cell: Formation of the electron donors NADH and FADH2: …dinucleotide (FAD), yielding NADH and FADH2. It is the subsequent oxidation of these hydrogen acceptors that leads eventually to the production of ATP.

alcohol consumption: Processing in the liver: …NAD is thus changed to NADH and becomes available again for the same reaction only after its own further oxidation. While adequate ADH seems always present for the first step of alcohol metabolism, the temporary reduction of the available NAD apparently acts as a limit on the rate at which…

major industrial polymers: Nitrile rubber (nitrile-butadiene rubber, NBR): A hydrogenated version, abbreviated as HNBR, is also highly resistant to thermal and oxidative deterioration and remains flexible at lower temperatures.

hydrogenation, chemical reaction between molecular hydrogen and an element or compound, ordinarily in the presence of a catalyst. The reaction may be one in which hydrogen simply adds to a double or triple bond connecting two atoms in the structure of the molecule or one in which the addition of

hydrogenation: …up) of the molecule (called hydrogenolysis, or destructive hydrogenation). Typical hydrogenation reactions include the reaction of hydrogen and nitrogen to form ammonia and the reaction of hydrogen and carbon monoxide to form methanol or hydrocarbons, depending on the choice of catalyst.

hydrogenosome, membrane-bound organelle found in the cytoplasm of eukaryotic cells (cells with clearly defined nuclei) that is so named because it releases molecular hydrogen (H2) as a by-product of energy generation under anaerobic (oxygen-deficient) conditions. The term hydrogenosome was

Jean-Baptiste Lamarck: Professorship at the National Museum of Natural History: …publish under the title of Hydrogéologie (1802). In his physico-chemical writings, he advanced an old-fashioned, four-element theory that was self-consciously at odds with the revolutionary advances of the emerging pneumatic chemistry of Antoine-Laurent Lavoisier. His colleagues at the Institute of France (the successor to the Academy of Sciences) saw Lamarck’s…

hydrography, the art and science of compiling and producing charts, or maps, of water-covered areas of Earth’s surface. A brief treatment of hydrography follows. For full treatment, see map and surveying: Hydrography. The terms hydrography and hydrographer are based on an analogy with geography and

hydrography, the art and science of compiling and producing charts, or maps, of water-covered areas of Earth’s surface. A brief treatment of hydrography follows. For full treatment, see map and surveying: Hydrography. The terms hydrography and hydrographer are based on an analogy with geography and

bryophyte: Form and function: …cylinder of water-conducting cells (the hydroids) surrounded by layers of living cells (leptoids) that conduct the sugars and other organic substances manufactured by the gametophore. This conducting system is analogous to that of the vascular plants, except that it lacks lignin (a carbohydrate polymer), and it closely resembles that found…

hydroid, any member of the invertebrate class Hydrozoa (phylum Cnidaria). Most hydroids inhabit marine environments, but some have invaded freshwater habitats. Hydroids may be either solitary or colonial, and there are about 3,700 known species. Hydroids have three basic life-cycle stages: (1) a

cnidarian: Size range and diversity of structure: …phase in groups such as hydroids and hydrocorals. Hydromedusae are smaller and more delicate than scyphomedusae or cubomedusae; they may be completely absent from the life cycle of some hydrozoan species. Some other species produce medusae, but the medusae never separate themselves from the polyps. Cubozoans have medusae commonly known…

annelid: Annotated classification: Serpula, Hydroides. Order Archiannelida Minute, primitive, with ciliated epidermis; prostomium small, with or without appendages; parapodia absent; septa reduced or absent; size, minute. Contains 4 groups of poorly known species considered separate orders by some (Nerillida, Dinophilida,

ether: Cleavage: …give alkyl bromides or by hydroiodic acid (HI) to give alkyl iodides.

molecular cloud: Composition: …the interstellar molecule HNC (hydroisocyanic acid) and its isomer HCN (hydrocyanic acid); in ordinary terrestrial conditions there is plenty of energy to allow the nitrogen and carbon atoms in HNC to exchange positions and produce HCN, by far the preferred species for equilibrium chemistry. In the cold clouds, however,…

ship construction: …century, it was inevitable that hydrokinetics (the study of fluids in motion), hydrostatics (the study of fluids at rest), and the science of materials and structures should augment the shipbuilder’s skill. The consequence of this was a rapid increase in the size, speed, commercial value, and safety of ships.

