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If it’s alive, biology will define it, study it, observe all its functions, follow its vital processes, and interact with it, all in order to understand the life that animates it. In one of biology's best-known examples of such studious investigation, Charles Darwin came up with his scientific theory of evolution by natural selection after systematically observing a variety of plants and animals; his work acted as the foundation upon which modern evolutionary theory is built. But biology’s principles also operate within a plethora of other related fields, including biochemistry, biomedicine, biophysics, and microbiology.
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Chordate, any member of the phylum Chordata, which includes the vertebrates (subphylum Vertebrata), the most highly evolved animals, as well as two other subphyla—the tunicates (subphylum Tunicata) and cephalochordates (subphylum Cephalochordata). Some classifications also include the phylum...
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Molecular biology
Molecular biology, field of science concerned with studying the chemical structures and processes of biological phenomena that involve the basic units of life, molecules. The field of molecular biology is focused especially on nucleic acids (e.g., DNA and RNA) and proteins—macromolecules that are...
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X-ray protein crystallography in molecular biology
Zoology, branch of biology that studies the members of the animal kingdom and animal life in general. It includes both the inquiry into individual animals and their constituent parts, even to the molecular level, and the inquiry into animal populations, entire faunas, and the relationships of...
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Blue wildebeests (Connochaetes taurinus) drinking at the water's edge, Masai Mara, Kenya.
Animal social behaviour
Animal social behaviour, the suite of interactions that occur between two or more individual animals, usually of the same species, when they form simple aggregations, cooperate in sexual or parental behaviour, engage in disputes over territory and access to mates, or simply communicate across...
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Serengeti National Park, Tanzania: herd of gnu (wildebeests)
Animal, (kingdom Animalia), any of a group of multicellular eukaryotic organisms (i.e., as distinct from bacteria, their deoxyribonucleic acid, or DNA, is contained in a membrane-bound nucleus). They are thought to have evolved independently from the unicellular eukaryotes. Animals differ from...
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Fallow deer (Dama dama)
Biological development
Biological development, the progressive changes in size, shape, and function during the life of an organism by which its genetic potentials (genotype) are translated into functioning mature systems (phenotype). Most modern philosophical outlooks would consider that development of some kind or other...
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Taxonomy, in a broad sense the science of classification, but more strictly the classification of living and extinct organisms—i.e., biological classification. The term is derived from the Greek taxis (“arrangement”) and nomos (“law”). Taxonomy is, therefore, the methodology and principles of...
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animal taxonomy
Life, living matter and, as such, matter that shows certain attributes that include responsiveness, growth, metabolism, energy transformation, and reproduction. Although a noun, as with other defined entities, the word life might be better cast as a verb to reflect its essential status as a...
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African elephants (Loxodonta africana) in Botswana.
Marine biology
Marine biology, the science that deals with animals and plants that live in the sea. It also deals with air-borne and terrestrial organisms that depend directly upon bodies of salt water for food and other necessities of life. In the broadest sense it attempts to describe all vital phenomena ...
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Microbiology, study of microorganisms, or microbes, a diverse group of generally minute, simple life-forms that include bacteria, archaea, algae, fungi, protozoa, and viruses. The field is concerned with the structure, function, and classification of such organisms and with ways of both exploiting...
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Streptococcus pyogenes
Genetics, study of heredity in general and of genes in particular. Genetics forms one of the central pillars of biology and overlaps with many other areas, such as agriculture, medicine, and biotechnology. Since the dawn of civilization, humankind has recognized the influence of heredity and...
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Biology Subcategories

Joshua Lederberg, 1958. Archaea & Bacteria
Even if you can't see them, that doesn't mean they're not there! Prokaryotes are one good example of why you can't always trust the naked eye to show you everything that's going on around you. Prokaryotes are single-celled organisms that lack a distinct nucleus and other organelles due to the absence of internal membranes. As microorganisms, they can't be seen without the use of a microscope. Prokaryotic organisms fall into one of two groups: bacteria and archaea. Bacteria, which make up the more prominent group of prokaryotes, live in staggering numbers in almost every environment on Earth, from deep-sea vents to the digestive tracts of humans. Despite their bad reputation—some bacteria can cause diseases in humans, animals, or plants—most bacteria are harmless, and they function as beneficial ecological agents. Archaea, which constitute the lesser-known group of prokaryotes, were originally discovered in extreme environments such as hydrothermal vents and terrestrial hot springs, but they have since been found in a diverse range of environments. Archaea, too, fulfill important ecological roles in cold and temperate ecosystems. Without archaea and bacteria, our lives would be much more difficult: soil would not be fertile, and our ability to prepare certain foods, chemicals, and antibiotics would be hindered, among other difficulties.
Andreas Vesalius, woodcut probably by Vesalius from his De humani corporis fabrica libri septem (1543), published in Basel, Switz. Biologists
Blue wildebeests (Connochaetes taurinus) drinking at the water's edge, Masai Mara, Kenya. Branches of Biology
This general category includes a selection of more specific topics.
immune stimulation by activated helper T cells Cells, Organs & Tissues
Even if you feel you have nothing in common with a or a stinkbug or a ficus, you're guaranteed to share one crucial aspect of life with these beings: you are all made up of cells, the fundamental molecules of life, of which all living things are composed. As an individual unit, the cell is capable of metabolizing its own nutrients, synthesizing many types of molecules, providing its own energy, and replicating itself. In a multicellular organism, however, cells become specialized to perform different functions, with each cell remaining in constant communication with its neighbors. Cooperative assemblies of similar cells form tissues, and a cooperation between tissues in turn forms organs, which carry out the functions necessary to sustain the life of an organism.
Hereditary information is contained in genes, which are carried on chromosomes. Evolution, Heredity & Genetics
Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms. The study of human heredity occupies a central position in genetics.
Following retrovirus infection, reverse transcriptase converts viral RNA into proviral DNA, which is then incorporated into the DNA of the host cell in the nucleus. Fungi, Protists & Viruses
The major groups of microorganisms—namely bacteria, archaea, fungi (yeasts and molds), algae, protozoa, and viruses—are summarized below. Links to the more detailed articles on each of the major groups are provided.
Sigmund Freud Life Cycle, Processes & Properties
Life cycle, in biology, the series of changes that the members of a species undergo as they pass from the beginning of a given developmental stage to the inception of that same developmental stage in a subsequent generation.

Biology Encyclopedia Articles

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