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Transport

Transport

Transport is the controlled movement of substances from one part of a cell to another, or from one side of a cell membrane to the other. Because each cell must maintain an internal environment different from the external environment, it must regulate the movement of ions, proteins, toxins, and other molecules both across the cell membrane and within its cytoplasm . This control over its molecular environment may be accomplished through a variety of measures, one of which is the establishment of a barrier membrane between the cell and the external world.

One such barrier, the bilipid membrane of a cell, is composed of two hydrophilic, or water-soluble, sheets of molecules separated by an intervening hydrophobic, also called oily or fatty, region. This property results from the structure of the phospholipid molecule composing the membrane: a polar, hydrophilic head region, and a nonpolar, hydrophobic tail region. The two layers of membrane are oriented so that the hydrophilic heads face the internal and external cell, and the fatty tails are positioned between the two head layers.

The structure of this membrane assures that any polar, water-soluble, molecules in the hydrophilic extracellular space will be unable to pass through the nonpolar, fatty, region within the membrane. If this barrier were completely impermeable, however, the cell would never be able to absorb nutrients or rid itself of wastes, let alone communicate with other cells. Thus the membrane is compromised by proteins that extend through both sides of the bilipid membrane. These proteins provide a watery pore region that connects the extracellular with the intracellular space, thereby allowing hydrophilic molecules to pass through.

There is a wide variety of membrane proteins, some of which are located within the outer cellular membrane, and some of which are imbedded in intracellular organelles . In addition to transport across membranes, substances must be transferred from one part of the cell to another, especially in very large cells and in single-celled organisms.

Osmosis

The simplest kind of cellular transport is osmosis . Osmosis is the passage of water molecules through a semipermeable membrane from a wet environment (a region of high water concentration), to a dry environment (a region of low water concentration). The defining characteristic of a wet environment is a low concentration of dissolved solute in the water. A dry environment has a high concentration of solute. Cells store a high concentration of proteins and other molecules within the membrane. If a cell were removed from biological conditions and placed in distilled water (water containing no dissolved substances), the small water molecules would rush through the bilipid membrane into the relatively dry interior of the cell. The membrane would expand with the increased water intake until the cell exploded.

This scenario does not normally occur in nature for two reasons. First, organisms balance their internal osmolarity. Internal osmolarity is the ratio of dissolved substance concentration between the inside and the outside of the cell. This balance is accomplished by maintaining a concentration of many small ions and molecules in the extracellular space, the areas between cells within an organism. Second, cells store many of their proteins within vesicles, within membranes, and inside organelles; this decreases the apparent concentration of free-floating soluble molecules.

Diffusion

The opposite of osmosis is diffusion, which means the passage of molecules from a region in which they are highly to a region in which they have a low concentration. This only occurs when the molecule has a concentration gradient, meaning that it exists in larger numbers per unit area in one location and in smaller numbers per unit area in an adjacent location. If a high concentration gradient is established, it means that the difference in concentration between two adjacent locations is great. In the case of a cellular membrane, this means that a certain substance is at very high concentrations on one side of the membrane and very low concentrations on the other side. The larger the concentration gradient, the stronger the driving force that powers the diffusion of molecules down the gradient. Whereas osmosis explains the movement of water molecules, diffusion explains the movement of other molecules within a liquid.

Passive Transport

For passive transport, no additional energy is needed to transfer molecules across the membrane. Instead, the concentration gradient of that molecule provides a driving force from high to low concentration, pushing the molecule across the membrane. This process is also known as facilitated diffusion because the membrane protein facilitates the natural diffusion tendency of the molecule by providing safe passage across the hydrophobic region of the lipid bilayer. Many sugars and amino acids are transported from the gut into the cells lining the gut through this mechanism.

When the protein forming the pore is constantly open to diffusable molecules, it is called a channel. The size of the pore, and any hydrophilic regions within the pore, can selectively allow certain molecules to pass while barring others. A uniport protein must first bind a molecule and then undergo a conformational change (a change in the shape of the protein) before it releases the molecule on the opposite side of the membrane.

