How are traits passed from one generation to another? The answer begins with heredity factors called genes, which are the blueprints for all new life.

Genes are chemical units found in the cells of all living things. Genes perform two functions: (1) They carry heredity traits; and (2) they give cells the day-to-day instructions for reproduction, growth, and development.

Each gene is a small section of a larger structure known as a chromosome. The word chromosome means "colored body." Chromosomes are dark, rodlike bodies found in the nucleus, or center of a cell. Each chromosome is composed of a long complex molecule known as DNA (deoxyribonucleic acid).

DNA looks like a twisted ladder with interlocking chemicals called bases forming each rung. DNA has only four different chemical bases. Yet these bases can be arranged in countless combinations along DNA's winding ladder. Each combination of three bases forms a chemical code that acts like a word in a sentence.

You can think of a gene as a chemical "sentence" that conveys information to the cell. A chromosome can contain hundreds of genes, or "sentences." Therfore, each chromosome contains much information that controls cell structure and function.

Have you noticed differences among members of the same species of plant or anmal? Though each species has its own specific genetic code, there are individual genetic variations that make a particular member of that species unique. Not all members of one species carry exactly the smae information in their genes.

Though every cell of your body carries your own unique genetic code, particular cells respond only to the geneticcide wirds that have meaning for them. For example, the genes that produce your eye color are not "active" or "switched on" in your skin cells. This is why as cellls reproduce each day they maintain their particular structure and function. Skin celles remain skin cells; they do not change into eye cells or muscle cells. Likewise, you maintain the genetic traits that make you a unique individual. If you have brown eyes today, you will always have brown eyes.

[Otto, J. (1987). Modern Health. New York: Hold, Rinehart and Winston, Publishers.]

No modern zoologist has the least doubt as to the general fact of organic evolution. Consequently anthropologists take as their starting poin the belief in the derivation of man from some other animal form. There is also no question as to where in a general way man's ancestry is to be sought. He is a mammal closely allied to the other mammals, and therfore has sprung from some mammalian type. His origin can be specified even more acfurately.

　The mammals fall into a number of fairly distict groups, such as the carnivores, or flesh-eating animals, the Ungulates r hoofed animals, the Rodents or gnawing animals, the Cetaceans or whales, and several others. The highest of these mammalian froups, as usually reckoned, is the Primate or "first" order of the animal kingdom. This Primate group includes the various monkeys and apes and man. The ancestors of the human race are therfore to be sought somewhere in the order of Primates, past or present.

The popular but inaccuate expression of this scientific conviction is that "man is descended from the monleys," but that a link has been lost in the chain of descent: the famous "missing link." In a loose way this statement reflects modern scientific opinion, but it certainly us oartly erroneous. Probably not a single authority maintains today that man is descended from any species of monkey now living. What students in the past have more and more convicted of, was already foreshadowed by Darwin: namely that man and the apes are both descended from a common ancestor. This common ancestor may be described as a primitive Primate, who differed in a good many details both from the monkeys and from man, and who has probably long since become extinct.

[Kroeber, A. (1948). Anthropology. New York: Harcourt Brace.]

Life theoretically originated on Earth 3.5 to 4 billion years ago. The atmosphere was thin: composed of methane, carbon dioxide, and water vapour. Any gaseous oxygen had been used up in the combustion (or oxidation) of materials when the Earth was very hot.

　The cooling water collected in pools, assimilating the nutrients from the rocks. As water evaporated, the nutrients concentrated, forming a rich soup. The first organisms would have made a good living off this food source, breaking down the complex molecules into water and carbon dioxide through respiration. Eventually, as life grew, the need arose to somehow resynthesize complex compounds, both to eat and to use for structure and function. Some organisms learned how to use the sun's energy to synthesize large molecules from small molecules. Other organisms learned to use other sources of reductive power. These organisms who have learned how to build the building blocks of life are called autotrophs, or self-feeders. Autotrophs are found in the bacterial and in the plant kingdom.

