Middle Levels Of Biological Organization Cells example essay topic

Biology is the science of living systems. Itis inherently interdisciplinary, requiring knowledge of the physical sciences and mathematics, although specialities may be oriented toward a group of organisms or a level of organization. BOTANY is concerned with plant life, ZOOLOGY with animal life, algology with ALGAE, MYCOLOGY with fungi, MICROBIOLOGY with microorganisms such as protozoa and bacteria, CYTOLOGY with CELLS, and so on. All biological specialties, however, are concerned with life and its characteristics. These characteristics include cellular organization, METABOLISM, response to stimuli, development and growth, and reproduction. Furthermore, the information needed to control the expression of such characteristics is contained within each organism.

FUNDAMENTAL DISCIPLINES Life is divided into many levels of organization -- atoms, molecules, cells, tissues, organs, organ systems, organisms, and populations. The basic disciplines of biology may study life at one or more of these levels. Taxonomy attempts to arrange organisms in natural groups based on common features. It is concerned with the identification, naming, and classification of organisms. The seven major taxonomic categories, or taxa, used in classification are kingdom, phylum, class, order, family, genus, and species.

Early systems used only two kingdoms, plant and animal, whereas most modern systems use five: MONERA (BACTERIA and BLUE-GREEN ALGAE), PROTIST A (PROTOZOA and the other ALGAE), FUNGI, PLANT, and ANIMAL. The discipline of ECOLOGY is concerned with the interrelationships of organisms, both among themselves and between them and their environment. Studies of the energy flow through communities of organisms and of the environment (the ecosystem approach) are especially valuable in assessing the effects of human activities. An ecologist must be knowledgeable in other disciplines of biology.

Organisms respond to stimuli from other organisms and from the environment; behaviorists are concerned with these responses. Most of them study animals -- as individuals, groups, or entire species -- in describing ANIMAL BEHAVIOR patterns. These patterns include ANIMAL MIGRATION, courtship and mating, social organization, TERRITORIALITY, INSTINCT, and learning. When humans are included, biology overlaps with psychology and sociology. Growth and orientation responses of plants can also be studied in the discipline of behavior, although they are traditionally considered as belonging under development and PHYSIOLOGY, respectively.

Descriptive and comparative EMBRYOLOGY are the classic areas of DEVELOPMENT studies, development, particularly the aging process, is also examined. The biochemical and biophysical mechanisms that control normal development are of particular interest when the yare related to birth defects, cancer, and other abnormalities. Inheritance of physical and biochemical characteristics, and the variations that appear from generation to generation, are the general subjects of GENETICS. The emphasis may be on improving domestic plants and animals through controlled breeding, or it may be on the more fundamental questions of molecular and cellular mechanisms of HEREDITY. A branch of biology growing in importance since the 1940's, molecular biology essentially developed out of genetics and biochemistry. It seeks to explain biological events by studying the molecules within cells, with a special emphasis on the molecular basis of genetics -- nucleic acids in particular -- and its relationship to energy cycling and replication.

Evolution, including the appearance of new species, the modification of existing species, and the characteristics of extinct ones, is based on genetic principles. Information about the structure and distribution of fossils that is provided by paleontologists is essential to understanding these changes. Morphology (from the Greek, meaning " form study') traditionally has examined the ANATOMY of all organisms. The middle levels of biological organization -- cells, tissues, and organs, are the usual topics -- with comparisons drawn among organisms to help establish taxonomic and evolutionary relationships. As important as the form of an organism are its functions. Physiology is concerned with the life processes of entire organisms as well as those of cells, tissues, and organs.

Metabolism and hormonal controls are some of the special interests of this discipline. HISTORY OF BIOLOGY Origin and Early Development. The oldest surviving archaeological records that indicate some rudimentary human knowledge of biological principles date from the Mesolithic Period. During the NEOLITHIC PERIOD, which began almost 10,000 years ago, various human groups developed agriculture and the medicinal use of plants. In ancient Egypt, for example, a number of herbs were being used medicinally and for embalming. Early Development As a science, however, biology did not develop until the last few centuries BC.

