Isotopes: Atomic species differing in mass number but having the same atomic number. (Grant & Hackh's Chemical Dictionary, 5th ed)Isotope Labeling: Techniques for labeling a substance with a stable or radioactive isotope. It is not used for articles involving labeled substances unless the methods of labeling are substantively discussed. Tracers that may be labeled include chemical substances, cells, or microorganisms.Nitrogen Isotopes: Stable nitrogen atoms that have the same atomic number as the element nitrogen, but differ in atomic weight. N-15 is a stable nitrogen isotope.Oxygen Isotopes: Stable oxygen atoms that have the same atomic number as the element oxygen, but differ in atomic weight. O-17 and 18 are stable oxygen isotopes.Carbon Isotopes: Stable carbon atoms that have the same atomic number as the element carbon, but differ in atomic weight. C-13 is a stable carbon isotope.Zinc Isotopes: Stable zinc atoms that have the same atomic number as the element zinc, but differ in atomic weight. Zn-66-68, and 70 are stable zinc isotopes.Sulfur Isotopes: Stable sulfur atoms that have the same atomic number as the element sulfur, but differ in atomic weight. S-33, 34, and 36 are stable sulfur isotopes.Deuterium: Deuterium. The stable isotope of hydrogen. It has one neutron and one proton in the nucleus.Iron Isotopes: Stable iron atoms that have the same atomic number as the element iron, but differ in atomic weight. Fe-54, 57, and 58 are stable iron isotopes.Strontium Isotopes: Stable strontium atoms that have the same atomic number as the element strontium, but differ in the atomic weight. Sr-84, 86, 87, and 88 are the stable strontium isotopes.Radioisotope Dilution Technique: Method for assessing flow through a system by injection of a known quantity of radionuclide into the system and monitoring its concentration over time at a specific point in the system. (From Dorland, 28th ed)Mass Spectrometry: An analytical method used in determining the identity of a chemical based on its mass using mass analyzers/mass spectrometers.Indicator Dilution Techniques: Methods for assessing flow through a system by injection of a known quantity of an indicator, such as a dye, radionuclide, or chilled liquid, into the system and monitoring its concentration over time at a specific point in the system. (From Dorland, 28th ed)Mercury Isotopes: Stable mercury atoms that have the same atomic number as the element mercury, but differ in atomic weight. Hg-196, 198-201, and 204 are stable mercury isotopes.Gas Chromatography-Mass Spectrometry: A microanalytical technique combining mass spectrometry and gas chromatography for the qualitative as well as quantitative determinations of compounds.Kinetics: The rate dynamics in chemical or physical systems.Deuterium Oxide: The isotopic compound of hydrogen of mass 2 (deuterium) with oxygen. (From Grant & Hackh's Chemical Dictionary, 5th ed) It is used to study mechanisms and rates of chemical or nuclear reactions, as well as biological processes.Evolution, Planetary: Creation and development of bodies within solar systems, includes study of early planetary geology.Radioisotopes: Isotopes that exhibit radioactivity and undergo radioactive decay. (From Grant & Hackh's Chemical Dictionary, 5th ed & McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Hydrogen: The first chemical element in the periodic table. It has the atomic symbol H, atomic number 1, and atomic weight [1.00784; 1.00811]. It exists, under normal conditions, as a colorless, odorless, tasteless, diatomic gas. Hydrogen ions are PROTONS. Besides the common H1 isotope, hydrogen exists as the stable isotope DEUTERIUM and the unstable, radioactive isotope TRITIUM.Carbon Radioisotopes: Unstable isotopes of carbon that decay or disintegrate emitting radiation. C atoms with atomic weights 10, 11, and 14-16 are radioactive carbon isotopes.Chromatography, Liquid: Chromatographic techniques in which the mobile phase is a liquid.Zinc Radioisotopes: Unstable isotopes of zinc that decay or disintegrate emitting radiation. Zn atoms with atomic weights 60-63, 65, 69, 71, and 72 are radioactive zinc isotopes.Geologic Sediments: A mass of organic or inorganic solid fragmented material, or the solid fragment itself, that comes from the weathering of rock and is carried by, suspended in, or dropped by air, water, or ice. It refers also to a mass that is accumulated by any other natural agent and that forms in layers on the earth's surface, such as sand, gravel, silt, mud, fill, or loess. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed, p1689)Meteoroids: Any solid objects moving in interplanetary space that are smaller than a planet or asteroid but larger than a molecule. Meteorites are any meteoroid that has fallen to a planetary surface. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Carbon: A nonmetallic element with atomic symbol C, atomic number 6, and atomic weight [12.0096; 12.0116]. It may occur as several different allotropes including DIAMOND; CHARCOAL; and GRAPHITE; and as SOOT from incompletely burned fuel.Radiometric Dating: Techniques used to determine the age of materials, based on the content and half-lives of the RADIOACTIVE ISOTOPES they contain.Tandem Mass Spectrometry: A mass spectrometry technique using two (MS/MS) or more mass analyzers. With two in tandem, the precursor ions are mass-selected by a first mass analyzer, and focused into a collision region where they are then fragmented into product ions which are then characterized by a second mass analyzer. A variety of techniques are used to separate the compounds, ionize them, and introduce them to the first mass analyzer. For example, for in GC-MS/MS, GAS CHROMATOGRAPHY-MASS SPECTROMETRY is involved in separating relatively small compounds by GAS CHROMATOGRAPHY prior to injecting them into an ionization chamber for the mass selection.Geological Phenomena: The inanimate matter of Earth, the structures and properties of this matter, and the processes that affect it.Food Chain: The sequence of transfers of matter and energy from organism to organism in the form of FOOD. Food chains intertwine locally into a food web because most organisms consume more than one type of animal or plant. PLANTS, which convert SOLAR ENERGY to food by PHOTOSYNTHESIS, are the primary food source. In a predator chain, a plant-eating animal is eaten by a larger animal. In a parasite chain, a smaller organism consumes part of a larger host and may itself be parasitized by smaller organisms. In a saprophytic chain, microorganisms live on dead organic matter.TritiumProteomics: The systematic study of the complete complement of proteins (PROTEOME) of organisms.Intestinal Absorption: Uptake of substances through the lining of the INTESTINES.Oxidation-Reduction: A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).Atmosphere: The gaseous envelope surrounding a planet or similar body. (From Random House Unabridged Dictionary, 2d ed)Catalysis: The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.Volcanic Eruptions: The ash, dust, gases, and lava released by volcanic explosion. The gases are volatile matter composed principally of about 90% water vapor, and carbon dioxide, sulfur dioxide, hydrogen, carbon monoxide, and nitrogen. The ash or dust is pyroclastic ejecta and lava is molten extrusive material consisting mainly of magnesium silicate. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Geology: The science of the earth and other celestial bodies and their history as recorded in the rocks. It includes the study of geologic processes of an area such as rock formations, weathering and erosion, and sedimentation. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Chemical Fractionation: Separation of a mixture in successive stages, each stage removing from the mixture some proportion of one of the substances, for example by differential solubility in water-solvent mixtures. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Models, Chemical: Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.History, Ancient: The period of history before 500 of the common era.Nitrogen: An element with the atomic symbol N, atomic number 7, and atomic weight [14.00643; 14.00728]. Nitrogen exists as a diatomic gas and makes up about 78% of the earth's atmosphere by volume. It is a constituent of proteins and nucleic acids and found in all living cells.Radioactive Tracers: Radioactive substances added in minute amounts to the reacting elements or compounds in a chemical process and traced through the process by appropriate detection methods, e.g., Geiger counter. Compounds containing tracers are often said to be tagged or labeled. (Hawley's Condensed Chemical Dictionary, 12th ed)Mummies: Bodies preserved either by the ancient Egyptian technique or due to chance under favorable climatic conditions.Water: A clear, odorless, tasteless liquid that is essential for most animal and plant life and is an excellent solvent for many substances. The chemical formula is hydrogen oxide (H2O). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Carbon-Carbon Lyases: Enzymes that catalyze the cleavage of a carbon-carbon bond by means other than hydrolysis or oxidation. This subclass contains the DECARBOXYLASES, the ALDEHYDE-LYASES, and the OXO-ACID-LYASES. EC 4.1.Paleontology: The study of early forms of life through fossil remains.Methane: The simplest saturated hydrocarbon. It is a colorless, flammable gas, slightly soluble in water. It is one of the chief constituents of natural gas and is formed in the decomposition of organic matter. (Grant & Hackh's Chemical Dictionary, 5th ed)Oceans and Seas: A great expanse of continuous bodies of salt water which together cover more than 70 percent of the earth's surface. Seas may be partially or entirely enclosed by land, and are smaller than the five oceans (Atlantic, Pacific, Indian, Arctic, and Antarctic).Absorption: The physical or physiological processes by which substances, tissue, cells, etc. take up or take in other substances or energy.Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.Ecosystem: A functional system which includes the organisms of a natural community together with their environment. (McGraw Hill Dictionary of Scientific and Technical Terms, 4th ed)Fossils: Remains, impressions, or traces of animals or plants of past geological times which have been preserved in the earth's crust.Animal Migration: Periodic movements of animals in response to seasonal changes or reproductive instinct. Hormonal changes are the trigger in at least some animals. Most migrations are made for reasons of climatic change, feeding, or breeding.Hydrogen-Ion Concentration: The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Proteome: The protein complement of an organism coded for by its genome.Amino Acids: Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.Seawater: The salinated water of OCEANS AND SEAS that provides habitat for marine organisms.Archaeology: The scientific study of past societies through artifacts, fossils, etc.Solar System: The group of celestial bodies, including the EARTH, orbiting around and gravitationally bound by the sun. It includes eight planets, one minor planet, and 34 natural satellites, more than 1,000 observed comets, and thousands of lesser bodies known as MINOR PLANETS (asteroids) and METEOROIDS. (From Academic American Encyclopedia, 1983)Protons: Stable elementary particles having the smallest known positive charge, found in the nuclei of all elements. The proton mass is less than that of a neutron. A proton is the nucleus of the light hydrogen atom, i.e., the hydrogen ion.Magnetic Resonance Spectroscopy: Spectroscopic method of measuring the magnetic moment of elementary particles such as atomic nuclei, protons or electrons. It is employed in clinical applications such as NMR Tomography (MAGNETIC RESONANCE IMAGING).Diet: Regular course of eating and drinking adopted by a person or animal.Spectrometry, Mass, Electrospray Ionization: A mass spectrometry technique used for analysis of nonvolatile compounds such as proteins and macromolecules. The technique involves preparing electrically charged droplets from analyte molecules dissolved in solvent. The electrically charged droplets enter a vacuum chamber where the solvent is evaporated. Evaporation of solvent reduces the droplet size, thereby increasing the coulombic repulsion within the droplet. As the charged droplets get smaller, the excess charge within them causes them to disintegrate and release analyte molecules. The volatilized analyte molecules are then analyzed by mass spectrometry.Biological Availability: The extent to which the active ingredient of a drug dosage form becomes available at the site of drug action or in a biological medium believed to reflect accessibility to a site of action.Technetium: The first artificially produced element and a radioactive fission product of URANIUM. Technetium has the atomic symbol Tc, atomic number 43, and atomic weight 98.91. All technetium isotopes are radioactive. Technetium 99m (m=metastable) which is the decay product of Molybdenum 99, has a half-life of about 6 hours and is used diagnostically as a radioactive imaging agent. Technetium 99 which is a decay product of technetium 99m, has a half-life of 210,000 years.Radionuclide Imaging: The production of an image obtained by cameras that detect the radioactive emissions of an injected radionuclide as it has distributed differentially throughout tissues in the body. The image obtained from a moving detector is called a scan, while the image obtained from a stationary camera device is called a scintiphotograph.Ammonium Compounds: Inorganic compounds that include a positively charged tetrahedral nitrogen (ammonium ion) as part of their structure. This class of compounds includes a broad variety of simple ammonium salts and derivatives.Deuterium Exchange Measurement: A research technique to measure solvent exposed regions of molecules that is used to provide insight about PROTEIN CONFORMATION.Reference Standards: A basis of value established for the measure of quantity, weight, extent or quality, e.g. weight standards, standard solutions, methods, techniques, and procedures used in diagnosis and therapy.Forensic Sciences: Disciplines that apply sciences to law. Forensic sciences include a wide range of disciplines, such as FORENSIC TOXICOLOGY; FORENSIC ANTHROPOLOGY; FORENSIC MEDICINE; FORENSIC DENTISTRY; and others.Solvents: Liquids that dissolve other substances (solutes), generally solids, without any change in chemical composition, as, water containing sugar. (Grant & Hackh's Chemical Dictionary, 5th ed)Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Hair: A filament-like structure consisting of a shaft which projects to the surface of the SKIN from a root which is softer than the shaft and lodges in the cavity of a HAIR FOLLICLE. It is found on most surfaces of the body.Feces: Excrement from the INTESTINES, containing unabsorbed solids, waste products, secretions, and BACTERIA of the DIGESTIVE SYSTEM.Sulfides: Chemical groups containing the covalent sulfur bonds -S-. The sulfur atom can be bound to inorganic or organic moieties.Mathematics: The deductive study of shape, quantity, and dependence. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Food Analysis: Measurement and evaluation of the components of substances to be taken as FOOD.Zinc: A metallic element of atomic number 30 and atomic weight 65.38. It is a necessary trace element in the diet, forming an essential part of many enzymes, and playing an important role in protein synthesis and in cell division. Zinc deficiency is associated with ANEMIA, short stature, HYPOGONADISM, impaired WOUND HEALING, and geophagia. It is known by the symbol Zn.Soil: The unconsolidated mineral or organic matter on the surface of the earth that serves as a natural medium for the growth of land plants.Gold Isotopes: Stable gold atoms that have the same atomic number as the element gold, but differ in atomic weight. Au-197 is a stable isotope.Lead Radioisotopes: Unstable isotopes of lead that decay or disintegrate emitting radiation. Pb atoms with atomic weights 194-203, 205, and 209-214 are radioactive lead isotopes.Chromatography, High Pressure Liquid: Liquid chromatographic techniques which feature high inlet pressures, high sensitivity, and high speed.Earth (Planet): Planet that is the third in order from the sun. It is one of the four inner or terrestrial planets of the SOLAR SYSTEM.Molecular Structure: The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.Uranium: Uranium. A radioactive element of the actinide series of metals. It has an atomic symbol U, atomic number 92, and atomic weight 238.03. U-235 is used as the fissionable fuel in nuclear weapons and as fuel in nuclear power reactors.Water Pollutants, Radioactive: Pollutants, present in water or bodies of water, which exhibit radioactivity.Methods: A series of steps taken in order to conduct research.Geography: The science dealing with the earth and its life, especially the description of land, sea, and air and the distribution of plant and animal life, including humanity and human industries with reference to the mutual relations of these elements. (From Webster, 3d ed)Leucine: An essential branched-chain amino acid important for hemoglobin formation.Mammoths: An extinct genus of large mammals in the family Elephantidae that fed by grazing on low vegetation. Most died out at the end of the last ice age.Body Water: Fluids composed mainly of water found within the body.Calibration: Determination, by measurement or comparison with a standard, of the correct value of each scale reading on a meter or other measuring instrument; or determination of the settings of a control device that correspond to particular values of voltage, current, frequency or other output.Sulfates: Inorganic salts of sulfuric acid.Plant Transpiration: The loss of water vapor by plants to the atmosphere. It occurs mainly from the leaves through pores (stomata) whose primary function is gas exchange. The water is replaced by a continuous column of water moving upwards from the roots within the xylem vessels. (Concise Dictionary of Biology, 1990)Evolution, Chemical: Chemical and physical transformation of the biogenic elements from their nucleosynthesis in stars to their incorporation and subsequent modification in planetary bodies and terrestrial biochemistry. It includes the mechanism of incorporation of biogenic elements into complex molecules and molecular systems, leading up to the origin of life.Potassium Isotopes: Stable potassium atoms that have the same atomic number as the element potassium, but differ in atomic weight. K-41 is a stable potassium isotope.Potassium Radioisotopes: Unstable isotopes of potassium that decay or disintegrate emitting radiation. K atoms with atomic weights 37, 38, 40, and 42-45 are radioactive potassium isotopes.Carbonates: Salts or ions of the theoretical carbonic acid, containing the radical CO2(3-). Carbonates are readily decomposed by acids. The carbonates of the alkali metals are water-soluble; all others are insoluble. (From Grant & Hackh's Chemical Dictionary, 5th ed)Pneumoencephalography: Radiographic visualization of the cerebral ventricles by