　Joseph Priestly, a chemist and minister, discovered that when he isolated a volume of air under an inverted jar, and burned a candle in it, the candle would burn out very quickly, much before it ran out of wax. He further discovered that a mouse could similarly "injure" air. He then showed that the air that had been "injured" by the candle and the mouse could be restored by a plant. In 1778, Jan Ingenhousz, court physician to the Austrian Empress, repeated Priestly's experiments. He discovered that it was the influence of sun and light on the plant that could cause it to rescue a mouse in a matter of hours.

In 1796, Jean Senebier, a French pastor, showed that CO2 was the "fixed" or "injured" air and that it was taken up by plants in photosynthesis. Soon afterwards, Theodore de Saussure showed that the increase in mass of the plant as it grows could not be due only to uptake of CO2, but also to the incorporation of water.

[http://esg-www.mit.edu:8001/esgbio/ps/intro.html]

　For millennia, farmers have battled insects, microorganisms, and weeds that destroy or compete with their crops--threatening their families with starvation. Indeed, many major events in history have resulted from devastating plant disease epidemics or insect infestations. The Irish potato famine of the mid-1800s, which was caused by the fungus Phytophthora infestans, killed more than a million people and prompted a massive Irish emigration to the United States.

　In hopes of preventing crop-plant destruction by pests, ancient Romans made sacrifices to their various gods. Modern farmers use other techniques in their attempts to kill pests, including spraying pesticide and herbicides, and plowing under weeds. They also make use of improved management practices and benefit from traditional breeding techniques to strengthen their crops. Some of the newer methods, however, have substantial costs and disadvantages. Excessive plowing can cause soil erosion, for instance. And pesticides and herbicides can pollute both soil and water as well as contribute to species extinction.

　Thanks to recent advances in the genetic engineering, or bioengineering, of plants, farmers are now beginning to have at their disposal crop seeds that are genetically endowed not only to resist damage from insects but also to be resistant to herbicides. These bioengineered seeds have the potential to revolutionize agriculture and improve environmental quality by making it possible to reduce the use of pesticides and keep plowing to a minimum.

　Like most scientific innovations that have had significant effects on society, bioengineered seeds did not emerge solely from the efforts of researchers to improve pest or weed control. Rather they were the by-product of earlier researchers' curiosity about such basic science questions as: How do bacteria cause plant tumors? How do some viruses protect plants from other viruses? What enables some bacteria to kill insects?

[http://www4.nationalacademies.org/beyond/beyonddiscovery.nsf/web/seeds?OpenDocument]

　The oceans of Earth cover more than 70 percent of the planet's surface, yet, until quite recently, we knew less about their depths than we did about the surface of the Moon. Distant as it is, the Moon has been far more accessible to study because astronomers long have been able to look at its surface, first with the naked eye and then with the telescope both instruments that focus light. And, with telescopes tuned to different wavelengths of light, modern astronomers can not only analyze Earth's atmosphere but also determine the temperature and composition of the Sun or of stars many hundreds of light-years away. Until the twentieth century, however, no analogous instruments were available for the study of Earth's oceans: Light, which can travel trillions of miles through the vast vacuum of space, cannot penetrate very far in seawater.

　It turns out that, for penetrating water, the phenomenon of choice is sound.　Water is an excellent medium for sound transmission. Sound travels almost five times faster in water than in air. 　

　Had the world known how to harness the extraordinary ability of sound to travel through water, in 1912, the Titanic might have had some warning of the iceberg that sent the luxury liner to the bottom of the North Atlantic and took the lives of 1,522 passengers and crew. This tragic event spurred the development of tools for echolocation, or echo ranging--the technique of detecting distant objects by sending out pulses of sound and listening for the return echo. Using these tools scientists and engineers went on to devise ever more sophisticated instruments for finding submarines during both World Wars.

Today, researchers apply their knowledge of how sound travels underwater to carry out myriad tasks, such as detecting nuclear explosions, earthquakes, and underwater volcanic eruptions. And just as astronomers use light to probe the secrets of the atmosphere, scientists in a field called acoustical oceanography use sound to study the temperature and structure of Earth's oceans measurements crucial to our ability to understand global climate change. Researchers in biological acoustics also use sound to study the behavior of marine mammals and their responses to human-generated underwater noise, helping to guide policies for protecting ocean wildlife.

