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prissygirl Tuesday, November 13, 2007 02:20 PM

gr8 work
 
2 Attachment(s)
welldone predator but i would like to add some diagramatic representations through which the posted topics can easily be understood.
[B]EYE[/B]

Predator Tuesday, November 13, 2007 02:35 PM

Aging
 
[B]Aging

I -INTRODUCTION[/B]

Aging, irreversible biological changes that occur in all living things with the passage of time, eventually resulting in death. Although all organisms age, rates of aging vary considerably. Fruit flies, for example, are born, grow old, and die in 30 or 40 days, while field mice have a life span of about three years. Dolphins may live to age 25, elephants to age 50, and Galápagos tortoises to 100. These life spans pale in comparison to those of some species of giant sequoia trees, which live hundreds of years.

Among humans, the effects of aging vary from one individual to another. The average life expectancy for Americans is around 75 years, almost twice what it was in the early 1900s. Although some people never reach this age, and others are beset with illnesses if they do, more and more people are living healthy lives well into their 90s and older. The study of the different aging processes that occur among individuals and the factors that cause these changes is known as gerontology. Geriatrics is a medical specialty concerned with the prevention, diagnosis, and treatment of diseases in the elderly.

[B]II -EFFECTS OF AGING ON THE HUMAN BODY[/B]
Several general changes take place in the human body as it ages: hearing and vision decline, muscle strength lessens, soft tissues such as skin and blood vessels become less flexible, and there is an overall decline in body tone.

Most of the body's organs perform less efficiently with advancing age. For example, the average amount of blood pumped by the heart drops from about 6.9 liters (7.3 quarts) per minute at age 20 to only 3.5 liters (3.7 quarts) pumped per minute at age 85. For this same age range, the average amount of blood flowing through the kidneys drops from approximately 0.6 liters (0.6 quarts) per minute to 0.3 liters (0.3 quarts). Not all people experience decreased organ function to the same degree—some individuals have healthier hearts and kidneys at age 85 than others do at age 50.

The immune system also changes with age. A healthy immune system protects the body against bacteria, viruses, and other harmful agents by producing disease-fighting proteins known as antibodies. A healthy immune system also prevents the growth of abnormal cells, which can become cancerous. With advancing age, the ability of the immune system to carry out these protective functions is diminished—the rate of antibody production may drop by as much as 80 percent between age 20 and age 85. This less-effective immune system explains why a bout of influenza, which may make a young adult sick for a few days, can be fatal for an elderly person. Thus, it is as important for an older person to be vaccinated against the flu and pneumonia as it is for young people to be vaccinated against childhood diseases.

Most of the glands of the endocrine system, the organs that secrete hormones regulating such functions as metabolism, temperature, and blood sugar levels, retain their ability to function into advanced age. However, these glands often become less sensitive to the triggers that direct hormone secretion. In the aging pancreas, for example, higher blood sugar levels are required to stimulate the release of insulin, a hormone that helps the muscles convert blood sugar to energy.

The ovaries and the testes, the endocrine glands that regulate many aspects of sexual reproduction, alter during the aging process. As a man ages, the testes produce less of the male sex hormone, testosterone. A woman's ovaries undergo marked changes from about age 45 to age 55 during a process known as menopause. The ovaries no longer release egg cells, and they no longer generate the hormones that stimulate monthly menstrual cycles. After women have gone through menopause, they are no longer capable of having children without the aid of reproductive technology. The physical changes associated with aging do not have a significant impact on sexual activity—most healthy people maintain an interest in sex all of their lives.

[B]III -THE EFFECTS OF AGING ON THE MIND[/B]
One of the myths of aging is that intelligence diminishes with age. Early studies that used intelligence tests designed for children revealed that older people scored lower than young adults. However, these tests relied heavily on skills commonly used in school classrooms, such as arithmetic, and required the test to be completed within a specific time limit. Older people may require more time to answer questions, and more recent studies based on untimed tests and other measures of intellectual activity, such as problem solving and concept formation, show that there is relatively little decline in mental ability in healthy people at least up to age 70.

The aging brain does undergo a progressive loss of neurons, or nerve cells, but these losses represent only a small percentage of neurons in the brain. The speed of conduction of a nerve impulse declines with age, but it drops only about 15 percent over the age span from 30 to 85 years. Although intelligence is generally not affected by the aging process, studies show that some older people may find it difficult to deal with many stimuli at once. For example, an older individual requires more time to sort out all of the information when many highway signs come into view simultaneously.

Traveling at 97 km/h (60 mph), an elderly driver may miss the information he or she needs or may act on the wrong information. But if older individuals recognize this limitation and adjust their behavior accordingly, they can continue driving safely well into old age.

