As recently as 1984, carbon was thought to exist in only two solid forms. There was graphite, in which the carbon atoms arranged themselves as layered sheets of hexagonally bonded atoms, and there was diamond, in which the carbon atoms formed octahedral structures in which each carbon atom had four nearest neighbors. When compressed to 70% of its initial volume, the buckminsterfullerene is expecte…
Bees belong to the insect order Hymenoptera, which includes wasps and ants. Its name is derived from Greek, meaning "winged membrane," and it is the third largest group of insects with more than a hundred thousand species in the order. Ants and bees play vital roles in agriculture, ants being useful in aerating soil and bees in pollinating plants. Wasps play an important part as pred…
Buckthorns are various species of shrubs and small trees in the family Rhamnaceae, a mostly tropical and subtropical family of about 600 species. Most of the buckthorns are in the genus Rhamnus. Buckthorns have a few economic applications, although none of these are very important. A dye known as sap green is made from the fruits of the European buckthorn (Rhamnus cathartica). Another pigment know…
Beet belongs to the genus Beta in the goosefoot family, Chenopodiaceae. There are several varieties of beet and all are used as food for either animals or humans. Most species of beet are biennial and are harvested after the first growing season when the roots are most nutritious. The wild beet, Beta maritima, is thought to be the species from which cultivated beets (Beta vulgaris), originate. Wil…
Buckwheat, Fagopyrum esculentum, is not really a wheat at all—it belongs to the family Polygonaceae, and hence is a dicotyledonous plant, not a monocotyledonous species. However, the starchy seeds of buckwheat are utilized in much the same way as the cereal grains of cultivated grasses, such as wheat (Triticum aestivum). The seeds of buckwheat can be used directly as poultry or animal feed.…
Bud is a term used to refer to three different types of undeveloped forms described in this article. …
Beetles make up the large, extremely diverse order Coleoptera of the class Insecta, and comprise the largest single group of animals on Earth. There are at least 250,000 species of beetles, compared to the 5,000 known species of mammals. The weevil family of beetles alone contains about 50,000 species, and is the largest family in the animal kingdom. Thus, the order Coleoptera, representing about …
In chemistry, a buffer is a system, usually an aqueous (water) solution, that resists having its pH changed when an acid or a base is added to it. Normally, the addition of acid to a solution will lower its pH and the addition of a base will raise its pH. If the solution is a buffer, however, its pH will be changed to a much lesser extent than would be expected from the amounts of acid or base tha…
Begonias (genus Begonia) are attractive perennial herbs with soft, succulent stems, and white, pink, red, orange, or yellow flowers. Begonias are members of the begonia family, Begoniaceae, order Violales, subclass Dilleniidae, class Magnoliopsida (dicotyledons), division Magnoliophyta (flowering plants). The begonia family consists of five genera and 920 true species, the majority of which belong…
Behavior is the way that living things respond to their environment. A behavior consists of a response to a stimulus or factor in an individual's internal or external environment. Stimuli include chemicals, heat, light, pressure, and gravity. All living things exhibit behavior. When dust irritates our throats, for example, we respond with coughing behavior. Plants respond with growth behavi…
The bennettites are an extinct group of gym nosperms—seed-bearing plants whose seeds are exposed to the air, not enclosed in the ovary of a flower. Botanists hypothesize that bennettites are related to the cycads, an extant group of gymnosperms, and paleobotanists believe the bennettites originated from the seed ferns (Pteridospermales) about 220 million years ago during the Triassic period…
Architects design buildings, but architecture is more than just building design and more than just art on a massive scale. Architecture is about light and space. It is about stimulating emotions in the people who see and inhabit the structure. Architecture creates an environment, whether it is the uplifted spirituality of the Chartres Cathedral, the drama and anticipation of the Schauspielhaus aud…
Bulbuls are about 120 species of medium-sized, perching birds, distributed among 15 genera, and making up the family Pyncnontidae. The most diverse genus is Pycnonotus, with about 50 species. Bulbuls are mostly tropical and subtropical birds, occurring in Africa, Asia, and Southeast Asia. Some relatively northern species are migratory, but most species of bulbuls are local birds. Bulbuls have rath…
Named after the German chemist Robert Wilhelm Bunsen, who contributed to its development, the Bunsen burner was already known to Michael Faraday, who may have created the first design. The idea behind the Bunsen burner is to reduce the considerable loss in heat energy typical in ordinary gas burners. This reduction of energy waste is accomplished by using a mixture of gas and air, the optimal prop…
Benzene is a clear, colorless, highly flammable liquid with a pronounced characteristic odor. It has a freezing point of 41.9°F (5.5°C), a boiling point of 176.2°F (80.1°C), and a density of 0.8787 g/mL. It is only slightly soluble in water (0.18 g/100 mL at 77°F [25°C]), but is completely miscible with alcohol, chloroform, ether, carbon disulfide, carbon …
A buret (also spelled burette) is a long glass tube open at both ends, that is used to measure out precise volumes of liquids or gases. Most burets are about 0.04 in (1 mm) in diameter and 30 in (75 cm) long. The bottom of a buret is tapered so that its diameter is only about 0.1 mm in diameter. Burets are most commonly designed to hold volumes of 1 ml or less. Fluid is dispensed form a buret thro…
In its pure form, benzoic acid exists as white needles or scales with a strong characteristic odor. It melts at 252.3°F (122.4°C), although it may also sublime at temperatures around 212°F (100°C). It dissolves only sparingly in cold water [0.4 g/100 g at 77°F (25°C)], but more completely in hot water [6.8 g/100 g at 203°F (95°C)]. Benzoic ac…
A burn is damage to the skin. Depending on the type of and severity of the burn, skin may be only superficially damaged, or damage may extend deep within the layers of the skin. Burns can be caused by extreme heat, extreme cold, chemicals, electricity, or radiant energy (i.e., ultraviolet rays from the sun or an artificial source, and x rays). The degree of damage of a burn can be classified in tw…
Bustards are 22 species of tall birds that make up the family Otidae. Bustards occur in relatively open habitats in Africa, central and southern Europe and Asia, Southeast Asia, and Australia. Most species, however, are African. Bustards are large birds, with species ranging in body length from 14.5-52 in (37-132 cm), and in weight from 1-48 lbs (0.6-22 kg). Bustards have a stocky body, a long nec…
Bernoulli's principle states that flowing fluids like air and water press less than still fluids and that pressure decreases quadratically with speed; i.e., with speed squared. …
Buttercups and crowfoots are about 275 species of plants in the genus Ranunculus, family Ranunculaceae. Buttercups mostly occur in cool and temperate regions of both hemispheres of the world, including mountains in tropical latitudes. Buttercups are annual or perennial, and they are herbaceous plants, dying back to the ground surface before the winter. The leaves of terrestrial species are simple …
Beta-blockers are medications used primarily for treating high blood pressure. The usefulness of these medications rests on their ability to block the effects of a nervous system transmitter chemical known as norepinephrine and the related "fight-or-flight" hormone epinephrine. Beta-blockers are also used to treat heart-related chest pain (angina pectoris, or simply angina), abnormal…
Butterflies are insects in the order Lepidoptera, which also includes the moths. Butterflies at rest fold their wings vertically over their head, whereas moths hold their wings horizontally. Most butterflies are active during daylight, while moths are mostly nocturnal. Butterflies undergo complete metamorphosis, that is, their egg hatches to a larva (or caterpillar), which pupates in a chrysalis, …
Butterfly fish (family Chaetodontidae) are some of the most colorful and varied fish of the oceans, the majority of which live on or close to coral reefs. Most species measure from 5-9.5 in (13-24 cm) in length and have deep, flattened bodies that are frequently adorned by extended fins. In some species these may form a large arc over the body. In addition to refinements in the body shape, the col…
The big bang theory is the conceptual and mathematical model that scientists use to describe the origin of the Universe. It states that the Universe began as a tiny, violent explosion about 15 billion years ago. That event produced all of the matter and energy in the universe, including its hydrogen and helium. Some of these light atoms were forged in the cores of stars, over billions of years, in…
bonds to other atoms via an end carbon atom, while the sec-butyl group bonds via an "inner" carbon atom. The boiling points of the butyl alcohols decrease regularly in moving down the above list, from 244°F (118°C) for n-butyl alcohol to 226°F (108°C) for isobutyl alcohol to 212°F (100°C) for sec-butyl alcohol to 180°F (82°C) fo…
Butylated hydroxyanisole is a food additive much more widely known by its abbreviation, BHA. BHA is an aromatic organic compound with the chemical names of 2- and 3-tert-butyl-4-methoxyphenol. It can exist in either of the two isomeric forms or as a mixture of the two isomers. In its pure form, BHA is a waxy white or pale yellow solid with a melting point of 118.4–131°F (48–55…
Butylated hydroxytoluene (BHT) is a derivative of cresol, an aromatic organic compound in which two additional hydrogen atoms in the benzene ring are replaced by tertiary butyl groups. Its technical name is 2,6-di-tert-butyl-p-cresol. In its pure form BHT is a white crystalline solid with a melting point of 158°F (70°C) and a boiling point of 509°F (265°C). It is normal…
The true buzzards are diurnal birds of prey in the genus Buteo, sub-family Buteonidae, family Accipitridae. In North America, buzzards are also commonly known as hawks, although other genera in the family Accipitridae are also given this common name, for example, the Accipiter hawks. There are 25 species of buzzards. Buzzards are in the order Falconiformes, which also includes other types of hawks…
Binary stars, often called double stars, refer to pairs of stars sufficiently close to each other in space to be gravitationally bound together. Following the laws of gravitation, each of the components revolves around the common center of mass of the system. At least 50% of stars are found to exist as binary systems, according to conservative statistics. There seems to be no obvious preference fo…
The cactus family or Cactaceae is made up of about 2,000 species of perennial plants with succulent stems, most of which are well-armed with sharp spines. The natural distribution of most cacti is American, ranging from southern British Columbia and southern Ontario in Canada, through much of the United States, to the tip of southern South America. One genus, Rhipsalis, occurs in Africa, Madagasca…
In 1823, a new optical instrument began to appear in French opera houses that allowed patrons in the distant (and less expensive) seats to view the opera as if they were in the front row. Called opera glasses, the device combined telescope lenses with stereoscopic prisms to provide a magnified, three-dimensional view. After many years (but relatively few modifications), opera glasses have evolved …
