HOME

TheInfoList




Biology is the
natural science Natural science is a Branches of science, branch of science concerned with the description, understanding and prediction of Phenomenon, natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer r ...

natural science
that studies
life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

life
and living
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s, including their
physical structure
physical structure
,
chemical processes A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which ...

chemical processes
, molecular interactions, physiological mechanisms,
development Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking#Development, Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material i ...
and
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
.Based on definition from: Despite the complexity of the science, certain unifying concepts consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life,
genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
as the basic unit of
heredity Heredity, also called inheritance or biological inheritance, is the passing on of traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for str ...

heredity
, and
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
as the engine that propels the
creation Creation may refer to: Religion * Creation ''ex nihilo'', the concept that matter was created by God out of nothing * Creation myth A creation myth (or cosmogonic myth) is a symbolic narrative of how the world began and how people first came t ...

creation
and
extinction Extinction is the termination of a kind of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by ...

extinction
of
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
.
Living organisms In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

Living organisms
are open systems that survive by transforming
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
and decreasing their local
entropy Entropy is a scientific concept as well as a measurable physical property that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics ...

entropy
to maintain a stable and vital condition defined as
homeostasis In , homeostasis is the state of steady internal, , and conditions maintained by . This is the condition of optimal functioning for the organism and includes many variables, such as and , being kept within certain pre-set limits (homeostatic r ...
. Sub-disciplines of biology are defined by the research methods employed and the kind of system studied:
theoretical biology Mathematical and theoretical biology or, Biomathematics, is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular bi ...
uses mathematical methods to formulate quantitative models while
experimental biology Experimental biology is the set of approaches in the field of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mol ...
performs empirical experiments to test the validity of proposed theories and understand the mechanisms underlying life and how it appeared and
evolved Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolved
from non-living matter about 4 billion years ago through a gradual increase in the complexity of the system.


Etymology

"Biology" derives from the
Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
words of βίος;
romanized Romanization or romanisation, in linguistics Linguistics is the scientific study of language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign lan ...
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 was the English and French (''biologie''). Historically there was another term for "biology" in English, lifelore; it is rarely used today. The Latin-language form of the term first appeared in 1736 when Swedish scientist
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomi ...

Carl Linnaeus
(Carl von Linné) used ''biologi'' in his ''
Bibliotheca Botanica ''Bibliotheca Botanica'' ("Bibliography of botany", Amsterdam, 1736, Salomen Schouten; 2nd edn., 1751) is a botany Botany, also called , plant biology or phytology, is the science Science (from the Latin word ''scientia'', meaning "kn ...
''. 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
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 Karl Friedrich Burdach (12 June 1776 – 16 July 1847) was a German physiologist. He was born in Leipzig and died in Königsberg. He was the first to use the word "biology" and was a pioneer of neuroanatomy. Life Burdach came from a family o ...

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 Gottfried Reinhold Treviranus (4 February 1776, Bremen – 16 February 1837, Bremen) was a Germany, German physician, naturalist, and proto-evolutionary biologist. His younger brother, Ludolph Christian Treviranus (1779–1864), was also a naturali ...

Gottfried Reinhold Treviranus
, who announced: :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 affected. The science that concerns itself with these objects we will indicate by the name biology iologieor the doctrine of life ebenslehre


History

Although modern biology is a relatively recent development, sciences related to and included within it have been studied since ancient times.
Natural philosophy Natural philosophy or philosophy of nature (from ''philosophia naturalis'') was the study of and the physical that was dominant before the development of . From the ancient world, at least since , to the 19th century, ''natural philosophy' ...
was studied as early as the ancient civilizations of
Mesopotamia Mesopotamia ( grc, Μεσοποταμία ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the ...

Mesopotamia
,
Egypt Egypt ( ar, مِصر, Miṣr), officially the Arab Republic of Egypt, is a spanning the and the of . It is bordered by the to , the () and to , the to the east, to , and to . In the northeast, the , which is the northern arm of the R ...

Egypt
, the Indian subcontinent, and
China China (), officially the People's Republic of China (PRC; ), is a country in . It is the world's , with a of more than 1.4 billion. China spans five geographical and 14 different countries, the in the world after . Covering an area of ap ...

