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 Climate Change · Part One
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 Introduction to Astronomy
 Life in the Universe

 Glossary: Climate Change
 Glossary: Astronomy
 Glossary: Life in Universe

    Glossary of Terms - M to R
    Index: A to F | G to L | M to R | S to Z

    Ma - (n.)

    Mega anna, one million (1,000,000 or 1 x 106) years.

    macromolecule - (n.)

    A molecule with a very high molecular mass; a polymer.

    magnetite - (n.)

    A mineral, the iron oxide Fe3O4.

    magnetofossil - (n.)

    Minute grains of the mineral magnetite present in sedimentary rocks suspected to be of bacterial origin.

    magnetosphere - (n.)

    A region, surrounding a star or planet, that is permeated by the magnetic field of that body.

    mantle - (n.)

    The shell of rock separating the core of a differentiated planet from its thin surface crust or lithosphere. The earth's mantle starts about 40 km below the surface and continues nearly half-way toward the center. Convection currents in the mantle are the cause of continental drift.

    mega - (n.)

    –106 (as in megahertz, MHz); one million.

    meiosis - (n.)

    The process of nuclear division that reduces the number of chromosomes from the diploid to the haploid number in each of four product cells (in animals, the sperm or egg).

    membrane - (n.)

    A biological, sheetlike structure made of a lipid bilayer and a number of inserted proteins.

    mesozoic era - (n.)

    The second oldest of three geologic eras of the Phanerozoic Eon of Earth's history, extending from the end of the Paleozoic Era, 251 Ma ago, to the beginning of the Cenozoic Era, 65 Ma ago.

    Index: A to F | G to L | M to R | S to Z

    messenger RNA (mRNA) - (n.)

    The type of RNA that contains the codons for a protein; mRNA travels from the nucleus of the cell to a ribosome, a the part of the cell outside the nucleus, where this information is used to manufacture proteins.

    metabolism - (n.)

    The sum of the energy-consuming and energy-producing processes that happen during the chemical buildup and breakdown of organic compounds in living systems.

    metamorphic rock - (n.)

    Rock derived as a result of mineralogical, chemical, and structural changes in a preexisting rock in response to changes in temperature, pressure, and chemical environment at depth in the Earth's crust.

    metazoan - (n.)

    A taxonomic category comprised of many-celled animals; an animal whose body is composed of cells differentiated into tissues and organs and (usually) a digestive cavity.

    methane - (n.)

    The colorless gaseous hydrocarbon CH4.

    methane-generating prokaryote - (n.)

    Any various archaeal microbes that give off methane gas as a product of their chemoautotrophic metabolism.

    MHz - (n.)

    One million Hertz; megahertz ; a million cycles per second.

    microalga - (n.)

    Any of diverse microscopic photoautotrophic protists, especially unicellular eukaryotic phytoplankton.

    microbe - (n.)

    Informal term for any of diverse types of prokaryotic bacteria or archaeans.

    microbiota - (n.)

    A population of microbes.

    Index: A to F | G to L | M to R | S to Z

    microfossils - (n.)

    Fossils of unicellular organisms that can only be seen under the microscope in specially prepared rock samples.

    micrometer (µ) - (n.)

    A unit of length, one-millionth (10-6 )of a meter.

    midocean ridge - (n.)

    A 40,000-mile-long continuous median mountain range in the Arctic, North and South Atlantic, and Indian Oceans. The crest of the ridge is usually found at 500 to 1300 fathoms below the surface; its width is usually a few hundred miles, and it has a relief of 10,000 - 33,000 ft.

    mitochondrion - (n.)

    Plural; mitochondria : An endosymbiont-derived organelle present in most eukaryotic cells and playing a major role in respiratory metabolism and energy retrieval. They are the site of oxidative respiration, i.e., where organic compounds are oxidised to produce energy. Mitochondria are relatively dense, oblong particles, about one twenty-thousandth of an inch in size, surrounded by two membranes, of which the inner one, a site of actively phosphorylating respiratory chains, forms many infoldings, or cristae. ~ See Also: Endosymbiont, Phosphorylation, Respiration.

    mitosis - (n.)

    A type of division of the cell nucleus resulting in formation of two daughter cells, each a genetic copy (clone) of the parent cell; in unicellular eukaryotes, a type of nonsexual reproduction.

    mole - (n.)

    The formula weight in grams of an element or compound; or a quantity of chemical substance that contains 6.02 x 1023 formula units of the substance.

    molecule - (n.)

