Equator The area around the earth with a latitude of 0° that divides the Northern and Southern Hemispheres. It lies equidistant from the poles.
Era A period or date of time used in geological time tables to locate historical events. Usually refers to longer periods of time and marks a new or distinctive period. See also epoch; geological time.
Erlanger, Joseph (1874-1965) American Neurosci-entist Joseph Erlanger was born on January 5, 1874, in San Francisco, California, to Herman and Sarah Erlanger. He received a B.S. in chemistry at the University of California and later attended Johns Hopkins University to study medicine, receiving an M.D. degree in 1899. He was appointed assistant in the department of physiology at the medical school, after spending a year of hospital training at Johns Hopkins Hospital, until 1906, moving up successively as instructor, associate, and associate professor. He was then appointed the first professor of physiology in the newly established Medical School of the University of Wisconsin. In 1910 he was appointed professor of physiology in the reorganized Medical School of the Washington University, St. Louis, retiring in 1946 as chairman of the school.
In 1922, in collaboration with his student Herbert Gasser, Erlanger adapted the cathode-ray oscillograph for the study of nerve-action potentials. They amplified the electrical responses of single nerve fibers and analyzed them by the use of the oscilloscope. The characteristic wave pattern of an impulse generated in a stimulated nerve fiber could be observed on the screen and the components of the nerve’s response studied.
Erlanger and Gasser were given the Nobel Prize in medicine or physiology in 1944 for this work. Erlanger later worked on the metabolism of dogs with shortened intestines, on traumatic shock, and on the mechanism of the production of sound in arteries.
With Gasser he wrote Electrical Signs of Nervous Activity (1937). He died on December 5, 1965, in St. Louis.
Erythrocyte A concave red blood cell that functions totally within the cardiovascular system. It does not have a nucleus or cytoplasmic organelles and produces little enzyme activity. It contains the red pigment hemoglobin, an oxygen-binding protein, and the cell functions as an efficient vessel for the exchange of respiratory gas. Originates from bone marrow in adult humans.
Escherichia coli A gram-negative, rodlike bacterium that forms acid and gas in the presence of carbohydrates and is commonly found in human intestines and in many other animals. It can be pathogenic and is implicated in a number of food-borne illnesses, with an estimated 10,000 to 20,000 cases of infection occurring in the United States each year. There are hundreds of strains of this one species.
Esophagus The muscular tube of the digestive tract between the throat (pharynx) and stomach.
Essential amino acids Amino acids that cannot be synthesized in the human body and must be provided from another source (food). These amino acids are his-tidine, isoleucine, leucine, lysine, methionine, pheny-lalanine, threonine, tryptophan, and valine. See also amino acid.
Estivation (aestivation) A state of stagnation or dormancy with slow metabolism (no eating, moving, or growing) during periods of hot temperature and little water supply; a physiological condition for survival.
Estrogens Primary female sex hormones. Estrogens cause growth and development of female sex organs and support the maintenance of sexual characteristics, including growth of underarm and pubic hair and shaping of body contours and skeleton; increase secretions from the cervix and growth of the endometrium (inner lining) of the uterus; and reduce concentrations of bad cholesterol (LDL cholesterol) while increasing good cholesterol (HDL). Estrogen is produced in the ovary by the developing follicle and by the corpus luteum.
Estrous cycle (heat cycle) The period from one ovulation to the next in female mammals; a period of sexual receptiveness preceding ovulation; in humans it occurs every 21 to 23 days. It is characterized by rising and falling levels of estrogens and progesterone in the bloodstream.
Estrus The "heat" cycle in reproduction, the time when the female is sexually receptive.
Ethology The study of natural animal behavior.
Ethylene (C2H4) A reactive chemical made from natural gas or crude-oil components (occurs naturally in both petroleum and natural gas) that acts as a plant hormone, the only gaseous hormone. It is used for accelerating fruit ripening (bananas); maturing citrus fruit color; increasing the growth rate of seedlings, vegetables, and fruit trees; leaf abscission; and aging.
Etiology (aetiology) The scientific study or theory of the causes of a certain disease.
Euchromatin Within a nucleus of eukaryotes there are two types of a mixture of nucleic acid and protein called chromatin that make up a chromosome: euchro-matin and heterochromatin. During interphase, the genetically active euchromatin is uncoiled and is available for transcription, while heterochromatin is denser and usually not transcribed.
Eudismic ratio The potency of the eutomer relative to that of the distomer.
Eukaryotes Organisms whose cells have their genetic material packed in a membrane-surrounded, structurally discrete nucleus and who have well-developed cell organelles.