China
. However, the origins of modern biology and its approach to the study of nature are most often traced back to
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of History of Greece, Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, antiquity ( AD 600). This era wa ...
. While the formal study of
medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge), skills (proced ...

medicine
dates back to
Pharaonic Egypt Ancient Egypt was a civilization A civilization (or civilisation) is any complex society that is characterized by urban development, social stratification, a form of government, and symbol A symbol is a mark, sign, or word t ...
, it was
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental quest ...

Aristotle
(384–322 BC) who contributed most extensively to the development of biology. Especially important are his ''
History of Animals ''History of Animals'' ( grc-gre, Τῶν περὶ τὰ ζῷα ἱστοριῶν, ''Ton peri ta zoia historion'', "Inquiries on Animals"; la, Historia Animalium, "History of Animals") is one of the major texts on biology by the ancient Gr ...
'' 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 The lyceum is a category of educational institution An educational institution is a place where people of different ages gain an education, including preschools, childcare, primary-elementary schools, secondary-high schools, and universities. ...

Lyceum
,
Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek native of Eresos Eresos (; el, Ερεσός; grc, Ἔρεσος) and its twin beach village Skala Eresou are located in the southwest part of the Greek island of Le ...

Theophrastus
, wrote a series of books on
botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ...

botany
that survived as the most important contribution of antiquity to the plant sciences, even into the
Middle Ages In the history of Europe The history of Europe concerns itself with the discovery and collection, the study, organization and presentation and the interpretation of past events and affairs of the people of Europe since the beginning of ...
. Scholars of the medieval Islamic world who wrote on biology included
al-Jahiz Abū ʿUthman ʿAmr ibn Baḥr al-Kinānī al-Baṣrī ( ar, أبو عثمان عمرو بن بحر الكناني البصري), commonly known as al-Jāḥiẓ ( ar, links=no, الجاحظ, ''The Bug Eyed'', born 776; died December 868/Januar ...

al-Jahiz
(781–869), Al-Dīnawarī (828–896), who wrote on botany, and
Rhazes Abū Bakr Muḥammad ibn Zakariyyāʾ al-Rāzī ( ar, أبو بكر محمد بن زكرياء الرازي, also known by his Persian name Rāzī and by his Latinization (literature), Latinized name Rhazes), 864 or 865 – 925 or 935  ...
(865–925) who wrote on
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...

anatomy
and
physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
.
Medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge), skills (proced ...

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 Antonie Philips van Leeuwenhoek ( ; ; 24 October 1632 – 26 August 1723) was a Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium ...

Anton van Leeuwenhoek
's dramatic improvement of the
microscope A microscope (from grc, μικρός ''mikrós'' 'small' and ''skopeîn'' 'to look (at); examine, inspect') is a used to examine objects that are too small to be seen by the . is the of investigating small objects and structures using a ...

microscope
. It was then that scholars discovered
spermatozoa A spermatozoon (pronounced , alternate spelling spermatozoön; plural spermatozoa; from grc, σπέρμα ("seed") and grc, ζῷον ("living being")) is a motile Motility is the ability of an organism In biology, an organism (from An ...

spermatozoa
,
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
,
infusoria Infusoria is a collective term for minute aquatic creatures such as ciliates, euglenoids, protozoa, unicellular algae and small invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a '' ...
and the diversity of microscopic life. Investigations by
Jan Swammerdam Jan Swammerdam (February 12, 1637 – February 17, 1680) was a Netherlands, Dutch biologist and microscopist. His work on insects demonstrated that the various phases during the life of an insect—Egg (biology), egg, larva, pupa, and adult—a ...

Jan Swammerdam
led to new interest in
entomology upright=1.2, A Phyllium sp., mimicking a leaf Entomology () is the scientific Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions abo ...
and helped to develop the basic techniques of microscopic
dissection Dissection (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

dissection
and
staining specimen, sandwiched between a glass microscope slide. Staining is a technique used to enhance contrast in samples, generally at the Microscope, microscopic level. Stains and dyes are frequently used in histology (the study of tissue under the ...
. Advances in
microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of micr ...

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 Schleiden is a town in North Rhine-Westphalia, Germany. It lies in the Eifel hills, in the district of Euskirchen (district), Euskirchen, and has 12,998 inhabitants as of 30 June 2017. Schleiden is connected by a tourist railway to Kall, Germany, K ...

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 Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

life
, although they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of
Robert Remak:''For the mathematician, Robert Remak (mathematician)'' Robert Remak (26 July 1815 – 29 August 1865) was a Jewish Jews ( he, יְהוּדִים ISO 259-2 , Israeli pronunciation ) or Jewish people are members of an ethnoreligious group ...

