210 résultats pour "biology"

• Fowl - biology.

  varieties, and the Dominique, Java, and Buckeye. Scientific classification: Fowl belong to the order Galliformes. The common domestic fowl, or chicken, belongs to the family Phasianidae and is classified as Gallus gallus. See separate articles on the individual breeds mentioned above. See also Duck; Fowl Cholera; Goose; Guinea Fowl; Incubator; Turkey; Veterinary Medicine. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

• Arthropod - biology.

  through a series of distinct phases to become adults. Larvae may also inhabit different environments and eat different foods than their parents. The life spans ofarthropods range from a few weeks to several decades. V ARTHROPOD EVOLUTION The evolutionary origins of modern arthropods are unclear and complex. It is generally accepted that the phylum is polyphyletic—that is, derived from several separateancestral lines. The ancestors of arthropods were ancient aquatic segmented worms, similar to p...

• Ape - biology.

  previous infant has been weaned. This process—like all aspects of ape development—takes a remarkable length of time. A gibbon is weaned by the age of about 2years, while chimps take more than 4 years. Like young monkeys, young apes are carried by their mothers. They either cling to the mother's belly or, in the case ofolder chimps, ride on her back. In great apes, infant care is largely the job of the females, while in some gibbons the mother hands over responsibility to the fatherwhen the infan...

• Prokaryote - biology.

  earliest organisms to evolve, an estimated 3.4 billion to 3.5 billion years ago. The environment of the early Earth lacked oxygen, and cyanobacteria probably usedfermentation (a chemical process performed without the presence of oxygen) to produce the energy molecule adenosine triphosphate (ATP). Cyanobacteria introduced oxygen into the atmosphere through the process of photosynthesis. As the oxygen content in the atmosphere increased over the centuries, bacteria evolved that usedthis oxygen in...

• Wolf - biology.

  VIII RED WOLF The red wolf is smaller than the gray wolf. An adult red wolf stands about 65 cm (about 2 ft) high at the shoulder, measures 100 to 130 cm (3 to 4 ft) in lengthexcluding the tail, and weighs 20 to 36 kg (45 to 80 lb). It has long legs and ears and its head is not as wide as that of the gray wolf. The coat of red wolves varies incolor from light tan to black with reddish head, ears, and legs. Scientists have debated whether the red wolf is a subspecies of the gray wolf, a separate...

• Vertebrate - biology.

  E Reptiles Compared to amphibians, reptiles are much more fully adapted to life on land. They have scaly, waterproof skin, and they either give birth to live young or lay eggs withwaterproof shells. There are about 7,000 species alive today, including snakes, alligators, and turtles. During the age of the dinosaurs, about 230 million to 65 millionyears ago, reptiles outnumbered all other land vertebrates put together. F Birds Birds evolved from flightless reptiles but underwent some major chan...

• Cotton - biology.

  VII COTTONSEED Once a waste-disposal problem for gins, cottonseed is now a valuable by-product. The seed goes to oil mills, where it is delinted of its linters in an operation similar toginning. The bare seed is then cracked and the kernel removed. The meal that remains after the oil has been extracted is high in protein. Linters are used for paddingin furniture and automobiles, for absorbent cotton swabs, and for manufacture of many cellulose products such as rayon, plastics, lacquers, and sm...

• Eukaryote - biology.

  The waste is then expelled through a hole in the fused membrane. In complex animals, cells generate wastes such as urea when nutrients are broken down within cells.These wastes are transported by blood to the kidneys. The kidneys process the waste and produce urine, which is removed from the body through the bladder.Undigested food travels through the tubelike intestines and is eliminated through the digestive system. V EVOLUTIONARY ORIGINS Eukaryotes evolved much later than prokaryotes, whose...

• Lion - biology.

  Lions usually hunt at night, alone, or in groups. Their preferred prey are large hoofed mammals, such as zebras and wildebeests, but they will go after small hares aswell as huge giraffes. Typically, a lion hunting alone will slowly and silently stalk its prospective victim, trying not to be seen, until it is about 30 m (about 98 ft) away.Then with a burst of speed, the lion will run toward the prey, grab it, and throw it to the ground. The lion kills the prey by biting the back of the animal’s...

