Paper 2000 Question: 1 (a) Al-Beruni
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| VII EARTH’S FUTURE
With the rise of human civilization about 8,000 years ago and especially since the Industrial Revolution in the mid-1700s, human beings began to alter the surface, water, and atmosphere of Earth. In doing so, they have become active geological agents, not unlike other forces of change that influence the planet. As a result, Earth’s immediate future depends to a great extent on the behavior of humans. For example, the widespread use of fossil fuels is releasing carbon dioxide and other greenhouse gases into the atmosphere and threatens to warm the planet’s surface. This global warming could melt glaciers and the polar ice caps, which could flood coastlines around the world and many island nations. In effect, the carbon dioxide that was removed from Earth’s early atmosphere by the oceans and by primitive plant and animal life, and subsequently buried as fossilized remains in sedimentary rock, is being released back into the atmosphere and is threatening the existence of living things. See also Global Warming. Even without human intervention, Earth will continue to change because it is geologically active. Many scientists believe that some of these changes can be predicted. For example, based on studies of the rate that the seafloor is spreading in the Red Sea, some geologists predict that in 200 million years the Red Sea will be the same size as the Atlantic Ocean is today. Other scientists predict that the continent of Asia will break apart millions of years from now, and as it does, Lake Baikal in Siberia will become a vast ocean, separating two landmasses that once made up the Asian continent. In the far, far distant future, however, scientists believe that Earth will become an uninhabitable planet, scorched by the Sun. Knowing the rate at which nuclear fusion occurs in the Sun and knowing the Sun’s mass, astrophysicists (scientists who study stars) have calculated that the Sun will become brighter and hotter about 3 billion years from now, when it will be hot enough to boil Earth’s oceans away. Based on studies of how other Sun-like stars have evolved, scientists predict that the Sun will become a red giant, a star with a very large, hot atmosphere, about 7 billion years from now. As a red giant the Sun’s outer atmosphere will expand until it engulfs the planet Mercury. The Sun will then be 2,000 times brighter than it is now and so hot it will melt Earth’s rocks. Earth will end its existence as a burnt cinder. See also Sun. Three billion years is the life span of millions of human generations, however. Perhaps by then, humans will have learned how to journey beyond the solar system to colonize other planets in the Milky Way Galaxy and find another place to call “home.” Reviewed By: Alan V. Morgan Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. Question No:3 (a) Endocrine System I INTRODUCTION Endocrine System, group of specialized organs and body tissues that produce, store, and secrete chemical substances known as hormones. As the body's chemical messengers, hormones transfer information and instructions from one set of cells to another. Because of the hormones they produce, endocrine organs have a great deal of influence over the body. Among their many jobs are regulating the body's growth and development, controlling the function of various tissues, supporting pregnancy and other reproductive functions, and regulating metabolism. Endocrine organs are sometimes called ductless glands because they have no ducts connecting them to specific body parts. The hormones they secrete are released directly into the bloodstream. In contrast, the exocrine glands, such as the sweat glands or the salivary glands, release their secretions directly to target areas—for example, the skin or the inside of the mouth. Some of the body's glands are described as endo-exocrine glands because they secrete hormones as well as other types of substances. Even some nonglandular tissues produce hormone-like substances—nerve cells produce chemical messengers called neurotransmitters, for example. The earliest reference to the endocrine system comes from ancient Greece, in about 400 BC. However, it was not until the 16th century that accurate anatomical descriptions of many of the endocrine organs were published. Research during the 20th century has vastly improved our understanding of hormones and how they function in the body. Today, endocrinology, the study of the endocrine glands, is an important branch of modern medicine. Endocrinologists are medical doctors who specialize in researching and treating disorders and diseases of the endocrine system. II COMPONENTS OF THE ENDOCRINE SYSTEM The primary glands that make up the human endocrine system are the hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal body, and reproductive glands—the ovary and testis. The pancreas, an organ often