2. Objetivos 21
3.4. Estudio de biomarcadores de inmunoterapia
area lying west of the Mid-Atlantic Ridge off the continental shelf of South America and terminating in the shallower Scotia Basin. The average depth of the Argentine Basin is 5,000 m (16,000 feet).
argon
A gas found in seawater at a near-saturation concentration (33.6 ml/1,000 g H2O at 20°C, 1 atm). The ratio of nitro-gen to argon in seawater is fairly stable at 37 to 39. This is used as a base for the determination of the concentration of other gases. Isotopic analysis of the ratio of radioactive nuclei of potassium and argon is used in dating fi nds that are too old to be reliably dated using carbon 14.See dating, isotopes.
Argentine Basin
The Arctic biome is unique because the photosynthesizers are all tiny protists.
Aristotle (384–322
B.
C.
E.)
A classical Greek philosopher and natural scientist;teacher of Alexander the Great. Aristotle was the son of a physician and as such had early exposure to medicine and the materia medica of his day, which consisted entirely of botanicals. He produced his Natural History and Zoology from 344 to 342 b.c.e. The Historia Animalium is based on the belief that there are “neces-sary causes” for structures, and that when these structures are observed in a plant or an animal, their function is apparent.
Aristotle attempted an elaborate clas-sifi cation scheme, known in Latin as the Scala Naturae. He ranked animals as more complex and important than plants and man as the most important and complex animal. He put animals into two large categories, blooded and nonblooded. The blooded animals included man, viviparous and oviparous quadrupeds, cetaceans, fi sh, and birds. These were subdivided according to the degree of perfection of the young at birth. The bloodless animals were mollusks, crustaceans, and insects.
Aristotle realized that he had omitted sponges and snakes from his scheme but was not sure where they belonged.
He named about 500 kinds of ani-mals, of about 550 to 600 species. Most of these were known in Greece either as native or available in menageries. His scheme contains about 130 fi sh and excel-lent descriptions of many invertebrates, crabs, lobsters, and cephalopods. The sea urchin’s mouth-parts, now known as the
“lantern of Aristotle,” remain today as he described them.
Examining live animals, Aristotle observed sense perception in scallops, fi sh, and sponges. He saw and commented on the ability of the cuttlefi sh to adhere to rocks and not be swept away in currents.
His statement that sea urchin eggs are larg-est at the full moon has been confi rmed in the 20th century. He opened developing eggs to observe the state of the embryo.
Aristotle was aware of his limitations.
He knew that he had not seen everything, nor did he totally understand everything
he observed. He noted “suspect entries”
and tried to comment on all of the work he did with regard to precision. In addi-tion to his very careful biological work he also observed and commented on the ocean’s tides and currents.
The infl uence of Aristotle’s work on European and Arab science endures to this day. Aristotle became the outstanding sci-entist of his time, and after the decline of science in general, the preservation of his work—however fragmentary—made it the only basis for later workers in science. His methodology was also important: he repeat-edly relied on observation—an approach often ignored as philosophy and science became more confused. Not until the idea that observation must be the beginning of science and that philosophy can only fol-low the facts became fi rmly established was Aristotle’s contribution to man’s knowledge of the world really appreciated.
arrow worm
See chaetognatha.artesian water
Water from a spring. If artesian water issues forth from the sea-fl oor with suffi cient force, it rises to the surface as fresh and sometimes hot water.Springs drowned by sea risings or col-lapsed limestone caves may produce arte-sian water. See blue holes.
Arthropoda
An extremely numerous phylum that is also very well represented in the fossil record. Arthropods are seg-mented; originally, each segment was an appendage, but some segments became fused together, and some appendages were lost. There is always a chitinous exoskel-eton which is periodically shed (a process called molting) to allow for growth. The shedding is hormonally controlled. The body cavity is not a true coelom (body cav-ity), and the circulatory system is an open one with a primary dorsal vessel (a primi-tive heart). Arthropods have well-devel-oped sense organs. They are distributed worldwide and adapted to all aquatic envi-ronments. This is the largest phylum. There are between 1 and 2 million species in fourArthropoda
subphyla: Crustacea, Chelicerata, Uniramia (myriapods and insects), and Pentastomida (all parasites). See Chelicerata, Crusta-cea, crab, lobster, shrimp.
Aschelminthes
A phylum of round-worms. Several rather disparate classes make up this phylum, the taxonomy of which is subject to discussion and revision.The similarity among the aschelminth classes Nematoda, Rotifera, Gastrotricha, Kinorhyncha, and Priapulida is in their body cavities. Most of these animals are small scavengers.
