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{{Other uses}}{{pp-semi-indef}}{{pp-move-indef}}{{short description|The study of life}}{{multiple image|perrow=2|total_width = 250|image1=EscherichiaColi NIAID.jpg|image2=Thompson's Gazelle.jpeg|image3=Goliath beetle.jpg|image4=Tree Fern.jpg|footer=Biology deals with the study of life and organisms. {{TopicTOC-Biology}}Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution.Based on definition from: WEB,weblinkweblink" title="">weblink 2004-06-08, Aquarena Wetlands Project glossary of terms, Texas State University at San Marcos, Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. 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 creation and extinction of species. Living organisms are open systems that survive by transforming energy and decreasing their local entropyJOURNAL, Davies, PC, Rieper, E, Tuszynski, JA, Self-organization and entropy reduction in a living cell, Bio Systems, 111, 1, 1–10, January 2013, 23159919, 3712629, 10.1016/j.biosystems.2012.10.005, to maintain a stable and vital condition defined as homeostasis.JOURNAL, Modell, Harold, Cliff, William, Michael, Joel, McFarland, Jenny, Wenderoth, Mary Pat, Wright, Ann, December 2015, A physiologist's view of homeostasis, Advances in Physiology Education, 39, 4, 259–66, 10.1152/advan.00107.2015, 1043-4046, 4669363, 26628646, Sub-disciplines of biology are defined by the research methods employed and the kind of system studied: theoretical biology uses mathematical methods to formulate quantitative models while experimental biology performs empirical experiments to test the validity of proposed theories and understand the mechanisms underlying life and how it appeared and evolved from non-living matter about 4 billion years ago through a gradual increase in the complexity of the system.BOOK, Molecular Biology, Principles of Genome Function, Craig, Nancy, 2014, 978-0-19-965857-2, JOURNAL, Mosconi, Francesco, Julou, Thomas, Desprat, Nicolas, Sinha, Deepak Kumar, Allemand, Jean-François, Vincent Croquette, Bensimon, David, 2008, Some nonlinear challenges in biology,weblink Nonlinearity, en, 21, 8, T131, 10.1088/0951-7715/21/8/T03, 0951-7715, 2008Nonli..21..131M, WEB,weblink How Did Life Become Complex, And Could It Happen Beyond Earth?, Howell, Elizabeth, 8 December 2014, Astrobiology Magazine, 14 February 2018, See branches of biology.


Biology derives from the Ancient Greek words of βίος; romanized bíos meaning "life" and -λογία; romanized logía (-logy) meaning "branch of study" or "to speak". Those combined make the Greek word βιολογία; romanized biología meaning biology. Despite this, the term βιολογία as a whole didn't exist in Ancient Greek. The first to borrow it were the English and French (biologie). Since the advent of the scientific era, reanalyzable as a compound using the combining forms bio + logy. {{Clarification needed|reason=|date=October 2019}}