associated with the digestive system, is also considered part of the endocrine system. In addition, some nonendocrine organs are known to actively secrete hormones. These include the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta. Almost all body cells can either produce or convert hormones, and some secrete hormones. For example, glucagon, a hormone that raises glucose levels in the blood when the body needs extra energy, is made in the pancreas but also in the wall of the gastrointestinal tract. However, it is the endocrine glands that are specialized for hormone production. They efficiently manufacture chemically complex hormones from simple chemical substances—for example, amino acids and carbohydrates—and they regulate their secretion more efficiently than any other tissues. The hypothalamus, found deep within the brain, directly controls the pituitary gland. It is sometimes described as the coordinator of the endocrine system. When information reaching the brain indicates that changes are needed somewhere in the body, nerve cells in the hypothalamus secrete body chemicals that either stimulate or suppress hormone secretions from the pituitary gland. Acting as liaison between the brain and the pituitary gland, the hypothalamus is the primary link between the endocrine and nervous systems. Located in a bony cavity just below the base of the brain is one of the endocrine system's most important members: the pituitary gland. Often described as the body’s master gland, the pituitary secretes several hormones that regulate the function of the other endocrine glands. Structurally, the pituitary gland is divided into two parts, the anterior and posterior lobes, each having separate functions. The anterior lobe regulates the activity of the thyroid and adrenal glands as well as the reproductive glands. It also regulates the body's growth and stimulates milk production in women who are breast-feeding. Hormones secreted by the anterior lobe include adrenocorticotropic hormone (ACTH), thyrotropic hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin. The anterior lobe also secretes endorphins, chemicals that act on the nervous system to reduce sensitivity to pain. The posterior lobe of the pituitary gland contains the nerve endings (axons) from the hypothalamus, which stimulate or suppress hormone production. This lobe secretes antidiuretic hormones (ADH), which control water balance in the body, and oxytocin, which controls muscle contractions in the uterus. The thyroid gland, located in the neck, secretes hormones in response to stimulation by TSH from the pituitary gland. The thyroid secretes hormones—for example, thyroxine and three-iodothyronine—that regulate growth and metabolism, and play a role in brain development during childhood. The parathyroid glands are four small glands located at the four corners of the thyroid gland. The hormone they secrete, parathyroid hormone, regulates the level of calcium in the blood. Located on top of the kidneys, the adrenal glands have two distinct parts. The outer part, called the adrenal cortex, produces a variety of hormones called corticosteroids, which include cortisol. These hormones regulate salt and water balance in the body, prepare the body for stress, regulate metabolism, interact with the immune system, and influence sexual function. The inner part, the adrenal medulla, produces catecholamines, such as epinephrine, also called adrenaline, which increase the blood pressure and heart rate during times of stress. The reproductive components of the endocrine system, called the gonads, secrete sex hormones in response to stimulation from the pituitary gland. Located in the pelvis, the female gonads, the ovaries, produce eggs. They also secrete a number of female sex hormones, including estrogen and progesterone, which control development of the reproductive organs, stimulate the appearance of female secondary sex characteristics, and regulate menstruation and pregnancy. Located in the scrotum, the male gonads, the testes, produce sperm and also secrete a number of male sex hormones, or androgens. The androgens, the most important of which is testosterone, regulate development of the reproductive organs, stimulate male secondary sex characteristics, and stimulate muscle growth. The pancreas is positioned in the upper abdomen, just under the stomach. The major part of the pancreas, called the exocrine pancreas, functions as an exocrine gland, secreting digestive enzymes into the gastrointestinal tract. Distributed through the pancreas are clusters of endocrine cells that secrete insulin, glucagon, and somastatin. These hormones all participate in regulating energy and metabolism in the body. The pineal body, also called the pineal gland, is located in the middle of the brain. It secretes melatonin, a hormone that may help regulate the wake-sleep cycle. Research has shown that disturbances in the secretion of melatonin are responsible, in