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Sunday, October 9, 2011

Albert Einstein

Albert Einstein (1879-1955), German-born American physicist and Nobel laureate, best known as the creator of the special and general theories of relativity and for his bold hypothesis concerning the particle nature of light. He is perhaps the most well-known scientist of the 20th century.Einstein was born in Ulm on March 14, 1879, and spent his youth in Munich, where his family owned a small shop that manufactured electric machinery. He did not talk until the age of three, but even as a youth he showed a brilliant curiosity about nature and an ability to understand difficult mathematical concepts. At the age of 12 he taught himself Euclidean geometry.
Einstein hated the dull regimentation and unimaginative spirit of school in Munich. When repeated business failure led the family to leave Germany for Milan, Italy, Einstein, who was then 15 years old, used the opportunity to withdraw from the school. He spent a year with his parents in Milan, and when it became clear that he would have to make his own way in the world, he finished secondary school in Aarau, Switzerland, and entered the Swiss Federal Institute of Technology in Zürich. Einstein did not enjoy the methods of instruction there. He often cut classes and used the time to study physics on his own or to play his beloved violin. He passed his examinations and graduated in 1900 by studying the notes of a classmate. His professors did not think highly of him and would not recommend him for a university position.
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Amino Acid


Amino Acids, important class of organic compounds that contain both the amino (8NH2) and carboxyl (8COOH) groups. Of these acids, 20 serve as the building blocks of proteins (see Protein). Known as the standard, or alpha, amino acids, they comprise alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. All 20 are constructed according to a general formula:

As the formula shows, the amino and carboxyl groups are both attached to a single carbon atom, which is called the alpha carbon atom. Attached to the carbon atom is a variable group (R); it is in their R groups that the molecules of the 20 standard amino acids differ from one another. In the simplest of the acids, glycine, the R consists of a single hydrogen atom. Other amino acids have more complex R groups that contain carbon as well as hydrogen and may include oxygen, nitrogen, or sulfur, as well.
When a living cell makes protein, the carboxyl group of one amino acid is linked to the amino group of another to form a peptide bond. The carboxyl group of the second amino acid is similarly linked to the amino group of a third, and so on, until a long chain is produced. This chainlike molecule, which may contain from 50 to several hundred amino acid subunits, is called a polypeptide. A protein may be formed of a single polypeptide chain, or it may consist of several such chains held together by weak molecular bonds. Each protein is formed according to a precise set of instructions contained within the nucleic acid (see Nucleic Acids), which is the genetic material of the cell. These instructions determine which of the 20 standard amino acids are to be incorporated into the protein, and in what sequence. The R groups of the amino acid subunits determine the final shape of the protein and its chemical properties; an extraordinary variety of proteins can be produced from the same 20 subunits.
The standard amino acids serve as raw materials for the manufacture of many other cellular products, including hormones (see Hormone) and pigments. In addition, several of these amino acids are key intermediates in cellular metabolism (see Metabolism).
Most plants and microorganisms are able to use inorganic compounds to make all the amino acids they require for normal growth. Animals, however, must obtain some of the standard amino acids from their diet in order to survive; these particular amino acids are called essential. Essential amino acids for humans include lysine, tryptophan, valine, histidine, leucine, isoleucine, phenylalanine, threonine, methionine, and arginine. They are found in adequate amounts in protein-rich foods from animal sources or in carefully chosen combinations of plant proteins.
In addition to the amino acids that form proteins, more than 150 other amino acids have been found in nature, including some that have the carboxyl and amino groups attached to separate carbon atoms. These unusually structured amino acids are most often found in fungi and higher plants.


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Tuesday, October 4, 2011

Monkey


Monkey (animal), any of about 160 species of primates that have grasping hands, forward-facing eyes, and highly developed brains. Most monkeys also have tails, a characteristic that distinguishes them from their larger primate cousins, the apes. Monkeys are highly skilled climbers, and most spend much of their lives in trees. Some have prehensile tails—that is, tails capable of grasping—that they can use as a fifth limb while foraging for food or climbing.


Zoologists classify monkeys into three distinct families: marmosets, Capuchin-like monkeys, and Old World monkeys. Marmosets and Capuchin-like monkeys are found only in Central and South America and are known collectively as New World monkeys. Marmosets are dainty animals with luxurious fur, which is sometimes strikingly colored. One species, the pygmy marmoset, is the world's smallest monkey, measuring just 30 cm (12 in) long, at least half of which is tail, and weighing as little as 113 g (4 oz) when fully grown. The average life span of a pygmy marmoset in the wild is 10 to 12 years. By comparison, the Capuchin-like monkeys, which include capuchin monkeys, douroucoulis, spider monkeys, woolly monkeys, and howler monkeys, are more robust, although they are still lightly built. Howler monkeys, for example, are among the largest species and measure up to 1.8 m (6 ft) from the top of the head to the tip of the tail. Even so, their maximum weight is only about 10 kg (22 lb). Howler monkeys living in the wild have an average life span of around 16 to 20 years. Many New World monkeys have prehensile tails, and all have broad noses with sideways-opening nostrils.