One example of a passive transport mechanism is the gap junction. This is a molecular conduit between two cells formed by a hexagonal array of rigid proteins that leaves a permanent pore open between two cells' cytoplasms. This opening allows inorganic ions and very small hydrophilic molecules to pass directly between cells. Gap junctions are particularly useful in heart muscle cells because they allow ions carrying electrical charge to flow directly from cell to cell, thereby inducing the smooth muscle fibers to contract in a coordinated motion. This simple method of communication makes it unnecessary for neuronal connections at each and every heart muscle cell to induce contraction at exactly the right time for a smooth muscle heartbeat. If gap junctions were blocked, heart muscle cells would contract at the incorrect time, or not at all, resulting in irregular or weak heartbeats, or even heart seizure, and death.

Active Transport

Active transport requires that energy be expended to bring a molecule across the membrane. Most often active transport is used when the molecule is to be transferred against its concentration gradient. However, occasionally the target molecule is carried along its concentration gradient, when the gradient is not strong enough to ensure a sufficiently quick flow of molecules across the membrane. For uncoupled active transport, ATP (adenosine triphosphate ) in the cell's cytoplasm binds to the carrier protein at the same time as the targeted molecule binds. ATP is a cellular molecule that contains a great deal of energy in its molecular bonds. The carrier protein breaks a phosphate off the ATP and uses the energy released from the broken bond to undergo a conformational change that carries the targeted molecule to the other side of the membrane.

One example of active transport is the sodium/potassium ATPase pump, by which sodium is transferred out of a neuron while potassium is transferred into a neuron, both counter to their individual concentration gradients. This is essential for maintaining electrically active nerve cells because it helps to establish a concentration gradient and electrical gradient across the cell membrane. When the cell is active, sodium and potassium are allowed to flow down their electrochemical gradients, whereas during periods of inactivity the sodium/potassium pump restores the resting state polarization of the cell.

There are two kinds of coupled active transport. Symport uses the concentration gradient of one molecule to help transport another molecule. Symport membrane proteins have two binding sites on the same side of the membrane. The targeted molecule binds at one site, and a coactivating molecule with a high concentration gradient favoring movement across the membrane binds at the other site. The driving force of the coactivating molecule causes a conformational change in the membrane protein, which transports both molecules across the membrane in the same direction. The other type of coupled transport is antiport, by which the coactivating molecule and the targeted molecule bind at sites on different sides of the membrane bilayer. The concentration gradient of the coactivating molecule still provides the energy for the conformational change, but in this case, the molecules are transported simultaneously in opposing directions across the membrane. Symport and antiport systems are also called carrier-assisted transport, because energy from the coactivator helps to carry the target molecule in an energetically unfavorable direction.

The most common method for cells to transfer very large molecules across the membrane is through the intermediary of a vesicle. Vesicles are small spheres of membrane that contain large molecules, toxins, nutrients, or signaling molecules. Proteins that are created in the endoplasmic reticulum can be packaged in vesicles in the golgi apparatus. Similarly, vesicles may contain transporter proteins similar to those located in the external cellular membrane, so that they can bring in certain cytoplasmic proteins. Vesicles called lysosomes process and sequester harmful metabolic side-products so that they do not do damage to organelles in the cytoplasm.

In each of these cases, vesicles are transported to the outer cell membrane, a process known as exocytosis. The vesicles travel along a system of structural proteins called microtubules with the help of an associated motor protein called kinesin. Kinesin molecules "grab" vesicles with their globular head region and then take turns binding to the microtubules, so that the net result is that of a cartwheeling vesicle moving in one direction. Some proteins can be transported by binding directly to microtubules and slowly "riding" them as they slide toward the membrane. When it arrives, the vesicle lipid bilayer fuses with that of the outer cell membrane, so that the internal contents of the vesicle are released into the extracellular space. In endocytosis, the mechanism is reversed. Pockets of cell membrane that have bound a particular molecule dimple inwards toward the cell cytoplasm forming a deep pit, and then pinch off so that a vesicle forms on the intracellular side. Phagocytosis refers to the consumption of small cells or cell-pieces by larger cells by surrounding and engulfing them.

