Pronunciation Key accessory A fruit, or assemblage of , Inherited characteristic of an - 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 . tion in a specific environment. – Glossary Ј Ј a/ah ash (uh-klı¯ -muh-tı¯-za -shun) adaptive A -specific Physiological adjustment to a change in an defense that is mediated by B ch chose . (B cells) and T lymphocytes (T cells). It e¯ meet acetyl CoA Acetyl ; the entry com- exhibits specificity, , and self-nonself e/eh bet pound for the citric in cellular respi- recognition. Also called acquired immunity. g ration, formed from a fragment of pyruvate adaptive of evolutionary change ı¯ attached to a coenzyme. in which groups of many new i hit (asЈ-uh-til-ko–Ј-le¯n) One of the whose allow them to fill dif- ks box most common ; 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 to specific the probability of any one of two or more - o- robe , either depolarizing or hyperpolarizing the tually exclusive events occurring can be deter- membrane. mined by adding their probabilities. o ox acid A substance that increases the triphosphate See ATP (adenosine oy of a . triphosphate). s say acid , , or fog that is (uh-denЈ-uh-lil) An 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 -bodied an extracellular . u¯ boot lacking a cavity between the gut and The clinging of one substance to u/uh up outer wall. another, such as to walls by – z acrosomal reaction (akЈ-ruh-somЈ-ul) The means of hydrogen bonds. discharge of hydrolytic from the adipose A that insulates Ј ϭ primary accent , a vesicle in the tip of a , the body and serves as a reserve; contains Јϭsecondary accent when the sperm approaches or contacts an . -storing cells called adipose cells. acrosome (akЈ-ruh-so–m) A vesicle in the tip of a adrenal (uh-dre¯Ј-nul) One of two en- sperm containing hydrolytic enzymes and other docrine located adjacent to the kidneys 5Ј cap A modified form of that help the sperm reach the egg. in . Endocrine cells in the outer por- added onto the 5Ј end of a pre-mRNA (akЈ-tin) A globular that links into tion () respond to adrenocorticotropic . chains, two of which twist helically about each (ACTH) by secreting hor- A site One of a ’s three binding sites for other, forming microfilaments (actin filaments) mones that help maintain during tRNA during . The A site holds the in muscle and other kinds of cells. long-term . Neurosecretory cells in the tRNA carrying the to be added An electrical signal that propa- central portion (medulla) secrete epinephrine to the polypeptide chain. (A stands for gates (travels) along the membrane of a and in response to sig- aminoacyl tRNA.) or other excitable cell as a nongraded (all-or- nals triggered by short-term stress. ABC A model of flower formation none) . adrenocorticotropic hormone (ACTH) A identifying three classes of organ identity action spectrum A graph that profiles the - tropic hormone that is produced and secreted that direct formation of the four types of tive effectiveness of different wavelengths of by the and that stimulates floral organs. radiation in driving a particular . the production and of steroid abiotic (a–Ј-bı¯-otЈ-) Nonliving; referring to The amount of energy that re- by the . the physical and chemical properties of an actants must absorb before a aerobic A catabolic pathway for

environment. will start; also called free energy of activation. organic , using (O2) as the abortion The termination of a in A protein that binds to DNA and final acceptor in an electron transport . stimulates . In , chain and ultimately producing ATP. is (ABA) (ab-sisЈ-ik) A plant hor- activators bind in or near the ; in the most efficient catabolic pathway and is mone that slows growth, often antagonizing , 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 active immunity Long-lasting immunity con- The relative number of and facilitate drought tolerance. ferred by the action of B cells and T cells and of each age in a . absorption The third of processing in the resulting B and T memory cells specific for aggregate fruit A fruit derived from a single : the uptake of small - a . Active immunity can develop as a flower that has more than one carpel. cules by an ’s body. result of natural or . AIDS (acquired immunodeficiency absorption spectrum The range of a ’s The specific region of an enzyme that ) The symptoms and signs ability to absorb various wavelengths of ; binds the and that forms the pocket during the late stages of HIV infection, defined also a graph of such a range. in which occurs. by a specified reduction in the number of T abyssal zone (uh-bisЈ-ul) The part of the ’s The movement of a substance cells and the appearance of characteristic between 2,000 and 6,000 m deep. across a against its concentra- secondary . acanthodian (akЈ-an-tho–Ј-de¯-un) Any of a group tion or , mediated by followed by of ancient jawed aquatic from the specific transport proteins and requiring an ex- the reduction of pyruvate to ethyl alcohol, re- ϩ and periods. penditure of energy. generating NAD and releasing dioxide.

G–1 GLOSSARY Ј – (al-dos -tuh-ron) A A small, toxic molecule (NH3) produced separated and the daughter are that acts on tubules of the to regulate by fixation or as a moving to the of the cell. ϩ the transport of ions (Na ) and of protein and . anatomy The structure of an organism. ϩ ions (K ). ammonite A member of a group of shelled anchorage dependence The requirement that A diverse grade of photosynthetic , 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 until to initiate cell . Algal species are included in three of the five their at the end of the (anЈ-dro– -jen) Any steroid hormone, supergroups (, period (65.5 million years ago). such as , that stimulates the , and ). amniocentesis (amЈ-ne¯-o– -sen-te¯Ј-sis) A tech- and maintenance of the male Ј Ј alimentary canal (al -uh-men -tuh-re¯) A com- nique associated with prenatal diagnosis in reproductive and secondary Glossary

plete digestive tract, consisting of a tube which amniotic fluid is obtained by aspiration characteristics. Glossary between a and an . from a needle inserted into the . The (anЈ-yu¯-ployЈ-de¯) A chromosomal (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 . number. allergen An that triggers an exaggerated (amЈ-ne¯-o–t) Member of a of angiosperm (anЈ-je¯-o– -sperm) A flowering plant, . named for a key derived character, which forms inside a protective chamber allopatric (alЈ-uh-patЈ-rik) The for- the amniotic egg, which contains specialized called an ovary. mation of new species in that are , including the fluid-filled amnion, II A hormone that stimu- geographically isolated from one another. that protect the . include constriction of precapillary and allopolyploid (alЈ-o– -polЈ-e¯-ployd) A fertile indi- mammals as as and other . increases of NaCl and water by vidual that has more than two 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 in protection, nour- and volume. breeding and combining their chromosomes. ishment, and exchange. The amniotic egg anhydrobiosis (an-hı¯Ј-dro– -bı¯-o–Ј-sis) A dormant The binding of a regula- was a evolutionary innovation, allowing state involving loss of almost all . tory molecule to a protein at one site that to develop on in a fluid-filled animal 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 is concen- ent site. on water for . trated; opposite of vegetal pole. alpha (␣) (alЈ-fuh he¯Ј-liks) A coiled region (uh-me¯Ј-buh) A grade character- anion (anЈ-ı¯-on) A negatively charged ion. constituting one form of the secondary struc- ized by the presence of . anterior Pertaining to the front, or , 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 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 A 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 , and a multicellular change into other cell types. anther In an angiosperm, the terminal 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 and some algae. clade that includes many species with - or sperm-producing male gametophytes form. alternative RNA splicing A of eukaryotic tube-shaped pseudopodia. (an-thuh-ridЈ-e¯-um) (plural, gene regulation at the RNA-processing level in Member of the antheridia) In plants, the male , which different mRNA molecules are produced Amphibia, including , , and a moist chamber in which develop. from the same , depending . anthropoid (anЈ-thruh-poyd) Member of a on which RNA segments are treated as amphipathic (amЈ-fe¯-pathЈ-ik) Having both a group made up of the monkeys and and which as . hydrophilic region and a hydrophobic region. the (, , , chim- (alЈ-tru¯-iz-um) Selflessness; amplification The strengthening of panzees, , and ). that reduces an individual’s fitness while energy during . A protein secreted by cells (dif- increasing the fitness of another individual. (uh-migЈ-duh-luh) A structure in the ferentiated B cells) that binds to a particular (al-ve¯Ј-uh-let) A protist with membrane- temporal lobe of the vertebrate that has antigen; also called immunoglobulin. All anti- bounded sacs (alveoli) located just under the a major role in the processing of . bodies have the same Y-shaped structure and plasma membrane. (amЈ-uh-–sЈ) An enzyme that hydro- in their form consist of two identical alveolus (al-ve¯Ј-uh-lus) (plural, alveoli) One of lyzes (a from plants) and heavy chains and two identical light chains. the dead-end air sacs where (a glucose polymer from animals) anticodon (anЈ-tı¯-ko–Ј-don) A nucleotide triplet at occurs in a mammalian . into smaller and the disaccha- one end of a tRNA molecule that base-pairs Alzheimer’s (altsЈ-hı¯-merz) An age- ride . with a particular complementary 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 , also known as va- that helps integrate before (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 amino acid (uh-me¯nЈ-o–) An organic molecule than oxygen accept 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 serve as the of analogous Having characteristics that are similar antigen (anЈ-ti-jen) A substance that elicits an polypeptides. because of convergent , not . immune response by binding to receptors of B amino group A chemical group consisting of a (an-alЈ-uh-je¯) Similarity between two cells, , or of T cells. nitrogen bonded to two hydrogen atoms; species that is due to 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- and acquiring a of 1ϩ. with the same trait. cellular protein antigen and carries it to the aminoacyl-tRNA synthetase An enzyme that The fourth stage of , in which cell surface, where it is displayed and can be joins each amino acid to the appropriate tRNA. the of each chromosome have recognized by a .