Old World monkeys include guenons, mangabeys, colobus monkeys, macaques, langurs, and baboons. Compared to New World monkeys, their noses are narrower and have downward-opening nostrils. Old World monkeys do not have prehensile tails; instead, most use their tails simply for balance. As a result, these monkeys are less acrobatic than their New World cousins. Most Old World monkeys spend at least part of their time on the ground. While many are careful not to stray too far from the protective cover of trees, baboons are strong and aggressive enough to defend themselves in the open. Armed with fearsome canine teeth and weighing up to 41 kg (90 lb), male baboons are more than a match for many predators. A baboon in the wild can live as long as 30 years.



The predators of Capuchin-like monkeys are humans and birds of prey. The predators of marmosets include small cats, birds of prey, and snakes. The predators of macaques include large cats, such as leopards, tigers, and panthers, and large snakes, such as pythons. The predators of langurs and colobus monkeys include large cats, humans, and some birds of prey. The biggest threat to all monkeys, however, is the loss of habitat









Monkeys are restricted to South and Central America, Africa, and the southern parts of Asia. Most monkeys live in the forests of the tropics and subtropics, where warm temperatures ensure a year-round supply of food. In rain forests, where food is abundant, monkeys often stay in the same area all year, but in drier habitats, they have to range further afield, possibly traveling more than 18 km (10 mi) a day.
Although most monkeys live in warm climates, some do survive in extreme environments. The Japanese macaque manages to survive the winter cold on the Japanese island of Honshū—the only nonhuman primate to survive that far north. A few tropical monkeys survive on high mountains well above the snow line, some at elevations as high as 4,000 m (13,000 ft). These high-altitude species include the Asian snub-nosed langurs, the African vervet, and several species of macaques. Monkeys can also survive in extreme deserts. In southwest Africa, for example, a troop of yellow baboons lives in the Namib Desert, where rainfall averages just a few inches a year.

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Monday, October 3, 2011

Dog


Dogs
Dog, mammal generally considered to be the first domesticated animal. This trusted work partner and beloved pet learned to live with humans more than 14,000 years ago. A direct descendant of the wolves that once roamed Europe, Asia, and North America, the domestic dog belongs to the dog family, which includes wolves, coyotes, foxes, and jackals. Dog ancestry has been traced to small, civet-like mammals, called miacis, which had short legs and a long body and lived approximately 40 million years ago.The evolving relationship between the domestic dog and humans has been documented in fossil evidence, artifacts, and records left by earlier civilizations. Prehistoric dog skeletal remains, excavated from sites in Denmark, England, Germany, Japan, and China, indicate the early coexistence of dogs with people. An ancient Persian cemetery, dating to the 5th century bc, contained thousands of dog skeletons. Their formal burial and the positioning of the dog remains reveal the esteem in which the ancient Persians held their dogs. The relationship shared by dogs and humans also is evident in cave drawings, early pottery, and Asian ivory carvings that depict dogs. A statue of Anubis, the half dog, half jackal Egyptian god, was discovered inside King Tutankhamen’s tomb, constructed in about 1330 bc.




Literary references to the dog include those found in the Bible and in the Greek classic the Odyssey by Homer. In 1576 an English physician and dog fancier, John Caius, wrote a detailed text on dog breeds, Of English Dogges. Dogs are featured in tapestries that were created in the Middle Ages (5th century to 15th century), and in the work of many artists, including 17th- and 18th-century European painters Peter Paul Rubens and Thomas Gainsborough.