CAD/CAM is an acronym for computer-aided design and computer-aided manufacturing. The use of A CAD system used for Boeing airplanes. © Ed Kashi/Phototake NYC. Reproduced by permission. computers in design and manufacturing applications makes it possible to remove much of the tedium and manual labor involved. For example, the many design specifications, blueprints, material lists, an…
The question of expanding an equation with two unknown variables called a binomial was posed early in the history of mathematics. One solution, known as Pascal's triangle, was determined in China as early as the thirteenth century by the mathematician Yang Hui. His solution was independently discovered in Europe 300 years later by Blaise Pascal whose name has been permanently associated wit…
North America's streams, rivers, and lakes are home to more than 1,200 different species of caddisflies, which are aquatic insects in the order Trichoptera. Adaptations to different water conditions and food types allow this group of insects to populate a variety of habitats in America's waters. Caddisflies are best known and most easily identified in their larval stages. Most caddis…
Bioaccumulation is the gradual build up over time of a chemical in a living organism. This occurs either because the chemical is taken up faster than it can be used, or because the chemical cannot be broken down for use by the organism (that is, the chemical cannot be metabolized). Bioaccumulation need not be a concern if the accumulated compound is not harmful. Compounds that are harmful to healt…
Caecilians are long, worm-like legless amphibians in the order Gymnophiona (sometimes known as Apoda, meaning without legs). There are 163 species of caecilians, in 35 genera. Little is known about these animals, and few species have common names. Most of the caecilians are tropical or sub-tropical, and occur in Central and South America, Africa, and south and southeast Asia. Caecilians grow up to…
A bioassay is the use of a living organism to test for the presence of a compound or to determine the amount of the compound that is present in a sample. The organism used is sensitive to the compound for which the test is conducted. Thus, the effect observed is typically the death or deteriorated health of the test organism. Depending on the test organism, soil, air, or liquid samples can be assa…
Oxygen is the molecule used by animals as a final electron acceptor for metabolism. Two electrons (one at a time) from metabolic products can chemically bind each oxygen molecule. While numerous molecules combine with oxygen in the human body, one of the major chemical reactions involving oxygen is the synthesis of the high-energy phosphate bonds in ATP. ATP is the cell's currency for gener…
The term authoritarianism can be applied to a great variety of contexts. It can refer to authoritarian behavior, leadership styles, or personality types in families, industrial enterprises, bureaucracies, and other forms of organizations. Here, it refers to political regimes that fall under this broad label. The major characteristics of authoritarian regimes include a limited political pluralism w…
Grand claims have been made about the superiority and inevitability of liberal democracy. Do they hold true for East Asian countries? According to typologies in political science, most East Asian countries are considered authoritarian. Japan, Philippines, Taiwan, Thailand, and South Korea are considered democracies; Indonesia is considered ambiguous while all other East Asian governments (Brunei, …
Biochemistry is the study of the molecular basis of life. The study of biochemistry includes the knowledge of the structure and function of molecules found in the biological world and an understanding of the precise biochemical pathways by which organic molecules are either put together or broken down. Biochemistry seeks to describe the structure, organization, and functions of living matter in mo…
Traditional interpretations of authoritarianism in Latin America root this phenomenon in the style of Iberian colonization in the region. The Hispanic world, this argument alleges, was naturally more authoritarian than Anglo-Saxon cultures. Furthermore, the cultures they encountered in the New World (particularly the Aztec and Inca Empires) were themselves very hierarchical, which further facilita…
The term biodegradable is used to describe materials that decompose through the actions of bacteria, fungi, and other living organisms. Temperature and sunlight may also play roles in the decomposition of biodegradable plastics and other substances. If such materials are not biodegradable, they remain in the environment for a long time, and, if these same substances are toxic, they may pollute the…
Caffeine is an alkaloid found in coffee, tea, chocolate, and other natural foods. It is also a component of cola soft drinks. Caffeine has been a part of the human diet for many centuries and is one of the most widely used central nervous system stimulants worldwide. In recent years, research has raised questions about possible deleterious health effects of caffeine, but no definitive conclusions …
The conceptual history of authority reveals it to be an essentially contested concept because of the many debates about its sources, purposes, and limits, as well as its proximity to the concept of power. Since Plato's critique of Athenian democracy, physical force and rhetorical persuasion have been viewed as types of power but not authority. Hannah Arendt observes that "[i]f author…
Growing scholarly interest in the relationship between truth and fiction, along with popular interest in personal life-narratives and the "culture of confession," have brought new prominence to the genre of autobiography. Indeed, according to Leigh Gilmore, the number of English-language autobiographies and memoirs roughly tripled from the 1940s to the 1990s (p. 1, n. 1), and scholar…
Autonomy was first used by the ancient Greeks to describe city-states that had the power to legislate their own laws and direct the course of their own affairs. The etymology (auto [self] nomos [law]) suggests self-governance or the imposition of law on oneself. The original implication of autonomy was pejorative when applied to the individual. When, for example, in Sophocles' tragedy, the …
A caisson is a hollow structure made of concrete, steel, or other materials that can be sunk into the earth. It used as the substructure for a bridge, a building, or other large structures. Caissons come in many sizes and shapes depending on their future use. The one shared feature is that their bottom edges are sharp so they easily can be sunk into the ground. These sharp edges are known as the c…
Beginning in the nineteenth century, the term avant-garde has been applied to a wide range of social activities, from military to political to artistic. Since the early twentieth century, however, it has most commonly been used to designate those artists who, in making works of art, knowingly transgress aesthetic and social norms, seeking thus to scandalize, to disrupt established canons of taste,…
Calcium is a chemical element, a member of the alkaline-earth metals group, represented by the atomic symbol Ca and the atomic number 20. It has an atomic weight of 40.08. In its pure form, calcium is a silvery-white metal, although it is never found in this free state naturally. It is, however, one of the most abundant substances on Earth, comprising approximately 3.64% of the earth's crus…
Gustave Courbet (1819–1877) was the first artist to assume the mantle of the avant-garde, savoring its military associations from within his outpost in the Pavillon du Réalisme he had constructed to exhibit his paintings that had been rejected by the official salon of the 1855 World's Fair. While the largest of these works—Studio of the Painter: A Real Allegory (1855)…
Biodiversity is the total richness of biological variation. The scope of biodiversity is usually considered to range from the genetic variation of individual organisms within and among populations of a species, to different species occurring together in ecological communities. Some definitions of biodiversity also include the spatial patterns and temporal dynamics of populations and communities on…
Calcium carbonate has two major crystalline formstwo different geometric arrangements of the calcium ions and carbonate ions that make up the compound. These two forms are called aragonite and calcite. All calcium carbonate minerals are conglomerations of various-sized crystals of these two forms, packed together in different ways and containing various impurities. The large, transparent crystals …
As a region in mythical geography, Aztlán (the land of the [white] herons) has a long history. According to the Náhuatl myth, the Aztecs (whose name is derived from Aztlán) were the last remaining tribe of seven, and they were advised by their god Huitzilopochtli to leave Aztlán in search of the promised land, which they would know by an eagle sitting on a cactus, devouring a s…
Calcium oxide (CaO), more commonly known as lime or quick lime, has been studied by scholars as far back as the pre-Christian era. In his book Historia Naturalis, for example, Pliny the Elder discussed the preparation, properties, and uses of lime. Probably the first scientific paper on the substance was Dr. Joseph Black's "Experiments Upon Magnesia, Alba, Quick-lime, and Some Other …
Barbarism and civilization are salt and pepper concepts that are inextricably interlinked. In the Western world, "barbarism" is derived from the classical Greek word barbaros (barbarian) that referred originally to foreigners who did not speak Greek. In the modern world, barbarism carries a negative connotation of unrefined and savage. "Civilization" is derived from the…
Bioenergy is energy derived using organic material, especially plant matter, as fuel. The material burned or processed to produce bioenergy (the "feedstock") is called biomass. Biomass has been an energy source for as long as humans have used wood fires to warm themselves and cook food. Wood is still the most commonly used biomass fuel. In some developing countries, crop and logging …
Calcium propionate is used as a food preservative in breads and other baked goods because of its ability to inhibit the growth of molds and other microorganisms. It is not toxic to these organisms, but does prevent them from reproducing and posing a health risk to humans. Propionic acid occurs naturally in some foods and acts as a preservative in those foods. Some types of cheese, for example, con…
Beauty is a vital and central element of human experience. It is associated with pleasure, which influences personal choices and cultural developments. Poets praise it, artists strive to capture it in their works, moralists warn against its deceiving influence, scientists seek to uncover its secrets, and philosophers reflect on its illusive nature. Expressions of the vitality of beauty in its role…
Among the many other uses of calcium sulfate are as a pigment in white paints, as a soil conditioner, in Portland cement, as a sizer, filler, and coating agent in papers, in the manufacture of sulfuric acid and sulfur, in the metallurgy of zinc ores, and as a drying agent in many laboratory and commercial processes. …
Behaviorism is a theoretical approach in psychology that emphasizes the study of behavior—that is, the outwardly observable reactions to a stimulus of an organism, whether animal or human—rather than the content of the mind or the physiological correlates of behavior. Largely centered in the United States, behaviorism had an early stage (1910–1930) that was dominated by the wo…
