39 résultats pour "divid"

• Cloning - biology.

  found that such embryo cells are totipotent (able to give rise to all the different cell types in the body). Exploiting this characteristic, scientists developed three techniques to clone embryo cells: blastomere separation, blastocyst division, and somatic cell nuclear transfer. A Blastomere Separation In blastomere separation, scientists fertilize an egg cell with a sperm cell in a laboratory dish. The resulting embryo is allowed to divide until it forms a mass of aboutfour cells. Scientist...

• Cancer (medicine).

  unable to repair the DNA damage, p53 instructs the cell to undergo programmed cell death, or apoptosis , putting a stop to runaway cell division before it starts. Programmed cell death is a normal part of cell life and is tightly controlled by many genes, primarily p53. In a cancerous cell, one or more mutations prevent these genes from doing their jobs. When mutated, p53 allows a cell to continue to divide, even with damaged DNA.This can lead to additional mutations in proto-oncogenes or tumor...

• Cell (biology) - biology.

  proteins, or other proteins required by the cell. While relatively simple in construction, prokaryotic cells display extremely complex activity. They have a greater range of biochemical reactions than those found in theirlarger relatives, the eukaryotic cells. The extraordinary biochemical diversity of prokaryotic cells is manifested in the wide-ranging lifestyles of the archaebacteria andthe bacteria, whose habitats include polar ice, deserts, and hydrothermal vents—deep regions of the ocean un...

• Aging - biology.

  Different theories have been proposed to explain how SF works. One theory is based on the assumption that aging, and diseases that occur more frequently withadvancing age, are caused by structural damage to cells. This damage accumulates in tiny amounts each time the cell divides, eventually preventing the cell fromcarrying out normal functions. One cause of this damage may be free radicals, which are chemical compounds found in the environment and also generated by normal chemical reactions in...

• Immune System.

  The humoral immune response involves a complex series of events after antigens enter the body. First, macrophages take up some of the antigen and attach it to classII MHC molecules, which then present the antigen to T helper cells. The T helper cells bind the presented antigen, which stimulates the T helper cells to divide andsecrete stimulatory molecules called interleukins. The interleukins in turn activate any B lymphocytes that have also bound the antigen. The activated B cells then divide...

• Nordamerika - geographie.

  Die Kontinentale oder Große Wasserscheide (amerikanisch Continental Divide ), die überwiegend entlang der Hauptkämme der Rocky Mountains verläuft, teilt Nordamerika in zwei große Einzugsgebiete: Auf der Ostseite der Wasserscheide fließt das Wasser zum Nordpolarmeer, zur Hudsonbai, zum Atlantischen Ozean und zum Golf von Mexiko;auf der Westseite der Continental Divide fließen die Flüsse dagegen zum Pazifischen Ozean. Zwei wichtige Entwässerungssysteme – das Flusssystem der Großen Seen mit dem Sa...

• North Carolina - geography.

  The drainage divide in North Carolina follows the Blue Ridge range on the eastern margin of the mountain region. This is called the “Eastern Continental Divide.” West ofthis divide, rivers drain into the Mississippi River through the Tennessee River and other tributaries of the Ohio River. The French Broad, the largest, and the LittleTennessee flow into the Tennessee River. The New River flows into the Kanawha River of West Virginia which in turn flows into the Ohio River. Most of the state’s ri...

• North Carolina - USA History.

  The drainage divide in North Carolina follows the Blue Ridge range on the eastern margin of the mountain region. This is called the “Eastern Continental Divide.” West ofthis divide, rivers drain into the Mississippi River through the Tennessee River and other tributaries of the Ohio River. The French Broad, the largest, and the LittleTennessee flow into the Tennessee River. The New River flows into the Kanawha River of West Virginia which in turn flows into the Ohio River. Most of the state’s ri...

• Anatomía - ciencias de la naturaleza.

  Sistema nervioso autónomo o vegetativoEl sistema nervioso autónomo dirige las actividades corporales sobre las que el individuo no tiene un control consciente, como larespiración o la digestión. Consta de dos partes: el sistema simpático y el parasimpático.© Microsoft Corporation. Reservados todos los derechos. El sistema nervioso se divide en somático, que efectúa el control voluntario sobre los músculos esqueléticos, y autónomo, que es involuntario y controla el músculo liso, elmúsculo cardiac...

• Cnidarios - ciencias de la naturaleza.

  Las medusas son solitarias y nadan libremente en el agua. En las medusas la capa gelatinosa de mesoglea es más gruesa que en los pólipos, proporcionándoles mayorflotabilidad. 4 NEMATOCISTOS El nombre cnidarios deriva de la palabra griega knidos, que significa ‘ortiga’ y hace referencia a los orgánulos urticantes conocidos como nematocistos que se encuentran en sus tentáculos y que son característicos de este filo. Los cnidarios atacan a las presas con los nematocistos y utilizan sus tentáculo...

