Pronunciation Key accessory fruit A fruit, or assemblage of fruits, adaptation Inherited characteristic of an organ- Pronounce in which the ﬂeshy parts are derived largely or ism that enhances its survival and reproduc- a- as in ace entirely from tissues other than the ovary. tion in a speciﬁc environment. – Glossary Ј Ј a/ah ash acclimatization (uh-klı¯ -muh-tı¯-za -shun) adaptive immunity A vertebrate-speciﬁc Physiological adjustment to a change in an defense that is mediated by B lymphocytes ch chose environmental factor. (B cells) and T lymphocytes (T cells). It e¯ meet acetyl CoA Acetyl coenzyme A; the entry com- exhibits speciﬁcity, memory, and self-nonself e/eh bet pound for the citric acid cycle in cellular respi- recognition. Also called acquired immunity. g game ration, formed from a fragment of pyruvate adaptive radiation Period of evolutionary change ı¯ ice attached to a coenzyme. in which groups of organisms form many new i hit acetylcholine (asЈ-uh-til-ko–Ј-le¯n) One of the species whose adaptations allow them to ﬁll dif- ks box most common neurotransmitters; functions by ferent ecological roles in their communities. kw quick binding to receptors and altering the perme- addition rule A rule of probability stating that ng song ability of the postsynaptic membrane to speciﬁc the probability of any one of two or more mu- o- robe ions, either depolarizing or hyperpolarizing the tually exclusive events occurring can be deter- membrane. mined by adding their individual probabilities. o ox acid A substance that increases the hydrogen ion adenosine triphosphate See ATP (adenosine oy boy concentration of a solution. triphosphate). s say acid precipitation Rain, snow, or fog that is adenylyl cyclase (uh-denЈ-uh-lil) An enzyme sh shell more acidic than pH 5.2. that converts ATP to cyclic AMP in response to th thin acoelomate (uh-se¯Ј-lo– -ma–t) A solid-bodied an extracellular signal. u¯ boot animal lacking a cavity between the gut and adhesion The clinging of one substance to u/uh up outer body wall. another, such as water to plant cell walls by – z zoo acrosomal reaction (akЈ-ruh-somЈ-ul) The means of hydrogen bonds. discharge of hydrolytic enzymes from the adipose tissue A connective tissue that insulates Ј ϭ primary accent acrosome, a vesicle in the tip of a sperm, the body and serves as a fuel reserve; contains Јϭsecondary accent when the sperm approaches or contacts an egg. fat-storing cells called adipose cells. acrosome (akЈ-ruh-so–m) A vesicle in the tip of a adrenal gland (uh-dre¯Ј-nul) One of two en- sperm containing hydrolytic enzymes and other docrine glands located adjacent to the kidneys 5Ј cap A modiﬁed form of guanine nucleotide proteins that help the sperm reach the egg. in mammals. Endocrine cells in the outer por- added onto the 5Ј end of a pre-mRNA actin (akЈ-tin) A globular protein that links into tion (cortex) respond to adrenocorticotropic molecule. chains, two of which twist helically about each hormone (ACTH) by secreting steroid hor- A site One of a ribosome’s three binding sites for other, forming microﬁlaments (actin ﬁlaments) mones that help maintain homeostasis during tRNA during translation. The A site holds the in muscle and other kinds of cells. long-term stress. Neurosecretory cells in the tRNA carrying the next amino acid to be added action potential An electrical signal that propa- central portion (medulla) secrete epinephrine to the polypeptide chain. (A stands for gates (travels) along the membrane of a neuron and norepinephrine in response to nerve sig- aminoacyl tRNA.) or other excitable cell as a nongraded (all-or- nals triggered by short-term stress. ABC hypothesis A model of ﬂower formation none) depolarization. adrenocorticotropic hormone (ACTH) A identifying three classes of organ identity action spectrum A graph that proﬁles the rela- tropic hormone that is produced and secreted genes that direct formation of the four types of tive effectiveness of different wavelengths of by the anterior pituitary and that stimulates ﬂoral organs. radiation in driving a particular process. the production and secretion of steroid abiotic (a–Ј-bı¯-otЈ-ik) Nonliving; referring to activation energy The amount of energy that re- hormones by the adrenal cortex. the physical and chemical properties of an actants must absorb before a chemical reaction aerobic respiration A catabolic pathway for
environment. will start; also called free energy of activation. organic molecules, using oxygen (O2) as the abortion The termination of a pregnancy in activator A protein that binds to DNA and ﬁnal electron acceptor in an electron transport progress. stimulates gene transcription. In prokaryotes, chain and ultimately producing ATP. This is abscisic acid (ABA) (ab-sisЈ-ik) A plant hor- activators bind in or near the promoter; in the most efﬁcient catabolic pathway and is mone that slows growth, often antagonizing eukaryotes, activators generally bind to control carried out in most eukaryotic cells and many the actions of growth hormones. Two of its elements in enhancers. prokaryotic organisms. many effects are to promote seed dormancy active immunity Long-lasting immunity con- age structure The relative number of individuals and facilitate drought tolerance. ferred by the action of B cells and T cells and of each age in a population. absorption The third stage of food processing in the resulting B and T memory cells speciﬁc for aggregate fruit A fruit derived from a single animals: the uptake of small nutrient mole- a pathogen. Active immunity can develop as a ﬂower that has more than one carpel. cules by an organism’s body. result of natural infection or immunization. AIDS (acquired immunodeﬁciency absorption spectrum The range of a pigment’s active site The speciﬁc region of an enzyme that syndrome) The symptoms and signs present ability to absorb various wavelengths of light; binds the substrate and that forms the pocket during the late stages of HIV infection, deﬁned also a graph of such a range. in which catalysis occurs. by a speciﬁed reduction in the number of T abyssal zone (uh-bisЈ-ul) The part of the ocean’s active transport The movement of a substance cells and the appearance of characteristic benthic zone between 2,000 and 6,000 m deep. across a cell membrane against its concentra- secondary infections. acanthodian (akЈ-an-tho–Ј-de¯-un) Any of a group tion or electrochemical gradient, mediated by alcohol fermentation Glycolysis followed by of ancient jawed aquatic vertebrates from the speciﬁc transport proteins and requiring an ex- the reduction of pyruvate to ethyl alcohol, re- ϩ Silurian and Devonian periods. penditure of energy. generating NAD and releasing carbon dioxide.
G–1 GLOSSARY Ј – aldosterone (al-dos -tuh-ron) A steroid hormone ammonia A small, toxic molecule (NH3) produced separated and the daughter chromosomes are that acts on tubules of the kidney to regulate by nitrogen ﬁxation or as a metabolic waste moving to the poles of the cell. ϩ the transport of sodium ions (Na ) and product of protein and nucleic acid metabolism. anatomy The structure of an organism. ϩ potassium ions (K ). ammonite A member of a group of shelled anchorage dependence The requirement that algae A diverse grade of photosynthetic protists, cephalopods that were important marine pred- a cell must be attached to a substratum in including unicellular and multicellular forms. ators for hundreds of millions of years until order to initiate cell division. Algal species are included in three of the ﬁve their extinction at the end of the Cretaceous androgen (anЈ-dro– -jen) Any steroid hormone, eukaryote supergroups (Chromalveolata, period (65.5 million years ago). such as testosterone, that stimulates the Rhizaria, and Archaeplastida). amniocentesis (amЈ-ne¯-o– -sen-te¯Ј-sis) A tech- development and maintenance of the male Ј Ј alimentary canal (al -uh-men -tuh-re¯) A com- nique associated with prenatal diagnosis in reproductive system and secondary sex Glossary
plete digestive tract, consisting of a tube which amniotic ﬂuid is obtained by aspiration characteristics. Glossary running between a mouth and an anus. from a needle inserted into the uterus. The aneuploidy (anЈ-yu¯-ployЈ-de¯) A chromosomal allele (uh-le¯Ј-ul) Any of the alternative versions ﬂuid and the fetal cells it contains are analyzed aberration in which one or more chromosomes of a gene that may produce distinguishable to detect certain genetic and congenital defects are present in extra copies or are deﬁcient in phenotypic effects. in the fetus. number. allergen An antigen that triggers an exaggerated amniote (amЈ-ne¯-o–t) Member of a clade of angiosperm (anЈ-je¯-o– -sperm) A ﬂowering plant, immune response. tetrapods named for a key derived character, which forms seeds inside a protective chamber allopatric speciation (alЈ-uh-patЈ-rik) The for- the amniotic egg, which contains specialized called an ovary. mation of new species in populations that are membranes, including the ﬂuid-ﬁlled amnion, angiotensin II A peptide hormone that stimu- geographically isolated from one another. that protect the embryo. Amniotes include lates constriction of precapillary arterioles and allopolyploid (alЈ-o– -polЈ-e¯-ployd) A fertile indi- mammals as well as birds and other reptiles. increases reabsorption of NaCl and water by vidual that has more than two chromosome amniotic egg An egg that contains specialized the proximal tubules of the kidney, increasing sets as a result of two different species inter- membranes that function in protection, nour- blood pressure and volume. breeding and combining their chromosomes. ishment, and gas exchange. The amniotic egg anhydrobiosis (an-hı¯Ј-dro– -bı¯-o–Ј-sis) A dormant allosteric regulation The binding of a regula- was a major evolutionary innovation, allowing state involving loss of almost all body water. tory molecule to a protein at one site that embryos to develop on land in a ﬂuid-ﬁlled animal pole The point at the end of an egg in affects the function of the protein at a differ- sac, thus reducing the dependence of tetrapods the hemisphere where the least yolk is concen- ent site. on water for reproduction. trated; opposite of vegetal pole. alpha (␣) helix (alЈ-fuh he¯Ј-liks) A coiled region amoeba (uh-me¯Ј-buh) A protist grade character- anion (anЈ-ı¯-on) A negatively charged ion. constituting one form of the secondary struc- ized by the presence of pseudopodia. anterior Pertaining to the front, or head, of a ture of proteins, arising from a speciﬁc pattern amoebocyte (uh-me¯Ј-buh-sı¯tЈ) An amoeba-like bilaterally symmetrical animal. of hydrogen bonding between atoms of the cell that moves by pseudopodia and is found anterior pituitary A portion of the pituitary polypeptide backbone (not the side chains). in most animals. Depending on the species, it that develops from nonneural tissue; consists alternation of generations A life cycle in may digest and distribute food, dispose of of endocrine cells that synthesize and secrete which there is both a multicellular diploid wastes, form skeletal ﬁbers, ﬁght infections, or several tropic and nontropic hormones. form, the sporophyte, and a multicellular change into other cell types. anther In an angiosperm, the terminal pollen sac haploid form, the gametophyte; characteristic amoebozoan (uh-me¯Ј-buh-zo–Ј-an) A protist in a of a stamen, where pollen grains containing of plants and some algae. clade that includes many species with lobe- or sperm-producing male gametophytes form. alternative RNA splicing A type of eukaryotic tube-shaped pseudopodia. antheridium (an-thuh-ridЈ-e¯-um) (plural, gene regulation at the RNA-processing level in amphibian Member of the tetrapod class antheridia) In plants, the male gametangium, which different mRNA molecules are produced Amphibia, including salamanders, frogs, and a moist chamber in which gametes develop. from the same primary transcript, depending caecilians. anthropoid (anЈ-thruh-poyd) Member of a on which RNA segments are treated as exons amphipathic (amЈ-fe¯-pathЈ-ik) Having both a primate group made up of the monkeys and and which as introns. hydrophilic region and a hydrophobic region. the apes (gibbons, orangutans, gorillas, chim- altruism (alЈ-tru¯-iz-um) Selﬂessness; behavior ampliﬁcation The strengthening of stimulus panzees, bonobos, and humans). that reduces an individual’s ﬁtness while energy during transduction. antibody A protein secreted by plasma cells (dif- increasing the ﬁtness of another individual. amygdala (uh-migЈ-duh-luh) A structure in the ferentiated B cells) that binds to a particular alveolate (al-ve¯Ј-uh-let) A protist with membrane- temporal lobe of the vertebrate brain that has antigen; also called immunoglobulin. All anti- bounded sacs (alveoli) located just under the a major role in the processing of emotions. bodies have the same Y-shaped structure and plasma membrane. amylase (amЈ-uh-la–sЈ) An enzyme that hydro- in their monomer form consist of two identical alveolus (al-ve¯Ј-uh-lus) (plural, alveoli) One of lyzes starch (a glucose polymer from plants) and heavy chains and two identical light chains. the dead-end air sacs where gas exchange glycogen (a glucose polymer from animals) anticodon (anЈ-tı¯-ko–Ј-don) A nucleotide triplet at occurs in a mammalian lung. into smaller polysaccharides and the disaccha- one end of a tRNA molecule that base-pairs Alzheimer’s disease (altsЈ-hı¯-merz) An age- ride maltose. with a particular complementary codon on an related dementia (mental deterioration) char- anabolic pathway (anЈ-uh-bolЈ-ik) A metabolic mRNA molecule. acterized by confusion and memory loss. pathway that consumes energy to synthesize a antidiuretic hormone (ADH) (anЈ-tı¯-dı¯-yu¯- amacrine cell (amЈ-uh-krin) A neuron of the complex molecule from simpler molecules. retЈ-ik) A peptide hormone, also known as va- retina that helps integrate information before anaerobic respiration (an-er-o–Ј-bik) A catabolic sopressin, that promotes water retention by it is sent to the brain. pathway in which inorganic molecules other the kidneys. Produced in the hypothalamus amino acid (uh-me¯nЈ-o–) An organic molecule than oxygen accept electrons at the “down- and released from the posterior pituitary, ADH possessing both a carboxyl and an amino hill” end of electron transport chains. also functions in the brain. group. Amino acids serve as the monomers of analogous Having characteristics that are similar antigen (anЈ-ti-jen) A substance that elicits an polypeptides. because of convergent evolution, not homology. immune response by binding to receptors of B amino group A chemical group consisting of a analogy (an-alЈ-uh-je¯) Similarity between two cells, antibodies, or of T cells. nitrogen atom bonded to two hydrogen atoms; species that is due to convergent evolution antigen presentation The process by which an can act as a base in solution, accepting a rather than to descent from a common ances- MHC molecule binds to a fragment of an intra- hydrogen ion and acquiring a charge of 1ϩ. tor with the same trait. cellular protein antigen and carries it to the aminoacyl-tRNA synthetase An enzyme that anaphase The fourth stage of mitosis, in which cell surface, where it is displayed and can be joins each amino acid to the appropriate tRNA. the chromatids of each chromosome have recognized by a T cell.
GLOSSARY G–2 antigen receptor The general term for a surface invagination of the host (plant) cells’ plasma plasma membrane in an animal cell undergo- protein, located on B cells and T cells, that membranes. ing mitosis. binds to antigens, initiating adaptive immune arbuscular mycorrhizal fungus A symbiotic astrocyte A glial cell with diverse functions, in- responses. The antigen receptors on B cells are fungus whose hyphae grow through the cell cluding providing structural support for neu- called B cell receptors, and the antigen recep- wall of plant roots and extend into the root rons, regulating the interstitial environment, tors on T cells are called T cell receptors. cell (enclosed in tubes formed by invagination facilitating synaptic transmission, and assisting antigen-presenting cell A cell that upon in- of the root cell plasma membrane). in regulating the blood supply to the brain. gesting pathogens or internalizing pathogen Archaea (arЈ-ke¯Ј-uh) One of two prokaryotic atherosclerosis A cardiovascular disease in proteins generates peptide fragments that are domains, the other being Bacteria. which fatty deposits called plaques develop in bound by class II MHC molecules and subse- Archaeplastida (arЈ-ke¯-plasЈ-tid-uh) One of ﬁve the inner walls of the arteries, obstructing the
Glossary quently displayed on the cell surface to T cells. supergroups of eukaryotes proposed in a current arteries and causing them to harden. Macrophages, dendritic cells, and B cells are hypothesis of the evolutionary history of atom The smallest unit of matter that retains the the primary antigen-presenting cells. eukaryotes. This monophyletic group, which properties of an element. antiparallel Referring to the arrangement of the includes red algae, green algae, and land plants, atomic mass The total mass of an atom, which sugar-phosphate backbones in a DNA double descended from an ancient protist ancestor that is the mass in grams of 1 mole of the atom. helix (they run in opposite 5Ј S 3Ј directions). engulfed a cyanobacterium. See also Excavata, atomic nucleus An atom’s dense central core, aphotic zone (a–Ј-fo–Ј-tik) The part of an ocean or Chromalveolata, Rhizaria, and Unikonta. containing protons and neutrons. lake beneath the photic zone, where light does archegonium (ar-ki-go–Ј-ne¯-um) (plural, atomic number The number of protons in the not penetrate sufﬁciently for photosynthesis archegonia) In plants, the female nucleus of an atom, unique for each element to occur. gametangium, a moist chamber in which and designated by a subscript to the left of the apical bud (a–Ј-pik-ul) A bud at the tip of a plant gametes develop. elemental symbol. stem; also called a terminal bud. archenteron (ar-kenЈ-tuh-ron) The endoderm- ATP (adenosine triphosphate) (a-denЈ-o– -se¯n apical dominance (a–Ј-pik-ul) Tendency for lined cavity, formed during gastrulation, that trı¯-fosЈ-fa–t) An adenine-containing nucleoside growth to be concentrated at the tip of a plant develops into the digestive tract of an animal. triphosphate that releases free energy when its shoot, because the apical bud partially inhibits archosaur (arЈ-ko– -so–r) Member of the reptilian phosphate bonds are hydrolyzed. This energy axillary bud growth. group that includes crocodiles, alligators and is used to drive endergonic reactions in cells. apical ectodermal ridge (AER) A thickened dinosaurs, including birds. ATP synthase A complex of several membrane area of ectoderm at the tip of a limb bud that arteriole (ar-terЈ-e¯-o–l) A vessel that conveys proteins that functions in chemiosmosis with promotes outgrowth of the limb bud. blood between an artery and a capillary bed. adjacent electron transport chains, using the apical meristem (a–Ј-pik-ul ma–rЈ-uh-stem) artery A vessel that carries blood away from the energy of a hydrogen ion (proton) concentra- Embryonic plant tissue in the tips of roots and heart to organs throughout the body. tion gradient to make ATP. ATP synthases are buds of shoots. The dividing cells of an apical arthropod A segmented ecdysozoan with a hard found in the inner mitochondrial membranes meristem enable the plant to grow in length. exoskeleton and jointed appendages. Familiar of eukaryotic cells and in the plasma mem- apicomplexan (apЈ-e¯-kom-pleksЈ-un) A protist examples include insects, spiders, millipedes, branes of prokaryotes. in a clade that includes many species that par- and crabs. atrial natriuretic peptide (ANP) (a–Ј-tre¯-ul asitize animals. Some apicomplexans cause artiﬁcial selection The selective breeding of naЈ-tre¯-yu¯-retЈ-ik) A peptide hormone secreted human disease. domesticated plants and animals to encourage by cells of the atria of the heart in response to apomixis (apЈ-uh-mikЈ-sis) The ability of some the occurrence of desirable traits. high blood pressure. ANP’s effects on the kid- plant species to reproduce asexually through ascocarp The fruiting body of a sac fungus ney alter ion and water movement and reduce seeds without fertilization by a male gamete. (ascomycete). blood pressure. apoplast (apЈ-o– -plast) Everything external to the ascomycete (asЈ-kuh-mı¯Ј-se¯t) Member of the atrioventricular (AV) node A region of special- plasma membrane of a plant cell, including fungal phylum Ascomycota, commonly called ized heart muscle tissue between the left and cell walls, intercellular spaces, and the space sac fungus. The name comes from the saclike right atria where electrical impulses are de- within dead structures such as xylem vessels structure in which the spores develop. layed for about 0.1 second before spreading to and tracheids. ascus (plural, asci) A saclike spore capsule both ventricles and causing them to contract. apoptosis (a–-puh-to–Ј-sus) A type of programmed located at the tip of a dikaryotic hypha of a atrioventricular (AV) valve A heart valve cell death, which is brought about by activa- sac fungus. located between each atrium and ventricle tion of enzymes that break down many chemi- asexual reproduction The generation of off- that prevents a backﬂow of blood when the cal components in the cell. spring from a single parent that occurs without ventricle contracts. aposematic coloration (apЈ-o– -si-matЈ-ik) The the fusion of gametes (by budding, division of atrium (a–Ј-tre¯-um) (plural, atria) A chamber of bright warning coloration of many animals a single cell, or division of the entire organism the vertebrate heart that receives blood from with effective physical or chemical defenses. into two or more parts). In most cases, the off- the veins and transfers blood to a ventricle. appendix A small, ﬁnger-like extension of the spring are genetically identical to the parent. autocrine Referring to a secreted molecule that vertebrate cecum; contains a mass of white assisted migration The translocation of a acts on the cell that secreted it. blood cells that contribute to immunity. species to a favorable habitat beyond its native autoimmune disease An immunological aquaporin A channel protein in the plasma range for the purpose of protecting the species disorder in which the immune system turns membrane of a plant, animal, or microorgan- from human-caused threats. against self. ism cell that speciﬁcally facilitates osmosis, assisted reproductive technology A fertiliza- autonomic nervous system (otЈ-o– -nomЈ-ik) An the diffusion of free water across the tion procedure that generally involves surgi- efferent branch of the vertebrate peripheral membrane. cally removing eggs (secondary oocytes) from a nervous system that regulates the internal en- aqueous solution (a–Ј-kwe¯-us) A solution in woman’s ovaries after hormonal stimulation, vironment; consists of the sympathetic, which water is the solvent. fertilizing the eggs, and returning them to the parasympathetic, and enteric divisions. arachnid A member of a major arthropod group, woman’s body. autopolyploid (otЈ-o– -polЈ-e¯-ployd) An individ- the chelicerates. Arachnids include spiders, associative learning The acquired ability to as- ual that has more than two chromosome sets scorpions, ticks, and mites. sociate one environmental feature (such as a that are all derived from a single species. arbuscular mycorrhiza (ar-busЈ-kyu¯-lur mı¯Ј-ko– - color) with another (such as danger). autosome (otЈ-o– -so–m) A chromosome that is not rı¯Ј-zuh) Association of a fungus with a plant aster A radial array of short microtubules that directly involved in determining sex; not a sex root system in which the fungus causes the extends from each centrosome toward the chromosome.
G–3 GLOSSARY autotroph (otЈ-o–-tro–f) An organism that obtains basidiomycete (buh-sidЈ-e¯-o– -mı¯Ј-se¯t) Member of bioﬁlm A surface-coating colony of one or more organic food molecules without eating other the fungal phylum Basidiomycota, commonly species of prokaryotes that engage in metabolic organisms or substances derived from other called club fungus. The name comes from the cooperation. organisms. Autotrophs use energy from the sun club-like shape of the basidium. biofuel A fuel produced from dry organic matter or from oxidation of inorganic substances to basidium (plural, basidia) (buh-sidЈ-e¯-um, buh- or combustible oils produced by plants. make organic molecules from inorganic ones. sidЈ-e¯-ah) A reproductive appendage that pro- biogenic amine A neurotransmitter derived auxin (ôkЈ-sin) A term that primarily refers to duces sexual spores on the gills of mushrooms from an amino acid. indoleacetic acid (IAA), a natural plant (club fungi). biogeochemical cycle Any of the various hormone that has a variety of effects, including Batesian mimicry (ba–tЈ-ze¯-un mimЈ-uh-kre¯) A chemical cycles, which involve both biotic and cell elongation, root formation, secondary type of mimicry in which a harmless species abiotic components of ecosystems.
growth, and fruit growth. looks like a species that is poisonous or other- biogeography The study of the past and present Glossary average heterozygosity (hetЈ-er-o– -zı¯-go–Ј-si-te¯) wise harmful to predators. geographic distribution of species. The percentage, on average, of a population’s behavior Individually, an action carried out by bioinformatics The use of computers, software, loci that are heterozygous in members of the muscles or glands under control of the nervous and mathematical models to process and inte- population. system in response to a stimulus; collectively, grate biological information from large data sets. avirulent Describing a pathogen that can mildly the sum of an animal’s responses to external biological augmentation An approach to harm, but not kill, the host. and internal stimuli. restoration ecology that uses organisms to add axillary bud (akЈ-sil-a–r-e¯) A structure that has behavioral ecology The study of the evolution essential materials to a degraded ecosystem. the potential to form a lateral shoot, or of and ecological basis for animal behavior. biological clock An internal timekeeper that branch. The bud appears in the angle formed benign tumor A mass of abnormal cells with controls an organism’s biological rhythms. The between a leaf and a stem. speciﬁc genetic and cellular changes such that biological clock marks time with or without axon (akЈ-son) A typically long extension, or the cells are not capable of surviving at a new environmental cues but often requires signals process, of a neuron that carries nerve impulses site and generally remain at the site of the from the environment to remain tuned to an away from the cell body toward target cells. tumor’s origin. appropriate period. See also circadian rhythm. B cells The lymphocytes that complete their de- benthic zone The bottom surface of an aquatic biological magniﬁcation A process in which velopment in the bone marrow and become ef- environment. retained substances become more concentrated fector cells for the humoral immune response. benthos (benЈ-tho–z) The communities of organ- at each higher trophic level in a food chain. Bacteria One of two prokaryotic domains, the isms living in the benthic zone of an aquatic biological species concept Deﬁnition of a other being Archaea. biome. species as a group of populations whose mem- bacterial artiﬁcial chromosome (BAC) A beta (␤) pleated sheet One form of the second- bers have the potential to interbreed in nature large plasmid that acts as a bacterial chromo- ary structure of proteins in which the polypep- and produce viable, fertile offspring, but do some and can carry inserts of 100,000 to tide chain folds back and forth. Two regions of not produce viable, fertile offspring with mem- 300,000 base pairs (100–300 kb). the chain lie parallel to each other and are bers of other such groups. bacteriophage (bak-te¯rЈ-e¯-o– -fa–j) A virus that held together by hydrogen bonds between biology The scientiﬁc study of life. infects bacteria; also called a phage. atoms of the polypeptide backbone (not the biomanipulation An approach that applies the bacteroid A form of the bacterium Rhizobium side chains). top-down model of community organization contained within the vesicles formed by the beta oxidation A metabolic sequence that to alter ecosystem characteristics. For example, root cells of a root nodule. breaks fatty acids down to two-carbon ecologists can prevent algal blooms and balancing selection Natural selection that fragments that enter the citric acid cycle as eutrophication by altering the density of maintains two or more phenotypic forms in acetyl CoA. higher-level consumers in lakes instead of by a population. bicoid A maternal effect gene that codes for a using chemical treatments. bark All tissues external to the vascular cam- protein responsible for specifying the anterior biomass The total mass of organic matter com- bium, consisting mainly of the secondary end in Drosophila melanogaster. prising a group of organisms in a particular phloem and layers of periderm. bilateral symmetry Body symmetry in which a habitat. Barr body A dense object lying along the inside central longitudinal plane divides the body biome (bı¯Ј-o–m) Any of the world’s major ecosys- of the nuclear envelope in cells of female into two equal but opposite halves. tem types, often classiﬁed according to the pre- mammals, representing a highly condensed, bilaterian (bı¯Ј-luh-terЈ-e¯-uhn) Member of a clade dominant vegetation for terrestrial biomes and inactivated X chromosome. of animals with bilateral symmetry and three the physical environment for aquatic biomes basal angiosperm A member of one of three germ layers. and characterized by adaptations of organisms clades of early-diverging lineages of ﬂowering bile A mixture of substances that is produced in to that particular environment. plants. Examples are Amborella, water lilies, the liver and stored in the gallbladder; enables bioremediation The use of organisms to detoxify and star anise and its relatives. formation of fat droplets in water as an aid in and restore polluted and degraded ecosystems. basal body (ba–Ј-sul) A eukaryotic cell structure the digestion and absorption of fats. biosphere The entire portion of Earth inhabited consisting of a “9 ϩ 0” arrangement of micro- binary ﬁssion A method of asexual reproduc- by life; the sum of all the planet’s ecosystems. tubule triplets. The basal body may organize tion by “division in half.” In prokaryotes, bi- biotechnology The manipulation of organisms or the microtubule assembly of a cilium or nary ﬁssion does not involve mitosis, but in their components to produce useful products. ﬂagellum and is structurally very similar to single-celled eukaryotes that undergo binary biotic (bı¯-otЈ-ik) Pertaining to the living factors— a centriole. ﬁssion, mitosis is part of the process. the organisms—in an environment. basal metabolic rate (BMR) The metabolic binomial The two-part, latinized format for bipolar cell A neuron that relays information rate of a resting, fasting, and nonstressed naming a species, consisting of the genus and between photoreceptors and ganglion cells in endotherm at a comfortable temperature. speciﬁc epithet; a binomen. the retina. basal taxon In a speciﬁed group of organisms, a biodiversity hot spot A relatively small area bipolar disorder A depressive mental illness taxon whose evolutionary lineage diverged with numerous endemic species and a large characterized by swings of mood from high to early in the history of the group. number of endangered and threatened low; also called manic-depressive disorder. base A substance that reduces the hydrogen ion species. birth control pill A chemical contraceptive that concentration of a solution. bioenergetics (1) The overall ﬂow and transfor- inhibits ovulation, retards follicular develop- basidiocarp Elaborate fruiting body of a mation of energy in an organism. (2) The ment, or alters a woman’s cervical mucus to dikaryotic mycelium of a club fungus. study of how energy ﬂows through organisms. prevent sperm from entering the uterus.