GLOSSARY G–2 antigen The general term for a surface of the (plant) cells’ plasma plasma membrane in an animal cell undergo- protein, located on B cells and T cells, that membranes. ing mitosis. binds to , initiating adaptive immune arbuscular mycorrhizal A symbiotic 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 receptors, and the antigen recep- wall of plant and extend into the rons, regulating the interstitial environment, tors on T cells are called T cell receptors. cell (enclosed in tubes formed by invagination facilitating synaptic , 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 or internalizing pathogen (arЈ-ke¯Ј-uh) One of two prokaryotic A cardiovascular disease in proteins generates peptide fragments that are domains, the other . 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 , obstructing the

Glossary quently displayed on the cell surface to T cells. supergroups of eukaryotes proposed in a arteries and causing them to harden. , dendritic cells, and B cells are hypothesis of the evolutionary of atom The smallest unit of 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 algae, algae, and land plants, atomic mass The total mass of an atom, which - backbones in a DNA double descended from an ancient protist 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 , An atom’s dense central core, aphotic zone (a–Ј-fo–Ј-tik) The part of an ocean or Chromalveolata, Rhizaria, and Unikonta. containing and . 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 archegonia) In plants, the 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 (a–Ј-pik-ul) A bud at the tip of a plant gametes develop. elemental symbol. stem; also called a terminal bud. (ar-kenЈ-tuh-ron) The - ATP () (a-denЈ-o– -se¯n apical (a–Ј-pik-ul) Tendency for lined cavity, formed during , that trı¯-fosЈ-fa–t) An -containing 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 , because the apical bud partially inhibits (arЈ-ko– -so–r) Member of the reptilian phosphate bonds are hydrolyzed. This energy axillary bud growth. group that includes , and is used to drive endergonic reactions in cells. apical ectodermal (AER) A thickened , including birds. ATP A complex of several membrane area of at the tip of a bud that (ar-terЈ-e¯-o–l) A vessel that conveys proteins that functions in with promotes outgrowth of the . blood between an and a capillary . adjacent electron transport chains, using the apical (a–Ј-pik-ul ma–rЈ-uh-stem) artery A vessel that carries blood away from the energy of a hydrogen ion () concentra- Embryonic plant tissue in the tips of roots and to organs throughout the body. tion gradient to make ATP. ATP are of . The dividing cells of an apical A segmented ecdysozoan with a hard found in the inner mitochondrial membranes meristem enable the plant to grow in length. and jointed . Familiar of eukaryotic cells and in the plasma mem- apicomplexan (apЈ-e¯-kom-pleksЈ-un) A protist examples include , , , branes of prokaryotes. in a clade that includes many species that par- and . atrial natriuretic peptide (ANP) (a–Ј-tre¯-ul asitize animals. Some apicomplexans cause artificial selection The of naЈ-tre¯-yu¯-retЈ-ik) A peptide hormone secreted disease. domesticated plants and animals to encourage by cells of the atria of the heart in response to (apЈ-uh-mikЈ-sis) The ability of some the occurrence of desirable traits. high . ANP’s effects on the kid- plant species to reproduce asexually through The fruiting body of a sac fungus ney alter ion and water movement and reduce seeds without fertilization by a male . (ascomycete). blood pressure. (apЈ-o– -plast) external to the ascomycete (asЈ-kuh-mı¯Ј-se¯t) Member of the atrioventricular (AV) node A region of special- plasma membrane of a , including fungal , commonly called ized heart between the left and cell walls, intercellular , and the sac fungus. The comes from the saclike right atria where electrical impulses are de- within dead such as vessels structure in which the develop. layed for about 0.1 second before spreading to and . (plural, asci) A saclike capsule both ventricles and causing them to contract. (a–-puh-to–Ј-sus) A type of programmed located at the tip of a dikaryotic of a atrioventricular (AV) valve A heart valve cell , which is brought about by activa- sac fungus. located between each and tion of enzymes that break down many chemi- The of off- that prevents a backflow of blood when the cal components in the cell. from a single that occurs without ventricle contracts. aposematic coloration (apЈ-o– -si-matЈ-ik) The the fusion of gametes (by , 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 and transfers blood to a ventricle. 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 assisted migration The translocation of a acts on the cell that secreted it. blood cells that contribute to immunity. species to a favorable beyond its native An immunological A channel protein in the plasma range for the purpose of protecting the species disorder in which the turns membrane of a plant, animal, or microorgan- from human-caused threats. against self. ism cell that specifically facilitates , assisted reproductive A fertiliza- autonomic (otЈ-o– -nomЈ-ik) An the of free water across the tion procedure that generally involves surgi- efferent branch of the vertebrate peripheral membrane. cally removing (secondary ) from a nervous system that regulates the internal en- aqueous solution (a–Ј-kwe¯-us) A solution in ’s after hormonal stimulation, vironment; consists of the sympathetic, which water is the . fertilizing the eggs, and returning them to the parasympathetic, and enteric divisions. A member of a major arthropod group, woman’s body. autopolyploid (otЈ-o– -polЈ-e¯-ployd) An individ- the chelicerates. include spiders, associative The acquired ability to as- ual that has more than two chromosome sets , , and . sociate one environmental feature (such as a that are all derived from a single species. arbuscular (ar-busЈ-kyu¯-lur mı¯Ј-ko– - color) with another (such as danger). (otЈ-o– -so–m) A chromosome that is not rı¯Ј-zuh) Association of a fungus with a plant A radial array of short that directly involved in determining sex; not a sex root system in which the fungus causes the extends from each toward the chromosome.

