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. Gay-Lussac, Joseph Louis (1778-1850), French chemist and physicist, known for his studies on the physical properties of gases . He was born in Saint Léonard and educated at the École Polytechnique and the École des Ponts et Chaussées in Paris. After holding several professorships he became professor of physics at the Sorbonne from 1808 to 1832. In 1804 he made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes. In 1809 he formulated a law of gases that is still associated with his name. Gay-Lussac's law of combining volumes states that the volumes of the gases involved in a chemical reaction (both reactants and products) are in the ratio of small whole numbers. In connection with these studies he investigated, with German naturalist Baron Alexander von Humboldt, the composition of water and found it forms when two parts of hydrogen and one of oxygen unite. In 1809 Gay-Lussac worked on the preparation of pot...

. Hofmann, August Wilhelm von (1818-1892), German chemist, born in Giessen, and educated at the University of Giessen. From 1845 to 1864 he was director of the Royal College of Chemistry in London. In 1865 he accepted a professorship in chemistry at the University of Berlin. He founded the German Chemical Society in 1868. Hofmann was one of the great organic chemists of his time. He worked with coal-tar products, from which he isolated benzene and aniline , and which he used in the synthesis of artificial dyes that formed the basis for a new industry. He studied and clarified the chemistry of amines, and his method for converting amides to amines is now called the Hofmann reaction. He also discovered many organic chemicals, including allyl alcohol and formaldehyde.

. Ramsay, Sir William (1852-1916), British chemist, best known for his work in the isolation of elemental gases from the atmosphere. Ramsay was born in Glasgow, Scotland, and educated at the universities of Glasgow and Tübingen. He served as professor of chemistry at the University of Bristol from 1880 to 1887 and at the University of London from 1887 until 1913. He was awarded the 1904 Nobel Prize in chemistry. In 1895 he became the first to isolate helium successfully from terrestrial sources. Ramsay also discovered argon , neon , krypton , and xenon and contributed to the discovery that helium is a product of the atomic disintegration of radium.

. McMillan, Edwin Mattison (1907-1991), American physicist and Nobel laureate, known for his work with the transuranium elements. He was born in Redondo Beach, California, and educated at the California Institute of Technology and Princeton University. Associated with the University of California at Berkeley after 1932, he became full professor of physics in 1946. After 1934 McMillan was also associated with the university's radiation laboratory; in 1958 he became its director. McMillan was codiscoverer (1940) of the first transuranium element, neptunium. Further research, conducted in collaboration with the American chemist Glenn Theodore Seaborg, led to the discovery, also in 1940, of plutonium. In addition, McMillan is noted for his work in sonar and radar and for the design and construction of particle accelerators. For their discoveries in the chemistry of transuranium elements, he and Seaborg shared the 1951 Nobel Prize in chemistry. McMillan shared the Atoms for Peace Award ...

. Seaborg, Glenn Theodore (1912-1999), American chemist and Nobel laureate, known for his discovery of new chemical elements. Seaborg was born in Ishpeming, Michigan, and was educated at the University of California. He taught chemistry at the university after 1939, becoming an assistant professor in 1941 and a full professor in 1945. He was chairman of the Atomic Energy Commission from 1961 to 1971 and then became professor at the University of California, Berkeley, and associate director of the Lawrence Berkeley Laboratory. From 1942 to 1946, at the Metallurgical Laboratory of the University of Chicago, he conducted research in nuclear chemistry and physics in connection with the atomic energy project. He is known particularly for his discovery and characterization of many radioactive isotopes (see Isotope) and for his share in the discovery of such elements as plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, and nobelium. Seaborg shared the 19...

. Curie, Marie (1867-1934), Polish-born French chemist who, with her husband Pierre Curie , was an early investigator of radioactivity . Radioactivity is the spontaneous decay of certain elements into other elements and energy. The Curies shared the 1903 Nobel Prize in physics with French physicist Antoine Henri Becquerel for fundamental research on radioactivity. Marie Curie went on to study the chemistry and medical applications of radium. She was awarded the 1911 Nobel Prize in chemistry in recognition of her work in discovering radium and polonium and in isolating radium Marie Curie's maiden name was Maria Skłodowska, and her nickname while growing up was Manya. She was born in Warsaw at a time when Poland was under Russian domination after the unsuccessful revolt of 1863. Her parents were teachers, but soon after Manya (their fifth child) was born, they lost their teaching posts and had to take in boarders. Their young daughter worked long hours helping with the meals, but ...