• Kangaroo - biology.

  ungulates, they have evolved multi-chambered stomachs containing bacteria that can break down plant cell walls and release the nutritious cell contents. V SOCIAL ORGANIZATION Kangaroo social life is poorly understood, as few species have been studied in detail. Small species, such as potoroos, bettongs, and musky rat-kangaroos, tend to besolitary and widely dispersed, with a male's territory encompassing those of several females. The animals come together briefly for mating, and mother and offs...

• Corn - biology.

  small larvae of the cucumber beetles feed on the root system of the developing plants. VII PRODUCTION AND CONSUMPTION World output of corn at the beginning of the 21 st century was about 603 million metric tons annually; in volume of production, corn ranked first, ahead of rice and wheat. A net gain of about 51 percent in production was realized during the last two decades; intensive cultivation with heavy use of fertilizer and herbicides wasresponsible for the increase. The United States is t...

• Duck - biology.

  from water. When ducks feed they push their tongue against the top of their mouth to squeeze water through the lamellae, leaving the food behind. Mergansers arefish-eating ducks with slender bills that are notched on the edges like the blade of a saw. These saw-toothed beaks help the ducks catch and hold their slippery prey. VI COURTSHIP AND REPRODUCTION Ducks form pairs long enough to mate, but most species find new mates each year. In a few species, including buffleheads and whistling ducks,...

• Owl - biology.

  Among the largest species of typical owls are the eagle owls. They have tufts of feathers on their heads that are called “ears.” The great horned owl is the only eagleowl found in the Americas. It is about 60 cm (25 in) in length with a wingspan of 1.4 m (60 in). Numerous species of eagle owls inhabit Europe, Africa, and Asia. Mostwidely distributed is the northern eagle owl, found from Scandinavia and Spain to Japan. It is about 71 cm (28 in) long with a wingspan of about 2m (72 in). Nearly asl...

• Rice - biology.

  V HISTORY According to the most widely accepted theory, rice cultivation originated as early as 10,000 BC in Asia. Archaeological evidence shows that rice was grown in Thailand as early as 4000 BC, and over the centuries spread to China, Japan, and Indonesia. By 400 BC rice was cultivated in the Middle East and Africa. The invading armies of Alexander the Great probably introduced rice to Greece and nearby Mediterranean countries around 330 BC. Rice was brought to the American colonies in t...

• Shrimp - biology.

  shrimp have a maximum length of about 20 cm (8 in). On the West Coast, the Franciscan Bay shrimp is caught commercially. Freshwater shrimp are most common in warm parts of the world. They include river shrimp, edible shrimp that are trapped or farmed in the tropics, and also all trueshrimp that have become adapted for life in caves. Cave shrimp are typically pale, with vestigial (nonfunctioning) eyes, and they find their way mainly by touch. Decapod shrimp also include animals that are rarely ea...

• Goose - biology.

  Branta comes from a German word meaning “burned” and all of the geese in this genus have black plumage somewhere on their bodies. The brant, a sea goose that also belongs to this genus, is found on both coasts of North America. Brants are darker than barnacle and Canada geese and similar in size to the smallest Canadageese. Like the Canada and barnacle goose, the brant nests in Arctic regions. But unlike them, it winters chiefly on salt water. Instead of the white cheeks of Canadaand barnacle g...

• Giraffe - biology.

  One of the most striking elements of giraffe behavior is the duel between males fighting for mating privileges. Giraffe duels are among the most extraordinary in theanimal kingdom. They start when two males approach each other and begin to rub and intertwine their necks. This behavior—known as necking—allows the opponentsto assess each other’s size and strength. Often, necking alone is enough to establish seniority. If not, the rivals begin to exchange blows with their heads. Each giraffebraces...

• Sleep - biology.

  V FUNCTIONS OF SLEEP Although no one knows for sure why we sleep, there are a number of theories. Sleep may have evolved to protect animals from their predators by reducing theiractivity during the times when they are most vulnerable. Research has shown that REM and NREM sleep may serve specific biological functions. Sleep deprivation studies reveal that humans and other animals respond to sleeploss in the same way. When study subjects are deprived of REM sleep, they tend to spend longer period...

• Hippopotamus - biology.

  hippo backs up to its droppings and uses its tail as a paddle, flicking the dung through the air. This creates a pile that can become several meters wide over time. Male river hippos start to establish territories when they are in their early 20s, and they may eventually control more than 250 m (820 ft) of the water's edge.Subordinate males come and go freely, but a rival male will spark a confrontation if it tries to intrude. The territory owner and intruder face each other open-mouthedand, if...