permafrost: Pingos: A hydrolaccolith (water mound) forms and freezes, heaving the overlying frozen and unfrozen ground to produce a mound.

hydrolase, any one of a class of more than 200 enzymes that catalyze the hydrolysis of several types of compounds. Esterases include lipases, which break ester bonds (between a carboxylic acid and an alcohol) in lipids, and phosphatases, which act analogously upon phosphates; a narrower category

water cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle

hydrologic sciences, the fields of study concerned with the waters of Earth. Included are the sciences of hydrology, oceanography, limnology, and glaciology. In its widest sense, hydrology encompasses the study of the occurrence, movement, and physical and chemical characteristics of water in all

hydrological map, chart showing such hydrologic features as rivers and streams; the purpose and content of these maps vary according to the country of their origin. Some maps are used as supplements to a detailed written text, whereas others, such as the USGS Hydrologic Investigations Atlases

hydrology, scientific discipline concerned with the waters of the Earth, including their occurrence, distribution, and circulation via the hydrologic cycle and interactions with living things. It also deals with the chemical and physical properties of water in all its phases. A brief treatment of

chemical hydrology, subdivision of hydrology that deals with the chemical characteristics of the water on and beneath the surface of the Earth. Water in all forms and modes of occurrence is affected chemically by the materials with which it comes into contact. Often called the universal solvent,

hydrolysis, in chemistry and physiology, a double decomposition reaction with water as one of the reactants. Thus, if a compound is represented by the formula AB in which A and B are atoms or groups and water is represented by the formula HOH, the hydrolysis reaction may be represented by the

tannin: Hydrolyzable tannins (decomposable in water, with which they react to form other substances) yield various water-soluble products, such as gallic acid and protocatechuic acid and sugars. Gallotannin, or common tannic acid, is the best known of the hydrolyzable tannins. It is produced by extraction with…

soap and detergent: Continuous soapmaking—the hydrolyzer process: The boiling process is very time consuming; settling takes days. To produce soap in quantity, huge kettles must be used. For this reason, continuous soapmaking has largely replaced the old boiling process. Most continuous processes today employ fatty acids in the saponification reaction…

magnetohydrodynamics (MHD), the description of the behaviour of a plasma (q.v.), or, in general, any electrically conducting fluid in the presence of electric and magnetic fields. A plasma can be defined in terms of its constituents, using equations to describe the behaviour of the electrons, ions,

divination: Interpretive divination: Hydromancy (divination by water) is usually less dramatic, ranging from the reading of reflections in a shallow surface, in the manner of the crystal gazer, to construing the movements of floating objects, as in the reading of tea leaves.

Caudata: Annotated classification: …Desmognathus in North America and Hydromantes in western North America and the central Mediterranean region) and about 105 species. Family Proteidae (olms and mud puppies) The olm is blind, has little pigment, has an elongated body, and is cave-dwelling; mud puppies

fluid mechanics, science concerned with the response of fluids to forces exerted upon them. It is a branch of classical physics with applications of great importance in hydraulic and aeronautical engineering, chemical engineering, meteorology, and zoology. The most familiar fluid is of course

cnidarian: Size range and diversity of structure: Hydromedusae are smaller and more delicate than scyphomedusae or cubomedusae; they may be completely absent from the life cycle of some hydrozoan species. Some other species produce medusae, but the medusae never separate themselves from the polyps. Cubozoans have medusae commonly known as box jellyfish,…

mead: …grapevines do not flourish; the hydromel of the Greeks and Romans was probably like the mead drunk by the Celts and Anglo-Saxons, although the Roman mulsum, or mulse, was not mead but wine sweetened with honey. In Celtic and Anglo-Saxon literature, such as the writings of Taliesin and in the…

gastropod: Reproduction and life cycles: One pteropod, Hydromeles, has an internal brood chamber that apparently ruptures, freeing the young into the body cavity of the parent; the escape of the young may cause the parent’s death.