A bilingual individual, generally, is someone who speaks two languages. An ideal or balanced bilingual speaks each language as proficiently as an educated native speaker. This is often referred to as an ideal type since few people are regarded as being able to reach this standard. Otherwise, a bilingual may be anywhere on a continuum of skills. Literacy abilities may be an additional dimension to …
Bioethics as a field is relatively new, emerging only in the late 1960s, though many of the questions it addresses are as old as medicine itself. When Hippocrates wrote his now famous dictum Primum non nocere (First, do no harm), he was grappling with one of the core issues still facing human medicine, namely, the role and duty of the physician. With the advent of late-twentieth-century science, a…
Biofeedback is a means by which a person can mentally influence a natural physiologic process that may or may not be consciously regulated under normal conditions. This could include lowering blood pressure, regulating the heart rate, or influencing the skin temperature. Deliberate control of bodily functions is not a new accomplishment. Many historical accounts exist of Indian yogis who controlle…
One of the oldest genres of literature, biography is a written account of a person's life. It is also known as "life writing," a broader term that encompasses autobiography and other narrative forms such as letters, memoirs, journals, and diaries. The term biography derives from the Greek bios (life) and graphein (to write). Latin and Greek terms for biography were used in ant…
A biofilm is a population of bacteria, algae, yeast, or fungi that is growing attached to a surface. The surface can be living or nonliving. Examples of living surfaces where biofilms may grow include the teeth, gums, and the cells that line the intestinal and vaginal tracts. Examples of nonliving surfaces include rocks in watercourses, and implanted medical devices such as catheters. Rudimentary …
Biology comes from the Greek word for life, bis, and the Greek word for thought or reasoning, logos. It denotes the science that studies life, the properties and processes that sustain life, the evolutionary history of life, and particular living organisms. It is a science of enormous diversity, breadth, and heterogeneity unified only by the conceptual framework provided by the theory of evolution…
Bioinformatics, or computational biology, refers to the development of new database methods to store genomic information, computational software programs, and methods to extract, process, and evaluate this information, and the refinement of existing techniques to acquire the genomic data. Finding genes and determining their function, predicting the structure of proteins and RNA sequences from the …
In writing The Black Atlantic: Modernity and Double Consciousness (1993), Paul Gilroy sought to devise a theoretical approach to understanding race that encompassed three crucial elements. First, the idea of race as fluid and ever-changing, rather than static; second, the idea of race as a transnational and intercultural, rather than strictly national, phenomenon; third, the focus on analyzing res…
In biology, the term species refers to all organisms of the same kind that are potentially capable, under natural conditions, of breeding and producing fertile offspring. The members of a species living in a given area at the same time constitute a population. All the populations living and interacting within a particular geographic area make up a biological (or biotic) community. The living organ…
Black consciousness is the name of a black nationalist political movement originating in South Africa during the 1960s and 1970s. It proclaimed the necessity of black South Africans to rely on themselves for liberation and to claim South Africa as an African nation. Black consciousness drew on a tradition of black nationalist thought in South Africa associated with Africanist political movements a…
What is "the body"? If the question seems ridiculous to you, you are undoubtedly not alone. At any given time, in any given culture, most people have an intuitive, if not always easy to articulate, notion of what the body is, and probably regard that notion as shared by all human beings. The fact is, however, that human cultures have not only done an amazing variety of things to huma…
The calculator is a computing machine. Its purpose is to do mathematics; basic calculators do the basic mathematical functions (addition, subtraction, division, and multiplication) while the more advanced ones, which are relatively new in the history of computing machines, do advanced calculations such as solving polynomials. The odometer, or mileage counter, in your car is a counting machine as i…
At first glance the concept of borders, borderlands, or frontiers would seem to be straightforward. A border or boundary is a line on a map delineating a territorial boundary or the limit of a political jurisdiction. Borders are primarily, but far from exclusively, seen as properties of and under the control of states. Nevertheless, this has generally not always been the case. Even in the contempo…
Buddhism has been known in the West since at least the time of Alexander the Great and possibly influenced some forms of Greek philosophy, the Gnostics, and early Christians. In modern times, as a result initially of immigration of Asians to Western countries in the nineteenth and twentieth centuries and increasingly because of interest among Westerners themselves, Buddhism can no longer be regard…
The idea of bureaucracy formally begins with Max Weber (1864–1920); indeed, the idea of bureaucracy ends with Weber as well. Prior to Weber's explication of the "ideal type" of rational, efficient organization of public or private business as a bureaucracy, the idea was simply a commonsense, practical method for the organization of economic or government action. While t…
Literally translated as "way of the warrior," Bushido evolved into a clearly defined ethical system of the bushi, or warrior class of Japan, during the seventeenth and eighteenth centuries; the term first appeared in the Kōyō gunkan in about 1625. In his 1899 Bushido: The Soul of Japan, Nitobe Inazō, the first to articulate the concept in English, enumerated seven e…
Biological rhythms are often referred to as biological clocks, since they operate on time schedules on a daily, monthly, seasonal, or annual basis. Some biological rhythms even occur on the basis of fractions of seconds. These internal clocks operate independent of the environment, but they are controlled by environmental conditions in changing situations. During times of change, such as seasonal …
Words containing the roots calcul- and comput- have existed since antiquity. The study of concepts used to indicate actions, professions, and (mental and material) artifacts suggests that calculation and computation have not been, as canonically assumed, an exclusive concern of modern times. The mere existence of both word clusters throughout the decades (and centuries) prior to World War II also …
A calendar is a system of reckoning and ordering time beyond the period of a day in a repetitive, usually annual, cycle. A calendar's primary function is regulating and organizing human activities; the word derives from the Latin calendarium or calendra, "account book," and kalendae or "calends," the new moon and first day of the Roman month, when Romans paid the…
Calculus is the branch of mathematics that deals with rates of change and motion. It grew out of a desire to understand various physical phenomena, such as the orbits of planets, and the effects of gravity. The immediate success of calculus in formulating physical laws and predicting their consequences led to development of a new division in mathematics called analysis, of which calculus remains a…
The possibility of cannibalism has been an object of thought and imagination in virtually every society. The idea of consuming human body substance as food or for symbolic purposes invokes emotionally charged cultural and psychological concerns with boundaries between self and other, persons and nonpersons, the meanings of food and ingestion, and the limits of a moral community. Many societies, bo…
Biological warfare is the use of living organisms (e.g., bacteria, virus) or biochemical agents (e.g., chemical neurotoxins) as strategic military weapons to cause harm in humans, animals, or plants. In contrast to bioterrorism, biological warfare is considered the governmentsanctioned use of biological weapons to attack a clearly defined military force or civilian population. These agents can be …
Capitalism has been the dominant economic system in the West since the nineteenth century and has increasingly spread across the globe. Characterized by unfettered markets in labor and natural resources, commodity production, and the reinvestment of profit, capitalism must be distinguished from other forms of commercial society that existed in early times or outside of the West, in which market-or…
Debates over capitalism in Africa revolve around the best means to rescue the continent from a prolonged period of stagnation and decline. Observers agree that the program, in the absence of a socialist alternative, must focus on capitalist development. There is disagreement, however, over the role of the African state in this process, as well as over whether to make raw materials exports or indus…
Biology is the scientific study of all forms of life, including plants, animals, and microorganisms. Among the numerous fields in biology are microbiology, the study of microscopic organisms like bacteria; cytology, the study of cells; embryology, the study of development; genetics, the study of heredity; biochemistry, the study of the chemical structures in living things; morphology, the study of…
When René Descartes died in 1650, his work had already attracted both critics and followers. In 1632 Cartesian philosophy was being taught in the Netherlands by his disciple Henri Reneri (1593–1639), and by the mid-1630s the far more independently minded Henri Regius (1598–1679) was setting out his own version of Cartesianism in a less guarded and more polemical way than had Des…
There are three units of time which have a direct basis in astronomy: the day, which is the period of time it takes for the Earth to make one rotation around its axis; the month, which is the period of time it takes for the Moon to revolve around the earth; and the year, which is the period of time it takes for the earth to make one revolution around the Sun. The week has an indirect basis in astr…
Calibration is the process of checking the performance of a measuring instrument or device against some commonly accepted standard. A watch, for example, has to be calibrated so that it keeps correct time, agreeing with the international standard. The dials on a radio must also be calibrated so that the correct frequency or station is actually being received. Calibration provides consistency in a …
Bioluminescence is the production of light by living organisms. Some single-celled organisms (bacteria and protista) as well as many multicellular animals and fungi demonstrate bioluminescence. …
A caliper is an instrument used for measuring linear dimensions that are not easily measured by devices such as meter sticks or rulers. Two examples of such measurements include the outer dimensions of a pipe or the internal diameter of a glass tube. Although many kinds of calipers exist, they are all designed on a common principle: two legs are hinged at one end to allow movement of the free ends…
A calorie is the amount of energy required to raise the temperature of 1g of pure water by 34°F (1°C) under standard conditions. These conditions include an atmospheric pressure of one atmosphere, and a temperature change from 60° to 62°F (15.5 to 16.5°C). The calorie is also sometimes designated as a gram-calorie or small calorie (abbreviated: cal), to distingui…