• Photosynthesis - biology.

  P680 in Photosystem II is now electron deficient because it has donated electrons to P700 in Photosystem I. P680 electrons are replenished by the water that has beenabsorbed by the plant roots and transported to the chloroplasts in the leaves. The movement of electrons in Photosystems I and II and the action of an enzyme split thewater into oxygen, hydrogen ions, and electrons. The electrons from water flow to Photosystem II, replacing the electrons lost by P680. Some of the hydrogen ions maybe...

• Camel - biology.

  of water in the stomach or hump as was once commonly believed. Unlike other mammals, however, the camel can survive as long as three weeks without drinking,depending on the water content of its food. It can survive a water loss of about 40 percent of its normal body weight. In comparison, a loss of 15 percent is usually fatalfor humans. Camels can go without water due to several unique adaptations to their environment. The camel conserves more water in its body than any other mammal. It excretes...

• Leaf - biology.

  The mesophyll, sandwiched between the upper and lower epidermis, consists of many thin-walled cells that are usually arranged in two layers. The palisade layer is next to the upper epidermis. It consists of cylindrical cells that are packed closely together. Next to the palisade layer and making up most of the thickness of the leaf bladeis the spongy layer. The spongy layer consists of roundish cells that are packed loosely together and have numerous air spaces between them. In most plants t...

• Penguin - biology.

  B Parents and Offspring Once female penguins lay their eggs, both the parents incubate the eggs. The incubation period varies according to species, ranging from 33 days for the little penguinto about 63 days for the emperor penguin. In most medium-sized penguins incubation takes 35 to 38 days. The incubation routine is highly variable among penguinspecies, although in general both sexes participate in incubation and feeding of young. Male and female Adélie penguins take turns incubating their e...

• Pollination - biology.

  rapidly as in cross-pollination, because one plant with a beneficial gene can transmit it only to its own offspring and not to other plants. Self-pollination evolved laterthan cross-pollination, and may have developed as a survival mechanism in harsh environments where pollinators were scarce. IV POLLEN TRANSFER Unlike animals, plants are literally rooted to the spot, and so cannot move to combine sex cells from different plants; for this reason, species have evolved effectivestrategies for ac...

• Eagle - biology.

  States, is a member of this group found only in North America. It is named for its snow-white head. However, the name bald does not refer to a lack of feathers but comes instead from an outdated word meaning marked with white, as in piebald. The adult bald eagle is blackish brown, with a white head and tail. Its bill, legs, and feet are bright yellow. The bill, which is longer and heavier than the gray bill of golden eagles, is useful for piercing the skin of fish. Bald eagles vary in size....

• 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...

• Zebra - biology.

  C Life Span Captive zebras have lived into their late 30s. Life expectancy in the wild, where predators abound, is probably not much more than 12 years. IV SOCIAL BEHAVIOR Like horses, zebras have large brains and a wide variety of social behaviors. Although they cannot match the overall intelligence of mammals that hunt, zebras interactwith each other in complex ways. Zebras usually live in groups known as herds, but the social structure of these groups depends on the species. The plains zeb...

• Tobacco - biology.

  quality cigars are made entirely by hand, most cigars are manufactured by machine. Chewing tobaccos are generally made from thick grades of leaves to which binders and flavorings are added. Chewing tobacco is formed by pressing the tobacco intoblocks known as plugs. Snuff is made by grinding tobacco into fine powder, which is then allowed to ferment for a long period of time. Frequently, snuff is scented withspices, such as jasmine or cloves. V TOBACCO INDUSTRY Over 6 million tons of commercial...

• Cheetah - biology.

  animals such as zebras. Unlike most cats, cheetahs hunt during the day, when lions and hyenas that compete with them for prey are less likely to be active. Still,scientists in Tanzania have observed that cheetahs lose 10 to 13 percent of their kills to lions and hyenas. Alerted by the panic of a gazelle herd or by the circling ofvultures, lions and hyenas close in and easily drive the more timid cheetah away from a fresh kill. A cheetah usually stalks prey to within about 10 m (about 33 ft) and...

• Koala - biology.

  V REPRODUCTION Female koalas become sexually mature around 18 to 24 months of age. They can produce one offspring a year until they reach about 13 years of age. Males begin toproduce sperm around age 2 and, in the absence of older, stronger males, they may breed at that young age. More often, however, a male must grow big enough tocompete with other males for females, and mating generally begins for males at about 4 years of age. The breeding season for koalas is from October to May, during the...