organometallic compound: Hydrometallation: The addition of a metal hydride to a multiple bond is called hydrometallation, and it leads to the formation of a metal-carbon bond. M―H + H2C=CH2 → MH2C―CH3 This reaction is driven mainly by the high C―H bond strength relative to most E―H bond…

hydrometallurgy, extraction of metal from ore by preparing an aqueous solution of a salt of the metal and recovering the metal from the solution. The operations usually involved are leaching, or dissolution of the metal or metal compound in water, commonly with additional agents; separation of the

hydrometeor, any water or ice particles that have formed in the atmosphere or at the Earth’s surface as a result of condensation or sublimation. Water or ice particles blown from the ground into the atmosphere are also classed as hydrometeors. Some well-known hydrometeors are clouds, fog, rain,

hydrometeorology, branch of meteorology that deals with problems involving the hydrologic cycle, the water budget, and the rainfall statistics of storms. The boundaries of hydrometeorology are not clear-cut, and the problems of the hydrometeorologist overlap with those of the climatologist, the

hydrometer, device for measuring some characteristics of a liquid, such as its density (weight per unit volume) or specific gravity (weight per unit volume compared with water). The device consists essentially of a weighted, sealed, long-necked glass bulb that is immersed in the liquid being

marsh treader, any insect of the family Hydrometridae (order Heteroptera), so named because of its slow, deliberate manner of moving as it walks along the surface of a pond or crawls among shore vegetation. Marsh treaders, worldwide in distribution, are usually found among the cattails in marshy

hydrous mica, any of the illite group of clay minerals, including illite, bramallite (a sodium illite), and glauconite. They are structurally related to the micas; glauconite is also a member of the common-mica group. The hydrous micas predominate in shales and mudstones, but they also occur in

tree: Tree roots: Hydrophytic trees have various modifications that facilitate their survival and growth in the aqueous environment. Some species produce a high frequency of lenticels on the bark that facilitate gas exchange. Others exhibit greater permeation of oxygen through the bark and into the cambium at lower…

water rat: Natural history: Water rats of the genus Hydromys live in the mountains and coastal lowlands of Australia, New Guinea, and some nearby islands. The earless water rat (Crossomys moncktoni) inhabits mountains of eastern New Guinea, where it prefers cold, fast-flowing streams bordered by tropical forest or grass. The African water rat is…

water rat: Natural history: The golden-bellied water rat (Hydromys chrysogaster) of Australia and New Guinea is the largest, with a body 20 to 39 cm long and a slightly shorter tail (20 to 33 cm). Living by freshwater lakes, estuaries, and rivers and in coastal mangrove swamps, it is tolerant…

renal system disease: Obstruction to the flow of urine: …leading to the condition called hydronephrosis, in which a greatly swollen sac is surrounded by a mere rind of atrophied renal tissue. A massive hydronephrosis, with negligible renal substance remaining, may suggest removal of the kidney.

acid–base reaction: The Brønsted–Lowry definition: The hydronium ion (H3O+), which is the hydrogen ion in aqueous solution, also belongs to this class. The charge of these ionic acids, of course, always must be balanced by ions of opposite charges, but these oppositely charged ions usually are irrelevant to the acid–base properties…

name: Categories of names: …names of bodies of water, hydronymy; and names of mountains, oronymy. Additional terms are not generally used (though one occasionally hears words like chrematonymy—names of things).

hydropathy, therapeutic system that professes to cure all disease with water, either by bathing in it or by drinking it. Although water therapy is currently used to treat certain ailments, its effectiveness is generally accepted to be limited. Most authorities agree that many disease and injury

opal: …extremely porous variety, known as hydrophane, can absorb surprising quantities of water; it is almost opaque when dry but nearly transparent when saturated. Light-coloured stones are often dyed to resemble rarer, more deeply coloured varieties.

jacana: …eastern Australian coast; and the pheasant-tailed jacana (Hydrophasianus chirurgus), of India and the Philippines, a handsome black, yellow, and white bird that acquires long tail feathers in breeding season.