Biomagnification (or bioaccumulation) refers to the ability of living organisms to accumulate certain chemicals to a concentration larger than that occurring in their inorganic, non-living environment, or in the case of animals, in the food that they eat. Of course, organisms accumulate any chemical needed for their nutrition. In environmental science, however, the major focus of biomagnification …
Biomass consists of living organisms, or parts of living organisms, as well as waste products and incompletely decomposed remains of living organisms. The term is quite encompassing and includes plants (referred to as phytomass), microbes, and animal material, or zoomass. Biomass density is a distinguishing feature of ecological systems and is usually presented as the amount of dry biomass per uni…
Calorimetry is the measurement of the amount of heat gained or lost during some particular physical or chemical change. Heats of fusion or vaporization, heats of solution, and heats of reaction are examples of the kinds of determination that can be made in calorimetry. The term itself derives the Latin word for heat, caloric, as is the name of the instrument used to make these determinations, the …
A biome is a major, geographically extensive ecosystem, structurally characterized by its dominant life forms. Terrestrial biomes are usually distinguished on the basis of the major components of their mature or climax vegetation, while aquatic biomes, especially marine ones, are often characterized by their dominant animals. Most of the oceans are considered part of a single biome, although areas…
Camels and their relatives, the llamas, are longlegged, hoofed mammals in the family Camelidae in order Artiodactyla, whose members have an even number of toes. All camels have a cleft in their upper lip, and all have the ability to withstand great heat and great cold. Camels evolved in North America and spread into South America, Asia, and Africa. Camels in Asia and Africa today have been domesti…
Biophysics is the integration and application of the principles of physics to explain and explore the form and function of living things. The most familiar examples of the role of physics in biology are the use of lenses to correct visual defects and the use of x rays to reveal the structure of bones. Principles of physics have been used to explain some of the most basic processes in biology such …
A canal is a man-made waterway or channel that is built for navigation, irrigation, drainage, or water supply. When the word is used today however, it is usually in the context of transport or navigation by boats. Canal transport should not be confused with navigating on a river, because a canal is entirely artificial (although canals are in many cases connected with a natural body of water). Ther…
Attention deficit/hyperactivity disorder (ADHD), also known as hyperkinetic disorder (HKD) outside of the United States, is estimated to affect 3–9% of children, and afflicts boys more often than girls. Although difficult to assess in infancy and toddlerhood, signs of ADHD may begin to appear as early as age two or three, but the symptom picture changes as adolescence approaches. Many sympt…
Cancel refers to an operation used in term mathematics to remove terms from an expression leaving it in a simpler form. For example, in the fraction 6/8, the factor 2 can be removed from both the numerator and the denominator leaving the irreducible fraction 3/4. In this instance the 2 is said to be canceled out of the expression. Canceling is particularly useful for solving algebraic equations. T…
Auks are penguinlike seabirds found in the Northern Hemisphere. These birds spend most of their lives in the coastal waters north of 25°N latitude, coming ashore only to lay their eggs and raise their young. There are 22 species of auks, including the Atlantic puffin, the common murre, the dovekie or lesser auk, and the extinct great auk. Called alcids, the members of the auk family fill an…
Bioremediation is a type of biotechnology in which living organisms or ecological processes are utilized to deal with some environmental problem. The most common use of bioremediation is to metabolically break down or otherwise remove toxic chemicals before or after they have been discharged into the environment. In such uses, bioremediation takes advantage of the fact that certain microorganisms …
The biosphere is the space on and near the earth's surface that contains and supports living organisms and ecosystems. It is typically subdivided into the lithosphere, atmosphere, and hydrosphere. The lithosphere is the earth's surrounding layer composed of solid soil and rock, the atmosphere is the surrounding gaseous envelope, and the hydrosphere refers to liquid environments such …
Cancer is not just one disease, but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death. One out of every four deaths in the United States is from cancer. It is second only to …
Canines are species in the carnivore family, Canidae, including the wolves, coyote, foxes, dingo, jackals, and several species of wild dog. The family also includes the domestic dog, which is believed to have descended from the wolf. The Canidae includes 10-14 genera with 30-35 species, depending on the taxonomic treatment. Canines originated in North America during the Eocene era (38-54 million y…
A cantilever, also called a fixed end beam, is a beam supported only at one end. The beam cannot rotate in any direction; thus it creates a solid support. The cantilever is considered the third of the three great structural methods, the other two being post-and-beam construction and arch construction. The cantilever thrusts down which is different from the thrust of an arch which is outward agains…
The Biosphere 2 Project is an experiment in which scientists, engineers, and some intrepid "biospherians" (or dwellers) within the Biosphere have recreated several of the main terrains and habitats of our planet and attempted to co-habit with these environments to the environments' benefit. Many environmentalists see planet Earth as the first, original, and only known biospher…
Biotechnology is the use of any technique involving living organisms to manufacture or change products, to improve the desired characteristics of a plant or animal, or to alter microorganisms for a purpose. Biotechnology has a long history. For example, yeast microorganisms were harnessed to prepare wine by Egyptians some 4,000 years before the birth of Christ. In 1865, Gregor Mendel presented his…
Bioterrorism is the use of a biological weapon against a civilian population. As with any form of terrorism, its purposes include the undermining of morale, creating chaos, or achieving political goals. Biological weapons use microorganisms and toxins to produce disease and death in humans, livestock, and crops. Biological, chemical, and nuclear weapons can all be used to achieve similar destructi…
The birch family is a group of flowering plants of tree or shrub form that includes the birches (Betula), alders (Alnus), hornbeams (Carpinus), and hazels (Corylus). Members of the birch family have simple and alternate leaves that bear appendages (stipules) where they join the branch. The leaves are also deciduous, generally thin and often doubly toothed along the margin. The flowers are densely …
Of the seven continents, Australia is the flattest, smallest, and except for Antarctica, the most arid. Including the southeastern island of Tasmania, the island continent is roughly equal in area to the United States, excluding Alaska and Hawaii. Millions of years of geographic isolation from other landmasses accounts for Australia's unique animal species, notably marsupial mammals like th…
Birds are vertebrate animals in the class Aves. There are approximately 8,800 species of birds, divided among 28 living orders. Of these, slightly more than 900 species are found in North America. There has been considerable disagreement among ornithologists about the appropriate level for differentiating species, leading to multiple classification schemes. But however one distinguishes between sp…
Capacitance is an electrical effect that opposes change in voltage between conducting surfaces separated by an insulator. Capacitance stores electrical energy when electrons are attracted to nearby but separate surfaces. The voltage across an unchanging capacitance value will stay constant unless the quantity of charge stored is changed. If the voltage across a capacitor is increased until charges…
Autism is a profound mental disorder marked by an inability to communicate and interact with others. The condition's characteristics include language abnormalities, restricted and repetitive interests, and the appearance of these characteristics in early childhood. The disorder begins in infancy, but typically is not diagnosed until the ages two to five. Although individuals with autism are…
A capacitor stores electrical energy. It is charged by hooking into an electrical circuit. When the capacitor is fully charged a switch is opened and the electrical energy is stored until it is needed. When the energy is needed, the switch is closed and a burst of electrical energy is released. A capacitor consists of two electrical conductors that are not in contact. The conductors are usually se…
The birds of paradise are some of the most fascinating birds in the world. This is due to the striking coloration of the males of most species, and the wide range of behaviors demonstrated in the group. Researchers of animal behavior are particularly interested in the elaborate mating displays performed by male birds of paradise. Birds of paradise are members of the family Paradisaeidae, which pro…
Capillaries are microscopic blood vessels that connect small arteries (arterioles) and small veins (venules). Within the tissues, arterioles terminate into a network of microscopic capillaries. Substances move in and out of the capillary walls as the blood exchanges materials with the cells. Before leaving the tissues, capillaries unite into venules, which merge to form larger and larger veins tha…
Birds of prey are predators that catch and eat other animals. These birds are called raptors (from the Latin rapere, meaning to snatch), a reference to their specialized, powerful feet, which are used to seize their prey. Raptorial birds eat birds, small mammals, reptiles, amphibians, fish, and large insects. Birds of prey are members of five avian families within the order Falconiformes. The Acci…
Capillary action is the tendency of a liquid to rise in narrow tubes or to be drawn into small openings such as those between grains of a rock. Capillary action, also known as capillarity, is a result of the intermolecular attraction within the liquid and solid materials. A familiar example of capillary action is the tendency of a dry paper towel to absorb a liquid by drawing it into the narrow op…
Autoimmunity is a condition where the immune system mistakenly recognizes host tissue or cells as foreign. (The word "auto" is the Greek word for self.) Because of this false recognition, the immune system reacts against the host components. There are a variety of autoimmune disorders (also called autoimmune diseases). An autoimmune disease can be very specific, involving a single or…
The automatic pilot has it roots in the gyroscope, a weighted, balanced wheel mounted in bearings and spinning at high velocity. As early as 1852 the French scientist Jean-Bernard-Léon Foucault had experimented with the gyroscope and found that it tended to stay aligned with its original position and also tended to orient itself parallel to Earth's axis in a north-south direction. Th…