[http://www4.nationalacademies.org/beyond/beyonddiscovery.nsf/web/ocean?OpenDocument]

By the 1960's and 1970's it was becoming ever more clear that serious damage was being done to the most essential of all the natural resources -- air, water, and the earth itself.

Clean air in many cities had been replaced by smog. Some 200 million tons of pollutants poured into the air each year from motor vehicles, industries, homes and power plants. Human and industrial wastes pouring into thje nation's rivers had turned many into virtual sewers. Growing shortages of fresh water in many areas of the country led to strcit regulations and sometimes to rationing.

The earth, as well as the air and the water, was deteriorating. Fertile land was being bulldozed to build highways, shopping malls, and housing developments. Irreplaceable farmland was vanishing at an estimated rate of 10,000 acres (4,000 hectares) every day.

The waters produced by our industrial society created problems for every form of life on the planet. Urban areas alone generated hundreds of thousands of tons of garbage and solid waste every day. Hazardous wastes fromchemical plants, nuclear reactors, and other industries polluted the air and accumulated in thousands of dumps across the countryside.

Finding proper ways to dispose of all the wastes, both liquid and solid, was difficult. Much of it could be burned. However, burning introduced pollutants into the air, and some burning wastes released poisonous fumes.

Burial was another widely used method of disposal. Some wastes decomposed safely or remained harmless underground. Other buried wastes could become deadly threats to the environment. This fact was driven home to the nation in a number of incidents.

[Todd, L. & M. Curti. (1982). Rise of the American Nation. New York: Harcourt Brace Jovanovich, Publishers.]

Ozone Loss: The Chemical Culprits

　In 1972, the life of atmospheric scientist F. Sherwood Rowland took a critical turn when he heard a lecture describing Lovelock's work. Like other researchers at the time, Rowland had no inkling that CFCs could harm the environment, but the injection into the atmosphere of large quantities of previously unknown compounds piqued his interest. What would be the ultimate fate of these compounds? Rowland, joined by Mario Molina, a colleague at the University of California, Irvine, decided to find out.

　The scientists showed that CFCs remained undisturbed in the lower atmosphere for decades. Invulnerable to visible sunlight, nearly insoluble in water, and resistant to oxidation, CFCs display an impressive durability in the atmosphere's lower depths. But at altitudes above 18 miles, with 99 percent of all air molecules lying beneath them, CFCs show their vulnerability. At this height, the harsh, high-energy ultraviolet radiation from the sun impinges directly on the CFC molecules, breaking them apart into chlorine atoms and residual fragments.

　If Rowland and Molina had ended their CFC study with these findings, no one other than atmospheric scientists would ever have heard about it. However, scientific completeness required that the researchers explore not only the fate of the CFCs, but also of the highly reactive atomic and molecular fragments generated by the ultraviolet radiation.

　In examining these fragments, Rowland and Molina were aided by prior basic research on chemical kinetics--the study of how quickly molecules react with one another and how such reactions take place. Scientists had demonstrated that a simple laboratory experiment will show how rapidly a particular reaction takes place, even if the reaction involves the interaction of a chlorine atom with methane at an altitude of 18 miles and a temperature of -60 degrees Fahrenheit.

　Rowland and Molina did not have to carry out even a single laboratory experiment on the reaction rates of chlorine atoms. They had only to look up the rates already measured by other scientists. Basic research into chemical kinetics had reduced a decade's worth of work to two or three days.

　After reviewing the pertinent reactions, the two researchers determined that most of the chlorine atoms combine with ozone, the form of oxygen that protects Earth from ultraviolet radiation. When chlorine and ozone react, they form the free radical chlorine oxide, which in turn becomes part of a chain reaction. As a result of that chain reaction, a single chlorine atom can remove as many as 100,000 molecules of ozone.

[http://www4.nas.edu/beyond/beyonddiscovery.nsf/web/ozone6?OpenDocument

　NASA's robotic missions to other planets have shown that all old, solid surfaces in the solar system are heavily cratered. Earth too must have been heavily bombarded, but the evidence has been largely hidden by the erosion acting on the surface of our dynamic planet. Even so, the many meteorite finds, Chicxulub, and the approximately 140 known craters around the world demonstrate that Earth has suffered massive hits.