Robert Remak
and
Rudolf Virchow Rudolf Ludwig Carl Virchow (; or ; 13 October 18215 September 1902) was a Germans, German physician, anthropologist, pathologist, prehistorian, biologist, writer, editor, and politician. He is known as "the father of modern pathology" and as th ...

Rudolf Virchow
, however, by the 1860s most biologists accepted all three tenets of what came to be known as
cell theory In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of Cell (biology), cells, that they are the basic structural/organizational unit of all organisms, and that all cells ...
. Meanwhile, taxonomy and classification became the focus of natural historians.
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomi ...

Carl Linnaeus
published a basic
taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
for the natural world in 1735 (variations of which have been in use ever since), and in the 1750s introduced
scientific names In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed ...
for all his species.
Georges-Louis Leclerc, Comte de Buffon Georges-Louis Leclerc, Count, Comte de Buffon (; 7 September 1707 – 16 April 1788) was a French people, French Natural history, naturalist, mathematician, cosmology, cosmologist, and Encyclopédistes, encyclopédiste. His works influenced the ...

Georges-Louis Leclerc, Comte de Buffon
, treated species as artificial categories and living forms as malleable—even suggesting the possibility of
common descent Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chem ...
. Although he was opposed to evolution, Buffon is a key figure in the
history of evolutionary thought Evolutionary thought, the recognition that species change over time and the perceived understanding of how such processes work, has roots in antiquity—in the ideas of the Ancient Greece, ancient Greeks, Ancient Rome, Romans, and Ancient China ...
; his work influenced the evolutionary theories of both
Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fu ...
and
Darwin Darwin most often refers to: * Charles Darwin (1809–1882), English naturalist and writer, best known as the originator of the theory of biological evolution by natural selection * Darwin, Northern Territory, a capital city in Australia * Darwin ( ...

Darwin
. Serious evolutionary thinking originated with the works of
Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fu ...

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. . 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 Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
, combining the biogeographical approach of
HumboldtHumboldt may refer to: People * Alexander von Humboldt, German natural scientist, brother of Wilhelm von Humboldt * Wilhelm von Humboldt, German linguist, philosopher, and diplomat, brother of Alexander von Humboldt Fictional characters * Hum ...

Humboldt
, the uniformitarian geology of
Lyell
Lyell
,
Malthus's
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 Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
; similar reasoning and evidence led
Alfred Russel Wallace Alfred Russel Wallace (8 January 18237 November 1913) was a British natural history, naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution throug ...
to independently reach the same conclusions. Although it was the subject of
controversy Controversy is a state of prolonged public dispute or debate, usually concerning a matter of conflicting opinion An opinion is a judgement Judgement (or US spelling judgment) is also known as ''adjudication'' which means the evaluation of ...
(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 Population genetics is a subfield of that deals with genetic differences within and between s, and is a part of . Studies in this branch of examine such phenomena as , , and . Population genetics was a vital ingredient in the of the . Its pri ...
. In the 1940s and early 1950s, experiments pointed to
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
as the component of
chromosomes A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and D ...
that held the trait-carrying units that had become known as
genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
. A focus on new kinds of model organisms such as
viruses A virus is a wikt:submicroscopic, submicroscopic infectious agent that Viral replication, replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, incl ...
and
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
, along with the discovery of the double-helical structure of DNA in 1953, marked the transition to the era of
molecular genetics Molecular genetics is a sub-field of biology that addresses how differences in the structures or expression of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image ...
. From the 1950s to the present times, biology has been vastly extended in the
molecular A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atom An atom is the smallest unit of ordinary matter In ...
domain. The
genetic code The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or rel ...

genetic code
was cracked by
Har Gobind Khorana Har Gobind Khorana (9 January 1922 – 9 November 2011) was an Indian Americans, Indian American biochemist. While on the faculty of the University of Wisconsin–Madison, he shared the 1968 Nobel Prize for Physiology or Medicine with Marshall ...