The frogmouths, oilbird, potoos, owlet frogmouths, and nightjars are five unusual families of birds that make up the order Caprimulgiformes, and are collectively referred to as caprimulgids. Caprimulgids have a large head, with a short but wide beak that can open with an enormous gape, fringed by long, stiff bristles. This apparatus is used by caprimulgids to catch their food of insects in flight.…
Birth, or parturition, in mammals is the process in which a fully developed fetus is expelled from the mother's uterus by the force of strong, rhythmic muscle contractions. The birth of live offspring is a reproductive feature shared by mammals, some fishes, and selected invertebrates (such as scorpions), as well as some reptiles and amphibians. Animals who give birth to live offspring are …
Automation is the use of scientific and technological principles in the manufacture of machines that take over work normally done by humans. This definition has been disputed by professional scientists and engineers, but in any case, the term is derived from the longer term automatization or from the phrase automatic operation. Delmar S. Harder, a plant manager for General Motors, is credited with…
Birth defects or congenital defects are present at birth. They result from heredity, environmental influences, or maternal illness. Such defects range from the very minor, such as a dark spot or birthmark that may appear anywhere on the body, to more serious conditions that may result in marked disfigurement, impaired functioning, or decreased lifespan. A number of factors individually or in combi…
In 1973, the Endangered Species Act was passed in the United States to protect species that are rapidly declining due to human influences. Captive breeding and release is one of the tools available to halt or reverse the decline of some species in the wild. Such programs may be carried out by zoos, aquaria, botanical gardens, or conservation organizations. In some cases the efforts have met with a…
Capuchins are New World monkeys characterized by a cap or crown patch of hair that resembles a hood, called a capuche, worn by Franciscan monks. Capuchins belong to the family Cebidae, which includes 31 species in 11 genera. The Cebidae is subdivided into seven subfamilies which include night monkeys, squirrel monkeys, titis, sakis, howlers, spider monkeys, and the capuchins. Monkeys in the family…
The American bison (Bison bison) is a large, herbivorous land mammal native to the grasslands and open forests of North America. It is a member of the family Bovidae, which also includes cattle, sheep, and goats. When French explorers first saw these large, shaggy, cow-like animals, they called them boeufs, the French word for "cattle." This later became anglicized into the word �…
Capybaras, also known as carpinchos or water hogs, are large South American rodents in the family Hydrochaeridae. Hydrochaeris hydrochaeris is the larger of the two species of capybaras, and is the world's largest rodent. It can reach a body weight of 110 lb (50 kg), a body length of 4.5 ft (1.3 m), and a height of 1.5 ft (50 cm). Hydrochaeris isthmius is about half this size. H. hydrochaer…
Carbohydrates are naturally occurring compounds composed of carbon, hydrogen, and oxygen. The carbohydrate group includes sugars, starches, cellulose, and a number of other chemically related substances. For the most part, these carbohydrates are produced by green plants through the process known as photosynthesis. Countless varieties of plants use this process to synthesize a simple sugar (glucos…
Bitterns are about 12 species of wading birds in the subfamily Botaurinae of the family Ardeidae, which also includes herons and egrets. There are two genera: four species of the relatively large and stocky true bitterns (Botaurus spp.), and eight species of the much smaller and more slender, least bitterns (Ixobrychus). Bitterns have brown-and-black, vertically streaked plumage, which renders the…
Bivalve molluscks belong to the class Bivalvia (or Lamellibranchia) of the phylum Mollusca. Known by such common names as clams, mussels, cockles, oysters, and scallops, bivalves are among the most familiar aquatic invertebrates. They occur in large numbers in marine, estuarine, The life cycle of a typical freshwater clam. For species that do not have the parasitic larval stage, the fertilize…
BL Lacertae objects, abbreviated BL Lac, are one subclass of active galactic nuclei (AGN), the extremely energetic nuclei of active galaxies. Roughly 40 BL Lac objects are known. Perhaps the most obvious property of BL Lac objects is that they look like stars. Astronomers originally thought the prototype, BL Lac, was a star. In fact, BL Lacertae is normally a variable star designation, two letters…
Carbon has been known since prehistoric times. It gets its name from carbo, the Latin word for charcoal, which is almost pure carbon. In various forms, carbon is found not only on Earth, but in the atmospheres of other planets, in the Sun and stars, in comets, and in some meteorites. On Earth, carbon can be considered to be the most important of all the chemical elements, because it is the essenti…
The concept of creolization lies at the very center of discussions of transculturalism, transnationalism, multiculturalism, diversity, and hybridization. This essay begins by examining the term's roots in the ethnic and cultural complexities of the Caribbean experience. It then goes on to look at the transformation of this experience into a theoretical framework for pluralism that conscious…
Few inventions in modern times have had as much impact on human life and on the global environment as the automobile. Automobiles and trucks have had a strong influence on the history, economy, and social life of much of the world. Entire societies, especially those of the industrialized countries, have been restructured around the power of rapid, long-distance movement that the automobile confers…
A sufficiently intense gravitational field can prevent the escape not only of matter, but even of light. Such gravitational fields are produced by the bodies known as black holes. The maximum intensity of a spherical object's gravitational field is a function both of the amount of matter it contains and of its volume. The more matter is contained in an object and the smaller its volume …
An autotroph is an organism able to make its own food. Autotrophic organisms take inorganic substances into their bodies and transform them into organic nourishment. Autotrophs are essential to all life because they are the primary producers at the base of all food chains. There are two categories of autotrophs, distinguished by the energy each uses to synthesize food. Photoautotrophs use light en…
The carbon cycle describes the movement of carbon in the atmosphere, where it is in the gaseous form carbon dioxide, through organisms, and then back into the atmosphere and the oceans. Carbon is a central element of the huge diversity of organic chemicals found in living things, such as the many kinds of carbohydrates, proteins, and fats. Energy is contained in the chemical bonds that hold the at…
The concept that a mole of any substance contains the same number of particles arose out of research conducted in the early 1800s by the Italian physicist Amedeo Avogadro (1776-1856). Avogadro based his work on the earlier discovery by Joseph Gay-Lussac that gases combine with each other in simple, whole-number ratios of volumes. For example, one liter of oxygen combines with two liters of hydroge…
Carbon dioxide was the first gas to be distinguished from ordinary air, perhaps because it is so intimately connected with the cycles of plant and animal life. When we breathe air or when we burn wood and other fuels, carbon dioxide is released; when plants store energy in the form of food, they use up carbon dioxide. Early scientists were able to observe the effects of carbon dioxide long before …
The aye-aye (Daubentonia madagascariensis) is a rare tree-dwelling animal that is found only at a few localities along the eastern half of Madagascar, off eastern Africa. It is a member of a group of primitive primates known as Prosimians, most of which are lemurs. The aye-aye is the only surviving member of the family Daubentoniidae; a slightly larger relative (D. robusta) became extinct about 1,…
The blackbird family (Icteridae) consists of 94 medium-sized species of birds that occur only in the Americas. Blackbirds are found in widespread habitats, ranging from wetlands, to prairies, to forests. The most common members of the family are various species of blackbirds, grackles, cowbirds, orioles, meadowlarks, bobolink, and others. …
Babblers are small to medium-sized passerine (perching) birds characterized by soft, fluffy plumage, strong, stout legs, and short rounded wings. Their wings make them poor fliers, and most are largely sedentary birds. Many species, particularly those that stay close to the ground, are gray, brown, or black, while the tree-living (arboreal) species are often green, yellow, or olive. Wren-babblers …
The term blackbody radiation refers to electromagnetic radiation emitted by a completely opaque object. Such an object is referred to as a blackbody since it absorbs all of the radiation that falls on it and thus appears to be colorless, or black. According to Kirchoff's law, any object that qualifies as a blackbody must also be a perfect emitter of radiation. In fact, no real object fits t…
Carbon monoxide is a compound of carbon and oxygen with the chemical formula CO. It is a colorless, odorless, tasteless, toxic gas. It has a density of 1.250 g/L at 32°F (0°C) and 760 mm Hg pressure. Carbon dioxide can be converted into a liquid at its boiling point of -312.7°F (-191.5°C) and then to a solid at its freezing point of -337°F (-205°C). …
Bleaches are substances that whiten textiles and paper by chemical reaction. These reactions usually involve processes that degrade color. They may destroy or modify chemical bonds or groups that give fabrics their characteristic colors. This process degrades color bodies into smaller, more soluble units that are easily removed in laundering. Conventional bleaching agents, include two types: chlor…
Carbon tetrachloride is an organic chemical that is commonly used as a solvent. It is also called tetra chloromethane and is composed of molecules that have one carbon atom and four chlorine atoms bonded together in the shape of a tetrahedron. It is made by combining elemental chlorine with simple carbon compounds like methane or carbon disulfide. It is a liquid at room temperature, with a freezin…
Blennies are small, primarily tropical and subtropical marine fish. They are elongated and often eel-like in shape, with a dorsal fin running from the back of the head almost to the tail fin, and small abdominal fins; the pelvic fin is often completely absent. Many species also lack scales. The blenny's anatomy is well suited for hiding in cracks and crevices along shallow, rocky shorelines…
Blindness is usually considered as an inability to see or a complete loss of vision, although legally, a blind person may retain some vision. In contrast, visual impairment indicates a loss of vision such that there is an impact on daily living, which usually implies partial loss of vision. There are many causes of visual impairment or blindness, and all parts of the eye (cornea, retina, lens, opt…
Baboons are ground-living monkeys in the primate family Cercopithecidae and are found in Africa and the Arabian Peninsula. Some taxonomists classify baboons in two genera, while others classify them in three or four. All baboons have a strong torso, a snout-like face, the same dentition with long, sharp canine teeth, powerful jaws, a ground-walking habit, coarse body hair, a naked rump, and a simi…
These tiny, primitive burrowers live underground and forage for ants, termites, soft-bodied insects, and insect larvae. The eyes of most blindsnakes are degenerate; they are covered by scales and do not function. However, the eyes do have light-sensitive cells (rods), so these snakes may not be completely blind. The head is large and the mouth, like a shark's, is below and behind the snout,…