　Trees near the Tunguska River in Siberia still looked devastated nearly two decades after a large meteorite exploded four miles above the ground in June 1908. The Tunguska event, which ranks as one of the most violent cosmic impacts of this century, leveled nearly 1,400 square miles of taiga forest.�Courtesy Sovfoto.�

�In modern times, the best known destructive impact occurred in a remote region of taiga forests near the Tunguska River in eastern Siberia at about 11:30 a.m. on June 30, 1908. The explosive energy released by the event was equivalent to roughly 15 million tons of TNT ― a thousand times more powerful than the Hiroshima bomb and matching a large hydrogen bomb. The meteorite, likely of stony composition with a diameter of 200 feet, exploded at an altitude of 5 miles, creating an air burst that leveled more than 1,200 square miles of forest. But this famous event is by no means unique even in the current century.

　Early on the morning of August 13, 1930, a large meteorite exploded over the Amazon jungles in an isolated area on the Curu釿 River with a force estimated to be a tenth of the Tunguska event. The bolide was heard as a shriek of artillery shells followed by great balls of fire that fell from the sky like thunderbolts. Three massive explosions and three shock waves ripped through the jungle, followed by a very light rain of ash that veiled the Sun until midday. The blasts were heard up to 150 miles away, while the resulting magnitude 7 earthquake was recorded 1,320 miles away in La Paz, Bolivia. This massive meteor explosion would not have been known to the outside world if not for a Capuchin monk, Father Fedele d'Alviano, who had visited the terrified population during his yearly apostolic mission and then written about the event for the papal newspaper.

[http://SkyandTelescope.com/observing/objects/meteors/article_122_9.asp]

Evolution of Physics

The earliest history of physics is interrelated with that of the other sciences. A number of contributions were made during the period of Greek civilization, dating from Thales and the early Ionian natural philosophers in the Greek colonies of Asia Minor (6th and 5th cent. B.C.).

　 Democritus (c.460-370 B.C.) proposed an atomic theory of matter and extended it to other phenomena as well, but the dominant theories of matter held that it was formed of a few basic elements, usually earth, air, fire, and water. In the school founded by Pythagoras of Samos the principal concept was that of number; it was applied to all aspects of the universe, from planetary orbits to the lengths of strings used to sound musical notes.

　The most important philosophy of the Greek period was produced by two men at Athens, Plato (427-347 B.C.) and his student Aristotle (384-322 B.C.); Aristotle in particular had a critical influence on the development of science in general and physics in particular.

　The Greek approach to physics was largely geometrical and reached its peak with Archimedes (287-212 B.C.), who studied a wide range of problems and anticipated the methods of the calculus.

　Another important scientist of the early Hellenistic period, centered in Alexandria, Egypt, was the astronomer Aristarchus (c.310-220 B.C.), who proposed a heliocentric, or sun-centered, system of the universe. However, just as the earlier atomic theory had not become generally accepted, so too the astronomical system that eventually prevailed was the geocentric system proposed by Hipparchus (190-120 B.C.) and developed in detail by Ptolemy (A.D. 85-A.D. 165).

[http://www.encyclopedia.com/articlesnew/10169EvolutionofPhysics.html]

　Evolution of Modern Chemistry

　In the hands of the Oxford Chemists (Robert Boyle, Robert Hooke, and John Mayow) chemistry began to emerge as distinct from the pseudoscience of alchemy. Boyle (1627-91) is often called the founder of modern chemistry (an honor sometimes also given Antoine Lavoisier, 1743-94). He performed experiments under reduced pressure, using an air pump, and discovered that volume and pressure are inversely related in gases (see gas laws). Hooke gave the first rational explanation of combustion-as combination with air-while Mayow studied animal respiration.

　Even as the English chemists were moving toward the correct theory of combustion, two Germans, J. J. Becher and G. E. Stahl, introduced the false phlogiston theory of combustion, which held that the substance phlogiston is contained in all combustible bodies and escapes when the bodies burn.