. Curie, Pierre (1859-1906), French physicist and Nobel laureate, best known for the work on radioactivity that he did with his wife, Marie Curie . In radioactive materials the atoms break down spontaneously, releasing radiation in the form of energy and subatomic particles. Pierre Curie also worked on important topics in the structure of crystals and helped discover the piezoelectric effect in crystals—a property of producing electrical voltages when they are compressed. Pierre Curie was born in Paris and educated at home by his parents. He studied physics at the University of Paris, earning a bachelor’s degree in 1875. He became an assistant teacher at the University of Paris in 1878 and turned his research to crystallography. In 1880 Pierre and his brother Jacques Curie discovered that some crystals developed positive electrical charges at one end and negative electrical charges at the other when the crystals were compressed. These crystals also change shape when exposed to elect...

. Becquerel, Antoine Henri (1852-1908), French physicist and Nobel laureate, who discovered radioactivity in uranium. He was the son of Alexandre Becquerel, who studied light and phosphorescence and invented the phosphoroscope, and grandson of Antoine César Becquerel, one of the founders of electrochemistry . Born in Paris, Becquerel became professor of physics at the Museum of Natural History in 1892 and at the Polytechnical School in 1895. In 1896 he accidentally discovered the phenomenon of radioactivity in the course of his research on fluorescence. After placing uranium salts on a photographic plate in a dark area, Becquerel found that the plate had become blackened. This proved that uranium must give off its own energy, which later became known as radiation. Becquerel also conducted important research on phosphorescence, spectrum analysis, and the absorption of light. In 1903 Becquerel shared the Nobel Prize in physics with the French physicists Pierre Curie and Marie Curie for...

. Meitner, Lise (1878-1968), Austrian-Swedish physicist, who first identified nuclear fission. She was born in Vienna, Austria, and educated at the Universities of Vienna and Berlin. In 1918, in association with German physical chemist Otto Hahn , she helped discover the element protactinium . From 1926 to 1933 she was a professor of physics at the University of Berlin in Germany. In 1938 restrictions against Jews imposed by the Nazi regime led Meitner to leave Germany. She ended up in Sweden, joining the atomic research staff at the University of Stockholm. In 1939 Meitner and her nephew, the British physicist Otto Robert Frisch, published the first paper to provide a theoretical explanation for the splitting of the atom and named the process fission (see Nuclear Energy ). In 1946 she was a visiting professor at Catholic University in Washington, D.C., and in 1959 she revisited the United States to lecture at Bryn Mawr College. In 1997 the International Union of Pure and Applied Chemi...

. Hahn, Otto (1879-1968), German physical chemist and Nobel laureate, best known for his contributions in the field of radioactivity. Hahn was born in Frankfort am Main and educated at the universities of Marburg and Munich. In 1911 he became a member of the Kaiser Wilhelm Institute for Physical Chemistry in Berlin. He served as director of the institute from 1928 to 1945, when it was taken into Allied custody after World War II. In 1918 he discovered, with Austrian physicist Lise Meitner , the element protactinium. Hahn, with his coworkers, Meitner and German chemist Fritz Strassmann, continued the research started by Italian physicist Enrico Fermi : bombarding uranium with neutrons. Until 1939 scientists believed that elements with atomic numbers higher than 92 (known as transuranium elements ) were formed when uranium was bombarded with neutrons. In 1938, however, Hahn and Strassmann, while searching for transuranium elements in a sample of uranium that had been irradiated with neu...

.. Fermi, Enrico (1901-1954), Italian-born American physicist and Nobel Prize winner, who made important contributions to both theoretical and experimental physics. Fermi’s most well-known contribution was the demonstration of the first controlled atomic fission reaction. Atomic fission occurs when an atom splits apart (see Atom ). Fermi was the first scientist to split an atom, although he misinterpreted his results for several years. He also had an important role in the development of fission for use as an energy source and as a weapon (see Nuclear Energy ; see Atomic Bomb ). He won the 1938 Nobel Prize in physics for his work in bombarding atoms with neutrons, subatomic particles with no electric charge. Initially, Fermi believed that this process created new chemical elements heavier than uranium (see Transuranium Elements ), but other scientists showed that he actually split atoms to create fission reactions. Fermi was born in Rome, Italy. At age 17 he earned a scholarship to the ...