G–3 GLOSSARY (otЈ-o–-–f) An organism that obtains basidiomycete (buh-sidЈ-e¯-o– -mı¯Ј-se¯t) Member of biofilm A surface-coating of one or more organic food molecules without other the fungal phylum , commonly species of prokaryotes that engage in metabolic organisms or substances derived from other called club fungus. The name comes from the . organisms. use energy from the club-like shape of the . A fuel produced from dry or from oxidation of inorganic substances to basidium (plural, basidia) (buh-sidЈ-e¯-um, buh- or combustible produced by plants. make organic molecules from inorganic ones. sidЈ-e¯-ah) A reproductive that pro- biogenic A derived (ôkЈ-sin) A term that primarily refers to duces sexual spores on the of from an amino acid. indoleacetic acid (IAA), a natural plant (club fungi). Any of the various hormone that has a of effects, including Batesian (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 .

growth, and fruit growth. looks like a species that is poisonous or other- The study of the 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 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 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 that uses organisms to add axillary bud (akЈ-sil-a–r-e¯) A structure that has The study of the evolution essential materials to a degraded . the potential to form a lateral shoot, or of and ecological basis for animal behavior. biological An internal timekeeper that branch. The bud appears in the angle formed A mass of abnormal cells with controls an organism’s biological rhythms. The between a and a stem. specific genetic and cellular changes such that biological clock marks with or without (akЈ-) A typically long extension, or the cells are not capable of surviving at a new environmental cues but often requires 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 . 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 marrow and become ef- environment. retained substances become more concentrated fector cells for the humoral immune response. (benЈ-tho–z) The communities of organ- at each higher in a . Bacteria One of two prokaryotic domains, the isms living in the benthic zone of an aquatic biological Definition of a other being Archaea. . species as a group of populations whose mem- bacterial artificial chromosome (BAC) A (␤) pleated sheet One form of the second- bers have the potential to interbreed in large that acts as a bacterial chromo- ary structure of proteins in which the polypep- and produce viable, fertile , but do some and can carry inserts of 100,000 to chain folds back and forth. Two regions of not produce viable, fertile offspring with mem- 300,000 base pairs (100–300 kb). the chain parallel to each other and are bers of other such groups. (bak-te¯rЈ-e¯-o– -fa–j) A 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 side chains). top-down model of organization contained within the vesicles formed by the A metabolic sequence that to alter ecosystem characteristics. For example, root cells of a . breaks fatty acids down to two-carbon ecologists can prevent algal blooms and that fragments that enter the cycle as by altering the density of maintains two or more phenotypic forms in acetyl CoA. higher-level consumers in instead of by a population. bicoid A gene that for a using chemical treatments. All tissues external to the vascular cam- protein responsible for specifying the anterior The total mass of organic matter com- bium, consisting mainly of the secondary end in . prising a group of organisms in a particular and layers of periderm. bilateral Body symmetry in which a habitat. A dense object lying along the inside central longitudinal divides the body biome (bı¯Ј-o–m) Any of the ’s major ecosys- of the 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 for terrestrial and inactivated . of animals with bilateral symmetry and three the physical environment for aquatic biomes angiosperm A member of one of three germ layers. and characterized by adaptations of organisms of early-diverging lineages of flowering A mixture of substances that is produced in to that particular environment. plants. Examples are , water lilies, the and stored in the ; enables The use of organisms to detoxify and anise and its relatives. formation of fat droplets in water as an aid in and restore polluted and degraded ecosystems. (ba–Ј-sul) A eukaryotic cell structure the and absorption of . The entire portion of inhabited consisting of a “9 ϩ 0” arrangement of micro- binary fission A method of asexual reproduc- by life; the sum of all the ’s ecosystems. tubule triplets. The basal body may organize tion by “division in half.” In prokaryotes, bi- The manipulation of organisms or the assembly of a 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 . fission, mitosis is part of the process. the organisms—in an environment. (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 and between photoreceptors and cells in at a comfortable . specific epithet; a binomen. the retina. basal In a specified group of organisms, a hot A relatively small area A depressive mental illness taxon whose evolutionary diverged with numerous endemic species and a large characterized by swings of 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. control pill A chemical contraceptive that concentration of a solution. (1) The overall flow and transfor- inhibits ovulation, retards follicular develop- Elaborate fruiting body of a mation of energy in an organism. (2) The ment, or alters a woman’s cervical to dikaryotic 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 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 . sis. (2) The flattened portion of a typical leaf. branch point The representation on a phylo- CAM plant A plant that uses crassulacean acid (blasЈ-tuh-se¯l) The fluid-filled cavity genetic 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 (blasЈ-tuh-sist) The blastula stage of point is usually shown as a dichotomy in dioxide entering open stomata during the mammalian , consist- which a branch representing the ancestral is converted to organic acids, which re-

ing of an , a cavity, and an outer lineage splits (at the branch point) into two lease CO2 for the during the day, layer, the . In humans, the blasto- branches, one for each of the two descendant when stomata are closed. forms 1 week after fertilization. lineages. explosion A relatively brief time in

Glossary An early embryonic cell arising brassinosteroid A steroid hormone in plants geologic history when many present-day during the stage of an early embryo. that has a variety of effects, including inducing of animals first appeared in the blastopore (blasЈ-to– -po–r) In a gastrula, the open- cell elongation, retarding leaf , 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 and the mouth Ventilation of the through alter- and saw the of the first large, in . nating inhalation and exhalation. hard-bodied animals. blastula (blasЈ-tyu¯-luh) A hollow ball of cells that (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. The uppermost layer of vegetation in a early embryonic development in animals. (brongЈ-kus) (plural, bronchi) One of terrestrial biome. blood A connective tissue with a fluid 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 into the lungs. sel that penetrates the tissues and consists of a blood cells, and cell fragments called brown alga A multicellular, photosynthetic pro- single layer of endothelial cells that allows are suspended. tist with a characteristic brown or color exchange between the blood and interstitial blue-light photoreceptor A type of light that results from in its . fluid. receptor in plants that initiates a variety of Most are marine, and some have a capillary bed A network of capillaries in a tissue responses, such as and slowing plantlike body (). or organ. of hypocotyl elongation. (brı¯Ј-uh-fı¯t) An informal name for a The protein shell that encloses a viral A fluid- or air-filled space between , liverwort, or ; a nonvascular . It may be rod-shaped, polyhedral, or the digestive tract and the body wall. plant that on land but lacks some of the more complex in shape. In multicellular eukaryotes, a 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 or protein are integrated into a functional whole—the liv- growths from the parent form and pinch off to that surrounds the 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 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 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 () bolus A lubricated ball of chewed food. to the solution. or (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 fibers embed- pieces of food. carbon from CO2 into an ded in . 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 ). internal chamber. photosynthetic cell arranged into tightly carbonyl group (kar-buh-ne¯lЈ) A chemical bottleneck effect that occurs packed sheaths around the veins of a leaf. group present in and 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 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 numbers, which in of which supplies CO2 for the Calvin cycle. (kar -de¯-ak) The alternating control numbers, which in turn (kalЈ-si-to–Ј-nin) A hormone secreted contractions and relaxations of the heart. control predator numbers. by the gland that lowers blood calcium A type of striated muscle that Bowman’s capsule (bo–Ј-munz) A cup-shaped levels by promoting calcium in forms the contractile wall of the heart. Its cells receptacle in the vertebrate kidney that is the bone and calcium from the kidneys; are joined by intercalated disks that relay the initial, expanded segment of the nonessential in 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 (braЈ-ke¯- uh-podЈ) A marine growing in culture. per minute by each ventricle of the heart. lophophorate with a shell divided into dorsal (cal) The amount of 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 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. A collection of structures in the verte- (with a capital C), usually used to indicate the An animal that mainly eats other brate brain, including the midbrain, the pons, energy content of food, is a kilocalorie. animals. and the ; functions in Calvin cycle The second of two major stages in (kuh-rotЈ-uh-noydЈ An accessory homeostasis, coordination of movement, and photosynthesis (following the light reactions), pigment, either or , in the