File:Hooke-bluefly.jpg|thumb|alt=A drawing of a fly from facing up, with wing detail|A Diagram of a fly from Robert Hooke's innovative MicrographiaMicrographiaFile:Tree of life by Haeckel.jpg|thumb|alt=Ernst Haeckel's pedigree of Man family tree from Evolution of Man|Ernst HaeckelErnst HaeckelThe term (wikt:biology|biology) is derived from the Greek word , vios, "life" and the suffix , -logia, "study of."WEB,weblink Who coined the term biology?,, 2012-06-03, dead,weblink" title="">weblink 2013-05-09, WEB, biology,weblink Online Etymology Dictionary, live,weblink" title="">weblink 2013-03-07, The Latin-language form of the term first appeared in 1736 when Swedish scientist Carl Linnaeus (Carl von Linné) used biologi in his Bibliotheca Botanica. It was used again in 1766 in a work entitled Philosophiae naturalis sive physicae: tomus III, continens geologian, biologian, phytologian generalis, by Michael Christoph Hanov, a disciple of Christian Wolff. The first German use, Biologie, was in a 1771 translation of Linnaeus' work. In 1797, Theodor Georg August Roose used the term in the preface of a book, Grundzüge der Lehre van der Lebenskraft. Karl Friedrich Burdach used the term in 1800 in a more restricted sense of the study of human beings from a morphological, physiological and psychological perspective (Propädeutik zum Studien der gesammten Heilkunst). The term came into its modern usage with the six-volume treatise Biologie, oder Philosophie der lebenden Natur (1802–22) by Gottfried Reinhold Treviranus, who announced:BOOK, Richards, Robert J., The Romantic Conception of Life: Science and Philosophy in the Age of Goethe, 2002, University of Chicago Press, 978-0-226-71210-9,weblink
The objects of our research will be the different forms and manifestations of life, the conditions and laws under which these phenomena occur, and the causes through which they have been effected. The science that concerns itself with these objects we will indicate by the name biology [Biologie] or the doctrine of life [Lebenslehre].
Although modern biology is a relatively recent development, sciences related to and included within it have been studied since ancient times. Natural philosophy was studied as early as the ancient civilizations of Mesopotamia, Egypt, the Indian subcontinent, and China. However, the origins of modern biology and its approach to the study of nature are most often traced back to ancient Greece.BOOK, Magner, Lois N., A History of the Life Sciences, Revised and Expanded,weblink 2002, CRC Press, 978-0-203-91100-6, live,weblink" title="">weblink 2015-03-24, BOOK, Anthony, Serafini, The Epic History of Biology, 2013,weblink 14 July 2015, 978-1-4899-6327-7, While the formal study of medicine dates back to Pharaonic Egypt, it was Aristotle (384–322 BC) who contributed most extensively to the development of biology. Especially important are his History of Animals and other works where he showed naturalist leanings, and later more empirical works that focused on biological causation and the diversity of life. Aristotle's successor at the Lyceum, Theophrastus, wrote a series of books on botany that survived as the most important contribution of antiquity to the plant sciences, even into the Middle Ages.{{EB1911|wstitle=Theophrastus|inline=1}}Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-Dīnawarī (828–896), who wrote on botany,BOOK, Fahd, Toufic, Botany and agriculture, 815, harv, Morelon, Régis, Rashed, Roshdi, 1996, Encyclopedia of the History of Arabic Science, 3, Routledge, 978-0-415-12410-2, Encyclopedia of the History of Arabic Science, and Rhazes (865–925) who wrote on anatomy and physiology. Medicine was especially well studied by Islamic scholars working in Greek philosopher traditions, while natural history drew heavily on Aristotelian thought, especially in upholding a fixed hierarchy of life.Biology began to quickly develop and grow with Anton van Leeuwenhoek's dramatic improvement of the microscope. It was then that scholars discovered spermatozoa, bacteria, infusoria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and helped to develop the basic techniques of microscopic dissection and staining.BOOK, Magner, Lois N., A History of the Life Sciences, Revised and Expanded,weblink 2002, CRC Press, 978-0-203-91100-6, 133–44, live,weblink" title="">weblink 2015-03-24, Advances in microscopy also had a profound impact on biological thinking. In the early 19th century, a number of biologists pointed to the central importance of the cell. Then, in 1838, Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life, although they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of Robert Remak and Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of what came to be known as cell theory.BOOK, Jan, Sapp, Jan Sapp, 2003, Genesis: The Evolution of Biology, 7, Oxford University Press, New York., 978-0-19-515618-8, BOOK, Coleman, William, 1977, Biology in the Nineteenth Century: Problems of Form, Function, and Transformation, Cambridge University Press, New York, 978-0-521-29293-1, Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus published a basic taxonomy for the natural world in 1735 (variations of which have been in use ever since), and in the 1750s introduced scientific names for all his species.Mayr, Ernst. The Growth of Biological Thought, chapter 4 Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent. Although he was opposed to evolution, Buffon is a key figure in the history of evolutionary thought; his work influenced the evolutionary theories of both Lamarck and Darwin.Mayr, Ernst. The Growth of Biological Thought, chapter 7Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, who was the first to present a coherent theory of evolution.Gould, Stephen Jay. The Structure of Evolutionary Theory. The Belknap Press of Harvard University Press: Cambridge, 2002. {{ISBN|0-674-00613-5}}. p. 187. He posited that evolution was the result of environmental stress on properties of animals, meaning that the more frequently and rigorously an organ was used, the more complex and efficient it would become, thus adapting the animal to its environment. Lamarck believed that these acquired traits could then be passed on to the animal's offspring, who would further develop and perfect them.Lamarck (1914) However, it was the British naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell, Malthus's writings on population growth, and his own morphological expertise and extensive natural observations, who forged a more successful evolutionary theory based on natural selection; similar reasoning and evidence led Alfred Russel Wallace to independently reach the same conclusions.Mayr, Ernst. The Growth of Biological Thought, chapter 10: "Darwin's evidence for evolution and common descent"; and chapter 11: "The causation of evolution: natural selection"BOOK, Larson, Edward J., Evolution: The Remarkable History of a Scientific Theory,weblink 2006, Random House Publishing Group, 978-1-58836-538-5, Ch. 3, live,weblink" title="">weblink 2015-03-24, Although it was the subject of controversy (which continues to this day), Darwin's theory quickly spread through the scientific community and soon became a central axiom of the rapidly developing science of biology.The discovery of the physical representation of heredity came along with evolutionary principles and population genetics. In the 1940s and early 1950s, experiments pointed to DNA as the component of chromosomes that held the trait-carrying units that had become known as genes. A focus on new kinds of model organisms such as viruses and bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of molecular genetics. From the 1950s to present times, biology has been vastly extended in the molecular domain. The genetic code was cracked by Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg after DNA was understood to contain codons. Finally, the Human Genome Project was launched in 1990 with the goal of mapping the general human genome. This project was essentially completed in 2003,NEWS,weblink Human genome finally complete, 2006-07-22, 2003-04-14, BBC News, Ivan, Noble, live,weblink" title="">weblink 2006-06-14, with further analysis still being published. The Human Genome Project was the first step in a globalized effort to incorporate accumulated knowledge of biology into a functional, molecular definition of the human body and the bodies of other organisms.