Physics is a major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. Sometimes in modern physics a more sophisticated approach is taken that incorporates elements of the three areas listed above; it relates to the laws of symmetry and conservation, such as those pertaining to energy, momentum, charge, and parity. See Atom ; Energy . Physics is closely related to the other natural sciences and, in a sense, encompasses them. Chemistry, for example, deals with the interaction of atoms to form molecules; much of modern geology is largely a study of the physics of the earth and is known as geophysics; and astronomy deals with the physics of the stars and outer space. Even living systems are made up of fundamental particles and, as studied in biophysics and biochemistry, they follow the same types of laws as the simpler particles traditionally studied by a physicist.

. Organic Chemistry, branch of chemistry in which carbon compounds and their reactions are studied. A wide variety of classes of substances—such as drugs, vitamins, plastics, natural and synthetic fibers, as well as carbohydrates, proteins, and fats—consist of organic molecules. Organic chemists determine the structures of organic molecules, study their various reactions, and develop procedures for the synthesis of organic compounds. Organic chemistry has had a profound effect on modern life: It has improved natural materials and it has synthesized natural and artificial materials that have, in turn, improved health, increased comfort, and added to the convenience of nearly every product manufactured today. The advent of organic chemistry is often associated with the discovery in 1828 by the German chemist Friedrich Wöhler that the inorganic, or mineral, substance called ammonium cyanate could be converted in the laboratory to urea, an organic substance found in the urine of many anima...

Mechanics, branch of physics concerning the motions of objects and their response to forces. Modern descriptions of such behavior begin with a careful definition of such quantities as displacement (distance moved), time, velocity, acceleration, mass, and force. Until about 400 years ago, however, motion was explained from a very different point of view. For example, following the ideas of Greek philosopher and scientist Aristotle , scientists reasoned that a cannonball falls down because its natural position is in the earth; the sun, the moon, and the stars travel in circles around the earth because it is the nature of heavenly objects to travel in perfect circles. The Italian physicist and astronomer Galileo brought together the ideas of other great thinkers of his time and began to analyze motion in terms of distance traveled from some starting position and the time that it took. He showed that the speed of falling objects increases steadily during the time of their fall. This accel...

Thermodynamics ->> ZEROTH LAW The vocabulary of empirical sciences is often borrowed from daily language. Thus, although the term temperature appeals to common sense, its meaning suffers from the imprecision of nonmathematical language. A precise, though empirical, definition of temperature is provided by the so-called zeroth law of thermodynamics as explained below. When two systems are in equilibrium, they share a certain property. This property can be measured and a definite numerical value ascribed to it. A consequence of this fact is the zeroth law of thermodynamics, which states that when each of two systems is in equilibrium with a third, the first two systems must be in equilibrium with each other. This shared property of equilibrium is the temperature. If any such system is placed in contact with an infinite environment that exists at some certain temperature, the system will eventually come into equilibrium with the environment—that is, reach the same temperature. (The ...

Chemistry is a study of the composition, structure, properties, and interactions of matter. Chemistry arose from attempts by people to transform metals into gold beginning about ad 100, an effort that became known as alchemy. Modern chemistry was established in the late 18th century, as scientists began identifying and verifying through scientific experimentation the elemental processes and interactions that create the gases, liquids, and solids that compose our physical world. As the field of chemistry developed in the 19th and 20th centuries, chemists learned how to create new substances that have many important applications in our lives. Much of chemistry can be described as taking substances apart and putting the parts together again in different ways. Using this approach, the chemical industry produces materials that are vital to the industrialized world. Resources such as coal, petroleum, ores, plants, the sea, and the air yield raw materials that are turned into metal alloys; de...