• Anatomía - ciencias de la naturaleza.

  Sistema nervioso autónomo o vegetativoEl sistema nervioso autónomo dirige las actividades corporales sobre las que el individuo no tiene un control consciente, como larespiración o la digestión. Consta de dos partes: el sistema simpático y el parasimpático.© Microsoft Corporation. Reservados todos los derechos. El sistema nervioso se divide en somático, que efectúa el control voluntario sobre los músculos esqueléticos, y autónomo, que es involuntario y controla el músculo liso, elmúsculo cardiac...

• Skin. I INTRODUCTION Skin, outer body covering of an animal. The term skin

  III SKIN APPENDAGES In humans, the skin appendages, or structures embedded in the skin, include hair, nails, and several types of glands. Glands are groups of cells that produce andsecrete substances needed by other parts of the body. In other vertebrates, the skin appendages include scales (in fish and reptiles) and feathers (in birds). Together,the skin and the skin appendages are known as the integumentary system of the body. A Hair Hair is a distinguishing characteristic of mammals, a gro...

• El tiempo geológico.

  DESPUÉS DE LOS DINOSAURIOS La era cenozoica comenzó hace unos 65 millones de años y llega hasta nuestros días. Numerosos tipos de mamíferos aparecieron durante esta era. Con el paso del tiempo, fueron surgiendo especies de mayor tamaño. Sin embargo, algunos de los mamíferos y avesque vivían hace unos 55 millones de años eran muy distintos de los actuales. Había una especie de loros gigantescos incapaces devolar, ¡tan altos como tú! Los geólogos dividen la era cenozoica en dos periodos, llamados...

• El tiempo geológico - (exposé gratuit en espagnol).

  DESPUÉS DE LOS DINOSAURIOS La era cenozoica comenzó hace unos 65 millones de años y llega hasta nuestros días. Numerosos tipos de mamíferos aparecieron durante esta era. Con el paso del tiempo, fueron surgiendo especies de mayor tamaño. Sin embargo, algunos de los mamíferos y avesque vivían hace unos 55 millones de años eran muy distintos de los actuales. Había una especie de loros gigantescos incapaces devolar, ¡tan altos como tú! Los geólogos dividen la era cenozoica en dos periodos, llamados...

• Ohio - geography.

  conflict with modified Gulf air and causing frontal or cyclonic storms. Gulf air is dominant in summer. In fall, polar air passing over Lake Erie is modified, delaying thekilling frost along the adjacent shoreline. C1 Temperatures The mean annual temperatures for the state range from 9° C (48° F) in the northeast to 13° C (55° F) in the south. Average January temperatures range from -4° C(24° F) in the west to 2° C (35° F) in the south. July averages are 24° C (76° F) in the south and 23° C (73...

• Ohio - USA History.

  conflict with modified Gulf air and causing frontal or cyclonic storms. Gulf air is dominant in summer. In fall, polar air passing over Lake Erie is modified, delaying thekilling frost along the adjacent shoreline. C1 Temperatures The mean annual temperatures for the state range from 9° C (48° F) in the northeast to 13° C (55° F) in the south. Average January temperatures range from -4° C(24° F) in the west to 2° C (35° F) in the south. July averages are 24° C (76° F) in the south and 23° C (73...

• Astronomy - astronomy.

  Telescopes may use either lenses or mirrors to gather visible light, permitting direct observation or photographic recording of distant objects. Those that use lenses arecalled refracting telescopes, since they use the property of refraction, or bending, of light ( see Optics: Reflection and Refraction ). The largest refracting telescope is the 40-in (1-m) telescope at the Yerkes Observatory in Williams Bay, Wisconsin, founded in the late 19th century. Lenses bend different colors of light by d...

• Afganistán - geografía.

  vertido de residuos al mar y prohibición de realizar ensayos nucleares. 3 POBLACIÓN La población, predominantemente rural y estructurada en tribus y clanes que dominan todos los ámbitos de la vida, se divide en cuatro grandes grupos étnicos. Los pashto(o pashtunes) forman un 42% de la población total y se dividen en dos subgrupos: los duranios y los ghilzais. Los tayikos, de etnia iraní, componen el 27% de la población,y el resto en su mayoría se compone de uzbekos (9%) y hazaras (9%), además d...

• Clasificación - ciencias de la naturaleza.

  Clasificación de los organismosLa clasificación de los seres vivos es motivo de controversia desde hace mucho tiempo. Arriba: El sistema aristotélico solo reconocíaplantas y animales, que se diferenciaban por el movimiento, el mecanismo de alimentación y la forma de crecimiento. Este sistemaagrupa procariotas, algas y hongos con las plantas, y protozoos móviles capaces de alimentarse con los animales. Centro: Elperfeccionamiento de las técnicas y los materiales de laboratorio puso de manifiesto...