Foundations of modern biology

Cell theory

File:HeLa Hoechst 33258.jpg|thumb|upright=1.15|right|alt=HeLa cells stained with Hoechst blue stain.|Human cancer cells with nuclei (specifically the DNA) stained blue. The central and rightmost cell are in interphase, so the entire nuclei are labeled. The cell on the left is going through mitosismitosisCell theory states that the cell is the fundamental unit of life, that all living things are composed of one or more cells, and that all cells arise from pre-existing cells through cell division. In multicellular organisms, every cell in the organism's body derives ultimately from a single cell in a fertilized egg. The cell is also considered to be the basic unit in many pathological processes.JOURNAL, Mazzarello, P, A unifying concept: the history of cell theory, Nature Cell Biology, 1, 1, E13–15, May 1999, 10559875, 10.1038/8964, In addition, the phenomenon of energy flow occurs in cells in processes that are part of the function known as metabolism. Finally, cells contain hereditary information (DNA), which is passed from cell to cell during cell division. Research into the origin of life, abiogenesis, amounts to an attempt to discover the origin of the first cells.


File:Mutation and selection diagram.svg|thumb|right|upright=1.15|alt=diagram showing Natural selection favoring predominance of surviving mutation|Natural selectionNatural selectionA central organizing concept in biology is that life changes and develops through evolution, and that all life-forms known have a common origin. The theory of evolution postulates that all organisms on the Earth, both living and extinct, have descended from a common ancestor or an ancestral gene pool. This universal common ancestor of all organisms is believed to have appeared about 3.5 billion years ago.BOOK, Life Evolving: Molecules, Mind, and Meaning, De Duve, Christian, New York, Oxford University Press, 2002, 44, 978-0-19-515605-8, Biologists regard the ubiquity of the genetic code as definitive evidence in favor of the theory of universal common descent for all bacteria, archaea, and eukaryotes (see: origin of life).BOOK, Futuyma, DJ, Evolution, 2005, Sinauer Associates, 978-0-87893-187-3, 57311264,weblink The term "evolution" was introduced into the scientific lexicon by Jean-Baptiste de Lamarck in 1809,BOOK, Packard, Alpheus Spring, Lamarck, the founder of Evolution: his life and work with translations of his writings on organic evolution, 1901, Longmans, Green., New York, 978-0-405-12562-1, and fifty years later Charles Darwin posited a scientific model of natural selection as evolution's driving force.WEB,weblink The Complete Works of Darwin Online – Biography,, 2006-12-15, live,weblink" title="">weblink 2007-01-07, JOURNAL, Dobzhansky, T., 1973, Nothing in biology makes sense except in the light of evolution, The American Biology Teacher, 35, 3, 125–29, 10.2307/4444260, 4444260,, BOOK, On the origin of species by means of natural selection, Carroll, Joseph, 2003, Broadview, Peterborough, Ontario, 978-1-55111-337-1, 15, As Darwinian scholar Joseph Carroll of the University of Missouri–St. Louis puts it in his introduction to a modern reprint of Darwin's work: "The Origin of Species has special claims on our attention. It is one of the two or three most significant works of all time—one of those works that fundamentally and permanently alter our vision of the world ... It is argued with a singularly rigorous consistency but it is also eloquent, imaginatively evocative, and rhetorically compelling.", (Alfred Russel Wallace is recognized as the co-discoverer of this concept as he helped research and experiment with the concept of evolution.)Shermer p. 149. Evolution is now used to explain the great variations of life found on Earth.Darwin theorized that species flourish or die when subjected to the processes of natural selection or selective breeding.Darwin, Charles (1859). On the Origin of Species, John Murray. Genetic drift was embraced as an additional mechanism of evolutionary development in the modern synthesis of the theory.BOOK, Simpson, George Gaylord, George Gaylord Simpson, 1967, The Meaning of Evolution, Yale University Press, Second, 978-0-300-00952-1, The evolutionary history of the species—which describes the characteristics of the various species from which it descended—together with its genealogical relationship to every other species is known as its phylogeny. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of DNA sequences, a product of molecular biology (more particularly genomics), and comparisons of fossils or other records of ancient organisms, a product of paleontology.WEB,weblink Phylogeny,, 2007-11-11, 2013-10-02, live,weblink" title="">weblink 2013-10-04, Biologists organize and analyze evolutionary relationships through various methods, including phylogenetics, phenetics, and cladistics. (For a summary of major events in the evolution of life as currently understood by biologists, see evolutionary timeline.)Evolution is relevant to the understanding of the natural history of life forms and to the understanding of the organization of current life forms. But, those organizations can only be understood in the light of how they came to be by way of the process of evolution. Consequently, evolution is central to all fields of biology.JOURNAL, Montévil, M, Mossio, M, Pocheville, A, Longo, G, Theoretical principles for biology: Variation, Progress in Biophysics and Molecular Biology, 122, 1, 36–50, October 2016, 27530930, 10.1016/j.pbiomolbio.2016.08.005,weblink From the Century of the Genome to the Century of the Organism: New Theoretical Approaches, live,weblink" title="">weblink 2018-03-20, {{clear right}}