    A collection of atoms bound together that is the smallest collection that exhibits a certain set of chemical properties, mollusk : Any of an animal phylum (Mollusca) characterized by a large muscular foot and a mantle that secretes spicules or shells, such as a snail, clam, or squid.

    monomer - (n.)

    A chemical compound, usually small, that can be linked to other monomers into a larger, multicomponent polymer. A simple chemical compound of relatively low molecular weight which can undergo polymerization.

    mononucleotide - (n.)

    A nucleotide composed of one monomer each of a nitrogenous base, a sugar, and a phosphoric acid.

    montmorillonite - (n.)

    Soft claylike mineral composed of hydrous aluminum silicate.

    Index: A to F | G to L | M to R | S to Z

    messenger RNA (mRNA) - (n.)

    The type of RNA that contains the codons for a protein; mRNA travels from the nucleus of the cell to a ribosome, a the part of the cell outside the nucleus, where this information is used to manufacture proteins.

    mutagen - (n.)

    Any entity that causes changes in genes without destroying the genetic material.

    mutation - (n.)

    An alteration of a gene, transmissible by replication. ~ See Also: Gene, Genetic drift : Natural selection.

    mycoplasma - (n.)

    Any of a genus (Mycoplasma) of extremely minute parasitic microorganisms that lack cell walls; known also as PPLO, Pleuropneumonia-like organisms. Mycoplasmas, small as they are, have over 500 genes.

    nanometer (nm) - (n.)

    A unit of length, one billionth (10-9) of a meter.

    natural selection - (n.)

    The method by which Darwinian evolution operates; the preferential survival of individuals having advantageous variations relative to other members of their population or species; for natural selection to operate, there must be competition for resources (a struggle for survival) and suitable variation among individuals. ~ See Also: Mutation

    neo-darwinian synthesis - (n.)

    A merging of the concepts of Darwinian selection, Mendelian genetics, random mutation, population biology, and paleontology in the 1930s and 1940s that resulted in the predominating theory that evolution is change in the genetics of species due to natural selection.

    neuron - (n.)

    A nerve cell, characteristically made of a cell body, an emitter extension, or axon, and a ramified receiving extension made of dendrites. ~ See Also: Axon, Dendrite, Synapse.

    neurotransmitter - (n.)

    A chemical, typically secreted at synapses, involved in the transmission of a nerve impulse to a neighboring cell.~ See Also: Chemical transmitter, Synapse.

    niche, ecologic - (n.)

    A unique way of life for a species of organism.

    Index: A to F | G to L | M to R | S to Z

    nitrate - (n.)

    NO3-, a biologically usable form of nitrogen.

    nitrogen fixation - (n.)

    The biologic process carried out by various bacterial and archaeal prokaryotes in which molecular nitrogen (N2) is combined with hydrogen to produce ammonia, a biologically useable form of nitrogen.

    nucleic acids - (n.)

    Long, chainlike molecules which, in the various combinations of constituent groups, embody the genetic code (DNA) and assist with its transmission (RNA).

    nucleolus - (n.)

    An inner structure of eukaryotic nuclei in which ribosomal RNAs are transcribed and processed. ~ See Also: Nucleus, Ribosomal RNA, Transcription.

    nucleon number - (n.)

    The total number of protons and neutrons in an atom; the mass number A.

    nucleoside - (n.)

    A chemical compound consisting of a purine or pyrimidine nitrogenous base combined with deoxyribose or ribose sugar.

    nucleotide - (n.)

    Any of several compounds that consist of a sugar (deoxyribose or ribose) linked to a purine (adenine [A] or guanine [G]) or a pyrimidine (thymine [T], cytosine [C], or uracil [U]) nitrogenous base and a phosphate group, the basic structural units of DNA and RNA.

    obligate aerobe - (n.)

    An organism unable to live in the absence of molecular oxygen (O2), needed to support its aerobic respiration.

    obligate anaerobe - (n.)

    An organism incapable of growth and reproduction in the presence of molecular oxygen (O2).

    oligomer - (n.)

    A molecule made by the association of a small number of identical or similar molecular units. ~ See Also: Multimer, Polymer.

    Index: A to F | G to L | M to R | S to Z

    ontogeny - (n.)

    The life history of an individual, as opposed to phylogeny, the evolutionary history of a group of organisms.

    optical activity - (n.)