Eumetazoa A subkingdom of the animalia kingdom that includes all animals with the exception of sponges; animals with cells that form tissues and organs, a mouth, and digestive tract. Two branches exist, the radiata and the bilateria. The radiata have radial symmetry, i.e., all longitudinal planes are equal around a central body axis, while the bilateria are animals that have bilateral symmetry, i.e., they have a definite front and rear, and left and right body surfaces.
Eurasia Europe plus Asia considered as one continent. Used in political, economic, and geographical terms.
Eusocial A social system of insects, belonging to the order Isoptera (termites) and the order Hymenoptera (ants, bees, and wasps), in which the individuals cooperate in caring for the young after one female produces offspring. There is a reproductive division of labor, and previous generations aid in rearing. This trait also occurs in two species of mammals (mole rats).
Eutherian mammals (placental mammals) The female has a placenta that is connected to an embryo within the uterus that supplies it with nutrients and oxygen and acts as an excretory system. Humans are eutherian mammals.
Eutomer The enantiomer of a chiral compound that is the more potent for a particular action.
Eutrophication The accelerated loading or dumping of nutrients in a lake by natural or human-induced causes. Natural eutrophication changes the character of a lake very gradually, sometimes taking centuries, but humanmade or cultural eutrophication speeds up the aging of a lake, changing its qualities quickly, often in a matter of years.
Eutrophic lake Any lake that has an excessive supply of nutrients, usually nitrates and phosphates. Eutrophic lakes are usually not deep, contain abundant algae or rooted plants, and contain limited oxygen in the bottom layer of water.
Evaporative cooling Temperature reduction when water absorbs latent heat from the surrounding air as it evaporates. Similarly, "cooling" of the skin from the evaporation of sweat is evaporative cooling and is a process for the body to lose excess heat.
Evolution The long process of change that occurs in populations of organisms. It began with the first life forms on Earth and created the diversity of life forms that exist today and that will exist in the future.
Evolutionary species concept A species comprises the totality of individuals that share a common evolutionary history. A species is a lineage evolving separately from others.
Evolve Change slowly.
Exaptation The adoption of an attribute that had one function in an ancestral form but now has a new and different form, e.g., swim bladders becoming lungs, or three jaw bones of mammal ancestors becoming the middle bones of the ear. Formerly called preadaptation.
Excitatory postsynaptic potential (EPSP) Electrical change in the membrane of a postsynaptic neuron caused by binding of an excitatory neurotransmitter from a presynaptic cell to a postsynaptic receptor. Promotes firing of an action potential in the postsynaptic cell.
Excretion The process of separating and removing waste products of metabolism from the body through the discharge of urine, feces, or expired air.
Exegetic reaction A spontaneous reaction in which energy flows out of the system; a decrease in free energy. A reaction that liberates heat.
Exobiology The study of the origin of life other than on planet Earth.
Exocytosis The process in which a cell discharges large substances to the outside using secretory vesicles, storage organelles, that are then fused with the plasma membrane where they open for export.
Exogenous Originating externally. In the context of metalloprotein ligands, exogenous describes ligands added from an external source, such as CO or O2.
Exon A section of DNA that carries the coding sequence for a protein or part of it. Exons are separated by intervening, noncoding sequences (called introns ). In eukaryotes, most genes consist of a number of exons.
Exoskeleton The hard external skeleton made from chitin and connective tissue that attaches it to the underlying parts of a body of animals such as arthropods (insects, spiders, crabs, lobsters). Serves as protection, antidessicant, and sensory interface with the environment.
Exothermic A reaction that produces heat and absorbs heat from the surroundings.
Exotoxin A toxic substance produced by bacteria and then released outside its cell into its environment.
Exponential population growth Rapid population growth; populations increase at a constant proportion from one generation to the next. For example, the human population is doubling every 40 years. The rate of increase is not limited by environmental factors, only biotic or intrinsic factors. If birth rates exceed death rates, population size will increase exponentially; likewise if death rates exceed birth, population size will decrease exponentially. Also known as J-shaped population growth.
Expression The cellular production of the protein encoded by a particular gene. The process includes transcription of DNA, processing of the resulting mRNA product, and its translation into an active protein. A recombinant gene inserted into a host cell by means of a vector is said to be expressed if the synthesis of the encoded polypeptide can be demonstrated. For the expression of metalloproteins, usually other gene products will be required.