File:Punnett square mendel flowers.svg|thumb|upright=1.15|alt=two by two table showing genetic crosses|A Punnett squarePunnett squareGenes are the primary units of inheritance in all organisms. A gene is a unit of heredity and corresponds to a region of DNA that influences the form or function of an organism in specific ways. All organisms, from bacteria to animals, share the same basic machinery that copies and translates DNA into proteins. Cells transcribe a DNA gene into an RNA version of the gene, and a ribosome then translates the RNA into a sequence of amino acids known as a protein. The translation code from RNA codon to amino acid is the same for most organisms. For example, a sequence of DNA that codes for insulin in humans also codes for insulin when inserted into other organisms, such as plants.Marcial, Gene G. (August 13, 2007) From SemBiosys, A New Kind Of Insulin {{webarchive|url= |date=2014-10-29 }}. businessweek.comDNA is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. A chromosome is an organized structure consisting of DNA and histones. The set of chromosomes in a cell and any other hereditary information found in the mitochondria, chloroplasts, or other locations is collectively known as a cell's genome. In eukaryotes, genomic DNA is localized in the cell nucleus, or with small amounts in mitochondria and chloroplasts. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the nucleoid.JOURNAL, Thanbichler, M, Wang, SC, Shapiro, L, The bacterial nucleoid: a highly organized and dynamic structure, Journal of Cellular Biochemistry, 96, 3, 506–21, October 2005, 15988757, 10.1002/jcb.20519, The genetic information in a genome is held within genes, and the complete assemblage of this information in an organism is called its genotype.WEB,weblink Genotype definition – Medical Dictionary definitions,, 2012-03-19, 2013-10-02, live,weblink" title="">weblink 2013-09-21,


File:ACTH Negative Feedback.svg|right|thumb|alt=diagram showing feedback loop of hormones|The hypothalamus secretes CRH, which directs the pituitary gland to secrete ACTH. In turn, ACTH directs the adrenal cortex to secrete glucocorticoids, such as cortisolcortisolHomeostasis is the ability of an open system to regulate its internal environment to maintain stable conditions by means of multiple dynamic equilibrium adjustments that are controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular, exhibit homeostasis.JOURNAL, Rodolfo, Kelvin, January 2000,weblink What is homeostasis?, Scientific American, live,weblink" title="">weblink 2013-12-03, To maintain dynamic equilibrium and effectively carry out certain functions, a system must detect and respond to perturbations. After the detection of a perturbation, a biological system normally responds through negative feedback that stabilize conditions by reducing or increasing the activity of an organ or system. One example is the release of glucagon when sugar levels are too low.File:Energy and life.svg|thumb|upright=1.1|left|alt=diagram showing human energy process from food input to heat and waste output|Basic overview of energy and human life.]]


The survival of a living organism depends on the continuous input of energy. Chemical reactions that are responsible for its structure and function are tuned to extract energy from substances that act as its food and transform them to help form new cells and sustain them. In this process, molecules of chemical substances that constitute food play two roles; first, they contain energy that can be transformed and reused in that organism's biological, chemical reactions; second, food can be transformed into new molecular structures (biomolecules) that are of use to that organism.The organisms responsible for the introduction of energy into an ecosystem are known as producers or autotrophs. Nearly all such organisms originally draw their energy from the sun.JOURNAL, Bryant, DA, Frigaard, NU, Prokaryotic photosynthesis and phototrophy illuminated, Trends in Microbiology, 14, 11, 488–96, November 2006, 16997562, 10.1016/j.tim.2006.09.001, Plants and other phototrophs use solar energy via a process known as photosynthesis to convert raw materials into organic molecules, such as ATP, whose bonds can be broken to release energy.BOOK, Smith, AL, Oxford dictionary of biochemistry and molecular biology, Oxford University Press, Oxford [Oxfordshire], 1997, 508, 978-0-19-854768-6, Photosynthesis – the synthesis by organisms of organic chemical compounds, esp. carbohydrates, from carbon dioxide using energy obtained from light rather than the oxidation of chemical compounds., A few ecosystems, however, depend entirely on energy extracted by chemotrophs from methane, sulfides, or other non-luminal energy sources.JOURNAL, Edwards, Katrina, Microbiology of a Sediment Pond and the Underlying Young, Cold, Hydrologically Active Ridge Flank, Woods Hole Oceanographic Institution, Some of the energy thus captured produces biomass and energy that is available for growth and development of other life forms. The majority of the rest of this biomass and energy are lost as waste molecules and heat. The most important processes for converting the energy trapped in chemical substances into energy useful to sustain life are metabolismBOOK, Campbell, Neil A., Reece, Jane B., Biology, Benjamin Cummings, 2001, 6, 978-0-8053-6624-2, 47521441,weblink and cellular respiration.BOOK, Bartsch, John, Colvard, Mary P., 2009, The Living Environment, New York State, Prentice Hall, 978-0-13-361202-8,