sea snake: …two independently evolved groups: the true sea snakes (subfamily Hydrophiinae), which are related to Australian terrestrial elapids, and the sea kraits (subfamily Laticaudinae), which are related to the Asian cobras. Although their venom is the most potent of all snakes, human fatalities are rare because sea snakes are not aggressive,…

alcohol: Physical properties of alcohols: …is referred to as a hydrophilic (“water-loving”) group, because it forms hydrogen bonds with water and enhances the solubility of an alcohol in water. Methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol are all miscible with water. Alcohols with higher molecular weights tend to be less water-soluble, because the…

water scavenger beetle, any of the approximately 3,200 species of the predominately aquatic insect superfamily Hydrophiloidea (order Coleoptera). These beetles are found swimming in marshy freshwater ponds throughout the world, especially in warm regions. Water scavenger beetles have smooth, oval,

Ceratophyllales: …unusual in that they have underwater pollination. When the male flowers are mature, the individual anthers break off and settle through the water until they reach a groove near the stigma of a female flower, leading to pollination.

sea snake: >Hydrophis specializes in burrowing eels.

sea snake: …a 2019 study of the blue-banded sea snake (or annulated sea snake, Hydrophis cyanocinctus) found a highly vascularized area between the snout and the top of the head, which allows oxygen to be transported directly from the water to the snake’s brain. Sea snakes give birth in the ocean to…

rabies, acute, ordinarily fatal, viral disease of the central nervous system that is usually spread among domestic dogs and wild carnivorous animals by a bite. All warm-blooded animals, including humans, are susceptible to rabies infection. The virus, a rhabdovirus, is often present in the salivary

skunk: Spotted skunks (genus Spilogale) live from southwestern Canada to Costa Rica. Except for a white spot between the eyes, their spots are actually a series of interrupted stripes running down their back and sides. The spotted skunks are the smallest skunks, about the size of…

cement: Types of portland cement: Hydrophobic cement is obtained by grinding portland cement clinker with a film-forming substance such as oleic acid in order to reduce the rate of deterioration when the cement is stored under unfavourable conditions.

alcohol: Physical properties of alcohols: …of the molecule, which is hydrophobic (“water-hating”), is larger with increased molecular weight. Because they are strongly polar, alcohols are better solvents than hydrocarbons for ionic compounds and other polar substances.

hydrophone, device for converting sound waves into electrical signals, similar in operation to a microphone but used primarily for detecting sound waves from an underwater source, such as a submarine. Usually an array of hydrophones is employed to pinpoint the source: the array is connected to an

undersea exploration: Collection of biological samples: …include the submarine photometer, the hydrophotometer, and the Secchi disk. The submarine photometer records directly to depths of about 150 metres the infrared, visible, and ultraviolet portions of the spectrum. The hydrophotometer has a self-contained light source that allows greater latitude in observation because it can be used at any…

Boraginaceae: The other group is Hydrophylloideae (formerly Hydrophyllaceae, or the waterleaf family), which includes Phacelia (150 species), Hydrophyllum, and Wigandia. They differ from other borages primarily in their parietal placentation and more numerous seeds.

Boraginaceae: The other group is Hydrophylloideae (formerly Hydrophyllaceae, or the waterleaf family), which includes Phacelia (150 species), Hydrophyllum, and Wigandia. They differ from other borages primarily in their parietal placentation and more numerous seeds.

waterleaf, any of about eight species of herbaceous plants constituting a genus (Hydrophyllum) in the borage family (Boraginaceae) and native to damp woodlands of North America. Light-greenish mottling on the leaves, suggesting watermarks on paper, gives the genus its name. Notable members of the

waterleaf: The broad-leaved waterleaf (H. canadense), also 60 cm tall, has maplelike leaves. Some species are used in wildflower gardens; they are valued for their attractive leaves and clusters of small white to purplish flowers with stamens that extend beyond the petals.

waterleaf: The large-leaved waterleaf (H. macrophyllum) is similar to the Virginia waterleaf but is rough and hairy and about 60 cm tall. The broad-leaved waterleaf (H. canadense), also 60 cm tall, has maplelike leaves. Some species are used in wildflower gardens; they are valued for their attractive…

waterleaf: 5-foot-) tall Virginia waterleaf (Hydrophyllum virginianum), with five- to seven-lobed leaves; it is also called Shawnee salad and John’s cabbage in reference to the edible tender young shoots. The large-leaved waterleaf (H. macrophyllum) is similar to the Virginia waterleaf but is rough and hairy and about 60…

tree: Tree roots: Hydrophytic trees have various modifications that facilitate their survival and growth in the aqueous environment. Some species produce a high frequency of lenticels on the bark that facilitate gas exchange. Others exhibit greater permeation of oxygen through the bark and into the cambium at lower…