Extended X-ray absorption fine structure (EXAFS) EXAFS effects arise because of electron scattering by atoms surrounding a particular atom of interest as that special atom absorbs x rays and emits electrons. The atom of interest absorbs photons at a characteristic wavelength, and the emitted electrons, undergoing constructive or destructive interference as they are scattered by the surrounding atoms, modulate the absorption spectrum. The modulation frequency corresponds directly to the distance of the surrounding atoms, while the amplitude is related to the type and number of atoms. EXAFS studies are a probe of the local structure. EXAFS can be applied to systems that have local structure, but not necessarily long-range structure, such as noncrystalline materials. In particular, bond lengths and local symmetry (coordination numbers) can be derived. The X-ray absorption spectrum can also show detailed structure below the absorption edge. This X-ray absorption near-edge structure (XANES) arises from excitation of core electrons to high-level vacant orbitals.
Extinct species A species no longer in existence..
Extirpated species A species no longer surviving in regions that were once part of its range.
Extracellular matrix (ECM) Material produced by animal cells and secreted into the surrounding area, serving as a glue to hold cells together in tissues. It is composed of proteoglycans, polysaccharides, and proteins. Plays a role in cell shape, growth, migration, and differentiation.
Material produced by animal cells and secreted into the surrounding area serves as a glue to hold cells together in tissues.
Extraembryonic membranes The yolk sac, amnion, chorion, and allantois, four membranes that support and nourish the developing embryo in reptiles, birds, and mammals. The allantois performs gas exchange and is a repository for the embryo’s nitrogenous waste. It is involved in the development of the urinary bladder. The chorion is the outermost layer and contributes to the formation of the placenta. The amnion, the innermost layer, forms a fluid-filled sac around the embryo to protect it from jarring. The yolk sac surrounds the yolk and is the site of blood-cell formation and germ-cell formation, which are the predecessors of male and female gametes.
Extrinsic asthma Asthma triggered by external agents such as pollen or chemicals. Most cases of extrinsic asthma have an allergic origin and are caused by an IgE-mediated response to an inhaled allergen. This is the type of asthma commonly diagnosed in early life. Many patients with extrinsic asthma respond to immunotherapy.
F-430 A tetrapyrrole structure containing nickel, a component of the enzyme methyl-coenzyme M reduc-tase, which is involved in the formation of methane in methanogenic bacteria. The highly reduced macrocyclic structure, related to porphyrins and corrins, is termed a corphin.
Facilitated diffusion A process by which carrier proteins, also called permeases or transporters or ion channels, in the cell membrane transport substances such as glucose, sodium, and chloride ions into or out of cells down a concentration (electrochemical) gradient; does not require the use of metabolic energy.
Facultative anaerobe A facultative anaerobe is a microorganism that makes atp by aerobic respiration if oxygen is present but, if absent, switches to fermentation under anaerobic conditions.
Facultative organism Any organism that changes a metabolic pathway to another when needed.
Facultative saprophyte Any organism that is usually parasitic but can also live as a saprophyte.
Facultative symbiont Any organism that chooses a symbiotic relationship with a host only if the relationship presents itself but is not physiologically required to do so for survival.
Fahrenheit, Daniel Gabriel (1686-1736) German Instrument Maker, Physicist Daniel Gabriel Fahrenheit, a German instrument maker and physicist, was born in Danzig, Germany (now Gdansk, Poland), in 1686, the oldest of five children. Fahrenheit’s major contributions lay in the creation of the first accurate thermometers in 1709 and a temperature scale in 1724 that bears his name today.
Bacillus cereus showing hemolysis on sheep-blood agar. B. cereus is a gram-positive beta hemolytic bacteria that can live in an environment with or without the presence of oxygen (i.e., a facultative anaerobe).
When he was 15 years of age, his parents died of mushroom poisoning. The city council placed the four younger Fahrenheit orphans in foster homes and apprenticed Daniel to a merchant who taught him bookkeeping. He was sent to Amsterdam around 1714, where he learned of the Florentine thermometer, invented in Italy 60 years prior in 1654 by the grand duke of Tuscany, Ferdinand II (1610-70), a member of the powerful Medici family. For some unknown reason, it sparked his curiosity and he decided to make thermometers for a living. He abandoned his bookkeeping apprenticeship, whereby Dutch authorities issued warrants for his arrest. While on the run, he spent several years traveling around Europe and meeting scientists, such as Danish astronomer Olaus Roemer. Eventually he returned to Amsterdam in 1717 and remained in the Netherlands for the rest of his life.