Rebecca M. Steinberg

Bibliography

Agutter, Paul S. Between Nucleus and Cytoplasm. London and New York: Chapman and Hall, 1991.

Weiss, Thomas Fischer. Cellular Biophysics. vol. 1: Transport. Cambridge, MA: MIT Press, 1996.

Wilson, G. Exploitation of Membrane Receptors and Intracellular Transport Pathways. New York: Elsevier Science Publishers, 1989.

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Transport

TRANSPORT

Ships, caravans, railroads, and pipelines carry Middle Eastern goods to market.

Until the twentieth century, and in many places until the middle of that century, people, animals, and water were the primary modes of transport in the Middle East.


Shipping

Waterways are few and not always navigable, but coastal navigation has always been important. Of the various river systems, only two were navigablethe Nile and the Tigris and Euphrates system. All were used for irrigation as well as transport, and canal systems were built to extend their benefits. The Nile runs north through East Africa, emptying across a broad delta into the eastern Mediterranean Sea. The longest river in the world, it flows from Lake Victoria through Uganda, Sudan, and Egypt. Since the prevailing winds are northerly, boats without motors can sail upstream and float downstream. The Tigris and Euphrates rivers are less suited to navigation, since their currents are swifter, their levels vary, and they often change course before merging into the Shatt al-Arab, which drains into the Persian Gulf. Because of these means of access to the sea, both areas have long transported bulk goods by water and built seaports that accommodated goods from other coastal trading areas, such as Turkey and Syria. Since antiquity, the coastal people of the Mediterranean have traded, traveled, and warred among themselves over the riches of one another's lands.


Caravans

For the local movement of goods to rivers or seaports, and even for long-distance overland journeys, caravans were relied on. Caravans of mules and, especially, camels, took over from wheeled traffic at the end of the Roman era. Camel loads varied, generally ranging from 550 to 660 pounds; the speed of a caravan was 2.5 to 3 miles per hour; the usual daily stage was 15 to 20 miles. Caravans differed greatly in size, depending on need and the availability of people and animals: In 1820, before the Suez Canal was built, the Suez caravan had about 500 camels; in 1847, the BaghdadDamascus caravan had some 1,500 to 2,000 camels; and the DamascusBaghdad caravan, some 800 to 1,200. During the 1870s, some 15,000 pack animals made three round trips a year on the TabrizTrabzon route (Iran to Turkey), carrying the equivalent of the contents of seven or eight sailing ships each way. Boats and pack animals were adequate for the
relatively small volume of traffic under traditional conditions before the advent of the industrial revolution and the expansion of European trade and imperialism into the Middle East.


Steamships

During the nineteenth century, transport was revolutionized. During the 1820s and 1830s, regular steamer lines linked the Middle East with Europe across the Mediterranean, with Russia and Austria across the Black Sea, and with India through the Red Sea. Later, services were established in the Caspian Sea and the gulf. By the closing decades of that century, the bulk of the region's foreign trade was carried on steamships, and freight costs were drastically reduced. Starting in the 1830s, steam tugs and steamboats were used on the Nile and on the Euphrates, soon carrying a large portion of domestic trade. Since no port improvements had occurred since Roman times, the steamers were loaded and unloaded by lighters, which were boats used to carry cargo from ships to ports. The first modern port facilities were installed in Alexandria in 1818 (followed by later improvements), at Suez in 1866, in İzmir in 1875, in Aden in 1888, in Beirut in 1895, and in Istanbul in 1902. Except for Alexandria and Suez, all these harbors were built with European capital. The opening of the Suez Canal in 1869 by a French company was a major advance for world navigation.