Inorganic Chemistry is a study of the structure, properties, and reactions of the chemical elements and their compounds. Inorganic chemistry does not include the investigation of hydrocarbons —compounds composed of carbon and hydrogen that are the parent material of all other organic compounds. The study of organic compounds is called organic chemistry . Inorganic chemists have made significant advances in understanding the minute particles that compose our world. These particles, called atoms, make up the elements, which are the building blocks of all the compounds and substances in the world around us. Just as the entire English language is constructed from combinations of the 26 letters in the alphabet, all chemical substances are made from combinations of the 112 chemical elements found on the periodic table (see Periodic Law ). Ninety elements are known to occur in nature, and 22 more have been made artificially. Elements—which include substances such as oxygen, nitrogen, and sulf...

Thermodynamics, field of physics that describes and correlates the physical properties of macroscopic systems of matter and energy . The principles of thermodynamics are of fundamental importance to all branches of science and engineering. A central concept of thermodynamics is that of the macroscopic system, defined as a geometrically isolable piece of matter in coexistence with an infinite, unperturbable environment. The state of a macroscopic system in equilibrium can be described in terms of such measurable properties as temperature, pressure, and volume, which are known as thermodynamic variables. Many other variables (such as density, specific heat, compressibility, and the coefficient of thermal expansion) can be identified and correlated, to produce a more complete description of an object and its relationship to its environment. When a macroscopic system moves from one state of equilibrium to another, a thermodynamic process is said to take place. Some processes are reversib...

. Species and Speciation, basic concepts in the classification of organisms. In simple terms, a single species is a distinct kind of organism, with a characteristic shape, size, behavior, and habitat that remains constant from year to year. A biological species is defined as a group of natural populations that mate and produce offspring with one another, but do not breed with other populations. This definition includes genealogical relationships as well as physical properties, and emphasizes that species evolve independently of one another. See Evolution . THE NATURE OF SPECIES Other conceptions of species exist, the oldest of which is the typological-species concept that originated with Plato and Aristotle. According to this concept, a species represents some ideal form, of which individual variation is merely the imperfect expression. The morphological-species definition, on the other hand, is purely observational: a group of individuals that resemble one another and are separated f...

Thermodynamics ->> FIRST LAW The first law of thermodynamics gives a precise definition of heat, another commonly used concept. When an object is brought into contact with a relatively colder object, a process takes place that brings about an equalization of temperatures of the two objects. To explain this phenomenon, 18th-century scientists hypothesized that a substance more abundant at higher temperature flowed toward the region at a lower temperature. This hypothetical substance, called “caloric,” was thought to be a fluid capable of moving through material media. The first law of thermodynamics instead identifies caloric, or heat, as a form of energy. It can be converted into mechanical work, and it can be stored, but is not a material substance. Heat, measured originally in terms of a unit called the calorie, and work and energy, measured in ergs, were shown by experiment to be totally equivalent. One calorie is equivalent to 4.186 × 107 ergs, or 4.186 joules. The first law,...

Thermodynamics ->> SECOND LAW The second law of thermodynamics gives a precise definition of a property called entropy. Entropy can be thought of as a measure of how close a system is to equilibrium; it can also be thought of as a measure of the disorder in the system. The law states that the entropy—that is, the disorder—of an isolated system can never decrease. Thus, when an isolated system achieves a configuration of maximum entropy, it can no longer undergo change: It has reached equilibrium. Nature, then, seems to “prefer” disorder or chaos. It can be shown that the second law stipulates that, in the absence of work, heat cannot be transferred from a region at a lower temperature to one at a higher temperature. The second law poses an additional condition on thermodynamic processes. It is not enough to conserve energy and thus obey the first law. A machine that would deliver work while violating the second law is called a “perpetual-motion machine of the second kind,” since,...

Thermodynamics ->> THERMODYNAMIC CYCLES All important thermodynamic relations used in engineering are derived from the first and second laws of thermodynamics. One useful way of discussing thermodynamic processes is in terms of cycles—processes that return a system to its original state after a number of stages, thus restoring the original values for all the relevant thermodynamic variables. In a complete cycle the internal energy of a system depends solely on these variables and cannot change. Thus, the total net heat transferred to the system must equal the total net work delivered from the system. An ideal cycle would be performed by a perfectly efficient heat engine—that is, all the heat would be converted to mechanical work. The 19th-century French scientist Nicolas Léonard Sadi Carnot, who conceived a thermodynamic cycle that is the basic cycle of all heat engines, showed that such an ideal engine cannot exist. Any heat engine must expend some fraction of its heat input as ...