GLOSSARY G–4 blade (1) A leaﬂike structure of a seaweed that pro- conduction of information to higher brain involving ﬁxation of atmospheric CO2 and re- vides most of the surface area for photosynthe- centers. duction of the ﬁxed carbon into carbohydrate. sis. (2) The ﬂattened portion of a typical leaf. branch point The representation on a phylo- CAM plant A plant that uses crassulacean acid blastocoel (blasЈ-tuh-se¯l) The ﬂuid-ﬁlled cavity genetic tree of the divergence of two or more metabolism, an adaptation for photosynthesis that forms in the center of a blastula. taxa from a common ancestor. A branch in arid conditions. In this process, carbon blastocyst (blasЈ-tuh-sist) The blastula stage of point is usually shown as a dichotomy in dioxide entering open stomata during the mammalian embryonic development, consist- which a branch representing the ancestral night is converted to organic acids, which re-
ing of an inner cell mass, a cavity, and an outer lineage splits (at the branch point) into two lease CO2 for the Calvin cycle during the day, layer, the trophoblast. In humans, the blasto- branches, one for each of the two descendant when stomata are closed. cyst forms 1 week after fertilization. lineages. Cambrian explosion A relatively brief time in
Glossary blastomere An early embryonic cell arising brassinosteroid A steroid hormone in plants geologic history when many present-day during the cleavage stage of an early embryo. that has a variety of effects, including inducing phyla of animals ﬁrst appeared in the fossil blastopore (blasЈ-to– -po–r) In a gastrula, the open- cell elongation, retarding leaf abscission, and record. This burst of evolutionary change ing of the archenteron that typically develops promoting xylem differentiation. occurred about 535–525 million years ago into the anus in deuterostomes and the mouth breathing Ventilation of the lungs through alter- and saw the emergence of the ﬁrst large, in protostomes. nating inhalation and exhalation. hard-bodied animals. blastula (blasЈ-tyu¯-luh) A hollow ball of cells that bronchiole (brongЈ-ke¯-o–lЈ) A ﬁne branch of the cAMP See cyclic AMP (cAMP). marks the end of the cleavage stage during bronchi that transports air to alveoli. canopy The uppermost layer of vegetation in a early embryonic development in animals. bronchus (brongЈ-kus) (plural, bronchi) One of terrestrial biome. blood A connective tissue with a ﬂuid matrix a pair of breathing tubes that branch from the capillary (kapЈ-il-a–rЈ-e¯) A microscopic blood ves- called plasma in which red blood cells, white trachea into the lungs. sel that penetrates the tissues and consists of a blood cells, and cell fragments called platelets brown alga A multicellular, photosynthetic pro- single layer of endothelial cells that allows are suspended. tist with a characteristic brown or olive color exchange between the blood and interstitial blue-light photoreceptor A type of light that results from carotenoids in its plastids. ﬂuid. receptor in plants that initiates a variety of Most brown algae are marine, and some have a capillary bed A network of capillaries in a tissue responses, such as phototropism and slowing plantlike body (thallus). or organ. of hypocotyl elongation. bryophyte (brı¯Ј-uh-fı¯t) An informal name for a capsid The protein shell that encloses a viral body cavity A ﬂuid- or air-ﬁlled space between moss, liverwort, or hornwort; a nonvascular genome. It may be rod-shaped, polyhedral, or the digestive tract and the body wall. plant that lives on land but lacks some of the more complex in shape. body plan In multicellular eukaryotes, a set of terrestrial adaptations of vascular plants. capsule (1) In many prokaryotes, a dense and morphological and developmental traits that budding Asexual reproduction in which out- well-deﬁned layer of polysaccharide or protein are integrated into a functional whole—the liv- growths from the parent form and pinch off to that surrounds the cell wall and is sticky, pro- ing organism. live independently or else remain attached to tecting the cell and enabling it to adhere to Bohr shift A lowering of the afﬁnity of hemoglo- eventually form extensive colonies. substrates or other cells. (2) The sporangium of bin for oxygen, caused by a drop in pH. It facil- buffer A solution that contains a weak acid and a bryophyte (moss, liverwort, or hornwort). itates the release of oxygen from hemoglobin its corresponding base. A buffer minimizes carbohydrate (karЈ-bo– -hı¯Ј-dra–t) A sugar (mono- in the vicinity of active tissues. changes in pH when acids or bases are added saccharide) or one of its dimers (disaccharides) bolus A lubricated ball of chewed food. to the solution. or polymers (polysaccharides). bone A connective tissue consisting of living cells bulk feeder An animal that eats relatively large carbon ﬁxation The initial incorporation of
held in a rigid matrix of collagen ﬁbers embed- pieces of food. carbon from CO2 into an organic compound ded in calcium salts. bulk ﬂow The movement of a ﬂuid due to a by an autotrophic organism (a plant, another book lung An organ of gas exchange in spiders, difference in pressure between two locations. photosynthetic organism, or a chemoau-
consisting of stacked plates contained in an bundle-sheath cell In C4 plants, a type of totrophic prokaryote). internal chamber. photosynthetic cell arranged into tightly carbonyl group (kar-buh-ne¯lЈ) A chemical bottleneck effect Genetic drift that occurs packed sheaths around the veins of a leaf. group present in aldehydes and ketones and
when the size of a population is reduced, as by C3 plant A plant that uses the Calvin cycle for consisting of a carbon atom double-bonded to
a natural disaster or human actions. Typically, the initial steps that incorporate CO2 into an oxygen atom. the surviving population is no longer geneti- organic material, forming a three-carbon carboxyl group (kar-bokЈ-sil) A chemical group cally representative of the original population. compound as the ﬁrst stable intermediate. present in organic acids and consisting of a
bottom-up model A model of community or- C4 plant A plant in which the Calvin cycle is single carbon atom double-bonded to an
ganization in which mineral nutrients inﬂu- preceded by reactions that incorporate CO2 oxygen atom and also bonded to a hydroxyl ence community organization by controlling into a four-carbon compound, the end product group. Ј plant or phytoplankton numbers, which in of which supplies CO2 for the Calvin cycle. cardiac cycle (kar -de¯-ak) The alternating turn control herbivore numbers, which in turn calcitonin (kalЈ-si-to–Ј-nin) A hormone secreted contractions and relaxations of the heart. control predator numbers. by the thyroid gland that lowers blood calcium cardiac muscle A type of striated muscle that Bowman’s capsule (bo–Ј-munz) A cup-shaped levels by promoting calcium deposition in forms the contractile wall of the heart. Its cells receptacle in the vertebrate kidney that is the bone and calcium excretion from the kidneys; are joined by intercalated disks that relay the initial, expanded segment of the nephron nonessential in adult humans. electrical signals underlying each heartbeat. where ﬁltrate enters from the blood. callus A mass of dividing, undifferentiated cells cardiac output The volume of blood pumped brachiopod (braЈ-ke¯- uh-podЈ) A marine growing in culture. per minute by each ventricle of the heart. lophophorate with a shell divided into dorsal calorie (cal) The amount of heat energy required cardiovascular system A closed circulatory and ventral halves; also called a lamp shell. to raise the temperature of 1 g of water by 1°C; system with a heart and branching network of brain Organ of the central nervous system where also the amount of heat energy that 1 g of wa- arteries, capillaries, and veins. The system is information is processed and integrated. ter releases when it cools by 1°C. The Calorie characteristic of vertebrates. brainstem A collection of structures in the verte- (with a capital C), usually used to indicate the carnivore An animal that mainly eats other brate brain, including the midbrain, the pons, energy content of food, is a kilocalorie. animals. and the medulla oblongata; functions in Calvin cycle The second of two major stages in carotenoid (kuh-rotЈ-uh-noydЈ An accessory homeostasis, coordination of movement, and photosynthesis (following the light reactions), pigment, either yellow or orange, in the
G–5 GLOSSARY chloroplasts of plants and in some prokaryotes. inside which the new cell wall forms during bodies of the cerebrum; the part of the verte- By absorbing wavelengths of light that chloro- cytokinesis. brate brain most changed through evolution. phyll cannot, carotenoids broaden the spectrum cell wall A protective layer external to the cerebral hemisphere The right or left side of of colors that can drive photosynthesis. plasma membrane in the cells of plants, the cerebrum. carpel (karЈ-pul) The ovule-producing reproduc- prokaryotes, fungi, and some protists. cerebrospinal ﬂuid (suh-re¯Ј-bro– -spı¯Ј-nul) tive organ of a ﬂower, consisting of the stigma, Polysaccharides such as cellulose (in plants Blood-derived ﬂuid that surrounds, protects style, and ovary. and some protists), chitin (in fungi), and against infection, nourishes, and cushions the carrier In genetics, an individual who is het- peptidoglycan (in bacteria) are important brain and spinal cord. erozygous at a given genetic locus for a reces- structural components of cell walls. cerebrum (suh-re¯Ј-brum) The dorsal portion of sively inherited disorder. The heterozygote cell-mediated immune response The branch the vertebrate forebrain, composed of right
is generally phenotypically normal for the of adaptive immunity that involves the activa- and left hemispheres; the integrating center for Glossary disorder but can pass on the recessive allele tion of cytotoxic T cells, which defend against memory, learning, emotions, and other highly to offspring. infected cells. complex functions of the central nervous carrying capacity The maximum population cellular respiration The catabolic pathways of system. size that can be supported by the available aerobic and anaerobic respiration, which break cervix (serЈ-viks) The neck of the uterus, which resources, symbolized as K. down organic molecules and use an electron opens into the vagina. cartilage (karЈ-til-ij) A ﬂexible connective tissue transport chain for the production of ATP. chaparral A scrubland biome of dense, spiny with an abundance of collagenous ﬁbers cellular slime mold A type of protist character- evergreen shrubs found at midlatitudes along embedded in chondroitin sulfate. ized by unicellular amoeboid cells and aggre- coasts where cold ocean currents circulate Casparian strip (ka-spa–rЈ-e¯-un) A water-imper- gated reproductive bodies in its life cycle. offshore; characterized by mild, rainy winters meable ring of wax in the endodermal cells of cellulose (selЈ-yu¯-lo–s) A structural polysaccharide and long, hot, dry summers. plants that blocks the passive ﬂow of water of plant cell walls, consisting of glucose chaperonin (shapЈ-er-o–Ј-nin) A protein complex and solutes into the stele by way of cell walls. monomers joined by β glycosidic linkages. that assists in the proper folding of other catabolic pathway (katЈ-uh-bolЈ-ik) A metabolic Celsius scale (selЈ-se¯-us) A temperature scale (°C) proteins. 5 pathway that releases energy by breaking down equal to /9(°F – 32) that measures the freezing character An observable heritable feature that complex molecules to simpler molecules. point of water at 0°C and the boiling point of may vary among individuals. catalyst (katЈ-uh-list) A chemical agent that water at 100°C. character displacement The tendency for selectively increases the rate of a reaction central canal The narrow cavity in the center of characteristics to be more divergent in sym- without being consumed by the reaction. the spinal cord that is continuous with the patric populations of two species than in al- catastrophism (kuh-tasЈ-truh-ﬁzЈ-um) The prin- ﬂuid-ﬁlled ventricles of the brain. lopatric populations of the same two species. ciple that events in the past occurred suddenly central nervous system (CNS) The portion of checkpoint A control point in the cell cycle and were caused by different mechanisms than the nervous system where signal integration where stop and go-ahead signals can regulate those operating today. See uniformitarianism. occurs; in vertebrate animals, the brain and the cycle. catecholamine (katЈ-uh-ko–lЈ-uh-me¯n) Any of a spinal cord. chelicera (ke¯-lihЈ-suh-ruh) (plural, chelicerae) class of neurotransmitters and hormones, central vacuole In a mature plant cell, a large One of a pair of clawlike feeding appendages including the hormones epinephrine and membranous sac with diverse roles in growth, characteristic of chelicerates. norepinephrine, that are synthesized from the storage, and sequestration of toxic substances. chelicerate (ke¯-lih-suhЈ-ra– te) An arthropod that amino acid tyrosine. centriole (senЈ-tre¯-o–l) A structure in the centro- has chelicerae and a body divided into a cation (catЈ-ı¯-on) A positively charged ion. some of an animal cell composed of a cylinder cephalothorax and an abdomen. Living cation exchange A process in which positively of microtubule triplets arranged in a 9 ϩ 0 chelicerates include sea spiders, horseshoe charged minerals are made available to a plant pattern. A centrosome has a pair of centrioles. crabs, scorpions, ticks, and spiders. when hydrogen ions in the soil displace centromere (senЈ-tro– -me¯r) In a duplicated chro- chemical bond An attraction between two mineral ions from the clay particles. mosome, the region on each sister chromatid atoms, resulting from a sharing of outer-shell cDNA library A gene library containing clones where they are most closely attached to each electrons or the presence of opposite charges that carry complementary DNA (cDNA) other by proteins that bind to speciﬁc DNA on the atoms. The bonded atoms gain inserts. The library includes only the genes sequences; this close attachment causes a complete outer electron shells. that were transcribed in the cells whose mRNA constriction in the condensed chromosome. chemical energy Energy available in molecules was isolated to make the cDNA. (An uncondensed, unduplicated chromosome for release in a chemical reaction; a form of cecum (se¯Ј-kum) (plural, ceca) The blind pouch has a single centromere, identiﬁed by its potential energy. forming one branch of the large intestine. DNA sequence.) chemical equilibrium In a chemical reaction, cell body The part of a neuron that houses the centrosome (senЈ-tro– -so–m) A structure present in the state in which the rate of the forward reac- nucleus and most other organelles. the cytoplasm of animal cells that functions as tion equals the rate of the reverse reaction, so cell cycle An ordered sequence of events in the a microtubule-organizing center and is impor- that the relative concentrations of the reac- life of a cell, from its origin in the division of a tant during cell division. A centrosome has tants and products do not change with time. parent cell until its own division into two. The two centrioles. chemical reaction The making and breaking of eukaryotic cell cycle is composed of interphase cephalization (sefЈ-uh-luh-za–Ј-shun) An evolu- chemical bonds, leading to changes in the
(including G1, S, and G2 subphases) and M tionary trend toward the concentration of composition of matter. phase (including mitosis and cytokinesis). sensory equipment at the anterior end of chemiosmosis (kemЈ-e¯-oz-mo–Ј-sis) An energy- cell cycle control system A cyclically operat- the body. coupling mechanism that uses energy stored ing set of molecules in the eukaryotic cell that cercozoan An amoeboid or ﬂagellated protist in the form of a hydrogen ion gradient across both triggers and coordinates key events in the that feeds with threadlike pseudopodia. a membrane to drive cellular work, such as cell cycle. cerebellum (sa–rЈ-ruh-belЈ-um) Part of the verte- the synthesis of ATP. Under aerobic condi- cell division The reproduction of cells. brate hindbrain located dorsally; functions in tions, most ATP synthesis in cells occurs by cell fractionation The disruption of a cell and unconscious coordination of movement and chemiosmosis. separation of its parts by centrifugation at balance. chemoautotroph (ke¯Ј-mo– -otЈ-o– -tro–f) An organ- successively higher speeds. cerebral cortex (suh-re¯Ј-brul) The surface of the ism that obtains energy by oxidizing inorganic cell plate A membrane-bounded, ﬂattened sac cerebrum; the largest and most complex part substances and needs only carbon dioxide as a located at the midline of a dividing plant cell, of the mammalian brain, containing nerve cell carbon source.
GLOSSARY G–6 chemoheterotroph (ke¯Ј-mo– -hetЈ-er-o– -tro–f) An chromosomes. When the cell is not dividing, cleavage (1) The process of cytokinesis in animal organism that requires organic molecules for chromatin exists in its dispersed form, as a cells, characterized by pinching of the plasma both energy and carbon. mass of very long, thin ﬁbers that are not membrane. (2) The succession of rapid cell chemoreceptor A sensory receptor that re- visible with a light microscope. divisions without signiﬁcant growth during sponds to a chemical stimulus, such as a solute chromosome (kro–Ј-muh-so–m) A cellular struc- early embryonic development that converts or an odorant. ture carrying genetic material, found in the the zygote to a ball of cells. chiasma (plural, chiasmata) (kı¯-azЈ-muh, kı¯- nucleus of eukaryotic cells. Each chromosome cleavage furrow The ﬁrst sign of cleavage in an azЈ-muh-tuh) The X-shaped, microscopically consists of one very long DNA molecule and animal cell; a shallow groove around the cell in visible region where crossing over has occurred associated proteins. (A bacterial chromosome the cell surface near the old metaphase plate. earlier in prophase I between homologous usually consists of a single circular DNA mole- climate The long-term prevailing weather condi-
Glossary nonsister chromatids. Chiasmata become cule and associated proteins. It is found in the tions at a given place. visible after synapsis ends, with the two nucleoid region, which is not membrane climograph A plot of the temperature and pre- homologs remaining associated due to sister bounded.) See also chromatin. cipitation in a particular region. chromatid cohesion. chromosome theory of inheritance A basic cline A graded change in a character along a chitin (kı¯Ј-tin) A structural polysaccharide, con- principle in biology stating that genes are geographic axis. sisting of amino sugar monomers, found in located at speciﬁc positions (loci) on chromo- clitoris (klitЈ-uh-ris) An organ at the upper inter- many fungal cell walls and in the exoskeletons somes and that the behavior of chromosomes section of the labia minora that engorges with of all arthropods. during meiosis accounts for inheritance blood and becomes erect during sexual arousal. chlorophyll (klo– rЈ-o– -ﬁl) A green pigment located patterns. cloaca (klo– -a–Ј-kuh) A common opening for the in membranes within the chloroplasts of chylomicron (kı¯Ј-lo– -mı¯Ј-kron) A lipid transport digestive, urinary, and reproductive tracts plants and algae and in the membranes of globule composed of fats mixed with choles- found in many nonmammalian vertebrates but certain prokaryotes. Chlorophyll a participates terol and coated with proteins. in few mammals. directly in the light reactions, which convert chyme (kı¯m) The mixture of partially digested clonal selection The process by which an anti- solar energy to chemical energy. food and digestive juices formed in the gen selectively binds to and activates only chlorophyll a A photosynthetic pigment that stomach. those lymphocytes bearing receptors speciﬁc participates directly in the light reactions, chytrid (kı¯Ј-trid) Member of the fungal phylum for the antigen. The selected lymphocytes pro- which convert solar energy to chemical energy. Chytridiomycota, mostly aquatic fungi with liferate and differentiate into a clone of effec- chlorophyll b An accessory photosynthetic pig- ﬂagellated zoospores that represent an early- tor cells and a clone of memory cells speciﬁc ment that transfers energy to chlorophyll a. diverging fungal lineage. for the stimulating antigen. chloroplast (klo–rЈ-o– -plast) An organelle found in ciliate (silЈ-e¯-it) A type of protist that moves by clone (1) A lineage of genetically identical plants and photosynthetic protists that absorbs means of cilia. individuals or cells. (2) In popular usage, an sunlight and uses it to drive the synthesis of cilium (silЈ-e¯-um) (plural, cilia) A short ap- individual that is genetically identical to organic compounds from carbon dioxide and pendage containing microtubules in eukary- another individual. (3) As a verb, to make one water. otic cells. A motile cilium is specialized for or more genetic replicas of an individual or cell. choanocyte (ko– -anЈ-uh-sı¯t) A ﬂagellated feeding locomotion or moving ﬂuid past the cell; it is See also gene cloning. cell found in sponges. Also called a collar cell, formed from a core of nine outer doublet mi- cloning vector In genetic engineering, a DNA it has a collar-like ring that traps food particles crotubules and two inner single microtubules molecule that can carry foreign DNA into a host around the base of its ﬂagellum. (the “9 ϩ 2” arrangement) ensheathed in an cell and replicate there. Cloning vectors include cholesterol (ko– -lesЈ-tuh-rol) A steroid that forms extension of the plasma membrane. A primary plasmids and bacterial artiﬁcial chromosomes an essential component of animal cell mem- cilium is usually nonmotile and plays a sen- (BACs), which move recombinant DNA from a branes and acts as a precursor molecule for the sory and signaling role; it lacks the two inner test tube back into a cell, and viruses that synthesis of other biologically important microtubules (the “9 ϩ 0” arrangement). transfer recombinant DNA by infection. steroids, such as many hormones. circadian rhythm (ser-ka–Ј-de¯-un) A physiologi- closed circulatory system A circulatory system chondrichthyan (kon-drikЈ-the¯-an) Member of cal cycle of about 24 hours that persists even in which blood is conﬁned to vessels and is the class Chondrichthyes, vertebrates with in the absence of external cues. kept separate from the interstitial ﬂuid. skeletons made mostly of cartilage, such as cis-trans isomer One of several compounds that cnidocyte (nı¯Ј-duh-sı¯t) A specialized cell unique sharks and rays. have the same molecular formula and covalent to the phylum Cnidaria; contains a capsule- chordate Member of the phylum Chordata, ani- bonds between atoms but differ in the spatial like organelle housing a coiled thread that, mals that at some point during their develop- arrangements of their atoms owing to the when discharged, explodes outward and ment have a notochord; a dorsal, hollow nerve inﬂexibility of double bonds; formerly called functions in prey capture or defense. cord; pharyngeal slits or clefts; and a muscular, a geometric isomer. cochlea (kokЈ-le¯-uh) The complex, coiled organ post-anal tail. citric acid cycle A chemical cycle involving of hearing that contains the organ of Corti. chorionic villus sampling (CVS) (ko–rЈ-e¯-onЈ- eight steps that completes the metabolic break- codominance The situation in which the ik vilЈ-us) A technique associated with prenatal down of glucose molecules begun in glycolysis phenotypes of both alleles are exhibited in diagnosis in which a small sample of the fetal by oxidizing acetyl CoA (derived from pyru- the heterozygote because both alleles affect the portion of the placenta is removed for analysis vate) to carbon dioxide; occurs within the phenotype in separate, distinguishable ways. to detect certain genetic and congenital defects mitochondrion in eukaryotic cells and in the codon (ko–Ј-don) A three-nucleotide sequence of in the fetus. cytosol of prokaryotes; together with pyruvate DNA or mRNA that speciﬁes a particular amino Chromalveolata One of ﬁve supergroups of oxidation, the second major stage in cellular acid or termination signal; the basic unit of the eukaryotes proposed in a current hypothesis respiration. genetic code. of the evolutionary history of eukaryotes. clade (klayd) A group of species that includes an coefﬁcient of relatedness The fraction of Chromalveolates may have originated by ancestral species and all of its descendants. genes that, on average, are shared by two secondary endosymbiosis and include two cladistics (kluh-disЈ-tiks) An approach to system- individuals. large protist clades, the alveolates and the atics in which organisms are placed into coelom (se¯Ј-lo– m) A body cavity lined by tissue stramenopiles. See also Excavata, Rhizaria, groups called clades based primarily on derived only from mesoderm. Archaeplastida, and Unikonta. common descent. coelomate (se¯Ј-lo– -ma–t) An animal that possesses chromatin (kro–Ј-muh-tin) The complex of class In Linnaean classiﬁcation, the taxonomic a true coelom (a body cavity lined by tissue DNA and proteins that makes up eukaryotic category above the level of order. completely derived from mesoderm).
G–7 GLOSSARY coenocytic fungus (se¯Ј-no-siЈ-tic) A fungus that community ecology The study of how interac- conjugation (konЈ-ju¯-ga–Ј-shun) (1) In prokary- lacks septa and hence whose body is made up tions between species affect community struc- otes, the direct transfer of DNA between two of a continuous cytoplasmic mass that may ture and organization. cells that are temporarily joined. When the contain hundreds or thousands of nuclei. companion cell A type of plant cell that is con- two cells are members of different species, con- coenzyme (ko– -enЈ-zı¯m) An organic molecule nected to a sieve-tube element by many jugation results in horizontal gene transfer. serving as a cofactor. Most vitamins function plasmodesmata and whose nucleus and (2) In ciliates, a sexual process in which two as coenzymes in metabolic reactions. ribosomes may serve one or more adjacent cells exchange haploid micronuclei but do not coevolution The joint evolution of two sieve-tube elements. reproduce. interacting species, each in response to competitive exclusion The concept that when connective tissue Animal tissue that functions selection imposed by the other. populations of two similar species compete for mainly to bind and support other tissues, hav- cofactor Any nonprotein molecule or ion that is the same limited resources, one population will ing a sparse population of cells scattered Glossary required for the proper functioning of an en- use the resources more efﬁciently and have a through an extracellular matrix. zyme. Cofactors can be permanently bound to reproductive advantage that will eventually conodont An early, soft-bodied vertebrate with the active site or may bind loosely and reversibly, lead to the elimination of the other population. prominent eyes and dental elements. along with the substrate, during catalysis. competitive inhibitor A substance that reduces conservation biology The integrated study of cognition The process of knowing that may in- the activity of an enzyme by entering the ecology, evolutionary biology, physiology, clude awareness, reasoning, recollection, and active site in place of the substrate, whose molecular biology, and genetics to sustain judgment. structure it mimics. biological diversity at all levels. cognitive map A neural representation of the complement system A group of about 30 blood contraception The deliberate prevention of abstract spatial relationships between objects proteins that may amplify the inﬂammatory pregnancy. in an animal’s surroundings. response, enhance phagocytosis, or directly contractile vacuole A membranous sac that cohesion The linking together of like molecules, lyse extracellular pathogens. helps move excess water out of certain often by hydrogen bonds. complementary DNA (cDNA) A double- freshwater protists. cohesion-tension hypothesis The leading stranded DNA molecule made in vitro using control element A segment of noncoding DNA explanation of the ascent of xylem sap. It mRNA as a template and the enzymes reverse that helps regulate transcription of a gene by states that transpiration exerts pull on xylem transcriptase and DNA polymerase. A cDNA serving as a binding site for a transcription sap, putting the sap under negative pressure molecule corresponds to the exons of a gene. factor. Multiple control elements are present or tension, and that the cohesion of water complete digestive tract A digestive tube that in a eukaryotic gene’s enhancer. molecules transmits this pull along the entire runs between a mouth and an anus; also called controlled experiment An experiment in length of the xylem from shoots to roots. an alimentary canal. which an experimental group is compared cohort A group of individuals of the same age in complete dominance The situation in which with a control group that varies only in the a population. the phenotypes of the heterozygote and domi- factor being tested. coitus (ko–Ј-uh-tus) The insertion of a penis into a nant homozygote are indistinguishable. convection The mass movement of warmed air vagina; also called sexual intercourse. complete ﬂower A ﬂower that has all four or liquid to or from the surface of a body or coleoptile (ko–Ј-le¯-opЈ-tul) The covering of the basic ﬂoral organs: sepals, petals, stamens, object. young shoot of the embryo of a grass seed. and carpels. convergent evolution The evolution of coleorhiza (ko–Ј-le¯-uh-rı¯Ј-zuh) The covering of complete metamorphosis The transformation similar features in independent the young root of the embryo of a grass seed. of a larva into an adult that looks very differ- evolutionary lineages. collagen A glycoprotein in the extracellular ent, and often functions very differently in its convergent extension A process in which the matrix of animal cells that forms strong environment, than the larva. cells of a tissue layer rearrange themselves in ﬁbers, found extensively in connective tissue compound A substance consisting of two or more such a way that the sheet of cells becomes and bone; the most abundant protein in the different elements combined in a ﬁxed ratio. narrower (converges) and longer (extends). animal kingdom. compound eye A type of multifaceted eye in cooperativity A kind of allosteric regulation collecting duct The location in the kidney insects and crustaceans consisting of up to whereby a shape change in one subunit of a where processed ﬁltrate, called urine, is several thousand light-detecting, focusing protein caused by substrate binding is trans- collected from the renal tubules. ommatidia. mitted to all the other subunits, facilitating collenchyma cell (ko– -lenЈ-kim-uh) A ﬂexible concentration gradient A region along which binding of additional substrate molecules to plant cell type that occurs in strands or cylin- the density of a chemical substance increases those subunits. ders that support young parts of the plant or decreases. copepod (co–Ј-puh-pod) Any of a group of small without restraining growth. conception The fertilization of an egg by a crustaceans that are important members of ma- colloid A mixture made up of a liquid and parti- sperm in humans. rine and freshwater plankton communities. cles that (because of their large size) remain condom A thin, latex rubber or natural coral reef Typically a warm-water, tropical suspended rather than dissolved in that liquid. membrane sheath that ﬁts over the penis to ecosystem dominated by the hard skeletal colon (ko–Ј-len) The largest section of the collect semen. structures secreted primarily by corals. Some vertebrate large intestine; functions in water conduction The direct transfer of thermal coral reefs also exist in cold, deep waters. absorption and formation of feces. motion (heat) between molecules of objects in corepressor A small molecule that binds to a commensalism (kuh-menЈ-suh-lizm) A symbi- direct contact with each other. bacterial repressor protein and changes the otic relationship in which one organism bene- cone A cone-shaped cell in the retina of the protein’s shape, allowing it to bind to the ﬁts but the other is neither helped nor harmed. vertebrate eye, sensitive to color. operator and switch an operon off. communication In animal behavior, a process conformer An animal for which an internal con- cork cambium (kamЈ-be¯-um) A cylinder of involving transmission of, reception of, and dition conforms to (changes in accordance meristematic tissue in woody plants that response to signals. The term is also used in with) changes in an environmental variable. replaces the epidermis with thicker, connection with other organisms, as well as conidium (plural, conidia) A haploid spore tougher cork cells. individual cells of multicellular organisms. produced at the tip of a specialized hypha in corpus callosum (korЈ-pus kuh-lo–Ј-sum) The community All the organisms that inhabit a ascomycetes during asexual reproduction. thick band of nerve ﬁbers that connects the particular area; an assemblage of populations conifer Member of the largest gymnosperm right and left cerebral hemispheres in of different species living close enough phylum. Most conifers are cone-bearing trees, mammals, enabling the hemispheres to together for potential interaction. such as pines and ﬁrs. process information together.
GLOSSARY G–8 corpus luteum (korЈ-pus lu¯Ј-te¯-um) A secreting crustacean (kruh-sta–Ј-shun) A member of a cytoplasmic streaming A circular ﬂow of tissue in the ovary that forms from the subphylum of mostly aquatic arthropods that cytoplasm, involving interactions of myosin collapsed follicle after ovulation and includes lobsters, crayﬁshes, crabs, shrimps, and actin ﬁlaments, that speeds the produces progesterone. and barnacles. distribution of materials within cells. cortex (1) The outer region of cytoplasm in a eu- cryptic coloration Camouﬂage that makes a cytoskeleton A network of microtubules, micro- karyotic cell, lying just under the plasma mem- potential prey difﬁcult to spot against its ﬁlaments, and intermediate ﬁlaments that ex- brane, that has a more gel-like consistency background. tend throughout the cytoplasm and serve a than the inner regions due to the presence of culture A system of information transfer through variety of mechanical, transport, and signaling multiple microﬁlaments. (2) In plants, ground social learning or teaching that inﬂuences the functions. tissue that is between the vascular tissue and behavior of individuals in a population. cytosol (sı¯Ј-to– -sol) The semiﬂuid portion of the
Glossary dermal tissue in a root or eudicot stem. cuticle (kyu¯Ј-tuh-kul) (1) A waxy covering on the cytoplasm. cortical nephron In mammals and birds, a surface of stems and leaves that prevents desic- cytotoxic T cell A type of lymphocyte that, nephron with a loop of Henle located almost cation in terrestrial plants. (2) The exoskeleton when activated, kills infected cells as well as entirely in the renal cortex. of an arthropod, consisting of layers of protein certain cancer cells and transplanted cells. corticosteroid Any steroid hormone produced and chitin that are variously modiﬁed for dif- dalton A measure of mass for atoms and and secreted by the adrenal cortex. ferent functions. (3) A tough coat that covers subatomic particles; the same as the atomic cotransport The coupling of the “downhill” the body of a nematode. mass unit, or amu. diffusion of one substance to the “uphill” cyclic AMP (cAMP) Cyclic adenosine monophos- data Recorded observations. transport of another against its own phate, a ring-shaped molecule made from ATP day-neutral plant A plant in which ﬂower concentration gradient. that is a common intracellular signaling mole- formation is not controlled by photoperiod cotyledon (kotЈ-uh-le¯Ј-dun) A seed leaf of an cule (second messenger) in eukaryotic cells. It is or day length. angiosperm embryo. Some species have one also a regulator of some bacterial operons. decapod A member of the group of crustaceans cotyledon, others two. cyclic electron ﬂow A route of electron ﬂow that includes lobsters, crayﬁshes, crabs, and countercurrent exchange The exchange of a during the light reactions of photosynthesis shrimps. substance or heat between two ﬂuids ﬂowing that involves only photosystem I and that pro- decomposer An organism that absorbs nutrients
in opposite directions. For example, blood in duces ATP but not NADPH or O2. from nonliving organic material such as a ﬁsh gill ﬂows in the opposite direction of cyclin (sı¯Ј-klin) A cellular protein that occurs in corpses, fallen plant material, and the wastes water passing over the gill, maximizing a cyclically ﬂuctuating concentration and of living organisms and converts them to diffusion of oxygen into and carbon dioxide that plays an important role in regulating the inorganic forms; a detritivore. out of the blood. cell cycle. deductive reasoning A type of logic in which countercurrent multiplier system A counter- cyclin-dependent kinase (Cdk) A protein speciﬁc results are predicted from a general current system in which energy is expended in kinase that is active only when attached to a premise. active transport to facilitate exchange of mate- particular cyclin. deep-sea hydrothermal vent A dark, hot, rials and generate concentration gradients. cystic ﬁbrosis (sisЈ-tik fı¯-bro–Ј-sis) A human ge- oxygen-deﬁcient environment associated with covalent bond (ko– -va–Ј-lent) A type of strong netic disorder caused by a recessive allele for a volcanic activity on or near the seaﬂoor. The chemical bond in which two atoms share one chloride channel protein; characterized by an producers in a vent community are or more pairs of valence electrons. excessive secretion of mucus and consequent chemoautotrophic prokaryotes. craniate A chordate with a head. vulnerability to infection; fatal if untreated. de-etiolation The changes a plant shoot crassulacean acid metabolism (CAM) An cytochrome (sı¯Ј-to– -kro–m) An iron-containing undergoes in response to sunlight; also known adaptation for photosynthesis in arid condi- protein that is a component of electron trans- informally as greening. tions, ﬁrst discovered in the family Crassu- port chains in the mitochondria and chloro- dehydration reaction A chemical reaction in
laceae. In this process, a plant takes up CO2 plasts of eukaryotic cells and the plasma which two molecules become covalently and incorporates it into a variety of organic membranes of prokaryotic cells. bonded to each other with the removal of a
acids at night; during the day, CO2 is released cytogenetic map A map of a chromosome that water molecule. from organic acids for use in the Calvin cycle. locates genes with respect to chromosomal deletion (1) A deﬁciency in a chromosome crista (plural, cristae) (krisЈ-tuh, krisЈ-te¯) An in- features distinguishable in a microscope. resulting from the loss of a fragment through folding of the inner membrane of a mitochon- cytokine (sı¯Ј-to– -kı¯nЈ) Any of a group of small breakage. (2) A mutational loss of one or more drion. The inner membrane houses electron proteins secreted by a number of cell types, nucleotide pairs from a gene. transport chains and molecules of the enzyme including macrophages and helper T cells, demographic transition In a stable popula- catalyzing the synthesis of ATP (ATP synthase). that regulate the function of other cells. tion, a shift from high birth and death rates to critical load The amount of added nutrient, cytokinesis (sı¯Ј-to– -kuh-ne¯Ј-sis) The division of low birth and death rates. usually nitrogen or phosphorus, that can be the cytoplasm to form two separate daughter demography The study of changes over time in absorbed by plants without damaging ecosys- cells immediately after mitosis, meiosis I, or the vital statistics of populations, especially tem integrity. meiosis II. birth rates and death rates. crop rotation The practice of planting non- cytokinin (sı¯Ј-to– -kı¯Ј-nin) Any of a class of related denaturation (de¯-na–Ј-chur-a–Ј-shun) In proteins, legumes one year and legumes in alternating plant hormones that retard aging and act in a process in which a protein loses its native years to restore concentrations of ﬁxed nitro- concert with auxin to stimulate cell division, shape due to the disruption of weak chemical gen in the soil. inﬂuence the pathway of differentiation, and bonds and interactions, thereby becoming bio- cross-fostering study A behavioral study in control apical dominance. logically inactive; in DNA, the separation of which the young of one species are placed in cytoplasm (sı¯Ј-to– -plazЈ-um) The contents of the the two strands of the double helix. Denatura- the care of adults from another species. cell bounded by the plasma membrane; in eu- tion occurs under extreme (noncellular) condi- crossing over The reciprocal exchange of karyotes, the portion exclusive of the nucleus. tions of pH, salt concentration, or temperature. genetic material between nonsister cytoplasmic determinant A maternal sub- dendrite (denЈ-drı¯t) One of usually numerous, chromatids during prophase I of meiosis. stance, such as a protein or RNA, that when short, highly branched extensions of a neuron cross-pollination In angiosperms, the transfer placed into an egg inﬂuences the course of that receive signals from other neurons. of pollen from an anther of a ﬂower on one early development by regulating the expres- dendritic cell An antigen-presenting cell, lo- plant to the stigma of a ﬂower on another sion of genes that affect the developmental cated mainly in lymphatic tissues and skin, plant of the same species. fate of cells. that is particularly efﬁcient in presenting anti-
G–9 GLOSSARY gens to helper T cells, thereby initiating a development The events involved in an organ- dinoﬂagellate (dı¯Ј-no– -ﬂajЈ-uh-let) Member of a primary immune response. ism’s changing gradually from a simple to a group of mostly unicellular photosynthetic al- density The number of individuals per unit area more complex or specialized form. gae with two ﬂagella situated in perpendicular or volume. diabetes mellitus (dı¯Ј-uh-be¯Ј-tis melЈ-uh-tus) grooves in cellulose plates covering the cell. density dependent Referring to any characteris- An endocrine disorder marked by an inability dinosaur Member of an extremely diverse clade tic that varies with population density. to maintain glucose homeostasis. The type 1 of reptiles varying in body shape, size, and density independent Referring to any charac- form results from autoimmune destruction of habitat. Birds are the only extant dinosaurs. teristic that is not affected by population insulin-secreting cells; treatment usually re- dioecious (dı¯-e¯Ј-shus) In plant biology, having density. quires daily insulin injections. The type 2 form the male and female reproductive parts on density-dependent inhibition The phenome- most commonly results from reduced respon- different individuals of the same species.