Although it is not known how humans and dogs first learned to coexist, people soon discovered the many ways dogs could enrich their lives. Dogs have been used to hunt for food, herd animals, guard livestock and property, destroy rats and other vermin, pull carts and sleds, perform rescues, and apprehend lawbreakers. They have been used during wartime as sentinels and message carriers. Today trained dogs are used to alert deaf people to common household sounds, such as the ringing telephone or doorbell; guide the blind; or retrieve objects for quadriplegics. Perhaps the most common of the many roles served by the domestic dog, however, is that of companion. As animals with strong social tendencies, dogs typically crave close contact with their owners. And people tend to form loving bonds with dogs. This companionship often helps to ease the pain and isolation of the elderly or people whose physical or mental health requires long-term convalescence or institutionalization.
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Sunday, October 2, 2011

Snake

Snake (reptile), legless animal with a long, flexible body covered with overlapping scales. Snakes are reptiles, a diverse group of animals that also includes lizards, turtles, and crocodiles. Snakes are thought to have evolved from lizards and share many characteristics with this group—particularly the so-called legless lizards, which have tiny, almost imperceptible legs. But unlike most lizards, snakes have thin, forked tongues, and they lack external ears. And while most lizards have movable eyelids that periodically close to protect and lubricate the eyes, a snake’s eyes are always open, protected by immobile, transparent scales.
Like all reptiles, snakes are cold-blooded, or more correctly, ectothermic—that is, they cannot produce their own body heat. Instead, they rely on the sun to heat their bodies and then regulate their temperature with behavior. Because they do not rely on energy from food to generate body heat, snakes can survive on an extremely meager diet. Some wait for months between successive meals, and a few survive by eating a single, large meal just once or twice a year. When they do eat, snakes swallow their prey whole rather than biting off small pieces. Many snakes have specialized jaws that enable them to swallow animals that are far larger than their own heads. Although uncommon, some snakes, such as the African rock python, have been observed eating animals as large as an antelope or a small cow.
With over 2,500 species belonging to more than 10 families, snakes are a large and successful group. They owe much of this success to their versatility—snakes occupy habitats ranging from underground burrows to the tops of trees to ocean depths as great as 150 m (490 ft). They are found on every continent except Antarctica, and although they are most abundant in tropical areas, many survive in regions marked by extreme cold. The range of the European adder, for instance, extends north of the Arctic Circle. The only places without snakes are parts of the polar regions and isolated islands, such as Ireland and New Zealand.
PHYSICAL CHARACTERISTICS

  Although all snakes have a long, cylindrical body, many species boast unique modifications suited to particular habitats and lifestyles. Burrowing snakes, for example, have muscular, stout bodies and solidly built heads that they use to push through soil. Sea snakes have flattened, paddlelike tails for swimming, and the long, thin shape of many arboreal, or tree-dwelling, snakes provides agility when navigating between branches. Some snakes, including pythons, retain characteristics that reflect their evolution from lizards or from lizardlike ancestors. These snakes have traces of hind limbs called spurs, which are usually more prominent in males than in females.The smallest snakes are the blind snakes. One member of this group, the Texas slender blind snake, reaches just 13 cm (slightly more than 5 in) in length when full grown and weighs less than 2 g (less than 0.1 oz). The largest snakes are the anaconda and the reticulated python, both of which grow as long as 10 m (about 33 ft) and can weigh up to 250 kg (about 550 lb). Among most species of snakes, females are larger than males.

Skin




Snake bodies are covered in overlapping scales composed of a horny material called keratin. These transparent scales make up the dry, smooth, outer layer of skin, whose primary function is to prevent water loss. Snakes owe their coloration to pigment cells located in the skin layer below the scales. Most snakes display drab earth tone colors to blend with their natural surroundings. Arboreal species, such as the emerald tree boa, are often vibrant shades of green, a coloration that helps them hide among leafy foliage. Some snakes, such as coral snakes, have brilliant yellow and orange stripes that warn predators of their venomous bite.

Snakes regularly shed the outer layer of their skin as they grow. Even in snakes that are not growing, the scales become drab and worn over time, and must be periodically replaced by a new, healthy layer. Some species of snakes shed their skin about every 20 days, but other species shed it only once a year. In the shedding process, a new layer develops below the surface of the old one, which gradually separates in preparation for being shed, or sloughed. The snake begins the shedding process by rubbing its nose against rocks or other hard objects to separate the old layer from its lips. After the old layer is loosened, the snake crawls out of its old skin, typically shedding it in a single piece.
Internal Organs


Snakes share an internal anatomy similar to that of other reptiles, but modified to fit within an extremely narrow space. The snake’s three-chambered heart can move sideways to accommodate large prey animals traveling from the mouth to the stomach. The snake’s respiratory system is also compact: Most snakes rely exclusively on the right lung for respiration. In these animals, the left lung is either very small or nonexistent. Snakes have two kidneys, which are positioned so that the left one lies behind the right one rather than beside it. Similarly, the reproductive organs—a pair of testes for males and a pair of ovaries for females—are situated end-to-end. The snake has an extremely muscular and flexible stomach, a narrow liver, and both large and small intestines. Unlike the small intestines of many other vertebrates, those of snakes are stretched out instead of coiled. Like other reptiles, snakes have a cloaca, an internal chamber that receives wastes from the digestive system and eggs or sperm from the reproductive system before they leave the body. Snakes do not have a urinary bladder; instead, they excrete all their wastes through the rectum.
Senses