G–5 GLOSSARY 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- . 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 -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 (in plants Blood-derived fluid that surrounds, protects style, and ovary. and some protists), (in fungi), and against infection, nourishes, and cushions the carrier In , an individual who is het- (in bacteria) are important brain and . erozygous at a given genetic 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 , 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 The maximum population The catabolic pathways of system. size that can be supported by the available aerobic and anaerobic respiration, which break (serЈ-viks) The of the uterus, which , symbolized as K. down organic molecules and use an electron opens into the . (karЈ-til-ij) A flexible connective tissue transport chain for the production of ATP. A scrubland biome of dense, spiny with an of collagenous fibers cellular slime A type of protist character- found at midlatitudes along embedded in chondroitin . 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 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 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 (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- (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 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 . 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, ) class of neurotransmitters and hormones, central 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 . 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 and an . Living cation exchange A process in which positively of microtubule triplets arranged in a 9 ϩ 0 chelicerates include sea spiders, horseshoe charged are made available to a plant pattern. A centrosome has a pair of . crabs, scorpions, ticks, and spiders. when hydrogen ions in the displace (senЈ-tro– -me¯r) In a duplicated chro- An attraction between two mineral ions from the . mosome, the region on each sister atoms, resulting from a sharing of outer-shell cDNA 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. 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 has a single centromere, identified by its . forming one branch of the . DNA sequence.) 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 . the 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 of the reac- life of a cell, from its origin in the division of a tant during . 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 (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 A cyclically operat- the body. 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 , such as cell cycle. (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 at balance. chemoautotroph (ke¯Ј-mo– -otЈ-o– -tro–f) An organ- successively higher speeds. (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 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 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 of rapid cell A sensory receptor that re- visible with a light . 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 to a ball of cells. (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 plate. earlier in I between homologous usually consists of a single circular DNA mole- The long-term prevailing condi-

Glossary nonsister chromatids. Chiasmata become cule and associated proteins. It is found in the tions at a given place. visible after ends, with the two 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 of inheritance A basic A graded change in a character along a chitin (kı¯Ј-tin) A structural polysaccharide, con- principle in biology stating that genes are geographic . sisting of amino sugar monomers, found in located at specific positions (loci) on chromo- (klitЈ-uh-ris) An organ at the upper inter- many fungal cell walls and in the somes and that the behavior of chromosomes of the minora that engorges with of all . during accounts for inheritance blood and becomes erect during . (klo– rЈ-o– -fil) A green pigment located patterns. (klo– -a–Ј-kuh) A common opening for the in membranes within the chloroplasts of (kı¯Ј-lo– -mı¯Ј-kron) A 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. 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- to chemical energy. food and digestive formed in the gen selectively binds to and activates only chlorophyll a A photosynthetic pigment that . 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. , mostly aquatic fungi with liferate and differentiate into a of effec- An accessory photosynthetic - flagellated 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. (klo–rЈ-o– -plast) An found in (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 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. (ko– -anЈ-uh-sı¯t) A flagellated feeding locomotion or moving fluid past the cell; it is See also gene . cell found in . Also called a collar cell, formed from a core of nine outer doublet mi- cloning In genetic , 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 (ko– -lesЈ-tuh-rol) A steroid that forms extension of the plasma membrane. A primary 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 molecule for the sory and signaling role; it lacks the two inner tube back into a cell, and that synthesis of other biologically important microtubules (the “9 ϩ 0” arrangement). transfer recombinant DNA by infection. , such as many hormones. circadian rhythm (ser-ka–Ј-de¯-un) A physiologi- closed 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 , vertebrates with in the absence of external cues. kept separate from the interstitial fluid. made mostly of cartilage, such as -trans One of several compounds that (nı¯Ј-duh-sı¯t) A specialized cell unique and rays. have the same molecular formula and covalent to the phylum ; contains a capsule- Member of the phylum Chordata, - bonds between atoms but differ in the spatial like organelle 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 ; 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. (kokЈ-le¯-uh) The complex, coiled organ post-anal . A chemical cycle involving of hearing that contains the organ of Corti. chorionic villus (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 of both 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 is removed for analysis vate) to carbon dioxide; occurs within the in separate, distinguishable ways. to detect certain genetic and congenital defects in eukaryotic cells and in the codon (ko–Ј-don) A three-nucleotide sequence of in the fetus. 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 . 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 (kluh-disЈ-tiks) An approach to system- individuals. large protist clades, the and the atics in which organisms are placed into (se¯Ј-lo– m) A body cavity lined by tissue . See also Excavata, Rhizaria, groups called clades based primarily on derived only from . Archaeplastida, and Unikonta. . 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 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 . serving as a . Most function plasmodesmata and whose nucleus and (2) In , a sexual process in which two as coenzymes in metabolic reactions. may serve one or more adjacent cells exchange haploid micronuclei but do not The 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 . zyme. Cofactors can be permanently bound to reproductive advantage that will eventually An early, soft-bodied vertebrate with the active site or may bind loosely and reversibly, to the elimination of the other population. prominent and dental elements. along with the substrate, during catalysis. competitive inhibitor A substance that reduces The integrated study of The process of knowing that may in- the activity of an enzyme by entering the ecology, , , clude awareness, reasoning, recollection, and active site in place of the substrate, whose , and genetics to sustain judgment. structure it mimics. biological diversity at all levels. cognitive A neural representation of the 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 , or directly 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 using control element A segment of noncoding DNA explanation of the ascent of xylem . It mRNA as a template and the enzymes reverse that helps regulate transcription of a gene by states that exerts pull on xylem transcriptase and DNA . A cDNA serving as a 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 . molecules transmits this pull along the entire runs between a mouth and an anus; also called controlled 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 of a into a nant homozygote are indistinguishable. convection The mass movement of warmed air vagina; also called . complete flower A flower that has all four or to or from the surface of a body or coleoptile (ko–Ј-le¯-opЈ-tul) The covering of the basic floral organs: sepals, , 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 The transformation similar features in independent the young root of the embryo of a grass seed. of a into an adult that looks very differ- evolutionary lineages. collagen A 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 . compound A type of multifaceted eye in A kind of allosteric regulation collecting The location in the kidney insects and consisting of up to whereby a shape change in one subunit of a where processed filtrate, called , 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 that occurs in strands or cylin- the density of a increases those subunits. ders that support young parts of the plant or decreases. (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- A mixture made up of a liquid and parti- sperm in humans. rine and freshwater communities. cles that (because of their large size) remain condom A thin, rubber or natural 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 (ko–Ј-len) The largest section of the collect . structures secreted primarily by . Some vertebrate large intestine; functions in water conduction The direct transfer of thermal coral reefs also exist in cold, deep . absorption and formation of . (heat) between molecules of objects in A that binds to a (kuh-menЈ-suh-lizm) A symbi- direct contact with each other. bacterial 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 off. In animal behavior, a process conformer An animal for which an internal con- 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 with thicker, connection with other organisms, as well as (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- 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 Member of the largest right and left cerebral hemispheres in of different species living close enough phylum. Most are cone-bearing , mammals, enabling the hemispheres to together for potential . such as and firs. process information together.

