Paper 2000 Question: 1 (a) Al-Beruni
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| Many organizations and government agencies have adopted a new approach to managing natural resources—naturally occurring materials that have economic or cultural value, such as commercial fisheries, timber, and water—in order to prevent their catastrophic depletion. This strategy, known as ecosystem management, treats resources as interdependent ecosystems rather than simply commodities to be extracted. Using advances in the study of ecology to protect the biodiversity of an ecosystem, ecosystem management encourages practices that enable humans to obtain necessary resources using methods that protect the whole ecosystem. Because regional economic prosperity may be linked to ecosystem health, the needs of the human community are also considered.
Ecosystem management often requires special measures to protect threatened or endangered species that play key roles in the ecosystem. In the commercial shrimp trawling industry, for example, ecosystem management techniques protect loggerhead sea turtles. In the last thirty years, populations of loggerhead turtles on the southeastern coasts of the United States have been declining at alarming rates due to beach development and the ensuing erosion, bright lights, and traffic, which make it nearly impossible for female turtles to build nests on beaches. At sea, loggerheads are threatened by oil spills and plastic debris, offshore dredging, injury from boat propellers, and getting caught in fishing nets and equipment. In 1970 the species was listed as threatened under the Endangered Species Act. When scientists learned that commercial shrimp trawling nets were trapping and killing between 5000 and 50,000 loggerhead sea turtles a year, they developed a large metal grid called a Turtle Excluder Device (TED) that fits into the trawl net, preventing 97 percent of trawl-related loggerhead turtle deaths while only minimally reducing the commercial shrimp harvest. In 1992 the National Marine Fisheries Service (NMFS) implemented regulations requiring commercial shrimp trawlers to use TEDs, effectively balancing the commercial demand for shrimp with the health and vitality of the loggerhead sea turtle population. Contributed By: Joel P. Clement Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. (c) Troposphere Troposphere Troposphere, lowest layer of the earth's atmosphere and site of all weather on the earth. The troposphere is bounded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on the bottom by the surface of the earth. The troposphere is wider at the equator (16 km/10 mi) than at the poles (8 km/5 mi). The temperature of the troposphere is warmest in the tropical (latitude 0º to about 30º north and south) and subtropical (latitude about 30º to about 40º north and south) climatic zones (see climate) and coldest at the polar climatic zones (latitude about 70º to 90º north and south). Observations from weather balloons have shown that temperature decreases with height at an average of 6.5º C per 1000 m (3.6º F per 1000 ft), reaching about -80º C (about -110º F) above the tropical regions and about -50º C (about -60º F) above the polar regions. The troposphere contains 75 percent of the atmosphere's mass—on an average day the weight of the molecules in air (see Pressure) is 1.03 kg/sq cm (14.7 lb/sq in)—and most of the atmosphere's water vapor. Water vapor concentration varies from trace amounts in polar regions to nearly 4 percent in the tropics. The most prevalent gases are nitrogen (78 percent) and oxygen (21 percent), with the remaining 1 percent consisting of argon (0.9 percent) and traces of hydrogen, ozone (a form of oxygen), methane, and other constituents. Carbon dioxide is present in small amounts, but its concentration has nearly doubled since 1900. Like water vapor, carbon dioxide is a greenhouse gas (see Greenhouse Effect), which traps some of the earth's heat close to the surface and prevents its release into space. Scientists fear that the increasing amounts of carbon dioxide could raise the earth's surface temperature during the next century, bringing significant changes to worldwide weather patterns. Such changes may include a shift in climatic zones and the melting of the polar ice caps, which could raise the level of the world's oceans. The uneven heating of the regions of the troposphere by the sun (the sun warms the air at the equator more than the air at the poles) causes convection currents (see Heat Transfer), large-scale patterns of winds that move heat and moisture around the globe. In the Northern and Southern hemispheres, air rises along the equator and subpolar (latitude about 50º to about 70º north and south) climatic regions and sinks in the polar and subtropical regions. Air is deflected by the earth's rotation as it moves between the poles and