A snake obtains information about its environment primarily through the Jacobson’s organ located in the roof of its mouth. The snake continuously flicks out its forked tongue to collect scent particles from the air and the ground. When the tongue draws back into the mouth, the forked tips fit into cell-lined pockets in the Jacobson’s organ, which detects the odors of the particles it receives. This system is keenly sensitive, and snakes rely on it to locate both mates and prey.
Vision and the ability to detect vibrations are also important to the survival of most snakes. Snakes lack eardrums and external ear openings, but they have small bones in their heads that conduct sound. They are able to hear low-frequency sounds and to sense vibrations that travel through the ground or water. The majority of snakes have good eyesight, especially for detecting moving objects, although most burrowing snakes can only distinguish between light and dark.
Pit vipers, boas, and pythons have an unusual adaptation for detecting warm-blooded prey and predators. On the heads of these snakes are small pits lined with cells that are extremely sensitive to heat. These pits enable the snakes to sense the presence of a warm-blooded animal and strike accurately, even in total darkness.

Feeding
Snakes have a wide range of food preferences. Many snakes eat worms, insects, lizards, small mammals, birds, and frogs. Some snakes, such as the Australian bandy-bandy, feed only on other snakes. Several groups of snakes, including the egg-eating snakes of Asia, prefer the eggs of other animals; these snakes have modified teeth and vertebrae in the throat for breaking eggshells. These teeth snag the shell as the egg, swallowed whole, starts down the digestive tract; the broken shell is regurgitated. Among some species, males and females eat different types of food. For example, male Arafura filesnakes eat small fish that inhabit shallow water, while females of the same species eat larger fish that live in deeper water. Many snakes change their diet as they grow larger, as in the reticulated pythons. When young, these snakes feed mostly on rats. When they reach about 4 m (13 ft) in length, they switch to larger prey, such as wild pigs, monkeys, and small deer.
Snakes use diverse strategies for capturing their prey. Slender and agile snakes actively pursue their prey, but snakes with thicker bodies, such as pythons, are more likely to wait in a coiled position and ambush their prey as it passes by. Many snakes begin to swallow their prey while it is still alive. The teeth of snakes point backward and are not designed for chewing—instead, snakes use their teeth to pin down their prey to prevent its escape. Others kill prey animals before eating them.
Snakes that kill their prey use one of two methods: constriction or envenomation—the injection of venom. Constrictors, such as pythons and kingsnakes, wrap their coils around a prey animal, tightening their grip each time the prey exhales. In this way, constrictors gradually suffocate their victims. Several groups of snakes kill their prey with venom. Copperheads, bushmasters, and other vipers inject their venom and then release the prey immediately, later following the scent trail to find the dead animal. Others, such as cobras, simply hang onto the prey they have poisoned and swallow it when its struggles have ceased.











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Saturday, October 1, 2011

Dinosaur

Dinosaur
Dinosaur, one of a group of extinct reptiles that lived from about 230 million to about 65 million years ago. The word dinosaur was coined in 1842 by British anatomist Sir Richard Owen, derived from the Greek words deinos, meaning “marvelous” or “terrible,” and sauros, meaning “lizard.” For more than 140 million years, dinosaurs reigned as the dominant animals on land.
Owen distinguished dinosaurs from other prehistoric reptiles by their upright rather than sprawling legs and by the presence of three or more vertebrae supporting the pelvis, or hipbone. Dinosaurs are classified into two orders according to differences in pelvic structure: Saurischia, or lizard-hipped dinosaurs, and Ornithischia, or bird-hipped dinosaurs. Dinosaur bones occur in sediments that were deposited during the Mesozoic Era, the so-called era of middle animals, also known as the age of reptiles. This era is divided into three periods: the Triassic (251 million to 200 million years ago), the Jurassic (200 million to 145 million years ago), and the Cretaceous (145 million to 65 million years ago).




Historical references to dinosaur bones may extend as far back as the 5th century bc. Some scholars think that Greek historian Herodotus was referring to fossilized dinosaur skeletons and eggs when he described griffins—legendary beasts that were part eagle and part lion—guarding nests in central Asia. “Dragon bones” mentioned in a 3rd century ad text from China are thought to refer to bones of dinosaurs.