    The property of some crystals, gases, liquids, and solutions to rotate plane-polarized light to the left or right. It occurs because the molecules that make up the substance through which the light beam is shone are asymmetric, i.e., they have no plane of symmetry. Asymmetric molecules are mirror images of each other that cannot be superimposed. This asymmetric property is also referred to as handedness. Examples are the L- and D- forms of amino acids.

    organelle - (n.)

    Any of various specialized membrane-enclosed structures in a cell, such as mitochondria or plastids, that perform a specific function.

    organic chemistry - (n.)

    Chemistry that deals with organic (carbon) compounds, including but not limited to chemical compounds and processes that occur in organisms.

    organic compound - (n.)

    A chemical compound of the type typical of (but not restricted to) living systems, composed commonly of carbon, hydrogen, oxygen, nitrogen, sulfur, and/or phosphorus.

    osmotic pressure - (n.)

    The force developed by the tendency of a solvent—for example, water—to diffuse from a region where dissolved substances are less concentrated to a region where they are more concentrated.

    oxic - (n.)

    Pertaining to the presence of molecular oxygen (O2).

    oxidation - (n.)

    A chemical process in which oxygen combines with another element (or in which hydrogen or electrons are removed from an element) and energy in the form of heat is released.

    oxidation-reduction - (n.)

    The electron-transfer process necessarily linking the oxidation of an electron donor to the reduction of an electron acceptor. ~ See Also: Electron transfer, Oxidation, Reduction, Redox.

    oxidative phosphorylation - (n.)

    The process coupling the assembly of ATP from ADP and inorganic phosphate to an electron-transfer reaction, usually, but not obligatorily, with oxygen as the final electron acceptor. ~ See Also: ATP, Carrier-level phosphorylation, Electron transfer : Substrate-level phosphorylation.

    Index: A to F | G to L | M to R | S to Z

    oxide - (n.)

    A chemical compound of oxygen and another element, as in the minerals hematite, Fe2O3, and magnetite, Fe3O4.

    oxygenic photosynthesis - (n.)

    Oxygen-producing photoautotrophy such as that in plants and plantlike organisms, including cyanobacteria.

    oxygen sink - (n.)

    Any of several molecular oxygen-consuming processes (such as aerobic respiration) or substances (such as unoxidized volcanic gases or dissolved ferrous iron).

    ozone layer - (n.)

    Layer of Earth's atmosphere at about 20 to 30 miles, marked by a high ozone (O3) content.

    PAHs - (n.)

    Polycyclic aromatic hydrocarbons, i.e., hydrocarbons in which the carbon atoms are arranged in rings which are themselves linked together.

    palaeobiology - (n.)

    The study of fossilized life.

    palaeontology - (n.)

    As for palaeobiology, except often considered to have more specific aims, for instance the classification of fossils and the dating of rocks.

    panspermia - (n.)

    The theory that life can arrive on a planet from a spore, seed, or cell derived from life elsewhere in the universe.

    paradigm - (n.)

    A well-established example or model, an archetype.

    peptide nucleic acid (PNA) - (n.)

    An artificial molecule constructed to look as much like a nucleic acid as possible.

    Index: A to F | G to L | M to R | S to Z

    period, geologic - (n.)

    A formal division of geologic time longer than an epoch and included in an era.

    periodic table - (n.)

    A systematic arrangement of the elements in columns and rows; elements in a given column have similar properties.

    permafrost - (n.)

    Underground permanent or semi-permanent water ice, permeating soil and rocks.

    petrify - (n.)

    The process by which organic-walled organisms can be preserved as fossils, embedded three-dimensionally in a siliceous, calcitic, or other mineral matrix; synonymous with permineralize.

    petroleum - (n.)

    A dark, oily mixture of hydrocarbons, mainly alkanes, occurring in various deposits around the world.

    phase change - (n.)

    Metamorphosis of a substance from one state to another, as from gas to liquid or from solid to gas.

    phenotype - (n.)

    The physical (including biochemical) products of gene expression of an organism, in contrast to its genetic constitution (the genotype).

    phospholipid - (n.)

    A phosphate-containing fatty substance with amphiphilic properties, the typical component of lipid bilayers in biological membranes. ~ See Also: Amphiphilic, Lipid bilayer : Membrane.

    phosphorylation - (n.)

    The attachment of a phosphate group (H2PO4) to another organic molecule. The phosphorylation of ADP to ATP is difficult to do, and adds a great deal of stored energy to the molecule.

    photic zone - (n.)