A carbonyl group is a group of atoms that consists of a carbon atom covalently attached to an oxygen atom by a double bond: C = O. The carbon atom, to satisfy its valence of 4, must also be attached by covalent bonds to two other atoms. The simplest type of molecule that contains a carbonyl group is a ketone. Other types of molecules that contain carbonyl groups are aldehydes, acids, esters, and a…
A carboxyl group, also called a carboxy group, is a characteristic group of atoms found in organic molecules. Organic compounds that contain carboxyl groups are called carboxylic acids. The carboxyl group occurs on the end or side of a molecule. The group consists of a carbon atom that forms two chemical bonds to one oxygen atom and one chemical bond to a second oxygen atom. This second oxygen is …
Blood is a liquid connective tissue that performs many functions in the body, including transport of oxygen, Red blood cells alongside the wall of the blood vessel. Photograph by Dennis Kunkel. Phototake NYC. Reproduced by permission. carbon dioxide, nutrients, waste products, and hormones; clotting; and defense against microorganisms. Blood consists of formed elements, or blood cells su…
Blood gas analysis is a means of determining the amount of oxygen or carbon dioxide being carried in the blood, and in some cases, of discovering the identity of a toxic gas, such as carbon monoxide, that may be present. Also, the determination can be made as to whether the blood is too acidic or too alkaline, which may help the physician in his diagnosis. Among other functions, blood carries oxyg…
Carboxylic acids are chemical compounds that contain a carboxyl group, which is -COOH. The carboxyl group is attached to another hydrogen atom or to one end of a larger molecule. Examples include formic acid, which is produced by some ants and causes their bites to sting. (In fact, the scientific name for ants, Formica, is what gives formic acid its name.) Another example is acetic acid, which is …
Bacteria are mostly unicellular organisms that lack chlorophyll and are among the smallest living things on earth—only viruses are smaller. Multiplying rapidly under favorable conditions, bacteria can aggregate into colonies of millions or even billions of organisms within a space as small as a drop of water. The Dutch merchant and amateur scientist Anton van Leeuwenhoek was the first to ob…
Blood supply refers to the blood resources in blood banks and hospitals that are critical to the health care community. The blood supply consists of donated blood units (in pints) that are used to replace blood lost during surgery or from trauma. Blood transfusions were attempted as early as 1667 when Jean-Baptiste Denis, a French physician, transfused 12 fl oz (355 ml) of lamb's blood into…
Blotting analysis describes a series of techniques used to determine and describe protein and nucleic acid (e.g., DNA, RNA) sequences. Blotting analysis allows scientists to transfer electrophoretically separated components from a gel to a solid support. This support may then be used for probing with reagents specific for particular sequences of amino acids or nucleotides. In this way, the size an…
A carcinogen is a substance that causes a normal cell to change into a cancerous cell. The word "car cinogen" is derived from Greek and means in English, cancer-causing. Carcinogens fall into two broad categories, naturally occurring substances that are found in food or soil, or artificial substances created by chemists for various industrial purposes. Although the way carcinogens ca…
The coordinated and rhythmic series of muscular contractions associated with the heart comprise the cardiac cycle. In humans, the cardiac cycle can be subdivided into two major phases, the systolic phase and the diastolic phase. Systole occurs when the ventricles of the heart contract. Accordingly, systole results in the highest pressures within the systemic and pulmonary circulatory systems. Dias…
Bacteriophage (also known as phages) are viruses that target and infect only bacterial cells. The first observation of what since turned out to be bacteriophage was made in 1896. Almost twenty years later, the British bacteriologist Frederick Twort demonstrated that an unknown microorganism that could pass through a filter that excluded bacteria was capable of destroying bacteria. He did not explo…
A measure of the number of elements in a group or a set. For example, the number of books on a shelf can be described by a single cardinal number. Similarly, the set can be assigned the cardinal number 3 because it has only three elements. Since cardinal numbers count the number of elements in a set, they are always positive whole integers. If the elements from two sets have a one-to-one relations…
The cardinals and grosbeaks belong to the subfamilies Cardinalinae, of the finch family (Fringillidae), which is the largest of all North American bird families. (Some researchers include the cardinals and grosbeaks with the Emberizidae, the buntings and tanagers). Cardinals and grosbeaks are New World birds, ranging from central Argentina as far north as central Canada. They live primarily in tem…
The caribou or reindeer (Rangifer tarandus) is a northern species of deer occurring in the boreal and arctic regions of North America and Eurasia. At one time, caribou and reindeer were considered to be separate species, but these animals are fully interfertile and are now considered to be the same species. In North America they are called caribou, whereas in Eurasia they are known as reindeer. Ho…
Badgers are eight species of robust, burrowing carnivores in the subfamily Melinae of the family Mustelidae, which also includes weasels, mink, marten, otters, and skunks. There are eight species of badgers, distributed among six genera. Badgers have a strong, sturdy body, with short, powerful, strong-clawed legs, and a short tail. The head is slender and triangular-shaped. The fur of badgers is l…
The term "blue revolution" refers to the remarkable emergence of aquaculture as an important and highly productive agricultural activity. Aquaculture refers to all forms of active culturing of aquatic animals and plants, occurring in marine, brackish, or fresh waters. Aquaculture has long been practiced in China and other places in eastern Asia, where freshwater fish have been grown …
In the literal sense, a carnivore is any flesh-eating organism. However, in the ecological usage of the word, carnivores kill animals before eating them (that is, they are predators), as opposed to feeding on animals that are already dead (the latter are called scavengers or detritivores). Trophic ecology deals with the feeding and nutritional relationships within ecosystems, and this field has de…
Ball bearings help reduce friction and improve efficiency by minimizing the frictional contact between machine parts through bearings and lubrication. Ball bearings allow rotary or linear movement between two surfaces. As the name indicates, a ball bearing involves a number of balls, typically steel, sandwiched between a spinning inner race (a small steel ring with a rounded grove on its outer sur…
Bluebirds are small blue-colored perching birds in the thrush family (Turdidae). There are three species of bluebirds in North America. All of these bluebirds nest in natural cavities or nest boxes. They tend to feed from perches, flying down to catch insects as they see them, and sometimes hawking insects in the air. The eastern bluebird (Sialia sialis) occurs in shrub-by habitats, old orchards, …
Boarfish is a common name, so it is not surprising that fish from two different marine families, from two different orders, with superficially similar snout-shaped faces share this name. One species that bears the common name boarfish comprises the few species of the genus Antigonia, which according to some experts is the only genus in the family Caprioidae. Others add the genus Capros to this fam…
Carnivorous plants are botanical oddities that supplement their requirement for nutrients by trapping, killing, and digesting small animals, mostly insects. Carnivorous plants are photosynthetic, and are therefore fundamentally autotrophic. Still, their feeding relationship with animals represents a reversal of the normal trophic connections between autotrophs and consumers. Carnivorous plants hav…
Any missile that lofts an explosive payload which descends to its target as a ballistic projectile—that is, solely under the influence of gravity and air resistance—is a ballistic missile. Missiles that do not deliver a free-falling payload, such as engine powered-cruise missiles (which fly to their targets as robotic airplanes), are not "ballistic." A ballistic missile…
Boas are a group of nonvenomous, constricting snakes (family Boidae), most of which are found in tropical America and in Madagascar. Boas bear live young, and in this way they differ from the Old World pythons, which lay eggs. Boas are of ancient derivation, retaining some of the features of their lizard-like ancestors, such as paired lungs (modern snakes have only one), tiny remnants of hind limb…
Carp are fish species in the minnow family (Cyprinidae), one of the major groups of freshwater fish. The most familiar species are the common carp (Cyprinus carpio) and the closely related goldfish (Carassius aureus). The minnow family is characterized by having no teeth in the jaws, although well-developed teeth occur on the pharyngeal bones (located behind the gill chamber) and are used to grind…
The Bohr model of atomic structure was developed by Danish physicist and Nobel laureate Niels Bohr (1885–1962). Published in 1913, Bohr's model improved the classical atomic models of physicists J. J. Thomson and Ernest Rutherford by incorporating quantum theory. While working on his doctoral dissertation at Copenhagen University, Bohr studied physicist Max Planck's quantum th…
Carpal tunnel syndrome results from compression and irritation of the median nerve where it passes through the wrist. In the end, the median nerve is responsible for both sensation and movement. When the median nerve is compressed, an individual's hand will feel as if it has "gone to sleep." The individual will experience numbness, tingling, and a prickly pin like sensation ov…
The boiling point of a liquid substance is the temperature at which the vapor pressure of the liquid equals the external pressure on the liquid. Vapor bubbles form in the liquid, rise to the surface and burst, causing the liquid to boil. At room temperature, in a closed system, there is an equilibrium between the liquid and its vapor phase. For example, if a glass of water is left open, the water …
In genetics, the term carrier describes an organism that carries two different forms (alleles) of a recessive gene (alleles of a gene linked to a recessive trait) and is thus heterozygous for that the recessive gene. Although carriers may act to convey and maintain recessive genes within a population by passing them on to offspring, the carriers themselves are not affected by the recessive trait a…
Bond energy is the strength of a chemical bond between atoms, expressed as the amount of energy required to break it apart. It is as if the bonded atoms were glued together: the stronger the glue is, the more energy would be needed to break them apart. A higher bond energy, therefore, means a stronger bond. Notice that ionic bonds are stronger than covalent bonds. Among covalent bonds, triple bond…
Ballistics is the study of projectile motion. A projectile is an object that has been launched, shot, hurled, thrown, or by other means projected, and continues in motion due to its own inertia. The path of the projectile is determined by its initial velocity (direction and speed) and the forces of gravity and air resistance. For objects projected close to Earth and with negligible air resistance,…