Although HIPPOCRATES, known as the father of medicine, influenced the development of medicine apart from its role in religion, it was ARISTOTLE, a student of Plato, who established observation and analysis as the basic tools of biology. Of particular importance were Aristotle's observations of reproduction and his concepts for a classification system. As the center of learning shifted from Greece to Rome and then to Alexandria, so did the study of biology. From the 3d century BC to the 2d century AD, studies primarily focused on agriculture and medicine. The Arabs dominated the study of biology during the Middle Ages and applied their knowledge of the Greeks' discoveries to medicine. The Renaissance was a period of rapid advances, especially in Italy, France, and Spain, where Greek culture was being rediscovered.

In the 15th and 16th centuries, Leonardo da Vinci and Michelangelo became skilled anatomists through their search for perfection in art. Andreas VESALIUS initiated the use of dissection as a teaching aid. His books, Fabrica (1543) and Fabrica, 2d ed. (1550), contained detailed anatomical illustrations that became standards.

In the 17th century, William HARVEY introduced the use of experimentation in his studies of the human circulatory system. Hiswork marked the beginning of mammalian physiology. Scientific Societies and Journals. Lack of communication was a problem for early biologists. To overcome this, scientific societies were organized. The first were in Europe, beginning with the Academy of the Lynx (Rome, 1603).

The Boston Philosophical Society, founded in 1683, was probably the first such society to be organized in colonial America. Later, specialized groups, principally of physicians, organized themselves, among them the American Association for the Advancement of Science ( S), founded in 1848. Much later, in 1951, the American Institute of Biological Science (A IBS) was formed as an alliance of the major biological societies in the United States. The first journals to present scientific discoveries were published in Europe starting in 1665; they were the Journal des Savants, in France, and Philosophical Transactions of the Royal Society, in London. Over the years, numerous other journals have been established, so that today nearly all societies record their transactions and discoveries. Development and Early Use of the Microscope.

Before 1300 optical lenses were unknown. At that time, except for crude spectacles used for reading. Modern optics began with the invention of the MICROSCOPE by Galileo Galilei about 1610. Microscopy originated in 1625 when the Italian FrancescoStelluti published his drawings of a honeybee magnified 10 times. The 17th century produced five microscopist's whose works are considered classics: Marcello MALPIGHI (Italy), Antoni van LEEUWENHOEK and Jan SWAMMERDAM (Holland), and Robert HOOKE and Nehemiah GREW (England). Notable among their achievements were Malpighi's description of lung capillaries and kidney corpuscles and Hooke " sMicrographia, in which the term cell was first used.

Basis for Modern Systematics. Consistent terminology and nomenclature were unknown in early biological studies, although Aristotle regularly described organisms by g enos and eidos (genus and species). Sir Isaac NEWTON's Principia (1687) describes a rigid universe with an equally rigid classification system. This was a typical approach of the period.

The leading botanical classification was that used in describing the medicinal values of plants. Modern nomenclature based on a practical binomial system originated with Karl von Line (Latinized to Carolus LINNAEUS). In addition to arranging plants and animals into genus and species based on structure, he introduced the categories of class and order. Jean Baptiste LAMARCK based his system on function, since this accommodated his view of the inheritance of acquired characteristics. In 1817, Georges, Baron CUVIER became the first to divide the entire animal kingdom into subgroups, for example, Vertebrata, Mollusca, Articulate, and Radiata. Explorations and Explorers.

During the 18th and 19th centuries numerous important biological expeditions were organized. Three of these, all British, made outstanding contributions to biology. Sir Joseph BANKS, on Captain Cook " ship Endeavor, explored (1768-71) the South Seas, collecting plants and animals of Australia. Robert BROWN, a stu dent of Banks, visited Australia from 1801 to 1805 on the Investigator and returned with more than 4,000 plant specimens. On perhaps the most famous voyage, Charles DARWIN circumnavigated (1831-36) the globe on the Beagle. His observations of birds, reptiles, and flowering plants in the Galapagos Islands in 1835 laid the foundation for his theories on evolution, later published in On the Origin of Species (1859).