Study and research


File:biological cell.svg|thumb|upright=1.35|alt=color diagram of cell as bowl|Schematic of typical animal cell depicting the various organelleorganelleMolecular biology is the study of biology at the molecular level.WEB,weblink Molecular Biology,, 2018-04-25, This field overlaps with other areas of biology, particularly those of genetics and biochemistry. Molecular biology is a study of the interactions of the various systems within a cell, including the interrelationships of DNA, RNA, and protein synthesis and how those interactions are regulated.The next larger scale, cell biology, studies the structural and physiological properties of cells, including their internal behavior, interactions with other cells, and with their environment. This is done on both the microscopic and molecular levels, for unicellular organisms such as bacteria, as well as the specialized cells of multicellular organisms such as humans. Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology.Anatomy is a treatment of the macroscopic forms of such structures organs and organ systems.BOOK, Gray, Henry, 1918,weblink Anatomy of the Human Body, 20th, live,weblink" title="">weblink 2007-03-16, Genetics is the science of genes, heredity, and the variation of organisms.BOOK, Anthony J.F., Griffiths, Jeffrey H., Miller, David T., Suzuki, Richard C., Lewontin, William M., Gelbart, An Introduction to Genetic Analysis, 2000, 978-0-7167-3520-5, 7th, W. H. Freeman, New York,weblink Genetics and the Organism: Introduction, BOOK, Hartl, D, Jones, E, Genetics: Analysis of Genes and Genomes, 6th, Jones & Bartlett, 2005, 978-0-7637-1511-3,weblink Genes encode the information needed by cells for the synthesis of proteins, which in turn play a central role in influencing the final phenotype of the organism. Genetics provides research tools used in the investigation of the function of a particular gene, or the analysis of genetic interactions. Within organisms, genetic information is physically represented as chromosomes, within which it is represented by a particular sequence of amino acids in particular DNA molecules.Developmental biology studies the process by which organisms grow and develop. Developmental biology, originated from embryology, studies the genetic control of cell growth, cellular differentiation, and "cellular morphogenesis," which is the process that progressively gives rise to tissues, organs, and anatomy.Model organisms for developmental biology include the round worm Caenorhabditis elegans,JOURNAL, Brenner, S, The genetics of Caenorhabditis elegans, Genetics, 77, 1, 71–94, May 1974, 4366476, 1213120,weblink live,weblink" title="">weblink 2015-06-29, the fruit fly Drosophila melanogaster,ENCYCLOPEDIA, Sang, James H., Eric C.R., Reeve, Encyclopedia of genetics, Drosophila melanogaster: The Fruit Fly,weblink 2001, Fitzroy Dearborn Publishers, I, USA, 157, 978-1-884964-34-3, the zebrafish Danio rerio,JOURNAL, Haffter, P, Nüsslein-Volhard, C, Large scale genetics in a small vertebrate, the zebrafish, The International Journal of Developmental Biology, 40, 1, 221–27, February 1996, 8735932,weblink live,weblink 2016-05-15, the mouse Mus musculus,JOURNAL, Keller G, Embryonic stem cell differentiation: emergence of a new era in biology and medicine, Genes & Development, 19, 10, 1129–55, May 2005, 15905405, 10.1101/gad.1303605, and the weed Arabidopsis thaliana.JOURNAL, Rensink, WA, Buell, CR, Arabidopsis to rice. Applying knowledge from a weed to enhance our understanding of a crop species, Plant Physiology, 135, 2, 622–29, June 2004, 15208410, 514098, 10.1104/pp.104.040170, JOURNAL, Coelho, SM, Peters, AF, Charrier, B, Roze, D, Destombe, C, Valero, M, Cock, JM, Complex life cycles of multicellular eukaryotes: new approaches based on the use of model organisms, Gene, 406, 1–2, 152–70, December 2007, 17870254, 10.1016/j.gene.2007.07.025, (A model organism is a species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in that organism provide insight into the workings of other organisms.)JOURNAL, Fields, S, Johnston, M, Cell biology. Whither model organism research?, Science, 307, 5717, 1885–86, March 2005, 15790833, 10.1126/science.1108872,


Physiology is the study of the mechanical, physical, and biochemical processes of living organisms function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but some principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Plant physiology borrows techniques from both research fields.Physiology is the study the interaction of how, for example, the nervous, immune, endocrine, respiratory, and circulatory systems, function and interact. The study of these systems is shared with such medically oriented disciplines as neurology and immunology.


Evolutionary research is concerned with the origin and descent of species, and their change over time. It employs scientists from many taxonomically oriented disciplines, for example, those with special training in particular organisms such as mammalogy, ornithology, botany, or herpetology, but are of use in answering more general questions about evolution.Evolutionary biology is partly based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution,JOURNAL, Jablonski D, The future of the fossil record, Science, 284, 5423, 2114–16, June 1999, 10381868, 10.1126/science.284.5423.2114, and partly on the developments in areas such as population genetics.BOOK, Gillespie, John H., John H. Gillespie, 1998, Population Genetics: A Concise Guide, Johns Hopkins Press, 978-0-8018-5755-3,weblink In the 1980s, developmental biology re-entered evolutionary biology after its initial exclusion from the modern synthesis through the study of evolutionary developmental biology.BOOK, Vassiliki Betta, Smocovitis, 1996, Unifying Biology: the evolutionary synthesis and evolutionary biology, Princeton University Press, 978-0-691-03343-3, Phylogenetics, systematics, and taxonomy are related fields often considered part of evolutionary biology.