injection of air or other gas.Reproducibility of Results: The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.Liver: A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances.Hydroxybenzoate Ethers: Benzoate derivatives that contain one or more alkyl or aryl groups linked to the benzene ring structure by OXYGEN.Substrate Specificity: A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Acetates: Derivatives of ACETIC ACID. Included under this heading are a broad variety of acid forms, salts, esters, and amides that contain the carboxymethane structure.Selenium Radioisotopes: Unstable isotopes of selenium that decay or disintegrate emitting radiation. Se atoms with atomic weights 70-73, 75, 79, 81, and 83-85 are radioactive selenium isotopes.Geological Processes: Events and activities of the Earth and its structures.Biocatalysis: The facilitation of biochemical reactions with the aid of naturally occurring catalysts such as ENZYMES.Time: The dimension of the physical universe which, at a given place, orders the sequence of events. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Sulfur: An element that is a member of the chalcogen family. It has an atomic symbol S, atomic number 16, and atomic weight [32.059; 32.076]. It is found in the amino acids cysteine and methionine.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Temperature: The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.Plant Leaves: Expanded structures, usually green, of vascular plants, characteristically consisting of a bladelike expansion attached to a stem, and functioning as the principal organ of photosynthesis and transpiration. (American Heritage Dictionary, 2d ed)Pacific OceanIodine Isotopes: Stable iodine atoms that have the same atomic number as the element iodine, but differ in atomic weight. I-127 is the only naturally occurring stable iodine isotope.Gallium Isotopes: Stable gallium atoms that have the same atomic number as the element gallium, but differ in atomic weight. Ga-71 is a stable gallium isotope.Ecology: The branch of science concerned with the interrelationship of organisms and their ENVIRONMENT, especially as manifested by natural cycles and rhythms, community development and structure, interactions between different kinds of organisms, geographic distributions, and population alterations. (Webster's, 3d ed)Photosynthesis: The synthesis by organisms of organic chemical compounds, especially carbohydrates, from carbon dioxide using energy obtained from light rather than from the oxidation of chemical compounds. Photosynthesis comprises two separate processes: the light reactions and the dark reactions. In higher plants; GREEN ALGAE; and CYANOBACTERIA; NADPH and ATP formed by the light reactions drive the dark reactions which result in the fixation of carbon dioxide. (from Oxford Dictionary of Biochemistry and Molecular Biology, 2001)Toluene: A widely used industrial solvent.Phosphorus Isotopes: Stable phosphorus atoms that have the same atomic number as the element phosphorus, but differ in atomic weight. P-31 is a stable phosphorus isotope.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Dysprosium: Dysprosium. An element of the rare earth family that has the atomic symbol Dy, atomic number 66, and atomic weight 162.50. Dysprosium is a silvery metal used primarily in the form of various salts.Climate: The longterm manifestations of WEATHER. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Neutron Activation Analysis: Activation analysis in which the specimen is bombarded with neutrons. Identification is made by measuring the resulting radioisotopes. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Nuclear Magnetic Resonance, Biomolecular: NMR spectroscopy on small- to medium-size biological macromolecules. This is often used for structural investigation of proteins and nucleic acids, and often involves more than one isotope.Tooth: One of a set of bone-like structures in the mouth used for biting and chewing.Glucose: A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement.Metabolic Flux Analysis: Measurement of cells' substrate utilization and biosynthetic output for modeling of METABOLIC NETWORKS.Stereoisomerism: The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Biodegradation, Environmental: Elimination of ENVIRONMENTAL POLLUTANTS; PESTICIDES and other waste using living organisms, usually involving intervention of environmental or sanitation engineers.Fresh Water: Water containing no significant amounts of salts, such as water from RIVERS and LAKES.Iron: A metallic element with atomic symbol Fe, atomic number 26, and atomic weight 55.85. It is an essential constituent of HEMOGLOBINS; CYTOCHROMES; and IRON-BINDING PROTEINS. It plays a role in cellular redox reactions and in the transport of OXYGEN.Proteins: Linear POLYPEPTIDES