What seems so simple today—having a fixed scale and fixed points on a thermometer—was not obvious in Fahrenheit’s time, when several makers used different types of scales and liquids for measuring. In 1694 Carlo Renaldini, a member of the Academia del Cimen-to and professor of philosophy at the university of Pisa, was the first to suggest taking the boiling and freezing points of water as the fixed points. The academy was founded by Prince Leopoldo de Medici and the Grand Duke Ferdinand II in 1657 with the purpose of examining the natural philosophy of Aristotle. The academy was active sporadically over 10 years and concluded its work in 1667 with the publication of the Saggi di Naturali Esperienze.
Unfortunately, Florentine thermometers, or any thermometers of the time, were not very accurate; no two thermometers gave the same temperature, since there was no universal acceptance of liquid type or agreement on what to use for a scale. Makers of Florentine thermometers marked the low end of the scale as the coldest day in Florence that year and the high end of the scale as the hottest day. Because temperature fluctuations naturally occur over the years, no two thermometers gave the same temperature. For several years Fahrenheit experimented with this problem, finally devising an accurate alcohol thermometer in 1709 and the first mercury or "quicksilver" thermometer in 1714.
Fahrenheit’s first thermometers, from about 1709 to 1715, contained a column of alcohol that directly expanded and contracted, based on a design made by Danish astronomer Olaus Romer in 1708, which Fahrenheit personally reviewed. Romer used alcohol (actually wine) as the liquid, but his thermometer had two fixed reference points. He selected 60 degrees for the temperature of boiling water and 7.5 degrees for melting ice.
Fahrenheit eventually devised a temperature scale for his alcohol thermometers with three points calibrated at 32 degrees for freezing water, 96 degrees for body temperature (based on the thermometer being in a healthy man’s mouth or under the armpit), and zero degrees fixed at the freezing point of ice and salt, believed at the time to be the coldest possible temperature. The scale was etched in 12 major points (with zero, four, and 12 as three points) and eight gradations between the major points, giving him a total of 96 points for his scale for body temperature on his thermometer.
Because his thermometers showed such consistency in their measurements, mathematician Christian Wolf at Halle, Prussia, devoted a whole paper in an edition of Acta Eruditorum, one of the most important international journals of the time, on two of Fahrenheit’s thermometers that were given to him in 1714. From 1682 until it ceased publication in 1731, the Latin Acta Eruditorum, published monthly in Leipzig and supported by the duke of Saxony, was one of the most important international journals. The periodical was founded by otto Mencke, professor of morals and practical philosophy, and mathematician Gottfried Wil-helm Leibnitz. Written in Latin, the journal covered science and social science and was primarily a vehicle for reviewing books. In 1724 Fahrenheit published a paper, "Experimenta circa gradum caloris liquorum nonnullo-rum ebullientium instituta (Experiments done on the degree of heat of a few boiling liquids), in the Royal Society’s publication Philosophical Transactions and was admitted to the Royal Society the same year.
Fahrenheit decided to substitute mercury for the alcohol because its rate of expansion was more constant than that of alcohol and could be used over a wider range of temperatures. Fahrenheit, like isaac newton before him, realized that it was more accurate to base the thermometer on a substance that changed consistently based on temperature instead of simply on the hottest or coldest day of the year, like the Florentine models. Mercury also had a much wider temperature range than alcohol. The choice of mercury as a benchmark was contrary to the common thought at the time, promoted by Halley as late as 1693, who believed that mercury could not be used for thermometers because of its low coefficient of expansion.
Fahrenheit later adjusted his temperature scale to ignore body temperature as a fixed point, bringing the scale to just the freezing and boiling of water. After his death, scientists recalibrated his thermometer so that the boiling point of water was the highest point, changing it to 212 degrees, as Fahrenheit had earlier indicated in a publication on the boiling points of various liquids. The freezing point became 32 degrees, and body temperature became 98.6 degrees. This is the scale that is presently used in thermometers in the United States and some English-speaking countries, although most scientists use the Celsius scale.
By 1779 there were some 19 different scales being used for thermometers, but it was Fahrenheit, along with astronomer anders Celsius and Jean Christin— whose scales were presented in 1742 and 1743—who helped finally set the standards for an accurate thermometer that are still used today. Besides making thermometers, Fahrenheit also was the first to show that the boiling point of liquids varies at different atmospheric pressures, and he suggested this as a principle for the construction of barometers. Among his other contributions were a pumping device for draining the Dutch polders and a hygrometer for measuring atmospheric humidity.
Fahrenheit died on September 16, 1736, in The Hague at the age of 50 years. There is virtually no one in the English-speaking countries today who does not have a thermometer with his initial (F) on it.