Bony fish (Osteichthyes) are distinguished from other fish species that have a cartilaginous skeleton (Chondrichthyes—sharks, rays and chimaeras, for example) by the presence of true bone—a mixture of calcium phosphates and carbonates—in their skeletons. Other differences between the two groups are modifications in the structure and arrangement of the scales and fins and the p…
The carrot family (Apiaceae, or Umbelliferae) is a diverse group of about 3,000 species of plants, occurring in all parts of the world. Most Umbellifers are herbaceous, perennial plants, often with aromatic foliage. Some species have poisonous foliage or roots. The leaves are typically alternately arranged on the stem, and in many species they are compound and divided into lobes. The flowers are s…
A balloon is a nonsteerable aircraft consisting of a thin envelope inflated with any gas lighter than the surrounding air. The balloon rises from the ground similar to a gas bubble in a glass of soda. The physical principle underlying this ability to ascend is Archimedes' law, according to which any immersed body is pushed upward by a force equal to the weight of the displaced fluid. If thi…
Carrying capacity refers to the maximum abundance of a species that can be sustained within a given area of habitat. When an ideal population is at equilibrium with the carrying capacity of its environment, the birth and death rates are equal, and size of the population does not change. Populations larger than the carrying capacity are not sustainable, and will degrade their habitat. In nature, ho…
Boobies and gannets are nine species of marine birds that make up the family Sulidae, in the order Pelecaniformes, which also includes the pelicans, cormorants, anhingas, tropic birds, and frigate birds. Boobies and gannets have a narrow, cigar-shaped body, a longish, pointed tail, and long, narrow wings. Their feet are fully webbed, and are used in swimming. The beak is strong, pointed, has a ser…
The Cartesian coordinate system is named after René Descartes (1596–1650), the noted French mathematician and philosopher, who was among the first to describe its properties. However, historical evidence shows that Pierre de Fermat (1601-1665), also a French mathematician and scholar, did more to develop the Cartesian system than did Descartes. To best understand the nature of the Ca…
Bananas, plantains, and their relatives are various species of plants in the family Musaceae. There are about 40 species in this family, divided among only two genera. The most diverse genus is Musa, containing 35 species of bananas and plantains, followed by Ensete, the Abyssinian bananas. The natural range of bananas and plantains is the tropics and subtropics of the Old World, but agricultural …
Cartilaginous fish such as sharks, skates, and rays are vertebrates whose internal skeleton is made entirely of cartilage and contains no ossified bone. Cartilaginous fish are also known as Chondrichthyes and have one or two dorsal fins, a caudal fin, an anal fin, and ventral fins which are supported by girdles of the internal skeleton. Placoid scales, or dermal teeth, are characteristic of the sk…
Australian wildlife holds many surprises, but few as intriguing as the widely distributed bandicoots. These small, rabbit-sized marsupials have a thick set body, short limbs, a pointed muzzle, short neck and short hairy tail. Their teeth are similar to those of insect- and flesh-eating mammals, but their hind feet resemble those of kangaroos and possums. The hindfeet are not only considerably long…
Almost everyone is familiar with the striped bars found on grocery and retail store items. These are bar codes, or more specifically, the Universal Product Code (UPC). UPC codes first appeared in stores in 1973 and have since revolutionized the sales industry. The UPC code consists of ten pairs of thick and thin vertical bars that represent the manufacturer's identity, The parts of the …
Barberries are about 600 species of plants in the genus Berberis, family Berberidaceae, occurring throughout the Northern Hemisphere and South America. Most species of barberry are shrubs or small trees, and many of these have persistent, evergreen leaves. The flowers are small, arranged in clusters, and insect pollinated. The fruits of barberries are multiple-seeded berries. Barberry hybrids are …
Boolean algebra is often referred to as the algebra of logic, because the English mathematician George Boole, who is largely responsible for its beginnings, was the first to apply algebraic techniques to logical methodology. Boole showed that logical propositions and their connectives could be expressed in the language of set theory. Thus, Boolean algebra is also the algebra of sets. Algebra, in g…
Barbets are about 76 species of medium-sized birds, divided among 13 genera. These comprise the family Capitonidae, in the order Piciformes, which also contains the woodpeckers, toucans, and their allies. Barbets are birds of tropical forests, occurring in Central and South America, Africa, and Asia as far south as Indonesia. However, none of the species of barbets occur in more than one continent…
Boric acid has a wide variety of industrial applications. It is used in the manufacture of heat-resistant borosilicate glass and other ceramics, such as crockery, porcelains, enamels, and artificial gemstones. It also used in waterproofing wood and fireproofing textiles. It also finds application as an insecticide for cockroaches and black carpet beetles and as an fungicide on citrus fruits. Its u…
Botany is the study of plants. It is one of the major fields of biology, together with zoology (the study of animals) and microbiology (the study of bacteria and viruses). Specializations within the field of botany include the study of mosses, algae, lichens, ferns, and fungi. Other specialties in botany include plant physiology, the study of the vital processes of plants, such as photosynthesis, …
Barbiturates are in the group of medicines known as central nervous system (CNS) depressants. Also known as sedative-hypnotic drugs, barbiturates make people very relaxed, calm, and sleepy. These drugs are sometimes used to help patients relax before surgery. Some may also be used to control seizures (convulsions). Although barbiturates have been used to treat nervousness and sleep problems, they …
Botulism is an extremely serious disease caused by the bacterium Clostridium botulinum. C. botulinum release one of the most potent toxins known—one gram of botulinum toxin theoretically can kill one million people. The toxin is swift-acting. It kills by binding to nerve cells, thereby causing paralysis of the muscles used in breathing. First coined in the 1870s, the term botulism comes fro…
Cartography is the creation, production, and study of maps. Cartographers are often geographers who specialize in the combination of art, science, and technology to make and study maps. Some cartographers teach mapmaking skills and techniques, some design and produce maps, and some are curators of map libraries. All cartographers, however, focus on maps as the object of their study or livelihood. …
Recent reports estimate that the proportion of individuals who are overweight in the United States surpasses 50% of the adult population. Such a staggering statistic has associated with it profound ramifications. Excess weight is a major contributor to serious health conditions that affect millions of people and can result in early death. Aside from tangible diseases, obesity is the root of much p…
As hot magma cools, it undergoes specific reactions. Bowen's reaction series describes the temperature Bowen's reaction series depicts mineral formation in a cooling magma. The discontinuous side depicts mineral formation at decreasing temperatures. The continuous side depicts a solid solution series. As the magma cools there is a trend towards molecular complexity. As the tempe…
Although pure barium is rarely used outside the laboratory, barium's many compounds have a number of practical applications. Perhaps the most familiar is the barium enema. When doctors need to examine a patient's digestive system, a mixture containing barium sulfate is used to coat the inner lining of the intestines. Similarly, to enhance examination of the stomach and esophagus, the…
The 18 species of bowerbirds are unique in that the males build and decorate a bower, a structure of sticks or grass on the ground, for the purpose of attracting and courting females. Members of the bowerbird family (Ptilonorhynchidae) are found in Australia and New Guinea, and are related to lyrebirds and birds of paradise. Most bowerbirds are about the size of a blue jay or grackle, and as a gro…
Barium sulfate occurs in nature as the mineral barite, or baryte, which is mined in Canada and Mexico and, in the United States in Arkansas, Missouri, Georgia, and Nevada. It is also prepared synthetically either by treating a solution of a barium salt with sodium sulfate or as a by-product in the manufacture of hydrogen peroxide. Barium sulfate is used in diagnostic radiology of the digestive sys…
The bowfin is a bony fish (Amia calva, family Amiidae) found in eastern North America. It is a relic species—the sole living representative of the order Amiiformes, which first appeared in the Triassic period more than 200 million years ago. Members of this family were common in Europe and Asia, as well as North America, during the Cretaceous and the early part of the Cenozoic. Fossil speci…
Bark is a protective, outer tissue that occurs on older stems and roots of woody coniferous and angiosperm plants. Bark is generally considered to occur on the outside of the tissue known as wood, or the water-conducting xylem tissues of woody plants. The inner cells of bark, known as phloem, grow by the division of outer cells in a generative layer called the vascular cambium, located between the…
Boxfish, also called trunkfish or cowfish, are a small group of shallow-water, marine fish in the family Ostraciontidae (order Tetraodontiformes). The family includes the genera Lactoria, Ostracion, and Tetrosomus and is closely related to the poisonous puffer fish of the family Tetraodontidae. To avoid confusion with these poisonous relatives, some people avoid eating boxfish despite their being …
Barley is one of the world's major cultivated crops. It is a member of the grass family (Poaceae). In 1999, approximately142 million acres (57.5 million ha) of barley were grown worldwide and the total production was 147.0 million tons of grain (133.6 million tonnes). Harvesting barley with a combine tractor. Photograph by Holt Studios Limited Ltd. Photo Researchers, Inc. Reproduced by…
Brachiopods, or lampshells, are a phylum of small marine animals with a two-valved shell that, at first glance, resemble bivalved mollusks such as clams. The resemblance, however, is quite superficial. The orientation of the shells of brachiopods is very different from that of bivalved mollusks, and brachiopods have two additional structures virtually unique to them, the lophophore (a ciliated fee…
The cashew family (Anacardiaceae) is a group of about 600 species of plants, most of which are tropical in distribution, although some occur in the temperate zone. Maturing pistachio (Pistacia vera) nuts on a tree in California. © Holt Studios International, National Audubon Society Collection/Photo Researchers, Inc. Reproduced with permission. Almost all members of the cashew famil…
The rocky shores of most coastlines are liberally dotted with clusters of barnacles (phylum Arthropoda, class Crustacea). Few people take any notice of these animals, despite their common occurrence. Barnacles are exclusively marine animals: some 900 species have been identified worldwide. Many are tiny organisms measuring just a few centimeters in diameter, while others such as the South American…
