Lewis/Life - Glossary

N

nastic movement NAS-tic MOVE-ment Plant growth or movement that is not oriented toward the stimulus. 581

natural selection The differential survival and reproduction of organisms whose genetic traits better adapt them to a particular environment. 11

necrosis neck-RO-sis A form of cell death. 178

negative feedback Turning off of an enzyme's synthesis or activity when the product of the reaction that the enzyme catalyzes accumulates. 122

nematocyst ne-MAT-o-cist Stinging cell of cnidaria. 516

neonatology NE-o-nah-TOL-eh-gee Study of the newborn. 249

nephridia nef-RID-ee-a Networks of tubules in some invertebrates that have an excretory function. 778

nephron NEF-ron A microscopic tubular subunit of a kidney, consisting of a renal tubule and peritubular capillaries. 780

nephron loop NEF-ron LOOP A tubular section of nephron (kidney subunit) that lies between the proximal and distal convoluted tubules, where water is conserved and urine concentrates by a countercurrent exchange system. 783

Neptunism NEP-tune-iz-um The idea that a single great flood organized the features of the earth's surface present today. 376

neritic zone ner-IT-ik ZONE The coastal region of an ocean. 883

nervous tissue A tissue whose cells (neurons and neuroglia) form a communication network. 594

net primary production Chemical energy in plants for growth and reproduction after cellular respiration. 863

neural tube NEUR-el TOOB Embryonic precursor of the central nervous system. 226, 620

neuroglia neur-o-GLEE-a Cells associated with neurons in nervous tissue. 596

neuron NEUR-on A nerve cell, consisting of a cell body, a long "sending" projection called an axon, and numerous "receiving" projections called dendrites. 596

neurosecretory cell NUR-o-SEK-rah-tore-ee SEL Cell in the hypothalamus that functions as a neuron at one end but as an endocrine cell at the other by receiving neural messages and secreting the hormones ADH and oxytocin. 661

neurotransmitter NEUR-o-TRANZ-mit-er A chemical passed from a neuron to receptors on another neuron or on a muscle or gland cell. 597, 616

neurulation NEUR-u-LAY-shun Physical contact between the notochord and nearby ectoderm that triggers formation of the nervous system. 226, 620

neustonic new-STON-ik Algae that live where the water meets the air. 463

neutron NEW-tron A particle in an atom's nucleus that is electrically neutral and has one mass unit. 32

nitrifying bacteria NI-tri-fy-ing bac-TEAR-e-a Bacteria that convert ammonia in dead organisms into nitrites and nitrates, which other organisms can use. 865

nitrogen fixation NI-tro-gen fix-A-shun A microbial process that reduces atmospheric nitrogen gas to ammonia, which other organisms can use. 452

nitrogenous base ni-TRODGE-eh-nus BASE A nitrogen-containing compound that forms part of a nucleotide, giving it individuality. 51

node Area of leaf attachment. 541

node of Ranvier NODE uv RON-vee-ay A short region of exposed axon between Schwann cells on neurons of the vertebrate peripheral nervous system. 614

nondisjunction NON-dis-JUNK-shun Unequal partition of chromosomes into gametes during meiosis. 298

nonpolar covalent bond non-POE-lar co-VAY-lent BOND A covalent bond in which atoms share electrons equally. 38

nonsense mutation NON-sents mu-TAY-shun A point mutation that alters a codon that encodes an amino acid to one that encodes a stop codon. 341

nonshivering thermogenesis non-SHIV-er-ing ther-mo-GEN-i-sis Hormone-directed internal heat. 772

norepinephrine NOR-ep-ee-NEF-rin A hormone produced in the adrenal medulla that raises blood pressure, constricts blood vessels, and slows digestion, in response to a threat. 670

notochord NO-toe-kord A semirigid rod running down the length of an animal's body. 226, 524

nuclear envelope NEW-klee-ar EN-vel-ope A two-layered structure bounding a cell's nucleus. 70

nuclear pore NEW-klee-ar POOR A hole in the nuclear envelope. 70

nucleic acid new-CLAY-ic AS-id A biochemical that encodes an amino acid sequence. 50

nucleoid NEW-klee-oid The part of a prokaryotic cell where the DNA is located. 66

nucleolus new-KLEE-o-lis A structure within the nucleus where RNA nucleotides are stored. 71

nucleosome NEW-klee-o-some DNA wrapped around eight histone proteins as part of chromosome structure. 313

nucleotide NEW-klee-o-tide The building block of a nucleic acid, consisting of a phosphate group, a nitrogenous base, and a five-carbon sugar. 51

nucleus NEW-klee-is The central region of an atom, consisting of protons and neutrons. A membrane-bounded sac in a eukaryotic cell that contains the genetic material. 32, 61

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