Har Gobind Khorana
, Robert W. Holley and Marshall Warren Nirenberg after DNA was understood to contain
codons The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or rel ...
. Finally, the
Human Genome Project The Human Genome Project (''HGP'') was an international scientific research The scientific method is an Empirical evidence, empirical method of acquiring knowledge that has characterized the development of science since at least the 17th cen ...
was launched in 1990 with the goal of mapping the general human
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
. This project was essentially completed in 2003, 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

Cell theory states that the cell is the fundamental unit of
life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

life
, that all living things are composed of one or more cells, and that all cells arise from pre-existing cells through
cell division Cell division is the process by which a parent cell (biology), cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; a vegetative ...

cell division
. In
multicellular organisms Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym for "Out ...
, every cell in the organism's body derives ultimately from a
single cell
single cell
in a fertilized
egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, although some, such as s, do not. eg ...
. The cell is also considered to be the basic unit in many pathological processes. In addition, the phenomenon of
energy flow
energy flow
occurs in cells in processes that are part of the function known as
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
. Finally, cells contain hereditary information (
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
), which is passed from cell to cell during cell division. Research into the origin of life,
abiogenesis In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molec ...
, amounts to an attempt to discover the origin of the first cells.


Evolution

A 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
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s on the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
, both living and extinct, have descended from a common ancestor or an ancestral
gene pool The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species. Description A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can surviv ...
. This universal common ancestor of all organisms is believed to have appeared about
3.5 billion years ago
3.5 billion years ago
. Biologists regard the ubiquity of the
genetic code The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or rel ...

genetic code
as definitive evidence in favor of the theory of universal common descent for all
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...
,
archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

archaea
, and
eukaryote Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

eukaryote
s (see:
origin of life In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molec ...
). The term "evolution" was introduced into the scientific lexicon by
Jean-Baptiste de Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fu ...

Jean-Baptiste de Lamarck
in 1809, and fifty years later
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
posited a scientific model of natural selection as evolution's driving force. (
Alfred Russel Wallace Alfred Russel Wallace (8 January 18237 November 1913) was a British natural history, naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution throug ...
is recognized as the co-discoverer of this concept as he helped research and experiment with the concept of evolution.) 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 Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
or
selective breeding Selective breeding (also called artificial selection) is the process by which humans use animal breeding Animal breeding is a branch of animal science Animal science (also bioscience) is described as "studying the biology Biology i ...
.
Genetic drift Genetic drift (allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical stru ...

Genetic drift
was embraced as an additional mechanism of evolutionary development in the
modern synthesis Modern synthesis or modern evolutionary synthesis refers to several perspectives on evolutionary biology, namely: * Modern synthesis (20th century), the term coined by Julian Huxley in 1942 to denote the synthesis between Mendelian genetics and s ...
of the theory. The evolutionary history of the
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

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 A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree (graph theory), tree showing the evolutionary relationships among va ...

phylogeny
. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of
DNA sequence DNA sequencing is the process of determining the nucleic acid sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic ...

DNA sequence
s, a product of
molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, P ...
(more particularly
genomics Genomics is an interdisciplinary field of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
), and comparisons of
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
s or other records of ancient organisms, a product of
paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (geology), epoch (roughly 11,700 years before present). It includes th ...
. Biologists organize and analyze evolutionary relationships through various methods, including
phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

phylogenetics
,
phenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
, and
cladistics Cladistics (; ) is an approach to biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

cladistics
. (For a summary of major events in the evolution of life as currently understood by biologists, see
evolutionary timeline This timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. In biology, evolution is any change across successive generations in the herit ...
.) 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 light of how they came to be by way of the process of evolution. Consequently, evolution is central to all fields of biology.


Genetics

Gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

Gene
s are the primary units of inheritance in all organisms. A gene is a unit of
heredity Heredity, also called inheritance or biological inheritance, is the passing on of traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for str ...

heredity
and corresponds to a region of
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

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
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s. Cells
transcribe Transcription refers to the process of producing a copy of something piece by small piece, including: Genetics * Transcription (biology) Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into ...
a DNA gene into an
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
version of the gene, and a
ribosome Ribosomes ( ), also called Palade granules, are molecular machine, macromolecular machines, found within all cell (biology), cells, that perform Translation (biology), biological protein synthesis (mRNA translation). Ribosomes link amino acids ...

ribosome
then
translates
translates
the RNA into a sequence of
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
s known as a protein. The
translation code
translation code
from RNA codon to amino acid is the same for most organisms. For example, a sequence of DNA that codes for
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets; it is considered to be the main Anabolism, anabolic hormone of the body. It regulates the metabolism of carbohydrates, fats and p ...