A disputed phylum, the most commonly recognized aschelminth phyla are
• Acanthocephala—spiny-headed parasitic worms; about 1,150 spe-cies known
• Chaetognatha—arrow worms;
about 70 species known
• Cycliophora—cycliophorans; 1 spe-cies known, microscopic
• Gastrotricha—gastrotrichs; about 430 species known, all microscopic
• Kinorhyncha—kinorhynchs; about 150 species known, all microscopic
• Loricifera—loriciferans; about 10 species known, all microscopic
• Nematoda—nematodes or round-worms; about 12,000 species known, but an estimated 200,000 more spe-cies extant, mostly microscopic
• Nematomorpha—horsehair worms;
about 320 species known
• Priapulida—priapulid worms; 16 spe-cies known, about half microscopic
• Rotifera—rotifers or “wheel animal-cules”; about 1,500 species known, all microscopic
See individual classes, scavenger, tax-onomy.
ascidian
A class of tunicates. See Tuni-cata.Ascothoracica
A genus of Cirripedia, parasites of coelenterates and echinoderms.aseismic ridge
Oceanic uplands that are not volcanic sites but may have been built up from volcanic products. The Wal-vis Ridge and the Emperor Seamount are examples of aseismic ridges. The Lomono-sov Ridge, once believed to be an aseismic ridge, may be the result of separated con-tinental rock that moved from its origi-nal site by seafl oor spreading. See Arctic Ocean, mid-ocean ridges.Asteroidea
A subclass of the stellate echinoderms. They are the familiar starfi sh or sea stars. The asteroidea are inverte-brates with a worldwide distribution, living along coasts and in deep ocean waters. The radially symmetric adult develops from a bilaterally symmetric juvenile. Asteroideans have a fl attened central disk surrounded by fi ve arms. The opening that regulates internal water—the madriporite—is on the spiny upper surface. The mouth, anus, gills, and tube feet are on the lower surface.The carnivorous starfi sh either swallow prey whole and then expel the indigestible parts through their mouth or, more com-monly, eject their stomach into or onto their prey and digest it in situ. The usual food of sea star is coral or bivalves. They move by retracting and extruding the papil-lae on their underside, which are part of their internal water canal system, and a dis-tinguishing feature of the Asteroidea. The canal is also the means by which the inte-rior of these animals is aerated. See Echi-nodermata, sand dollar, sea star.
asthenosphere
The semifl uid layer in the Earth’s mantle. It exists at a depth of 80 to 200 km (50 to 125 miles). Its fl uidity makes possible the lateral motion (sidewide slide) of crustal plates. See crust, mantle.astrobiology
A broad discipline that looks for extraterrestrial life in water on Mars, Titan (one of Saturn’s moons), and other planets. The underlying assumption is that if life on Earth originated in the oceans, then any water environment in space should be explored for possible life forms or their remains.Aschelminthes
astrolabe
This instrument for determin-ing the altitude of stars and planets was developed in ancient Greece. Sighting is done along a pivoted rod that points to a circular disk marked off in degrees of a circle. Martin Behaim (1459–1507), a Ger-man navigator and geographer, adapted the astrolabe for determining latitude for navi-gation. It was later replaced by the sextant.Atlantic Ocean
The Earth’s largest body of water, accounting for about 20% of the Earth’s surface. The Atlan-tic Ocean is surrounded by more conti-nental land than any other ocean, and receives the most riverine runoff. It is divided into the North and South Atlan-tic Oceans by the equator. The outstand-ing geological feature of the Atlantic is the Mid-Atlantic Ridge, which runs from the Arctic Ocean to the Scotia Sea. The ridge breaks at the Romanche Deep (or Fracture Zone) near the equator. There are two transverse ridges, the Walvis Ridge off the South African coast and the Rio Grande Ridge near the Brazilian coast. The large islands of the Atlantic are for the most part of continental ori-gin, while the small ones are volcanic or, in the case of the Bermudas, coral.The winds and weather in the Atlantic are also divided into northern and south-ern segments, and the wind-generating currents that cross the ocean move clock-wise. The Labrador Current is the cold current in the north that moves south along the North American coast. In the South Atlantic, warm water moves north and south as it approaches the Americas and arches counterclockwise. There is con-siderable sinking of cold, dense, southern water in winter and thus considerable stir-ring. The result is water of fairly constant temperature and salinity, the latter about 3.5%. The deep water of the Atlantic is oxygen and nutrient rich, supplying the raw materials needed by plankton, pelagic (open-sea) communities in general, and the predators that feed on them.
Radionuclide studies have shown that the Atlantic Ocean dominates the
world’s oceans by means of the Antarc-tic Circumpolar Current, which moves a considerable proportion of the world’s ocean water through the Drake Passage.
While this thorough mixing makes the global ocean fairly homogeneous, there are temperature and salinity variations that become more intense in shallow or restricted waters. The extent of variation in salinity for the period 1960 to 1981 was only 0.02 parts per million. See Arc-tic, Coriolis force, currents, Drake Passage, Gulf Stream, pollution.