• Coral - biology.

  Soft corals lack a distinct skeleton. Although they live in colonies, the individual polyps are fused into a complex body, usually strengthened by small lumps or spikesknown as sclerites, which are made of protein and calcite. Soft corals come in a variety of shapes, including undulating sheets, upright mushroomlike shapes, andbeautiful shapes that form branches. A number of other octocorals have skeletons made from a hard or horny protein, sometimes strengthened with more brittle calcareous dep...

• Invertebrate - biology.

  animals with a five-pointed design. They live in the sea and move with the help of tiny fluid-filled feet—another feature found nowhere else in the animal world. Zoologists recognize several different groups of worms. The phylum known as flatworms contains the simplest animals possessing heads. Nerves and sense organs areconcentrated in the head. Most flatworms are paper-thin and live in a variety of wet or damp habitats, including the digestive systems of other animals. Roundwormsrepresent anot...

• Invertebrate - biology.

  animals with a five-pointed design. They live in the sea and move with the help of tiny fluid-filled feet—another feature found nowhere else in the animal world. Zoologists recognize several different groups of worms. The phylum known as flatworms contains the simplest animals possessing heads. Nerves and sense organs areconcentrated in the head. Most flatworms are paper-thin and live in a variety of wet or damp habitats, including the digestive systems of other animals. Roundwormsrepresent anot...

• Ecology - biology.

  an input of nutrients exceeding the capability of the ecosystem to process them. Nutrients eroded and leached from agricultural lands, along with sewage and industrialwastes accumulated from urban areas, all drain into streams, rivers, lakes, and estuaries. These pollutants destroy plants and animals that cannot tolerate theirpresence or the changed environmental conditions caused by them; at the same time they favor a few organisms more tolerant to changed conditions. Thus,precipitation filled...

• Fruit - biology.

  from a flower with several pistils. The ovary may have a single compartment, or carpel, which houses the ovule or ovules. Or the ovary may consist of two or morecarpels, each of which may contain one or more ovules. A drupe develops from an ovary with a single carpel and is characterized by an edible exocarp and mesocarp and an inedible, hard endocarp, or pit that encloses asingle seed. Cherries, peaches, apricots, and plums are examples of drupes. Almonds also are classified as drupes, but in a...

• Dog - biology.

  French word for butterfly because it has ears that resemble butterfly wings, is a happy, friendly dog, suitable for small living spaces. The final dog group, nonsporting ,includes a wide variety of purebreds that differ in size, coat, overall appearance, and personality, from the shorthaired spotted dalmatian to the curly-haired poodle. V DOG BEHAVIOR Instinctive behaviors of the domestic dog are comparable to those of its wild relatives, the wolf, coyote, fox, and jackal. Unlike trained behavi...

• Gardening - biology.

  of synthetic and organic fertilizers, see Organic Farming.) Fertilizers usually are sold in packages, on which the percentage by weight of the macronutrients nitrogen (N), phosphorus (P), and potassium (K) are listed on thelabel—always in the order N-P-K. For example, a fertilizer that is labeled 10-5-3 is 10 percent nitrogen, 5 percent phosphorus, and 3 percent potassium. V PLANTING AND TRANSPLANTING Before planting seeds, gardeners prepare, or till, the soil using a variety of methods. Some...

• Rhinoceros - biology.

  Male and female rhinos have a similar physical appearance, although male rhinos are usually larger than females, with the size difference varying between species. Inthe wild, some rhinos probably live into their late 40s, and they have survived into their 30s in captivity. IV TYPES OF RHINOCEROSES Until recently, mammalogists divided the rhinoceros family into three subfamilies, each with different characteristics. Scientists now believe that living rhinos belong to asingle subfamily, although...

• Fungus - biology.

  Many fungi can reproduce by the fragmentation of their hyphae. Each fragment develops into a new individual. Yeast, a small, single-celled fungus, reproduces bybudding, in which a bump forms on the yeast cell, eventually partitioning from the cell and growing into a new yeast cell. V CLASSIFICATION OF FUNGI Scientists have long disagreed about how to classify fungi, and the classification systems are still developing. The first description of fungi was published in 1729 byItalian botanist Pier...