    The surface layers of oceans or lakes where sufficient light penetrates to support photosynthesis.

    Index: A to F | G to L | M to R | S to Z

    pH scale - (n.)

    An exponential scale of acidity; below 7, acidic; 7, neutral; above 7, basic.

    phylogeny - (n.)

    The evolutionary history of a group of organisms, as opposed to ontogeny, the life history of an individual. ~ See Also: Ontogeny, Recapitulation

    phylum - (n.)

    category of taxonomic classification just above class.

    physical properties - (n.)

    The qualities of a substance that can be demonstrated without changing the composition of the substance.

    pilus - (n.)

    Plural: pili : A long, slender, hairlike projection on the surface of certain bacterial cells and involved in cellular attachment and conjugation. ~ See Also: Conjugation.

    plankton - (n.)

    Organisms inhabiting the surface layers of a sea or lake, such as small drifting algae, protozoans, and animals.

    plasma membrane - (n.)

    Or cell membrane, the peripheral membrane surrounding all cells.

    plasmids - (n.)

    small, usually circular, DNA molecules that can carry a number of genes from one species of bacterium to another. Other kinds of such transposable elements can pass genes back and forth among eukaryotic species.

    plate tectonics - (n.)

    the theory that the Earth's continental and oceanic crust and outermost portion of the mantle is fractured into large plates that move relative to each other. Convective currents in the mantle provide the driving force for this motion. The plate motion is responsible for global mountain building, earthquake activity, and volcanism, all of which are most pronounced along plate boundaries ~ See Also: continental drift).

    peptide nucleic acid (PNA) - (n.)

    an artificial molecule constructed to look as much like a nucleic acid as possible.

    Index: A to F | G to L | M to R | S to Z

    polymer - (n.)

    A molecule made by the association of a large number of identical or similar molecular units. ~ See Also: Multimer, Oligomer.

    polymerase - (n.)

    An enzyme that builds polymers from monomeric subunits.

    population - (n.)

    Any naturally occurring group of organisms of the same species that occupies a relatively well-defined geographic region and has reproductive continuity from generation to generation.

    prebiotic - (n.)

    relating to the chemical or environmental precursors of the origin of life.

    Precambrian-Cambrian boundary problem - (n.)

    The series of interrelated scientific questions relating to the first appearance of diverse shelled metazoans at the beginning of the Cambrian Period of Earth's history.

    Precambrian eon - (n.)

    The older of two principal divisions (eons) of Earth's history, extending from the formation of the planet, 4,550 Ma ago, to the beginning of the Cambrian Period, 543 Ma ago; the Precambrian and the younger Phanerozoic Eon comprise all geologic time.

    primary plant nutrients - (n.)

    Nitrogen, phosphorus, and potassium.

    primary structure - (n.)

    The amino acid sequence in a protein or of nucleotides in a nucleic acid.

    prokaryotes - (n.)

    organisms that have no cell nucleus but do have chromosomes. They include the bacteria, blue-green algae, and archaea.

    prosthetic group - (n.)

    nonprotein group of a conjugated protein (i.e., a compound of a protein with a nonprotein).

    Index: A to F | G to L | M to R | S to Z

    protein - (n.)

    complex polymer built of amino acids that contains the elements carbon, hydrogen, nitrogen, oxygen, sometimes sulfur. and occasionally others such as phosphorus and iron. Proteins are essential constituents of all living cells; they are synthesized from raw materials by plants but assimilated as separate amino acids by animals.

    protist - (n.)

    any of a kingdom of living organisms (Protista) that includes algae, slime molds, protozoa, and fungi, usually characterized by unicellular reproductive structures, true nuclei, and chromosomes.

    protobionts - (n.)

    The first complex structures that arose during the formation of life that were capable of reproduction. Although protobionts can be considered the first living cells, they were very different from present-day cells and probably only parts of them were capable of accurate replication.

    protometabolism - (n.)

    The set of chemical reactions that supported emerging life until the development of enzyme-catalyzed metabolism. ~ See Also: Metabolism.

    purines - (n.)

    A group of nitrogenous bases comprising two main constituents of nucleic acids, adenine and guanine. ~ See Also: Base pairing, Nucleic acid, Nucleotide.

    pyrimidines - (n.)

    A group of bases comprising three main constituents of nucleic acids, cyto sine, uracil (present only in RNA), and thymine (present only in DNA). ~ See Also: Base pairing, Nucleic acid, Nucleotide.

    pyrophosphate bond - (n.)

