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94 Cards in this Set

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NAD+ nicotinamide adenine dinucleotide, an organic molecule that serves as an electron carrier by being oxidized to NAD+ and reduced to NADH
NADP+ nicotinamide adenine dinucleotide phosphate, an organic molecule that is composed of NAD plus an extra phosphate group and that acts as a hydrogen acceptor by being reduced to NADPH
narcotic a drug that is derived from opium and that relieves pain and induces sleep; examples include heroine, morphine, and codeine
NASA National Aeronautics and Space Administration, the agency of the U.S. federal government that was established in 1958 to conduct all nonmilitary space activities
nastic movement a type of plant response that is independent of the direction of a stimulus
nastic movement
natural bridge an arch of rock that forms by water erosion
natural bridge
natural gas a mixture of gaseous hydrocarbons located under the surface of the Earth, often near petroleum deposits; used as a fuel
natural gas
natural killer cell a type of white blood cell that is present in individuals who have not been immunized and that kills a variety of cells
natural killer cell
natural levee a raised riverbank that results when a river deposits its load at the river's edges
natural levee
natural resource any natural material that is used by humans, such as water, petroleum, minerals, forests, and animals
natural resource
natural selection the process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do; a theory to explain the mechanism of evolution
natural selection
nauplius the free-swimming larva of most crustaceans
Neanderthal a species of hominids that lived in Europe, Africa, and western Asia from 125,000 years ago to about 35,000 years ago
neap tide a tide of minimum range that occurs during the first and third quarters of the moon
neap tide
nebula a large cloud of gas and dust in interstellar space; a region in space where stars are born
nebular hypothesis a model for the formation of the solar system in which the sun and planets condense from a cloud (or nebula) of gas and dust
nebular hypothesis
nectar a sugar-containing fluid secreted by flowers to attract birds or insects for pollination
nekton all organisms that swim actively in open water, independent of currents
nematocyst in cnidarians, a stinging cell that is used to inject a toxin into prey
neon light light emitted by atoms of certain gases, such as neon, when the atoms are ionized by an electric current
neon light
nephridium a tubule through which some invertebrates eliminate wastes
nephron the functional unit of the kidney
neritic zone a shallow marine environment that is near the shore or over the continental shelf and that is rich in minerals and nutrients produced by biotic activity
neritic zone
nerve a collection of nerve fibers through which impulses travel between the central nervous system and other parts of the body
nerve net in cnidarians, a network of nerve cells that lacks a central control; impulses pass in any or all directions to produce a generalized response
nerve net
nervous system the structures that control the actions and reactions of the body in response to stimuli from the environment; it is formed by billions of specialized nerve cells, called neurons
nervous system
nervous tissue the tissue of the nervous system, which consists of neurons, their supporting cells, and connective tissue
nervous tissue
net force a single force whose external effects on a rigid body are the same as the effects of several actual forces acting on the body
net force
net primar productivity the rate at which biomass accumulates in an ecosystem
net primary productivity
neuron a nerve cell that is specialized to receive and conduct electrical impulses
nerve cells in the hypothalamus that synthesize and secrete hormones
neurosecretory cells
neurotransmitter a chemical substance that transmits nerve impulses across a synapse
neutralization reactionthe reaction of the ions that characterize acids (hydronium ions) and the ions that characterize bases (hydroxide ions) to form water molecules and a salt
neutralization reaction
neutron a subatomic particle that has no charge and that is located in the nucleus of an atom
neutron star a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons
neutron star
neutrophil a large leukocyte that contains a lobed nucleus and many cytoplasmic granules
new moon the phase of the moon during which the side of the moon facing the Earth is unlit by the sun
new moon
newton the SI unit for force; the force that will increase the speed of a 1 kg mass by 1 m/s each second that the force is applied (symbol, N)
niche the unique position occupied by a species, both in terms of its physical use of its habitat and its function within an ecological community
nicotine a toxic, addictive alkaloid that is derived from tobacco and that is one of the major contributors to the harmful effects of smoking
nictitating membrane a third eyelid found under the lower eyelid of many vertebrates, including birds, reptiles, and amphibians
nictitating membrane
nitrification the process by which nitrites and nitrates are produced by bacteria in the soil
nitrogen cycle the process in which nitrogen circulates among the air, soil, water, plants, and animals in an ecosystem
nitrogen cycle
nitrogen fixation the process by which gaseous nitrogen is converted into ammonia, a compound that organisms can use to make amino acids and other nitrogen-containing organic molecules
nitrogen fixation
nitrogen-fixing bacteria bacteria that convert atmospheric nitrogen into ammonia
nitrogen-fixing bacteria
nitrogenous base an organic base that contains nitrogen, such as a purine or pyrimidine; a subunit of a nucleotide in DNA and RNA