Thermodynamics ->> THIRD LAW The second law suggests the existence of an absolute temperature scale that includes an absolute zero of temperature. The third law of thermodynamics states that absolute zero cannot be attained by any procedure in a finite number of steps. Absolute zero can be approached arbitrarily closely, but it can never be reached.

Thermodynamics ->> MICROSCOPIC BASIS OF THERMODYNAMICS The recognition that all matter is made up of molecules provided a microscopic foundation for thermodynamics. A thermodynamic system consisting of a pure substance can be described as a collection of like molecules, each with its individual motion describable in terms of such mechanical variables as velocity and momentum. At least in principle, it should therefore be possible to derive the collective properties of the system by solving equations of motion for the molecules. In this sense, thermodynamics could be regarded as a mere application of the laws of mechanics to the microscopic system. Objects of ordinary size—that is, ordinary on the human scale—contain immense numbers (on the order of 1024) of molecules. Assuming the molecules to be spherical, each would need three variables to describe its position and three more to describe its velocity. Describing a macroscopic system in this way would be a task that even the lar...

Relativity, theory, developed in the early 20th century, which originally attempted to account for certain anomalies in the concept of relative motion, but which in its ramifications has developed into one of the most important basic concepts in physical science (see Physics ). The theory of relativity, developed primarily by German American physicist Albert Einstein , is the basis for later demonstration by physicists of the essential unity of matter and energy, of space and time, and of the forces of gravity and acceleration (see Acceleration ; Energy ; Gravitation ).

. Newton, Sir Isaac (1642-1727), English physicist, mathematician, and natural philosopher, considered one of the most important scientists of all time. Newton formulated laws of universal gravitation and motion—laws that explain how objects move on Earth as well as through the heavens (see Mechanics ). He established the modern study of optics—or the behavior of light —and built the first reflecting telescope . His mathematical insights led him to invent the area of mathematics called calculus (which German mathematician Gottfried Wilhelm Leibniz also developed independently). Newton stated his ideas in several published works, two of which, Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy, 1687) and Opticks (1704), are considered among the greatest scientific works ever produced. Newton’s revolutionary contributions explained the workings of a large part of the physical world in mathematical terms, and they suggested that science may provide...

Phylum Phylum, in biology , major category, or taxon, of organisms with a common design or organization. This design is shared by all members of the phylum, even though structural details may differ greatly because of evolution . The assumption is made by biologists that all members of a phylum have a common ancestry. A phylum is part of the hierarchy of classification of organisms. It is an arbitrary grouping; that is, it is developed from a combination of scientific observation, theorizing, and guesswork in an attempt to find order in the complexity of living and extinct life forms. The same is true of all classification levels above and below it except for species, which consist of organisms known to be capable, at least potentially, of interbreeding (see Species and Speciation ). related topics: animal phyla plant phyla

Grouping organisms according to shared characteristics is not a simple task, and scientists often disagree about the best way to classify organisms. Some think that organisms should be grouped according to differences or similarities in the way they look or act. Other scientists argue that classification should be based on characteristics derived from a shared evolution. Conflicting philosophies about classification have resulted in a variety of classification methods, each with their own set of assumptions, techniques, and results. related articles: how species are grouped taxonomy classification

. Scientists classify organisms using a series of hierarchical categories called taxa (taxon, singular). This hierarchical system moves upward from a base containing a large number of organisms with very specific characteristics. This base taxon is part of a larger taxon, which in turn becomes part of an even larger taxon. Each successive taxon is distinguished by a broader set of characteristics. The base level in the taxonomic hierarchy is the species. Broadly speaking, a species is a group of closely related organisms that are able to interbreed and produce fertile offspring. On the next tier of the hierarchy, similar species are grouped into a broader taxon called a genus (genera, plural). The remaining tiers within the hierarchy are formed by grouping genera into families, then families into orders, and orders into classes. In the classification of animals, bacteria, protists (unicellular organisms, such as amoebas, with characteristics of both plants and animals), and fungi, cla...