• Rubáiyát of Omar Khayyam - anthology.

  That just divides the desert from the sown,Where name of Slave and Sultán is forgot—And Peace to Mahmúd on his golden Throne! 12A Book of Verses underneath the Bough,A Jug of Wine, a Loaf of Bread—and ThouBeside me singing in the Wilderness—Oh, Wilderness were Paradise enow! 13Some for the Glories of This World; and someSigh for the Prophet’s Paradise to come;Ah, take the Cash, and let the Credit go,Nor heed the rumble of a distant Drum! 14Look to the blowing Rose about us—”Lo,Laughing,” she say...

• Paleontología - ciencias de la naturaleza.

  a menudo aparecen en orden cronológico. Por lo general, los fósiles más antiguos surgen en los estratos más profundos y los fósilesmás recientes en los estratos más superficiales, de modo que su emplazamiento puede ayudar a datar la edad de los especímenes.© Microsoft Corporation. Reservados todos los derechos. Los fósiles proporcionan muchos datos útiles para poder comparar los estratos. Algunos de ellos, llamados fósiles guía, son de gran importancia debido a su ampliadistribución geográfica y...

• Classification - biology.

  species based on the fewest number of shared changes that have occurred from generation to generation. IV HISTORY OF CLASSIFICATION SYSTEMS Classification is one of the oldest sciences, but despite its age it is still a vigorous field full of new discoveries and methods. Much like other fields of science, greatthinkers have shaped the course of classification. One of the earliest classification schemes was established by Greek philosopher Aristotle, who lived in the 300s BC. Aristotle believe...

• Plate Tectonics.

  ridges. The Mid-Atlantic Ridge is an underwater mountain range created at a divergent plate boundary in the middle of the Atlantic Ocean. It is part of a worldwidesystem of ridges made by seafloor spreading. The Mid-Atlantic Ridge is currently spreading at a rate of 2.5 cm per year (1 in per year). The mid-ocean ridges today are60,000 km (about 40,000 mi) long, forming the largest continuous mountain chain on earth. Earthquakes, faults, underwater volcanic eruptions, and vents, oropenings, along...

• Elementary Particles I INTRODUCTION Structure of Matter Modern physics has revealed successively deeper layers of structure in ordinary matter.

  The most fundamental particles that make up matter fall into the fermion category. These fermions cannot be split into anything smaller. The particles that carry theforces acting on matter and antimatter are bosons called force carriers. Force carriers are also fundamental particles, so they cannot be split into anything smaller.These bosons carry the four basic forces in the universe: the electromagnetic, the gravitational, the strong (force that holds the nuclei of atoms together), and the wea...

• Turtle.

  Turtles use their jaws to cut and handle food. Instead of teeth, a turtle’s upper and lower jaws are covered by horny ridges, similar to a bird’s beak. Meat-eating turtlescommonly have knife-sharp ridges for slicing through their prey. Plant-eating turtles often have ridges with serrated edges that help them cut through tough plants.Turtles use their tongues in swallowing food, but unlike many other reptiles, such as chameleons, they cannot stick out their tongues to capture food. C Limb Structu...

• Turtle - biology.

  Turtles use their jaws to cut and handle food. Instead of teeth, a turtle’s upper and lower jaws are covered by horny ridges, similar to a bird’s beak. Meat-eating turtlescommonly have knife-sharp ridges for slicing through their prey. Plant-eating turtles often have ridges with serrated edges that help them cut through tough plants.Turtles use their tongues in swallowing food, but unlike many other reptiles, such as chameleons, they cannot stick out their tongues to capture food. C Limb Structu...

• Brazil - country.

  occasional droughts. Brazil contains a wealth of mineral and plant resources that have not yet been fully explored. It possesses some of the world’s largest deposits of iron ore and containsrich deposits of many other minerals, including gold and copper. Brazil’s fossil fuel resources are modest, but this limitation is offset by the considerable hydroelectricpotential of the nation’s many rivers. Although Brazil is an important producer of tropical crops, areas of highly fertile land are limited...

• La división de la célula - (exposé gratuit en espagnol).

• Arithmetic I INTRODUCTION Arithmetic, branch of mathematics that arises from counting, the most basic mathematical operation.

  Subtract the units: 6 - 3 = 3. Then subtract the tens column: 6 – 2 = 4. The results of these two single-digit subtractions, written side by side, provide the answer: Subtraction is a bit more complicated if we need to subtract a larger digit from a smaller one. For example, when subtracting 47 from 92, the units value (7) of 47 isgreater than the units value (2) of 92. We can handle this situation using a procedure called borrowing, which is like carrying in reverse. Ten units can be borrowe...

• Embarazo y parto - ciencias de la naturaleza.