non observed in normal animal cells that siveness of target cells to insulin; obesity and diploblastic Having two germ layers. Glossary causes them to stop dividing when they come lack of exercise are risk factors. diploid cell (dipЈ-loyd) A cell containing two into contact with one another. diacylglycerol (DAG) (dı¯-aЈ-sil-glisЈ-er-ol) A sec- sets of chromosomes (2n), one set inherited deoxyribonucleic acid (DNA) (de¯-okЈ-se¯-rı¯Ј- ond messenger produced by the cleavage of the from each parent. – –Ј bo-nu¯-kla -ik) A nucleic acid molecule, usually phospholipid PIP2 in the plasma membrane. diplomonad A protist that has modiﬁed a double-stranded helix, in which each diaphragm (dı¯Ј-uh-framЈ) (1) A sheet of muscle mitochondria, two equal-sized nuclei, and polynucleotide strand consists of nucleotide that forms the bottom wall of the thoracic cav- multiple ﬂagella. monomers with a deoxyribose sugar and the ity in mammals. Contraction of the diaphragm directional selection Natural selection in nitrogenous bases adenine (A), cytosine (C), pulls air into the lungs. (2) A dome-shaped which individuals at one end of the guanine (G), and thymine (T); capable of being rubber cup ﬁtted into the upper portion of the phenotypic range survive or reproduce more replicated and determining the inherited vagina before sexual intercourse. It serves as a successfully than do other individuals. structure of a cell’s proteins. physical barrier to the passage of sperm into disaccharide (dı¯-sakЈ-uh-rı¯d) A double sugar, deoxyribose (de¯-okЈ-si-rı¯Ј-bo–s) The sugar compo- the uterus. consisting of two monosaccharides joined by nent of DNA nucleotides, having one fewer diapsid (dı¯-apЈ-sid) Member of an amniote clade a glycosidic linkage formed by a dehydration hydroxyl group than ribose, the sugar distinguished by a pair of holes on each side of reaction. component of RNA nucleotides. the skull. Diapsids include the lepidosaurs and dispersal The movement of individuals or depolarization A change in a cell’s membrane archosaurs. gametes away from their parent location. potential such that the inside of the mem- diastole (dı¯-asЈ-to– -le¯) The stage of the cardiac This movement sometimes expands the brane is made less negative relative to the cycle in which a heart chamber is relaxed geographic range of a population or species. outside. For example, a neuron membrane is and ﬁlls with blood. dispersion The pattern of spacing among indi- depolarized if a stimulus decreases its voltage diastolic pressure Blood pressure in the arteries viduals within the boundaries of a population. from the resting potential of Ϫ70 mV in the when the ventricles are relaxed. disruptive selection Natural selection in direction of zero voltage. dicot A term traditionally used to refer to ﬂower- which individuals on both extremes of a dermal tissue system The outer protective ing plants that have two embryonic seed phenotypic range survive or reproduce more covering of plants. leaves, or cotyledons. Recent molecular successfully than do individuals with inter- desert A terrestrial biome characterized by very evidence indicates that dicots do not form a mediate phenotypes. low precipitation. clade; species once classiﬁed as dicots are now distal tubule In the vertebrate kidney, the desmosome A type of intercellular junction in grouped into eudicots, magnoliids, and several portion of a nephron that helps reﬁne ﬁltrate animal cells that functions as a rivet, fastening lineages of basal angiosperms. and empties it into a collecting duct. cells together. differential gene expression The expression disturbance A natural or human-caused event determinate cleavage A type of embryonic of different sets of genes by cells with the same that changes a biological community and usu- development in protostomes that rigidly genome. ally removes organisms from it. Disturbances, casts the developmental fate of each embryonic differentiation The process by which a cell or such as ﬁres and storms, play a pivotal role in cell very early. group of cells become specialized in structure structuring many communities. determinate growth A type of growth charac- and function. disulﬁde bridge A strong covalent bond formed teristic of most animals and some plant diffusion The spontaneous movement of a sub- when the sulfur of one cysteine monomer bonds organs, in which growth stops after a certain stance down its concentration or electrochemi- to the sulfur of another cysteine monomer. size is reached. cal gradient, from a region where it is more DNA (deoxyribonucleic acid) (de¯-okЈ-se¯-rı¯Ј- determination The progressive restriction of concentrated to a region where it is less bo– -nu¯-kla–Ј-ik) A double-stranded, helical nu- developmental potential in which the possible concentrated. cleic acid molecule, consisting of nucleotide fate of each cell becomes more limited as an digestion The second stage of food processing in monomers with a deoxyribose sugar and the embryo develops. At the end of determination, animals: the breaking down of food into mol- nitrogenous bases adenine (A), cytosine (C), a cell is committed to its fate. ecules small enough for the body to absorb. guanine (G), and thymine (T); capable of being detritivore (deh-trı¯Ј-tuh-vo–r) A consumer that dihybrid (dı¯Ј-hı¯Ј-brid) An organism that is replicated and determining the inherited struc- derives its energy and nutrients from nonliv- heterozygous with respect to two genes of ture of a cell’s proteins. ing organic material such as corpses, fallen interest. All the offspring from a cross between DNA ligase (lı¯Ј-ga–s) A linking enzyme essential plant material, and the wastes of living organ- parents doubly homozygous for different for DNA replication; catalyzes the covalent isms; a decomposer. alleles are dihybrids. For example, parents of bonding of the 3Ј end of one DNA fragment detritus (di-trı¯Ј-tus) Dead organic matter. genotypes AABB and aabb produce a dihybrid (such as an Okazaki fragment) to the 5Ј end of deuteromycete (du¯Ј-tuh-ro– -mı¯Ј-se¯t) Traditional of genotype AaBb. another DNA fragment (such as a growing classiﬁcation for a fungus with no known dihybrid cross A cross between two organisms DNA chain). sexual stage. that are each heterozygous for both of the char- DNA methylation The presence of methyl deuterostome development (du¯Ј-tuh-ro– -sto–mЈ) acters being followed (or the self-pollination groups on the DNA bases (usually cytosine) of In animals, a developmental mode distin- of a plant that is heterozygous for both plants, animals, and fungi. (The term also guished by the development of the anus from characters). refers to the process of adding methyl groups the blastopore; often also characterized by dikaryotic (dı¯Ј-ka–r-e¯-otЈ-ik) Referring to a fungal to DNA bases.) radial cleavage and by the body cavity mycelium with two haploid nuclei per cell, DNA microarray assay A method to detect and forming as outpockets of mesodermal tissue. one from each parent. measure the expression of thousands of genes
GLOSSARY G–10 at one time. Tiny amounts of a large number homologous chromosome, such that a portion not cause invagination of the host (plant) cells’ of single-stranded DNA fragments representing of a chromosome is duplicated. plasma membranes. different genes are ﬁxed to a glass slide and dynamic stability hypothesis The concept ectomycorrhizal fungus A symbiotic fungus tested for hybridization with samples of that long food chains are less stable than short that forms sheaths of hyphae over the surface labeled cDNA. chains. of plant roots and also grows into extracellular DNA polymerase (puh-limЈ-er-a–s) An enzyme dynein (dı¯Ј-ne¯-un) In cilia and ﬂagella, a large spaces of the root cortex. that catalyzes the elongation of new DNA (for motor protein extending from one micro- ectoparasite A parasite that feeds on the example, at a replication fork) by the addition of tubule doublet to the adjacent doublet. ATP external surface of a host. nucleotides to the 3Ј end of an existing chain. hydrolysis drives changes in dynein shape that ectopic Occurring in an abnormal location. There are several different DNA polymerases; lead to bending of cilia and ﬂagella. ectoproct A sessile, colonial lophophorate; also
Glossary DNA polymerase III and DNA polymerase I play E site One of a ribosome’s three binding sites for called a bryozoan. major roles in DNA replication in E. coli. tRNA during translation. The E site is the place ectothermic Referring to organisms for which DNA replication The process by which a DNA where discharged tRNAs leave the ribosome. external sources provide most of the heat for molecule is copied; also called DNA synthesis. (E stands for exit.) temperature regulation. domain (1) A taxonomic category above the ecdysozoan Member of a group of animal phyla Ediacaran biota (e¯Ј-de¯-uh-kehЈ-run bı¯-o–Ј-tuh) kingdom level. The three domains are Archaea, identiﬁed as a clade by molecular evidence. An early group of soft-bodied, multicellular Bacteria, and Eukarya. (2) A discrete structural Many ecdysozoans are molting animals. eukaryotes known from fossils that range in and functional region of a protein. ecdysteroid A steroid hormone, secreted by the age from 565 million to 550 million years old. dominant allele An allele that is fully expressed prothoracic glands, that triggers molting in effective population size An estimate of the in the phenotype of a heterozygote. arthropods. size of a population based on the numbers of dominant species A species with substantially echinoderm (i-kı¯Ј-no– -derm) A slow-moving or females and males that successfully breed; higher abundance or biomass than other sessile marine deuterostome with a water vas- generally smaller than the total population. species in a community. Dominant species cular system and, in larvae, bilateral symmetry. effector cell (1) A muscle cell or gland cell that exert a powerful control over the occurrence Echinoderms include sea stars, brittle stars, sea performs the body’s response to stimuli as and distribution of other species. urchins, feather stars, and sea cucumbers. directed by signals from the brain or other dopamine A neurotransmitter that is a ecological footprint The aggregate land and processing center of the nervous system. catecholamine, like epinephrine and water area required by a person, city, or nation (2) A lymphocyte that has undergone clonal norepinephrine. to produce all of the resources it consumes and selection and is capable of mediating an dormancy A condition typiﬁed by extremely to absorb all of the wastes it generates. adaptive immune response. low metabolic rate and a suspension of growth ecological niche (nich) The sum of a species’ egg The female gamete. and development. use of the biotic and abiotic resources in its egg-polarity gene A gene that helps control the dorsal Pertaining to the top of an animal with environment. orientation (polarity) of the egg; also called a radial or bilateral symmetry. ecological species concept A deﬁnition of maternal effect gene. dorsal lip The region above the blastopore on species in terms of ecological niche, the ejaculation The propulsion of sperm from the the dorsal side of the amphibian embryo. sum of how members of the species interact epididymis through the muscular vas deferens, double bond A double covalent bond; the with the nonliving and living parts of their ejaculatory duct, and urethra. sharing of two pairs of valence electrons by environment. ejaculatory duct In mammals, the short section two atoms. ecological succession Transition in the species of the ejaculatory route formed by the conver- double circulation A circulatory system composition of a community following a gence of the vas deferens and a duct from the consisting of separate pulmonary and systemic disturbance; establishment of a community seminal vesicle. The ejaculatory duct circuits, in which blood passes through the in an area virtually barren of life. transports sperm from the vas deferens to heart after completing each circuit. ecology The study of how organisms interact the urethra. double fertilization A mechanism of fertiliza- with each other and their environment. electrocardiogram (ECG or EKG) A record of tion in angiosperms in which two sperm cells ecosystem All the organisms in a given area as the electrical impulses that travel through unite with two cells in the female gameto- well as the abiotic factors with which they heart muscle during the cardiac cycle. phyte (embryo sac) to form the zygote and interact; one or more communities and the electrochemical gradient The diffusion endosperm. physical environment around them. gradient of an ion, which is affected by both double helix The form of native DNA, referring ecosystem ecology The study of energy ﬂow the concentration difference of an ion across to its two adjacent antiparallel polynucleotide and the cycling of chemicals among the a membrane (a chemical force) and the ion’s strands wound around an imaginary axis into various biotic and abiotic components in tendency to move relative to the membrane a spiral shape. an ecosystem. potential (an electrical force). Down syndrome A human genetic disease usu- ecosystem engineer An organism that electrogenic pump An active transport protein ally caused by the presence of an extra chro- inﬂuences community structure by causing that generates voltage across a membrane mosome 21; characterized by developmental physical changes in the environment. while pumping ions. delays and heart and other defects that are ecosystem service A function performed by an electromagnetic receptor A receptor of generally treatable or non-life-threatening. ecosystem that directly or indirectly beneﬁts electromagnetic energy, such as visible light, Duchenne muscular dystrophy (duh-shenЈ) humans. electricity, or magnetism. A human genetic disease caused by a ecotone The transition from one type of habitat electromagnetic spectrum The entire sex-linked recessive allele; characterized by or ecosystem to another, such as the transition spectrum of electromagnetic radiation, progressive weakening and a loss of muscle from a forest to a grassland. ranging in wavelength from less than a tissue. ectoderm (ekЈ-to– -durm) The outermost of the nanometer to more than a kilometer. duodenum (du¯Ј-uh-de¯nЈ-um) The ﬁrst section of three primary germ layers in animal embryos; electron A subatomic particle with a single nega- the small intestine, where chyme from the gives rise to the outer covering and, in some tive electrical charge and a mass about 1/2,000 stomach mixes with digestive juices from the phyla, the nervous system, inner ear, and lens that of a neutron or proton. One or more elec- pancreas, liver, and gallbladder as well as from of the eye. trons move around the nucleus of an atom. gland cells of the intestinal wall. ectomycorrhiza (ekЈ-to– -mı¯Ј-ko– -rı¯Ј-zuh) Associa- electron microscope (EM) A microscope that duplication An aberration in chromosome tion of a fungus with a plant root system in uses magnets to focus an electron beam on or structure due to fusion with a fragment from a which the fungus surrounds the roots but does through a specimen, resulting in a practical
G–11 GLOSSARY resolution of a hundredfold greater than that endocytosis (enЈ-do– -sı¯-to–Ј-sis) Cellular uptake of endotoxin A toxic component of the outer of a light microscope using standard tech- biological molecules and particulate matter membrane of certain gram-negative bacteria niques. A transmission electron microscope via formation of vesicles from the plasma that is released only when the bacteria die. (TEM) is used to study the internal structure of membrane. energetic hypothesis The concept that the thin sections of cells. A scanning electron endoderm (enЈ-do– -durm) The innermost of the length of a food chain is limited by the inefﬁ- microscope (SEM) is used to study the ﬁne three primary germ layers in animal embryos; ciency of energy transfer along the chain. details of cell surfaces. lines the archenteron and gives rise to the energy The capacity to cause change, especially electron shell An energy level of electrons at liver, pancreas, lungs, and the lining of the to do work (to move matter against an a characteristic average distance from the digestive tract in species that have these opposing force). nucleus of an atom. structures. energy coupling In cellular metabolism, the use electron transport chain A sequence of endodermis In plant roots, the innermost layer of energy released from an exergonic reaction Glossary electron carrier molecules (membrane pro- of the cortex that surrounds the vascular to drive an endergonic reaction. teins) that shuttle electrons down a series of cylinder. enhancer A segment of eukaryotic DNA contain- redox reactions that release energy used to endomembrane system The collection of ing multiple control elements, usually located far make ATP. membranes inside and surrounding a eukary- from the gene whose transcription it regulates. electronegativity The attraction of a given otic cell, related either through direct physical enteric division One of three divisions of the atom for the electrons of a covalent bond. contact or by the transfer of membranous autonomic nervous system; consists of electroporation A technique to introduce re- vesicles; includes the plasma membrane, the networks of neurons in the digestive tract, combinant DNA into cells by applying a brief nuclear envelope, the smooth and rough pancreas, and gallbladder; normally regulated electrical pulse to a solution containing the endoplasmic reticulum, the Golgi apparatus, by the sympathetic and parasympathetic cells. The pulse creates temporary holes in the lysosomes, vesicles, and vacuoles. divisions of the autonomic nervous system. cells’ plasma membranes, through which DNA endometriosis (enЈ-do– -me¯-tre¯-o–Ј-sis) The entropy A measure of disorder, or randomness. can enter. condition resulting from the presence of enzymatic hydrolysis The process in digestion element Any substance that cannot be broken endometrial tissue outside of the uterus. that splits macromolecules from food by the down to any other substance by chemical endometrium (enЈ-do– -me¯Ј-tre¯-um) The inner enzymatic addition of water. reactions. lining of the uterus, which is richly supplied enzyme (enЈ-zı¯m) A macromolecule serving as a elimination The fourth and ﬁnal stage of with blood vessels. catalyst, a chemical agent that increases the food processing in animals: the passing of endoparasite A parasite that lives within a host. rate of a reaction without being consumed by undigested material out of the body. endophyte A fungus that lives inside a leaf or the reaction. Most enzymes are proteins. embryo sac (emЈ-bre¯-o– ) The female gametophyte other plant part without causing harm to enzyme-substrate complex A temporary of angiosperms, formed from the growth and the plant. complex formed when an enzyme binds to its division of the megaspore into a multicellular endoplasmic reticulum (ER) (enЈ-do– -plazЈ-mik substrate molecule(s). structure that typically has eight haploid ruh-tikЈ-yu¯-lum) An extensive membranous epicotyl (epЈ-uh-kotЈ-ul) In an angiosperm nuclei. network in eukaryotic cells, continuous with embryo, the embryonic axis above the point of embryonic lethal A mutation with a phenotype the outer nuclear membrane and composed of attachment of the cotyledon(s) and below leading to death of an embryo or larva. ribosome-studded (rough) and ribosome-free the ﬁrst pair of miniature leaves. embryophyte Alternate name for land plants (smooth) regions. epidemic A general outbreak of a disease. that refers to their shared derived trait of endorphin (en-do–rЈ-ﬁn) Any of several hor- epidermis (1) The dermal tissue system of non- multicellular, dependent embryos. mones produced in the brain and anterior pi- woody plants, usually consisting of a single emergent properties New properties that arise tuitary that inhibit pain perception. layer of tightly packed cells. (2) The outermost with each step upward in the hierarchy of life, endoskeleton A hard skeleton buried within the layer of cells in an animal. owing to the arrangement and interactions of soft tissues of an animal. epididymis (epЈ-uh-didЈ-uh-mus) A coiled tubule parts as complexity increases. endosperm In angiosperms, a nutrient-rich located adjacent to the mammalian testis emigration The movement of individuals out of tissue formed by the union of a sperm with where sperm are stored. a population. two polar nuclei during double fertilization. epigenetic inheritance Inheritance of traits enantiomer (en-anЈ-te¯-o– -mer) One of two com- The endosperm provides nourishment to the transmitted by mechanisms not directly in- pounds that are mirror images of each other developing embryo in angiosperm seeds. volving the nucleotide sequence of a genome. and that differ in shape due to the presence of endospore A thick-coated, resistant cell epinephrine (epЈ-i-nefЈ-rin) A catecholamine an asymmetric carbon. produced by some bacterial cells when they that, when secreted as a hormone by the endangered species A species that is in danger are exposed to harsh conditions. adrenal medulla, mediates “ﬁght-or-ﬂight” of extinction throughout all or a signiﬁcant endosymbiont theory The theory that mito- responses to short-term stresses; also released portion of its range. chondria and plastids, including chloroplasts, by some neurons as a neurotransmitter; also endemic (en-demЈ-ik) Referring to a species that originated as prokaryotic cells engulfed by an known as adrenaline. is conﬁned to a speciﬁc geographic area. ancestral eukaryotic cell. The engulfed cell and epiphyte (epЈ-uh-fı¯t) A plant that nourishes itself endergonic reaction (enЈ-der-gonЈ-ik) A non- its host cell then evolved into a single organism. but grows on the surface of another plant for spontaneous chemical reaction, in which free endosymbiosis A process in which a unicellular support, usually on the branches or trunks of energy is absorbed from the surroundings. organism (the “host”) engulfs another cell, trees. endocrine gland (enЈ-do– -krin) A ductless gland which lives within the host cell and ultimately epistasis (epЈ-i-sta–Ј-sis) A type of gene interaction that secretes hormones directly into the becomes an organelle in the host cell. See also in which the phenotypic expression of one interstitial ﬂuid, from which they diffuse into endosymbiont theory. gene alters that of another independently the bloodstream. endothelium (enЈ-do– -the¯Ј-le¯-um) The simple inherited gene. endocrine system The internal system of com- squamous layer of cells lining the lumen of epithelial tissue (epЈ-uh-the¯Ј-le¯-ul) Sheets of munication involving hormones, the ductless blood vessels. tightly packed cells that line organs and body glands that secrete hormones, and the molecu- endothermic Referring to organisms that are cavities as well as external surfaces. lar receptors on or in target cells that respond warmed by heat generated by their own epithelium An epithelial tissue. to hormones; functions in concert with the metabolism. This heat usually maintains a epitope A small, accessible region of an antigen nervous system to effect internal regulation relatively stable body temperature higher to which an antigen receptor or antibody and maintain homeostasis. than that of the external environment. binds; also called an antigenic determinant.
GLOSSARY G–12 EPSP See excitatory postsynaptic potential. eumetazoan (yu¯Ј-met-uh-zo–Ј-un) Member of a exocytosis (ekЈ-so–-sı¯-to–Ј-sis) The cellular secretion equilibrium potential (Eion) The magnitude clade of animals with true tissues. All animals of biological molecules by the fusion of vesicles of a cell’s membrane voltage at equilibrium; except sponges and a few other groups are containing them with the plasma membrane. calculated using the Nernst equation. eumetazoans. exon A sequence within a primary transcript that erythrocyte (eh-rithЈ-ruh-sı¯t) A blood cell that eurypterid (yur-ipЈ-tuh-rid) An extinct carnivo- remains in the RNA after RNA processing; also contains hemoglobin, which transports rous chelicerate; also called a water scorpion. refers to the region of DNA from which this oxygen; also called a red blood cell. Eustachian tube (yu¯-sta–Ј-shun) The tube that sequence was transcribed. erythropoietin (EPO) (eh-rithЈ-ro– -poyЈ-uh-tin) connects the middle ear to the pharynx. exoskeleton A hard encasement on the surface A hormone that stimulates the production of eutherian (yu¯-the¯rЈ-e¯-un) Placental mammal; of an animal, such as the shell of a mollusc or erythrocytes. It is secreted by the kidney when mammal whose young complete their embry- the cuticle of an arthropod, that provides
Glossary body tissues do not receive enough oxygen. onic development within the uterus, joined to protection and points of attachment for esophagus (eh-sofЈ-uh-gus) A muscular tube that the mother by the placenta. muscles. conducts food, by peristalsis, from the pharynx eutrophic lake (yu¯-tro–fЈ-ik) A lake that has a exotoxin (ekЈ-so– -tokЈ-sin) A toxic protein that is to the stomach. high rate of biological productivity supported secreted by a prokaryote or other pathogen essential amino acid An amino acid that an by a high rate of nutrient cycling. and that produces speciﬁc symptoms, even if animal cannot synthesize itself and must be eutrophication A process by which nutrients, the pathogen is no longer present. obtained from food in prefabricated form. particularly phosphorus and nitrogen, become expansin Plant enzyme that breaks the cross- essential element A chemical element required highly concentrated in a body of water, links (hydrogen bonds) between cellulose for an organism to survive, grow, and reproduce. leading to increased growth of organisms microﬁbrils and other cell wall constituents, essential fatty acid An unsaturated fatty acid such as algae or cyanobacteria. loosening the wall’s fabric. that an animal needs but cannot make. evaporation The process by which a liquid exponential population growth Growth of a essential nutrient A substance that an organism changes to a gas. population in an ideal, unlimited environ- cannot synthesize from any other material and evaporative cooling The process in which the ment, represented by a J-shaped curve when therefore must absorb in preassembled form. surface of an object becomes cooler during population size is plotted over time. estradiol (esЈ-truh-dı¯Ј-ol) A steroid hormone that evaporation, a result of the molecules with the expression vector A cloning vector that stimulates the development and maintenance greatest kinetic energy changing from the contains a highly active bacterial promoter of the female reproductive system and second- liquid to the gaseous state. just upstream of a restriction site where a ary sex characteristics; the major estrogen in evapotranspiration The total evaporation of eukaryotic gene can be inserted, allowing the mammals. water from an ecosystem, including water gene to be expressed in a bacterial cell. estrogen (esЈ-tro– -jen) Any steroid hormone, such transpired by plants and evaporated from a Expression vectors are also available that have as estradiol, that stimulates the development landscape, usually measured in millimeters been genetically engineered for use in speciﬁc and maintenance of the female reproductive and estimated for a year. types of eukaryotic cells. system and secondary sex characteristics. evo-devo Evolutionary developmental biology; a external fertilization The fusion of gametes estrous cycle (esЈ-trus) A reproductive cycle ﬁeld of biology that compares developmental that parents have discharged into the characteristic of female mammals except processes of different multicellular organisms environment. humans and certain other primates, in which to understand how these processes have extinction vortex A downward population spi- the nonpregnant endometrium is reabsorbed evolved and how changes can modify existing ral in which inbreeding and genetic drift com- rather than shed, and sexual response occurs organismal features or lead to new ones. bine to cause a small population to shrink and, only during mid-cycle at estrus. evolution Descent with modiﬁcation; the idea unless the spiral is reversed, become extinct. estuary The area where a freshwater stream or that living species are descendants of ancestral extracellular digestion The breakdown of food river merges with the ocean. species that were different from the present- in compartments that are continuous with the ethylene (ethЈ-uh-le¯n) A gaseous plant hormone day ones; also deﬁned more narrowly as the outside of an animal’s body. involved in responses to mechanical stress, change in the genetic composition of a extracellular matrix (ECM) The meshwork programmed cell death, leaf abscission, and population from generation to generation. surrounding animal cells, consisting of glyco- fruit ripening. evolutionary tree A branching diagram that proteins, polysaccharides, and proteoglycans etiolation Plant morphological adaptations for reﬂects a hypothesis about evolutionary synthesized and secreted by the cells. growing in darkness. relationships among groups of organisms. extraembryonic membrane One of four euchromatin (yu¯-kro–Ј-muh-tin) The less Excavata One of ﬁve supergroups of eukaryotes membranes (yolk sac, amnion, chorion, and condensed form of eukaryotic chromatin proposed in a current hypothesis of the allantois) located outside the embryo that that is available for transcription. evolutionary history of eukaryotes. Excavates support the developing embryo in reptiles and eudicot (yu¯-dı¯Ј-kot) Member of a clade that have unique cytoskeletal features, and some mammals. contains the vast majority of ﬂowering plants species have an “excavated” feeding groove extreme halophile An organism that lives in a that have two embryonic seed leaves, or on one side of the cell body. See also highly saline environment, such as the Great cotyledons. Chromalveolata, Rhizaria, Archaeplastida, Salt Lake or the Dead Sea. euglenid (yu¯Ј-glen-id) A protist, such as Euglena and Unikonta. extreme thermophile An organism that thrives or its relatives, characterized by an anterior excitatory postsynaptic potential in hot environments (often 60–80°C or hotter). pocket from which one or two ﬂagella emerge. (EPSP) An electrical change (depolarization) extremophile An organism that lives in envi- euglenozoan Member of a diverse clade of in the membrane of a postsynaptic cell ronmental conditions so extreme that few ﬂagellated protists that includes predatory caused by the binding of an excitatory other species can survive there. Extremophiles heterotrophs, photosynthetic autotrophs, neurotransmitter from a presynaptic cell to a include extreme halophiles (“salt lovers”) and and pathogenic parasites. postsynaptic receptor; makes it more likely extreme thermophiles (“heat lovers”). Eukarya (yu¯-karЈ-e¯-uh) The domain that includes for a postsynaptic cell to generate an action F factor In bacteria, the DNA segment that all eukaryotic organisms. potential. confers the ability to form pili for conjugation eukaryotic cell (yu¯Ј-ker-e¯-otЈ-ik) A type of cell excretion The disposal of nitrogen-containing and associated functions required for the with a membrane-enclosed nucleus and metabolites and other waste products. transfer of DNA from donor to recipient. The membrane-enclosed organelles. Organisms exergonic reaction (ekЈ-ser-gonЈ-ik) A sponta- F factor may exist as a plasmid or be integrated with eukaryotic cells (protists, plants, fungi, neous chemical reaction, in which there is a into the bacterial chromosome. and animals) are called eukaryotes. net release of free energy. F plasmid The plasmid form of the F factor.
G–13 GLOSSARY F1 generation The ﬁrst ﬁlial, hybrid (hetero- ﬁbronectin An extracellular glycoprotein food vacuole A membranous sac formed by zygous) offspring arising from a parental secreted by animal cells that helps them phagocytosis of microorganisms or particles to (P generation) cross. attach to the extracellular matrix. be used as food by the cell.
F2 generation The offspring resulting from ﬁlament In an angiosperm, the stalk portion of food web The interconnected feeding relation- interbreeding (or self-pollination) of the the stamen, the pollen-producing reproductive ships in an ecosystem.
hybrid F1 generation. organ of a ﬂower. foot (1) The portion of a bryophyte sporophyte facilitated diffusion The passage of molecules ﬁltrate Cell-free ﬂuid extracted from the body that gathers sugars, amino acids, water, and or ions down their electrochemical gradient ﬂuid by the excretory system. minerals from the parent gametophyte via across a biological membrane with the ﬁltration In excretory systems, the extraction of transfer cells. (2) One of the three main parts assistance of speciﬁc transmembrane transport water and small solutes, including metabolic of a mollusc; a muscular structure usually used
proteins, requiring no energy expenditure. wastes, from the body ﬂuid. for movement. See also mantle, visceral mass. Glossary facilitation An interaction in which one species ﬁmbria (plural, ﬁmbriae) A short, hairlike foraging The seeking and obtaining of food. has a positive effect on the survival and appendage of a prokaryotic cell that helps it foram (foraminiferan) An aquatic protist that reproduction of another species without the adhere to the substrate or to other cells. secretes a hardened shell containing calcium intimate association of a symbiosis. ﬁrst law of thermodynamics The principle of carbonate and extends pseudopodia through facultative anaerobe (fakЈ-ul-ta–Ј-tiv anЈ-uh-ro–b) conservation of energy: Energy can be trans- pores in the shell. An organism that makes ATP by aerobic ferred and transformed, but it cannot be forebrain One of three ancestral and embryonic respiration if oxygen is present but that created or destroyed. regions of the vertebrate brain; develops into switches to anaerobic respiration or fermen- ﬁssion The separation of an organism into two or the thalamus, hypothalamus, and cerebrum. tation if oxygen is not present. more individuals of approximately equal size. fossil A preserved remnant or impression of an family In Linnaean classiﬁcation, the taxonomic ﬁxed action pattern In animal behavior, a organism that lived in the past. category above genus. sequence of unlearned acts that is essentially founder effect Genetic drift that occurs when a fast block to polyspermy The depolarization unchangeable and, once initiated, usually few individuals become isolated from a larger of the egg plasma membrane that begins carried to completion. population and form a new population whose within 1–3 seconds after a sperm binds to an ﬂaccid (ﬂasЈ-id) Limp. Lacking turgor (stiffness or gene pool composition is not reﬂective of that egg membrane protein. The depolarization ﬁrmness), as in a plant cell in surroundings of the original population. lasts about 1 minute and prevents additional where there is a tendency for water to leave fovea (fo–Ј-ve¯-uh) The place on the retina at the sperm from fusing with the egg during that the cell. (A walled cell becomes ﬂaccid if it has eye’s center of focus, where cones are highly time. a higher water potential than its surroundings, concentrated. fast-twitch ﬁber A muscle ﬁber used for rapid, resulting in the loss of water.) fragmentation A means of asexual reproduction powerful contractions. ﬂagellum (ﬂuh-jelЈ-um) (plural, ﬂagella) A long whereby a single parent breaks into parts that fat A lipid consisting of three fatty acids cellular appendage specialized for locomotion. regenerate into whole new individuals. linked to one glycerol molecule; also called a Like motile cilia, eukaryotic ﬂagella have a core frameshift mutation A mutation occurring triacylglycerol or triglyceride. with nine outer doublet microtubules and two when nucleotides are inserted in or deleted fate map A territorial diagram of embryonic de- inner single microtubules (the “9 ϩ 2” arrange- from a gene and the number inserted or velopment that displays the future derivatives ment) ensheathed in an extension of the deleted is not a multiple of three, resulting in of individual cells and tissues. plasma membrane. Prokaryotic ﬂagella have a the improper grouping of the subsequent fatty acid A carboxylic acid with a long carbon different structure. nucleotides into codons. chain. Fatty acids vary in length and in the ﬂorigen A ﬂowering signal, probably a protein, free energy The portion of a biological system’s number and location of double bonds; three that is made in leaves under certain conditions energy that can perform work when tempera- fatty acids linked to a glycerol molecule form a and that travels to the shoot apical meristems, ture and pressure are uniform throughout the fat molecule, also known as a triacylglycerol or inducing them to switch from vegetative to system. The change in free energy of a system triglyceride. reproductive growth. (ΔG) is calculated by the equation ΔG ϭ ΔH – feces (fe¯Ј-se¯z) The wastes of the digestive tract. ﬂower In an angiosperm, a specialized shoot TΔS, where ΔH is the change in enthalpy (in feedback inhibition A method of metabolic with up to four sets of modiﬁed leaves, biological systems, equivalent to total energy), control in which the end product of a bearing structures that function in sexual T is the absolute temperature, and ΔS is the metabolic pathway acts as an inhibitor of reproduction. change in entropy. an enzyme within that pathway. ﬂuid feeder An animal that lives by sucking frequency-dependent selection Selection in fermentation A catabolic process that makes nutrient-rich ﬂuids from another living organism. which the ﬁtness of a phenotype depends on a limited amount of ATP from glucose (or ﬂuid mosaic model The currently accepted how common the phenotype is in a population. other organic molecules) without an electron model of cell membrane structure, which envi- fruit A mature ovary of a ﬂower. The fruit transport chain and that produces a character- sions the membrane as a mosaic of protein protects dormant seeds and often aids in istic end product, such as ethyl alcohol or molecules drifting laterally in a ﬂuid bilayer of their dispersal. lactic acid. phospholipids. functional group A speciﬁc conﬁguration of fertilization (1) The union of haploid gametes follicle (folЈ-uh-kul) A microscopic structure in atoms commonly attached to the carbon to produce a diploid zygote. (2) The addition the ovary that contains the developing oocyte skeletons of organic molecules and involved of mineral nutrients to the soil. and secretes estrogens. in chemical reactions. fetus (fe¯Ј-tus) A developing mammal that has all follicle-stimulating hormone (FSH) A tropic G protein A GTP-binding protein that relays sig- the major structures of an adult. In humans, hormone that is produced and secreted by the nals from a plasma membrane signal receptor, the fetal stage lasts from the 9th week of anterior pituitary and that stimulates the known as a G protein-coupled receptor, to other gestation until birth. production of eggs by the ovaries and sperm signal transduction proteins inside the cell. ﬁber A ligniﬁed cell type that reinforces the by the testes. G protein-coupled receptor (GPCR) A signal xylem of angiosperms and functions in follicular phase That part of the ovarian cycle receptor protein in the plasma membrane mechanical support; a slender, tapered scle- during which follicles are growing and oocytes that responds to the binding of a signaling renchyma cell that usually occurs in bundles. maturing. molecule by activating a G protein. Also ﬁbroblast (fı¯Ј-bro– -blast) A type of cell in loose food chain The pathway along which food called a G protein-linked receptor.
connective tissue that secretes the protein energy is transferred from trophic level to G0 phase A nondividing state occupied by cells ingredients of the extracellular ﬁbers. trophic level, beginning with producers. that have left the cell cycle, sometimes reversibly.