. Taxonomy, science of classifying organisms. Probably the first scientific study of plants was the attempt to classify them. At first, because of the limited knowledge of plant structures, artificial classifications, beginning with the most ancient one into herbs, shrubs, and trees, were necessary. These simple categories merely cataloged, in a tentative way, the rapidly accumulating material, in preparation for a classification based on natural relationships. Modern taxonomic classification, based on the natural concepts and system of the Swedish botanist Carolus Linnaeus, has progressed steadily since the 18th century, modified by advances in knowledge of morphology, evolution, and genetics. For more information about Taxonomy, read the full article at wikipedia.org. related articles: classification how species are grouped

. The classification of living organisms has been controversial throughout time, and these schemes are among those in use today. Firstly, Aristotle’s system distinguished only between plants and animals on the basis of movement, feeding mechanism, and growth patterns. This system groups prokaryotes, algae, and fungi with the plants, and moving, feeding protozoa with the animals. Then, the increasing sophistication of laboratory methods and equipment, however, revealed the differences between prokaryotic and eukaryotic cells, prompting a classification system that reflects them; then most recently, five kingdoms have emerged to take both cellular organization and mode of nutrition into account. Greek philosopher Aristotle (384-322 bc) grouped life forms as either plant or animal. Microscopic organisms were unknown. Plants - Plants and Fungi Animals - Animals In 1735 Swedish naturalist Carolus Linnaeus formalized the use of two Latin names to identify each organism, a system called binom...

. Classification, in biology, is identification, naming, and grouping of organisms into a formal system based on similarities such as internal and external anatomy, physiological functions, genetic makeup, or evolutionary history. With an estimated 10 million to 13 million species on Earth, the diversity of life is immense. Determining an underlying order in the complex web of life is a difficult undertaking that encompasses advanced scientific methods as well as fundamental philosophical issues about how to view the living world. Among the scientists who work on classification problems are systematists, biologists who study the diversity of organisms and their evolutionary relationship. In a related field known as taxonomy , scientists identify new organisms and determine how to place them into an existing classification scheme. Classification determines methods for organizing the diversity of life on Earth. It is a dynamic process that reflects the very nature of organisms, which are...

. Evolution, in biology, complex process by which the characteristics of living organisms change over many generations as traits are passed from one generation to the next. The science of evolution seeks to understand the biological forces that caused ancient organisms to develop into the tremendous and ever-changing variety of life seen on Earth today. It addresses how, over the course of time, various plant and animal species branch off to become entirely new species, and how different species are related through complicated family trees that span millions of years. Evolution provides an essential framework for studying the ongoing history of life on Earth. A central, and historically controversial, component of evolutionary theory is that all living organisms, from microscopic bacteria to plants , insects , birds , and mammals , share a common ancestor. Species that are closely related share a recent common ancestor, while distantly related species have a common ancestor further i...

. Extinction (biology), the end of existence of a group of organisms, caused by their inability to adapt to changing environmental conditions. Extinction affects individual species—that is, groups of interbreeding organisms—as well as collections of related species , such as members of the same family, order, or class (see Classification ). The dodo, for example, a species of flightless pigeon formerly living on the island of Mauritius, became extinct in 1665. About 10,000 to 12,000 years ago, the most of the woolly mammoths and the last of the mastodons , both members of the elephant family, died. And about 245 million years ago at the end of the Paleozoic Era, an entire class of primitive marine animals called trilobites disappeared forever. Fossils , the remains of prehistoric plants and animals buried and preserved in sedimentary rock or trapped in amber or other deposits of ancient organic matter, provide a record of the history of life on Earth. Scientists who study this foss...

. Genetics is a study of the function and behavior of genes . Genes are bits of biochemical instructions found inside the cells of every organism from bacteria to humans. Offspring receive a mixture of genetic information from both parents. This process contributes to the great variation of traits that we see in nature, such as the color of a flower’s petals, the markings on a butterfly’s wings, or such human behavioral traits as personality or musical talent. Geneticists seek to understand how the information encoded in genes is used and controlled by cells and how it is transmitted from one generation to the next. Geneticists also study how tiny variations in genes can disrupt an organism’s development or cause disease. Increasingly, modern genetics involves genetic engineering, a technique used by scientists to manipulate genes. Genetic engineering has produced many advances in medicine and industry, but the potential for abuse of this technique has also presented society with many ...