GLOSSARY G–8 corpus luteum (korЈ-pus lu¯Ј-te¯-um) A secreting (kruh-sta–Ј-shun) A member of a A circular flow of tissue in the ovary that forms from the of mostly aquatic arthropods that cytoplasm, involving of collapsed follicle after ovulation and includes , crayfishes, crabs, shrimps, and actin filaments, that speeds the produces . and . distribution of materials within cells. cortex (1) The outer region of cytoplasm in a eu- cryptic coloration Camouflage that makes a 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 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. (kyu¯Ј-tuh-kul) (1) A waxy covering on the cytoplasm. cortical nephron In mammals and birds, a surface of stems and that prevents desic- A type of that, nephron with a 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 cells and transplanted cells. Any steroid hormone produced and chitin that are variously modified for dif- 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 . mass unit, or amu. diffusion of one substance to the “uphill” cyclic AMP (cAMP) Cyclic adenosine monophos- data Recorded . 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 (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 . 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 The exchange of a during the light reactions of photosynthesis shrimps. substance or heat between two fluids flowing that involves only I and that pro- 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 flows in the opposite direction of (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 . out of the blood. cell cycle. deductive reasoning A type of logic in which countercurrent multiplier system A counter- cyclin-dependent (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 A dark, hot, rials and generate concentration gradients. cystic fibrosis (sisЈ-tik fı¯-bro–Ј-sis) A human - oxygen-deficient environment associated with (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 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. A chordate with a head. vulnerability to infection; fatal if untreated. de-etiolation The changes a plant shoot crassulacean acid metabolism (CAM) An (sı¯Ј-to– -kro–m) An -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 Crassu- port chains in the mitochondria and chloro- 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 (1) A deficiency in a chromosome (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- (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 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 , 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 of populations, especially tem integrity. meiosis II. birth rates and death rates. rotation The practice of planting non- (sı¯Ј-to– -kı¯Ј-nin) Any of a class of related denaturation (de¯-na–Ј-chur-a–Ј-shun) In proteins, one 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 . Denatura- the care of 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, concentration, or temperature. genetic material between nonsister cytoplasmic determinant A maternal sub- (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- In angiosperms, the transfer placed into an egg influences the course of that receive signals from other . of pollen from an anther of a flower on one early development by regulating the expres- 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 , 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. 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 Member of an extremely diverse clade tic that varies with . 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 -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 - 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; and diploblastic Having two germ layers. Glossary causes them to stop dividing when they come lack of 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 PIP2 in the plasma membrane. 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 strand consists of nucleotide that forms the bottom wall of the thoracic cav- multiple flagella. monomers with a sugar and the ity in mammals. Contraction of the diaphragm Natural selection in nitrogenous bases adenine (A), (C), pulls air into the lungs. (2) A dome-shaped which individuals at one end of the guanine (G), and (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 (dı¯-sakЈ-uh-rı¯d) A double sugar, deoxyribose (de¯-okЈ-si-rı¯Ј-bo–s) The sugar compo- the uterus. consisting of two joined by nent of DNA , having one fewer (dı¯-apЈ-sid) Member of an amniote clade a glycosidic linkage formed by a dehydration hydroxyl group than , the sugar distinguished by a pair of on each side of reaction. component of RNA nucleotides. the . include the lepidosaurs and dispersal The movement of individuals or depolarization A change in a cell’s membrane . gametes away from their parent location. potential such that the inside of the mem- (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. The pattern of spacing among indi- depolarized if a stimulus decreases its diastolic pressure Blood pressure in the arteries viduals within the boundaries of a population. from the of Ϫ70 mV in the when the ventricles are relaxed. 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 . Recent molecular successfully than do individuals with inter- 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 A type of intercellular junction in grouped into , , 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 The expression 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 of one 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 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 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 (lı¯Ј-ga–s) A linking enzyme essential plant material, and the wastes of living organ- 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 (di-trı¯Ј-tus) Dead organic matter. 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 AaBb. another DNA fragment (such as a growing classification for a fungus with no known A cross between two organisms DNA chain). sexual stage. that are each heterozygous for both of the char- DNA The presence of methyl 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 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 , 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 (dı¯Ј-ne¯-un) In cilia and flagella, a large spaces of the root cortex. that catalyzes the elongation of new DNA (for 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. drives changes in dynein shape that ectopic Occurring in an abnormal location. There are several different DNA ; 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. (1) A taxonomic category above the ecdysozoan Member of a group of animal phyla 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 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 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 (i-kı¯Ј-no– -derm) A slow-moving or and males that successfully ; higher abundance or biomass than other sessile marine deuterostome with a water - generally smaller than the total population. species in a community. Dominant species cular system and, in larvae, bilateral symmetry. cell (1) A or gland cell that exert a powerful control over the occurrence include sea , brittle stars, sea performs the body’s response to stimuli as and distribution of other species. urchins, stars, and sea . directed by signals from the brain or other 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 (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 The region above the blastopore on species in terms of ecological niche, the ejaculation The of sperm from the the dorsal side of the amphibian embryo. sum of how members of the species interact through the muscular , A double covalent bond; the with the nonliving and living parts of their , and . sharing of two pairs of valence electrons by environment. ejaculatory duct In mammals, the short section two atoms. 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 . physical environment around them. gradient of an ion, which is affected by both double helix The form of native DNA, referring 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 shape. an ecosystem. potential (an electrical force). A human genetic disease usu- ecosystem An organism that electrogenic pump An active 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 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 (duh-shenЈ) humans. electricity, or magnetism. A human genetic disease caused by a The transition from one type of habitat 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 to a . ranging in wavelength from less than a tissue. ectoderm (ekЈ-to– -durm) The outermost of the nanometer to more than a kilometer. (du¯Ј-uh-de¯nЈ-um) The first section of three primary germ layers in animal embryos; electron A subatomic with a single nega- the , 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 , and that of a or proton. One or more elec- , liver, and gallbladder as well as from of the eye. trons move around the nucleus of an atom. gland cells of the intestinal wall. (ekЈ-to– -mı¯Ј-ko– -rı¯Ј-zuh) Associa- (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 (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 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 A sequence of endodermis In plant roots, the innermost layer of energy released from an Glossary electron carrier molecules (membrane pro- of the cortex that surrounds the vascular to drive an endergonic reaction. teins) that shuttle electrons down a of cylinder. enhancer A segment of eukaryotic DNA contain- reactions that release energy used to 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. 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 ; consists of 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 to a solution containing the , the , by the sympathetic and parasympathetic cells. The pulse creates temporary holes in the , vesicles, and . divisions of the autonomic nervous system. cells’ plasma membranes, through which DNA (enЈ-do– -me¯-tre¯-o–Ј-sis) The 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 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 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. A fungus that lives inside a leaf or the reaction. Most enzymes are proteins. embryo sac (emЈ-¯-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 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. 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 . layer of tightly packed cells. (2) The outermost with each step upward in the of life, A hard 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-) A coiled tubule parts as 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 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. , mediates “fight-or-flight” of extinction throughout all or a significant theory The theory that mito- responses to short-term stresses; also released portion of its range. 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 . is confined to a specific geographic area. ancestral eukaryotic cell. The engulfed cell and (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. (enЈ-do– -krin) A ductless gland which lives within the host cell and ultimately (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. (enЈ-do– -the¯Ј-le¯-um) The simple inherited gene. The internal system of com- squamous layer of cells lining the 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 An epithelial tissue. to hormones; functions in concert with the metabolism. This heat usually maintains a 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 . eumetazoan (yu¯Ј-met-uh-zo–Ј-un) Member of a (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 . eumetazoans. A sequence within a primary transcript that erythrocyte (eh-rithЈ-ruh-sı¯t) A that (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 . refers to the region of DNA from which this oxygen; also called a . (yu¯-sta–Ј-shun) The tube that sequence was transcribed. (EPO) (eh-rithЈ-ro– -poyЈ-uh-tin) connects the to the . exoskeleton A hard encasement on the surface A hormone that stimulates the production of eutherian (yu¯-the¯rЈ-e¯-un) Placental ; 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 (eh-sofЈ-uh-gus) A muscular tube that the by the placenta. muscles. conducts food, by , from the pharynx eutrophic lake (yu¯-tro–fЈ-ik) A lake that has a (ekЈ-so– -tokЈ-sin) A toxic protein that is to the stomach. high rate of biological supported secreted by a prokaryote or other pathogen 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 required highly concentrated in a , 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 An unsaturated fatty acid such as algae or . loosening the wall’s fabric. that an animal needs but cannot make. The process by which a liquid exponential Growth of a essential nutrient A substance that an organism changes to a gas. population in an , 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. (esЈ-truh-dı¯Ј-ol) A steroid hormone that evaporation, a result of the molecules with the A that stimulates the development and maintenance greatest kinetic energy changing from the contains a highly active bacterial promoter of the female and second- liquid to the gaseous state. just upstream of a restriction site where a ary sex characteristics; the major in 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 , 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 ; a The fusion of gametes (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 , 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 and genetic drift com- rather than , 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 unless the spiral is reversed, become extinct. estuary The area where a freshwater or that living species are descendants of ancestral The breakdown of food merges with the ocean. species that were different from the present- in compartments that are continuous with the (ethЈ-uh-le¯n) A gaseous 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 , leaf abscission, and population from generation to generation. surrounding animal cells, consisting of glyco- fruit . evolutionary tree A branching diagram that proteins, polysaccharides, and 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 (yu¯-kro–Ј-muh-tin) The less Excavata One of five supergroups of eukaryotes membranes (, 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 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, or the Dead Sea. (yu¯Ј-glen-id) A protist, such as and Unikonta. extreme 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) 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. , photosynthetic autotrophs, neurotransmitter from a presynaptic cell to a include extreme (“salt lovers”) and and pathogenic parasites. postsynaptic receptor; makes it more likely extreme (“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 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, (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 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 The interconnected feeding relation- interbreeding (or self-pollination) of the the stamen, the pollen-producing reproductive in an ecosystem.