equator, creating belts of surface winds moving from east to west (easterly winds) in tropical and polar regions, and winds moving from west to east (westerly winds) in the middle latitudes. This global circulation is disrupted by the circular wind patterns of migrating high and low air pressure areas, plus locally abrupt changes in wind speed and direction known as turbulence. A common feature of the troposphere of densely populated areas is smog, which restricts visibility and is irritating to the eyes and throat. Smog is produced when pollutants accumulate close to the surface beneath an inversion layer (a layer of air in which the usual rule that temperature of air decreases with altitude does not apply), and undergo a series of chemical reactions in the presence of sunlight. Inversions suppress convection, or the normal expansion and rise of warm air, and prevent pollutants from escaping into the upper atmosphere. Convection is the mechanism responsible for the vertical transport of heat in the troposphere while horizontal heat transfer is accomplished through advection. The exchange and movement of water between the earth and atmosphere is called the water cycle. The cycle, which occurs in the troposphere, begins as the sun evaporates large amounts of water from the earth's surface and the moisture is transported to other regions by the wind. As air rises, expands, and cools, water vapor condenses and clouds develop. Clouds cover large portions of the earth at any given time and vary from fair-weather cirrus to towering cumulus clouds (see Cloud). When liquid or solid water particles grow large enough in size, they fall toward the earth as precipitation. The type of precipitation that reaches the ground, be it rain, snow, sleet, or freezing rain, depends upon the temperature of the air through which it falls. As sunlight enters the atmosphere, a portion is immediately reflected back to space, but the rest penetrates the atmosphere and is absorbed by the earth's surface. This energy is then reemitted by the earth back into the atmosphere as long-wave radiation. Carbon dioxide and water molecules absorb this energy and emit much of it back toward the earth again. This delicate exchange of energy between the earth's surface and atmosphere keeps the average global temperature from changing drastically from year to year. Contributed By: Frank Christopher Hawthorne Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. (d) Carbon Cycle Carbon Cycle (ecology) I INTRODUCTION Carbon Cycle (ecology), in ecology, the cycle of carbon usage by which energy flows through the earth's ecosystem. The basic cycle begins when photosynthesizing plants (see Photosynthesis) use carbon dioxide (CO2) found in the atmosphere or dissolved in water. Some of this carbon is incorporated in plant tissue as carbohydrates, fats, and protein; the rest is returned to the atmosphere or water primarily by aerobic respiration. Carbon is thus passed on to herbivores that eat the plants and thereby use, rearrange, and degrade the carbon compounds. Much of it is given off as CO2, primarily as a by-product of aerobic respiration, but some is stored in animal tissue and is passed on to carnivores feeding on the herbivores. Ultimately, all the carbon compounds are broken down by decomposition, and the carbon is released as CO2 to be used again by plants. II AIR-WATER EXCHANGES On a global scale the carbon cycle involves an exchange of CO2 between two great reservoirs: the atmosphere and the earth's waters. Atmospheric CO2 enters water by diffusion across the air-water surface. If the CO2 concentration in the water is less than that in the atmosphere, it diffuses into water, but if the CO2 concentration is greater in the water than in the atmosphere, CO2 enters the atmosphere. Additional exchanges take place within aquatic ecosystems. Excess carbon may combine with water to form carbonates and bicarbonates. Carbonates may precipitate out and become deposited in bottom sediments. Some carbon is incorporated in the forest-vegetation biomass (living matter) and may remain out of circulation for hundreds of years. Incomplete decomposition of organic matter in wet areas results in the accumulation of peat. Such accumulation during the Carboniferous period created great stores of fossil fuels: coal, oil, and gas. III TOTAL CARBON POOL The total carbon pool, estimated at about 49,000 metric gigatons (1 metric gigaton equals 109 metric tons), is distributed among organic and inorganic forms. Fossil carbon accounts for 22 percent of the total pool. The oceans contain 71 percent of the world's carbon, mostly in the form of bicarbonate and carbonate ions. An additional 3 percent is in dead organic matter and phytoplankton. Terrestrial ecosystems, in which forests are the main reservoir, hold about 3 percent of the total carbon. The remaining 1 percent is held in the