Railroads

The first railway in the Middle East was begun in 1851, at British insistence, to link Alexandria with Cairo and Suez, speeding transport on the MediterraneanIndia route. Like all Egypt's main lines, it was financed by the government. Soon after, British capital built two lines from İzmir in Turkey to the countryside. The Ottoman Empire, however, wanted a railroad that linked Istanbul with their provinces of Anatolia, Syria, and Iraq; following the completion of the ViennaIstanbul line in 1888 (which became the Orient Express), it gave a concession to a German company for an IstanbulAnkara line, later extended to Basra. This BerlinBaghdad Railway aroused much international controversy, which was settled just before the outbreak of World War I. When the war ended in 1918, the line reached Aleppo in northern Syria, and a small stretch had been built in Iraq. Other foreign-owned short lines were built in Palestine, Lebanon, and Syria. The Hijaz Railroad (19031908), linking Damascus, in Syria, to Medina, in western Saudi Arabia (near Mecca), was financed by contributions from Muslims throughout the world. During World War I, the British army built extensive rail lines in Iraq and Palestine and put the Arabian section of the Hijaz railroad out of service. In Iran, the Russians built a line to Tabriz. After the war, Turkey doubled its mileage and Iran built a railroad between the Caspian Sea and the Persian Gulf. Since then, important lines have been built in Iran, Saudi Arabia, and Syria. Table 1 shows the length of rail lines built from 1870 to 2000. Rail service reduced both the time and costs of transport. On the AnkaraIstanbul route, the rate per ton-mile fell from 10 cents to 1 cent; on the DamascusBeirut line, from 4.5 cents to 1.5 cents; the journey from Damascus to Cairo was reduced from 25 days to 18 hours. In some areas, telegraph lines accompanied or preceded the railroads.

Length of rail service (in kilometers)
country 1870 1890 1914 1939 1948 1975 2000
SOURCE: the international year book and statesmen's who's who, 2003. east grinstead, u.k.: csa, 2002. africa south of the sahara, 2003.
london: europa publications, 2002. the middle east and north africa, 2003. london: europa publications, 2002. statistical yearbook 1999.
new york: united nations, 2002.
table by ggs information services, the gale group.
egypt 1,400 1,797 4,314 5,606 6,092 4,856 8,600
iran 1,700 3,180 4,944 6,600
iraq 132 1,304 1,555 2,203 2,000
jordan 332 332 420 700
lebanon 232 423 417 200
palestine/israel (as of 1948) 1,188 1,225 902 n.d
saudi arabia 800 612 700
sudan 2,396 3,206 3,242 4,556 5,000
syria 854 867 1,761 2,400
turkey 230 1,443 3,400 7,324 7,634 8,138 10,300
total 1,630 3,240 11,042 21,746 24,550 28,809 36,500
Modern means of transport, as of 2003
  paved roads (thousands of km) passenger motor vehicles (thousands) commercial motor vehicles (thousands) ships (thousands of grt/tons)* airlines (millions of passenger/km)
* grt is gross registered tons
note: the dates for the figures in this table range from 1993 to 2001. n.d. = no data available.
source: The International Year Book and Statesmen's Who's Who, 2003. East Grinstead, U.K.: CSA, 2002. Africa South of the Sahara, 2003.
London: Europa Publications, 2002. The Middle East and North Africa, 2003. London: Europa Publications, 2002. Statistical Yearbook 1999.
New York: United Nations, 2002.
table by ggs information services, the gale group.
egypt 39.0 1,154 554 1,350 8,036
iran 93.5 1,793 235 3,943 8,539
iraq 39.9 773 323 240 20
israel 16.5 1,460 371 611 12,418
jordan 5.5 245 112 42 4,065
kuwait 3.8 747 140 2,291 6,207
lebanon 6.2 1,299 92 301 1,504
saudi arabia 47.3 2,762 2,340 1,133 18,820
sudan 3.9 285 53 43 148
syria 43.3 138 322 498 1,410
turkey 62.6 4,539 1,590 5,896 n.d.
united arab emirates 3.3 346 89 746 15,633



Modern Services

From the mid-1900s on, the Middle East has been served by an extensive network of telegraph and telephone lines, which extend to all cities and towns, and to almost all villages. Computer, electronic mail, and Internet and fax services exist in main centers as well.