{{PhylomapB|caption=A phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains bacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains are still being debated.}}File:Biological classification L Pengo.svg|thumb|left|alt=color diagram of taxonomy|The hierarchy of biological classification's eight major taxonomic ranks. Intermediate minorrankings are not shown. This diagram uses a 3 Domains / 6 Kingdoms format]]Multiple speciation events create a tree structured system of relationships between species. The role of systematics is to study these relationships and thus the differences and similarities between species and groups of species.BOOK, Neill, Campbell, Biology; Fourth edition, The Benjamin/Cummings Publishing Company, 1996, 978-0-8053-1940-8, G-21 (Glossary), However, systematics was an active field of research long before evolutionary thinking was common.BOOK, Douglas, Futuyma, Douglas Futuyma, Evolutionary Biology; Third edition, Sinauer Associates, 1998, 978-0-87893-189-7, 88, Traditionally, living things have been divided into five kingdoms: Monera; Protista; Fungi; Plantae; Animalia.BOOK, Margulis, Lynn, Schwartz, KV, Lynn Margulis, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, 3rd, WH Freeman & Co, 1997, 978-0-7167-3183-2, 223623098, However, many scientists now consider this five-kingdom system outdated. Modern alternative classification systems generally begin with the three-domain system: Archaea (originally Archaebacteria); Bacteria (originally Eubacteria) and Eukaryota (including protists, fungi, plants, and animals).JOURNAL, Woese, CR, Kandler, O, Wheelis, ML, Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya, Proceedings of the National Academy of Sciences of the United States of America, 87, 12, 4576–79, June 1990, 2112744, 54159, 10.1073/pnas.87.12.4576, 1990PNAS...87.4576W, These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of key biomolecules such as ribosomes.Further, each kingdom is broken down recursively until each species is separately classified. The order is:Domain; Kingdom; Phylum; Class; Order; Family; Genus; Species.Outside of these categories, there are obligate intracellular parasites that are "on the edge of life"JOURNAL, Rybicki, EP, 1990, The classification of organisms at the edge of life, or problems with virus systematics, S Afr J Sci, 86,weblink 182–86, live,weblink 2017-07-18, in terms of metabolic activity, meaning that many scientists do not actually classify such structures as alive, due to their lack of at least one or more of the fundamental functions or characteristics that define life. They are classified as viruses, viroids, prions, or satellites.The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens. Homo is the genus, and sapiens the species. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the species in lowercase.BOOK, McNeill, J, Barrie, FR, Buck, WR, Demoulin, V, Greuter, W, Hawksworth, DL, Herendeen, PS, Knapp, S, Marhold, K, Prado, J, Prud'homme Van Reine, WF, Smith, GF, Wiersema, JH, Turland, NJ, 6, 2012, Regnum Vegetabile 154, International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011, A.R.G. Gantner Verlag KG, 978-3-87429-425-6,weblink live,weblink" title="">weblink 2013-11-04, Recommendation 60F Additionally, the entire term may be italicized or underlined.BOOK,weblink 198, Writing for Science and Engineering: Papers, Presentation, Silyn-Roberts, Heather, 2000, 978-0-7506-4636-9, Butterworth-Heinemann, Oxford, The dominant classification system is called the Linnaean taxonomy. It includes ranks and binomial nomenclature. How organisms are named is governed by international agreements such as the International Code of Nomenclature for algae, fungi, and plants (ICN), the International Code of Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB). The classification of viruses, viroids, prions, and all other sub-viral agents that demonstrate biological characteristics is conducted by the International Committee on Taxonomy of Viruses (ICTV) and is known as the International Code of Viral Classification and Nomenclature (ICVCN).WEB,weblink ICTV Virus Taxonomy 2009,, 2013-10-02, dead,weblink" title="">weblink 2013-10-04, weblink" title="">Index of Viruses – Pospiviroidae (2006). In: ICTVdB – The Universal Virus Database, version 4. Büchen-Osmond, C (Ed), Columbia University, New York, USA.Version 4 is based on weblink" title="">Virus Taxonomy, Classification and Nomenclature of Viruses, 8th ICTV Report of the International Committee on Taxonomy of Viruses. Fauquet, CM; Mayo, MA; Maniloff, J; Desselberger, U; Ball, LA (editors) (2005) Elsevier/Academic Press, pp. 1259.WEB,weblinkweblink" title="">weblink 2009-08-27, 90. Prions – ICTVdB Index of Viruses, Prusiner, SB, Baldwin, M, Collinge, J, DeArmond, SJ, Marsh, R, Tateishi, J, Weissmann, C, United States National Institutes of Health, 2009-10-28, WEB,weblinkweblink" title="">weblink 2009-05-01, 81. Satellites – ICTVdB Index of Viruses, Mayo, MA, Berns, KI, Fritsch, C, Jackson, AO, Leibowitz, MJ, Taylor, JM, United States National Institutes of Health, 2009-10-28, However, several other viral classification systems do exist.A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature in these three areas, but has yet to be formally adopted.CONFERENCE, The BioCode: Integrated biological nomenclature for the 21st century?, Proceedings of a Mini-Symposium on Biological Nomenclature in the 21st Century, McNeill, John, November 1996,weblink dead,weblink" title="">weblink 2014-01-04, 2014-01-04, The BioCode draft has received little attention since 1997; its originally planned implementation date of January 1, 2000, has passed unnoticed. A revised BioCode that, instead of replacing the existing codes, would provide a unified context for them, was proposed in 2011.WEB,weblink The Draft BioCode (2011), International Committee on Bionomenclature (ICB), live,weblink" title="">weblink 2013-06-13, JOURNAL,weblink Greuter, W, Garrity, G, Hawksworth, DL, Jahn, R, Kirk, PM, Knapp, S, McNeill, J, Michel, E, Patterson, DJ, Pyle, R, Tindall, BJ, 2011, Draft BioCode (2011): Principles and rules regulating the naming of organisms, Taxon, 60, 201–12, live,weblink" title="">weblink 2012-10-24, 10.1002/tax.601019, JOURNAL,weblink 2011, Taxon, 60, 199–200, Introducing the Draft BioCode (2011), Hawksworth, David L, live,weblink" title="">weblink 2012-10-24, 10.1002/tax.601018, However, the International Botanical Congress of 2011 declined to consider the BioCode proposal. The ICVCN remains outside the BioCode, which does not include viral classification.