GLOSSARY G–14 G1 phase The ﬁrst gap, or growth phase, of the channels may alter a cell’s membrane ing a certain phenotype or disease, with the cell cycle, consisting of the portion of potential. aim of ﬁnding genetic markers that correlate interphase before DNA synthesis begins. gel electrophoresis (e¯-lekЈ-tro– -fo–r-e¯Ј-sis) A tech- with that phenotype or disease.
G2 phase The second gap, or growth phase, of nique for separating nucleic acids or proteins genomic imprinting A phenomenon in which the cell cycle, consisting of the portion of on the basis of their size and electrical charge, expression of an allele in offspring depends on interphase after DNA synthesis occurs. both of which affect their rate of movement whether the allele is inherited from the male gallbladder An organ that stores bile and through an electric ﬁeld in a gel made of or female parent. releases it as needed into the small intestine. agarose or another polymer. genomic library A set of cell clones containing game theory An approach to evaluating alterna- gene A discrete unit of hereditary information all the DNA segments from a genome, each tive strategies in situations where the outcome consisting of a speciﬁc nucleotide sequence in within a plasmid, BAC, or other cloning vector. – Glossary of a particular strategy depends on the DNA (or RNA, in some viruses). genomics (juh-noЈ-miks) The study of whole sets strategies used by other individuals. gene annotation Analysis of genomic of genes and their interactions within a species, gametangium (gamЈ-uh-tanЈ-je¯-um) (plural, sequences to identify protein-coding genes as well as genome comparisons between species. gametangia) Multicellular plant structure in and determine the function of their products. genotype (je¯Ј-no– -tı¯p) The genetic makeup, or set which gametes are formed. Female gametangia gene cloning The production of multiple copies of alleles, of an organism. are called archegonia, and male gametangia are of a gene. genus (je¯Ј-nus) (plural, genera) A taxonomic cat- called antheridia. gene expression The process by which informa- egory above the species level, designated by the gamete (gamЈ-e¯t) A haploid reproductive cell, such tion encoded in DNA directs the synthesis of ﬁrst word of a species’ two-part scientiﬁc name. as an egg or sperm. Gametes unite during sexual proteins or, in some cases, RNAs that are not geographic variation Differences between the reproduction to produce a diploid zygote. translated into proteins and instead function gene pools of geographically separate popula- gametogenesis The process by which gametes as RNAs. tions or population subgroups. are produced. gene ﬂow The transfer of alleles from one popu- geologic record The division of Earth’s history gametophore (guh-me¯Ј-to– -fo–r) The mature lation to another, resulting from the move- into time periods, grouped into three eons— gamete-producing structure of a moss ment of fertile individuals or their gametes. Archaean, Proterozoic, and Phanerozoic—and gametophyte. gene pool The aggregate of all copies of every further subdivided into eras, periods, and gametophyte (guh-me¯Ј-to– -fı¯t) In organisms type of allele at all loci in every individual in a epochs. (plants and some algae) that have alternation population. The term is also used in a more re- germ layer One of the three main layers in a of generations, the multicellular haploid form stricted sense as the aggregate of alleles for just gastrula that will form the various tissues and that produces haploid gametes by mitosis. one or a few loci in a population. organs of an animal body. The haploid gametes unite and develop into gene therapy The introduction of genes into an gestation (jes-ta–Ј-shun) Pregnancy; the state of sporophytes. afﬂicted individual for therapeutic purposes. carrying developing young within the female gamma-aminobutyric acid (GABA) An gene-for-gene recognition A widespread form reproductive tract. amino acid that functions as a CNS of plant disease resistance involving recogni- gibberellin (jibЈ-uh-relЈ-in) Any of a class of neurotransmitter in the central nervous tion of pathogen-derived molecules by the pro- related plant hormones that stimulate growth system of vertebrates. tein products of speciﬁc plant disease in the stem and leaves, trigger the germination ganglia (gangЈ-gle¯-uh) (singular, ganglion) resistance genes. of seeds and breaking of bud dormancy, and Clusters (functional groups) of nerve cell genetic drift A process in which chance events (with auxin) stimulate fruit development. bodies in a centralized nervous system. cause unpredictable ﬂuctuations in allele glans The rounded structure at the tip of the clitoris ganglion cell A type of neuron in the retina frequencies from one generation to the next. or penis that is involved in sexual arousal. that synapses with bipolar cells and transmits Effects of genetic drift are most pronounced glia (glial cells) Cells of the nervous system that action potentials to the brain via axons in the in small populations. support, regulate, and augment the functions optic nerve. genetic engineering The direct manipulation of neurons. gap junction A type of intercellular junction in of genes for practical purposes. global climate change Increase in temperature animal cells, consisting of proteins surround- genetic map An ordered list of genetic loci and change in weather patterns all around the ing a pore that allows the passage of materials (genes or other genetic markers) along a planet, due mostly to increasing atmospheric
between cells. chromosome. CO2 levels from the burning of fossil fuels. The gas exchange The uptake of molecular oxygen genetic proﬁle An individual’s unique set of increase in temperature, called global warm- from the environment and the discharge of genetic markers, detected most often today ing, is a major aspect of global climate change. carbon dioxide to the environment. by PCR or, previously, by electrophoresis and global ecology The study of the functioning gastric juice A digestive ﬂuid secreted by the nucleic acid probes. and distribution of organisms across the stomach. genetic recombination General term for the biosphere and how the regional exchange of gastrovascular cavity A central cavity with a production of offspring with combinations of energy and materials affects them. single opening in the body of certain animals, traits that differ from those found in either glomeromycete (glo– Ј-mer-o– -mı¯Ј-se¯t) Member of including cnidarians and ﬂatworms, that func- parent. the fungal phylum Glomeromycota, character- tions in both the digestion and distribution of genetic variation Differences among individu- ized by a distinct branching form of mycor- nutrients. als in the composition of their genes or other rhizae called arbuscular mycorrhizae. gastrula (gasЈ-tru¯-luh) An embryonic stage in DNA segments. glomerulus (glo– -ma–rЈ-yu¯-lus) A ball of capillaries animal development encompassing the forma- genetically modiﬁed (GM) organism An surrounded by Bowman’s capsule in the tion of three layers: ectoderm, mesoderm, and organism that has acquired one or more nephron and serving as the site of ﬁltration in endoderm. genes by artiﬁcial means; also known as a the vertebrate kidney. gastrulation (gasЈ-tru¯-la–Ј-shun) In animal develop- transgenic organism. glucagon (glu¯Ј-kuh-gon) A hormone secreted by ment, a series of cell and tissue movements in genetics The scientiﬁc study of heredity and pancreatic alpha cells that raises blood glucose which the blastula-stage embryo folds inward, hereditary variation. levels. It promotes glycogen breakdown and producing a three-layered embryo, the gastrula. genome (je¯Ј-no–m) The genetic material of an or- release of glucose by the liver. gated channel A transmembrane protein ganism or virus; the complete complement of glucocorticoid A steroid hormone that is secreted channel that opens or closes in response to a an organism’s or virus’s genes along with its by the adrenal cortex and that inﬂuences particular stimulus. noncoding nucleic acid sequences. glucose metabolism and immune function. gated ion channel A gated channel for a genome-wide association study A large-scale glutamate An amino acid that functions as a speciﬁc ion. The opening or closing of such analysis of the genomes of many people hav- neurotransmitter in the central nervous system.
G–15 GLOSSARY glyceraldehyde 3-phosphate (G3P) (glisЈ-er- some of whose members are more closely re- heart rate The frequency of heart contraction (in alЈ-de-hı¯d) A three-carbon carbohydrate that is lated to land plants than they are to other beats per minute). the direct product of the Calvin cycle; it is also green algae. heat The total amount of kinetic energy due to an intermediate in glycolysis. greenhouse effect The warming of Earth due to the random motion of atoms or molecules glycogen (glı¯Ј-ko– -jen) An extensively branched the atmospheric accumulation of carbon in a body of matter; also called thermal glucose storage polysaccharide found in the dioxide and certain other gases, which absorb energy. Heat is energy in its most random liver and muscle of animals; the animal reﬂected infrared radiation and reradiate some form. equivalent of starch. of it back toward Earth. heat of vaporization The quantity of heat a glycolipid A lipid with one or more covalently gross primary production (GPP) The total liquid must absorb for 1 g of it to be converted attached carbohydrates. primary production of an ecosystem. from the liquid to the gaseous state. glycolysis (glı¯-kolЈ-uh-sis) A series of reactions ground tissue system Plant tissues that are nei- heat-shock protein A protein that helps protect Glossary that ultimately splits glucose into pyruvate. ther vascular nor dermal, fulﬁlling a variety of other proteins during heat stress. Heat-shock Glycolysis occurs in almost all living cells, functions, such as storage, photosynthesis, and proteins are found in plants, animals, and serving as the starting point for fermentation support. microorganisms. or cellular respiration. growth An irreversible increase in size or biomass. heavy chain One of the two types of polypep- glycoprotein A protein with one or more growth factor (1) A protein that must be pres- tide chains that make up an antibody molecule covalently attached carbohydrates. ent in the extracellular environment (culture and B cell receptor; consists of a variable glycosidic linkage A covalent bond formed be- medium or animal body) for the growth and region, which contributes to the antigen- tween two monosaccharides by a dehydration normal development of certain types of cells. binding site, and a constant region. reaction. (2) A local regulator that acts on nearby helicase An enzyme that untwists the double gnathostome (naЈ-thu-sto–m) Member of the cells to stimulate cell proliferation and helix of DNA at replication forks, separating vertebrate subgroup possessing jaws. differentiation. the two strands and making them available as golden alga A biﬂagellated, photosynthetic growth hormone (GH) A hormone that is pro- template strands. protist named for its color, which results from duced and secreted by the anterior pituitary helper T cell A type of T cell that, when its yellow and brown carotenoids. and that has both direct (nontropic) and tropic activated, secretes cytokines that promote Golgi apparatus (golЈ-je¯) An organelle in effects on a wide variety of tissues. the response of B cells (humoral response) eukaryotic cells consisting of stacks of ﬂat guard cells The two cells that ﬂank the stomatal and cytotoxic T cells (cell-mediated response) membranous sacs that modify, store, and pore and regulate the opening and closing of to antigens. route products of the endoplasmic reticulum the pore. hemoglobin (he¯Ј-mo–-glo–Ј-bin) An iron-containing and synthesize some products, notably gustation The sense of taste. protein in red blood cells that reversibly binds noncellulose carbohydrates. guttation The exudation of water droplets from oxygen. gonads (go–Ј-nadz) The male and female sex leaves, caused by root pressure in certain plants. hemolymph (he¯Ј-mo– -limfЈ) In invertebrates organs; the gamete-producing organs in gymnosperm (jimЈ-no– -sperm) A vascular plant with an open circulatory system, the body most animals. that bears naked seeds—seeds not enclosed in ﬂuid that bathes tissues. grade A group of organisms that share the same protective chambers. hemophilia (he¯Ј-muh-ﬁlЈ-e¯-uh) A human level of organizational complexity or share a hair cell A mechanosensory cell that alters genetic disease caused by a sex-linked key adaptation. output to the nervous system when hairlike recessive allele resulting in the absence of one graded potential In a neuron, a shift in the projections on the cell surface are displaced. or more blood-clotting proteins; characterized membrane potential that has an amplitude half-life The amount of time it takes for 50% of by excessive bleeding following injury. proportional to signal strength and that decays a sample of a radioactive isotope to decay. hepatic portal vein A large vessel that conveys as it spreads. Hamilton’s rule The principle that for natural nutrient-laden blood from the small intestine Gram stain A staining method that distin- selection to favor an altruistic act, the beneﬁt to the liver, which regulates the blood’s guishes between two different kinds of bacter- to the recipient, devalued by the coefﬁcient nutrient content. ial cell walls; may be used to help determine of relatedness, must exceed the cost to the herbivore (hurЈ-bi-vo–rЈ) An animal that mainly medical response to an infection. altruist. eats plants or algae. gram-negative Describing the group of bacteria haploid cell (hapЈ-loyd) A cell containing only herbivory An interaction in which an organism that have a cell wall that is structurally more one set of chromosomes (n). eats parts of a plant or alga. complex and contains less peptidoglycan than Hardy-Weinberg principle The principle that heredity The transmission of traits from one the cell wall of gram-positive bacteria. Gram- frequencies of alleles and genotypes in a popu- generation to the next. negative bacteria are often more toxic than lation remain constant from generation to hermaphrodite (hur-mafЈ-ruh-dı¯tЈ) An individ- gram-positive bacteria. generation, provided that only Mendelian ual that functions as both male and female in gram-positive Describing the group of bacteria segregation and recombination of alleles are sexual reproduction by producing both sperm that have a cell wall that is structurally less at work. and eggs. complex and contains more peptidoglycan haustorium (plural, haustoria) (ho-sto–rЈ-e¯-um, hermaphroditism (hur-mafЈ-ro– -dı¯-tizm) A con- than the cell wall of gram-negative bacteria. ho-sto–rЈ-e¯-uh) In certain symbiotic fungi, a dition in which an individual has both female Gram-positive bacteria are usually less toxic specialized hypha that can penetrate the and male gonads and functions as both a male than gram-negative bacteria. tissues of host organisms. and female in sexual reproduction by granum (granЈ-um) (plural, grana) A stack of heart A muscular pump that uses metabolic producing both sperm and eggs. membrane-bounded thylakoids in the chloro- energy to elevate the hydrostatic pressure of heterochromatin (hetЈ-er-o– -kro–Ј-muh-tin) plast. Grana function in the light reactions of the circulatory ﬂuid (blood or hemolymph). Eukaryotic chromatin that remains highly photosynthesis. The ﬂuid then ﬂows down a pressure gradient compacted during interphase and is generally gravitropism (gravЈ-uh-tro–Ј-pizm) A response of through the body and eventually returns to not transcribed. a plant or animal to gravity. the heart. heterochrony (hetЈ-uh-rokЈ-ruh-ne¯) Evolution- gray matter Regions of dendrites and clustered heart attack The damage or death of cardiac ary change in the timing or rate of an neuron cell bodies within the CNS. muscle tissue resulting from prolonged block- organism’s development. green alga A photosynthetic protist, named for age of one or more coronary arteries. heterocyst (hetЈ-er-o– -sist) A specialized cell green chloroplasts that are similar in structure heart murmur A hissing sound that most often that engages in nitrogen ﬁxation in some and pigment composition to those of land results from blood squirting backward through ﬁlamentous cyanobacteria; also called a plants. Green algae are a paraphyletic group, a leaky valve in the heart. heterocyte.
GLOSSARY G–16 heterokaryon (hetЈ-er-o– -ka–rЈ-e¯-un) A fungal plants, and fungi by controlling the develop- Huntington’s disease A human genetic disease mycelium that contains two or more haploid mental fate of groups of cells. caused by a dominant allele; characterized by nuclei per cell. hominin (ho–Ј-mi-nin) A member of the human uncontrollable body movements and degener- heteromorphic (hetЈ-er-o– -mo–rЈ-ﬁk) Referring to branch of the evolutionary tree. Hominins in- ation of the nervous system; usually fatal 10 to a condition in the life cycle of plants and cer- clude Homo sapiens and our ancestors, a group 20 years after the onset of symptoms. tain algae in which the sporophyte and game- of extinct species that are more closely related hybrid Offspring that results from the mating of tophyte generations differ in morphology. to us than to chimpanzees. individuals from two different species or from heterosporous (het-er-osЈ-po–r-us) Referring to a homologous chromosomes (ho– -molЈ-uh-gus) two true-breeding varieties of the same species. plant species that has two kinds of spores: A pair of chromosomes of the same length, hybrid zone A geographic region in which microspores, which develop into male centromere position, and staining pattern that members of different species meet and mate,
Glossary gametophytes, and megaspores, which possess genes for the same characters at corre- producing at least some offspring of mixed develop into female gametophytes. sponding loci. One homologous chromosome ancestry. heterotroph (hetЈ-er-o– -tro–f) An organism that is inherited from the organism’s father, the hybridization In genetics, the mating, or cross- obtains organic food molecules by eating other other from the mother. Also called homologs, ing, of two true-breeding varieties. organisms or substances derived from them. or a homologous pair. hydration shell The sphere of water molecules heterozygote advantage Greater reproductive homologous structures Structures in different around a dissolved ion. success of heterozygous individuals compared species that are similar because of common hydrocarbon An organic molecule consisting with homozygotes; tends to preserve variation ancestry. only of carbon and hydrogen. in a gene pool. homology (ho– -molЈ-o– -je¯) Similarity in character- hydrogen bond A type of weak chemical bond heterozygous (hetЈ-er-o– -zı¯Ј-gus) Having two istics resulting from a shared ancestry. that is formed when the slightly positive different alleles for a given gene. homoplasy (ho–Ј-muh-playЈ-ze¯) A similar (analo- hydrogen atom of a polar covalent bond in hexapod An insect or closely related wingless, gous) structure or molecular sequence that has one molecule is attracted to the slightly six-legged arthropod. evolved independently in two species. negative atom of a polar covalent bond in hibernation A long-term physiological state homosporous (ho– -mosЈ-puh-rus) Referring to a another molecule or in another region of in which metabolism decreases, the heart and plant species that has a single kind of spore, the same molecule. respiratory system slow down, and body which typically develops into a bisexual hydrogen ion A single proton with a charge of ϩ temperature is maintained at a lower level gametophyte. 1 . The dissociation of a water molecule (H2O) than normal. homozygous (ho–Ј-mo– -zı¯Ј-gus) Having two leads to the generation of a hydroxide ion ϩ ϩ high-density lipoprotein (HDL) A particle in identical alleles for a given gene. (OH–) and a hydrogen ion (H ); in water, H is the blood made up of thousands of cholesterol horizontal cell A neuron of the retina that not found alone but associates with a water molecules and other lipids bound to a protein. helps integrate the information that is sent to molecule to form a hydronium ion. HDL scavenges excess cholesterol. the brain. hydrolysis (hı¯-drolЈ-uh-sis) A chemical reaction hindbrain One of three ancestral and embry- horizontal gene transfer The transfer of genes that breaks bonds between two molecules by onic regions of the vertebrate brain; develops from one genome to another through mecha- the addition of water; functions in disassembly into the medulla oblongata, pons, and nisms such as transposable elements, plasmid of polymers to monomers. cerebellum. exchange, viral activity, and perhaps fusions of hydronium ion A water molecule that has an Ј ϩ histamine (his -tuh-me¯n) A substance released different organisms. extra proton bound to it; H3O , commonly ϩ by mast cells that causes blood vessels to dilate hormone In multicellular organisms, one of represented as H . and become more permeable in inﬂammatory many types of secreted chemicals that are hydrophilic (hı¯Ј-dro– -ﬁlЈ-ik) Having an afﬁnity and allergic responses. formed in specialized cells, travel in body ﬂu- for water. histone (hisЈ-to–n) A small protein with a high ids, and act on speciﬁc target cells in other hydrophobic (hı¯Ј-dro– -fo–Ј-bik) Having no afﬁnity proportion of positively charged amino acids parts of the body, changing the target cells’ for water; tending to coalesce and form that binds to the negatively charged DNA and functioning. Hormones are thus important in droplets in water. plays a key role in chromatin structure. long-distance signaling. hydrophobic interaction A type of weak histone acetylation The attachment of acetyl hornwort A small, herbaceous, nonvascular chemical interaction caused when molecules groups to certain amino acids of histone plant that is a member of the phylum that do not mix with water coalesce to proteins. Anthocerophyta. exclude water. HIV (human immunodeﬁciency virus) The host The larger participant in a symbiotic hydroponic culture A method in which plants infectious agent that causes AIDS. HIV is a relationship, often providing a home and are grown in mineral solutions rather than retrovirus. food source for the smaller symbiont. in soil. holdfast A rootlike structure that anchors a host range The limited number of species whose hydrostatic skeleton A skeletal system com- seaweed. cells can be infected by a particular virus. posed of ﬂuid held under pressure in a closed holoblastic (ho– Ј-lo– -blasЈ-tik) Referring to a type human chorionic gonadotropin body compartment; the main skeleton of of cleavage in which there is complete divi- (hCG) (ko–rЈ-e¯-onЈ-ik go– -naЈ-do– -tro–Ј-pin) A hor- most cnidarians, ﬂatworms, nematodes, and sion of the egg; occurs in eggs that have little mone secreted by the chorion that maintains annelids. yolk (such as those of the sea urchin) or a the corpus luteum of the ovary during the ﬁrst hydroxide ion A water molecule that has lost a moderate amount of yolk (such as those of three months of pregnancy. proton; OH–. the frog). Human Genome Project An international hydroxyl group (hı¯-drokЈ-sil) A chemical group homeobox (ho–Ј-me¯-o– -boksЈ) A 180-nucleotide collaborative effort to map and sequence the consisting of an oxygen atom joined to a hy- sequence within homeotic genes and some DNA of the entire human genome. drogen atom. Molecules possessing this group other developmental genes that is widely humoral immune response (hyu¯Ј-mer-ul) are soluble in water and are called alcohols. conserved in animals. Related sequences The branch of adaptive immunity that hymen A thin membrane that partly covers the occur in plants and yeasts. involves the activation of B cells and that vaginal opening in the human female. The homeostasis (ho–Ј-me¯-o– -sta–Ј-sis) The steady-state leads to the production of antibodies, which hymen is ruptured by sexual intercourse or physiological condition of the body. defend against bacteria and viruses in body other vigorous activity. homeotic gene (ho– -me¯-oЈ-tik) Any of the master ﬂuids. hyperpolarization A change in a cell’s mem- regulatory genes that control placement and humus (hyu¯Ј-mus) Decomposing organic brane potential such that the inside of the mem- spatial organization of body parts in animals, material that is a component of topsoil. brane becomes more negative relative to the
G–17 GLOSSARY outside. Hyperpolarization reduces the chance in vitro mutagenesis A technique used to transmitter from a presynaptic cell to a post- that a neuron will transmit a nerve impulse. discover the function of a gene by cloning it, synaptic receptor; makes it more difﬁcult for hypersensitive response A plant’s localized de- introducing speciﬁc changes into the cloned a postsynaptic neuron to generate an action fense response to a pathogen, involving the gene’s sequence, reinserting the mutated gene potential. death of cells around the site of infection. into a cell, and studying the phenotype of the innate behavior Animal behavior that is devel- hypertension A disorder in which blood mutant. opmentally ﬁxed and under strong genetic pressure remains abnormally high. inclusive ﬁtness The total effect an individual control. Innate behavior is exhibited in hypertonic Referring to a solution that, when has on proliferating its genes by producing its virtually the same form by all individuals in surrounding a cell, will cause the cell to lose own offspring and by providing aid that a population despite internal and external water. enables other close relatives to increase environmental differences during development hypha (plural, hyphae) (hı¯Ј-fuh, hı¯Ј-fe¯) One of production of their offspring. and throughout their lifetimes. Glossary many connected ﬁlaments that collectively incomplete dominance The situation in innate immunity A form of defense common make up the mycelium of a fungus. which the phenotype of heterozygotes is to all animals that is active immediately upon hypocotyl (hı¯Ј-puh-cotЈ-ul) In an angiosperm intermediate between the phenotypes of exposure to pathogens and that is the same embryo, the embryonic axis below the point individuals homozygous for either allele. whether or not the pathogen has been of attachment of the cotyledon(s) and above incomplete ﬂower A ﬂower in which one or encountered previously. the radicle. more of the four basic ﬂoral organs (sepals, inner cell mass An inner cluster of cells at one hypothalamus (hı¯Ј-po– -thalЈ-uh-mus) The ven- petals, stamens, or carpels) are either absent or end of a mammalian blastocyst that subse- tral part of the vertebrate forebrain; functions nonfunctional. quently develops into the embryo proper and in maintaining homeostasis, especially in coor- incomplete metamorphosis A type of some of the extraembryonic membranes. dinating the endocrine and nervous systems; development in certain insects, such as inner ear One of three main regions of the verte- secretes hormones of the posterior pituitary grasshoppers, in which the young (called brate ear; includes the cochlea (which in turn and releasing factors that regulate the anterior nymphs) resemble adults but are smaller and contains the organ of Corti) and the semicircu- pituitary. have different body proportions. The nymph lar canals. Ј –Ј hypothesis (hı¯-poth -uh-sis) A testable explana- goes through a series of molts, each time inositol trisphosphate (IP3) (in-o -suh-tol) A tion for a set of observations based on the looking more like an adult, until it reaches second messenger that functions as an inter- available data and guided by inductive reason- full size. mediate between certain signaling molecules ϩ ing. A hypothesis is narrower in scope than a indeterminate cleavage A type of embryonic and a subsequent second messenger, Ca2 , ϩ theory. development in deuterostomes in which each by causing a rise in cytoplasmic Ca2 hypotonic Referring to a solution that, when cell produced by early cleavage divisions concentration. surrounding a cell, will cause the cell to take retains the capacity to develop into a inquiry The search for information and explana- up water. complete embryo. tion, often focusing on speciﬁc questions. imbibition The physical adsorption of water indeterminate growth A type of growth insertion A mutation involving the addition of onto the internal surfaces of structures. characteristic of plants, in which the organism one or more nucleotide pairs to a gene. immigration The inﬂux of new individuals into continues to grow as long as it lives. insulin (inЈ-suh-lin) A hormone secreted by a population from other areas. induced ﬁt Caused by entry of the substrate, the pancreatic beta cells that lowers blood glucose immune system An animal body’s system of change in shape of the active site of an enzyme levels. It promotes the uptake of glucose by defenses against agents that cause disease. so that it binds more snugly to the substrate. most body cells and the synthesis and storage immunization The process of generating a state inducer A speciﬁc small molecule that binds to a of glycogen in the liver and also stimulates of immunity by artiﬁcial means. In active bacterial repressor protein and changes the protein and fat synthesis. immunization, also called vaccination, an repressor’s shape so that it cannot bind to an integral protein A transmembrane protein inactive or weakened form of a pathogen is operator, thus switching an operon on. with hydrophobic regions that extend into administered, inducing B and T cell responses induction The process in which one group of and often completely span the hydrophobic and immunological memory. In passive immu- embryonic cells inﬂuences the development of interior of the membrane and with nization, antibodies speciﬁc for a particular mi- another, usually by causing changes in gene hydrophilic regions in contact with the crobe are administered, conferring immediate expression. aqueous solution on one or both sides of the but temporary protection. inductive reasoning A type of logic in which membrane (or lining the channel in the case immunodeﬁciency A disorder in which the generalizations are based on a large number of of a channel protein). ability of an immune system to protect against speciﬁc observations. integrin In animal cells, a transmembrane pathogens is defective or absent. inﬂammatory response An innate immune de- receptor protein with two subunits that immunoglobulin (Ig) (imЈ-yu¯-no– -globЈ-yu¯-lin) fense triggered by physical injury or infection interconnects the extracellular matrix and the Any of the class of proteins that function as of tissue involving the release of substances cytoskeleton. antibodies. Immunoglobulins are divided that promote swelling, enhance the inﬁltration integument (in-tegЈ-yu¯-ment) Layer of sporo- into ﬁve major classes that differ in their of white blood cells, and aid in tissue repair phyte tissue that contributes to the structure of distribution in the body and antigen disposal and destruction of invading pathogens. an ovule of a seed plant. activities. inﬂorescence A group of ﬂowers tightly integumentary system The outer covering of a imprinting In animal behavior, the formation clustered together. mammal’s body, including skin, hair, and at a speciﬁc stage in life of a long-lasting ingestion The ﬁrst stage of food processing in nails, claws, or hooves. behavioral response to a speciﬁc individual or animals: the act of eating. intercalated disk (in-terЈ-kuh-la–Ј-ted) A special- object. See also genomic imprinting. ingroup A species or group of species whose evo- ized junction between cardiac muscle cells in situ hybridization A technique using lutionary relationships we seek to determine. that provides direct electrical coupling nucleic acid hybridization with a labeled probe inhibin A hormone produced in the male and fe- between the cells. to detect the location of a speciﬁc mRNA in male gonads that functions in part by regulat- interferon (inЈ-ter-fe¯rЈ-on) A protein that has an intact organism. ing the anterior pituitary by negative feedback. antiviral or immune regulatory functions. in vitro fertilization (IVF) (ve¯Ј-tro–) Fertiliza- inhibitory postsynaptic potential (IPSP) An Interferon-α and interferon-β, secreted by tion of oocytes in laboratory containers electrical change (usually hyperpolarization) in virus-infected cells, help nearby cells resist followed by artiﬁcial implantation of the the membrane of a postsynaptic neuron viral infection; interferon-γ, secreted by T cells, early embryo in the mother’s uterus. caused by the binding of an inhibitory neuro- helps activate macrophages.