    The bond joining phosphates in pyrophosphate and polyphosphates, also joining the three terminal phosphates of ATP, where it serves as the main conveyer of biological energy. ~ See Also: ATP, Polyphosphate, Pyrophosphate.

    quartz - (n.)

    A mineral, silicon dioxide, SiO2.

    racemic mixture - (n.)

    a mixture that contains exactly equal amounts of the asymmetric forms of an optically active molecule (see optical activity). Such a mixture does not cause plane-polarized light to rotate in either direction.

    radioactive dating - (n.)

    A technique for estimating the age of material, such as rock, based on the known initial isotopic composition and the known rate of radioactive decay for unstable isotopes originally present.

    Index: A to F | G to L | M to R | S to Z

    radioactive decay - (n.)

    Disintegration of an unstable atomic nucleus by spontaneous emission of radiation.

    Rb/Sr ratio - (n.)

    strontium isotope ratio is used as a corrective factor in rubidium-strontium dating for studying the ultimate age of origin of igneous rock.

    recombinant DNA - (n.)

    DNA in an organism that contains genetic material from another organism.

    redox reaction - (n.)

    A reaction in which oxidation and reduction occur.

    reduction - (n.)

    The gain of one or more electrons or hydrogen atoms (electrons + protons) by an atom or molecule. ~ See Also: Electron, Oxidation, Proton. In cell biology, chromosome reduction refers to the halving of the chromosome number that occurs at meiosis. ~ See Also: Diploid, Haploid, Meiosis.

    refractory - (n.)

    The property of being able to exist in solid form under conditions of very high temperature. Refractory elements are characterized by a high temperature of vaporization; they are the first to condense into solid form when a gas cools, as in the solar nebula.

    regolith - (n.)

    The mantle of unconsolidated fragmental material that covers a land surface; i.e., soil and fractured rock.

    replicase - (n.)

    The viral enzyme that replicates RNA molecules. ~ See Also: Replication, Virus.

    replication - (n.)

    The copying of nucleic acids by the synthesis of a molecule complementary to a template strand of the same nature (DNA on DNA, RNA on RNA). ~ See Also: Base pairing.

    respiration - (n.)

    The utilization of oxygen as an electron acceptor, or the breathing of air that provides oxygen to fulfill this function. ~ See Also: Electron transfer.

    Index: A to F | G to L | M to R | S to Z

    retrovirus - (n.)

    A virus with an RNA genome replicated and expressed by way of the complementary DNA synthesized by a viral reverse transcriptase. ~ See Also: Reverse transcriptase, Virus.

    reverse osmosis - (n.)

    A method of pressure filtration through a semipermeable membrane; water flows from an area of high salt concentration to an area of low salt concentration.

    reverse transcription - (n.)

    The synthesis of DNA on an RNA template. ~See Also: Base pairing, Transcription.

    ribonucleic acid or RNA - (n.)

    a nucleic acid made of ribonucleotides, most often transcribed from DNA, except in certain viruses, and serving mostly in protein synthesis and RNA splicing. ~ See Also: Messenger RNA, Ribonucleotide, Ribosomal RNA, Ribozyme, RNA splicing : Transcription, Transfer RNA, Virus.

    ribose - (n.)

    The 5-carbon sugar constituent of ribonucleotides and RNAs.

    ribosome - (n.)

    A compact particle, one-millionth of an inch in size, that serves as the site of protein assembly in all living cells : Consists of two subunits of unequal size, each made of protein and RNA molecules. ~ See Also: Protein, Ribosomal RNA.

    ribozyme - (n.)

    A molecule of RNA that has catalytic activity. Ribozymes are rare in living cells today, but may have been much more common when life began.

    RNA (t) m) - (n.)

    ribonucleic acid; a nucleic acid generally associated with the control of chemical reactions. Transfer RNAs move particular amino acids to growing polypeptide chains in protein synthesis; messenger RNAs act as templates for the formation of proteins.

    RNA splicing - (n.)

    The end-to-end joining of two RNA stretches belonging either to distinct molecules (trans splicing) or to the same molecule in which they were separated by an intron, which is removed in the process (cis splicing) : See Cis splicing, Exon, Intron, Split genes, Trans splicing.

    ribosomal ribonucleic acid (rRNA) - (n.)

    Any of several RNAs present in ribosomes.

    Index: A to F | G to L | M to R | S to Z


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