File:Guriezo Adino vaca toro terneras.jpg|Animalia – Bos primigenius taurusFile:Zboże.jpg|Plantae – TriticumFile:Morchella esculenta 08.jpg|Fungi – Morchella esculentaFile:Fucus serratus2.jpg|Stramenopila/Chromista – Fucus serratusFile:Gemmatimonas aurantiaca.jpg|Bacteria – Gemmatimonas aurantiaca (-=1 Micrometer)File:Halobacteria.jpg|Archaea – HalobacteriaFile:Gamma phage.png|Virus – Gamma phage

Ecological and environmental

File:Common clownfish.jpg|thumb|upright=1.15|right|alt=a colorful cloudfish swimming near a sea anemone|Mutual symbiosis between clownfish of the genus Amphiprion that dwell among the tentacles of tropical sea anemonesea anemoneEcology is the study of the distribution and abundance of living organisms, the interaction between them and their environment.BOOK, Begon, M, Townsend, CR, Harper, JL, Ecology: From individuals to ecosystems, 4th, 2006, Blackwell, 978-1-4051-1117-1, An organism shares an environment that includes other organisms and biotic factors as well as local abiotic factors (non-living) such as climate and ecology.BOOK, Habitats of the world, 2004,weblink Marshall Cavendish, New York, 978-0-7614-7523-1, 238, One reason that biological systems can be difficult to study is that so many different interactions with other organisms and the environment are possible, even on small scales. A microscopic bacterium responding to a local sugar gradient is responding to its environment as much as a lion searching for food in the African savanna. For any species, behaviors can be co-operative, competitive, parasitic, or symbiotic. Matters become more complex when two or more species interact in an ecosystem.Ecological systems are studied at several different levels, from the scale of the ecology of individual organisms, to those of populations, to the ecosystems and finally the biosphere. The term population biology is often used interchangeably with population ecology, although population biology is more frequently used in the case of diseases, viruses, and microbes, while the term population ecology is more commonly applied to the study of plants and animals. Ecology draws on many subdisciplines.Ethology is the study of animal behavior (particularly that of social animals such as primates and canids), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book, The Expression of the Emotions in Man and Animals, influenced many ethologists to come.JOURNAL, Black, J, Darwin in the world of emotions, Journal of the Royal Society of Medicine, 95, 6, 311–13, June 2002, 12042386, 1279921, 10.1258/jrsm.95.6.311, Biogeography studies the spatial distribution of organisms on the Earth, focusing on such topics as plate tectonics, climate change, dispersal and migration, and cladistics.

Basic unresolved problems in biology

Despite the profound advances made over recent decades in our understanding of life's fundamental processes, some basic problems have remained unresolved. One of the major unresolved problems in biology is the primary adaptive function of sex, and particularly its key processes in eukaryotes of meiosis and homologous recombination. One view is that sex evolved primarily as an adaptation that promoted increased genetic diversity (see references e.g.JOURNAL, Otto, SP, Gerstein, AC, Why have sex? The population genetics of sex and recombination, Biochemical Society Transactions, 34, Pt 4, 519–22, August 2006, 16856849, 10.1042/BST0340519, JOURNAL, Agrawal, AF, Evolution of sex: why do organisms shuffle their genotypes?, Current Biology, 16, 17, R696–704, September 2006, 16950096, 10.1016/j.cub.2006.07.063, 1996CBio....6.1213A, ). An alternative view is that sex is an adaptation for promoting accurate DNA repair in germ-line DNA, and that increased genetic diversity is primarily a byproduct that may be useful in the long run.BOOK, Bernstein, Harris, Bernstein, Carol, Michod, Richard E., 2011, Meiosis as an Evolutionary Adaptation for DNA Repair Chapter 19, DNA Repair, Inna, Kruman, InTech, 10.5772/25117, live, 978-953-307-697-3, BOOK, Hörandl, Elvira, 2013,weblink Meiosis and the Paradox of Sex in Nature, Meiosis, Carol, Bernstein, 978-953-51-1197-9, InTech, 10.5772/56542, live,weblink" title="">weblink 2013-10-29, (See also Evolution of sexual reproduction).Another basic unresolved problem in biology is the biologic basis of aging. At present, there is no consensus view on the underlying cause of aging. Various competing theories are outlined in Ageing Theories.