. Cytology, branch of biology concerned with the study of the structure and function of cells as individual units, supplementing histology, which deals with cells as components of tissues. Cytology is concerned with the structure and activities of the various parts of the cell and cell membrane; the mechanism of cell division; the development of sex cells, fertilization, and the formation of the embryo; cell derangements such as those occurring in cancer; cellular immunity; and the problems of heredity. Cytology, branch of biology concerned with the study of the structure and function of cells as individual units, supplementing histology, which deals with cells as components of tissues. Cytology is concerned with the structure and activities of the various parts of the cell and cell membrane; the mechanism of cell division; the development of sex cells, fertilization, and the formation of the embryo; cell derangements such as those occurring in cancer; cellular immunity; and the proble...

Zoology is the branch of biology devoted to the study of the animal kingdom (Animalia). This article discusses the history and concerns of that study. For a discussion of animals and a description of animal groups. The current study of zoology has two main focuses: on particular taxonomic groups, and on the structures and processes common to most of them. Taxonomically oriented studies concentrate on the different divisions of animal life. Invertebrate zoology deals with multicellular animals without backbones; its subdivisions include entomology (the study of insects) and malacology (the study of mollusks). Vertebrate zoology, the study of animals with backbones, is divided into ichthyology (fish), herpetology (amphibians and reptiles), ornithology (birds), and mammalogy (mammals). Paleontology , the study of fossils, is subdivided by taxonomic groups. In each of these fields, researchers investigate the classification, distribution, life cycle, and evolutionary history of the parti...

Anatomy (Greek anatomē, “dissection”), branch of natural science dealing with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. For centuries anatomical knowledge consisted largely of observations of dissected plants and animals. The proper understanding of structure, however, implies a knowledge of function in the living organism. Anatomy is therefore almost inseparable from physiology , which is sometimes called functional anatomy. As one of the basic life sciences, anatomy is closely related to medicine and to other branches of biology. It is convenient to subdivide the study of anatomy in several different ways. One classification is based on the type of organisms studied, the major subdivisions being plant anatomy (see Plant ) and animal anatomy. Animal anatomy is further subdivided into human anatomy and comparative anatomy, which seeks out similarities and differences among animal types (see Animal ). Anatomy can a...

Botany, branch of biology concerned with the study of plants (kingdom Plantae; see Plant). Plants are now defined as multicellular organisms that carry out photosynthesis. Organisms that had previously been called plants, however, such as bacteria, algae, and fungi, continue to be the province of botany, because of their historical connection with the discipline and their many similarities to true plants, and because of the practicality of not fragmenting the study of organisms into too many separate fields. Botany is concerned with all aspects of the study of plants, from the smallest and simplest forms to the largest and most complex, from the study of all aspects of an individual plant to the complex interactions of all the different members of a complicated botanical community of plants with their environment and with animals (see Ecology ). Botany today does not depend on the fossil record for information concerning evolution and classification as much as does zoology, becau...

Biology, the science of life. The term was introduced in Germany in 1800 and popularized by the French naturalist Jean-Baptiste de Lamarck as a means of encompassing the growing number of disciplines involved with the study of living forms. The unifying concept of biology received its greatest stimulus from the English zoologist Thomas Henry Huxley, who was also an important educator. Huxley insisted that the conventional segregation of zoology and botany was intellectually meaningless and that all living things should be studied in an integrated way. Huxley’s approach to the study of biology is even more cogent today, because scientists now realize that many lower organisms are neither plants nor animals (see Prokaryote ; Protista ). The limits of the science, however, have always been difficult to determine, and as the scope of biology has shifted over the years, its subject areas have been changed and reorganized. Today biology is subdivided into hierarchies based on the molecule , ...