Modern roadways were first built during the late nineteenth century; except for those in northern Iran and Lebanon, they played no significant role in the transport system of the period. After World War I, and then again after World War II, they were greatly expanded and improved. Motor vehicles, which came to the Middle East before World War I, carry the bulk of inland transport. Air transport has a similar history: every country has its own airline and the region has become a hub of air traffic, connecting North America and Europe with Africa, India, and Asia.


Because of the Suez Canal, the Middle East plays an important part in world navigation. Just before Egypt nationalized the canal in 1956, it carried 13 percent of world shipping but 20 percent of oil tankers. The canal has been repeatedly enlarged and deepened to accommodate increasingly larger tankers and supertankers. During the 1990s, most petroleum producers maintained a large fleet of tankers, and oil-refining and consumer nations had sizeable merchant and tanker fleets; still, the share of the Middle East in world shipping was only 1 percent, and its share in world tankers only 3 percent. Nationalization of all transport facilities has been a fact of Middle Eastern life, beginning with Turkey's railways during the 1920s.

Oil has brought another form of transport to the region: pipelines. The first, opened in 1934, carried Iraq's oil to the Mediterranean. Since then, far longer and larger pipelines have been built to transport Saudi Arabian and Iraqi oil through Syria to the Mediterranean, as well as Iraqi oil through Turkey and Saudi Arabia. Many pipelines no longer operate due to various political conflicts. Oil-producing countries also have extensive networks of internal pipelines that transport crude petroleum to refineries.

see also berlinbaghdad railway; hijaz railroad; persian (arabian) gulf; shatt al-arab.


Bibliography

American Automobile Manufacturers Association. World Motor Vehicles Data. Detroit, 1989.

Earle, Edward. Turkey, the Great Powers, and the Bagdad Railway: A Study in Imperialism. New York: Macmillan, 1923.

International Air Transport Association. World Air Transport Statistics. Montréal: Author, 1991.

Issawi, Charles. An Economic History of the Middle East and North Africa. New York: Columbia University Press, 1982.

Kark, Ruth. "The Pilgrimage to Budding Tourism: The Role of Thomas Cook in the Rediscovery of the Holy Land." Travellers in the Levant: Voyagers and Visionaries, edited by Sarah Searight and Malcolm Wagstaff. Durham, U.K.: Astene, 2001.

charles issawi
updated by anthony b. toth

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transport

transport was critical to the evolution of the nation state, and explains some of Britain's historical differences from its European neighbours. It helped to determine the early success of England as a political entity, its patterns of social and geographical mobility, and the close economic integration that helped to make Britain the first ‘industrial nation’.

Post-Roman Britain lacked a single capital, and its transport system was diffuse, focused on the port, market, church, and seigneurial hall in a plurality of political and economic zones. In England, the gradual emergence of London as capital city in the 13th and 14th cents. re-established the hub of a transport system, and the crown, the law, the court, the Exchequer, and associated institutions created a powerful centripetal influence, never replicated in Scotland or Wales. London's influence on Britain's transport grew thereafter, through its disproportionate demand for provisions and its dominance in international trade. Its function as central location for services, and for craft and business training, meant that by 1700 perhaps a quarter of England's population had experienced life in the capital. turnpikes reinforced this focus, but after 1750 canals and railways also reflected other urban demands, and created a transport system profiled as a St Andrew's cross, centred on the midlands, and framed by coastal shipping, and the Edinburgh–Glasgow route. The decline of traditional industries in the 20th cent., with the growth of air travel, and the rise of services and big government, increasingly restored London as the sole hub of British transport.

Transport influenced perceptions of distance and time, and through this the sense of place. In the horse-drawn world before 1770, market and county town were objects of weekly and seasonal travel, the capital a place for temporary or life-cycle migration; a century later, London and Edinburgh were accessible to overnight visitors from most parts of England and Scotland; by the 1980s London's rail commuting zone, bounded by the 100-minute journey, enveloped Bristol (122 miles distant), Birmingham (105), Norwich (114), and Doncaster (159), radically ‘reshaping’ the country. The railways also unified Britain into a single time zone in the 1850s, and the telegraph's instantaneous communication transformed the transmission of news beyond that of the fastest post or courier. With such transport change, and the induced shift in the perception of this island, the linguistic confusion of ‘county’ and ‘country’, so common before 1700, declined and disappeared.