Gold Cup: …boats since 1911 have been hydroplanes, usually of unlimited engine displacement. The Gold Cup is one of a series of unlimited hydroplane races sponsored annually by the American Power Boat Association and culminating with the award of a national championship.

Citation: Breeding and early years: In 1941 Wright purchased Hydroplane II from Britain and had her shipped to America via the Pacific Ocean to avoid the Atlantic conflicts of World War II. Her first two foals proved rather ordinary, but on April 11, 1945, out of a mating with Bull Lea, she dropped her…

hydroponics, the cultivation of plants in nutrient-enriched water, with or without the mechanical support of an inert medium such as sand, gravel, or perlite. Plants have long been grown with their roots immersed in solutions of water and fertilizer for scientific studies of their nutrition. Early

Chinese water deer, (Hydropotes inermis), very small Asian deer of the family Cervidae (order Artiodactyla), native to fertile river bottoms in Korea and the Yangtze River (Chang Jiang) valley in China. It is the only species of deer in which males lack antlers; instead, they are armed with long,

hydroelectric power, electricity produced from generators driven by turbines that convert the potential energy of falling or fast-flowing water into mechanical energy. In the early 21st century, hydroelectric power was the most widely utilized form of renewable energy; in 2019 it accounted for more

edema, in medicine, an abnormal accumulation of watery fluid in the intercellular spaces of connective tissue. Edematous tissues are swollen and, when punctured, secrete a thin incoagulable fluid. This fluid is essentially an ultrafiltrate of serum but also contains small amounts of protein. Minor

erythroblastosis fetalis: Hydrops fetalis, which is characterized by extreme edema (abnormal accumulation of serous fluid) and congestive heart failure, is the most severe form of the disease in newborns. Usually the infant dies, unless an exchange transfusion in which the Rh-positive blood of the infant is replaced…

caddisfly: General features: …family (Hydroptilidae), commonly known as microcaddis, are only 1.5 millimetres in length, with anterior wings of 2 to 5 millimetres. Caddisfly wings either are covered with hairs or have hairs on the veins. The posterior wings are often broader than the anterior wings.

hydroquinone, colourless, crystalline organic compound formed by chemical reduction of benzoquinone. See

coleopteran: Annotated classification: Family Hydroscaphidae (skiff beetles) Size about 1.5 mm; found in algae on rocks in streams; sometimes placed in Staphylinoidea; generic example Hydroscapha; widely distributed. Family Lepiceridae (toadlet beetles) A few Central American species. Family Sphaeriusidae (

organometallic compound: Hydrometallation: …hydrometallation reactions are hydroboration and hydrosilation, illustrated, respectively, by the following examples.

animal: Types of skeletons and their distribution: Hydrostatic skeletons are the most prevalent skeletal system used by animals for movement and support. A minimal hydroskeleton resembles a closed container. The walls are two layers of muscles (antagonists) oriented at right angles to one another; the inside contains an incompressible fluid or gel.…

petroleum refining: Topping and hydroskimming refineries: …results in a more flexible hydroskimming refinery, which can also produce desulfurized distillate fuels and high-octane gasoline. Still, these refineries may produce up to half of their output as residual fuel oil, and they face increasing economic hardship as the demand for high-sulfur fuel oils declines.

sol: …colloid may be called a hydrosol; and if air, an aerosol. Lyophobic (Greek: “liquid-hating”) sols are characterized by particles that are not strongly attracted to molecules of the dispersion medium and that are relatively easily coagulated and precipitated. Lyophilic (“liquid-loving”) sols are more stable and more closely resemble true solutions.…

hydrosphere, discontinuous layer of water at or near Earth’s surface. It includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour. Water is the most abundant substance at the surface of Earth. About 1.4 billion cubic km (326 million cubic miles)

