Kabbalah is a Hebrew term that has many meanings. Its basic meaning is derived from the root QBL, which means to receive, and thus the term means "reception." In rabbinic literature it stands mainly for a tradition that is received orally. However, beginning in the tenth century, testimonies appeared for a more specific form of Kabbalah: an esoteric tradition dealing basically with …
Kangaroos rats are small burrowing mammals with fur-lined cheek pouches, making up the rodent family Ord's kangaroo rat. Photograph by Larry L. Miller. The National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission. Heteromyidae, found principally in North and Central America. There are five genera of rodents with external pouches in this family but only two…
Kangaroos and wallabies are pouched mammals, or marsupials, of Australia and nearby islands. Kangaroos and wallabies have hind legs enlarged for leaping. Most species live on the ground, and some in trees. The name kangaroo is usually used for large species, and wallaby for smaller ones. They all belong to the family Macropodidae, meaning "big footed," and they are herbivorous, or pl…
Karst is a German name for an unusual and distinct limestone terrain in Slovenia, called Kras. The karst region in Slovenia, located just north of the Adriatic Sea, is an area of barren, white, fretted rock. The main feature of a karst region is the absence of surface water flow. Rainfall and surface waters (streams, for example) disappear into a drainage system produced in karst areas. Another fe…
A karyotype is a technique that allows geneticists to visualize chromosomes under a microscope. The chromosomes can be seen using proper extraction and staining techniques when the chromosomes are in the metaphase portion of the cell cycle. Detecting chromosomal abnormalities is important for prenatal diagnosis, detection of carrier status for certain genetic diseases or traits, and for general di…
Johannes Kepler made it his life's work to create a heliocentric (sun-centered) model of the solar system which would accurately represent the observed motion in the sky of the Moon and planets over many centuries. Models using many geometric curves and surfaces to define planetary orbits, including one with the orbits of the six known planets fitted inside the five perfect solids of Pythag…
A keystone species is a particular species that has a great influence on the structure or functioning of its ecological community. This influence is far out of proportion to the relative biomass or productivity of the keystone species within its community. Most keystone species are top predators, although a few are influential because they play a critical role as herbivores or in nutrient cycling.…
There are 87 species of kingfishers (family Alcedinidae) which are brightly-colored birds ranging in size from the 4 in (11 cm) long malachite-crested kingfisher, to the laughing kookaburra of Australia, which is 18 in (46 cm) long, weighing 2 lb (0.5 kg). Kingfishers have a stocky body, with a large head equipped with a large, stout, dagger-like bill for grasping their food of fish or other small…
Kinglets are small forest birds in the subfamily Silviinae, family Muscicapidae, within the largest of the avian orders, Passeriformes, the perching birds. Kinglets are the most common North American representatives of their rather large subfamily, which is much more diverse in Europe, Asia, and Australia, and includes some 279 species. There are two species of kinglets in North America, both of w…
Kinship—which can be initially described as the study of the links between people established on the basis of descent, marriage, or adoption—has been a defining domain of anthropological investigation since the inception of this discipline in the last twenty years of the nineteenth century. The detailed description of the complexities of kinship systems was for many decades considere…
Four words of ancient Greek are important to the first philosophical discussions of knowledge in the Western tradition. In a given context any of them might be translated with the word "knowledge": epistēmē, technē, mētis, and gnōsis. Epistēmē names the most philosophical idea of knowledge: contemplative, disinterested, logical knowledge of t…
The koala (Phascolarctos cinereus) is a tree-living Australian marsupial, or pouched mammal, which early English settlers in Australia called the native bear. The koala is not a bear, but is the only living species in the family Phascolarctidae, though fossils indicate that there were once were a number of species of koala. The name is derived from an Aboriginal word meaning "animal that do…
Kola is a member of the tropical family Sterculiaceae, and it grows as a tree form. Kola nuts from two species, Cola nitida and C. acuminata, have been important objects of trade for at least 1,000 years. These nuts are perhaps most well known now as a constituent of soft drinks. There are over 50 species of kola. Of these seven have edible nuts, but only two have been commercially exploited (C. n…
Korsakoff's syndrome is a memory disorder which is caused by a deficiency of vitamin B1, also called thiamine. In the United States, the most common cause of such a deficiency is alcoholism. Other conditions which cause thiamine deficiency occur quite rarely, but can be seen in patients undergoing dialysis (a procedure during which the individual's blood circulates outside of the bod…
The citric acid cycle (also called the tricarboxylic acid cycle) is the common pathway by which organic fuel molecules of the cell are oxidized during cellular respiration. These fuel molecules, glucose, fatty acids, and amino acids, are broken down and fed into the Krebs cycle, becoming oxidized to acetyl coenzyme A (acetyl CoA) before entering the cycle. The Krebs cycle is part of the aerobic de…
Kuiper belt objects (KBOs) are chunks of rock, dust and ice found in the area of the solar system just beyond the orbit of Neptune, starting at about 30 astronomical units (AU) to about 50 AU. In 1992, astronomers proposed that there must be at least 70,000 of these objects with diameters larger than 60 mi (100 km). It is estimated that there are many more such bodies beyond 50 AU, but these are s…