Many older people experience problems with memory, and up to 10 percent of the elderly have memory problems significant enough to interfere with their ability to function independently. Memory problems were once considered an inevitable effect of the aging process, but researchers have determined that many of the brain-related changes often observed in elderly people, including memory loss, are actually a result of such diseases as Alzheimer’s disease and diseases associated with blood vessels and blood flow in the brain, such as stroke. Memory loss is sometimes treatable, and certain memory-aiding strategies have been found to help reverse the short-term memory loss experienced by many older people.

Another myth about aging is that people tend to grow sour and mean-spirited with age. Research shows that personalities really do not change much over time. A mean-spirited, grumpy old person was probably that way when he or she was 30. And, as humans age, most still like to do the things they did when they were young. For example those who were athletic in their youth may continue to enjoy athletic activities as they age.

An older person's social environment, however, can have a marked impact on personality. The social isolation that often exists among older people can dramatically influence mental attitudes and behavior. In the United States, 33 percent of all older people live alone, most of them widowed women over the age of 85. About 5 percent of elderly Americans live in some type of long-term care facility, and almost 25 percent of all older Americans live under or near the federal poverty level. These people have little or no money for recreational activities. This poverty and isolation often leads to clinical depression and other problems, such as alcoholism.

[B]IV -CAUSES OF AGING [/B]
Although the exact causes of aging remain unknown, scientists are learning a great deal about the aging process and the mechanisms that drive it. Some of the most promising research on the aging process focuses on the microscopic changes that occur in all living cells as organisms age. In 1965 American microbiologist Leonard Hayflick observed that under laboratory conditions, human cells can duplicate up to 50 times before they stop. Hayflick also noted that when cells stop normal cell division (see Mitosis), they start to age, or senesce. Since Hayflick’s groundbreaking observations, scientists have been searching for the underlying cause, known as the senescent factor (SF), of why cells stop dividing and thus age.

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 with advancing age, are caused by structural damage to cells. This damage accumulates in tiny amounts each time the cell divides, eventually preventing the cell from carrying 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 the body. Free radicals contain unpaired electrons and so carry an electric charge that makes them highly reactive. In an effort to neutralize their electric charge, free radicals constantly bombard cells in order to steal electrons in a process called oxidation. Free radicals are thought to greatly increase the severity of—or perhaps even cause—such life-shortening diseases as diabetes mellitus, strokes, and heart attacks. Researchers have observed that free radicals exist in smaller amounts in those species with relatively long life spans. Increasing human life span may depend on our ability to prevent free radical damage, and scientists are currently examining the role of chemical compounds, called antioxidants, that prevent or reverse oxidative damage in the aging process.

Another theory suggests that SF is genetically regulated—that is, cells are genetically programmed to carry out about 50 cell divisions and then die. Researchers have identified at least three genes that are involved with human cellular senescence. They have also discovered a protein on the surface membranes of senescent cells that inhibits production of deoxyribonucleic acid (DNA), the essential molecule that carries all genetic information.

Another theory proposes that extra, useless bits of DNA accumulate over time within a cell's nucleus. Eventually this so-called junk DNA builds up to levels that clog normal cell action. If this idea is correct, scientists may be able to find ways to prevent accumulation of junk DNA, thereby slowing down the process of senescence in cells.

Other studies focus on cell division limits. Each time a cell divides, it duplicates its DNA, and in each division the sections at the ends of DNA, called the telomeres, are gradually depleted, or shortened. Eventually the telomeres become so depleted that normal cell division halts, typically within 50 cell divisions. Scientists have found that an enzyme produced by the human body, called telomerase, can prolong the life of the telomeres, thus extending the number of cell divisions. In laboratory studies, cells injected with telomerase continue to divide well beyond the normal limit of 50 cell divisions. These promising results have triggered worldwide attention on telomerase and its relationship to aging.

A number of other studies are underway to investigate the effects of aging. Scientists have found, for example, a possible explanation for why women have longer average life spans than men. The difference seems to be biologically determined, and male and female sex hormones are probably responsible. The blood levels of female sex hormones drop sharply during menopause. At that time, the incidence of heart disease and high blood pressure in women increases to match the incidence in men, suggesting that the presence of female sex hormones offers some protection against heart disease.

[B]V -AGING POPULATIONS[/B]
In developed nations, life expectancy has increased more in the 20th century than it has in all of recorded history. A person born in the United States in 1995 can expect to live more than 35 years longer than a person born in
1900. Today more than 34 million Americans are 65 or older, accounting for about 13 percent of the population. By the year 2030, their numbers will more than double: One in every five Americans will be over age 65.