GLOSSARY G–18 intermediate disturbance hypothesis The membrane down its concentration or electro- kinetoplastid A protist, such as a trypanosome, concept that moderate levels of disturbance chemical gradient. that has a single large mitochondrion that can foster greater species diversity than low or ionic bond (ı¯-onЈ-ik) A chemical bond resulting houses an organized mass of DNA. high levels of disturbance. from the attraction between oppositely kingdom A taxonomic category, the second intermediate ﬁlament A component of the charged ions. broadest after domain. cytoskeleton that includes ﬁlaments ionic compound A compound resulting from the K-selection Selection for life history traits that intermediate in size between microtubules formation of an ionic bond; also called a salt. are sensitive to population density; also called and microﬁlaments. IPSP See inhibitory postsynaptic potential. density-dependent selection. internal fertilization The fusion of eggs and iris The colored part of the vertebrate eye, formed labia majora A pair of thick, fatty ridges that sperm within the female reproductive tract. by the anterior portion of the choroid. encloses and protects the rest of the vulva. – Glossary The sperm are typically deposited in or near isomer (ı¯Ј-so-mer) One of several compounds labia minora A pair of slender skin folds that the tract. with the same molecular formula but different surrounds the openings of the vagina and interneuron An association neuron; a nerve cell structures and therefore different properties. urethra. within the central nervous system that forms The three types of isomers are structural labor A series of strong, rhythmic contractions of synapses with sensory and/or motor neurons isomers, cis-trans isomers, and enantiomers. the uterus that expels a baby out of the uterus and integrates sensory input and motor output. isomorphic Referring to alternating generations and vagina during childbirth. internode A segment of a plant stem between in plants and certain algae in which the lactation The continued production of milk the points where leaves are attached. sporophytes and gametophytes look alike, from the mammary glands. interphase The period in the cell cycle when the although they differ in chromosome number. lacteal (lakЈ-te¯-ul) A tiny lymph vessel extending cell is not dividing. During interphase, cellular isopod A member of one of the largest groups of into the core of an intestinal villus and serving metabolic activity is high, chromosomes and crustaceans, which includes terrestrial, fresh- as the destination for absorbed chylomicrons. organelles are duplicated, and cell size may in- water, and marine species. Among the terres- lactic acid fermentation Glycolysis followed crease. Interphase often accounts for about trial isopods are the pill bugs, or wood lice. by the reduction of pyruvate to lactate, ϩ 90% of the cell cycle. isotonic (ı¯Ј-so– -tonЈ-ik) Referring to a solution regenerating NAD with no release of carbon intersexual selection Selection whereby indi- that, when surrounding a cell, causes no net dioxide. viduals of one sex (usually females) are choosy movement of water into or out of the cell. lagging strand A discontinuously synthesized in selecting their mates from individuals of the isotope (ı¯Ј-so– -to–pЈ) One of several atomic forms DNA strand that elongates by means of Okazaki other sex; also called mate choice. of an element, each with the same number of fragments, each synthesized in a 5Ј S 3Ј interspeciﬁc competition Competition for re- protons but a different number of neutrons, direction away from the replication fork. sources between individuals of two or more thus differing in atomic mass. lancelet Member of the clade Cephalochordata, species when resources are in short supply. iteroparity Reproduction in which adults small blade-shaped marine chordates that lack interspeciﬁc interaction A relationship produce offspring over many years; also a backbone. between individuals of two or more species known as repeated reproduction. landscape An area containing several different in a community. joule (J) A unit of energy: 1 J ϭ 0.239 cal; ecosystems linked by exchanges of energy, interstitial ﬂuid The ﬂuid ﬁlling the spaces 1 cal ϭ 4.184 J. materials, and organisms. between cells in most animals. juxtaglomerular apparatus (JGA) (juksЈ-tuh- landscape ecology The study of how the spatial intertidal zone The shallow zone of the ocean gluh-ma–rЈ-yu¯-ler) A specialized tissue in arrangement of habitat types affects the adjacent to land and between the high- and nephrons that releases the enzyme renin in re- distribution and abundance of organisms and low-tide lines. sponse to a drop in blood pressure or volume. ecosystem processes. intracytoplasmic sperm injection (ICSI) The juxtamedullary nephron In mammals and large intestine The portion of the vertebrate fertilization of an egg in the laboratory by the birds, a nephron with a loop of Henle that alimentary canal between the small intestine direct injection of a single sperm. extends far into the renal medulla. and the anus; functions mainly in water intrasexual selection Selection in which there karyogamy (ka–rЈ-e¯-ogЈ-uh-me¯) In fungi, the absorption and the formation of feces. is direct competition among individuals of one fusion of haploid nuclei contributed by the larva (larЈ-vuh) (plural, larvae) A free-living, sex for mates of the opposite sex. two parents; occurs as one stage of sexual sexually immature form in some animal life introduced species A species moved by hu- reproduction, preceded by plasmogamy. cycles that may differ from the adult animal in mans, either intentionally or accidentally, karyotype (ka–rЈ-e¯-o– -tı¯p) A display of the chromo- morphology, nutrition, and habitat. from its native location to a new geographic some pairs of a cell arranged by size and shape. larynx (la–rЈ-inks) The portion of the respiratory region; also called non-native or exotic species. keystone species A species that is not necessar- tract containing the vocal cords; also called the intron (inЈ-tron) A noncoding, intervening ily abundant in a community yet exerts strong voice box. sequence within a primary transcript that is control on community structure by the nature lateral geniculate nucleus One of a pair of removed from the transcript during RNA of its ecological role or niche. structures in the brain that are the destination processing; also refers to the region of DNA kidney In vertebrates, one of a pair of excretory for most of the ganglion cell axons that form from which this sequence was transcribed. organs where blood ﬁltrate is formed and the optic nerves. invasive species A species, often introduced by processed into urine. lateral inhibition A process that sharpens the humans, that takes hold outside its native kilocalorie (kcal) A thousand calories; the edges and enhances the contrast of a perceived range. amount of heat energy required to raise the image by inhibiting receptors lateral to those inversion An aberration in chromosome struc- temperature of 1 kg of water by 1°C. that have responded to light. ture resulting from reattachment of a chromo- kin selection Natural selection that favors lateral line system A mechanoreceptor system somal fragment in a reverse orientation to the altruistic behavior by enhancing the consisting of a series of pores and receptor chromosome from which it originated. reproductive success of relatives. units along the sides of the body in ﬁshes and invertebrate An animal without a backbone. kinetic energy (kuh-netЈ-ik) The energy associ- aquatic amphibians; detects water movements Invertebrates make up 95% of animal species. ated with the relative motion of objects. Mov- made by the animal itself and by other ion (ı¯Ј-on) An atom or group of atoms that has ing matter can perform work by imparting moving objects. gained or lost one or more electrons, thus motion to other matter. lateral meristem (ma–rЈ-uh-stem) A meristem acquiring a charge. kinetochore (kuh-netЈ-uh-ko–r) A structure of that thickens the roots and shoots of woody ion channel A transmembrane protein channel proteins attached to the centromere that links plants. The vascular cambium and cork that allows a speciﬁc ion to diffuse across the each sister chromatid to the mitotic spindle. cambium are lateral meristems.
G–19 GLOSSARY lateral root A root that arises from the pericycle molecule (ligand), allowing or blocking the logistic population growth Population of an established root. ﬂow of speciﬁc ions; also called an ionotropic growth that levels off as population size lateralization Segregation of functions in receptor. approaches carrying capacity. the cortex of the left and right cerebral light chain One of the two types of polypeptide long-day plant A plant that ﬂowers (usually in hemispheres. chains that make up an antibody molecule and late spring or early summer) only when the law of conservation of mass A physical law B cell receptor; consists of a variable region, light period is longer than a critical length. stating that matter can change form but can- which contributes to the antigen-binding site, long-term memory The ability to hold, associ- not be created or destroyed. In a closed system, and a constant region. ate, and recall information over one’s lifetime. the mass of the system is constant. light microscope (LM) An optical instrument long-term potentiation (LTP) An enhanced law of independent assortment Mendel’s with lenses that refract (bend) visible light to responsiveness to an action potential (nerve
second law, stating that each pair of alleles magnify images of specimens. signal) by a receiving neuron. Glossary segregates, or assorts, independently of each light reactions The ﬁrst of two major stages in loop of Henle The hairpin turn, with a descend- other pair during gamete formation; applies photosynthesis (preceding the Calvin cycle). ing and ascending limb, between the proximal when genes for two characters are located on These reactions, which occur on the thylakoid and distal tubules of the vertebrate kidney; different pairs of homologous chromosomes membranes of the chloroplast or on mem- functions in water and salt reabsorption. or when they are far enough apart on the branes of certain prokaryotes, convert solar lophophore (lofЈ-uh-fo–r) In some lophotro- same chromosome to behave as though they energy to the chemical energy of ATP and chozoan animals, including brachiopods, a are on different chromosomes. NADPH, releasing oxygen in the process. crown of ciliated tentacles that surround the law of segregation Mendel’s ﬁrst law, stating light-harvesting complex A complex of pro- mouth and function in feeding. that the two alleles in a pair segregate (separate teins associated with pigment molecules lophotrochozoan Member of a group of animal from each other) into different gametes during (including chlorophyll a, chlorophyll b, phyla identiﬁed as a clade by molecular evi- gamete formation. and carotenoids) that captures light energy dence. Lophotrochozoans include organisms leading strand The new complementary DNA and transfers it to reaction-center pigments that have lophophores or trochophore larvae. strand synthesized continuously along the in a photosystem. low-density lipoprotein (LDL) A particle in template strand toward the replication fork in lignin (ligЈ-nin) A hard material embedded in the the blood made up of thousands of cholesterol the mandatory 5Ј S 3Ј direction. cellulose matrix of vascular plant cell walls molecules and other lipids bound to a protein. leaf The main photosynthetic organ of vascular that provides structural support in terrestrial LDL transports cholesterol from the liver for plants. species. incorporation into cell membranes. leaf primordium A ﬁnger-like projection along limiting nutrient An element that must be added lung An infolded respiratory surface of a terres- the ﬂank of a shoot apical meristem, from for production to increase in a particular area. trial vertebrate, land snail, or spider that con- which a leaf arises. limnetic zone In a lake, the well-lit, open nects to the atmosphere by narrow tubes. learning The modiﬁcation of behavior based on surface waters far from shore. luteal phase That portion of the ovarian cycle speciﬁc experiences. linear electron ﬂow A route of electron ﬂow during which endocrine cells of the corpus lens The structure in an eye that focuses light during the light reactions of photosynthesis luteum secrete female hormones. rays onto the photoreceptors. that involves both photosystems (I and II) and luteinizing hormone (LH) (lu¯Ј-te¯-uh-nı¯Ј-zing) Ј lenticel (len -ti-sel) A small raised area in the produces ATP, NADPH, and O2. The net A tropic hormone that is produced and ϩ bark of stems and roots that enables gas ex- electron ﬂow is from H2O to NADP . secreted by the anterior pituitary and that change between living cells and the outside air. linkage map A genetic map based on the stimulates ovulation in females and androgen lepidosaur (leh-pidЈ-uh-so–r) Member of the frequencies of recombination between production in males. reptilian group that includes lizards, snakes, markers during crossing over of homologous lycophyte (lı¯Ј-kuh-fı¯t) An informal name for a and two species of New Zealand animals called chromosomes. member of the phylum Lycophyta, which tuataras. linked genes Genes located close enough includes club mosses, spike mosses, and leptin A hormone produced by adipose (fat) together on a chromosome that they tend to quillworts. cells that acts as a satiety factor in regulating be inherited together. lymph The colorless ﬂuid, derived from appetite. lipid (lipЈ-id) Any of a group of large biological interstitial ﬂuid, in the lymphatic system leukocyte (lu¯Ј-ko– -sı¯tЈ) A blood cell that molecules, including fats, phospholipids, and of vertebrates. functions in ﬁghting infections; also called a steroids, that mix poorly, if at all, with water. lymph node An organ located along a lymph white blood cell. littoral zone In a lake, the shallow, well-lit vessel. Lymph nodes ﬁlter lymph and contain Leydig cell (lı¯Ј-dig) A cell that produces testos- waters close to shore. cells that attack viruses and bacteria. terone and other androgens and is located be- liver A large internal organ in vertebrates that lymphatic system A system of vessels and tween the seminiferous tubules of the testes. performs diverse functions, such as producing nodes, separate from the circulatory system, lichen The mutualistic association between bile, maintaining blood glucose level, and that returns ﬂuid, proteins, and cells to the a fungus and a photosynthetic alga or detoxifying poisonous chemicals in the blood. blood. cyanobacterium. liverwort A small, herbaceous, nonvascular lymphocyte A type of white blood cell that life cycle The generation-to-generation sequence plant that is a member of the phylum mediates immune responses. The two main of stages in the reproductive history of an Hepatophyta. classes are B cells and T cells. organism. loam The most fertile soil type, made up of lysogenic cycle (lı¯Ј-so– -jenЈ-ik) A type of phage life history The traits that affect an organism’s roughly equal amounts of sand, silt, and clay. replicative cycle in which the viral genome schedule of reproduction and survival. lobe-ﬁn Member of the vertebrate clade becomes incorporated into the bacterial host life table An age-speciﬁc summary of the Sarcopterygii, osteichthyans with rod- chromosome as a prophage, is replicated survival pattern of a population. shaped muscular ﬁns, including coelacanths, along with the chromosome, and does not ligament A ﬁbrous connective tissue that joins lungﬁshes, and tetrapods. kill the host. bones together at joints. local regulator A secreted molecule that lysosome (lı¯Ј-suh-so–m) A membrane-enclosed ligand (ligЈ-und) A molecule that binds speciﬁ- inﬂuences cells near where it is secreted. sac of hydrolytic enzymes found in the cyto- cally to another molecule, usually a larger one. locomotion Active motion from place to place. plasm of animal cells and some protists. ligand-gated ion channel A transmembrane locus (lo–Ј-kus) (plural, loci) A speciﬁc place along lysozyme (lı¯Ј-so–-zı¯m) An enzyme that destroys protein containing a pore that opens or closes the length of a chromosome where a given bacterial cell walls; in mammals, found in as it changes shape in response to a signaling gene is located. sweat, tears, and saliva.
GLOSSARY G–20 lytic cycle (litЈ-ik) A type of phage replicative mark-recapture method A sampling technique meiosis I The ﬁrst division of a two-stage process cycle resulting in the release of new phages by used to estimate the size of animal populations. of cell division in sexually reproducing organ- lysis (and death) of the host cell. marsupial (mar-su¯Ј-pe¯-ul) A mammal, such as a isms that results in cells with half the number macroclimate Large-scale patterns in climate; koala, kangaroo, or opossum, whose young of chromosome sets as the original cell. the climate of an entire region. complete their embryonic development inside meiosis II The second division of a two-stage macroevolution Evolutionary change above a maternal pouch called the marsupium. process of cell division in sexually reproducing the species level. Examples of macro- mass extinction The elimination of a large organisms that results in cells with half the evolutionary change include the origin of a number of species throughout Earth, the result number of chromosome sets as the original cell. new group of organisms through a series of of global environmental changes. melanocyte-stimulating hormone (MSH) A speciation events and the impact of mass mass number The sum of the number of hormone produced and secreted by the
Glossary extinctions on the diversity of life and its protons and neutrons in an atom’s nucleus. anterior pituitary with multiple activities, subsequent recovery. mast cell A vertebrate body cell that produces including regulating the behavior of macromolecule A giant molecule formed by the histamine and other molecules that trigger pigment-containing cells in the skin of some joining of smaller molecules, usually by a inﬂammation in response to infection and in vertebrates. dehydration reaction. Polysaccharides, allergic reactions. melatonin A hormone that is secreted by the proteins, and nucleic acids are macromolecules. mate-choice copying Behavior in which indi- pineal gland and that is involved in the regula- macronutrient An essential element that an viduals in a population copy the mate choice of tion of biological rhythms and sleep. organism must obtain in relatively large others, apparently as a result of social learning. membrane potential The difference in electri- amounts. See also micronutrient. maternal effect gene A gene that, when cal charge (voltage) across a cell’s plasma mem- macrophage (makЈ-ro– -fa–j) A phagocytic cell pres- mutant in the mother, results in a mutant brane due to the differential distribution of ent in many tissues that functions in innate phenotype in the offspring, regardless of the ions. Membrane potential affects the activity immunity by destroying microbes and in ac- offspring’s genotype. Maternal effect genes, of excitable cells and the transmembrane quired immunity as an antigen-presenting cell. also called egg-polarity genes, were ﬁrst movement of all charged substances. magnoliid Member of the angiosperm clade identiﬁed in Drosophila melanogaster. memory cell One of a clone of long-lived lym- that is most closely related to the combined matter Anything that takes up space and has mass. phocytes, formed during the primary immune eudicot and monocot clades. Extant examples maximum likelihood As applied to molecular response, that remains in a lymphoid organ are magnolias, laurels, and black pepper systematics, a principle that states that when until activated by exposure to the same anti- plants. considering multiple phylogenetic hypotheses, gen that triggered its formation. Activated major depressive disorder A mood disorder one should take into account the hypothesis memory cells mount the secondary immune characterized by feelings of sadness, lack of that reﬂects the most likely sequence of evolu- response. self-worth, emptiness, or loss of interest in tionary events, given certain rules about how menopause The cessation of ovulation and nearly all things. DNA changes over time. menstruation marking the end of a human major histocompatibility complex (MHC) maximum parsimony A principle that states female’s reproductive years. molecule A host protein that functions in that when considering multiple explanations menstrual cycle (menЈ-stru¯-ul) In humans and antigen presentation. Foreign MHC molecules for an observation, one should ﬁrst investigate certain other primates, a type of reproductive on transplanted tissue can trigger T cell the simplest explanation that is consistent cycle in which the nonpregnant endometrium responses that may lead to rejection of the with the facts. is shed through the cervix into the vagina; also transplant. mechanoreceptor A sensory receptor that called the uterine cycle. malignant tumor A cancerous tumor contain- detects physical deformation in the body’s menstrual ﬂow phase That portion of the ing cells that have signiﬁcant genetic and cel- environment associated with pressure, touch, uterine (menstrual) cycle when menstrual lular changes and are capable of invading and stretch, motion, or sound. bleeding occurs. surviving in new sites. Malignant tumors can medulla oblongata (meh-dulЈ-uh o–bЈ-long-goЈ- menstruation The shedding of portions of the impair the functions of one or more organs. tuh) The lowest part of the vertebrate brain, endometrium during a uterine (menstrual) Malpighian tubule (mal-pigЈ-e¯-un) A unique commonly called the medulla; a swelling of cycle. excretory organ of insects that empties into the hindbrain anterior to the spinal cord that meristem (ma–rЈ-uh-stem) Plant tissue that the digestive tract, removes nitrogenous controls autonomic, homeostatic functions, remains embryonic as long as the plant lives, wastes from the hemolymph, and functions including breathing, heart and blood vessel allowing for indeterminate growth. in osmoregulation. activity, swallowing, digestion, and vomiting. meristem identity gene A plant gene that mammal Member of the class Mammalia, Medusa (plural, medusae) (muh-du¯Ј-suh) The promotes the switch from vegetative growth amniotes that have hair and mammary ﬂoating, ﬂattened, mouth-down version of to ﬂowering. glands (glands that produce milk). the cnidarian body plan. The alternate form meroblastic (ma–rЈ-o– -blasЈ-tik) Referring to a type mammary gland An exocrine gland that se- is the polyp. of cleavage in which there is incomplete cretes milk to nourish the young. Mammary megapascal (MPa) (megЈ-uh-pas-kalЈ) A unit of division of a yolk-rich egg, characteristic of glands are characteristic of mammals. pressure equivalent to about 10 atmospheres of avian development. mandible One of a pair of jaw-like feeding pressure. mesoderm (mezЈ-o– -derm) The middle primary appendages found in myriapods, hexapods, megaphyll (mehЈ-guh-ﬁl) A leaf with a highly germ layer in a triploblastic animal embryo; and crustaceans. branched vascular system, characteristic of develops into the notochord, the lining of the mantle One of the three main parts of a mollusc; the vast majority of vascular plants. See coelom, muscles, skeleton, gonads, kidneys, a fold of tissue that drapes over the mollusc’s microphyll. and most of the circulatory system in species visceral mass and may secrete a shell. See also megaspore A spore from a heterosporous that have these structures. foot, visceral mass. plant species that develops into a female mesohyl (mezЈ-o– -hı¯l) A gelatinous region mantle cavity A water-ﬁlled chamber that gametophyte. between the two layers of cells of a sponge. houses the gills, anus, and excretory pores of a meiosis (mı¯-o–Ј-sis) A modiﬁed type of cell divi- mesophyll (mezЈ-o– -ﬁl) Leaf cells specialized
mollusc. sion in sexually reproducing organisms con- for photosynthesis. In C3 and CAM plants, map unit A unit of measurement of the distance sisting of two rounds of cell division but only mesophyll cells are located between the upper
between genes. One map unit is equivalent to one round of DNA replication. It results in and lower epidermis; in C4 plants, they are a 1% recombination frequency. cells with half the number of chromosome sets located between the bundle-sheath cells and marine benthic zone The ocean ﬂoor. as the original cell. the epidermis.
G–21 GLOSSARY messenger RNA (mRNA) A type of RNA, syn- micronutrient An essential element that an metaphase, anaphase, and telophase. Mitosis thesized using a DNA template, that attaches organism needs in very small amounts. See conserves chromosome number by allocating to ribosomes in the cytoplasm and speciﬁes also macronutrient. replicated chromosomes equally to each of the the primary structure of a protein. (In eukary- microphyll (mı¯Ј-kro– -ﬁl) In lycophytes, a small daughter nuclei. otes, the primary RNA transcript must undergo leaf with a single unbranched vein. See mitotic (M) phase The phase of the cell cycle RNA processing to become mRNA.) megaphyll. that includes mitosis and cytokinesis. metabolic pathway A series of chemical reac- micropyle A pore in the integuments of an mitotic spindle An assemblage of microtubules tions that either builds a complex molecule ovule. and associated proteins that is involved in the (anabolic pathway) or breaks down a complex microRNA (miRNA) A small, single-stranded movement of chromosomes during mitosis. molecule to simpler molecules (catabolic RNA molecule, generated from a hairpin struc- mixotroph An organism that is capable of both
pathway). ture on a precursor RNA transcribed from a photosynthesis and heterotrophy. Glossary metabolic rate The total amount of energy an particular gene. The miRNA associates with model organism A particular species chosen for animal uses in a unit of time. one or more proteins in a complex that can research into broad biological principles metabolism (muh-tabЈ-uh-lizm) The totality of degrade or prevent translation of an mRNA because it is representative of a larger group an organism’s chemical reactions, consisting of with a complementary sequence. and usually easy to grow in a lab. catabolic and anabolic pathways, which microspore A spore from a heterosporous plant molarity A common measure of solute concen- manage the material and energy resources of species that develops into a male gametophyte. tration, referring to the number of moles of the organism. microtubule A hollow rod composed of tubulin solute per liter of solution. metagenomics The collection and sequencing proteins that makes up part of the cytoskele- mold Informal term for a fungus that grows as a of DNA from a group of species, usually an ton in all eukaryotic cells and is found in cilia ﬁlamentous fungus, producing haploid spores environmental sample of microorganisms. and ﬂagella. by mitosis and forming a visible mycelium. Computer software sorts partial sequences microvillus (plural, microvilli) One of many mole (mol) The number of grams of a substance and assembles them into genome sequences ﬁne, ﬁnger-like projections of the epithelial that equals its molecular weight in daltons and of individual species making up the sample. cells in the lumen of the small intestine that contains Avogadro’s number of molecules. metamorphosis (metЈ-uh-mo–rЈ-fuh-sis) A devel- increase its surface area. molecular clock A method for estimating the opmental transformation that turns an animal midbrain One of three ancestral and embryonic time required for a given amount of evolu- larva into either an adult or an adult-like stage regions of the vertebrate brain; develops into tionary change, based on the observation that is not yet sexually mature. sensory integrating and relay centers that send that some regions of genomes evolve at metanephridium (metЈ-uh-nuh-fridЈ-e¯-um) sensory information to the cerebrum. constant rates. (plural, metanephridia) An excretory organ middle ear One of three main regions of the molecular mass The sum of the masses of all found in many invertebrates that typically vertebrate ear; in mammals, a chamber the atoms in a molecule; sometimes called consists of tubules connecting ciliated internal containing three small bones (the malleus, molecular weight. openings to external openings. incus, and stapes) that convey vibrations from molecular systematics A scientiﬁc discipline metaphase The third stage of mitosis, in which the eardrum to the oval window. that uses nucleic acids or other molecules to the spindle is complete and the chromosomes, middle lamella (luh-melЈ-uh) In plants, a thin infer evolutionary relationships between attached to microtubules at their kinetochores, layer of adhesive extracellular material, prima- different species. are all aligned at the metaphase plate. rily pectins, found between the primary walls molecule Two or more atoms held together by metaphase plate An imaginary structure lo- of adjacent young cells. covalent bonds. cated at a plane midway between the two poles migration A regular, long-distance change in molting A process in ecdysozoans in which the of a cell in metaphase on which the cen- location. exoskeleton is shed at intervals, allowing tromeres of all the duplicated chromosomes mineral In nutrition, a simple nutrient that is growth by the production of a larger are located. inorganic and therefore cannot be synthesized exoskeleton. metapopulation A group of spatially separated in the body. monoclonal antibody (monЈ-o– -klo–nЈ-ul) Any populations of one species that interact mineralocorticoid A steroid hormone secreted of a preparation of antibodies that have been through immigration and emigration. by the adrenal cortex that regulates salt and produced by a single clone of cultured cells metastasis (muh-tasЈ-tuh-sis) The spread of water homeostasis. and thus are all speciﬁc for the same epitope. cancer cells to locations distant from their minimum viable population (MVP) The monocot Member of a clade consisting of ﬂower- original site. smallest population size at which a species is ing plants that have one embryonic seed leaf, methanogen (meth-anЈ-o– -jen) An organism that able to sustain its numbers and survive. or cotyledon. produces methane as a waste product of the mismatch repair The cellular process that uses monogamous (muh-nogЈ-uh-mus) Referring to way it obtains energy. All known methanogens speciﬁc enzymes to remove and replace a type of relationship in which one male mates are in domain Archaea. incorrectly paired nucleotides. with just one female. methyl group A chemical group consisting of a missense mutation A nucleotide-pair substitu- monohybrid An organism that is heterozygous carbon bonded to three hydrogen atoms. The tion that results in a codon that codes for a with respect to a single gene of interest. All the methyl group may be attached to a carbon or different amino acid. offspring from a cross between parents to a different atom. mitochondrial matrix The compartment of homozygous for different alleles are mono- microclimate Climate patterns on a very ﬁne the mitochondrion enclosed by the inner hybrids. For example, parents of genotypes AA scale, such as the speciﬁc climatic conditions membrane and containing enzymes and and aa produce a monohybrid of genotype Aa. underneath a log. substrates for the citric acid cycle, as well as monohybrid cross A cross between two organ- microevolution Evolutionary change below the ribosomes and DNA. isms that are heterozygous for the character species level; change in the allele frequencies mitochondrion (mı¯Ј-to– -konЈ-dre¯-un) (plural, being followed (or the self-pollination of a in a population over generations. mitochondria) An organelle in eukaryotic heterozygous plant). microﬁlament A cable composed of actin cells that serves as the site of cellular respira- monomer (monЈ-uh-mer) The subunit that proteins in the cytoplasm of almost every eu- tion; uses oxygen to break down organic serves as the building block of a polymer. karyotic cell, making up part of the cytoskele- molecules and synthesize ATP. monophyletic (monЈ-o– -fı¯-letЈ-ik) Pertaining to a ton and acting alone or with myosin to cause mitosis (mı¯-to–Ј-sis) A process of nuclear division group of taxa that consists of a common ances- cell contraction; also known as an actin in eukaryotic cells conventionally divided into tor and all of its descendants. A monophyletic ﬁlament. ﬁve stages: prophase, prometaphase, taxon is equivalent to a clade.
GLOSSARY G–22 monosaccharide (monЈ-o– -sakЈ-uh-rı¯d) The mutagen (myu¯Ј-tuh-jen) A chemical or physical nephron (nefЈ-ron) The tubular excretory unit of simplest carbohydrate, active alone or serving agent that interacts with DNA and can cause a the vertebrate kidney. as a monomer for disaccharides and poly- mutation. neritic zone The shallow region of the ocean saccharides. Also known as simple sugars, mutation (myu¯-ta–Ј-shun) A change in the overlying the continental shelf. monosaccharides have molecular formulas nucleotide sequence of an organism’s DNA or nerve A ﬁber composed primarily of the bundled
that are generally some multiple of CH2O. in the DNA or RNA of a virus. axons of PNS neurons. monosomic Referring to a diploid cell that has mutualism (myu¯Ј-chu¯-ul-izm) A symbiotic rela- nerve net A weblike system of neurons, charac- only one copy of a particular chromosome tionship in which both participants beneﬁt. teristic of radially symmetrical animals, such instead of the normal two. mycelium (mı¯-se¯Ј-le¯-um) The densely branched as hydras. monotreme An egg-laying mammal, such as a network of hyphae in a fungus. nervous system The fast-acting internal system – Glossary platypus or echidna. Like all mammals, mycorrhiza (mı¯Ј-ko-rı¯Ј-zuh) (plural, of communication involving sensory receptors, monotremes have hair and produce milk, but mycorrhizae) A mutualistic association of networks of nerve cells, and connections to they lack nipples. plant roots and fungus. muscles and glands that respond to nerve sig- morphogen A substance, such as Bicoid protein mycosis (mı¯-ko–Ј-sis) General term for a fungal nals; functions in concert with the endocrine in Drosophila, that provides positional informa- infection. system to effect internal regulation and main- tion in the form of a concentration gradient myelin sheath (mı¯Ј-uh-lin) Wrapped around tain homeostasis. along an embryonic axis. the axon of a neuron, an insulating coat of cell nervous tissue Tissue made up of neurons and morphogenesis (mo–rЈ-fo– -jenЈ-uh-sis) The cellu- membranes from Schwann cells or oligoden- supportive cells. lar and tissue-based processes by which an drocytes. It is interrupted by nodes of Ranvier, net ecosystem production (NEP) The gross animal body takes shape. where action potentials are generated. primary production of an ecosystem minus the morphological species concept A deﬁnition myoﬁbril (mı¯Ј-o– -fı¯Ј-bril) A longitudinal bundle energy used by all autotrophs and heterotrophs of species in terms of measurable anatomical in a muscle cell (ﬁber) that contains thin for respiration. criteria. ﬁlaments of actin and regulatory proteins net primary production (NPP) The gross pri- moss A small, herbaceous, nonvascular plant that and thick ﬁlaments of myosin. mary production of an ecosystem minus the is a member of the phylum Bryophyta. myoglobin (mı¯Ј-uh-glo–Ј-bin) An oxygen-storing, energy used by the producers for respiration. motor neuron A nerve cell that transmits pigmented protein in muscle cells. neural crest In vertebrates, a region located signals from the brain or spinal cord to myosin (mı¯Ј-uh-sin) A type of motor protein along the sides of the neural tube where it muscles or glands. that associates into ﬁlaments that interact with pinches off from the ectoderm. Neural crest motor protein A protein that interacts with cy- actin ﬁlaments to cause cell contraction. cells migrate to various parts of the embryo toskeletal elements and other cell components, myotonia (mı¯Ј-uh-to–Ј-nı¯-uh) Increased muscle and form pigment cells in the skin and parts of producing movement of the whole cell or parts tension, characteristic of sexual arousal in the skull, teeth, adrenal glands, and peripheral of the cell. certain human tissues. nervous system. motor system An efferent branch of the verte- myriapod (mirЈ-e¯-uh-podЈ) A terrestrial arthro- neural plasticity The capacity of a nervous brate peripheral nervous system composed of pod with many body segments and one or two system to change with experience. motor neurons that carry signals to skeletal pairs of legs per segment. Millipedes and neural tube A tube of infolded ectodermal cells muscles in response to external stimuli. centipedes are the two major groups of living that runs along the anterior-posterior axis of a motor unit A single motor neuron and all the myriapods. vertebrate, just dorsal to the notochord. It will ؉ muscle ﬁbers it controls. NAD Nicotinamide adenine dinucleotide, a give rise to the central nervous system. movement corridor A series of small clumps or coenzyme that cycles easily between oxidized neurohormone A molecule that is secreted by a ϩ a narrow strip of quality habitat (usable by (NAD ) and reduced (NADH) states, thus neuron, travels in body ﬂuids, and acts on spe- organisms) that connects otherwise isolated acting as an electron carrier. ciﬁc target cells, changing their functioning. ؉ patches of quality habitat. NADP Nicotinamide adenine dinucleotide neuron (nyu¯rЈ-on) A nerve cell; the fundamental MPF Maturation-promoting factor (or M-phase- phosphate, an electron acceptor that, as unit of the nervous system, having structure promoting factor); a protein complex required NADPH, temporarily stores energized electrons and properties that allow it to conduct signals for a cell to progress from late interphase to produced during the light reactions. by taking advantage of the electrical charge mitosis. The active form consists of cyclin and natural family planning A form of contracep- across its plasma membrane. a protein kinase. tion that relies on refraining from sexual neuropeptide A relatively short chain of amino mucus A viscous and slippery mixture of glyco- intercourse when conception is most likely to acids that serves as a neurotransmitter. proteins, cells, salts, and water that moistens occur; also called the rhythm method. neurotransmitter A molecule that is released and protects the membranes lining body natural killer cell A type of white blood cell from the synaptic terminal of a neuron at a cavities that open to the exterior. that can kill tumor cells and virus-infected chemical synapse, diffuses across the synaptic Müllerian mimicry (myu¯-la–rЈ-e¯-un) Reciprocal cells as part of innate immunity. cleft, and binds to the postsynaptic cell, mimicry by two unpalatable species. natural selection A process in which individu- triggering a response. multifactorial Referring to a phenotypic charac- als that have certain inherited traits tend to neutral theory The hypothesis that much ter that is inﬂuenced by multiple genes and survive and reproduce at higher rates than evolutionary change in genes and proteins has environmental factors. other individuals because of those traits. no effect on ﬁtness and therefore is not multigene family A collection of genes with negative feedback A form of regulation in inﬂuenced by natural selection. similar or identical sequences, presumably of which accumulation of an end product of a neutral variation Genetic variation that common origin. process slows the process; in physiology, a does not provide a selective advantage or multiple fruit A fruit derived from an entire primary mechanism of homeostasis, whereby disadvantage. inﬂorescence. a change in a variable triggers a response neutron A subatomic particle having no electri- multiplication rule A rule of probability stating that counteracts the initial change. cal charge (electrically neutral), with a mass of Ϫ that the probability of two or more independent negative pressure breathing A breathing about 1.7 ϫ 10 24 g, found in the nucleus of events occurring together can be determined by system in which air is pulled into the lungs. an atom. multiplying their individual probabilities. nematocyst (nemЈ-uh-tuh-sistЈ) In a cnidocyte neutrophil The most abundant type of white muscle tissue Tissue consisting of long muscle of a cnidarian, a capsule-like organelle contain- blood cell. Neutrophils are phagocytic and cells that can contract, either on its own or ing a coiled thread that when discharged can tend to self-destruct as they destroy foreign in- when stimulated by nerve impulses. penetrate the body wall of the prey. vaders, limiting their life span to a few days.