hybrid F1 generation. organ of a flower. (1) The portion of a bryophyte sporophyte The passage of molecules filtrate Cell-free fluid extracted from the body that gathers , amino acids, water, and or ions down their electrochemical gradient fluid by the . minerals from the parent gametophyte via across a with the filtration In excretory , 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 , visceral mass. Glossary facilitation An interaction in which one species fimbria (plural, fimbriae) A short, hairlike 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 . first law of The principle of carbonate and extends pseudopodia through facultative anaerobe (fakЈ-ul-ta–Ј-tiv anЈ-uh-ro–b) : 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 composition is not reflective of that egg . 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 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 molecule; also called a Like motile cilia, eukaryotic flagella have a core A mutation occurring triacylglycerol or . 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 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 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 ’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 , 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 (in inhibition A method of metabolic with up to four sets of modified leaves, biological systems, 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 acts as an inhibitor of reproduction. change in entropy. an enzyme within that pathway. fluid feeder An animal that lives by sucking -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 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. . . 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 skeletons of organic molecules and involved of mineral nutrients to the soil. and secretes . in chemical reactions. fetus (fe¯Ј-tus) A developing mammal that has all follicle-stimulating hormone (FSH) A tropic G 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 -coupled receptor, to other until birth. production of eggs by the ovaries and sperm 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 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– -) 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 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 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 (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 A 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. or another polymer. A set of cell clones containing 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). (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 - 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, 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- The process by which gametes as RNAs. tions or population subgroups. are produced. gene flow The transfer of alleles from one popu- 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, , and —and gametophyte. gene pool The aggregate of all copies of every further subdivided into , 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- One of the three main layers in a of generations, the multicellular haploid form stricted 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 The introduction of genes into an gestation (jes-ta–Ј-shun) Pregnancy; the state of . afflicted individual for therapeutic purposes. carrying developing young within the female -aminobutyric acid (GABA) An gene-for-gene recognition A widespread form reproductive tract. amino acid that functions as a CNS of plant disease involving recogni- (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 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 with bipolar cells and transmits Effects of genetic drift are most pronounced (glial cells) Cells of the nervous system that action potentials to the brain via in the in small populations. support, regulate, and augment the functions optic nerve. The direct manipulation of neurons. A type of intercellular junction in of genes for practical purposes. global 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 . 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 A digestive fluid secreted by the nucleic acid probes. and distribution of organisms across the stomach. 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 , character- tions in both the digestion and distribution of 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. (glu¯Ј-kuh-gon) A hormone secreted by ment, a series of cell and tissue movements in genetics The scientific study of 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 ganism or virus; the complete complement of 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 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 of many people hav- neurotransmitter in the central nervous system.

G–15 GLOSSARY 3-phosphate (G3P) (glisЈ-er- some of whose members are more closely re- 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 . heat The total amount of kinetic energy due to an intermediate in glycolysis. 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 , which absorb energy. Heat is energy in its most random liver and muscle of animals; the animal reflected radiation and reradiate some form. equivalent of starch. of it back toward Earth. heat of vaporization The quantity of heat a A lipid with one or more covalently gross (GPP) The total liquid must absorb for 1 g of it to be converted attached . primary production of an ecosystem. from the liquid to the gaseous state. glycolysis (glı¯-kolЈ-uh-sis) A series of reactions system Plant tissues that are nei- heat- 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 (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 An enzyme that untwists the double gnathostome (naЈ-thu-sto–m) Member of the cells to stimulate 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 (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 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 . protein in red blood cells that reversibly binds noncellulose carbohydrates. guttation The exudation of water droplets from oxygen. (go–Ј-nadz) The male and female sex leaves, caused by root pressure in certain plants. (he¯Ј-mo– -limfЈ) In organs; the gamete-producing organs in gymnosperm (jimЈ-no– -sperm) A with an open circulatory system, the body most animals. that 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 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 In a neuron, a shift in the projections on the cell surface are displaced. or more blood-clotting proteins; characterized 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 to decay. hepatic portal A large vessel that conveys as it spreads. Hamilton’s rule The principle that for natural nutrient-laden blood from the small intestine A 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 (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 by producing both sperm that have a cell wall that is structurally less at work. and eggs. complex and contains more peptidoglycan (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 in the chloro- energy to elevate the hydrostatic pressure of (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 (gravЈ-uh-tro–Ј-pizm) A response of through the body and eventually returns to not transcribed. a plant or animal to . the heart. (hetЈ-uh-rokЈ-ruh-ne¯) Evolution- gray matter Regions of 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. (hetЈ-er-o– -sist) A specialized cell green chloroplasts that are similar in structure heart 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 (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 sapiens and our , 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 of tophyte generations differ in . to us than to . 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, 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. (hetЈ-er-o– -tro–f) An organism that is inherited from the organism’s , 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 Greater reproductive homologous structures Structures in different around a dissolved ion. success of heterozygous individuals compared species that are similar because of common 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- 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. (ho–Ј-muh-playЈ-ze¯) A similar (analo- of a polar covalent bond in hexapod An 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 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. 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 to the generation of a ion ϩ ϩ high-density (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 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 (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. (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 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 and are grown in mineral rather than . food source for the smaller symbiont. in soil. holdfast A rootlike structure that anchors a host range The limited number of species whose 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 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, , and sion of the egg; occurs in eggs that have little mone secreted by the chorion that maintains . yolk (such as those of the ) 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 ). Project An international hydroxyl group (hı¯-drokЈ-sil) A chemical group (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 . conserved in animals. Related sequences The branch of adaptive immunity that hymen A thin membrane that partly covers the occur in plants and . 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. (ho– -me¯-oЈ-tik) Any of the master fluids. hyperpolarization A change in a cell’s mem- regulatory genes that control placement and (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 . brane becomes more negative relative to the

G–17 GLOSSARY outside. Hyperpolarization reduces the chance in vitro 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- A disorder in which blood . 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 . 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 One of three main regions of the verte- secretes hormones of the posterior pituitary , 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 lar canals. Ј –Ј hypothesis (hı¯-poth -uh-sis) A testable explana- through a series of molts, each time 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 - 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 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. 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 . 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 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 , 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 . 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. 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. 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 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 The first stage of food processing in nails, , 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 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- (inЈ-ter-fe¯rЈ-on) A protein that has an intact organism. ing the anterior pituitary by . 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 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 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 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. The fusion of eggs and 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 . – 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 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 . internode A segment of a between in plants and certain algae in which the lactation The continued production of 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 vessel extending cell is not dividing. During interphase, cellular isopod A member of one of the largest groups of into the core of an and serving metabolic activity is high, chromosomes and crustaceans, which includes terrestrial, fresh- as the destination for absorbed . organelles are duplicated, and cell size may in- water, and marine species. Among the terres- Glycolysis followed crease. Interphase often accounts for about trial isopods are the pill bugs, or 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 . of an element, each with the same number of fragments, each synthesized in a 5Ј S 3Ј interspecific 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. Member of the clade Cephalochordata, species when resources are in short supply. iteroparity Reproduction in which adults small blade-shaped marine 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. (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- 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 that releases the enzyme 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 (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 A species moved by hu- reproduction, preceded by . cycles that may differ from the adult animal in mans, either intentionally or accidentally, (ka–rЈ-e¯-o– -tı¯p) A of the chromo- morphology, , and habitat. from its native location to a new geographic some pairs of a cell arranged by size and shape. (la–rЈ-inks) The portion of the respiratory region; also called non-native or exotic species. A species that is not necessar- tract containing the vocal cords; also called the (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 . A species, often introduced by processed into urine. lateral inhibition A process that sharpens the humans, that takes outside its native kilocalorie (kcal) A thousand ; 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- selection Natural selection that favors system A 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 An animal without a backbone. kinetic energy (kuh-netЈ-ik) The energy associ- aquatic ; 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. (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 . cambium are lateral meristems.