nitrogenous base
noble gas one of the elements of Group 18 of the periodic table (helium, neon, argon, krypton, xenon, and radon); noble gases are unreactive
noble gas
node in biology, a joint between two adjacent sections in the stem of a plant where buds form and leaves or branches start to grow; usually marked by a knot or swelling
node in physics, a point in a standing wave that maintains zero amplitude
nodule a lump of minerals whose composition differs from the composition of the surrounding sediment or rock; also a lump of minerals that is made of oxides of manganese, iron, copper, or nickel and that is found in scattered groups on the ocean floor
noise a sound that consists of a random mix of frequencies
nomenclature a naming system
nonconformity an unconformity in which younger sedimentary rocks rest on top of older igneous or metamorphic rocks
nondisjunction the failure of homologous chromosomes to separate during meiosis I or the failure of sister chromatids to separate during mitosis or meiosis II
nonelectrolyte a liquid or solid substance or mixture that does not allow an electric current
nonfoliated the metamorphic rock texture in which mineral grains are not arranged in planes or bands
noninfectious disease a disease that cannot spread from one individual to another
noninfectious disease
nonmetal an element that conducts heat and electricity poorly and that does not form positive ions in an electrolytic solution
pollution that comes from many sources rather than from a single specific site; an example is pollution that reaches a body of water from streets and storm sewers
nonpolar compound a compound whose electrons are equally distributed among its atoms
nonpolar compound
nonpolar covalent bond a covalent bond in which the bonding electrons are equally attracted to both bonded atoms
nonpolar covalent bond
a resource that forms at a rate that is much slower than the rate at which the resource is consumed
nonrenewable resource
nonsilicate mineral a mineral that does not contain compounds of silicon and oxygen
nonsilicate mineral
nonvascular plant a plant that belongs to one of the three groups of plants (liverworts, hornworts, and mosses) that lack specialized conducting tissues and true roots, stems, and leaves
nonvascular plant
norepinephrine a chemical that is both a neurotransmitter produced by the sympathetic nerve endings in the autonomic nervous system and a hormone secreted by the adrenal medulla to stimulate the functions of the circulatory and respiratory systems especially (abbreviation, NE)
normal distribution a distribution of numerical data whose graph forms a bell-shaped curve that is symmetrical about the mean
normal distribution
normal fault a fault in which the hanging wall moves down relative to the footwall
normal fault
normal force a force that acts on a surface in a direction perpendicular to the surface
normal force
no-till farming a technique in which little or no plowing occurs before crops are planted; used to prevent soil erosion
no-till farming
notochord the rod-shaped supporting axis found in the dorsal part of the embryos of all chordates, including vertebrates
nova a star that suddenly becomes brighter
nuclear chain reaction a continuous series of nuclear fission reactions
nuclear chain reaction
nuclear energy the energy released by a fission or fusion reaction; the binding energy of the atomic nucleus
nuclear energy
nuclear envelope the double membrane that surrounds the nucleus of a eukaryotic cell
nuclear envelope
nuclear fission the process by which the nucleus of a heavy atom splits into two or more fragments; the process releases neutrons and energy
nuclear fission
nuclear forces the interaction that binds protons and neutrons, protons and protons, and neutrons and neutrons together in a nucleus
nuclear forces
nuclear fusion the process by which nuclei of small atoms combine to form a new, more massive nucleus; the process releases energy
nuclear fusion
nuclear matrix the fibrous skeletal structure found in the nucleus of a eukaryotic cell
nuclear matrix
nuclear pore one of the small holes in the nuclear envelope through which substances pass between the nucleus and the cytoplasm
nuclear pore
nuclear power plant a facility that uses heat from nuclear reactors to produce electrical energy
nuclear power plant
nuclear radiation the particles that are released from the nucleus during radioactive decay, such as neutrons, electrons, and photons
nuclear radiation
nuclear reaction a reaction that affects the nucleus of an atom
nuclear reaction
nuclear reactor a device that uses controlled nuclear reactions to produce energy or nuclides
nuclear reactor
waste that contains radioisotopes
nuclear waste
nucleic acid an organic compound, either RNA or DNA, whose molecules are made up of one or two chains of nucleotides and carry genetic information
nucleic acid
nucleolus the part of the eukaryotic nucleus where ribosomal RNA is synthesized
nucleon a proton or neutron
nucleotide in a nucleic-acid chain, a subunit that consists of a sugar, a phosphate, and a nitrogenous base
nucleus in physical science, an atom's central region, which is made up of protons and neutrons
nucleus in a eukaryotic cell, a membrane-bound organelle that contains the cell’s DNA and that has a role in processes such as growth, metabolism, and reproduction
nuclide an atom that is identified by the number of protons and neutrons in its nucleus
nut a dry fruit that has one seed and a hard shell; cultivated as a food crop
nutrient a substance or compound that provides nourishment (or food) or raw materials needed for life processes
nymph an immature stage of some insects that is similar in function and structure to the adult