through heredity , variations exhibited by individuals can accumulate and cause some species to evolve through the natural selection of specific phenotype traits . The study of heredity in biology is called genetics , which includes the field of epigenetics . Multicellular organisms are organisms that consist of more than one ___MASK59___ , in contrast to unicellular organisms . Conservation ___MASK42___ is the management of ___MASK21___ and of Earth ' s biodiversity with the aim of protecting species , their habitats , and ecosystems from excessive rates of extinction and the erosion of biotic interactions . It is an interdisciplinary subject drawing on natural and social sciences , and the practice of natural resource management . Conservation is the practice of protecting ___MASK39___ ___MASK80___ and animal ___MASK87___ and their habitats . The goal of wildlife conservation is to ensure that ___MASK21___ will be around for future generations to enjoy and also to recognize the importance of wildlife and wilderness for humans and other ___MASK87___ alike . Many nations have ___MASK94___ agencies and NGO ' s dedicated to wildlife conservation , which help to implement policies designed to protect wildlife . Numerous independent non - profit organizations also promote various wildlife conservation causes . Natural resource management refers to the management of natural resources such as land , water , soil , plants and ___MASK99___ , with a particular focus on how management affects the quality of life for both present and future generations ( stewardship ). Homeostasis or homoeostasis is the property of a ___MASK77___ in which a variable ( for example , the concentration of a substance in solution , or its temperature ) is actively regulated to remain very nearly constant . This regulation occurs inside a defined environment ( mostly within a living ___MASK58___ ' s body ). Examples of homeostasis include the regulation of the body temperature of an animal , the pH of its extracellular fluids , or the concentrations of sodium ( Na ) and calcium ( Ca ) ions or of glucose in the blood plasma , despite changes in the animal  s environment , or what it has eaten , or what it is doing ( for example , resting or exercising ). Each of these variables is controlled by a separate  homeostat  ( or regulator ), which , together , maintain life . Homeostats are energy - consuming physiological mechanisms . Niche construction is the ___MASK69___ in which an ___MASK58___ alters its own ( or other species ') environment , often but not always in a manner that increases its chances of survival . Changes that organisms bring about in their worlds that are of no evolutionary or ecological consequence are not examples of niche construction . Several biologists have argued that niche construction is as important to evolution as natural selection ( i . e ., not only does an environment cause changes in species through selection , but species also cause changes in their environment through niche construction ). This back - and - forth creates a feedback relationship between natural selection and niche - construction : when organisms affect their environment , that change can then cause a shift in what traits are being naturally selected for . The effect of niche construction is especially pronounced in situations where environmental alterations persist for several generations , introducing the evolutionary role of ecological inheritance . Less drastic niche - constructing behaviors are also quite possible for an ___MASK58___ . This theory , in conjunction with natural selection , shows that organisms inherit two legacies from their ancestors : genes and a modified environment . Together , these two evolutionary mechanisms determine a population ' s fitness and what adaptations those organisms develop in the continuation for their survival . The microscopic scale ( from , " mikrós ", " small " and  , " skopé " " look ") is the scale of objects and events smaller than those that can easily be seen by the naked ___MASK93___ , requiring a lens or microscope to see them clearly . In ___MASK81___ , the microscopic scale is sometimes considered the scale between the macroscopic and the quantum regime . ___MASK42___ is a natural ___MASK30___ concerned with the study of life and living organisms , including their structure , function , growth , evolution , distribution , identification and ___MASK98___ . Modern biology is a vast and eclectic field , composed of many branches and subdisciplines . However , despite the broad scope of biology , there are certain general and unifying concepts within it that govern all study and research , consolidating it into single , coherent field . In general , biology recognizes the cell as the basic unit of life , genes as the basic unit of heredity , and evolution as the engine that propels the synthesis and creation of new species . It is also understood today that all the organisms survive by consuming and transforming energy and by regulating their internal environment to maintain a stable and vital condition known as homeostasis . Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature , each in their own broad field of organisms . To an end - user who only deals with names of ___MASK87___ , with some awareness that ___MASK87___ are assignable to families , it ___MASK91___ not be noticeable that there is more than one code , but beyond this basic level these are rather different in the way they work . In ___MASK81___ , energy is the property that must be transferred to an object in ___MASK29___ to perform work on  or to heat  the object , and can be converted in form , but not created or destroyed . The SI unit of energy is the joule , which is the energy transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton . Humankind benefits in a multitude of ways from ecosystems . Collectively , these benefits are becoming known as ___MASK48___ services . ___MASK48___ services are regularly involved in the provisioning of clean drinking water and the decomposition of wastes . While scientists and environmentalists have discussed ___MASK48___ services implicitly for decades , the ___MASK48___ services concept itself was popularized by the Millennium ___MASK48___ Assessment ( ___MASK28___ ) in the early 2000s . This grouped ___MASK48___ services into four broad categories : " provisioning ", such as the production of food and water ; " regulating ", such as the control of climate and disease ; " supporting ", such as nutrient cycles and crop pollination ; and " cultural ", such as spiritual and recreational benefits . To help inform decision - makers , many ___MASK48___ services are being assigned economic values . ___MASK75___ , otherwise known as the world , is the third planet from the Sun and the only object in the ___MASK55___ known to harbor life . It is the densest planet in the Solar ___MASK77___ and the largest of the four terrestrial planets . In ___MASK42___ , an ___MASK58___ is any contiguous living system , such as an animal , plant , fungus , archaeon , or bacterium . All known types of organisms are capable of some degree of response to stimuli , reproduction , growth and development