part, for the jet lag associated with long-distance air travel. III HOW THE ENDOCRINE SYSTEM WORKS Hormones from the endocrine organs are secreted directly into the bloodstream, where special proteins usually bind to them, helping to keep the hormones intact as they travel throughout the body. The proteins also act as a reservoir, allowing only a small fraction of the hormone circulating in the blood to affect the target tissue. Specialized proteins in the target tissue, called receptors, bind with the hormones in the bloodstream, inducing chemical changes in response to the body’s needs. Typically, only minute concentrations of a hormone are needed to achieve the desired effect. Too much or too little hormone can be harmful to the body, so hormone levels are regulated by a feedback mechanism. Feedback works something like a household thermostat. When the heat in a house falls, the thermostat responds by switching the furnace on, and when the temperature is too warm, the thermostat switches the furnace off. Usually, the change that a hormone produces also serves to regulate that hormone's secretion. For example, parathyroid hormone causes the body to increase the level of calcium in the blood. As calcium levels rise, the secretion of parathyroid hormone then decreases. This feedback mechanism allows for tight control over hormone levels, which is essential for ideal body function. Other mechanisms may also influence feedback relationships. For example, if an individual becomes ill, the adrenal glands increase the secretions of certain hormones that help the body deal with the stress of illness. The adrenal glands work in concert with the pituitary gland and the brain to increase the body’s tolerance of these hormones in the blood, preventing the normal feedback mechanism from decreasing secretion levels until the illness is gone. Long-term changes in hormone levels can influence the endocrine glands themselves. For example, if hormone secretion is chronically low, the increased stimulation by the feedback mechanism leads to growth of the gland. This can occur in the thyroid if a person's diet has insufficient iodine, which is essential for thyroid hormone production. Constant stimulation from the pituitary gland to produce the needed hormone causes the thyroid to grow, eventually producing a medical condition known as goiter. IV DISEASES OF THE ENDOCRINE SYSTEM Endocrine disorders are classified in two ways: disturbances in the production of hormones, and the inability of tissues to respond to hormones. The first type, called production disorders, are divided into hypofunction (insufficient activity) and hyperfunction (excess activity). Hypofunction disorders can have a variety of causes, including malformations in the gland itself. Sometimes one of the enzymes essential for hormone production is missing, or the hormone produced is abnormal. More commonly, hypofunction is caused by disease or injury. Tuberculosis can appear in the adrenal glands, autoimmune diseases can affect the thyroid, and treatments for cancer—such as radiation therapy and chemotherapy—can damage any of the endocrine organs. Hypofunction can also result when target tissue is unable to respond to hormones. In many cases, the cause of a hypofunction disorder is unknown. Hyperfunction can be caused by glandular tumors that secrete hormone without responding to feedback controls. In addition, some autoimmune conditions create antibodies that have the side effect of stimulating hormone production. Infection of an endocrine gland can have the same result. Accurately diagnosing an endocrine disorder can be extremely challenging, even for an astute physician. Many diseases of the endocrine system develop over time, and clear, identifying symptoms may not appear for many months or even years. An endocrinologist evaluating a patient for a possible endocrine disorder relies on the patient's history of signs and symptoms, a physical examination, and the family history—that is, whether any endocrine disorders have been diagnosed in other relatives. A variety of laboratory tests—for example, a radioimmunoassay—are used to measure hormone levels. Tests that directly stimulate or suppress hormone production are also sometimes used, and genetic testing for deoxyribonucleic acid (DNA) mutations affecting endocrine function can be helpful in making a diagnosis. Tests based on diagnostic radiology show anatomical pictures of the gland in question. A functional image of the gland can be obtained with radioactive labeling techniques used in nuclear medicine. One of the most common diseases of the endocrine systems is diabetes mellitus, which occurs in two forms. The first, called diabetes mellitus Type 1, is caused by inadequate secretion of insulin by the pancreas. Diabetes mellitus Type 2 is caused by the body's inability to respond to insulin. Both types have similar symptoms, including excessive thirst, hunger, and urination as