These are the main branches of biology:WEB,weblink Branches of Biology,, 2013-10-02, live,weblink" title="">weblink 2013-07-27, WEB,weblink Biology on,, 2013-10-02, live,weblink" title="">weblink 2013-10-05, {{efn|For a more detailed list, see Outline of biology.}}
  • Anatomy – the study of organisms structures
    • Comparative anatomy – the study of evolution of species through similarities and differences in their anatomy
    • Histology – the study of tissues, a microscopic branch of anatomy
  • Astrobiology (also known as exobiology, exopaleontology, and bioastronomy) – the study of evolution, distribution, and future of life in the universe
  • Biochemistry – the study of the chemical reactions required for life to exist and function, usually a focus on the cellular level
  • Biological engineering – the attempt to create products inspired by biological systems or to modify and interact with the biological systems
  • Biogeography – the study of the distribution of species spatially and temporally
  • Bioinformatics – the use of information technology for the study, collection, and storage of genomic and other biological data
  • Biolinguistics – the study of the biology and evolution of language
  • Biomechanics – the study of the mechanics of living beings
  • Biomedical research – the study of health and disease
  • Biophysics – the study of biological processes by applying the theories and methods traditionally employed in the physical sciences
  • Biotechnology – the study of the manipulation of living matter, including genetic modification and synthetic biology
    • Synthetic biology – research integrating biology and engineering; construction of biological functions not found in nature
  • Botany – the study of plants
  • Cell biology – the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell
  • Chronobiology – the study of periodic events in living systems
  • Cognitive biology – the study of cognition
  • Conservation biology – the study of the preservation, protection, or restoration of the natural environment, natural ecosystems, vegetation, and wildlife
  • Cryobiology – the study of the effects of lower than normally preferred temperatures on living beings
  • Developmental biology – the study of the processes through which an organism forms, from zygote to full structure
    • Embryology – the study of the development of embryo (from fecundation to birth)
    • Gerontology – study of ageing processes
  • Ecology – the study of the interactions of living organisms with one another and with the non-living elements of their environment
  • Evolutionary biology – the study of the origin and descent of species over time
  • Genetics – the study of genes and heredity
    • Genomics – the study of genomes
    • Epigenetics – the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence
  • Immunology – the study of the immune system
  • Marine biology (or biological oceanography) – the study of ocean ecosystems, plants, animals, and other living beings
  • Microbiology – the study of microscopic organisms (microorganisms) and their interactions with other living things
    • Bacteriology – the study of bacteria
    • Mycology – the study of fungi
    • Parasitology – the study of parasites and parasitism
    • Virology – the study of viruses and some other virus-like agents
  • Molecular biology – the study of biology and biological functions at the molecular level, some cross over with biochemistry
  • Nanobiology – the application of nanotechnology in biological research, and the study of living organisms and parts on the nanoscale level of organization
  • Neuroscience – the study of the nervous system
  • Paleontology – the study of fossils and sometimes geographic evidence of prehistoric life
  • Pathobiology or pathology – the study of diseases, and the causes, processes, nature, and development of disease
  • Pharmacology – the study of the interactions between drugs and organisms
  • Physiology – the study of the functions and mechanisms occurring in living organisms
  • Phytopathology – the study of plant diseases (also called Plant Pathology)
  • Psychobiology – the application of methods traditionally used in biology to study human and non-human animals behaviour
  • Quantum biology – the study of the role of quantum phenomena in biological processes
  • Systems biology – the study complex interactions within biological systems through a holistic approach
  • Structural biology – a branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules
  • Theoretical biology – the branch of biology that employs abstractions and mathematical models to explain biological phenomena
  • Zoology – the study of animals, including classification, physiology, development, evolution and behaviour, including:

See also

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Further reading

  • BOOK, Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P, Molecular Biology of the Cell, 4th, Garland, 2002, 978-0-8153-3218-3, 145080076,
  • BOOK, Begon M, Townsend CR, Harper JL, Ecology: From Individuals to Ecosystems, 4th, Blackwell Publishing Limited, 2005, 978-1-4051-1117-1, 57639896, Ecology: From Individuals to Ecosystems,
  • BOOK, Campbell, Neil, vanc, Neil Campbell (scientist), Biology, 7th, Benjamin-Cummings Publishing Company, 2004, 978-0-8053-7146-8, 71890442,
  • BOOK, Colinvaux, Paul, vanc, Paul Colinvaux, Why Big Fierce Animals are Rare: An Ecologist's Perspective, reissue, Princeton University Press, 1979, 978-0-691-02364-9, 10081738,weblink
  • BOOK, Mayr, Ernst, The Growth of Biological Thought: Diversity, Evolution, and Inheritance,weblink 1982, Harvard University Press, 978-0-674-36446-2,
  • BOOK, Hoagland, Mahlon, vanc, The Way Life Works, reprint, Jones and Bartlett Publishers inc, 2001, 978-0-7637-1688-2, 223090105,
  • BOOK, Janovy, John, On Becoming a Biologist, 2nd, Bison Books, 2004, 978-0-8032-7620-8, 55138571,
  • BOOK, Johnson, George B., Johnson George B., Biology, Visualizing Life, Holt, Rinehart, and Winston, 2005, 978-0-03-016723-2, 36306648,weblink
  • BOOK, Tobin, Allan, Dusheck, Jennie, Asking About Life, 3rd, Wadsworth, Belmont, CA, 2005, 978-0-534-40653-0,

External links

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Journal links
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