and homeostasis . An ___MASK58___ consists of one or more cells ; when it has one cell it is known as a unicellular ___MASK58___ ; and when it has more than one it is known as a multicellular ___MASK58___ . Most unicellular organisms are of microscopic scale and are thus loosely described as microorganisms . Humans are multicellular organisms composed of many trillions of cells grouped into specialized tissues and organs . Natural resources are resources that exist without actions of humankind . This includes all valued characteristics such as magnetic , gravitational , and electrical properties and forces . On ___MASK75___ it includes : sunlight , atmosphere , water , land ( includes all minerals ) along with all vegetation and animal life that naturally subsists upon or within the heretofore identified characteristics and substances . Biodiversity , a contraction of " biological diversity ," generally refers to the ___MASK74___ and variability of life on Earth . One of the most widely used definitions defines it in terms of the variability within species , between species and between ecosystems . It is a measure of the ___MASK74___ of organisms present in different ecosystems . This can refer to genetic variation , ___MASK48___ variation , or species variation ( number of species ) within an area , biome , or planet . Terrestrial biodiversity tends to be greater near the equator , which seems to be the result of the warm climate and high primary productivity . Biodiversity is not distributed evenly on Earth . It is richest in the tropics . Marine biodiversity tends to be highest along coasts in the Western Pacific , where ___MASK17___ surface temperature is highest and in the mid - latitudinal band in all oceans . There are latitudinal gradients in species diversity . Biodiversity generally tends to cluster in hotspots , and has been increasing through time , but will be likely to slow in the future . In ___MASK42___ and ___MASK37___ , extinction is the end of an ___MASK58___ or of a group of organisms ( taxon ), normally a species . The moment of extinction is generally considered to be the death of the last individual of the species , although the capacity to breed and recover may have been lost before this point . Because a species ' potential range may be very large , determining this moment is difficult , and is usually done retrospectively . This difficulty leads to phenomena such as Lazarus taxa , where a species presumed extinct abruptly " reappears " ( typically in the fossil record ) after a period of apparent absence . ___MASK88___ is a branch of physical science that studies the composition , structure , properties and change of matter . ___MASK88___ includes topics such as the properties of individual atoms , how atoms form chemical bonds to create chemical compounds , the interactions of substances through intermolecular forces that give matter its general properties , and the interactions between substances through chemical reactions to form different substances . In ___MASK42___ , a taxon ( plural taxa ; ___MASK5___ - formation from " ___MASK98___ ") is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit . Although neither is required , a taxon is usually known by a particular name and given a particular ranking , especially if and when it is accepted or becomes established . It is not uncommon , however , for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion . If a taxon is given a formal scientific name , its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping . Pedogenesis ( from the Greek " pedo "-, or " pedon ", meaning ' soil , ___MASK75___ ,' and " ___MASK62___ ", meaning ' origin , birth ') ( also termed soil development , soil evolution , soil formation , and soil ___MASK62___ ) is the process of soil formation as regulated by the effects of place , environment , and ___MASK67___ . Biogeochemical processes act to both create and destroy order ( anisotropy ) within soils . These alterations lead to the development of layers , termed soil horizons , distinguished by differences in color , structure , texture , and chemistry . These features occur in patterns of soil type distribution , forming in response to differences in soil forming factors . ___MASK75___ ___MASK30___ or geoscience is a widely embraced term for the fields of ___MASK30___ related to the planet ___MASK75___ . ___MASK75___ ___MASK30___ can be considered to be a branch of planetary ___MASK30___ , but with a much older ___MASK67___ . There are both reductionist and holistic approaches to ___MASK75___ sciences . The ___MASK75___ sciences can include the study of geology , the lithosphere , and the large - scale structure of the ___MASK75___ ' s interior , as well as the atmosphere , hydrosphere , and biosphere . Typically , ___MASK75___ scientists use tools from geography , chronology , physics , chemistry , biology , and mathematics to build a quantitative understanding of how the ___MASK75___ system works and evolves . ___MASK99___ are multicellular , eukaryotic organisms of the kingdom Animalia ( also called Metazoa ). The animal kingdom emerged as a basal clade within Apoikozoa as a sister of the choanoflagellates . Sponges are the most basal clade of ___MASK99___ . ___MASK99___ are motile , meaning they can move spontaneously and independently at some point in their lives . Their body plan eventually becomes fixed as they develop , although some undergo a process of metamorphosis later in their lives . All ___MASK99___ are heterotrophs : they must ingest other organisms or their products for sustenance . ___MASK38___ ( from Greek , " klima ", " place , zone "; and , "- logia ") or climate ___MASK30___ is the study of climate , scientifically defined as weather conditions averaged over a period of time . This modern field of study is regarded as a branch of the atmospheric sciences and a subfield of physical ___MASK27___ , which is one of the Earth sciences . ___MASK38___ now includes aspects of oceanography and biogeochemistry . Basic knowledge of climate can be used within shorter term weather forecasting using analog techniques such as the El Niño  Southern Oscillation ( ENSO ), the Madden  Julian oscillation ( MJO ), the North Atlantic oscillation ( NAO ), the Northern Annular Mode ( NAM ) which is also known as the Arctic oscillation ( AO ), the Northern Pacific ( NP ) Index , the Pacific decadal oscillation ( PDO ), and the Interdecadal Pacific Oscillation ( IPO ). Climate models are used for a variety of purposes from study of the ___MASK19___ of the weather and climate system to projections of future climate . A ___MASK52___ is a locus ( or region ) of DNA which is made up of nucleotides and is the molecular unit of heredity . The transmission of genes to an ___MASK58___ ' s offspring is the basis of the inheritance of phenotypic traits . Most biological traits are under the influence of polygenes ( many different genes ) as well as ___MASK52___  environment interactions . Some genetic traits are instantly visible , such as eye colour or number of limbs , and some are not , such as blood type , risk for specific diseases , or the thousands of basic biochemical processes that comprise life .