  La toxemia es otra complicación seria de la última etapa del embarazo. Los síntomas son hipertensión, aumento súbito y cuantioso de peso debido a un edema, llegando aganar de 11 a 13 kilos en un mes, y aparición de proteínas en la orina. Si no se trata, llega a producir ataques de apoplejía y coma que, en casos extremos, puede conducira la muerte del niño. Cuando se diagnostica una toxemia grave, hay que extraer al niño lo antes posible para protegerlo tanto a él como a la madre. Esta situaciónd...

• Aparato circulatorio - ciencias de la naturaleza.

  es completa. Sus paredes musculares se contraen e impulsan todo su contenido a través de los orificios auriculoventriculares hacia los ventrículos. Este proceso es rápido yse produce casi de forma simultánea en ambas aurículas. La masa de sangre en las venas hace imposible el reflujo. La fuerza del flujo de la sangre en los ventrículos no eslo bastante poderosa para abrir las válvulas semilunares, pero distiende los ventrículos, que se encuentran aún en un estado de relajación. Las válvulas mitr...

• Perú - geografía.

  hierbas y eucaliptos. En la altiplanicie y en la puna la vegetación se reduce a algunas especies, como el ichu, la puya Raimondi ( véase Bromeliáceas) y varias cactáceas. Otras plantas que crecen en territorio peruano son el condurango, el cenízaro, la capuchina, el cují, la quinua, el guácimo, el molle, la tagua y el quillay. La fauna del Perú es variada. En la región de La Costa y las islas habitan toda clase de aves guaneras ( véase Guano): cormoranes, alcatraces, pelícanos, gaviotas, golon...

• Colorado - geography.

  Although the rivers of Colorado are navigable only by small boats, they are important as a source of irrigation water for use in Colorado and adjoining states. However,the water level of the rivers fluctuates seasonally and from year to year. The level is generally low in winter and high in spring and summer, during the runoff of meltedsnow from the mountains. Colorado has no large lakes of natural origin, but there are numerous small lakes in the mountains. The largest bodies of water in Colora...

• Colorado - USA History.

  Although the rivers of Colorado are navigable only by small boats, they are important as a source of irrigation water for use in Colorado and adjoining states. However,the water level of the rivers fluctuates seasonally and from year to year. The level is generally low in winter and high in spring and summer, during the runoff of meltedsnow from the mountains. Colorado has no large lakes of natural origin, but there are numerous small lakes in the mountains. The largest bodies of water in Colora...

• Israel (república) - geografía.

  En los últimos años se ha aumentado el número de robles enanos, de árboles de hoja caduca y de coníferas. Desde 1948 se han plantado en Israel más de 200 millones deárboles, y actualmente las zonas boscosas cubren un 8,1% del territorio. Entre las plantas y frutos de valor económico figuran los cítricos, los plátanos, el algodón, eltabaco, las uvas, los dátiles, los higos, las aceitunas, las ciruelas y las almendras. En Israel hay 116 especies conocidas de mamíferos y 180 de aves. Entre los anim...

• Egipto (república) - geografía.

  costa mediterránea. El limo que depositan los afluentes Rosetta (en árabe, Rashid ), Damieta (en árabe, Dumyat ) y otros más hacen del delta la región más fértil del país. Sin embargo, la presa de Asuán ha reducido el caudal del Nilo, causando que las aguas saladas del Mediterráneo penetren en el terreno a lo largo de la costa cercana a ladesembocadura del Nilo. Una serie de cuatro lagos poco profundos y salobres se extienden por la zona del delta en contacto con el mar. Otro gran lago, Birkat...

• Taxation.

  Thus, corporate income faces a higher tax burden than income earned by individuals or by other types of businesses. Tax legislation passed in 2003 in the United Statesattempted to address this issue by lowering the tax rate on dividends. Some economists have proposed abolishing the corporate income tax and instead taxing the owners of corporations (shareholders) through the personal income tax.Other students of the tax system see the corporate income tax as the price corporations pay in return f...

• Washington (state) - geography.

  The crest of the Cascade Range divides Washington into two distinct climatic regions. The area west of the Cascades, which is exposed throughout the year to rain-bearing winds from the Pacific Ocean, has a temperate marine type of climate that is characterized by mild wet winters and cool summers. The Cascades prevent themoist air blowing in from the Pacific from reaching eastern Washington. The Rocky Mountains on the eastern border also represent a climatic barrier. As a result, thesevere winte...

• Washington (state) - USA History.

  The crest of the Cascade Range divides Washington into two distinct climatic regions. The area west of the Cascades, which is exposed throughout the year to rain-bearing winds from the Pacific Ocean, has a temperate marine type of climate that is characterized by mild wet winters and cool summers. The Cascades prevent themoist air blowing in from the Pacific from reaching eastern Washington. The Rocky Mountains on the eastern border also represent a climatic barrier. As a result, thesevere winte...