atmosphere, circulated, and used in photosynthesis. IV ADDITIONS TO ATMOSPHERE Because of the burning of fossil fuels, the clearing of forests, and other such practices, the amount of CO2 in the atmosphere has been increasing since the Industrial Revolution. Atmospheric concentrations have risen from an estimated 260 to 300 parts per million (ppm) in preindustrial times to more than 350 ppm today. This increase accounts for only half of the estimated amount of carbon dioxide poured into the atmosphere. The other 50 percent has probably been taken up by and stored in the oceans. Although terrestrial vegetation may take up considerable quantities of carbon, it is also an additional source of CO2. Atmospheric CO2 acts as a shield over the earth. It is penetrated by short-wave radiation from outer space but blocks the escape of long-wave radiation. As increased quantities of CO2 are added to the atmosphere, the shield thickens and more heat is retained, increasing global temperatures. Although such increases have not yet been great enough to cancel out natural climatic variability, projected increases in CO2 from the burning of fossil fuels suggest that global temperatures could rise some 2° to 6° C (about 4° to 11° F) by early in the 21st century. This increase would be significant enough to alter global climates and thereby affect human welfare. See also Air Pollution; Greenhouse Effect. Contributed By: Robert Leo Smith Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. (e) Meningitis Meningitis I INTRODUCTION Meningitis, inflammation of the meninges, the membranes that surround the brain and spinal cord. Meningitis may be caused by a physical injury, a reaction to certain drugs, or more commonly, infection by certain viruses, bacteria, fungi, or parasites. This article focuses on meningitis caused by viral or bacterial infection. In the United States viral meningitis is the most common form of the disease, while bacterial meningitis, which affects an estimated 17,500 people each year, is the most serious form of the disease. Most cases of both viral and bacterial meningitis occur in the first five years of life. II CAUSE The most common causes of viral meningitis are coxsackie viruses and echoviruses, although herpesviruses, the mumps virus, and many other viruses can also cause the disease. Viral meningitis is rarely fatal, and most patients recover from the disease completely. Most cases of bacterial meningitis are caused by one of three species of bacteria—Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. Many other bacteria, including Escherichia coli and the bacteria that are responsible for tuberculosis and syphilis, can also cause the disease. Bacterial meningitis can be fatal if not treated promptly. Some children who survive the infection are left with permanent neurological impairments, such as hearing loss or learning disabilities. Many of the microorganisms that cause meningitis are quite common in the environment and are usually harmless. The microorganisms typically enter the body through the respiratory system or, sometimes, through the middle ear or nasal sinuses. Many people carry these bacteria or viruses without having any symptoms at all, while others experience minor, coldlike symptoms. Meningitis only develops if these microorganisms enter a patient’s bloodstream and then the cerebrospinal fluid (CSF), which surrounds the brain and spinal cord. The CSF contains no protective white blood cells to fight infection, so once the microorganisms enter the CSF, they multiply rapidly and make a person sick. Although the viruses and bacteria that cause meningitis are contagious, not everyone who comes in contact with someone with meningitis will develop the disease. In fact, meningitis typically occurs in isolated cases. Occasionally outbreaks of meningitis caused by Neisseria meningitidis, also known as meningococcal meningitis, occur in group living situations, such as day-care centers, college dormitories, or military barracks. A child whose immune system is weakened—due to a disease or genetic disorder, for instance--is at increased risk for developing meningitis. In general, however, scientists do not know why microorganisms that are usually harmless are able to cross into the CSF and cause meningitis in some people but not others. III SYMPTOMS AND DIAGNOSIS No matter what the cause, the symptoms of meningitis are always similar and usually develop rapidly, often over the course of a few hours. Nearly all patients with meningitis experience vomiting, high fever, and a stiff neck. Meningitis may also cause severe headache, back pain, muscle aches, sensitivity of the eyes to light, drowsiness, confusion, and even loss of consciousness. Some children have convulsions. In infants, the symptoms of meningitis are often more difficult to detect and may include irritability, lethargy, and loss of