Brackish refers to water with a salinity intermediate to that of fresh water and sea water (the latter has a salt concentration of about 3.5%, or 35 parts per thousand). Brackish waters originate by the mixing of sea water and freshwater, and are most common near the coasts of the oceans. Brackish waters can occur as enclosed systems such as lakes and ponds that receive occasional inputs of oceani…
In the fall of 1997, the Cassini spacecraft began a seven-year, 2.175 billion mi (3.5 billion km) journey to Saturn. The 22.3 ft (6.8 m) robotic spacecraft is still functioning perfectly. When it arrives on July 1, 2004, it will spend four years probing the Saturnian system. Cassini, the first spacecraft to visit Saturn since Voyager 2 swung past it in 1980 and the first spacecraft ever to take up…
A barometer is an instrument for measuring atmospheric pressure. Two kinds of barometers are in common use, a mercury barometer and an aneroid barometer. The first makes use of a long narrow glass tube filled with mercury supported in a container of mercury, and the second makes use of a diaphragm whose size changes as a result of air pressure. The barometer described above is adequate for making …
The brain is a mass of nerve tissue located in an animal's head that controls the body's functions. In simple animals, the brain functions like a switchboard picking up signals from sense organs and passing information to muscles. The brain is also responsible for a variety of involuntary behavior, including keeping the heart beating, and maintaining blood pressure and temperature. I…
A barracuda is a long, cylindrical, silvery fish. It has two widely separated dorsal fins, in roughly the same location as the two fins on its belly, and a forked tail. The largest species, the great barracuda, seldom grows longer than 6.5 ft (2 m) and is an aggressive fearsome predator of other fish. All barracudas have an underhung jaw that houses long, incredibly sharp teeth; their teeth are co…
A barrier island is a long, thin, sandy stretch of land oriented parallel to the mainland coast, which protects the coast from the full force of powerful storm waves. Between the barrier island and the mainland is a lagoon or bay. Barrier islands are dynamic systems that migrate under the influence of changing sea levels, storms, waves, tides, and longshore currents. Approximately 2,100 barrier is…
Brewing is a multi-stage process during which the brewer encourages a grain such as barley to germinate briefly, steeps the grain in water to release its sugars, and adds yeast to the mixture, which ferments the sugar, turning it into alcohol and carbon dioxide. Around the world, people have brewed grains and starchy vegetables for thousands of years from ingredients as varied as rice, corn, cassa…
Within the broad field of geology, the term basin can be used to represent a number of features. These include topographic or drainage basins, structural basins, and sedimentary basins. In some cases, a single basin can include aspects of more than one of these types of basins. A topographic, or drainage, basin is a sloping or depressed area from which runoff collects and flows into a channel, str…
Bass is the common name for a number of popular freshwater and saltwater fish, which include the wide mouth bass, the striped bass, groupers, jewfish, and wreckfish, which are some of the finest sports and food fish in the world. Fish known as bass actually belong to different families and are distributed worldwide in tropical and temperate waters. The freshwater family Centrarchidae includes the …
Basswoods are about 30 species of trees in the genus Tilia, in the linden family Tiliaceae. In North America, these trees are generally known as basswoods in forestry, and as lindens in horticulture. Basswoods have simple, long-petioled, coarsely toothed, broadly heart-shaped leaves, arranged alternately on their twigs. The flowers occur in clusters, and emerge from a specialized leaf known as a b…
Throughout human history, the sea has yielded an abundance of resources for man's existence and provided efficient routes for exploration and transportation. In return, it has exacted a toll in terms of human life and property. The fear and respect that it earned from those who ventured out upon its surface was itself a deterrent to learning more about its mysteries. The physical restrictio…
Bricks are one of the oldest types of building blocks. They are an ideal building material because they are relatively cheap to make, very durable, and require little maintenance. Bricks are usually made of kiln-baked mixtures of clay. In ancient times, bricks were made of mud and dried in the sun; modern bricks are made from concrete, sand and lime, and glass. The physical and chemical characteri…
Bats are one of the most diverse and widely distributed groups of mammals on Earth, second only to rodents in the number of species. More than 900 species of bats have been described. They occur in most terrestrial biomes, except for the high Arctic and all of Antarctica. Bats are the only truly flying mammals, and are distinct from the flying lemurs and flying squirrels, which actually glide. Bat…
If two metals are immersed in an aqueous solution that can conduct electricity (electrolyte), they will have different tendencies to dissolve in the solution. A difference in voltage arises because one of the metals appears positive or negative relative to the other. The combination of two metals (electrodes) in an aqueous solution for the purpose of producing electrical energy from chemical energ…
Beach nourishment is the artificial process of adding sediment to a beach for recreational and aesthetic purposes, as well as to provide a buffer to coastal erosion. The sand may be dredged from nearby and pumped onto the beach, or transported in from outside areas. It is considered a soft method of stabilizing the shoreline, as opposed to rock and concrete structures meant to capture sand or prot…
Bridges are structures that join two otherwise inaccessible points of land, such as the two shores of a river or lake, or the two sides of a canyon or deep gully. Bridges are designed to carry railroad cars, motor vehicle traffic, or foot travel by pedestrians and/or animals, or to support pipes, troughs, or other conduits used for the movement of goods and materials, such as an oil pipeline or a …
Beardworms are slim, wormlike, deep-sea creatures so named for the thick cluster of long, fine, hairlike tentacles projecting from the front of the first section of a three-segmented body. There are approximately 120 species of beardworms, which belong to the phylum Pogonophora-from the Greek pogon, meaning beard, and phoron, meaning bearer. The front section of the beardworm's body, which …
Bristletails are about 300-400 species of small, elongate, terrestrial insects in the order Thysanura. Bristletails have an ancient evolutionary lineage, and they are believed to be relatively primitive, that is, similar in form and function to the most early evolved insects. Bristletails have a simple metamorphosis, with three life-history stages: egg, nymph, and adult. Both the nymphal and adult…
Brittle stars are starfishlike echinoderms (phylum Echinodermata) in the family Ophiodermatidae, whose star-shaped bodies are radially symmetrical and are supported by a hard endoskeleton made of calcium salts. Brittle stars are closely related to basket stars, and more distantly related to starfish, sand dollars, and sea urchins. Brittle stars are named for the ease by which their arms fall off w…
The pineapple family (Bromeliaceae) consists of about 1,500 species of flowering plants. Most species are medium-sized herbs with tightly packed, thick, stiff, spiralling leaves that usually have spiny margins. Some species are semi-woody, and a few rare ones, such as Puya raimondii, are trees that can reach 33 ft (10 m) in height. Most species of bromeliads are epiphytes in rainforests, while oth…
Bronchitis is the inflammation of the bronchi and is a commonly seen winter condition. The bronchi (the air passages leading into the lungs) are formed by the division of the trachea (the main windpipe leading from the larynx [Adam's apple] down through the neck into the chest). The trachea branches left and right into the bronchi which branch to supply lung lobe with the means for air to p…
A brown dwarf is a pseudostar; a body of gas not massive enough for the gravitational pressure in its core to ignite the hydrogen-fusion reaction that powers true stars. The name "brown dwarf" is a play on the name of the smallest class of true stars, "red dwarf," but while red dwarfs are actually red, brown dwarfs are not brown, but purple or magenta. Objects ranging i…
Brownian motion is the constant but irregular zigzag motion of small colloidal particles such as smoke, soot, dust, or pollen that can be seen quite clearly through a microscope. In 1827, Robert Brown, a Scottish botanist, prepared a slide by adding a drop of water to pollen grains. As he watched the tiny particles of pollen under his microscope, Brown noticed that they were constantly jiggling ab…
Bears are large carnivores of the family Ursidae. They are members of the order Carnivora, which also includes dogs, cats, and seals, although these animals are in different families than bears. All of these carnivores have a pair of modified teeth in the upper and lower jaw, called carnassials, that are used to tear meat into smaller chunks during feeding. Bears are not strictly meat-eaters, howe…
Brucellosis is a disease caused by bacteria in the genus Brucella. The disease infects animals such as swine, cattle, and sheep; humans can become infected indirectly through contact with infected animals or by drinking Brucella-contaminated milk. In the United States, most domestic animals are vaccinated against the bacteria, but brucellosis remains a risk with imported animal products. Brucella …
The true beavers are robust, aquatic herbivores in the family Castoridae, order Rodentia. Many taxonomists believe that two, closely related species of true beavers exist—the American beaver (Castor canadensis) and the Eurasian beaver (C. fiber). Other taxonomists, however, classify these as closely related variants of the same species, under the name Castor fiber. A few other rodents are a…
Bedrock is the solid rock that is exposed at the earth's surface, or buried beneath one or more layers of loose sediment. It is of igneous, sedimentary or metamorphic origin and forms the upper surface of the rocky foundation that composes the earth's crust. …
Bryophytes include the mosses, liverworts, and hornworts. Bryophytes are the simplest of plants (excluding the algae, which are not considered plants by most botanists). Bryophytes are small, seldom exceeding 6-8 in (15-20 cm) in height, and usually much smaller. They are attached to the substrate (ground, rock, or bark) by rhizoids, which are one or a few-celled, root-like threads that serve only…
Bee-eaters are 24 species of birds that make up the family Meropidae. Bee-eaters occur in open habitats and savannas of the south-temperate and tropical zones, ranging through Africa, southern Europe, southern Asia, Southeast Asia, and many Pacific Islands. Species that breed in temperate habitats migrate to the tropics for the winter. Bee-eaters have large, pointed wings and a long tail, usually …
The beech family is an important group of flowering plants that includes the beeches, oaks, and sweet chestnuts. Most members of the family are deciduous or evergreen trees or shrubs. The leaves are arranged alternately along branches, are leathery in texture, often strongly ribbed, and have margins that are entire, toothed, or deeply lobed. The flowers are unisexual. Male flowers are usually arra…