The first dinosaurs studied by paleontologists (scientists who study prehistoric life) were Megalosaurus and Iguanodon, whose partial bones were discovered early in the 19th century in England. The shape of their bones indicates that these animals resembled large, land-dwelling reptiles. The teeth of Megalosaurus, which are pointed and have serrated edges, indicate that this animal was a flesh eater, while the flattened, grinding surfaces of Iguanodon teeth indicate that it was a plant eater. Megalosaurus lived during the Jurassic Period, and Iguanodon lived during the early part of the Cretaceous Period. Later in the 19th century, paleontologists collected and studied more complete skeletons of related dinosaurs found in New Jersey. From these finds they learned that Megalosaurus and Iguanodon walked on two legs, not four, as had been thought.



In the late 19th and early 20th centuries, as the science of paleontology grew and the search for dinosaur remains was extended around the world, new kinds of dinosaurs were discovered. Hundreds of different varieties of dinosaur have been identified from bones found on all of the continents as well as on the islands of Greenland, Madagascar, and New Zealand.
ANCESTRY



Dinosaurs belong to a group of advanced reptiles called archosaurs, which appeared late in the Permian Period. Archosaurs survive today in the form of crocodiles and birds. In addition to dinosaurs, extinct archosaurs included pterosaurs (flying reptiles) and a number of other types of reptiles formerly grouped together under the name thecodonts. During the Triassic, two distinct groups of archosaurs evolved, one related to crocodiles and the other related to dinosaurs, birds, and pterosaurs.

Scientists were once confused about the early ancestors of dinosaurs because some of the archosaurs related to crocodiles developed a number of dinosaur-like features, including walking upright on two hind legs. This phenomenon is known as parallel evolution, in which animals that are not directly related come to resemble each other because they have similar life styles or diets. New fossils have allowed paleontologists to better recognize the true ancestors of dinosaurs. The ancestors of dinosaurs also walked on two hind legs, but had S-shaped necks; simple, hingelike ankle bones; and other distinctive features.
Fossil evidence of the earliest dinosaurs dates from about 230 million years ago. This evidence, found in Madagascar in 1999, consists of bones of an animal about the size of a kangaroo. This dinosaur was a type of saurischian and was a member of the plant-eating prosauropods, which were related to ancestors of the giant, long-necked sauropods that included the Apatosaurus. Prior to this discovery, the earliest known dinosaur on record was the Eoraptor, which lived 227 million years ago. Discovered in Argentina in 1992, the Eoraptor was an early saurischian, 1 m (3 ft) long, with a primitive skull.




Scientists have identified remains of a few small dinosaurs representing ornithischians dating from the end of the Triassic Period before about 200 million years ago. By the middle of the Jurassic Period, around 180 million years ago, most of the basic varieties of saurischian and ornithischian dinosaurs had appeared, including some that far surpassed modern elephants in size. Dinosaurs had evolved into the most abundant large animals on land, and the dinosaurian age had begun.




Earth’s environment during the dinosaurian era was far different than it is today. The days were several minutes shorter than they are today because the gravitational pull of the sun and the moon have over time had a braking influence on Earth’s rotation. Radiation from the Sun was not as strong as it is today because the Sun has been slowly brightening over time.


Other changes in the environment may be linked to the atmosphere. Carbon dioxide, a gas that traps heat from the Sun in Earth’s atmosphere—the so-called greenhouse effect—was several times more abundant in the air during the dinosaurian age. As a result, surface temperatures were warmer and no polar ice caps could form.


The pattern of continents and oceans was also very different during the age of dinosaurs. At the beginning of the dinosaurian era, the continents were united into a gigantic supercontinent called Pangaea (all lands), and the oceans formed a vast world ocean called Panthalassa (all seas). About 200 million years ago, movements of Earth’s crust caused the supercontinent to begin slowly separating into northern and southern continental blocks, which broke apart further into the modern continents by the end of the dinosaurian era.


give the egg
As a result of these movements of Earth’s crust (see Plate Tectonics), there was less land in equatorial regions than there is at present. Deserts, possibly produced by the warm, greenhouse atmosphere, were widespread across equatorial land, and the tropics were not as rich an environment for life forms as they are today. Plants and animals may have flourished instead in the temperate zones north and south of the equator.


The most obvious differences between dinosaurian and modern environments are the types of life forms present. There were fewer than half as many species of plants and animals on land during the Mesozoic Era than there are today. Bushes and trees appear to have provided the most abundant sources of food for dinosaurs, rather than the rich grasslands that feed most animals today. Although flowering plants appeared during the dinosaurian era, few of them bore nuts or fruit.


The animals of the period had slower metabolisms and smaller brains, suggesting that the pace of life was relatively languid and the behavior patterns were simple. The more active animals—such as ants, wasps, birds, and mammals—first made their appearance during the dinosaurian era but were not as abundant as they are now.



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