well as weight loss. Laboratory tests that detect glucose in the urine and elevated levels of glucose in the blood usually confirm the diagnosis. Treatment of diabetes mellitus Type 1 requires regular injections of insulin; some patients with Type 2 can be treated with diet, exercise, or oral medication. Diabetes can cause a variety of complications, including kidney problems, pain due to nerve damage, blindness, and coronary heart disease. Recent studies have shown that controlling blood sugar levels reduces the risk of developing diabetes complications considerably. Diabetes insipidus is caused by a deficiency of vasopressin, one of the antidiuretic hormones (ADH) secreted by the posterior lobe of the pituitary gland. Patients often experience increased thirst and urination. Treatment is with drugs, such as synthetic vasopressin, that help the body maintain water and electrolyte balance. Hypothyroidism is caused by an underactive thyroid gland, which results in a deficiency of thyroid hormone. Hypothyroidism disorders cause myxedema and cretinism, more properly known as congenital hypothyroidism. Myxedema develops in older adults, usually after age 40, and causes lethargy, fatigue, and mental sluggishness. Congenital hypothyroidism, which is present at birth, can cause more serious complications including mental retardation if left untreated. Screening programs exist in most countries to test newborns for this disorder. By providing the body with replacement thyroid hormones, almost all of the complications are completely avoidable. Addison's disease is caused by decreased function of the adrenal cortex. Weakness, fatigue, abdominal pains, nausea, dehydration, fever, and hyperpigmentation (tanning without sun exposure) are among the many possible symptoms. Treatment involves providing the body with replacement corticosteroid hormones as well as dietary salt. Cushing's syndrome is caused by excessive secretion of glucocorticoids, the subgroup of corticosteroid hormones that includes hydrocortisone, by the adrenal glands. Symptoms may develop over many years prior to diagnosis and may include obesity, physical weakness, easily bruised skin, acne, hypertension, and psychological changes. Treatment may include surgery, radiation therapy, chemotherapy, or blockage of hormone production with drugs. Thyrotoxicosis is due to excess production of thyroid hormones. The most common cause for it is Graves' disease, an autoimmune disorder in which specific antibodies are produced, stimulating the thyroid gland. Thyrotoxicosis is eight to ten times more common in women than in men. Symptoms include nervousness, sensitivity to heat, heart palpitations, and weight loss. Many patients experience protruding eyes and tremors. Drugs that inhibit thyroid activity, surgery to remove the thyroid gland, and radioactive iodine that destroys the gland are common treatments. Acromegaly and gigantism both are caused by a pituitary tumor that stimulates production of excessive growth hormone, causing abnormal growth in particular parts of the body. Acromegaly is rare and usually develops over many years in adult subjects. Gigantism occurs when the excess of growth hormone begins in childhood. Contributed By: Gad B. Kletter Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved. (b) Eco-System Ecosystem I INTRODUCTION Ecosystem, organisms living in a particular environment, such as a forest or a coral reef, and the physical parts of the environment that affect them. The term ecosystem was coined in 1935 by the British ecologist Sir Arthur George Tansley, who described natural systems in “constant interchange” among their living and nonliving parts. The ecosystem concept fits into an ordered view of nature that was developed by scientists to simplify the study of the relationships between organisms and their physical environment, a field known as ecology. At the top of the hierarchy is the planet’s entire living environment, known as the biosphere. Within this biosphere are several large categories of living communities known as biomes that are usually characterized by their dominant vegetation, such as grasslands, tropical forests, or deserts. The biomes are in turn made up of ecosystems. The living, or biotic, parts of an ecosystem, such as the plants, animals, and bacteria found in soil, are known as a community. The physical surroundings, or abiotic components, such as the minerals found in the soil, are known as the environment or habitat. Any given place may have several different ecosystems that vary in size and complexity. A tropical island, for example, may have a rain forest ecosystem that covers hundreds of square miles, a mangrove swamp ecosystem along the coast, and an underwater coral reef ecosystem. No matter how the size or complexity of an ecosystem is characterized, all ecosystems exhibit a constant exchange of matter and energy between the biotic and abiotic community. Ecosystem components