that are synthesized on RIBOSOMES and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of AMINO ACIDS determines the shape the polypeptide will take, during PROTEIN FOLDING, and the function of the protein.Lead: A soft, grayish metal with poisonous salts; atomic number 82, atomic weight 207.19, symbol Pb. (Dorland, 28th)Indium: A metallic element, atomic number 49, atomic weight 114.82, symbol In. It is named from its blue line in the spectrum. (From Dorland, 28th ed)Metabolomics: The systematic identification and quantitation of all the metabolic products of a cell, tissue, organ, or organism under varying conditions. The METABOLOME of a cell or organism is a dynamic collection of metabolites which represent its net response to current conditions.Bacteria: One of the three domains of life (the others being Eukarya and ARCHAEA), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classified by their response to OXYGEN: aerobic, anaerobic, or facultatively anaerobic; by the mode by which they obtain their energy: chemotrophy (via chemical reaction) or PHOTOTROPHY (via light reaction); for chemotrophs by their source of chemical energy: CHEMOLITHOTROPHY (from inorganic compounds) or chemoorganotrophy (from organic compounds); and by their source for CARBON; NITROGEN; etc.; HETEROTROPHY (from organic sources) or AUTOTROPHY (from CARBON DIOXIDE). They can also be classified by whether or not they stain (based on the structure of their CELL WALLS) with CRYSTAL VIOLET dye: gram-negative or gram-positive.Phytic Acid: Complexing agent for removal of traces of heavy metal ions. It acts also as a hypocalcemic agent.Feeding Behavior: Behavioral responses or sequences associated with eating including modes of feeding, rhythmic patterns of eating, and time intervals.Yttrium Isotopes: Stable yttrium atoms that have the same atomic number as the element yttrium, but differ in atomic weight. Y-89 is the only naturally occurring stable isotope of yttrium.Escherichia coli: A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.Plants: Multicellular, eukaryotic life forms of kingdom Plantae (sensu lato), comprising the VIRIDIPLANTAE; RHODOPHYTA; and GLAUCOPHYTA; all of which acquired chloroplasts by direct endosymbiosis of CYANOBACTERIA. They are characterized by a mainly photosynthetic mode of nutrition; essentially unlimited growth at localized regions of cell divisions (MERISTEMS); cellulose within cells providing rigidity; the absence of organs of locomotion; absence of nervous and sensory systems; and an alternation of haploid and diploid generations.Iodine Radioisotopes: Unstable isotopes of iodine that decay or disintegrate emitting radiation. I atoms with atomic weights 117-139, except I 127, are radioactive iodine isotopes.Actinium: Actinium. A trivalent radioactive element and the prototypical member of the actinide family. It has the atomic symbol Ac, atomic number 89, and atomic weight 227.0278. Its principal isotope is 227 and decays primarily by beta-emission.Phenylalanine: An essential aromatic amino acid that is a precursor of MELANIN; DOPAMINE; noradrenalin (NOREPINEPHRINE), and THYROXINE.Strontium Radioisotopes: Unstable isotopes of strontium that decay or disintegrate spontaneously emitting radiation. Sr 80-83, 85, and 89-95 are radioactive strontium isotopes.Chromium Radioisotopes: Unstable isotopes of chromium that decay or disintegrate emitting radiation. Cr atoms with atomic weights of 46-49, 51, 55, and 56 are radioactive chromium isotopes.Plutonium: Plutonium. A naturally radioactive element of the actinide metals series. It has the atomic symbol Pu, atomic number 94, and atomic weight 242. Plutonium is used as a nuclear fuel, to produce radioisotopes for research, in radionuclide batteries for pacemakers, and as the agent of fission in nuclear weapons.Mars: The fourth planet in order from the sun. Its two natural satellites are Deimos and Phobos. It is one of the four inner or terrestrial planets of the solar system.Canavalia: A plant genus of the family FABACEAE. Canavalia ensiformis is the source of CONCANAVALIN A.Peptides: Members of the class of compounds composed of AMINO ACIDS joined together by peptide bonds between adjacent amino acids into linear, branched or cyclical structures. OLIGOPEPTIDES are composed of approximately 2-12 amino acids. Polypeptides are composed of approximately 13 or more amino acids. PROTEINS are linear polypeptides that are normally synthesized on RIBOSOMES.Selenium: An element with the atomic symbol Se, atomic number 34, and atomic weight 78.96. It is an essential micronutrient for mammals and other animals but is toxic in large amounts. Selenium protects intracellular structures against oxidative damage. It is an essential component of GLUTATHIONE PEROXIDASE.Coprophagia: Eating of excrement by animal species.