Kuru, a disease once endemic to Papua New Guinea and now virtually extinct, is one of several types of diseases called spongiform encephalopathies, all thought to be caused by abnormal proteins called prions, which riddle the brain with holes. According to proponents of the prion hypothesis, these diseases can arise by direct infection with prions, by inheriting genes that produce faulty proteins,…
Lacewings are insects in the order Neuroptera, sub-order Planipennia. Lacewings are named after the fine, complex, cross-branched venation of their four wings, which presents a beautiful, lacelike pattern. Lacewings are rather poor, fluttery fliers. When at rest, they hold their wings tentlike over their back. Lacewings have a complete metamorphosis, with four life history stages: egg, larva, pupa…
The "hydroxy" portion of the name tells chemists that there is an alcohol (OH) group in the molecule, and the "alpha" part of the name means that the alcohol is attached to the carbon atom adjacent to the acid (COOH) group. The "prop" portion of the name indicates that there are three carbon atoms. Lactic acid can also be called 2-hydroxypropanoic aci…
Lagomorphs are herbivorous mammals such as rabbits, hares, and pikas, in the order Lagomorpha. Because they exploit similar ecological niches, lagomorphs and rodents (order Rodentia) are rather similar in many aspects of their morphology and behavior. However, these orders are also different in important respects, and each represents an ancient evolutionary lineage. One distinguishing feature of t…
Lakes are inland bodies of water—millions of which are scattered over the earth's surface. Lakes are classified on the basis of origin, age, salinity, fertility, and water circulation. Lakes can be formed by glaciers, tectonic plate movements, river and wind currents, and volcanic or meteorite activity. Lakes can also be a phase of evolution in the aging process of a bay or estuary. …
Chevalier de Lamarck was a French naturalist and invertebrate zoologist who lived from 1844-1829. He is best known for a theory of evolution developed in his book, Philosophie zoologique, published in 1809. This theory, known today as Lamarckism, is based on the socalled "inheritance of acquired traits," meaning that characteristics that an organism may develop during its lifetime ar…
Lampreys and hagfishes are unusual, jaw-less fish that comprise the order Cyclostomata, so named because of the circular shape of the mouth. The 41 species of lampreys are in the superfamily Petromyzontoidea, while the approximately 35 species of hagfishes and slime hags are in the superfamily Myxinoidea. Lampreys and hagfishes lack the scales typical of most fish, and are covered with a slimy muc…
Land and sea breezes are wind and weather phenomena associated with coastal areas. A land breeze is a breeze blowing from land out toward a body of water. A sea breeze is a wind blowing from the water onto the land. Land breezes and sea breezes arise because of differential heating between land and water surfaces. Land and sea breezes can extend inland up to 100 mi (161 km), or manifest as local p…
The term "sanitary landfill" was first used in the 1930s to refer to the compacting of solid waste materials. Initially adopted by New York City and Fresno, California, the sanitary landfill used heavy earth-moving equipment to compress waste materials and then cover them with soil. The practice of covering solid waste was evident in Greek civilization over 2,000 years ago, but the G…
A landform is a natural sculpture of the surface of the earth. Most landforms are produced by the actions of weathering and erosion, carving away material from higher elevations and depositing it down lower. Different kinds of rock erode at a variety of rates under particular climatic conditions. As softer rock is worn away the more resistant rock is exposed, producing another series of landforms.…
The Oxford English Dictionary defines landscape as both a verb and a noun, signifying not simply its multiple references in vernacular and specialized parlance or its active and passive modes but more importantly the varying perceptions of landscape as an artistic, cultural, and religious entity. Among the definitions of landscape as a noun, the OED proffers first "A picture representing na…
Estimates of the number of languages spoken on earth at the turn of the twenty-first century range between four and six thousand. Considering that this number has been rapidly declining for the last couple of centuries, there must at one time have been many more languages, perhaps upwards of ten thousand. Of the languages spoken in the twenty-first century, a few have tens or hundreds of millions …
Langurs belong to the primate family Cercopitecidae, of which 13 species are represented in the genus Semnopithecus. This represents one of the largest and most diverse groups of colobine monkeys in Asia, with most species restricted to the south and southeast. Many species are distinguished by their vocalizations and the color of their fur, which ranges from a silver-grey in the common or Hanuman…
Light plays a vital role in the life of all oceans. At the simplest level, it provides one of the basic requirements for photosynthesis and promotes development of a food chain. Some species of fish that live in the darker reaches of the oceans also rely on light for survival. Some of these species, such as lantern fish, have even developed their own artificial means of generating light. Lantern f…
Larks are 75 species of small, terrestrial songbirds that make up the family Alaudidae. Larks breed on all of the continents except Antarctica. Their usual habitats are all open areas and typically include prairies, savannas, alpine and arctic tundras, heathlands, and some types of agricultural fields. Larks have long, pointed wings, a notched tail, and rather long legs and toes, with the hind, ba…
Laryngitis is an inflammation of the larynx. Located at the upper end of the trachea, or windpipe, the larynx contains the vocal chords that are used to form sounds. Because the larynx plays such an important role in speech, it is sometimes called the "voice box." When the larynx becomes inflamed in laryngitis, it swells and reddens. The major symptom of laryngitis is hoarseness. Oth…