appetite. Most patients with meningococcal meningitis develop a rash of red, pinprick spots on the skin. The spots do not turn white when pressed, and they quickly grow to look like purple bruises. Meningitis is diagnosed by a lumbar puncture, or spinal tap, in which a doctor inserts a needle into the lower back to obtain a sample of CSF. The fluid is then tested for the presence of bacteria and other cells, as well as certain chemical changes that are characteristic of meningitis. IV TREATMENT AND PREVENTION It is imperative to seek immediate medical attention if the symptoms of meningitis develop in order to determine whether the meningitis is viral or bacterial. Any delays in treating bacterial meningitis can lead to stroke, severe brain damage, and even death. Patients with bacterial meningitis are usually hospitalized and given large doses of intravenous antibiotics. The specific antibiotic used depends on the bacterium responsible for the infection. Antibiotic therapy is very effective, and if treatment begins in time, the risk of dying from bacterial meningitis today is less than 15 percent. No specific treatment is available for viral meningitis. With bed rest, plenty of fluids, and medicine to reduce fever and control headache, most patients recover from viral meningitis within a week or two and suffer no lasting effects. Good hygiene to prevent the spread of viruses is the only method of preventing viral meningitis. To help prevent the spread of bacterial meningitis, antibiotics are sometimes given to family members and other people who have had close contact with patients who develop the disease. Vaccines are also available against some of the bacteria that can cause meningitis. A vaccine against one strain of Haemophilus influenzae, once the most common cause of bacterial meningitis, was introduced during the 1980s and has been a part of routine childhood immunization in the United States since 1990. This vaccine has dramatically reduced the number of cases of bacterial meningitis. Vaccines also exist for certain strains of Neisseria meningitidis and Streptococcus pneumoniae but are not a part of routine immunization. The Neisseria meningitidis vaccine is given to military recruits and people who are planning travel to areas of the world where outbreaks of meningococcal meningitis are common. The Streptococcus pneumoniae vaccine is recommended for people over age 65. Contributed By: David Spilker Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Question NO:4 Excretion The energy required for maintenance and proper functioning of the human body is supplied by food. After it is broken into fragments by chewing (see Teeth) and mixed with saliva, digestion begins. The food passes down the gullet into the stomach, where the process is continued by the gastric and intestinal juices. Thereafter, the mixture of food and secretions, called chyme, is pushed down the alimentary canal by peristalsis, rhythmic contractions of the smooth muscle of the gastrointestinal system. The contractions are initiated by the parasympathetic nervous system; such muscular activity can be inhibited by the sympathetic nervous system. Absorption of nutrients from chyme occurs mainly in the small intestine; unabsorbed food and secretions and waste substances from the liver pass to the large intestines and are expelled as feces. Water and water-soluble substances travel via the bloodstream from the intestines to the kidneys, which absorb all the constituents of the blood plasma except its proteins. The kidneys return most of the water and salts to the body, while excreting other salts and waste products, along with excess water, as urine. Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Blood enters the kidney through the renal artery. The artery divides into smaller and smaller blood vessels, called arterioles, eventually ending in the tiny capillaries of the glomerulus. The capillary walls here are quite thin, and the blood pressure within the capillaries is high. The result is that water, along with any substances that may be dissolved in it—typically salts, glucose or sugar, amino acids, and the waste products urea and uric acid—are pushed out through the thin capillary walls, where they are collected in Bowman's capsule. Larger particles in the blood, such as red blood cells and protein molecules, are too bulky to pass through the capillary walls and they remain in the bloodstream. The blood, which is now filtered, leaves the glomerulus through another arteriole, which branches into the meshlike network of blood vessels around the renal tubule. The blood then exits the kidney through the renal vein. Approximately 180 liters (about 50 gallons) of blood moves through the two kidneys every day. Urine production begins with the substances that the blood leaves behind during its passage through the kidney—the water, salts, and