insulin
in humans also codes for insulin when inserted into other organisms, such as plants. DNA is found as linear
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
s in
eukaryote Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

eukaryote
s, and circular chromosomes in
prokaryote A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual conti ...
s. A chromosome is an organized structure consisting of
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
and
histone In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
s. The set of chromosomes in a cell and any other hereditary information found in the
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
,
chloroplasts Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules Adenosine triphosphate, ATP and NADPH while fr ...

chloroplasts
, or other locations is collectively known as a cell's
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
. In eukaryotes, genomic DNA is localized in the
cell nucleus In cell biology, the nucleus (pl. ''nuclei''; from Latin or , meaning ''kernel'' or ''seed'') is a biological membrane#Function, membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotes usually have a single n ...

cell nucleus
, or with small amounts in
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
and
chloroplast A chloroplast is a type of membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structure ...

chloroplast
s. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the
nucleoid The nucleoid (meaning ''nucleus-like'') is an irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material. The chromosome A chromosome is a long DNA molecule with part or all of the genetic mate ...
. The genetic information in a genome is held within genes, and the complete assemblage of this information in an organism is called its
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific ...
.


Homeostasis

Homeostasis is the ability of an open system to regulate its internal environment to maintain stable conditions by means of multiple
dynamic equilibrium In chemistry, and in physics, a dynamic equilibrium exists once a reversible reaction occurs. Substances transition between the reactants and products at equal rates, meaning there is no net change. Reactants and products are formed at such a rate ...

dynamic equilibrium
adjustments that are controlled by interrelated regulation mechanisms. All living
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s, whether
unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Or ...
or
multicellular A multicellular organism is an organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular ...

multicellular
, exhibit homeostasis. 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 Negative feedback (or balancing feedback) occurs when some function Function or functionality may refer to: Computing * Function key A function key is a key on a computer A computer is a machine that can be programmed to carry out se ...
that stabilize conditions by reducing or increasing the activity of an organ or system. One example is the release of
glucagon Glucagon is a peptide hormonePeptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine ...

glucagon
when sugar levels are too low.


Energy

The survival of a living organism depends on the continuous input of
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
. Chemical reactions that are responsible for its structure and function are tuned to extract
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
from substances that act as its food and transform them to help form new cells and sustain them. In this process,
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
s of
chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which ...
s that constitute
food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contains essential nutrients, such as carbohydrates, fats, protein (nutrient), proteins, vi ...

food
play two roles; first, they contain energy that can be transformed and reused in that organism's biological,
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...

chemical reaction
s; 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
autotroph An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bo ...
s. Nearly all such organisms originally draw their energy from the sun. Plants and other
phototroph Terrestrial and aquatic phototrophs: plants grow on a fallen log floating in algae-rich water Phototrophs ('' Gr'': φῶς, φωτός = light, τροϕή = nourishment) are organism In biology, an organism (from Ancient Greek, Greek: ...
s use solar energy via a process known as
photosynthesis Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthesis
to convert raw materials into organic molecules, such as
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
, whose bonds can be broken to release energy. A few
ecosystems An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
, however, depend entirely on energy extracted by
chemotroph Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic molecule, organic (chemoorganotrophs) or inorganic compound, inorganic (chemolithotrophs). The chemotroph design ...
s from
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
,
sulfides Sulfide (British English British English (BrE) is the standard dialect of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, whi ...
, or other non-
luminal
luminal
energy sources. Some of the energy thus captured produces
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...

biomass
and energy that is available for growth and development of other
life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

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
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
and
cellular respiration Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such a ...

cellular respiration
.


Study and research


Structural

Molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, P ...
is the study of biology at the molecular level. 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 physiology, physiological properties of cell (biology), cells, including their internal behavior, interactions with other cells, and with their natural environment, environment. This is done on both the microscope, microscopic and molecule, molecular levels, for unicellular organisms such as
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...
, 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 organ (biology), organs and organ systems. Genetics is the science of genes,
heredity Heredity, also called inheritance or biological inheritance, is the passing on of traits Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for str ...

heredity
, and the variation of
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s. 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
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
s, within which it is represented by a particular DNA sequence, sequence of amino acids in particular
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
s. 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 biological tissue, tissues, organ (anatomy), organs, and
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...

anatomy
. Model organisms for developmental biology include the round worm ''Caenorhabditis elegans,'' the fruit fly ''Drosophila melanogaster,'' the zebrafish ''Danio rerio,'' the mouse ''Mus musculus'', and the weed ''Arabidopsis thaliana''. (A model organism is a
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

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.)