The Discovery of Microorganisms. Arguments about the spontaneous generation of organisms had been going on since the time of Aristotle, and various inconclusive experiments had been conducted. Louis PASTEUR clearly demonstrated in 1864 that no organisms emerged from his heat-sterilized growth medium as long as the medium remained in sealed flasks, thereby disproving spontaneous generation. Based on Edward JENNER's studies of smallpox, Pasteur later developed a vaccine for anthrax and in 1885 became the first to successfully treat a human bitten by a rabid dog. Beginning in 1876, Robert KOCH developed pure-culture techniques for microorganisms. Hiswork verified the germ theory of disease.

One of his students, Paul EHRLICH, developed chemotherapy and in 1909 devised a chemical cure for syphilis. The value of ANTIBIOTICS became evident when Sir Alexander FLEMING discovered penicillin in 1928. An intensive search, between 1940 and 1960, for other antibiotics resulted in the development of several dozen that were used extensively. Although antibiotics have not been the panacea once anticipated, their use has resulted in a decreased incidence of most infectious diseases. The Role of the Cell.

Following Hooke's use of the term cell, biologists gradually came to recognize this unit as common throughout living systems. The cell theory was published in 1839 by Matthias Schleiden a plant anatomist. Schleiden saw cells as the basic unit of organization and perceived each as having a double life, one 'pertaining to its own development' and the other 'as an integral part of plant. ' Schwann, an animal histologist, noticed that not all parts of an organism are comprised of cells. He added to the theory in 1840 by establishing that these parts are at least 'cell products. ' Between 1868 and 1898 the cell theory was enlarged as substructures of the cell -- for example, plastids and mitochondria -- were observed and described.

Basic Life Functions. Until the 17th century it was believed that plants took in food, preformed, from the soil. Jan Baptista van HELMONT, the first experimental physiologist, around 1640 concluded that water is the only soil component required for plant growth. Stephen HALES showed (1727) that air held the additional ingredient for food synthesis. In 1779, Ingenhousz identified this as carbon dioxide. The study of PHOTOSYNTHESIS began with a demonstration by Sachs and Pringsheim in the mid-19th century that light is the energy source of green plants.

Blackman showed (1905) that not all parts of this process require sunlight. Results of work done during the 1920's and '30's proved that chloroplasts produce oxygen. Subsequently, it was shown that the light-dependent reactions cause two types of high-energy molecules to be formed that use the energy from light. The route of carbon dioxide in photosynthesis was worked out by Melvin CALVIN in the early 1950's, using the radioisotope carbon-14. His results proved Blackman correct: there exist two distinct but closely coordinated sets of chloroplast reactions, one light-dependent and the other light-independent. High-energy products of the light-dependent reactions are required for incorporation of carbon dioxide into sugars in the light-independent reactions.

The earliest demonstration of ferments (the word ENZYME was not coined until 1878) in pancreatic juice was made by Claude BERNARD in France. Bernard also experimentally determined numerous functions of the liver as well as the influence of vasomotor nerves on blood pressure. In the 1930's, Otto WARBURG discovered a series of cellular enzymes that start the process of glucose breakdown to produce energy for biological activity. When Hans KREBS demonstrated (1950s) an additional series of enzyme reactions (the citric acid cycle) that completes the oxidation process, the general respiration scheme of cells became known. Chemical synchronization of body functions without direct control by the nervous system was discovered in 1905 by Sir William M. BAYLISS and Ernest Henry STARLING (the first to use the term hormone). Steroids we rediscovered in 1935.

Continuity in Living Systems. The early biologists known as that animals exist preformed, either in sperm (the's view) or in the egg (theorist's belief). Embryology actually began when Karl Ernst von BAER, using the microscope, observed that no preformed embryos exist. Modern interpretations of developmental control in embryo genesis can be traced to HansSPEMANN's discovery in 1915 of an 'organizer " area in frog embryos. More recent research has shown the importance of other factors, such as chemical gradients. Genetics, the study of heredity, began with the work of Gregor Johann MENDEL, who published his findings in 1866.