The transport of information interacted with that of goods, and thus personal experiences of scarcity or plenty, and local and regional autonomy in the supply of food or fuel. The provisioning of medieval London, in 1400 around 4 per cent of the nation, was a complex transport problem demanding the integration of carts, river vessels, and coasters, which increased as that proportion rose to 11 per cent in 1700. Londoners dined on the meat of the Highland and Welsh cattle that had walked in droves south; on Dales sheep and Norfolk turkeys and geese also driven overland; on Thames-borne cheese, treated generically as ‘Double Gloucester’; with Fulham or Putney vegetables, sustained by the reciprocating transport of manure; and washed them down with London porter, brewed from the dark malts shipped down the River Lea. Each shift in transport dislocated the equilibrium of supplies, and induced hostility from the threatened or the dispossessed: from the early modern grain wagon attacked by villagers as the proximate cause of their hunger, to Newcastle upon Tyne's vehement opposition to the navigation of Sunderland's river Wear, to those who mobbed James Brindley or George Stephenson as they came to survey their parish for canal or railway, and to the modern road ‘nimby’, transport has been keenly political, carrying high economic stakes. Britain's relatively small size and favourable endowment with water transport permitted its pre-railway transport systems to induce intense regional specialization, urbanization, and the economic growth of the first ‘industrial revolution’, where other nations attained merely developed industrial regions without complete social transformation.

Transport too provided for personal travel long before the coming of modern systems. The great pilgrimages developing from the 14th cent., to Canterbury, Walsingham, or even Compostella, crowded the roads and led to the creation of commercial inns. Medieval law implied a fifteen-mile round trip for market day, a near-universal transport experience, and marriage horizons commonly extended beyond the parish boundary, with courtship energetically pursued by foot or horse.

The cheapening effect of successive transport innovations has democratized travel over the very long term, especially train, bus, and motor car, but we must not allow suburban prejudices to blind us to the extent to which their impact was creative. Neither have six centuries of transport change, mass urbanization through migration, and industrialization been sufficient wholly to dissociate surnames from the pays from which they stemmed. By the mid-19th cent. Britain had the transport almost perfectly to integrate its political, economic, urban, and social systems, and yet preserved specificity of place and voice long afterwards. Transport must therefore be seen as a critical contributory factor in the historical process, not a dominant determinant.

J. A. Chartres

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transport

transport In a physiological sense transport generally means the movement of substances across the membranes of cells. This is an important process as, without transport, products of digestion would be unable to move from the alimentary tract into the body. Clearly the bounding membranes of cells cannot be generally permeable to all bodily substances, otherwise important cellular components would be able to leak out. Some substances, such as weak acids or bases in their undissociated form, are soluble in lipids and will dissolve in the lipid bilayer of the cell membrane. Later the substances may dissociate from the membrane, but statistically more molecules will move by diffusion across the cell membrane from a high concentration to a lower one, than in the reverse direction. This process is known as non-ionic diffusion. However many important substances, such as sugars, amino acids, and ions, are completely insoluble in cell membranes, and cross them by specialized processes. Many cell membranes contain a number of specialized molecules which combine specifically with one of the substances to be transported. Such a molecule is called a carrier, and the complex resulting from the combination can cross the membrane and release the substrate. As with non-ionic diffusion, more carrier–substrate complexes cross the membrane in a direction such that the substrate moves from high to low concentration. This carrier-mediated transport process is known as facilitated diffusion.