G–19 GLOSSARY A root that arises from the pericycle molecule (), 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 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 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 (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 , a are on different chromosomes. NADPH, releasing oxygen in the process. of ciliated 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 that have or larvae. strand synthesized continuously along the in a photosystem. low-density lipoprotein (LDL) A particle in template strand toward the replication fork in (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 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 , or that con- which a leaf arises. limnetic zone In a lake, the well-lit, open nects to the 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 (I and II) and (LH) (lu¯Ј-te¯-uh-nı¯Ј-zing) Ј (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 , , markers during crossing over of homologous (lı¯Ј-kuh-fı¯t) An informal name for a and two species of animals called chromosomes. member of the phylum Lycophyta, which . linked genes Genes located close enough includes club , spike mosses, and 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 . lipid (lipЈ-id) Any of a group of large biological interstitial fluid, in the 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. An organ located along a lymph . 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 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, 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 , 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 , osteichthyans with rod- chromosome as a , is replicated survival pattern of a population. shaped muscular fins, including , along with the chromosome, and does not A fibrous connective tissue that joins lungfishes, and tetrapods. kill the host. together at . local regulator A secreted molecule that (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 (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 .

GLOSSARY G–20 (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- (and death) of the host cell. (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; , , or , 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 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. -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 on the diversity of life and its protons and neutrons in an atom’s nucleus. anterior pituitary with multiple activities, subsequent recovery. 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. A hormone that is secreted by the proteins, and nucleic acids are macromolecules. mate-choice copying Behavior in which indi- 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 . organism must obtain in relatively large others, apparently as a result of social learning. membrane potential The difference in electri- amounts. See also . maternal effect gene A gene that, when cal charge (voltage) across a cell’s plasma mem- (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 . 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 , laurels, and black pepper , 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. 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 (menЈ-stru¯-ul) In humans and antigen presentation. Foreign MHC molecules for an , 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 (-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 allowing for indeterminate growth. in . activity, swallowing, digestion, and . 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 An that se- is the . 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 of avian development. 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 (mezЈ-o– -hı¯l) A gelatinous region mantle cavity A water-filled chamber that gametophyte. between the two layers of cells of a . 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 . 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 , 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- 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 A particular species chosen for animal uses in a unit of time. one or more proteins in a complex that can 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 solute per liter of solution. The collection and 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 (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. 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 , 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 to the . that uses nucleic acids or other molecules to the spindle is complete and the chromosomes, middle (luh-melЈ-uh) In plants, a thin infer evolutionary relationships between attached to microtubules at their , layer of adhesive extracellular material, prima- different species. are all aligned at the metaphase plate. rily , 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. A group of spatially separated in the body. (monЈ-o– -klo–nЈ-ul) Any populations of one species that interact 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 (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, (meth-anЈ-o– -jen) An organism that able to sustain its numbers and survive. or cotyledon. produces 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 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 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. 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 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 A cross between two organ- 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, , taxon is equivalent to a clade.

GLOSSARY G–22 (monЈ-o– -sakЈ-uh-rı¯d) The (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 (myu¯Ј-chu¯-ul-izm) A symbiotic rela- 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. An egg-laying mammal, such as a network of hyphae in a fungus. nervous system The fast-acting internal system – Glossary or . Like all mammals, mycorrhiza (mı¯Ј-ko-rı¯Ј-zuh) (plural, of communication involving sensory receptors, have hair and produce milk, but mycorrhizae) A mutualistic association of networks of nerve cells, and connections to they lack . plant roots and fungus. muscles and glands that respond to nerve sig- A substance, such as Bicoid protein (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 sheath (mı¯Ј-uh-lin) Wrapped around tain homeostasis. along an embryonic axis. the axon of a neuron, an insulating coat of cell Tissue made up of neurons and (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. (mı¯Ј-uh-glo–Ј-bin) An oxygen-storing, energy used by the producers for respiration. A nerve cell that transmits pigmented protein in muscle cells. 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 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 per segment. Millipedes and neural tube A tube of infolded ectodermal cells muscles in response to external stimuli. 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 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 A form of contracep- across its plasma membrane. a . tion that relies on refraining from sexual 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 , 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 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 The most abundant type of white muscle tissue Tissue consisting of long muscle of a cnidarian, a capsule-like organelle contain- blood cell. 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 (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. 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- (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. (obЈ-lig-et anЈ-uh-ro–b) An or- released, acted on by bacteria, and made avail- nuclear 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 (no–Ј-si-sepЈ-) A sensory receptor 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 . 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 , 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 . nodule A swelling on the root of a . Nod- base pairing between a gene and a comple- 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, . An in meiosis or mitosis fluorescent, or other labeling of the probe 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 fail nucleoid (nu¯Ј-kle¯-oyd) A non-membrane- (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 (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. 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- (nu¯Ј-kle¯-o– -so–mЈ) The basic, - (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 , or norepinephrine A catecholamine that is chemi- sisting of a segment of DNA wound around a downy , 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 (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 A plowing technique that - 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. (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. 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 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

Glossary fingers. up of the auditory canal and, in many birds features of its evolutionary ancestors. A membrane protein bound to a light- and mammals, the . pain receptor A sensory receptor that responds absorbing pigment molecule. A species or group of species from an to noxious or painful stimuli; also called a optic 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 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 (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 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, (-je¯Ј-uh) The that organ identity gene A plant homeotic gene regulated by hormones. formed near the end of the , when that uses positional information to determine ovary (o–Ј-vuh-re¯) (1) In flowers, the portion of a plate movements brought all the of which emerging leaves develop into which carpel in which the egg-containing de- Earth together. types of floral organs. velop. (2) In animals, the structure that produces 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 (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 A group of organs that work a . 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 The study of carbon from eggs that are retained in the mother’s mostly of large, stocky quadrupedal . compounds (organic compounds). uterus. Parareptiles died out in the late 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. (o–r-ganЈ-o– -jenЈ-uh-sis) The female gametophyte. (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 Rhythmic, involuntary contractions of redox reaction. living either within or on the host. certain reproductive structures in both oxidative (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- 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 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 (okЈ-si-to–Ј-sen) A hormone produced by gland, that secrete . 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 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 . 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 off- 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 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 - 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 , 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 (parЈ-thuh-no–Ј-jenЈ-uh-sis) A A ring of interlocking, -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- 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. 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 (puh-rokЈ-suh-so–mЈ) An organelle ciently for photosynthesis to occur. or nursing . containing enzymes that transfer hydrogen photoautotroph (fo–Ј-to– -otЈ-o– -tro–f) An organism 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). (fo -to-het -er-o-trof) An pathogen An organism, virus, , or 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. The development of a multi- advertise it to insects and other . Effects of light on plant cellular organism’s spatial organization, the (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. (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. (fo–Ј-to– -pe¯rЈ-e¯-o– -dizm) A physi- the moss . 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 (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 . detects the radiation known as visible light. An enzyme present in gastric juice that pharyngeal slit (fuh-rinЈ-je¯-ul) In chordate em- 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 The covalent bond between the 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 . amino group on another, formed by a from the ventral side of the 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. (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 (PS I) A light-capturing unit in a during , 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 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- (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 A free-living flatworm found in plant. dividing plant cell. and . 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 The antibody-secreting effector cell pollen tube A tube that forms after germination organisms based on evolutionary relationships: of . 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 . stranded DNA molecule that carries accessory nucleotides added onto the 3Ј end of a 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 (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 (PCR) (puh-limЈ- the number of base pairs along the DNA. plasmodial (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 (fı¯Ј-tuh-kro–m) A type of light re- cycle. nucleotides. ceptor in plants that mostly absorbs red light 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 avoidance. the life cycle of some slime . chain. The nucleotides can be those of DNA 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 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 (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. (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. One of a family of closely related (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 , and . 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. (pı¯Ј-no– -sı¯-to–Ј-sis) A type of endo- The theory that the polyribosome (polysome) (polЈ-e¯-rı¯Ј-buh- in which the cell ingests extracellular are part of great plates of Earth’s 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, A pinched-off cytoplasmic fragment of a of many monosaccharides, formed by parenchyma cells that form the central core of specialized 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 (puh-tu¯Ј-uh-ta–rЈ-e¯) An endo- (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 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 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. 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 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. 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. 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 An enzyme that joins RNA nucleotides disappears but the nucleus remains intact. bilaterally symmetrical animal. to make a primer during DNA replication, (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 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 A thickening along the future component of semen. ductive barrier that prevents hybrid anterior-posterior axis on the surface of an 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 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 . arrangement (structure). sion of a normal cellular protein. appear protein (pro–Ј-te¯n) A biologically functional 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. 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 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 (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 (pro–Ј-te¯-o–Ј-miks) The systematic membrane of a young cell. in mammals. study of the full protein sets () 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 (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 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- 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- 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. The opening in the iris, which admits light pair of 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. (pyu¯Ј-re¯n) One of two types of nitroge- On an mRNA, the triplet group- protonephridium (pro–Ј-to– -nuh-fridЈ-e¯-uhm) nous bases found in nucleotides, character- ing of 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 . stem that is the site of attachment of the floral