• Fish - biology.

  pectoral fins provide fine movements, add forward thrust, or, together with the pelvic fins, serve as brakes. Typically, fins consist of a thin membrane stretched over afanlike series of thin rods called spines or rays. Most fish breathe underwater with the help of special respiratory organs called gills. Gills are made of a series of thin sheets or filaments through which blood circulates.As water moves into a fish’s mouth and passes over the gills, dissolved oxygen passes across the thin gill...

• Bat - biology.

  tomb bat has rather small ears. The shapes of bat ears are extremely varied. The wide ears of the Australian false vampire bat meet above the head and are fused.Many bats are able to turn their ears in the direction of faint noises. Bat hearing and its use in echolocation are highly developed. Some bats have large, conspicuous eyes, while others may have small beady eyes. This variation suggests that vision plays different roles in the lives of various species.Despite the familiar expression, 'b...

• Primate - biology.

  The primate order includes a handful of species that live entirely on meat (carnivores) and also a few that are strict vegetarians (herbivores), but it is composed chieflyof animals that have varied diets (omnivores). The carnivorous primates are the four species of tarsiers, which live in Southeast Asia. Using their long back legs, thesepocket-sized nocturnal hunters leap on their prey, pinning it down with their hands and then killing it with their needle-sharp teeth. Tarsiers primarily eat in...

• Heredity - biology.

  allele from the mother and a mutated allele from the father. In both of these cases, the child will be a carrier. The child develops the disease only if he or she receives amutated allele from each parent. When both parents are carriers, there is a 25 percent chance that a child will be disease-free, a 25 percent chance that it will have thedisease, and a 50 percent chance that it will be a carrier. Examples of genetic diseases that follow the dominant-recessive pattern include sickle-cell anemi...

• Cat - biology.

  D Coat Colors The domestic cat's original coat color was probably grayish-brown with darker tabby stripes, a color that provides excellent camouflage in a variety of environments. Allother coat colors and patterns are the result of genetic mutations; for example, solid coat colors such as black and blue are the result of a gene that suppresses tabbystripes; an orange coat is the result of a gene that transforms black pigment to orange; and a solid white coat is the result of a gene that complet...

• Flower - biology.

  insects. The sepals unfurl as the flower opens and often resemble small green leaves at the flower’s base. In some flowers, the sepals are colorful and work with thepetals to attract pollinators. E Variations in Structure Like virtually all forms in nature, flowers display many variations in their structure. Most flowers have all four whorls—pistil, stamens, petals, and sepals. Botanists callthese complete flowers. But some flowers are incomplete, meaning they lack one or more whorls. Incomplet...

• Antelope - biology.

  antelopes still display complex patterns of behavior, although much of it is instinctive rather than learned. In open habitats, antelopes run a high risk of predation (being preyed upon). To survive they use several kinds of defensive strategy, including living in herds. Herd living ensures that many pairs of eyes and ears are on the alert for danger. Herd living also gives individuals a better chance of avoiding attack, because predators canchoose from many potential targets. When danger thre...

• Tree - biology.

  The major parts of a tree are its roots, trunk, leaves, flowers, and seeds. These components play vital roles in a tree’s growth, development, and reproduction. A Roots Trees are held in place by anchoring organs called roots. In addition to anchoring the tree, roots also absorb water and minerals through tiny structures called roothairs. From the roots the water and mineral nutrients are carried upward through the wood cells to the leaves. Although the internal structure of most kinds of roots...

• Plant - biology.

  B1 Vacuoles Vacuoles are membrane-bound cavities filled with cell sap, which is made up mostly of water containing various dissolved sugars, salts, and other chemicals. B2 Plastids Plastids are types of organelles, structures that carry out specialized functions in the cell. Three kinds of plastids are important here. Chloroplasts contain chlorophyllsand carotenoid pigments; they are the site of photosynthesis, the process in which light energy from the sun is fixed as chemical energy in the b...

• Birding - biology.

  swallows, and rock doves nest on buildings in cities, towns, and farms. The chimney swift has abandoned hollow trees for chimneys as a nest site in urban areas.Mallards and Canada geese—once exclusively wild, migratory species—now live year-round in the open spaces found in city parks and golf courses. Nearly all purplemartins, a songbird species that once used the abandoned nests of woodpeckers or the natural cavities of cliffs or dead trees, now live primarily in structures specificallyconstru...

• 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...