Physiological

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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

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 of the interaction of how, for example, the nervous system, nervous, immune system, immune, endocrine system, endocrine, respiratory system, respiratory, and circulatory system, circulatory systems, function and interact. The study of these systems is shared with such medicine, medically oriented disciplines as neurology and immunology.


Evolutionary

Current research in evolutionary biology, Evolutionary research is concerned with the origin and descent of
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
, and their change over time. It employs scientists from many taxonomically oriented disciplines; for example, those with special training in particular
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s such as mammalogy, ornithology,
botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ...

botany
, or herpetology, but are of use in answering more general questions about evolution. Evolutionary biology is partly based on
paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (geology), epoch (roughly 11,700 years before present). It includes th ...
, which uses the
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
record to answer questions about the mode and tempo of evolution, and partly on the developments in areas such as
population genetics Population genetics is a subfield of that deals with genetic differences within and between s, and is a part of . Studies in this branch of examine such phenomena as , , and . Population genetics was a vital ingredient in the of the . Its pri ...
. In the 1980s, developmental biology re-entered evolutionary biology after its initial exclusion from the
modern synthesis Modern synthesis or modern evolutionary synthesis refers to several perspectives on evolutionary biology, namely: * Modern synthesis (20th century), the term coined by Julian Huxley in 1942 to denote the synthesis between Mendelian genetics and s ...
through the study of evolutionary developmental biology. Phylogenetics, systematics, and alpha taxonomy, taxonomy are related fields often considered part of evolutionary biology.


Systematic

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. However, systematics was an active field of research long before evolutionary thinking was common. Traditionally, living things have been divided into five kingdoms: Monera; Protista; Fungus, Fungi; Plantae; Animalia. 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 Eukaryote, Eukaryota (including protists, fungi, plants, and animals). These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of key biomolecules such as
ribosome Ribosomes ( ), also called Palade granules, are molecular machine, macromolecular machines, found within all cell (biology), cells, that perform Translation (biology), biological protein synthesis (mRNA translation). Ribosomes link amino acids ...

ribosome
s. Further, each kingdom is broken down recursively until each species is separately classified. The order is: Domain (biology), Domain; Kingdom (biology), Kingdom; Phylum; Class (biology), Class; Order (biology), Order; Family (biology), Family; Genus; Species. Outside of these categories, there are obligate intracellular parasites that are "on the edge of life" in terms of metabolism, 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 virus (biology), viruses, viroids, prions, or Satellite (biology), 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. Additionally, the entire term may be italicized or underlined. 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 A virus is a wikt:submicroscopic, submicroscopic infectious agent that Viral replication, replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, incl ...
, 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).
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 o

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.
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. 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. However, the International Botanical Congress of 2011 declined to consider the BioCode proposal. The International Committee on Taxonomy of Viruses, ICVCN remains outside the BioCode, which does not include viral classification.


Kingdoms

File:Guriezo Adino vaca toro terneras.jpg, Animalia – ''Bos primigenius taurus'' File:Zboże.jpg, Plantae – ''Triticum'' File:Morchella esculenta 08.jpg, Fungi – ''Morchella esculenta'' File:Mikrofoto.de-Blepharisma japonicum 15.jpg, Protista/Protozoa – ''Blepharisma japonicum'' File:Fucus serratus2.jpg, Stramenopila/Chromista – ''Fucus serratus'' File:Gemmatimonas aurantiaca.jpg, Bacteria – ''Gemmatimonas aurantiaca'' (-=1 Micrometer) File:Halobacteria.jpg, Archaea – Halobacteria File:Gamma phage.png, Virus – Gamma phage


Ecological and environmental

Ecology is the study of the distribution and abundance of life, living organisms, the interaction between them and their natural environment, environment. 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. 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-operation, co-operative, Competition (biology), competitive, parasite, parasitic, or symbiosis, 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 A virus is a wikt:submicroscopic, submicroscopic infectious agent that Viral replication, replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, incl ...
, 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 canidae, canids), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
of behavior and the understanding of behavior in terms of the theory of
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of peta ...
. In one sense, the first modern ethologist was
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
, whose book, ''The Expression of the Emotions in Man and Animals,'' influenced many ethologists to come. Biogeography studies the spatial distribution of organisms on the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
, focusing on such topics as plate tectonics, climate change (general concept), climate change, Biological dispersal, dispersal and Animal migration, migration, and
cladistics Cladistics (; ) is an approach to biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