Neither non-ionic diffusion nor carrier-mediated diffusion require the expenditure of energy, relying simply on the concentration gradients existing across the cell membranes. However, some transport processes require the ‘uphill’ movement of substances. An example here will be useful, by considering how the body maintains a constant internal environment. We take a small amount of salt (sodium chloride) in the diet to replace that lost in the urine, sweat, saliva, and other secretions. To move salt from a low concentration in the gut, into the blood where it is at high concentration, means that the movement is up a concentration gradient, and therefore cannot occur by diffusion. The body deals with this by using a two-stage process in which sodium ions are actively transported. The first stage is the movement of sodium ions from the gut cavity across the face of the cells lining the gut; since the concentration of sodium ions inside these cells, as in all cells, is low, movement is by diffusion using specific sodium ion channels. The second stage is the movement of the sodium ions from these lining cells, across the membrane on their opposite face, away from the gut, into the tissue fluid, where the sodium ion concentration is high. This is achieved using a molecular pump, called the sodium pump (otherwise known as sodium– potassium ATPase: a protein molecule that spans the cell membrane). The pump causes a net movement of sodium ions, along with the expenditure of energy, yielded by the hydrolysis of ATP. This transfer of sodium ions across the gut epithelium results in the transfer of positive charge to the outer side of the cells. Because the pump transfers electrical charge in this way, it is said to be electrogenic. The transfer of positive charges provides the driving force for the movement of the negatively-charged chloride ions across the gut lining; thus the transfer of salt is achieved.

Similar two-stage active transport processes are responsible for the absorption or secretion of other salts, as well as sodium chloride, across many epithelial membranes. They occur in glands (such as salivary glands, the pancreas, and sweat glands) in organs such as the kidneys and the liver, as well as in epithelial membranes over the cornea and covering the brain.

Transport processes are also involved in other homeostatic processes, such as the regulation of cellular pH. Here carrier-mediated processes are used which, for instance, exchange a sodium ion for a proton (hydrogen ion) or exchange a chloride anion for a bicarbonate anion. These carriers are said to facilitate exchange-diffusion. As well as the sodium pump described above there are other molecular pumps which consume energy (obtained by the hydrolysis of ATP); for example, the calcium pump maintains low levels of calcium ions inside cells, and the proton pump is involved in generating the hydrochloric acid secreted into the stomach.

Although we refer to ‘the sodium pump’ and others in the singular, a single cell may have for example, hundreds of thousands of sodium pumps, with the number varying to suit local conditions. The body's energy requirement for these active transport processes accounts for at least a fifth of the metabolic rate of the whole body at rest.

Thus carriers, exchangers, pumps, and ion channels are the molecular machines which drive the body's transport processes.

Alan W. Cuthbert


See also cell membranes; diffusion; ion channels.

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Transport

TRANSPORT

British footwear firm

Founded: by Jimmy Sarvea. Company History: Opened first shop, Reading, Berkshire, 1970; firm bought by Allied Shoes Ltd. Company Address: Allied Shoes, 77-79 Great Eastern St., London EC2A 3HU, UK.

***

Transport shoes probably epitomized the growth of modern foot-wear fashion and the looks we took for granted as the street level expression of the young. The originator of the label, Jimmy Sarvea, previously a boxer, was first a shoe repairer, became an assistant manager for a major footwear retailer, and went on to become one of the leading shoe entrepreneurs of the 1970s and 1980s. From the opening of his first shop in Reading, Berkshire, in 1970 to his continued presence on the High Street, Sarvea helped ensure that the avant-garde, trend-conscious customer was well served.

Whether classic or high fashion, the original Transport shoes, manufactured in Italy, created an impressive turnover. One of the most famous outlets for their men's shoes was Succhi, a mecca for the discriminating. The menswear market in general had become increasingly aware of fashion as the decade progressed, and the individuality of the footwear sold under the Transport label became an essential ingredient of a positive statement. Sarvea was joined by Carol Sullivan and the influence they found from streetwear added charisma and a new visual freedom to their shoes. The collection continued to grow, with exciting and innovative designs for both sexes. Many styles were unisex, with wide use of the unexpected, including glitter fabrics, stinging shades of orange and purple, unforgettable last and heel shapes, platform soles, chunky silhouettes, and interesting and unusual use of laces and buckles.