A person who lives 100 years or more—a centenarian—was once a rarity, but today about 60,000 Americans are 100 years or older. By the year 2060, there may be as many as 2.5 million centenarians in the United States. The number of supercentenarians—people 105 years of age and older—will probably be as commonplace in the next century as centenarians are fast becoming now.

In some parts of the world, 16 to 18 percent of the population is already age 65 or older. By the year 2025, Japan is expected to have twice as many old people as children. Also by that time, there will be more than one billion older people worldwide. This increase in life expectancy is the result of better public health measures, improvements in living conditions, and advances in medical care. A marked reduction in infant mortality rates has also contributed to increased life expectancy statistics.

Aging populations are expected to have profound effects on the way societies care for their elderly members. With a larger proportion of the population over age 65, medical care must become better equipped to deal with the disorders and diseases of the elderly. All health care professionals should have special training in geriatrics. As the percentage of older people in the population exceeds the percentage of young working people, traditional methods for caring for older people may need to be modified. For example, in the United States, workers pay taxes throughout their careers so that when they retire, usually around the age of 65, they can receive money from the federal government to survive. This system, called Social Security, may be in jeopardy as the percentage of retired people increases, placing inordinate demands on the smaller number of people working and supporting them.

In many parts of the world, including the United States, older people who cannot work and have health problems live in long-term care facilities such as nursing homes, where they receive care 24 hours a day. But many families are unable to bear the costs of nursing homes and medical care for the elderly, and health insurance is unable to cover the expense. Other countries face similar problems, and multinational efforts are underway to explore new methods to finance the care of the world’s older persons, soon to number one billion.

prissygirl Tuesday, November 13, 2007 02:51 PM

structure of DNA and its bonding
 
3 Attachment(s)
[B][I]the structure of DNA according to the watson and crick model and the bonding within the nucleotides and between the two strands of DNA[/I][/B].

It should be kept in mind that the Gaunine of one strand is bonded through the hydrogen bond with the cytosine of the complementary strand and adenine with thymine.There are two hydrogen bonds between adenine and thymine and three hydrogen bonds between guanine and cytosine.

the nitrogenous bases are categorised as[LIST][*]Double ringed Purines including adenine and guanine[*]single ringed pryrimidines including thymine and cytosine.[/LIST]the two strand of DNA are anti parrallel to each other.
regards

prissygirl Tuesday, November 13, 2007 03:07 PM

transcription Of mRNA
 
2 Attachment(s)
the formation of the single stranded RNA from one of the two strands of DNA for the purpose of protein synthesis is called transcription.

Predator Tuesday, November 13, 2007 03:20 PM

Ecosystem
 
[B]Ecosystem[/B]

[B]I -INTRODUCTION[/B]
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.

[B]II -HOW ECOSYSTEMS WORK[/B]
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.

[B]III -ECOSYSTEM MANAGEMENT[/B]
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.

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.

prissygirl Tuesday, November 13, 2007 03:22 PM

translation/protein synthesis
 
2 Attachment(s)
simply, in protein synthesis the the mRNA enteres the cytoplasm where ribosomes get attached to it.....read the genetic code and translate it into amino acids resulting in the formation of polypeptides and proteins.

prissygirl Tuesday, November 13, 2007 03:40 PM

replication Of DNA
 
2 Attachment(s)
the single molecule of double sranded DNA,before cell division,replicates and give rise to two daughter molecules.in this process each strand acts as a tepelate and synthesize its complementary strand.now each newly formed DNA molecule has one parent and one daughter or newly formed strand.

prissygirl Tuesday, November 13, 2007 03:44 PM

Red blood cells
 
1 Attachment(s)
The red color of the blood is due to the presence of the protein called Haemoglobin in specialised blood cells called red blood cells.these are biconcave bean shaped cells which are non-nucleated.

prissygirl Tuesday, November 13, 2007 04:00 PM

White blood cells
 
2 Attachment(s)
white blood cells are the leukocytes which are an important figure of the body's defense system.
they are divided into
Agranulocyte: their cytoplasm is clear and donot contain any granules in it.it includes [B]lymphocytes and monocytes[/B]
granulocyte:their cytoplasm is rich in granule like structure which are basically the lysosomes.these lysosomes help the white blood cell to act upon other foreign agents,phagocytose or engulf them because of such characteristics of lysosomes.Examples are [B]Eosinophil,Basophil,neutrophil[/B].
All these WBC's can be recognised on the basis of staining method and the shape of their nucleus

prissygirl Tuesday, November 13, 2007 04:10 PM

platelets
 
1 Attachment(s)
the component of the blood responsible for clotting is called platelets.the activity of the platelets is promoted by thrombin,a coagulation protein present in blood.


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