are so interconnected that a change in any one component of an ecosystem will cause subsequent changes throughout the system. II HOW ECOSYSTEMS WORK The living portion of an ecosystem is best described in terms of feeding levels known as trophic levels. Green plants make up the first trophic level and are known as primary producers. Plants are able to convert energy from the sun into food in a process known as photosynthesis. In the second trophic level, the primary consumers—known as herbivores—are animals and insects that obtain their energy solely by eating the green plants. The third trophic level is composed of the secondary consumers, flesh-eating or carnivorous animals that feed on herbivores. At the fourth level are the tertiary consumers, carnivores that feed on other carnivores. Finally, the fifth trophic level consists of the decomposers, organisms such as fungi and bacteria that break down dead or dying matter into nutrients that can be used again. Some or all of these trophic levels combine to form what is known as a food web, the ecosystem’s mechanism for circulating and recycling energy and materials. For example, in an aquatic ecosystem algae and other aquatic plants use sunlight to produce energy in the form of carbohydrates. Primary consumers such as insects and small fish may feed on some of this plant matter, and are in turn eaten by secondary consumers, such as salmon. A brown bear may play the role of the tertiary consumer by catching and eating salmon. Bacteria and fungi may then feed upon and decompose the salmon carcass left behind by the bear, enabling the valuable nonliving components of the ecosystem, such as chemical nutrients, to leach back into the soil and water, where they can be absorbed by the roots of plants. In this way nutrients and the energy that green plants derive from sunlight are efficiently transferred and recycled throughout the ecosystem. In addition to the exchange of energy, ecosystems are characterized by several other cycles. Elements such as carbon and nitrogen travel throughout the biotic and abiotic components of an ecosystem in processes known as nutrient cycles. For example, nitrogen traveling in the air may be snatched by a tree-dwelling, or epiphytic, lichen that converts it to a form useful to plants. When rain drips through the lichen and falls to the ground, or the lichen itself falls to the forest floor, the nitrogen from the raindrops or the lichen is leached into the soil to be used by plants and trees. Another process important to ecosystems is the water cycle, the movement of water from ocean to atmosphere to land and eventually back to the ocean. An ecosystem such as a forest or wetland plays a significant role in this cycle by storing, releasing, or filtering the water as it passes through the system. Every ecosystem is also characterized by a disturbance cycle, a regular cycle of events such as fires, storms, floods, and landslides that keeps the ecosystem in a constant state of change and adaptation. Some species even depend on the disturbance cycle for survival or reproduction. For example, longleaf pine forests depend on frequent low-intensity fires for reproduction. The cones of the trees, which contain the reproductive structures, are sealed shut with a resin that melts away to release the seeds only under high heat. III ECOSYSTEM MANAGEMENT Humans benefit from these smooth-functioning ecosystems in many ways. Healthy forests, streams, and wetlands contribute to clean air and clean water by trapping fast-moving air and water, enabling impurities to settle out or be converted to harmless compounds by plants or soil. The diversity of organisms, or biodiversity, in an ecosystem provides essential foods, medicines, and other materials. But as human populations increase and their encroachment on natural habitats expands, humans are having detrimental effects on the very ecosystems on which they depend. The survival of natural ecosystems around the world is threatened by many human activities: bulldozing wetlands and clear-cutting forests—the systematic cutting of all trees in a specific area—to make room for new housing and agricultural land; damming rivers to harness the energy for electricity and water for irrigation; and polluting the air, soil, and water. Directory: 2014 2014 -> For want of a nail 2014 -> The Global Warming that Wasn’t 2014 -> Assembly, No. 3901 state of new jersey 216th legislature 2014 -> Stop Militarizing Law Enforcement Act of 2014 2014 -> Ihbb asian Championships 2014 middle school bowl Round 4 First Quarter 2014 -> Unit: Automotive and Auto Body 2014 -> Ihbb european Championships 2014 Bowl Round 4 First Quarter 2014 -> International History Bee and Bowl 2013-14 Asian Division Question Set Bowl Round Six 2014 -> United states patent and trademark office 2014 -> Walnut creek, ca branch executive committee meeting minutes Download 0.98 Mb. 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