Transport shoes were featured on Top of the Pops, a BBC television musical program for the young, and potential customers eagerly sought out the shoes. Transport had created the most anticipatory underground footwear fashion statement of the 1980s. Their ultimate goal, total originality, assisted in attracting celebrities of the period, and George Michael, Five Star, Duran Duran, and Ian Dury were the pioneers for those who desired, for personal or professional reasons, that their footwear be the center of attention.

Angela Pattison

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transport

trans·port • v. / transˈpôrt/ [tr.] take or carry (people or goods) from one place to another by means of a vehicle, aircraft, or ship: the bulk of freight traffic was transported by truck. ∎ fig. cause (someone) to feel that they are in another place or time: for a moment she was transported to a warm summer garden on the night of a ball. ∎  (usu. be transported) overwhelm (someone) with a strong emotion, esp. joy: she was transported with pleasure. ∎ hist. send (a convict) to a penal colony. • n. / ˈtransˌpôrt/ 1. a system or means of conveying people or goods from place to place by means of a vehicle, aircraft, or ship: many possess their own forms of transport air transport. ∎  the action of transporting something or the state of being transported: the transport of crude oil. ∎  a large vehicle, ship, or aircraft used to carry troops or stores. ∎ hist. a convict who was transported to a penal colony. 2. (usu. transports) an overwhelmingly strong emotion: art can send people into transports of delight.

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"transport." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 21 Jun. 2017 <http://www.encyclopedia.com>.

"transport." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (June 21, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/transport-0

"transport." The Oxford Pocket Dictionary of Current English. . Retrieved June 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/transport-0

transport

transport convey from place to place XIV; carry away with emotion XVI. — OF. transporter or L. transportāre, f. TRANS- + portāre carry.
Hence or — (O)F. transport conveyance from one place to another or means of this XV; state of being ‘carried out of oneself’ XVII. Hence transportation conveyance XVI; penal removal XVII. transpose †change into something else XIV; change the position or order of XVI. — (O)F. transposer, f. trans- TRANS- + poser POSE. So transposition XVI. — F. or late L.

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"transport." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 21 Jun. 2017 <http://www.encyclopedia.com>.

"transport." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (June 21, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/transport-1

"transport." The Concise Oxford Dictionary of English Etymology. . Retrieved June 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/transport-1

transport

transport
1. A mechanism for transporting an information storage medium past an access station. The word is most frequently used to refer to either a document or a tape transport.

2. A service provided by a (local or wide area) communication network, or the architectural layer or interface with this service.

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"transport." A Dictionary of Computing. . Encyclopedia.com. 21 Jun. 2017 <http://www.encyclopedia.com>.

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transport

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"transport." World Encyclopedia. . Encyclopedia.com. 21 Jun. 2017 <http://www.encyclopedia.com>.

"transport." World Encyclopedia. . Encyclopedia.com. (June 21, 2017). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/transport

"transport." World Encyclopedia. . Retrieved June 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/transport

transport

transportabort, apport, assort, athwart, aught, besought, bethought, bort, bought, brought, caught, cavort, comport, consort, contort, Cort, court, distraught, escort, exhort, export, extort, fort, fought, fraught, import, methought, misreport, mort, naught, nought, Oort, ought, outfought, port, Porte, purport, quart, rort, short, snort, sort, sought, sport, support, swart, taught, taut, thought, thwart, tort, transport, wart, wrought •cohort • backcourt • Port Harcourt •forecourt • onslaught • dreadnought •Connacht • aeronaut • Argonaut •juggernaut • cosmonaut • astronaut •aquanaut • davenport • carport •passport • airport •Freeport, seaport •Shreveport •heliport, teleport •Stockport • outport • Coalport •spoilsport •Newport, viewport •hoverport •forethought, malice aforethought •afterthought • worrywart

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"transport." Oxford Dictionary of Rhymes. . Encyclopedia.com. 21 Jun. 2017 <http://www.encyclopedia.com>.

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"transport." Oxford Dictionary of Rhymes. . Retrieved June 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/transport