　The discovery of various gases and the analysis of air as a mixture of gases occurred during the phlogiston period. Carbon dioxide, first described by J. B. van Helmont and rediscovered by Joseph Black in 1754, was originally called fixed air. Hydrogen, discovered by Boyle and carefully studied by Henry Cavendish, was called inflammable air and was sometimes identified with phlogiston itself. Cavendish also showed that the explosion of hydrogen and oxygen produces water. C. W. Scheele found that air is composed of two fluids, only one of which supports combustion. He was the first to obtain pure oxygen (1771-73), although he did not recognize it as an element. Joseph Priestley independently discovered oxygen by heating the red oxide of mercury with a burning glass; he was the last great defender of the phlogiston theory.

[http://www.encyclopedia.com/articlesnew/02613HistoryofChemistry.html]

Scarcity of water, like scarcity of wood, was a problem that pioneer farm families had never had to face in the eastern part of the United States. Eastern farmers took their water from springs bubbling to the surface or from shallow wells.

On the great Plains, where the water was much deeper underground, machinery was needed to drill deeper wells. Once the well shafts had reached the water, the farmers then needed mechanical pumps to draw the water to the surface.

In a search for oil during the 1860's, petroleum companies developed new drilling machinery capable of penetrating farther beneath the surface than ever before. This machinery speedily found its way to the Great Plains. Farmers and ranchers used it to tap water supplies deep underground.

Meanwhile, other inventors were developing windmills capable of operating pumps to draw water to the surface. Daniel Halladay of Connecticut developed the self-governing windmill. This device automatically adjusted itself to wind pressure and thus operated at a uniform speed. The circular motion of the windmill blades was translated by a series of gears into the up-and-down motion of a rod. The rod powered a pump that brought water from the water table to the surface. Here the water flowed into tanks from which livestock could drink.

Windmills were first used on the Great Plains to provide water for steam locomotives crossing the plains and for herds of cattle. The windmill really came into its own when farmers began to settle on the semiarid lands. Factories producing windmills were soon doing a thriving business.

[Todd, L. & M. Curti. (1982). Rise of the American Nation. New York: Harcourt Brace Jovanovich, Publishers.]

　A computer virus is typically a short program designed to disperse copies of itself to other computers and disrupt those computers' normal operations. A computer virus usually attaches or inserts itself to or in an executable file or the boot sector (the area that contains the first instructions executed by a computer when it is started or restarted) of a disk; those that infect both files and boot records are called bimodal viruses.

　Although some viruses are merely disruptive, others can destroy or corrupt data or cause an operating system or applications program to malfunction. Computer viruses are spread via floppy disks, networks, or on-line services. Several thousand computer viruses are known, and on average three to five new strains are discovered every day.

　Antivirus programs and hardware have been developed to combat viruses. These search for evidence of a virus program (by checking for appearances or behavior that are characteristic of computer viruses), isolate infected files, and remove viruses from a computer's software.

　Researchers are working to sidestep the tedious process of manually analyzing viruses and creating protections against each by developing an automated immune system for computers patterned after biological processes. In 1995 Israel became the first country to legislate penalties both for those who write virus programs and those who spread the programs.

　A distinction should be made between a virus-which must attach itself of another program to be transmitted-and a bomb, a worm, and a Trojan horse. A bomb is a program that resides silently in a computer's memory until it is triggered by a specific condition, such as a date.

　A worm is a destructive program that propagates itself over a network, reproducing as it goes. A Trojan horse is a malicious program that passes itself off as a benign application; it cannot reproduce itself and, like a virus, must be distributed by diskette or electronic mail.

[http://www.encyclopedia.com/articlesnew/03021.html]

Geometry is the study of figures in a space of a given number of dimensions and of a given type. The most common types of geometry are plane geometry (dealing with objects like the line, circle, triangle, and polygon), solid geometry (dealing with objects like the line, sphere, and polyhedron), and spherical geometry (dealing with objects like the spherical triangle and spherical polygon). Geometry was part of the quadrivium taught in medieval universities.