G–23 GLOSSARY nitric oxide (NO) A gas produced by many notochord (no–Ј-tuh-kordЈ) A longitudinal, ﬂexi- eukaryotic cell that contains the genetic mate- types of cells that functions as a local regulator ble rod made of tightly packed mesodermal rial in the form of chromosomes, made up of and as a neurotransmitter. cells that runs along the anterior-posterior axis chromatin. (3) A cluster of neurons. nitrogen cycle The natural process by which of a chordate in the dorsal part of the body. nutrition The process by which an organism nitrogen, either from the atmosphere or from nuclear envelope In a eukaryotic cell, the dou- takes in and makes use of food substances. decomposed organic material, is converted by ble membrane that surrounds the nucleus, per- obligate aerobe (obЈ-lig-et a–rЈ-o–b) An organism soil bacteria to compounds assimilated by forated with pores that regulate trafﬁc with the that requires oxygen for cellular respiration plants. This incorporated nitrogen is then cytoplasm. The outer membrane is continuous and cannot live without it. taken in by other organisms and subsequently with the endoplasmic reticulum. obligate anaerobe (obЈ-lig-et anЈ-uh-ro–b) An or- released, acted on by bacteria, and made avail- nuclear lamina A netlike array of protein ganism that only carries out fermentation or
able again to the nonliving environment. ﬁlaments that lines the inner surface of the anaerobic respiration. Such organisms cannot Glossary nitrogen ﬁxation The conversion of atmo- nuclear envelope and helps maintain the shape use oxygen and in fact may be poisoned by it.
spheric nitrogen (N2) to ammonia (NH3). of the nucleus. ocean acidiﬁcation Decreasing pH of ocean Biological nitrogen ﬁxation is carried out by nucleariid Member of a group of unicellular, waters due to absorption of excess atmospheric
certain prokaryotes, some of which have mutu- amoeboid protists that are more closely related CO2 from the burning of fossil fuels. alistic relationships with plants. to fungi than they are to other protists. oceanic pelagic zone Most of the ocean’s nociceptor (no–Ј-si-sepЈ-tur) A sensory receptor nuclease An enzyme that cuts DNA or RNA, waters far from shore, constantly mixed by that responds to noxious or painful stimuli; either removing one or a few bases or ocean currents. also called a pain receptor. hydrolyzing the DNA or RNA completely odorant A molecule that can be detected by node A point along the stem of a plant at which into its component nucleotides. sensory receptors of the olfactory system. leaves are attached. nucleic acid (nu¯-kla–Ј-ik) A polymer (polynu- Okazaki fragment (o–Ј-kah-zahЈ-ke¯) A short seg- node of Ranvier (ronЈ-ve¯-a–Ј) Gap in the myelin cleotide) consisting of many nucleotide ment of DNA synthesized away from the repli- sheath of certain axons where an action poten- monomers; serves as a blueprint for proteins cation fork on a template strand during DNA tial may be generated. In saltatory conduction, and, through the actions of proteins, for all replication. Many such segments are joined an action potential is regenerated at each cellular activities. The two types are DNA together to make up the lagging strand of node, appearing to “jump” along the axon and RNA. newly synthesized DNA. from node to node. nucleic acid hybridization The process of olfaction The sense of smell. nodule A swelling on the root of a legume. Nod- base pairing between a gene and a comple- oligodendrocyte A type of glial cell that forms ules are composed of plant cells that contain mentary sequence on another nucleic acid insulating myelin sheaths around the axons of nitrogen-ﬁxing bacteria of the genus Rhizobium. molecule. neurons in the central nervous system. noncompetitive inhibitor A substance that re- nucleic acid probe In DNA technology, a oligotrophic lake A nutrient-poor, clear lake duces the activity of an enzyme by binding to labeled single-stranded nucleic acid molecule with few phytoplankton. a location remote from the active site, chang- used to locate a speciﬁc nucleotide sequence in ommatidium (o–mЈ-uh-tidЈ-e¯-um) (plural, ing the enzyme’s shape so that the active site a nucleic acid sample. Molecules of the probe ommatidia) One of the facets of the com- no longer effectively catalyzes the conversion hydrogen-bond to the complementary pound eye of arthropods and some of substrate to product. sequence wherever it occurs; radioactive, polychaete worms. nondisjunction An error in meiosis or mitosis ﬂuorescent, or other labeling of the probe omnivore An animal that regularly eats animals in which members of a pair of homologous allows its location to be detected. as well as plants or algae. chromosomes or a pair of sister chromatids fail nucleoid (nu¯Ј-kle¯-oyd) A non-membrane- oncogene (onЈ-ko– -je¯n) A gene found in viral or to separate properly from each other. bounded region in a prokaryotic cell where the cellular genomes that is involved in triggering nonequilibrium model A model that main- DNA is concentrated. molecular events that can lead to cancer. tains that communities change constantly nucleolus (nu¯-kle¯Ј-o– -lus) (plural, nucleoli) A oocyte A cell in the female reproductive system after being buffeted by disturbances. specialized structure in the nucleus, consisting that differentiates to form an egg. nonpolar covalent bond A type of covalent of chromosomal regions containing ribosomal oogenesis (o–Ј-uh-jenЈ-uh-sis) The process in the bond in which electrons are shared equally be- RNA (rRNA) genes along with ribosomal pro- ovary that results in the production of female tween two atoms of similar electronegativity. teins imported from the cytoplasm; site of gametes. nonsense mutation A mutation that changes rRNA synthesis and ribosomal subunit assem- oogonium (o–Ј-uh- go–Ј-ne¯-em) (plural, oogonia) an amino acid codon to one of the three stop bly. See also ribosome. A cell that divides mitotically to form oocytes. codons, resulting in a shorter and usually non- nucleosome (nu¯Ј-kle¯-o– -so–mЈ) The basic, bead- oomycete (o–Ј-uh-mı¯Ј-se¯t) A protist with ﬂagel- functional protein. like unit of DNA packing in eukaryotes, con- lated cells, such as a water mold, white rust, or norepinephrine A catecholamine that is chemi- sisting of a segment of DNA wound around a downy mildew, that acquires nutrition mainly cally and functionally similar to epinephrine protein core composed of two copies of each of as a decomposer or plant parasite. and acts as a hormone or neurotransmitter; four types of histone. open circulatory system A circulatory system also known as noradrenaline. nucleotide (nu¯Ј-kle¯-o– -tı¯dЈ) The building block of in which ﬂuid called hemolymph bathes the norm of reaction The range of phenotypes a nucleic acid, consisting of a ﬁve-carbon sugar tissues and organs directly and there is no produced by a single genotype, due to covalently bonded to a nitrogenous base and distinction between the circulating ﬂuid and environmental inﬂuences. one or more phosphate groups. the interstitial ﬂuid. Northern blotting A technique that enables nucleotide excision repair A repair system operator In bacterial and phage DNA, a sequence speciﬁc nucleotide sequences to be detected in that removes and then correctly replaces a of nucleotides near the start of an operon to samples of mRNA. It involves gel electrophore- damaged segment of DNA using the undam- which an active repressor can attach. The bind- sis of RNA molecules and their transfer to a aged strand as a guide. ing of the repressor prevents RNA polymerase membrane (blotting), followed by nucleic acid nucleotide-pair substitution A type of point from attaching to the promoter and transcrib- hybridization with a labeled probe. mutation in which one nucleotide in a DNA ing the genes of the operon. northern coniferous forest A terrestrial biome strand and its partner in the complementary operculum (o– -perЈ-kyuh-lum) In aquatic characterized by long, cold winters and strand are replaced by another pair of osteichthyans, a protective bony ﬂap that dominated by cone-bearing trees. nucleotides. covers and protects the gills. no-till agriculture A plowing technique that mini- nucleus (1) An atom’s central core, containing operon (opЈ-er-on) A unit of genetic function mally disturbs the soil, thereby reducing soil loss. protons and neutrons. (2) The organelle of a found in bacteria and phages, consisting of a
GLOSSARY G–24 promoter, an operator, and a coordinately reg- osmoregulator An animal that controls its P site One of a ribosome’s three binding sites for ulated cluster of genes whose products func- internal osmolarity independent of the tRNA during translation. The P site holds the tion in a common pathway. external environment. tRNA carrying the growing polypeptide chain. opisthokont (uh-pisЈ-thuh-kontЈ) Member of osmosis (oz-mo–Ј-sis) The diffusion of free water (P stands for peptidyl tRNA.) the diverse clade Opisthokonta, organisms that across a selectively permeable membrane. p53 gene A tumor-suppressor gene that codes for descended from an ancestor with a posterior osteichthyan (osЈ-te¯-ikЈ-the¯-an) Member of a a speciﬁc transcription factor that promotes ﬂagellum, including fungi, animals, and vertebrate clade with jaws and mostly bony the synthesis of proteins that inhibit the certain protists. skeletons. cell cycle. opposable thumb A thumb that can touch outer ear One of three main regions of the ear in paedomorphosis (pe¯Ј-duh-mo–rЈ-fuh-sis) The the ventral surface of the ﬁngertips of all four reptiles (including birds) and mammals; made retention in an adult organism of the juvenile
Glossary ﬁngers. up of the auditory canal and, in many birds features of its evolutionary ancestors. opsin A membrane protein bound to a light- and mammals, the pinna. pain receptor A sensory receptor that responds absorbing pigment molecule. outgroup A species or group of species from an to noxious or painful stimuli; also called a optic chiasm The place where the two optic evolutionary lineage that is known to have nociceptor. nerves meet and axons representing distinct diverged before the lineage that contains the paleoanthropology The study of human sides of the visual ﬁeld are segregated from one group of species being studied. An outgroup is origins and evolution. another before reaching the brain. selected so that its members are closely related paleontology (pa–Ј-le¯-un-tolЈ-o– -je¯) The scientiﬁc optimal foraging model The basis for analyz- to the group of species being studied, but not study of fossils. ing behavior as a compromise between feeding as closely related as any study-group members pancreas (panЈ-kre¯-us) A gland with exocrine costs and feeding beneﬁts. are to each other. and endocrine tissues. The exocrine portion oral cavity The mouth of an animal. oval window In the vertebrate ear, a membrane- functions in digestion, secreting enzymes and orbital The three-dimensional space where an covered gap in the skull bone, through which an alkaline solution into the small intestine via electron is found 90% of the time. sound waves pass from the middle ear to the a duct; the ductless endocrine portion func- order In Linnaean classiﬁcation, the taxonomic inner ear. tions in homeostasis, secreting the hormones category above the level of family. ovarian cycle (o– -va–rЈ-e¯-un) The cyclic recurrence insulin and glucagon into the blood. organ A specialized center of body function of the follicular phase, ovulation, and the pandemic A global epidemic. composed of several different types of tissues. luteal phase in the mammalian ovary, Pangaea (pan-je¯Ј-uh) The supercontinent that organ identity gene A plant homeotic gene regulated by hormones. formed near the end of the Paleozoic era, when that uses positional information to determine ovary (o–Ј-vuh-re¯) (1) In ﬂowers, the portion of a plate movements brought all the landmasses of which emerging leaves develop into which carpel in which the egg-containing ovules de- Earth together. types of ﬂoral organs. velop. (2) In animals, the structure that produces parabasalid A protist, such as a trichomonad, organ of Corti The actual hearing organ of the female gametes and reproductive hormones. with modiﬁed mitochondria. vertebrate ear, located in the ﬂoor of the oviduct (o–Ј-vuh-duct) A tube passing from the paracrine Referring to a secreted molecule that cochlear duct in the inner ear; contains the ovary to the vagina in invertebrates or to the acts on a neighboring cell. receptor cells (hair cells) of the ear. uterus in vertebrates, where it is also known as paralogous genes Homologous genes that are organ system A group of organs that work a fallopian tube. found in the same genome as a result of gene together in performing vital body functions. oviparous (o– -vipЈ-uh-rus) Referring to a type of duplication. organelle (o–r-guh-nelЈ) Any of several mem- development in which young hatch from eggs paraphyletic (pa–rЈ-uh-fı¯-letЈ-ik) Pertaining to a brane-enclosed structures with specialized laid outside the mother’s body. group of taxa that consists of a common ances- functions, suspended in the cytosol of ovoviviparous (o–Ј-vo– -vı¯-vipЈ-uh-rus) Referring to tor and some, but not all, of its descendants. eukaryotic cells. a type of development in which young hatch parareptile A basal group of reptiles, consisting organic chemistry The study of carbon from eggs that are retained in the mother’s mostly of large, stocky quadrupedal herbivores. compounds (organic compounds). uterus. Parareptiles died out in the late Triassic period. organismal ecology The branch of ecology ovulation The release of an egg from an ovary. parasite (pa–rЈ-uh-sı¯t) An organism that feeds on concerned with the morphological, physiologi- In humans, an ovarian follicle releases an egg the cell contents, tissues, or body ﬂuids of an- cal, and behavioral ways in which individual during each uterine (menstrual) cycle. other species (the host) while in or on the host organisms meet the challenges posed by their ovule (oЈ-vyu¯l) A structure that develops within organism. Parasites harm but usually do not biotic and abiotic environments. the ovary of a seed plant and contains the kill their host. organogenesis (o–r-ganЈ-o– -jenЈ-uh-sis) The female gametophyte. parasitism (pa–rЈ-uh-sit-izm) A symbiotic rela- process in which organ rudiments develop oxidation The complete or partial loss of tionship in which one organism, the parasite, from the three germ layers after gastrulation. electrons from a substance involved in a beneﬁts at the expense of another, the host, by orgasm Rhythmic, involuntary contractions of redox reaction. living either within or on the host. certain reproductive structures in both sexes oxidative phosphorylation (fosЈ-fo–r-uh-la–Ј- parasympathetic division One of three divi- during the human sexual response cycle. shun) The production of ATP using energy sions of the autonomic nervous system; gener- origin of replication Site where the replication derived from the redox reactions of an ally enhances body activities that gain and of a DNA molecule begins, consisting of a electron transport chain; the third major stage conserve energy, such as digestion and reduced speciﬁc sequence of nucleotides. of cellular respiration. heart rate. orthologous genes Homologous genes that are oxidizing agent The electron acceptor in a parathyroid gland One of four small endocrine found in different species because of speciation. redox reaction. glands, embedded in the surface of the thyroid osculum (osЈ-kyuh-lum) A large opening in a oxytocin (okЈ-si-to–Ј-sen) A hormone produced by gland, that secrete parathyroid hormone. sponge that connects the spongocoel to the the hypothalamus and released from the poste- parathyroid hormone (PTH) A hormone environment. rior pituitary. It induces contractions of the secreted by the parathyroid glands that raises osmoconformer An animal that is isoosmotic uterine muscles during labor and causes the blood calcium level by promoting calcium with its environment. mammary glands to eject milk during nursing. release from bone and calcium retention by osmolarity (ozЈ-mo– -la–rЈ-uh-te¯) Solute concentra- P generation The true-breeding (homozygous) the kidneys. Ј tion expressed as molarity. parent individuals from which F1 hybrid off- parenchyma cell (puh-ren -ki-muh) A relatively osmoregulation Regulation of solute concentra- spring are derived in studies of inheritance; P unspecialized plant cell type that carries out tions and water balance by a cell or organism. stands for “parental.” most of the metabolism, synthesizes and stores
G–25 GLOSSARY organic products, and develops into a more integral protein and not embedded in the lipid phosphate group A chemical group consisting differentiated cell type. bilayer. of a phosphorus atom bonded to four oxygen parental type An offspring with a phenotype peristalsis (pa–rЈ-uh-stalЈ-sis) (1) Alternating atoms; important in energy transfer. that matches one of the true-breeding parental waves of contraction and relaxation in the phospholipid (fosЈ-fo– -lipЈ-id) A lipid made up of (P generation) phenotypes; also refers to the smooth muscles lining the alimentary canal glycerol joined to two fatty acids and a phos- phenotype itself. that push food along the canal. (2) A type of phate group. The hydrocarbon chains of the Parkinson’s disease A progressive brain disease movement on land produced by rhythmic fatty acids act as nonpolar, hydrophobic tails, characterized by difﬁculty in initiating move- waves of muscle contractions passing from while the rest of the molecule acts as a polar, ments, slowness of movement, and rigidity. front to back, as in many annelids. hydrophilic head. Phospholipids form bilayers parthenogenesis (parЈ-thuh-no–Ј-jenЈ-uh-sis) A peristome A ring of interlocking, tooth-like that function as biological membranes.
form of asexual reproduction in which females structures on the upper part of a moss capsule phosphorylated intermediate A molecule (of- Glossary produce offspring from unfertilized eggs. (sporangium), often specialized for gradual ten a reactant) with a phosphate group cova- partial pressure The pressure exerted by a par- spore discharge. lently bound to it, making it more reactive ticular gas in a mixture of gases (for instance, peritubular capillary One of the tiny blood (less stable) than the unphosphorylated the pressure exerted by oxygen in air). vessels that form a network surrounding the molecule. passive immunity Short-term immunity con- proximal and distal tubules in the kidney. photic zone (fo–Ј-tic) The narrow top layer of an ferred by the transfer of antibodies, as occurs permafrost A permanently frozen soil layer. ocean or lake, where light penetrates sufﬁ- in the transfer of maternal antibodies to a fetus peroxisome (puh-rokЈ-suh-so–mЈ) An organelle ciently for photosynthesis to occur. or nursing infant. containing enzymes that transfer hydrogen photoautotroph (fo–Ј-to– -otЈ-o– -tro–f) An organism passive transport The diffusion of a substance atoms from various substrates to oxygen (O2), that harnesses light energy to drive the synthe- across a biological membrane with no producing and then degrading hydrogen sis of organic compounds from carbon dioxide. –Ј – Ј – – expenditure of energy. peroxide (H2O2). photoheterotroph (fo -to-het -er-o-trof) An pathogen An organism, virus, viroid, or prion petal A modiﬁed leaf of a ﬂowering plant. Petals organism that uses light to generate ATP but that causes disease. are the often colorful parts of a ﬂower that must obtain carbon in organic form. pattern formation The development of a multi- advertise it to insects and other pollinators. photomorphogenesis Effects of light on plant cellular organism’s spatial organization, the petiole (petЈ-e¯-o–l) The stalk of a leaf, which joins morphology. arrangement of organs and tissues in their char- the leaf to a node of the stem. photon (fo–Ј-ton) A quantum, or discrete quan- acteristic places in three-dimensional space. pH A measure of hydrogen ion concentration tity, of light energy that behaves as if it were a ϩ peat Extensive deposits of partially decayed equal to –log [H ] and ranging in value from particle. organic material often formed primarily from 0 to 14. photoperiodism (fo–Ј-to– -pe¯rЈ-e¯-o– -dizm) A physi- the wetland moss Sphagnum. phage (fa–j) A virus that infects bacteria; also ological response to photoperiod, the relative pedigree A diagram of a family tree with conven- called a bacteriophage. lengths of night and day. An example of pho- tional symbols, showing the occurrence of phagocytosis (fagЈ-o– -sı¯-to–Ј-sis) A type of endocy- toperiodism is ﬂowering. heritable characters in parents and offspring tosis in which large particulate substances or photophosphorylation (fo–Ј-to– -fosЈ-fo–r-uh-la–Ј- over multiple generations. small organisms are taken up by a cell. It is shun) The process of generating ATP from ADP pelagic zone The open-water component of carried out by some protists and by certain and phosphate by means of chemiosmosis, aquatic biomes. immune cells of animals (in mammals, mainly using a proton-motive force generated across penis The copulatory structure of male mammals. macrophages, neutrophils, and dendritic cells). the thylakoid membrane of the chloroplast or Ј PEP carboxylase An enzyme that adds CO2 to pharyngeal cleft (fuh-rin -je¯-ul) In chordate the membrane of certain prokaryotes during phosphoenolpyruvate (PEP) to form oxaloac- embryos, one of the grooves that separate a se- the light reactions of photosynthesis.
etate in mesophyll cells of C4 plants. It acts ries of pouches along the sides of the pharynx photoreceptor An electromagnetic receptor that prior to photosynthesis. and may develop into a pharyngeal slit. detects the radiation known as visible light. pepsin An enzyme present in gastric juice that pharyngeal slit (fuh-rinЈ-je¯-ul) In chordate em- photorespiration A metabolic pathway that begins the hydrolysis of proteins. bryos, one of the slits that form from the pharyn- consumes oxygen and ATP, releases carbon pepsinogen The inactive form of pepsin secreted geal clefts and communicate to the outside, later dioxide, and decreases photosynthetic output. by chief cells located in gastric pits of the developing into gill slits in many vertebrates. Photorespiration generally occurs on hot, dry, stomach. pharynx (fa–rЈ-inks) (1) An area in the vertebrate bright days, when stomata close and the peptide bond The covalent bond between the throat where air and food passages cross. (2) In O2/CO2 ratio in the leaf increases, favoring the
carboxyl group on one amino acid and the ﬂatworms, the muscular tube that protrudes binding of O2 rather than CO2 by rubisco. amino group on another, formed by a from the ventral side of the worm and ends in photosynthesis (fo–Ј-to– -sinЈ-thi-sis) The conver- dehydration reaction. the mouth. sion of light energy to chemical energy that is peptidoglycan (pepЈ-tid-o– -glı¯Ј-kan) A type of phase change A shift from one developmental stored in sugars or other organic compounds; polymer in bacterial cell walls consisting of phase to another. occurs in plants, algae, and certain prokaryotes. modiﬁed sugars cross-linked by short phenotype (fe¯Ј-no– -tı¯p) The observable physical photosystem A light-capturing unit located in polypeptides. and physiological traits of an organism, which the thylakoid membrane of the chloroplast or perception The interpretation of sensory system are determined by its genetic makeup. in the membrane of some prokaryotes, consist- input by the brain. pheromone (fa–rЈ-uh-mo–n) In animals and fungi, ing of a reaction-center complex surrounded pericycle The outermost layer in the vascular a small molecule released into the environ- by numerous light-harvesting complexes. cylinder, from which lateral roots arise. ment that functions in communication There are two types of photosystems, I and II; periderm (pa–rЈ-uh-dermЈ) The protective coat between members of the same species. In they absorb light best at different wavelengths. that replaces the epidermis in woody plants animals, it acts much like a hormone in photosystem I (PS I) A light-capturing unit in a during secondary growth, formed of the cork inﬂuencing physiology and behavior. chloroplast’s thylakoid membrane or in the and cork cambium. phloem (ﬂo–Ј-em) Vascular plant tissue consisting membrane of some prokaryotes; it has two peripheral nervous system (PNS) The sensory of living cells arranged into elongated tubes molecules of P700 chlorophyll a at its reaction and motor neurons that connect to the central that transport sugar and other organic center. nervous system. nutrients throughout the plant. photosystem II (PS II) One of two light- peripheral protein A protein loosely bound phloem sap The sugar-rich solution carried capturing units in a chloroplast’s thylakoid to the surface of a membrane or to part of an through a plant’s sieve tubes. membrane or in the membrane of some
GLOSSARY G–26 prokaryotes; it has two molecules of P680 placental transfer cell A plant cell that en- polar molecule A molecule (such as water) with chlorophyll a at its reaction center. hances the transfer of nutrients from parent to an uneven distribution of charges in different phototropism (fo–Ј-to– -tro–Ј-pizm) Growth of a embryo. regions of the molecule. plant shoot toward or away from light. placoderm A member of an extinct group of polarity A lack of symmetry; structural differ- phragmoplast (fragЈ-mo– -plastЈ) An alignment of ﬁshlike vertebrates that had jaws and were ences in opposite ends of an organism or struc- cytoskeletal elements and Golgi-derived enclosed in a tough outer armor. ture, such as the root end and shoot end of a vesicles that forms across the midline of a planarian A free-living ﬂatworm found in ponds plant. dividing plant cell. and streams. pollen grain In seed plants, a structure consist- phyllotaxy (ﬁlЈ-uh-takЈ-se¯) The pattern of leaf plasma (plazЈ-muh) The liquid matrix of blood ing of the male gametophyte enclosed within a attachment to the stem of a plant. in which the blood cells are suspended. pollen wall.
Glossary PhyloCode Proposed system of classiﬁcation of plasma cell The antibody-secreting effector cell pollen tube A tube that forms after germination organisms based on evolutionary relationships: of humoral immunity. Plasma cells arise from of the pollen grain and that functions in the Only groups that include a common ancestor antigen-stimulated B cells. delivery of sperm to the ovule. and all of its descendants are named. plasma membrane The membrane at the bound- pollination (polЈ-uh-na–Ј-shun) The transfer of phylogenetic species concept A deﬁnition of ary of every cell that acts as a selective barrier, pollen to the part of a seed plant containing species as the smallest group of individuals regulating the cell’s chemical composition. the ovules, a process required for fertilization. that share a common ancestor, forming one plasmid (plazЈ-mid) A small, circular, double- poly-A tail A sequence of 50–250 adenine branch on the tree of life. stranded DNA molecule that carries accessory nucleotides added onto the 3Ј end of a phylogenetic tree A branching diagram that genes separate from those of a bacterial chro- pre-mRNA molecule. represents a hypothesis about the evolutionary mosome; in DNA cloning, used as vectors polygamous Referring to a type of relationship history of a group of organisms. carrying up to about 10,000 base pairs (10 kb) in which an individual of one sex mates with phylogeny (fı¯-lojЈ-uh-ne¯) The evolutionary of DNA. Plasmids are also found in some several of the other. history of a species or group of related species. eukaryotes, such as yeasts. polygenic inheritance (polЈ-e¯-jenЈ-ik) An phylum (fı¯Ј-lum) (plural, phyla) In Linnaean plasmodesma (plazЈ-mo– -dezЈ-muh) (plural, additive effect of two or more genes on a classiﬁcation, the taxonomic category above plasmodesmata) An open channel through single phenotypic character. class. the cell wall that connects the cytoplasm of polymer (polЈ-uh-mer) A long molecule consist- physical map A genetic map in which the adjacent plant cells, allowing water, small ing of many similar or identical monomers actual physical distances between genes or solutes, and some larger molecules to pass linked together by covalent bonds. other genetic markers are expressed, usually as between the cells. polymerase chain reaction (PCR) (puh-limЈ- the number of base pairs along the DNA. plasmodial slime mold (plaz-mo–Ј-de¯-ul) A type uh-ra–s) A technique for amplifying DNA in physiology The processes and functions of an of protist that has amoeboid cells, ﬂagellated vitro by incubating it with speciﬁc primers, organism. cells, and a plasmodial feeding stage in its life a heat-resistant DNA polymerase, and phytochrome (fı¯Ј-tuh-kro–m) A type of light re- cycle. nucleotides. ceptor in plants that mostly absorbs red light plasmodium A single mass of cytoplasm con- polynucleotide (polЈ-e¯-nu¯Ј-kle¯-o– -tı¯d) A polymer and regulates many plant responses, such as taining many diploid nuclei that forms during consisting of many nucleotide monomers in a seed germination and shade avoidance. the life cycle of some slime molds. chain. The nucleotides can be those of DNA phytoremediation An emerging technology plasmogamy (plaz-mohЈ-guh-me¯) In fungi, the or RNA. that seeks to reclaim contaminated areas by fusion of the cytoplasm of cells from two indi- polyp The sessile variant of the cnidarian body taking advantage of some plant species’ ability viduals; occurs as one stage of sexual reproduc- plan. The alternate form is the medusa. to extract heavy metals and other pollutants tion, followed later by karyogamy. polypeptide (polЈ-e¯-pepЈ-tı¯d) A polymer of from the soil and to concentrate them in easily plasmolysis (plaz-molЈ-uh-sis) A phenomenon many amino acids linked together by peptide harvested portions of the plant. in walled cells in which the cytoplasm shrivels bonds. pilus (plural, pili) (pı¯Ј-lus, pı¯Ј-lı¯) In bacteria, a and the plasma membrane pulls away from the polyphyletic (polЈ-e¯-fı¯-letЈ-ik) Pertaining to a structure that links one cell to another at the cell wall; occurs when the cell loses water to a group of taxa derived from two or more start of conjugation; also known as a sex pilus hypertonic environment. different ancestors. or conjugation pilus. plastid One of a family of closely related polyploidy (polЈ-e¯-ployЈ-de¯) A chromosomal pineal gland (pı¯Ј-ne¯-ul) A small gland on the organelles that includes chloroplasts, alteration in which the organism possesses dorsal surface of the vertebrate forebrain that chromoplasts, and amyloplasts. Plastids are more than two complete chromosome sets. It secretes the hormone melatonin. found in cells of photosynthetic eukaryotes. is the result of an accident of cell division. pinocytosis (pı¯Ј-no– -sı¯-to–Ј-sis) A type of endo- plate tectonics The theory that the continents polyribosome (polysome) (polЈ-e¯-rı¯Ј-buh- cytosis in which the cell ingests extracellular are part of great plates of Earth’s crust that so–mЈ) A group of several ribosomes attached ﬂuid and its dissolved solutes. ﬂoat on the hot, underlying portion of the to, and translating, the same messenger RNA pistil A single carpel or a group of fused carpels. mantle. Movements in the mantle cause the molecule. pith Ground tissue that is internal to the vascular continents to move slowly over time. polysaccharide (polЈ-e¯-sakЈ-uh-rı¯d) A polymer tissue in a stem; in many monocot roots, platelet A pinched-off cytoplasmic fragment of a of many monosaccharides, formed by parenchyma cells that form the central core of specialized bone marrow cell. Platelets circulate dehydration reactions. the vascular cylinder. in the blood and are important in blood clotting. polytomy (puh-litЈ-uh-me¯) In a phylogenetic pituitary gland (puh-tu¯Ј-uh-ta–rЈ-e¯) An endo- pleiotropy (plı¯Ј-o-truh-pe¯) The ability of a single tree, a branch point from which more than crine gland at the base of the hypothalamus; gene to have multiple effects. two descendant taxa emerge. A polytomy consists of a posterior lobe, which stores and pluripotent Describing a cell that can give rise indicates that the evolutionary relationships releases two hormones produced by the to many, but not all, parts of an organism. between the descendant taxa are not yet clear. hypothalamus, and an anterior lobe, which point mutation A change in a single nucleotide pons A portion of the brain that participates in produces and secretes many hormones that pair of a gene. certain automatic, homeostatic functions, such regulate diverse body functions. polar covalent bond A covalent bond between as regulating the breathing centers in the placenta (pluh-senЈ-tuh) A structure in the preg- atoms that differ in electronegativity. The medulla. nant uterus for nourishing a viviparous fetus shared electrons are pulled closer to the more population A group of individuals of the same with the mother’s blood supply; formed from electronegative atom, making it slightly nega- species that live in the same area and inter- the uterine lining and embryonic membranes. tive and the other atom slightly positive. breed, producing fertile offspring.