Mendel's extensive experiments with garden peas led him to conclude that the inheritance of each characteristic is controlled by a pair of physical units, or genes. These units, one from each parent (the law of segregation), were passed on to offspring, apparently independent of the distribution of another pairs (the law of independent assortment). The gene concept was amplified by the rediscovery and confirmation of Mendel's work in 1900 by Hugo DE VRIES in Holland, Karl ErichCorrens in Germany, and Gustav Tschermak vonSeysenegg in Austria. De Vries's mutation theory became the foundation of modern genetics. The chromosome theory is based on the speculations of Pierre Paul ROUX in 1883 that cell nuclei contain linear arrangements of which replicate (produce exact copies) during cell division. Many important contributions were made early in the 20th century by the American Thomas Hunt MORGAN.

These included sex-linked inheritance and the association with gene theory of the crossing over of chromosomes. The discovery by Geoffrey Hardy and William Weinberg of the equilibrium relationship that exists between frequency of alleles (a term originated by William Bateson in 1909 for alternate forms of a gene) in a population led to formulation of the law bearing their names. The role of genetics in evolution was publicized in 1937 by Theodosius DOBZHANSKY's Genetics and the Origin of Species. Molecular biology, the most recent branch of biology, began early in the 20th century with Archibald Garrod's work on the biochemical genetics of various diseases. The concept of one gene producing one enzyme was established in 1941 by George W. BEADLE and Edward L. TATUM. The work on protein synthesis by Jacques MOOD and Francois JACOB and others in 1961 has modified the one gene-one enzyme concept to one gene-one protein.

Essential to the understanding of protein synthesis were the advances made in the 1940 sand '50's in understanding the role and structure of nucleic acids. The structural model proposed in 1953 by James D. WATSON and F.H.C. CRICK is a landmark in biology. It has given biologists a feasible way to explain the storage and precise transmission of genetic information from one generation to the next. Knowledge of biological processes at the molecular level has also enabled scientists to develop techniques for the direct manipulation of genetic information, a field now called GENETIC ENGINEERING. UNITY OF LIVING SYSTEMS Despite the astounding diversity of organisms that have been discovered, an equally astounding degree of unity of structure and function has been discerned. The structure of flagella is essentially the same in all cells having nuclei.

The molecules involved in growth and metabolism are remarkably similar, and often the yare constructed of identical subunits. Furthermore, enzymes, the catalysts of biological chemistry, are now known to act similarly in all organisms. Phenomena such as cell division and the transmission of the genetic code also appear to be universal. Larry A. Gies mann

Bibliography

An gros, Robert, and Stancil, George, The New Biology (1987);
Ante bi, Elizabeth, and Fish lock, David, Biotechnology (1987);
Asimov, Isaac, A Short History of Biology (1964;
repr. 1980), and The Intelligent Man's Guide to the Biological Sciences (1968);
Bored, Ernest, The Sculpture of Life (1973);
Darnell, James, et al., Molecular Cell Biology (1986);
Ebert, J.D., et al., Biology (1973);
Ehrlich, Paul, The Machinery of Nature (1987);
Ehrlich, Paul R., et al., Introductory Biology (1973);
Gardner, Eldon J., History of Biology, 3d ed. (1972);
Hana walt, P.C., and Haynes, R.H., eds., The Chemical Basis of Life (1973);
Handler, Philip, ed., Biology and the Future of Man (1970);
Lanham, U.N., The Origins of Modern Biology (1968);
Maynard Smith, John, The Problems of Biology (1986);
Mayr, Ernst, The Growth of Biological Thought (1982);
Medawar, P.B., and J.S., Life Science (1978);
Pauley, Philip, Controlling Life (1987);
Swanson, Carl P., and Webster, Peter, The Cell, 4th ed. (1977);
Watson, J.D., et al., Molecular Biology of the Gene, 2 vols., 4th ed. (1987).