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. Some examples are Abiogenesis, Origin of life. While there is very good evidence for the abiotic origin of biological compounds such as amino acids, Nucleotide, nucleotides and Lipid, lipids, it is largely unclear how these molecules came together to form the first Cell (biology), cells. Related is the question of Extraterrestrial life, extra-terrestrial life. If we understand how life originated on earth, we can predict more reliably which conditions are required to generate life on other planets. Aging. At present, there is no consensus view on the underlying cause of aging. Various competing theories are outlined in Ageing#Theories, Ageing Theories. Pattern formation. We have a good understanding of pattern formation in some systems, such as the early insect embryo, but the generation of many patterns in nature cannot be explained easily, e.g. the stripes in Zebra, zebras or many Snake, snakes, such as Coral snake, coral snakes. While we know that the patterns are generated by selective Regulation of gene expression, activation or repression of genes, many of these genes and their regulatory mechanisms remain unknown.


Branches and career options

Biology is an area of science with numerous subdisciplines that are concerned with all aspects of life, in fact all aspects of modern human life. That said, there are countless career options, ranging from basic science to industrial or agricultural applications. These are the main branches of biology: * Aerobiology – the study of organic particles in the air * Anatomy – the study of organisms’ structures ** Comparative anatomy – the study of evolution of species through similarities and differences in their
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...

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 * Bioengineering, 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 ** Computational biology – the development and application of data-analytical and theoretical methods, mathematical modelling and computational simulation techniques to the study of biology * 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, 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 ** Palynology – the study of pollen ** Phycology – the scientific study of algae ** Phytopathology – the study of plant diseases (also called Plant Pathology) ** Plant physiology – concerned with the functioning, or
physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
, of plants ** Astrobotany – the study of plants in space * 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 the embryo (from fecundation to birth) ** Evolutionary developmental biology – the study of the ancestral relationships between developmental processes and how they evolved ** Gerontology – the study of ageing processes ** Teratology – the study of abnormalities of physiological development. * 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 ** Molecular genetics – the study of how differences in the structures or expression of DNA manifest as variations among organisms * 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 ** Parasitology – the study of parasites and parasitism ** Virology – the study of viruses and some other virus-like agents *
Molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, P ...
– the study of biology and biological functions at the molecular level, some cross over with biochemistry * Mycology – the study of fungi * Nanobiology – the application of nanotechnology in biological research, and the study of living organisms and parts on the Nanoscopic scale, nanoscale level of organization * Neuroscience – the study of the nervous system * Paleontology – the study of fossils and sometimes geographic evidence of prehistoric life * Pathology, 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 * Phycology – the study of seaweeds and other algae * Physiology – the study of the functions and mechanisms occurring in living organisms * 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 mechanics, quantum phenomena in biological processes * Sociobiology – the study of social behavior in terms of evolution * Systems biology – the study of complex interactions within biological systems through a holistic approach * Structural biology – a branch of
molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, P ...
, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules * Mathematical and theoretical biology, 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: ** Carcinology – the study of crustaceans ** Ethology – the study of animal behaviour ** Entomology – the study of insects and other arthropods ** Herpetology – the study of reptiles and amphibians ** Ichthyology – the study of fish ** Malacology – the study of molluscs ** Mammalogy – the study of mammals ** Ornithology – the study of birds


See also

* Biology in fiction * Glossary of biology * List of biological websites * List of biologists * List of biology journals * List of biology topics * List of life sciences * List of omics topics in biology * National Association of Biology Teachers * Outline of biology * Periodic table of life sciences in Tinbergen's four questions * Reproduction * Science tourism * :Biology terminology, Terminology of biology


Notes


References


Further reading

* * * * * * * * *


External links

*
OSU's Phylocode

Biology Online – Wiki Dictionary

MIT video lecture series on biology


A multi-authored, distributed Internet project containing information about phylogeny and biodiversity. Journal links
PLos Biology
A peer-reviewed, open-access journal published by the Public Library of Science
''Current Biology''
General journal publishing original research from all areas of biology
''Biology Letters''
A Impact factor, high-impact Royal Society journal publishing peer-reviewed Biology papers of general interest
''Science''
Internationally renowned American Association for the Advancement of Science, AAAS science journal – see sections of the life sciences
''International Journal of Biological Sciences''
A biological journal publishing significant peer-reviewed scientific papers

An interdisciplinarity, interdisciplinary scholarly method, scholarly journal publishing essays of broad relevance {{Good article Biology, Biology terminology,