Glossary lacking internal openings. (puh-rimЈ-uh-de¯n) One of two types organs. proton-motive force The potential energy of nitrogenous bases found in nucleotides, char- 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 (U) are . 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 (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 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 often respond to the protoplast fusion The fusing of two 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 . cytoplasmic portion of the other receptor in development In animals, a devel- radial cleavage A type of embryonic develop- the dimer. The phosphorylated on opmental mode distinguished by the develop- ment in deuterostomes in which the 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- 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- 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. (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 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 . refers to the phenotype itself. pterophyte (terЈ-uh-fı¯t) An informal name for radula A straplike scraping organ used by many 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 , 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 Winged that lived during the factor receptor on the plasma membrane to color, which results from a red pigment that era. a cascade of protein kinases, ultimately masks the green of chlorophyll. Most pulmocutaneous circuit A branch of the resulting in stimulation of the cell cycle. are multicellular and marine. circulatory system in many amphibians (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 -finned fish Member of the class one or more electrons from one reactant to an- circulatory system that supplies the lungs. , aquatic osteichthyans with fins other; short for reduction-oxidation reaction. pulse The rhythmic bulging of the artery walls supported by long, flexible rays, including The in a redox with each heartbeat. , 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. 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 (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 to sodium channels. about by a transduced signal from outside the the ground. Unlike roots, 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 . fluctuation of that variable. acteristic of a nonconducting excitable cell, 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. An (type of (ro– -dopЈ-sin) A visual pigment con- reinforcement In evolutionary biology, a enzyme) that recognizes and cuts DNA mol- sisting of 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 A DNA segment that re- relies on refraining from sexual intercourse occur only if hybrid offspring are less fit than sults from the 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 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 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 . 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 . 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 (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 (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, 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 (tran-skripЈ-ta–s) An en- RNA processing Modification of RNA primary binding to DNA. zyme encoded by certain viruses () transcripts, including splicing out of introns, 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, , 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 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. A tiny extension of a root epidermal coexisting species. rhizobacterium A soil bacterium whose popula- cell, growing just behind the root tip and 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 . soil or substrate intact. root system All of a plant’s roots, which anchor (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 . 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 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 . group that includes the phyla Lycophyta (club the first step of the Calvin cycle (the addition 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). (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 , with multiple stomach com- required for spermatogenesis. membranes that allows them to regulate the partments specialized for an herbivorous . second law of thermodynamics The princi- passage of substances across them. 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. . 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 (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. from several glands of the male pathogens. secondary cell wall In plant cells, a strong and reproductive tract. 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 leaves the left ven- the myelin-sheathed regions of membrane. secondary growth Growth produced by lateral tricle and the pulmonary artery leaves the (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 (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. (se-nesЈ-ens) The growth phase in a 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 A tropical grassland biome with scat- cal energy in consumers’ food that is converted can take place; also called a tered individual trees and large herbivores and to their own new biomass during a given time . maintained by occasional fires and drought. period. 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 A nerve cell that receives infor- short (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 ) 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 ␤- 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 . While joined, two sister (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- 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 (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 , 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. A sequence of about 20 amino an egg’s surface that prevent fusion of the egg (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. 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 . stimulus to a specific cellular response. siRNA associates with one or more proteins (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 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 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 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 The study of 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 ) flowers. the population. potassium into the cell.

GLOSSARY G–32 A soil layer with physical character- spermatogenesis The continuous and prolific (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. (splı¯Ј-so– -so–m) A large complex Any relatively unspecialized cell that 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 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 (plural, soredia) In , a small 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- (plural, sori) A cluster of sporangia on a that is energetically favorable. stranded restriction fragment. 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 A stemlike structure of a seaweed. samples of DNA. It involves 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, (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 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 layer species (spe¯Ј-se¯z) A population or group of popu- generations, the multicellular diploid form formed when new layers of 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. (spo–r-uh-polЈ-eh-nin) A durable light and dark bands. species diversity The number and relative polymer that covers exposed zygotes of 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 seeds, and stimulates the The number of species in a 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 - of a resting, fasting, and nonstressed 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- (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 Layered rock that results from the In plants, the continuum of cytoplasm (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. 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. 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 on each side of the cytokinesis has typically begun. at the base and the stigma at the top. skull. 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 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 . 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 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 (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 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 In bacteria, a sequence of nu- to stretch or break the surface of a liquid. Wa- the ; 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 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. consumer (ter-she¯-a–rЈ-e¯) A carnivore suspension feeder An , such as a taste bud A collection of modified epithelial cells that eats other . sponge, , or baleen , that feeds by on the 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- 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. (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. (tak-sonЈ-uh-me¯) A scientific disci- unknown genotype. 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 , 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 , 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, (sim-patЈ-rik) The forma- in . amphibians, and birds and other reptiles. tion of new species in populations that live in 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. 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 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 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- 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 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. model. genome contains a gene introduced from thick filament A filament composed of stag- 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 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 “” increased ethylene production. An example is living organisms, and decaying organic mate- from nucleotides to amino acids. thickening stems in response to strong . rial (humus). translocation (1) An aberration in chromosome (thig-moЈ-truh-pizm) A direc- 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. 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 A fibrin-containing clot that forms in trachea (–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 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. (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 -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 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 A plasmid of a tumor-inducing bac- specific genes. intermediate. terium (the plant pathogen ) 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 – (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 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 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. The force directed against a penis and receives sperm. triplet code A genetic 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. 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 raised apart with that of identical twins between molecules or parts of molecules that animals, including some annelids and molluscs. raised in the same . 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 . 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 . terized by relatively high 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. A soluble nitrogenous waste produced in the vascular plant. Xylem transports water and tropics between 23.5° north and south. liver by a metabolic cycle that combines am- minerals; phloem transports sugars, the A growth response that results in the 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 . deferens to prevent sperm from entering the cell elongation. urethra (yu¯-re¯Ј-thruh) A tube that releases urine urethra. 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 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. A decrease in the diameter of thin filament. 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 , and many reptiles. 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 (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 female; also called the menstrual cycle. trated; opposite of animal pole. function in locomotion and feeding. uterus A female organ where eggs are fertilized 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 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 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 , 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. 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 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. A short, wide water-conducting vulva term for the female external (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 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 and emigration. vestigial structure A feature of an organism pressure. 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 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 The phenotype most commonly is transmitted to humans from other animals. nucleotides long. observed in natural populations; also refers to 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. 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 , characterized by a lytic cycle. wobble 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 struc- (capsid) and, for some viruses, a membranous position (3Ј end) of a codon. ture in which karyogamy and meiosis occur. envelope. 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.