Ecology, the study of the relationship of plants and animals to their physical and biological environment. The physical environment includes light and heat or solar radiation, moisture, wind, oxygen, carbon dioxide, nutrients in soil, water, and atmosphere. The biological environment includes organisms of the same kind as well as other plants and animals. Because of the diverse approaches required to study organisms in their environment, ecology draws upon such fields as climatology, hydrology, oceanography, physics, chemistry, geology, and soil analysis. To study the relationships between organisms, ecology also involves such disparate sciences as animal behavior, taxonomy, physiology, and mathematics. An increased public awareness of environmental problems has made ecology a common but often misused word. It is confused with environmental programs and environmental science (see Environment ). Although the field is a distinct scientific discipline, ecology does indeed contribute to th...

Paleontology, study of prehistoric animal and plant life through the analysis of fossil remains. The study of these remains enables scientists to trace the evolutionary history of extinct as well as living organisms (see Evolution ). Paleontologists also play a major role in unraveling the mysteries of the earth's rock strata (layers). Using detailed information on how fossils are distributed in these layers of rock, paleontologists help prepare accurate geologic maps, which are essential in the search for oil, water, and minerals. See Dating Methods . Most people did not understand the true nature of fossils until the beginning of the 19th century, when the basic principles of modern geology were established. Since about 1500, scholars had engaged in a bitter controversy over the origin of fossils. One group held the modern view that fossils are the remains of prehistoric plants and animals. This group was opposed by another, which declared that fossils were either freaks of nat...

. Veterinary Medicine, branch of medical science that deals with the health and welfare of animals. Doctors of veterinary medicine diagnose and treat the diseases and injuries of household pets, livestock, laboratory animals, zoo animals, and wildlife (see Diseases of Animals ). They promote public health by combating zoonotic diseases (animal diseases that can be transmitted to humans) and by inspecting livestock and food processing procedures to insure a safe food supply. Some veterinarians actively participate in wildlife preservation and conservation, while others conduct scientific research into the causes and prevention of disease. Veterinary medicine is a challenging field. One significant difference between human and animal medicine is that veterinarians must be familiar with the anatomy and diseases of several different species. An appropriate treatment for one species might be ineffective or harmful if applied to another. Veterinarians must be proficient in both medicine and ...

Surgery, branch of medicine concerned with treatment of diseases, deformities, and injuries through manual procedures called operations. Surgery can be used to repair broken bones, stop uncontrolled bleeding, remove injured or diseased tissue and organs, and reattach severed limbs. Exploratory surgery helps physicians diagnose conditions that cannot be detected by traditional tests. It allows for examination of internal organs for signs of disease. People have practiced surgery since ancient times, but it did not become a respected science until the 19th century. Increasing knowledge of the human body, the discovery of anesthesia (a loss of physical sensation that can be induced with drugs), and the use of germ-free, or sterile, operating procedures combined to make surgery a safe and effective method of medical treatment. In the 20th century advances in technology have helped the field of surgery grow at a rapid pace. Surgery is performed by specially trained medical physicians know...

Internal Medicine, nonsurgical medical specialty concerned with diseases of internal organs in adults. Physicians who specialize in the field, known as internists, are skilled in disease prevention and in managing complex disorders of the body. Internists may be either generalists or specialists. General internists typically act as personal physicians, developing long-term relationships with patients. Internists give patients regular physical examinations, offer preventive care, diagnose and treat most nonsurgical illnesses, and refer serious or unusual cases to an appropriate specialist. If a patient complains of persistent stomach problems, for example, a general internist might refer the patient to a gastroenterologist, an internist who specializes in disorders of the digestive system. Within the field of internal medicine, nine subspecialties are recognized: cardiology , the treatment of diseases of the heart and blood vessels; endocrinology , the study of glands and other structur...

Pediatrics, branch of medicine , that comprises the care and treatment of the diseases of childhood and the study of normal growth. Pediatricians are trained to recognize congenital defects (see Birth Defects ) and to treat them when possible. One important treatable class of these conditions is congenital heart malformations; surgical correction of these defects has become increasingly successful. Other congenital illnesses that must be diagnosed and treated soon after birth are phenylketonuria and congenital hypothyroidism (see Cretinism ). Pediatricians must also handle a number of infectious diseases that are most often seen in childhood. These include recurrent ear infections such as otitis media (see Ear ), mumps , measles , whooping cough , poliomyelitis , and croup . Many of these diseases can be prevented by immunization, which is the responsibility of the pediatrician. Pediatricians also monitor the normal growth and development of a child according to important motor and int...