Hydrostachyaceae, plant family in the order Cornales, composed of a single genus (Hydrostachys) of some 20 species. Most members of the family are aquatic herbs native to central and southern Africa and Madagascar. The leaves form rosettes that can be highly divided and usually have small scaly or

Hydrostachyaceae: …of a single genus (Hydrostachys) of some 20 species. Most members of the family are aquatic herbs native to central and southern Africa and Madagascar. The leaves form rosettes that can be highly divided and usually have small scaly or fringed appendages. The unisexual flowers are very small and…

climate: Characteristics: The atmosphere is mainly in hydrostatic balance, or equilibrium, between the upward-directed pressure gradient force and the downward-directed force of gravity. This circumstance is expressed in the following relationship: ∂p/∂z = –ρg (1) where ∂p/∂z is the partial derivative of p with respect to z, p is the pressure, z…

human ear: Detection of angular acceleration: dynamic equilibrium: …Friedrich Goltz formulated the “hydrostatic concept” in 1870 to explain the working of the semicircular canals. He postulated that the canals are stimulated by the weight of the fluid they contain, the pressure it exerts varying with the head position. In 1873 Austrian scientists Ernst Mach and Josef Breuer…

ocean current: Pressure gradients: This is called the hydrostatic equation, which is a good approximation for the equation of motion for forces acting along the vertical. Horizontal differences in density (due to variations of temperature and salinity) measured along a specific depth cause the hydrostatic pressure to vary along a horizontal plane or…

bearing: …this is known as a hydrostatic film.

fluid mechanics: Basic properties of fluids: …arises when adjacent layers of fluid slip over one another. It follows that the shear stresses are everywhere zero in a fluid at rest and in equilibrium, and from this it follows that the pressure (that is, force per unit area) acting perpendicular to all planes in the fluid is…

animal: Types of skeletons and their distribution: Hydrostatic skeletons are the most prevalent skeletal system used by animals for movement and support. A minimal hydroskeleton resembles a closed container. The walls are two layers of muscles (antagonists) oriented at right angles to one another; the inside contains an incompressible fluid or gel.…

hydrostatics, Branch of physics that deals with the characteristics of fluids at rest, particularly with the pressure in a fluid or exerted by a fluid (gas or liquid) on an immersed body. In applications, the principles of hydrostatics are used for problems relating to pressure in deep water

chemical compound: Acids: …water are called hydrocyanic and hydrosulfuric acids, respectively.

hydrotherapy, external use of water in the medical treatment of disease and injury. Its primary value is as a medium for application or reduction of heat. Wet heat helps relieve pain and improves circulation; it also promotes relaxation and rest and, in some mental disturbances, may be used to calm

metamorphism: …than one metamorphic event; and hydrothermal metamorphism, the changes that occur in the presence of water at high temperature and pressure which affect the resulting mineralogy and rate of reaction.

hydrothermal mineral deposit, any concentration of metallic minerals formed by the precipitation of solids from hot mineral-laden water (hydrothermal solution). The solutions are thought to arise in most cases from the action of deeply circulating water heated by magma. Other sources of heating

hydrothermal mineral deposit, any concentration of metallic minerals formed by the precipitation of solids from hot mineral-laden water (hydrothermal solution). The solutions are thought to arise in most cases from the action of deeply circulating water heated by magma. Other sources of heating

mineral deposit: Hydrothermal solution: Hydrothermal mineral deposits are those in which hot water serves as a concentrating, transporting, and depositing agent. They are the most numerous of all classes of deposit.

deep-sea vent, hydrothermal (hot-water) vent formed on the ocean floor when seawater circulates through hot volcanic rocks, often located where new oceanic crust is being formed. Vents also occur on submarine volcanoes. In either case, the hot solution emerging into cold seawater precipitates

fungus: Basic features of lichens: …frequent rainfall; two foliose lichens, Hydrothyria venosa and Dermatocarpon fluviatile, grow on rocks in freshwater streams of North America. Fruticose (stalked) thalli and filamentous forms prefer to utilize water in vapour form and are prevalent in humid, foggy areas such as seacoasts and mountainous regions of the tropics.