G–27 GLOSSARY population dynamics The study of how com- primary producer An autotroph, usually a pho- proliferative phase That portion of the uterine plex interactions between biotic and abiotic tosynthetic organism. Collectively, autotrophs (menstrual) cycle when the endometrium factors inﬂuence variations in population size. make up the trophic level of an ecosystem that regenerates and thickens. population ecology The study of populations ultimately supports all other levels. prometaphase The second stage of mitosis, in in relation to their environment, including en- primary production The amount of light en- which the nuclear envelope fragments and the vironmental inﬂuences on population density ergy converted to chemical energy (organic spindle microtubules attach to the kineto- and distribution, age structure, and variations compounds) by the autotrophs in an chores of the chromosomes. in population size. ecosystem during a given time period. promiscuous Referring to a type of relationship positional information Molecular cues that primary structure The level of protein structure in which mating occurs with no strong pair- control pattern formation in an animal or referring to the speciﬁc linear sequence of bonds or lasting relationships.
plant embryonic structure by indicating a cell’s amino acids. promoter A speciﬁc nucleotide sequence in the Glossary location relative to the organism’s body axes. primary succession A type of ecological succes- DNA of a gene that binds RNA polymerase, These cues elicit a response by genes that sion that occurs in an area where there were positioning it to start transcribing RNA at the regulate development. originally no organisms present and where soil appropriate place. positive feedback A form of regulation in which has not yet formed. prophage (pro–Ј-fa–j) A phage genome that has an end product of a process speeds up that primary transcript An initial RNA transcript been inserted into a speciﬁc site on a bacterial process; in physiology, a control mechanism in from any gene; also called pre-mRNA when chromosome. which a change in a variable triggers a response transcribed from a protein-coding gene. prophase The ﬁrst stage of mitosis, in which the that reinforces or ampliﬁes the change. primary visual cortex The destination in the chromatin condenses into discrete chromo- positive pressure breathing A breathing occipital lobe of the cerebrum for most of the somes visible with a light microscope, the mi- system in which air is forced into the lungs. axons from the lateral geniculate nuclei. totic spindle begins to form, and the nucleolus posterior Pertaining to the rear, or tail end, of a primase An enzyme that joins RNA nucleotides disappears but the nucleus remains intact. bilaterally symmetrical animal. to make a primer during DNA replication, prostaglandin (prosЈ-tuh-glanЈ-din) One of a posterior pituitary An extension of the using the parental DNA strand as a template. group of modiﬁed fatty acids secreted by virtu- hypothalamus composed of nervous tissue primer A short stretch of RNA with a free 3Ј end, ally all tissues and performing a wide variety of that secretes oxytocin and antidiuretic bound by complementary base pairing to the functions as local regulators. hormone made in the hypothalamus; template strand and elongated with DNA prostate gland (prosЈ-ta–t) A gland in human a temporary storage site for these hormones. nucleotides during DNA replication. males that secretes an acid-neutralizing postzygotic barrier (po–stЈ-zı¯-gotЈ-ik) A repro- primitive streak A thickening along the future component of semen. ductive barrier that prevents hybrid zygotes anterior-posterior axis on the surface of an protease An enzyme that digests proteins by produced by two different species from early avian or mammalian embryo, caused by a hydrolysis. developing into viable, fertile adults. piling up of cells as they congregate at the proteasome A giant protein complex that potential energy The energy that matter midline before moving into the embryo. recognizes and destroys proteins tagged for possesses as a result of its location or spatial prion An infectious agent that is a misfolded ver- elimination by the small protein ubiquitin. arrangement (structure). sion of a normal cellular protein. Prions appear protein (pro–Ј-te¯n) A biologically functional predation An interaction between species in to increase in number by converting correctly molecule consisting of one or more poly- which one species, the predator, eats the other, folded versions of the protein to more prions. peptides folded and coiled into a speciﬁc the prey. problem solving The cognitive activity of devis- three-dimensional structure. pregnancy The condition of carrying one or ing a method to proceed from one state to an- protein kinase An enzyme that transfers more embryos in the uterus. other in the face of real or apparent obstacles. phosphate groups from ATP to a protein, thus prepuce (pre¯Ј-pyu¯s) A fold of skin covering the producer An organism that produces organic phosphorylating the protein.
head of the clitoris or penis. compounds from CO2 by harnessing light protein phosphatase An enzyme that removes Ψ pressure potential ( P) A component of water energy (in photosynthesis) or by oxidizing phosphate groups from (dephosphorylates) potential that consists of the physical pressure inorganic chemicals (in chemosynthetic proteins, often functioning to reverse the effect on a solution, which can be positive, zero, or reactions carried out by some prokaryotes). of a protein kinase. negative. product A material resulting from a chemical proteoglycan (pro–Ј-te¯-o– -glı¯Ј-kan) A large mol- prezygotic barrier (pre¯Ј-zı¯-gotЈ-ik) A reproduc- reaction. ecule consisting of a small core protein with tive barrier that impedes mating between production efﬁciency The percentage of many carbohydrate chains attached, found species or hinders fertilization if interspeciﬁc energy stored in assimilated food that is not in the extracellular matrix of animal cells. mating is attempted. used for respiration or eliminated as waste. A proteoglycan may consist of up to 95% primary cell wall In plants, a relatively thin progesterone A steroid hormone that prepares carbohydrate. and ﬂexible layer that surrounds the plasma the uterus for pregnancy; the major progestin proteomics (pro–Ј-te¯-o–Ј-miks) The systematic membrane of a young cell. in mammals. study of the full protein sets (proteomes) primary consumer An herbivore; an organism progestin Any steroid hormone with progesterone- encoded by genomes. that eats plants or other autotrophs. like activity. protist An informal term applied to any eukary- primary electron acceptor In the thylakoid progymnosperm (pro–Ј-jimЈ-no– -sperm) An ote that is not a plant, animal, or fungus. Most membrane of a chloroplast or in the mem- extinct seedless vascular plant that may be protists are unicellular, though some are brane of some prokaryotes, a specialized mol- ancestral to seed plants. colonial or multicellular. ecule that shares the reaction-center complex prokaryotic cell (pro–Ј-ka–rЈ-e¯-otЈ-ik) A type of protocell An abiotic precursor of a living cell with a pair of chlorophyll a molecules and that cell lacking a membrane-enclosed nucleus and that had a membrane-like structure and that accepts an electron from them. membrane-enclosed organelles. Organisms maintained an internal chemistry different primary growth Growth produced by apical with prokaryotic cells (bacteria and archaea) from that of its surroundings. meristems, lengthening stems and roots. are called prokaryotes. proton (pro–Ј-ton) A subatomic particle with a primary immune response The initial adap- prolactin A hormone produced and secreted by single positive electrical charge, with a mass Ϫ tive immune response to an antigen, which the anterior pituitary with a great diversity of of about 1.7 ϫ 10 24 g, found in the nucleus appears after a lag of about 10 to 17 days. effects in different vertebrate species. In mam- of an atom. primary oocyte (o–Ј-uh-sı¯t) An oocyte prior to mals, it stimulates growth of and milk produc- proton pump An active transport protein in completion of meiosis I. tion by the mammary glands. a cell membrane that uses ATP to transport
GLOSSARY G–28 hydrogen ions out of a cell against their con- results of random fertilization in genetic crosses this complex triggers the light reactions of centration gradient, generating a membrane between individuals of known genotype. photosynthesis. Excited by light energy, the potential in the process. pupil The opening in the iris, which admits light pair of chlorophylls donates an electron to the protonema (plural, protonemata) A mass of into the interior of the vertebrate eye. Muscles primary electron acceptor, which passes an green, branched, one-cell-thick ﬁlaments in the iris regulate its size. electron to an electron transport chain. produced by germinating moss spores. purine (pyu¯Ј-re¯n) One of two types of nitroge- reading frame On an mRNA, the triplet group- protonephridium (pro–Ј-to– -nuh-fridЈ-e¯-uhm) nous bases found in nucleotides, character- ing of ribonucleotides used by the translation (plural, protonephridia) An excretory ized by a six-membered ring fused to a ﬁve- machinery during polypeptide synthesis. system, such as the ﬂame bulb system of membered ring. Adenine (A) and guanine (G) receptacle The base of a ﬂower; the part of the ﬂatworms, consisting of a network of tubules are purines. stem that is the site of attachment of the ﬂoral
Glossary lacking internal openings. pyrimidine (puh-rimЈ-uh-de¯n) One of two types organs. proton-motive force The potential energy of nitrogenous bases found in nucleotides, char- receptor potential An initial response of a stored in the form of a proton electrochemical acterized by a six-membered ring. Cytosine (C), receptor cell to a stimulus, consisting of a gradient, generated by the pumping of hydro- thymine (T), and uracil (U) are pyrimidines. change in voltage across the receptor mem- ϩ gen ions (H ) across a biological membrane quantitative character A heritable feature that brane proportional to the stimulus strength. during chemiosmosis. varies continuously over a range rather than in receptor tyrosine kinase (RTK) A receptor proto-oncogene (pro–Ј-to– -onЈ-ko– -je¯n) A normal an either-or fashion. protein spanning the plasma membrane, the cellular gene that has the potential to become quaternary structure (kwot-er-na–r-e¯) The par- cytoplasmic (intracellular) part of which can an oncogene. ticular shape of a complex, aggregate protein, catalyze the transfer of a phosphate group protoplast The living part of a plant cell, which deﬁned by the characteristic three-dimensional from ATP to a tyrosine on another protein. Re- also includes the plasma membrane. arrangement of its constituent subunits, each a ceptor tyrosine kinases often respond to the protoplast fusion The fusing of two protoplasts polypeptide. binding of a signaling molecule by dimerizing from different plant species that would other- R plasmid A bacterial plasmid carrying genes and then phosphorylating a tyrosine on the wise be reproductively incompatible. that confer resistance to certain antibiotics. cytoplasmic portion of the other receptor in protostome development In animals, a devel- radial cleavage A type of embryonic develop- the dimer. The phosphorylated tyrosines on opmental mode distinguished by the develop- ment in deuterostomes in which the planes of the receptors then activate other signal trans- ment of the mouth from the blastopore; often cell division that transform the zygote into a duction proteins within the cell. also characterized by spiral cleavage and by the ball of cells are either parallel or perpendicular receptor-mediated endocytosis (enЈ-do– -sı¯-to–Ј- body cavity forming when solid masses of to the vertical axis of the embryo, thereby sis) The movement of speciﬁc molecules into a mesoderm split. aligning tiers of cells one above the other. cell by the inward budding of vesicles contain- provirus A viral genome that is permanently radial symmetry Symmetry in which the body ing proteins with receptor sites speciﬁc to the inserted into a host genome. is shaped like a pie or barrel (lacking a left side molecules being taken in; enables a cell to ac- proximal tubule In the vertebrate kidney, the and a right side) and can be divided into quire bulk quantities of speciﬁc substances. portion of a nephron immediately downstream mirror-imaged halves by any plane through recessive allele An allele whose phenotypic from Bowman’s capsule that conveys and helps its central axis. effect is not observed in a heterozygote. reﬁne ﬁltrate. radiation The emission of electromagnetic waves reciprocal altruism Altruistic behavior between pseudocoelomate (su¯Ј-do– -se¯Ј-lo– -ma–t) An animal by all objects warmer than absolute zero. unrelated individuals, whereby the altruistic whose body cavity is lined by tissue derived radicle An embryonic root of a plant. individual beneﬁts in the future when the from mesoderm and endoderm. radioactive isotope An isotope (an atomic form beneﬁciary reciprocates. pseudogene (su¯Ј-do– -je¯n) A DNA segment very of a chemical element) that is unstable; the recombinant chromosome A chromosome similar to a real gene but which does not yield nucleus decays spontaneously, giving off created when crossing over combines DNA a functional product; a DNA segment that for- detectable particles and energy. from two parents into a single chromosome. merly functioned as a gene but has become radiolarian A protist, usually marine, with a recombinant DNA A DNA molecule made in inactivated in a particular species because of shell generally made of silica and pseudopodia vitro with segments from different sources. mutation. that radiate from the central body. recombinant type (recombinant) An off- pseudopodium (su¯Ј-do– -po–Ј-de¯-um) (plural, radiometric dating A method for determining spring whose phenotype differs from that of pseudopodia) A cellular extension of the absolute age of rocks and fossils, based on the true-breeding P generation parents; also amoeboid cells used in moving and feeding. the half-life of radioactive isotopes. refers to the phenotype itself. pterophyte (terЈ-uh-fı¯t) An informal name for radula A straplike scraping organ used by many rectum The terminal portion of the large a member of the phylum Pterophyta, which molluscs during feeding. intestine, where the feces are stored prior to includes ferns, horsetails, and whisk ferns ras gene A gene that codes for Ras, a G protein elimination. and their relatives. that relays a growth signal from a growth red alga A photosynthetic protist, named for its pterosaur Winged reptile that lived during the factor receptor on the plasma membrane to color, which results from a red pigment that Mesozoic era. a cascade of protein kinases, ultimately masks the green of chlorophyll. Most red algae pulmocutaneous circuit A branch of the resulting in stimulation of the cell cycle. are multicellular and marine. circulatory system in many amphibians ratite (ratЈ-ı¯t) Member of the group of ﬂightless redox reaction (re¯Ј-doks) A chemical reaction that supplies the lungs and skin. birds. involving the complete or partial transfer of pulmonary circuit The branch of the ray-ﬁnned ﬁsh Member of the class one or more electrons from one reactant to an- circulatory system that supplies the lungs. Actinopterygii, aquatic osteichthyans with ﬁns other; short for reduction-oxidation reaction. pulse The rhythmic bulging of the artery walls supported by long, ﬂexible rays, including reducing agent The electron donor in a redox with each heartbeat. tuna, bass, and herring. reaction. punctuated equilibria In the fossil record, long reabsorption In excretory systems, the recovery reduction The complete or partial addition of periods of apparent stasis, in which a species of solutes and water from ﬁltrate. electrons to a substance involved in a redox undergoes little or no morphological change, reactant A starting material in a chemical reaction. reaction. interrupted by relatively brief periods of reaction-center complex A complex of pro- reﬂex An automatic reaction to a stimulus, sudden change. teins associated with a special pair of chloro- mediated by the spinal cord or lower brain. Punnett square A diagram used in the study of phyll a molecules and a primary electron refractory period (re¯-fraktЈ-o–r-e¯) The short time inheritance to show the predicted genotypic acceptor. Located centrally in a photosystem, immediately after an action potential in which
G–29 GLOSSARY the neuron cannot respond to another stimu- response (1) In cellular communication, the rhizoid (rı¯Ј-zoyd) A long, tubular single cell or lus, owing to the inactivation of voltage-gated change in a speciﬁc cellular activity brought ﬁlament of cells that anchors bryophytes to sodium channels. about by a transduced signal from outside the the ground. Unlike roots, rhizoids are not com- regulator An animal for which mechanisms of cell. (2) In feedback regulation, a physiological posed of tissues, lack specialized conducting homeostasis moderate internal changes in a activity triggered by a change in a variable. cells, and do not play a primary role in water particular variable in the face of external resting potential The membrane potential char- and mineral absorption. ﬂuctuation of that variable. acteristic of a nonconducting excitable cell, rhizosphere The soil region close to plant roots regulatory gene A gene that codes for a protein, with the inside of the cell more negative than and characterized by a high level of microbio- such as a repressor, that controls the transcrip- the outside. logical activity. tion of another gene or group of genes. restriction enzyme An endonuclease (type of rhodopsin (ro– -dopЈ-sin) A visual pigment con- reinforcement In evolutionary biology, a enzyme) that recognizes and cuts DNA mol- sisting of retinal and opsin. Upon absorbing Glossary process in which a process in which natural ecules foreign to a bacterium (such as phage light, the retinal changes shape and dissociates selection strengthens prezygotic barriers to genomes). The enzyme cuts at speciﬁc from the opsin. reproduction, thus reducing the chances of nucleotide sequences (restriction sites). rhythm method A form of contraception that hybrid formation. Such a process is likely to restriction fragment A DNA segment that re- relies on refraining from sexual intercourse occur only if hybrid offspring are less ﬁt than sults from the cutting of DNA by a restriction when conception is most likely to occur; also members of the parent species. enzyme. called natural family planning. relative abundance The proportional abun- restriction fragment length polymorphism ribonucleic acid (RNA) (rı¯Ј-bo– -nu¯-kla–Ј-ik) A dance of different species in a community. (RFLP) A single nucleotide polymorphism type of nucleic acid consisting of a polynu- relative ﬁtness The contribution an individual (SNP) that exists in the restriction site for a cleotide made up of nucleotide monomers makes to the gene pool of the next generation, particular enzyme, thus making the site unrec- with a ribose sugar and the nitrogenous bases relative to the contributions of other individu- ognizable by that enzyme and changing the adenine (A), cytosine (C), guanine (G), and als in the population. lengths of the restriction fragments formed by uracil (U); usually single-stranded; functions in renal cortex The outer portion of the vertebrate digestion with that enzyme. A RFLP can be in protein synthesis, gene regulation, and as the kidney. coding or noncoding DNA. genome of some viruses. renal medulla The inner portion of the restriction site A speciﬁc sequence on a DNA ribose The sugar component of RNA nucleotides. vertebrate kidney, beneath the renal cortex. strand that is recognized and cut by a ribosomal RNA (rRNA) (rı¯Ј-buh-so–Ј-mul) RNA renal pelvis The funnel-shaped chamber that restriction enzyme. molecules that, together with proteins, make receives processed ﬁltrate from the vertebrate reticular formation (re-tikЈ-yu¯-ler) A diffuse up ribosomes; the most abundant type of RNA. kidney’s collecting ducts and is drained by the network of neurons in the core of the brain- ribosome (rı¯Ј-buh-so–mЈ) A complex of rRNA and ureter. stem that ﬁlters information traveling to the protein molecules that functions as a site of renin-angiotensin-aldosterone system cerebral cortex. protein synthesis in the cytoplasm; consists of (RAAS) A hormone cascade pathway that helps retina (retЈ-i-nuh) The innermost layer of the a large and a small subunit. In eukaryotic cells, regulate blood pressure and blood volume. vertebrate eye, containing photoreceptor cells each subunit is assembled in the nucleolus. See repetitive DNA Nucleotide sequences, usually (rods and cones) and neurons; transmits im- also nucleolus. noncoding, that are present in many copies in ages formed by the lens to the brain via the ribozyme (rı¯Ј-buh-zı¯m) An RNA molecule that a eukaryotic genome. The repeated units may optic nerve. functions as an enzyme, such as an intron that be short and arranged tandemly (in series) or retinal The light-absorbing pigment in rods and catalyzes its own removal during RNA splicing. long and dispersed in the genome. cones of the vertebrate eye. RNA interference (RNAi) A technique used to replication fork A Y-shaped region on a retrotransposon (reЈ-tro– -trans-po–Ј-zon) A trans- silence the expression of selected genes. RNAi replicating DNA molecule where the parental posable element that moves within a genome uses synthetic double-stranded RNA molecules strands are being unwound and new strands by means of an RNA intermediate, a transcript that match the sequence of a particular gene are being synthesized. of the retrotransposon DNA. to trigger the breakdown of the gene’s messen- repressor A protein that inhibits gene transcrip- retrovirus (reЈ-tro– -vı¯Ј-rus) An RNA virus that ger RNA. tion. In prokaryotes, repressors bind to the replicates by transcribing its RNA into DNA RNA polymerase An enzyme that links ribonu- DNA in or near the promoter. In eukaryotes, and then inserting the DNA into a cellular cleotides into a growing RNA chain during repressors may bind to control elements chromosome; an important class of cancer- transcription, based on complementary bind- within enhancers, to activators, or to other causing viruses. ing to nucleotides on a DNA template strand. proteins in a way that blocks activators from reverse transcriptase (tran-skripЈ-ta–s) An en- RNA processing Modiﬁcation of RNA primary binding to DNA. zyme encoded by certain viruses (retroviruses) transcripts, including splicing out of introns, reproductive isolation The existence of biolog- that uses RNA as a template for DNA synthesis. joining together of exons, and alteration of the ical factors (barriers) that impede members of reverse transcriptase–polymerase chain re- 5Ј and 3Ј ends. two species from producing viable, fertile action (RT-PCR) A technique for determin- RNA splicing After synthesis of a eukaryotic offspring. ing expression of a particular gene. It uses primary RNA transcript, the removal of reproductive table An age-speciﬁc summary of reverse transcriptase and DNA polymerase to portions of the transcript (introns) that will the reproductive rates in a population. synthesize cDNA from all the mRNA in a sam- not be included in the mRNA and the joining reptile Member of the clade of amniotes that ple and then subjects the cDNA to PCR ampli- together of the remaining portions (exons). includes tuataras, lizards, snakes, turtles, ﬁcation using primers speciﬁc for the gene of rod A rodlike cell in the retina of the vertebrate crocodilians, and birds. interest. eye, sensitive to low light intensity. residual volume The amount of air that Rhizaria (rı¯-zaЈ-re¯-uh) One of ﬁve supergroups of root An organ in vascular plants that anchors the remains in the lungs after forceful exhalation. eukaryotes proposed in a current hypothesis of plant and enables it to absorb water and resource partitioning The division of environ- the evolutionary history of eukaryotes; a mor- minerals from the soil. mental resources by coexisting species such phologically diverse protist clade that is deﬁned root cap A cone of cells at the tip of a plant root that the niche of each species differs by one or by DNA similarities. See also Excavata, Chroma- that protects the apical meristem. more signiﬁcant factors from the niches of all lveolata, Archaeplastida, and Unikonta. root hair A tiny extension of a root epidermal coexisting species. rhizobacterium A soil bacterium whose popula- cell, growing just behind the root tip and respiratory pigment A protein that transports tion size is much enhanced in the rhizosphere, increasing surface area for absorption of oxygen in blood or hemolymph. the soil region close to a plant’s roots. water and minerals.
GLOSSARY G–30 root pressure Pressure exerted in the roots of scanning electron microscope (SEM) A mi- secondary succession A type of succession that plants as the result of osmosis, causing croscope that uses an electron beam to scan occurs where an existing community has been exudation from cut stems and guttation of the surface of a sample, coated with metal cleared by some disturbance that leaves the water from leaves. atoms, to study details of its topography. soil or substrate intact. root system All of a plant’s roots, which anchor schizophrenia (skitЈ-suh-fre¯Ј-ne¯-uh) A severe secretion (1) The discharge of molecules synthe- it in the soil, absorb and transport minerals mental disturbance characterized by psychotic sized by a cell. (2) The discharge of wastes from and water, and store food. episodes in which patients have a distorted the body ﬂuid into the ﬁltrate. rooted Describing a phylogenetic tree that con- perception of reality. secretory phase That portion of the uterine tains a branch point (often, the one farthest to Schwann cell A type of glial cell that forms (menstrual) cycle when the endometrium con- the left) representing the most recent common insulating myelin sheaths around the axons tinues to thicken, becomes more vascularized,
Glossary ancestor of all taxa in the tree. of neurons in the peripheral nervous system. and develops glands that secrete a ﬂuid rich in rough ER That portion of the endoplasmic science An approach to understanding the glycogen. reticulum with ribosomes attached. natural world. seed An adaptation of some terrestrial plants round window In the mammalian ear, the scion (sı¯Ј-un) The twig grafted onto the stock consisting of an embryo packaged along with point of contact where vibrations of the stapes when making a graft. a store of food within a protective coat. create a traveling series of pressure waves in sclereid (skla–rЈ-e¯-id) A short, irregular scle- seed coat A tough outer covering of a seed, the ﬂuid of the cochlea. renchyma cell in nutshells and seed coats. Scle- formed from the outer coat of an ovule. In a r-selection Selection for life history traits that reids are scattered throughout the parenchyma ﬂowering plant, the seed coat encloses and maximize reproductive success in uncrowded of some plants. protects the embryo and endosperm. environments; also called density-independent sclerenchyma cell (skluh-renЈ-kim-uh) A rigid, seedless vascular plant An informal name for a selection. supportive plant cell type usually lacking a plant that has vascular tissue but lacks seeds. rubisco (ru¯-bisЈ-ko–) Ribulose bisphosphate protoplast and possessing thick secondary Seedless vascular plants form a paraphyletic (RuBP) carboxylase, the enzyme that catalyzes walls strengthened by lignin at maturity. group that includes the phyla Lycophyta (club the ﬁrst step of the Calvin cycle (the addition scrotum A pouch of skin outside the abdomen mosses and their relatives) and Pterophyta
of CO2 to RuBP). that houses the testes; functions in maintain- (ferns and their relatives). ruminant (ru¯Ј-muh-nent) An animal, such as a ing the testes at the lower temperature selective permeability A property of biological cow or a sheep, with multiple stomach com- required for spermatogenesis. membranes that allows them to regulate the partments specialized for an herbivorous diet. second law of thermodynamics The princi- passage of substances across them. S phase The synthesis phase of the cell cycle; the ple stating that every energy transfer or trans- self-incompatibility The ability of a seed plant portion of interphase during which DNA is formation increases the entropy of the to reject its own pollen and sometimes the replicated. universe. Usable forms of energy are at least pollen of closely related individuals. saccule In the vertebrate ear, a chamber in the partly converted to heat. semelparity Reproduction in which an organism vestibule behind the oval window that second messenger A small, nonprotein, water- produces all of its offspring in a single event; participates in the sense of balance. soluble molecule or ion, such as a calcium ion also known as big-bang reproduction. ϩ salicylic acid (salЈ-i-silЈ-ik) A signaling molecule (Ca2 ) or cyclic AMP, that relays a signal to a semen (se¯Ј-mun) The ﬂuid that is ejaculated by in plants that may be partially responsible for cell’s interior in response to a signaling mol- the male during orgasm; contains sperm and activating systemic acquired resistance to ecule bound by a signal receptor protein. secretions from several glands of the male pathogens. secondary cell wall In plant cells, a strong and reproductive tract. salivary gland A gland associated with the oral durable matrix that is often deposited in sev- semicircular canals A three-part chamber of cavity that secretes substances that lubricate eral laminated layers around the plasma mem- the inner ear that functions in maintaining food and begin the process of chemical brane and provides protection and support. equilibrium. digestion. secondary consumer A carnivore that eats semiconservative model Type of DNA replica- salt A compound resulting from the formation of herbivores. tion in which the replicated double helix an ionic bond; also called an ionic compound. secondary endosymbiosis A process in eukary- consists of one old strand, derived from the saltatory conduction (solЈ-tuh-to–rЈ-e¯) Rapid otic evolution in which a heterotrophic eu- parental molecule, and one newly made transmission of a nerve impulse along an axon, karyotic cell engulfed a photosynthetic strand. resulting from the action potential jumping eukaryotic cell, which survived in a symbiotic semilunar valve A valve located at each exit of from one node of Ranvier to another, skipping relationship inside the heterotrophic cell. the heart, where the aorta leaves the left ven- the myelin-sheathed regions of membrane. secondary growth Growth produced by lateral tricle and the pulmonary artery leaves the sarcomere (sarЈ-ko– -me¯r) The fundamental, meristems, thickening the roots and shoots of right ventricle. repeating unit of striated muscle, delimited woody plants. seminal vesicle (semЈ-i-nul vesЈ-i-kul) A gland by the Z lines. secondary immune response The adaptive in males that secretes a ﬂuid component of sarcoplasmic reticulum (SR) (sarЈ-ko– -plazЈ- immune response elicited on second or subse- semen that lubricates and nourishes sperm. mik ruh-tikЈ-yu¯-lum) A specialized endoplas- quent exposures to a particular antigen. The seminiferous tubule (semЈ-i-nifЈ-er-us) A highly mic reticulum that regulates the calcium secondary immune response is more rapid, of coiled tube in the testis in which sperm are concentration in the cytosol of muscle cells. greater magnitude, and of longer duration produced. saturated fatty acid A fatty acid in which all than the primary immune response. senescence (se-nesЈ-ens) The growth phase in a carbons in the hydrocarbon tail are connected secondary oocyte (o–Ј-uh-sı¯t) An oocyte that plant or plant part (as a leaf) from full maturity by single bonds, thus maximizing the number has completed the ﬁrst of the two meiotic to death. of hydrogen atoms that are attached to the divisions. sensitive period A limited phase in an animal’s carbon skeleton. secondary production The amount of chemi- development when learning of particular savanna A tropical grassland biome with scat- cal energy in consumers’ food that is converted behaviors can take place; also called a tered individual trees and large herbivores and to their own new biomass during a given time critical period. maintained by occasional ﬁres and drought. period. sensor In homeostasis, a receptor that detects a scaffolding protein A type of large relay secondary structure Regions of repetitive coil- stimulus. protein to which several other relay proteins ing or folding of the polypeptide backbone of a sensory adaptation The tendency of sensory are simultaneously attached, increasing the protein due to hydrogen bonding between con- neurons to become less sensitive when they efﬁciency of signal transduction. stituents of the backbone (not the side chains). are stimulated repeatedly.
G–31 GLOSSARY sensory neuron A nerve cell that receives infor- short tandem repeat (STR) Simple sequence single-lens eye The camera-like eye found in mation from the internal or external environ- DNA containing multiple tandemly repeated some jellies, polychaete worms, spiders, and ment and transmits signals to the central units of two to ﬁve nucleotides. Variations in many molluscs. nervous system. STRs act as genetic markers in STR analysis, single-strand binding protein A protein that sensory reception The detection of a stimulus used to prepare genetic proﬁles. binds to the unpaired DNA strands during DNA by sensory cells. short-day plant A plant that ﬂowers (usually in replication, stabilizing them and holding them sensory receptor An organ, cell, or structure late summer, fall, or winter) only when the apart while they serve as templates for the within a cell that responds to speciﬁc stimuli light period is shorter than a critical length. synthesis of complementary strands of DNA. from an organism’s external or internal short-term memory The ability to hold infor- sinoatrial (SA) node A region in the right environment. mation, anticipations, or goals for a time and atrium of the heart that sets the rate and sensory transduction The conversion of stimu- then release them if they become irrelevant. timing at which all cardiac muscle cells Glossary lus energy to a change in the membrane sickle-cell disease A recessively inherited contract; the pacemaker. potential of a sensory receptor cell. human blood disorder in which a single sister chromatids Two copies of a duplicated sepal (se¯Ј-pul) A modiﬁed leaf in angiosperms nucleotide change in the ␤-globin gene causes chromosome attached to each other by that helps enclose and protect a ﬂower bud hemoglobin to aggregate, changing red blood proteins at the centromere and, sometimes, before it opens. cell shape and causing multiple symptoms in along the arms. While joined, two sister septum (plural, septa) One of the cross-walls afﬂicted individuals. chromatids make up one chromosome. that divide a fungal hypha into cells. Septa sieve plate An end wall in a sieve-tube element, Chromatids are eventually separated during generally have pores large enough to allow which facilitates the ﬂow of phloem sap in mitosis or meiosis II. ribosomes, mitochondria, and even nuclei angiosperm sieve tubes. sister taxa Groups of organisms that share an to ﬂow from cell to cell. sieve-tube element A living cell that conducts immediate common ancestor and hence are serial endosymbiosis A hypothesis for the ori- sugars and other organic nutrients in the each other’s closest relatives. gin of eukaryotes consisting of a sequence of phloem of angiosperms; also called a sieve- skeletal muscle A type of striated muscle that is endosymbiotic events in which mitochondria, tube member. Connected end to end, they generally responsible for the voluntary move- chloroplasts, and perhaps other cellular struc- form sieve tubes. ments of the body. tures were derived from small prokaryotes that sign stimulus An external sensory cue that sliding-ﬁlament model The idea that muscle had been engulfed by larger cells. triggers a ﬁxed action pattern by an animal. contraction is based on the movement of thin serotonin (serЈ-uh-to–Ј-nin) A neurotransmitter, signal In animal behavior, transmission of a (actin) ﬁlaments along thick (myosin) ﬁla- synthesized from the amino acid tryptophan, stimulus from one animal to another. The term ments, shortening the sarcomere, the basic that functions in the central nervous system. is also used in the context of communication unit of muscle organization. set point In homeostasis in animals, a value in other kinds of organisms and in cell-to-cell slow block to polyspermy The formation of maintained for a particular variable, such as communication in all multicellular organisms. the fertilization envelope and other changes in body temperature or solute concentration. signal peptide A sequence of about 20 amino an egg’s surface that prevent fusion of the egg seta (se¯Ј-tuh) (plural, setae) The elongated stalk acids at or near the leading (amino) end of a with more than one sperm. The slow block of a bryophyte sporophyte. polypeptide that targets it to the endoplasmic begins about 1 minute after fertilization. sex chromosome A chromosome responsible reticulum or other organelles in a eukaryotic cell. slow-twitch ﬁber A muscle ﬁber that can for determining the sex of an individual. signal transduction The linkage of a mechani- sustain long contractions. sex-linked gene A gene located on either sex cal, chemical, or electromagnetic stimulus to a small interfering RNA (siRNA) One of mul- chromosome. Most sex-linked genes are on the speciﬁc cellular response. tiple small, single-stranded RNA molecules X chromosome and show distinctive patterns signal transduction pathway A series of steps generated by cellular machinery from a long, of inheritance; there are very few genes on the linking a mechanical, chemical, or electrical linear, double-stranded RNA molecule. The Y chromosome. stimulus to a speciﬁc cellular response. siRNA associates with one or more proteins sexual dimorphism (dı¯-mo–rЈ-ﬁzm) Differences signal-recognition particle (SRP) A protein- in a complex that can degrade or prevent between the secondary sex characteristics of RNA complex that recognizes a signal peptide translation of an mRNA with a complemen- males and females. as it emerges from a ribosome and helps direct tary sequence. In some cases, siRNA can also sexual reproduction A type of reproduction in the ribosome to the endoplasmic reticulum block transcription by promoting chromatin which two parents give rise to offspring that (ER) by binding to a receptor protein on the ER. modiﬁcation. have unique combinations of genes inherited silent mutation A nucleotide-pair substitution small intestine The longest section of the from both parents via the gametes. that has no observable effect on the pheno- alimentary canal, so named because of its sexual selection A form of selection in which type; for example, within a gene, a mutation small diameter compared with that of the large individuals with certain inherited characteris- that results in a codon that codes for the same intestine; the principal site of the enzymatic tics are more likely than other individuals to amino acid. hydrolysis of food macromolecules and the obtain mates. simple fruit A fruit derived from a single carpel absorption of nutrients. Shannon diversity An index of community or several fused carpels. smooth ER That portion of the endoplasmic diversity symbolized by H and represented by simple sequence DNA A DNA sequence that reticulum that is free of ribosomes. ϭ ϩ ϩ the equation H –(pA ln pA pB ln pB contains many copies of tandemly repeated smooth muscle A type of muscle lacking the ϩ pC ln pC . . .), where A, B, C . . . are species, short sequences. striations of skeletal and cardiac muscle be- p is the relative abundance of each species, single bond A single covalent bond; the sharing cause of the uniform distribution of myosin ﬁl- and ln is the natural logarithm. of a pair of valence electrons by two atoms. aments in the cells; responsible for involuntary shared ancestral character A character, shared single circulation A circulatory system consist- body activities. by members of a particular clade, that origi- ing of a single pump and circuit, in which social learning Modiﬁcation of behavior nated in an ancestor that is not a member of blood passes from the sites of gas exchange to through the observation of other individuals. that clade. the rest of the body before returning to the sociobiology The study of social behavior based shared derived character An evolutionary heart. on evolutionary theory. novelty that is unique to a particular clade. single nucleotide polymorphism (SNP) sodium-potassium pump A transport protein shoot system The aerial portion of a plant body, A single base-pair site in a genome where in the plasma membrane of animal cells that consisting of stems, leaves, and (in angio- nucleotide variation is found in at least 1% of actively transports sodium out of the cell and sperms) ﬂowers. the population. potassium into the cell.