other substances collected from the glomerulus in Bowman’s capsule. This liquid, called glomerular filtrate, moves from Bowman’s capsule through the renal tubule. As the filtrate flows through the renal tubule, the network of blood vessels surrounding the tubule reabsorbs much of the water, salt, and virtually all of the nutrients, especially glucose and amino acids, that were removed in the glomerulus. This important process, called tubular reabsorption, enables the body to selectively keep the substances it needs while ridding itself of wastes. Eventually, about 99 percent of the water, salt, and other nutrients is reabsorbed. At the same time that the kidney reabsorbs valuable nutrients from the glomerular filtrate, it carries out an opposing task, called tubular secretion. In this process, unwanted substances from the capillaries surrounding the nephron are added to the glomerular filtrate. These substances include various charged particles called ions, including ammonium, hydrogen, and potassium ions. Together, glomerular filtration, tubular reabsorption, and tubular secretion produce urine, which flows into collecting ducts, which guide it into the microtubules of the pyramids. The urine is then stored in the renal cavity and eventually drained into the ureters, which are long, narrow tubes leading to the bladder. From the roughly 180 liters (about 50 gallons) of blood that the kidneys filter each day, about 1.5 liters (1.3 qt) of urine are produced. IV. OTHER FUNCTIONS OF THE KIDNEYS In addition to cleaning the blood, the kidneys perform several other essential functions. One such activity is regulation of the amount of water contained in the blood. This process is influenced by antidiuretic hormone (ADH), also called vasopressin, which is produced in the hypothalamus (a part of the brain that regulates many internal functions) and stored in the nearby pituitary gland. Receptors in the brain monitor the blood’s water concentration. When the amount of salt and other substances in the blood becomes too high, the pituitary gland releases ADH into the bloodstream. When it enters the kidney, ADH makes the walls of the renal tubules and collecting ducts more permeable to water, so that more water is reabsorbed into the bloodstream. The hormone aldosterone, produced by the adrenal glands, interacts with the kidneys to regulate the blood’s sodium and potassium content. High amounts of aldosterone cause the nephrons to reabsorb more sodium ions, more water, and fewer potassium ions; low levels of aldosterone have the reverse effect. The kidney’s responses to aldosterone help keep the blood’s salt levels within the narrow range that is best for crucial physiological activities. Aldosterone also helps regulate blood pressure. When blood pressure starts to fall, the kidney releases an enzyme (a specialized protein) called renin, which converts a blood protein into the hormone angiotensin. This hormone causes blood vessels to constrict, resulting in a rise in blood pressure. Angiotensin then induces the adrenal glands to release aldosterone, which promotes sodium and water to be reabsorbed, further increasing blood volume and blood pressure. The kidney also adjusts the body's acid-base balance to prevent such blood disorders as acidosis and alkalosis, both of which impair the functioning of the central nervous system. If the blood is too acidic, meaning that there is an excess of hydrogen ions, the kidney moves these ions to the urine through the process of tubular secretion. An additional function of the kidney is the processing of vitamin D; the kidney converts this vitamin to an active form that stimulates bone development. Several hormones are produced in the kidney. One of these, erythropoietin, influences the production of red blood cells in the bone marrow. When the kidney detects that the number of red blood cells in the body is declining, it secretes erythropoietin. This hormone travels in the bloodstream to the bone marrow, stimulating the production and release of more red cells. V. KIDNEY DISEASE AND TREATMENT Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Urine, pale yellow fluid produced by the kidneys, composed of dissolved wastes and excess water or chemical substances from the body. It is produced when blood filters through the kidneys, which remove about 110 liters (230 pints) of watery fluid from the blood every day. Most of this fluid is reabsorbed into the blood, but the remainder is passed from the body as urine. Urine leaves the kidneys, passes to the bladder through two slender tubes, the ureters, and exits the body through the urethra. A healthy adult can produce between 0.5 to 2 liters (1 to 4 pints) of urine a day, but the quantity varies considerably, depending on fluid intake and loss of fluid from sweating, vomiting, or diarrhea. 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