　Historically, the study of geometry proceeds from a small number of accepted truths (axioms or postulates), then builds up true statements using a systematic and rigorous step-by-step proof. However, there is much more to geometry than this relatively dry textbook approach, as evidenced by some of the beautiful and unexpected results of projective geometry (not to mention Schubert's powerful but questionable enumerative geometry).

　The late mathematician E.�T.�Bell has described geometry as follows: "With a literature much vaster than those of algebra and arithmetic combined, and at least as extensive as that of analysis, geometry is a richer treasure house of more interesting and half-forgotten things, which a hurried generation has no leisure to enjoy, than any other division of mathematics." While the literature of algebra, arithmetic, and analysis has grown extensively since Bell's day, the remainder of his commentary holds even more so today.

Curing Childhood Leukemia

　Cancer is an insidious disease. The culprit is not a foreign invader, but the altered descendants of our own cells, which reproduce uncontrollably. In this civil war, it is hard to distinguish friend from foe, to target the cancer cells without killing the healthy cells. Most of our current cancer therapies, including the cure for childhood leukemia described here, are based on the fact that cancer cells reproduce without some of the safeguards present in normal cells. If we can interfere with cell reproduction, the cancer cells will be hit disproportionately hard and often will not recover.

　The scientists and physicians who devised the cure for childhood leukemia pioneered a rational approach to destroying cancer cells, using knowledge about the cell built up from a series of basic research discoveries earlier in this century. That research had shown that the machinery of the cell is based on a large set of chemical reactions that follow one after another like the steps in a production line. These reactions, known as the cell's metabolism, convert food to fat, muscle, and energy--with the starting materials for each step supplied by the previous step. Any one of the many production lines will grind to a halt if one of its steps is faulty. The scientists' approach was to take a chemical that they knew was essential for cell reproduction--a building block for making DNA--and modify it so that it jammed the cell's works when the cell mistook it for the usual chemical. Such deliberately defective materials are called antimetabolites. Many of them are now used as drugs to treat not only cancer, but also gout, bacterial infections, viral infections, and many other illnesses.

　The fight against cancer has been more of a war of attrition than a series of spectacular, instantaneous victories, and the research into childhood leukemia over the last 40 years is no exception. But most of the children who are victims of this disease can now be cured, and the drugs that made this possible are the antimetabolite drugs that will be described here. The logic behind those drugs came from a wide array of research that defined the chemical workings of the cell--research done by scientists who could not know that their findings would eventually save the lives of up to thirty thousand children in the United States.

[http://www4.nationalacademies.org/beyond/beyonddiscovery.nsf/web/leukemia?OpenDocument]

The human body has always been admired for its symmetry and beauty. But the image of the ideal physique has varied throughout history and among cultures. What is your ideal body image? Does it reflect health as well as appearance? The health male or female body has a proper balance between muscle tissue and fat; thus, it is neither obese nor underweight. Good nutrition and a fitness program are the keys to a healthful, more attractive self-image.

The second dietary guideline stresses weight control for the sake oof health, not appearance. Obesity increases the risk of both heart disease and strokes. Can you imagine carrying a 13.5-kilogram (30-lb) backpack with you everywhere you go? A person who gains 13.5 kilograms adds this burden to the body. The body adjusts to carrying this extra load as best it can, but there are dangers. Blood pressure increases and the heart enlarges. Too often the body gives up long before it would if proper weight were maintained. Obesity also increases, and posture problems.

Weght charts can help people determine if they are obese. However, these charts can sometimes be misleading. Muscle tissue weights more than fat. Active, well-muscled people may exceed their so-called "ideal" body weight by as much as 20 percent, and yet not be obese.

Obese people are "over-fat." They have an excess of bodyfat compared to leaner, heavier muscle tissue. People can even weigh in at an ideal weight, yet still be obese. If inactive, they may have too much fat and too little muscle tissue. There is one basic cause for being overweight, The body takes in more calories than it burns. Just 15 extra calories a day can add .68 kilograms (1.5 lb) to a person's weight each year. At this rate, how much weight would a person slowly gain betweem the ages of 18 and 38?

[Otto, J. (1987). Modern Health. New York: Hold, Rinehart and Winston, Publishers.]