GLOSSARY G–32 soil horizon A soil layer with physical character- spermatogenesis The continuous and proliﬁc statocyst (statЈ-uh-sistЈ) A type of mechanorecep- istics that differ from those of the layers above production of mature sperm cells in the testis. tor that functions in equilibrium in inverte- or beneath. spermatogonium (plural, spermatogonia) A cell brates by use of statoliths, which stimulate hair solute (solЈ-yu¯t) A substance that is dissolved in a that divides mitotically to form spermatocytes. cells in relation to gravity. solution. sphincter (sﬁnkЈ-ter) A ringlike band of muscle statolith (statЈ-uh-lithЈ) (1) In plants, a special- Ψ solute potential ( S) A component of water ﬁbers that controls the size of an opening in ized plastid that contains dense starch grains potential that is proportional to the molarity the body, such as the passage between the and may play a role in detecting gravity. (2) In of a solution and that measures the effect of esophagus and the stomach. invertebrates, a dense particle that settles in solutes on the direction of water movement; spiral cleavage A type of embryonic develop- response to gravity and is found in sensory also called osmotic potential, it can be either ment in protostomes in which the planes of organs that function in equilibrium.
Glossary zero or negative. cell division that transform the zygote into a stele (ste¯l) The vascular tissue of a stem or root. solution A liquid that is a homogeneous mixture ball of cells are diagonal to the vertical axis of stem A vascular plant organ consisting of an al- of two or more substances. the embryo. As a result, the cells of each tier sit ternating system of nodes and internodes that solvent The dissolving agent of a solution. Water in the grooves between cells of adjacent tiers. support the leaves and reproductive structures. is the most versatile solvent known. spliceosome (splı¯Ј-so– -so–m) A large complex stem cell Any relatively unspecialized cell that somatic cell (so– -matЈ-ik) Any cell in a multicel- made up of proteins and RNA molecules that can produce, during a single division, one lular organism except a sperm or egg or their splices RNA by interacting with the ends of an identical daughter cell and one more special- precursors. RNA intron, releasing the intron and joining ized daughter cell that can undergo further somite One of a series of blocks of mesoderm the two adjacent exons. differentiation. that exist in pairs just lateral to the notochord spongocoel (sponЈ-jo– -se¯l) The central cavity of a steroid A type of lipid characterized by a carbon in a vertebrate embryo. sponge. skeleton consisting of four fused rings with soredium (plural, soredia) In lichens, a small spontaneous process A process that occurs various chemical groups attached. cluster of fungal hyphae with embedded algae. without an overall input of energy; a process sticky end A single-stranded end of a double- sorus (plural, sori) A cluster of sporangia on a that is energetically favorable. stranded restriction fragment. fern sporophyll. Sori may be arranged in sporangium (spo–r-anЈ-je¯-um) (plural, sporangia) stigma (plural, stigmata) The sticky part of a various patterns, such as parallel lines or A multicellular organ in fungi and plants in ﬂower’s carpel, which receives pollen grains. dots, which are useful in fern identiﬁcation. which meiosis occurs and haploid cells develop. stimulus In feedback regulation, a ﬂuctuation in Southern blotting A technique that enables spore (1) In the life cycle of a plant or alga under- a variable that triggers a response. speciﬁc nucleotide sequences to be detected in going alternation of generations, a haploid cell stipe A stemlike structure of a seaweed. samples of DNA. It involves gel electrophoresis produced in the sporophyte by meiosis. A spore stock The plant that provides the root system of DNA molecules and their transfer to a mem- can divide by mitosis to develop into a multicel- when making a graft. brane (blotting), followed by nucleic acid lular haploid individual, the gametophyte, stoma (sto–Ј-muh) (plural, stomata) A micro- hybridization with a labeled probe. without fusing with another cell. (2) In fungi, scopic pore surrounded by guard cells in the spatial learning The establishment of a a haploid cell, produced either sexually or epidermis of leaves and stems that allows gas memory that reﬂects the environment’s asexually, that produces a mycelium after exchange between the environment and the spatial structure. germination. interior of the plant. spatial summation A phenomenon of neural sporocyte A diploid cell, also known as a spore stomach An organ of the digestive system that integration in which the membrane potential mother cell, that undergoes meiosis and stores food and performs preliminary steps of of the postsynaptic cell is determined by the generates haploid spores. digestion. combined effect of EPSPs or IPSPs produced sporophyll (spo–Ј-ruh-ﬁl) A modiﬁed leaf that stramenopile A protist in which a “hairy” nearly simultaneously by different synapses. bears sporangia and hence is specialized for ﬂagellum (one covered with ﬁne, hairlike speciation (spe¯Ј-se¯-a–Ј-shun) An evolutionary reproduction. projections) is paired with a shorter, smooth process in which one species splits into two or sporophyte (spo– -ruh-fı¯tЈ) In organisms (plants ﬂagellum. more species. and some algae) that have alternation of stratum (strahЈ-tum) (plural, strata) A rock layer species (spe¯Ј-se¯z) A population or group of popu- generations, the multicellular diploid form formed when new layers of sediment cover lations whose members have the potential to that results from the union of gametes. The older ones and compress them. interbreed in nature and produce viable, fertile sporophyte produces haploid spores by meiosis striated muscle Muscle in which the regular offspring, but do not produce viable, fertile that develop into gametophytes. arrangement of ﬁlaments creates a pattern of offspring with members of other such groups. sporopollenin (spo–r-uh-polЈ-eh-nin) A durable light and dark bands. species diversity The number and relative polymer that covers exposed zygotes of strigolactones A class of plant hormone that abundance of species in a biological charophyte algae and forms the walls of plant inhibits shoot branching, triggers the germina- community. spores, preventing them from drying out. tion of parasitic plant seeds, and stimulates the species richness The number of species in a stabilizing selection Natural selection in association of plant roots with mycorrhizal biological community. which intermediate phenotypes survive or fungi. species-area curve The biodiversity pattern that reproduce more successfully than do extreme strobilus (stro– -bı¯Ј-lus) (plural, strobili) The tech- shows that the larger the geographic area of a phenotypes. nical term for a cluster of sporophylls known community is, the more species it has. stamen (sta–Ј-men) The pollen-producing repro- commonly as a cone, found in most gymno- speciﬁc heat The amount of heat that must be ductive organ of a ﬂower, consisting of an sperms and some seedless vascular plants. absorbed or lost for 1 g of a substance to anther and a ﬁlament. stroke The death of nervous tissue in the brain, change its temperature by 1°C. standard metabolic rate (SMR) Metabolic rate usually resulting from rupture or blockage of spectrophotometer An instrument that mea- of a resting, fasting, and nonstressed ectotherm arteries in the head. sures the proportions of light of different at a particular temperature. stroke volume The volume of blood pumped by wavelengths absorbed and transmitted by a starch A storage polysaccharide in plants, con- a heart ventricle in a single contraction. pigment solution. sisting entirely of glucose monomers joined by stroma (stro–Ј-muh) The dense ﬂuid within the sperm The male gamete. α glycosidic linkages. chloroplast surrounding the thylakoid mem- spermatheca (sperЈ-muh-the¯Ј-kuh) In many start point In transcription, the nucleotide posi- brane and containing ribosomes and DNA; insects, a sac in the female reproductive tion on the promoter where RNA polymerase involved in the synthesis of organic molecules system where sperm are stored. begins synthesis of RNA. from carbon dioxide and water.
G–33 GLOSSARY stromatolite Layered rock that results from the symplast In plants, the continuum of cytoplasm telomere (telЈ-uh-me¯r) The tandemly repetitive activities of prokaryotes that bind thin ﬁlms of connected by plasmodesmata between cells. DNA at the end of a eukaryotic chromosome’s sediment together. synapse (sinЈ-aps) The junction where a neuron DNA molecule. Telomeres protect the organ- structural isomer One of several compounds communicates with another cell across a nar- ism’s genes from being eroded during successive that have the same molecular formula but row gap via a neurotransmitter or an electrical rounds of replication. See also repetitive DNA. differ in the covalent arrangements of their coupling. telophase The ﬁfth and ﬁnal stage of mitosis, atoms. synapsid Member of an amniote clade distin- in which daughter nuclei are forming and style The stalk of a ﬂower’s carpel, with the ovary guished by a single hole on each side of the cytokinesis has typically begun. at the base and the stigma at the top. skull. Synapsids include the mammals. temperate broadleaf forest A biome located substrate The reactant on which an enzyme synapsis (si-napЈ-sis) The pairing and physical throughout midlatitude regions where there is
works. connection of duplicated homologous sufﬁcient moisture to support the growth of Glossary substrate feeder An animal that lives in or on chromosomes during prophase I of meiosis. large, broadleaf deciduous trees. its food source, eating its way through the systematics A scientiﬁc discipline focused on temperate grassland A terrestrial biome that food. classifying organisms and determining their exists at midlatitude regions and is dominated substrate-level phosphorylation The enzyme- evolutionary relationships. by grasses and forbs. catalyzed formation of ATP by direct transfer systemic acquired resistance A defensive re- temperate phage A phage that is capable of of a phosphate group to ADP from an interme- sponse in infected plants that helps protect replicating by either a lytic or lysogenic cycle. diate substrate in catabolism. healthy tissue from pathogenic invasion. temperature A measure of the intensity of heat sugar sink A plant organ that is a net consumer systemic circuit The branch of the circulatory in degrees, reﬂecting the average kinetic energy or storer of sugar. Growing roots, shoot tips, system that supplies oxygenated blood to and of the molecules. stems, and fruits are examples of sugar sinks carries deoxygenated blood away from organs template strand The DNA strand that provides supplied by phloem. and tissues throughout the body. the pattern, or template, for ordering, by com- sugar source A plant organ in which sugar is systems biology An approach to studying biol- plementary base pairing, the sequence of being produced by either photosynthesis or ogy that aims to model the dynamic behavior nucleotides in an RNA transcript. the breakdown of starch. Mature leaves are the of whole biological systems based on a study of temporal summation A phenomenon of neu- primary sugar sources of plants. the interactions among the system’s parts. ral integration in which the membrane poten- sulfhydryl group A chemical group consisting systole (sisЈ-to– -le¯) The stage of the cardiac cycle tial of the postsynaptic cell in a chemical of a sulfur atom bonded to a hydrogen atom. in which a heart chamber contracts and synapse is determined by the combined effect suprachiasmatic nucleus (SCN) A group of pumps blood. of EPSPs or IPSPs produced in rapid succession. neurons in the hypothalamus of mammals systolic pressure Blood pressure in the arteries tendon A ﬁbrous connective tissue that attaches that functions as a biological clock. during contraction of the ventricles. muscle to bone. surface tension A measure of how difﬁcult it is T cells The class of lymphocytes that mature in terminator In bacteria, a sequence of nu- to stretch or break the surface of a liquid. Wa- the thymus; they include both effector cells for cleotides in DNA that marks the end of a gene ter has a high surface tension because of the the cell-mediated immune response and helper and signals RNA polymerase to release the hydrogen bonding of surface molecules. cells required for both branches of adaptive newly made RNA molecule and detach from surfactant A substance secreted by alveoli that immunity. the DNA. decreases surface tension in the ﬂuid that coats taproot A main vertical root that develops from territoriality A behavior in which an animal the alveoli. an embryonic root and gives rise to lateral defends a bounded physical space against survivorship curve A plot of the number of (branch) roots. encroachment by other individuals, usually of members of a cohort that are still alive at each tastant Any chemical that stimulates the sensory its own species. age; one way to represent age-speciﬁc mortality. receptors in a taste bud. tertiary consumer (ter-she¯-a–rЈ-e¯) A carnivore suspension feeder An aquatic animal, such as a taste bud A collection of modiﬁed epithelial cells that eats other carnivores. sponge, clam, or baleen whale, that feeds by on the tongue or in the mouth that are tertiary structure The overall shape of a protein sifting small organisms or food particles from receptors for taste in mammals. molecule due to interactions of amino acid the water. TATA box A DNA sequence in eukaryotic side chains, including hydrophobic interac- sustainable agriculture Long-term productive promoters crucial in forming the transcription tions, ionic bonds, hydrogen bonds, and farming methods that are environmentally initiation complex. disulﬁde bridges. safe. taxis (takЈ-sis) An oriented movement toward or testcross Breeding an organism of unknown sustainable development Development that away from a stimulus. genotype with a homozygous recessive individ- meets the needs of people today without limit- taxon (plural, taxa) A named taxonomic unit at ual to determine the unknown genotype. The ing the ability of future generations to meet any given level of classiﬁcation. ratio of phenotypes in the offspring reveals the their needs. taxonomy (tak-sonЈ-uh-me¯) A scientiﬁc disci- unknown genotype. swim bladder In aquatic osteichthyans, an air pline concerned with naming and classifying testis (plural, testes) The male reproductive sac that enables the animal to control its the diverse forms of life. organ, or gonad, in which sperm and repro- buoyancy in the water. Tay-Sachs disease A human genetic disease ductive hormones are produced. symbiont (simЈ-be¯-ont) The smaller participant caused by a recessive allele for a dysfunctional testosterone A steroid hormone required for in a symbiotic relationship, living in or on enzyme, leading to accumulation of certain development of the male reproductive system, the host. lipids in the brain. Seizures, blindness, and spermatogenesis, and male secondary sex char- symbiosis An ecological relationship between degeneration of motor and mental perfor- acteristics; the major androgen in mammals. organisms of two different species that live mance usually become manifest a few months tetanus (tetЈ-uh-nus) The maximal, sustained together in direct and intimate contact. after birth, followed by death within a contraction of a skeletal muscle, caused by a sympathetic division One of three divisions of few years. very high frequency of action potentials the autonomic nervous system; generally technology The application of scientiﬁc knowl- elicited by continual stimulation. increases energy expenditure and prepares the edge for a speciﬁc purpose, often involving tetrapod A vertebrate clade whose members have body for action. industry or commerce but also including uses limbs with digits. Tetrapods include mammals, sympatric speciation (sim-patЈ-rik) The forma- in basic research. amphibians, and birds and other reptiles. tion of new species in populations that live in telomerase An enzyme that catalyzes the length- thalamus (thalЈ-uh-mus) An integrating center of the same geographic area. ening of telomeres in eukaryotic germ cells. the vertebrate forebrain. Neurons with cell bodies
GLOSSARY G–34 in the thalamus relay neural input to speciﬁc tidal volume The volume of air a mammal in- transduction (1) A process in which phages areas in the cerebral cortex and regulate what hales and exhales with each breath. (viruses) carry bacterial DNA from one bacter- information goes to the cerebral cortex. tight junction A type of intercellular junction ial cell to another. When these two cells are thallus (plural, thalli) A seaweed body that is between animal cells that prevents the leakage members of different species, transduction re- plantlike, consisting of a holdfast, stipe, and of material through the space between cells. sults in horizontal gene transfer. (2) In cellular blades, yet lacks true roots, stems, and leaves. tissue An integrated group of cells with a communication, the conversion of a signal theory An explanation that is broader in scope common structure, function, or both. from outside the cell to a form that can bring than a hypothesis, generates new hypotheses, tissue system One or more tissues organized about a speciﬁc cellular response; also called and is supported by a large body of evidence. into a functional unit connecting the organs of signal transduction. thermal energy See heat. a plant. transfer RNA (tRNA) An RNA molecule that
Glossary thermocline A narrow stratum of abrupt Toll-like receptor (TLR) A membrane receptor functions as a translator between nucleic acid temperature change in the ocean and in on a phagocytic white blood cell that and protein languages by carrying speciﬁc many temperate-zone lakes. recognizes fragments of molecules common amino acids to the ribosome, where they rec- thermodynamics (therЈ-mo– -dı¯-namЈ-iks) The to a set of pathogens. ognize the appropriate codons in the mRNA. study of energy transformations that occur in a tonicity The ability of a solution surrounding a transformation (1) The conversion of a normal collection of matter. See ﬁrst law of thermo- cell to cause that cell to gain or lose water. animal cell to a cancerous cell. (2) A change in dynamics; second law of thermodynamics. top-down model A model of community genotype and phenotype due to the assimila- thermoreceptor A receptor stimulated by either organization in which predation inﬂuences tion of external DNA by a cell. When the ex- heat or cold. community organization by controlling ternal DNA is from a member of a different thermoregulation The maintenance of internal herbivore numbers, which in turn control species, transformation results in horizontal body temperature within a tolerable range. plant or phytoplankton numbers, which in gene transfer. theropod Member of a group of dinosaurs that turn control nutrient levels; also called the transgenic Pertaining to an organism whose were bipedal carnivores. trophic cascade model. genome contains a gene introduced from thick ﬁlament A ﬁlament composed of stag- topoisomerase A protein that breaks, swivels, another organism of the same or a different gered arrays of myosin molecules; a compo- and rejoins DNA strands. During DNA replica- species. nent of myoﬁbrils in muscle ﬁbers. tion, topoisomerase helps to relieve strain in translation The synthesis of a polypeptide using thigmomorphogenesis A response in plants to the double helix ahead of the replication fork. the genetic information encoded in an mRNA chronic mechanical stimulation, resulting from topsoil A mixture of particles derived from rock, molecule. There is a change of “language” increased ethylene production. An example is living organisms, and decaying organic mate- from nucleotides to amino acids. thickening stems in response to strong winds. rial (humus). translocation (1) An aberration in chromosome thigmotropism (thig-moЈ-truh-pizm) A direc- torpor A physiological state in which activity is structure resulting from attachment of a chro- tional growth of a plant in response to touch. low and metabolism decreases. mosomal fragment to a nonhomologous chro- thin ﬁlament A ﬁlament consisting of two torsion In gastropods, a developmental process mosome. (2) During protein synthesis, the strands of actin and two strands of regulatory in which the visceral mass rotates up to 180°, third stage in the elongation cycle, when the protein coiled around one another; a compo- causing the animal’s anus and mantle cavity to RNA carrying the growing polypeptide moves nent of myoﬁbrils in muscle ﬁbers. be positioned above its head. from the A site to the P site on the ribosome. threatened species A species that is considered totipotent (to–Ј-tuh-po–tЈ-ent) Describing a cell (3) The transport of organic nutrients in the likely to become endangered in the foreseeable that can give rise to all parts of the embryo phloem of vascular plants. future. and adult, as well as extraembryonic mem- transmission The passage of a nerve impulse threshold The potential that an excitable cell branes in species that have them. along axons. membrane must reach for an action potential trace element An element indispensable for life transmission electron microscope (TEM) A to be initiated. but required in extremely minute amounts. microscope that passes an electron beam thrombus A ﬁbrin-containing clot that forms in trachea (tra–Ј-ke¯-uh) The portion of the respira- through very thin sections stained with metal a blood vessel and blocks the ﬂow of blood. tory tract that passes from the larynx to the atoms and is primarily used to study the inter- thylakoid (thı¯Ј-luh-koyd) A ﬂattened, membra- bronchi; also called the windpipe. nal ultrastructure of cells. nous sac inside a chloroplast. Thylakoids often tracheal system In insects, a system of transpiration The evaporative loss of water from exist in stacks called grana that are intercon- branched, air-ﬁlled tubes that extends a plant. nected; their membranes contain molecular throughout the body and carries oxygen transport epithelium One or more layers of “machinery” used to convert light energy to directly to cells. specialized epithelial cells that carry out and chemical energy. tracheid (tra–Ј-ke¯-id) A long, tapered water- regulate solute movement. thymus (thı¯Ј-mus) A small organ in the thoracic conducting cell found in the xylem of nearly transport protein A transmembrane protein cavity of vertebrates where maturation of T cells all vascular plants. Functioning tracheids are that helps a certain substance or class of closely is completed. no longer living. related substances to cross the membrane. thyroid gland An endocrine gland, located on trait One of two or more detectable variants in a transport vesicle A small membranous sac in a the ventral surface of the trachea, that secretes genetic character. eukaryotic cell’s cytoplasm carrying molecules two iodine-containing hormones, triiodothy- trans fat An unsaturated fat, formed artiﬁcially produced by the cell.
ronine (T3) and thyroxine (T4), as well as during hydrogenation of oils, containing one transposable element A segment of DNA that calcitonin. or more trans double bonds. can move within the genome of a cell by
thyroxine (T4) One of two iodine-containing transcription The synthesis of RNA using a DNA means of a DNA or RNA intermediate; also hormones that are secreted by the thyroid template. called a transposable genetic element. gland and that help regulate metabolism, transcription factor A regulatory protein that transposon A transposable element that development, and maturation in vertebrates. binds to DNA and affects transcription of moves within a genome by means of a DNA Ti plasmid A plasmid of a tumor-inducing bac- speciﬁc genes. intermediate. terium (the plant pathogen Agrobacterium) that transcription initiation complex The com- transverse (T) tubule An infolding of the integrates a segment of its DNA (T DNA) into a pleted assembly of transcription factors and plasma membrane of skeletal muscle cells. chromosome of a host plant. The Ti plasmid is RNA polymerase bound to a promoter. triacylglycerol (trı¯-asЈ-ul-glisЈ-uh-rol) A lipid con- frequently used as a vector for genetic transcription unit A region of DNA that is sisting of three fatty acids linked to one glycerol engineering in plants. transcribed into an RNA molecule. molecule; also called a fat or triglyceride.
G–35 GLOSSARY Ј –Ј – Ј – triiodothyronine (T3) (trı¯ -ı¯-o -do-thı¯ -ro-ne¯n) tundra A terrestrial biome at the extreme limits vaccination See immunization. One of two iodine-containing hormones that of plant growth. At the northernmost limits, it vaccine A harmless variant or derivative of a are secreted by the thyroid gland and that help is called arctic tundra, and at high altitudes, pathogen that stimulates a host’s immune sys- regulate metabolism, development, and where plant forms are limited to low shrubby tem to mount defenses against the pathogen. maturation in vertebrates. or matlike vegetation, it is called alpine tundra. vacuole (vakЈ-yu¯-o–lЈ) A membrane-bounded trimester In human development, one of three tunicate Member of the clade Urochordata, vesicle whose specialized function varies in 3-month-long periods of pregnancy. sessile marine chordates that lack a backbone. different kinds of cells. triple response A plant growth maneuver in turgid (terЈ-jid) Swollen or distended, as in plant vagina Part of the female reproductive system response to mechanical stress, involving cells. (A walled cell becomes turgid if it has a between the uterus and the outside opening; slowing of stem elongation, thickening of the lower water potential than its surroundings, the birth canal in mammals. During copula-
stem, and a curvature that causes the stem to resulting in entry of water.) tion, the vagina accommodates the male’s Glossary start growing horizontally. turgor pressure The force directed against a penis and receives sperm. triplet code A genetic information system in plant cell wall after the inﬂux of water and valence The bonding capacity of a given atom; which a set of three-nucleotide-long words swelling of the cell due to osmosis. usually equals the number of unpaired specify the amino acids for polypeptide chains. turnover The mixing of waters as a result of electrons required to complete the atom’s triploblastic Possessing three germ layers: the changing water-temperature proﬁles in a lake. outermost (valence) shell. endoderm, mesoderm, and ectoderm. Most turnover time The time required to replace the valence electron An electron in the outermost eumetazoans are triploblastic. standing crop of a population or group of popu- electron shell. trisomic Referring to a diploid cell that has three lations (for example, of phytoplankton), calcu- valence shell The outermost energy shell of an copies of a particular chromosome instead of lated as the ratio of standing crop to production. atom, containing the valence electrons in- the normal two. twin study A behavioral study in which re- volved in the chemical reactions of that atom. trochophore larva (tro–Ј-kuh-fo–r) Distinctive searchers compare the behavior of identical van der Waals interactions Weak attractions larval stage observed in some lophotrochozoan twins raised apart with that of identical twins between molecules or parts of molecules that animals, including some annelids and molluscs. raised in the same household. result from transient local partial charges. trophic efﬁciency The percentage of produc- tympanic membrane Another name for the variation Differences between members of the tion transferred from one trophic level to eardrum, the membrane between the outer same species. the next. and middle ear. vas deferens In mammals, the tube in the male trophic structure The different feeding relation- uniformitarianism The principle that mecha- reproductive system in which sperm travel ships in an ecosystem, which determine the nisms of change are constant over time. See from the epididymis to the urethra. route of energy ﬂow and the pattern of catastrophism. vasa recta The capillary system in the kidney chemical cycling. Unikonta (yu¯Ј-ni-konЈ-tuh) One of ﬁve super- that serves the loop of Henle. trophoblast The outer epithelium of a mam- groups of eukaryotes proposed in a current vascular cambium A cylinder of meristematic malian blastocyst. It forms the fetal part of the hypothesis of the evolutionary history of tissue in woody plants that adds layers of placenta, supporting embryonic development eukaryotes. This clade, which is supported by secondary vascular tissue called secondary but not forming part of the embryo proper. studies of myosin proteins and DNA, consists xylem (wood) and secondary phloem. tropic hormone A hormone that has an of amoebozoans and opisthokonts. See also vascular plant A plant with vascular tissue. endocrine gland or cells as a target. Excavata, Chromalveolata, Rhizaria, and Vascular plants include all living plant species tropical dry forest A terrestrial biome charac- Archaeplastida. except liverworts, mosses, and hornworts. terized by relatively high temperatures and unsaturated fatty acid A fatty acid that has vascular tissue Plant tissue consisting of cells precipitation overall but with a pronounced one or more double bonds between carbons in joined into tubes that transport water and dry season. the hydrocarbon tail. Such bonding reduces nutrients throughout the plant body. tropical rain forest A terrestrial biome charac- the number of hydrogen atoms attached to the vascular tissue system A transport system terized by relatively high precipitation and carbon skeleton. formed by xylem and phloem throughout a temperatures year-round. urea A soluble nitrogenous waste produced in the vascular plant. Xylem transports water and tropics Latitudes between 23.5° north and south. liver by a metabolic cycle that combines am- minerals; phloem transports sugars, the tropism A growth response that results in the monia with carbon dioxide. products of photosynthesis. curvature of whole plant organs toward or ureter (yu¯-re¯Ј-ter) A duct leading from the kidney vasectomy The cutting and sealing of each vas away from stimuli due to differential rates of to the urinary bladder. deferens to prevent sperm from entering the cell elongation. urethra (yu¯-re¯Ј-thruh) A tube that releases urine urethra. tropomyosin The regulatory protein that blocks from the mammalian body near the vagina in vasocongestion The ﬁlling of a tissue with the myosin-binding sites on actin molecules. females and through the penis in males; also blood, caused by increased blood ﬂow through troponin complex The regulatory proteins that serves in males as the exit tube for the repro- the arteries of that tissue. control the position of tropomyosin on the ductive system. vasoconstriction A decrease in the diameter of thin ﬁlament. uric acid A product of protein and purine metab- blood vessels caused by contraction of smooth true-breeding Referring to organisms that pro- olism and the major nitrogenous waste prod- muscles in the vessel walls. duce offspring of the same variety over many uct of insects, land snails, and many reptiles. vasodilation An increase in the diameter of generations of self-pollination. Uric acid is relatively nontoxic and largely blood vessels caused by relaxation of smooth tubal ligation A means of sterilization in which insoluble. muscles in the vessel walls. a woman’s two oviducts (fallopian tubes) are urinary bladder The pouch where urine is vector An organism that transmits pathogens tied closed to prevent eggs from reaching the stored prior to elimination. from one host to another. uterus. A segment of each oviduct is removed. uterine cycle The changes that occur in the vegetal pole The point at the end of an egg in tube foot One of numerous extensions of an uterus during the reproductive cycle of the hu- the hemisphere where most yolk is concen- echinoderm’s water vascular system. Tube feet man female; also called the menstrual cycle. trated; opposite of animal pole. function in locomotion and feeding. uterus A female organ where eggs are fertilized vegetative reproduction Cloning of plants by tumor-suppressor gene A gene whose protein and/or development of the young occurs. asexual means. product inhibits cell division, thereby prevent- utricle In the vertebrate ear, a chamber in the vein (1) In animals, a vessel that carries blood ing the uncontrolled cell growth that con- vestibule behind the oval window that opens toward the heart. (2) In plants, a vascular tributes to cancer. into the three semicircular canals. bundle in a leaf.
GLOSSARY G–36 ventilation The ﬂow of air or water over a visceral mass One of the three main parts of a X-linked gene A gene located on the X chromo- respiratory surface. mollusc; the part containing most of the some; such genes show a distinctive pattern of ventral Pertaining to the underside, or bottom, internal organs. See also foot, mantle. inheritance. of an animal with radial or bilateral symmetry. visible light That portion of the electromag- X-ray crystallography A technique used to study ventricle (venЈ-tri-kul) (1) A heart chamber that netic spectrum that can be detected as the three-dimensional structure of molecules. It pumps blood out of the heart. (2) A space in various colors by the human eye, ranging depends on the diffraction of an X-ray beam by the vertebrate brain, ﬁlled with cerebrospinal in wavelength from about 380 nm to about the individual atoms of a crystallized molecule. ﬂuid. 750 nm. xylem (zı¯Ј-lum) Vascular plant tissue consisting venule (venЈ-yu¯l) A vessel that conveys blood vital capacity The maximum volume of air that mainly of tubular dead cells that conduct most between a capillary bed and a vein. a mammal can inhale and exhale with each of the water and minerals upward from the
Glossary vernalization The use of cold treatment to breath. roots to the rest of the plant. induce a plant to ﬂower. vitamin An organic molecule required in the xylem sap The dilute solution of water and vertebrate A chordate animal with a backbone, diet in very small amounts. Many vitamins dissolved minerals carried through vessels including sharks and rays, ray-ﬁnned ﬁshes, serve as coenzymes or parts of coenzymes. and tracheids. coelacanths, lungﬁshes, amphibians, reptiles, viviparous (vı¯-vipЈ-uh-rus) Referring to a type of yeast Single-celled fungus. Yeasts reproduce asexu- and mammals. development in which the young are born ally by binary ﬁssion or by the pinching of vesicle (vesЈ-i-kul) A membranous sac in the alive after having been nourished in the uterus small buds off a parent cell. Many fungal cytoplasm of a eukaryotic cell. by blood from the placenta. species can grow both as yeasts and as a net- vessel A continuous water-conducting micropipe voltage-gated ion channel A specialized ion work of ﬁlaments; relatively few species grow found in most angiosperms and a few channel that opens or closes in response to only as yeasts. nonﬂowering vascular plants. changes in membrane potential. yolk Nutrients stored in an egg. vessel element A short, wide water-conducting vulva Collective term for the female external zero population growth (ZPG) A period of cell found in the xylem of most angiosperms genitalia. stability in population size, when additions to and a few nonﬂowering vascular plants. Dead water potential (Ψ) The physical property pre- the population through births and immigra- at maturity, vessel elements are aligned end to dicting the direction in which water will ﬂow, tion are balanced by subtractions through end to form micropipes called vessels. governed by solute concentration and applied deaths and emigration. vestigial structure A feature of an organism pressure. zona pellucida The extracellular matrix that is a historical remnant of a structure that water vascular system A network of hydraulic surrounding a mammalian egg. served a function in the organism’s ancestors. canals unique to echinoderms that branches zone of polarizing activity (ZPA) A block of villus (plural, villi) (1) A ﬁnger-like projection of into extensions called tube feet, which func- mesoderm located just under the ectoderm the inner surface of the small intestine. (2) A tion in locomotion and feeding. where the posterior side of a limb bud is attached ﬁnger-like projection of the chorion of the wavelength The distance between crests of to the body; required for proper pattern forma- mammalian placenta. Large numbers of villi waves, such as those of the electromagnetic tion along the anterior-posterior axis of the limb. increase the surface areas of these organs. spectrum. zoned reserve An extensive region that includes viral envelope A membrane, derived from wetland A habitat that is inundated by water at areas relatively undisturbed by humans sur- membranes of the host cell, that cloaks the least some of the time and that supports plants rounded by areas that have been changed by capsid, which in turn encloses a viral genome. adapted to water-saturated soil. human activity and are used for economic gain. viroid (vı¯Ј-royd) A plant pathogen consisting of a white matter Tracts of axons within the CNS. zoonotic pathogen A disease-causing agent that molecule of naked, circular RNA a few hundred wild type The phenotype most commonly is transmitted to humans from other animals. nucleotides long. observed in natural populations; also refers to zoospore Flagellated spore found in chytrid virulent Describing a pathogen against which an the individual with that phenotype. fungi and some protists. organism has little speciﬁc defense. wilting The drooping of leaves and stems as a zygomycete (zı¯Ј-guh-mı¯Ј-se¯t) Member of the virulent phage A phage that replicates only by result of plant cells becoming ﬂaccid. fungal phylum Zygomycota, characterized by a lytic cycle. wobble Flexibility in the base-pairing rules in the formation of a sturdy structure called a virus An infectious particle incapable of replicat- which the nucleotide at the 5Ј end of a tRNA zygosporangium during sexual reproduction. ing outside of a cell, consisting of an RNA or anticodon can form hydrogen bonds with zygosporangium (zı¯Ј-guh-spo– r-anЈ-je¯-um) In DNA genome surrounded by a protein coat more than one kind of base in the third zygomycete fungi, a sturdy multinucleate struc- (capsid) and, for some viruses, a membranous position (3Ј end) of a codon. ture in which karyogamy and meiosis occur. envelope. xerophyte A plant adapted to an arid climate. zygote (zı¯Ј-go–t) The diploid cell produced by the union of haploid gametes during fertilization; a fertilized egg.