B

b-carotene An important plant carotenoid and precursor of vitamin A.

b-galactosidase The enzyme responsible for the splitting of lactose into glucose and galactose.

B-lymphocytes Cells that manufacture antibodies involved in immunity.

b.p. Before the present.

bacillary bands Lateral zones in the body wall of some nematodes, consisting of glandular and nonglandular cells of unknown function.

bacillus A rod-shaped bacterium.

back reef The inner part of a barrier reefor atoll.

backcross Crossing a hybrid offspring back to either parent.

bacteria Prokaryotic and unicellular microorganisms included in the kingdom Monera.

bacteriochlorophyll A type of chlorophyll found only in bacterial systems.

bacteriophage A virus that attacks bacterial cells.

bacterioplankton The component of the plankton that consists of bacteria. Also see picoplankton.

Baculum baculum = rod. Penis bone.

Baer's disc Large, ventral sucker of an aspidogastrean trematode.

balanced polymorphism Occurs when different phenotypic expressions are maintained at a relatively stable frequency in a population.

baleen The filtering plates that hang from the upper jaws of baleen whales.

baleen plate A keratined growth in toothless whales.

baleen whales The filter-feeding whales.

ballonets Four inflated areas within the "head" of nematodes of the family Gnathostomatidae; each is connected to an internal cervical sac of unknown function.

bar-built estuary An estuary that is formed when a barrier island or sand bar separates a section of the coast where fresh water enters.

bare sensory nerve endings Nerve endings that are sensitive to pain.

bark Those portions of a woody plant stem or trunk exterior to the vascular cambium.

barnacles Crustaceans that live attached to surfaces and are typically enclosed by heavy calcareous plates.

baroreceptor A specialized nerve ending that is stimulated by changes in pressure.

Barr body A heterochromatic X chromosome usually found in the nucleus of female mammals.

barrier island A long and narrow island that is built by waves along the coast.

barrier reef A coral reef that runs approximately parallel to the shore and is separated from the shore by a lagoon.

basal body A centriole that has given rise to the microtubular system of a cilium or flagellum, and is located just beneath the plasma membrane. Serves as a nucleation site for the growth of the axoneme.

basal rosette Leaves clustered at ground level; can be alternate or whorled, but with extremely short internodes.

basalt A semiviscous layer of igneous rock underlying the granitic continental plates.

basalt The dark-colored rock that forms the sea floor, or oceanic crust.

base A substance that ionizes in water to release hydroxyl ions (OH_) or other ions that combine with hydrogen ions.

basic Possessing a large number of hydroxyl (OH_) ions; a pH of more than 7.0.

basic research Research conducted to elucidate basic concepts alone with no direct application in mind.

basidiocarp The densely packed hyphae of the fruiting body in the Basidiomycetes.

Basidiomycetes A group of fungi whose spores are borne in a basidium.

basidiospores A haploid spore produced by a basidium in the Basidiomycetes.

basidium Club-shaped reproductive cell in basidiomycetes undergoes meiosis to produce four haploid cells called basidiospores.

basihyo- bas = foundation, step; G. hyo = Y-shaped. A hyoid bone.

basilar membrane A flat band of tissue that bears the auditory hair cells in the cochlea of the vertebrate ear; the membrane vibrates in response to pressure waves.

basilar bas = foundation. Forming a foundation.

basipetal Movement down the stem as with auxin moving from the shoot apex downward.

basis (basipodite) Joint of a crustacean appendage from which the exopod and the endopod originate; that is, the joint between the coxa and the exopod and endopod.

basophil White blood cell characterized by the presence of cytoplasmic granules that become stained by a basophilic dye.

bast fiber Fibers located in phloem.

Bateman effect The large variation in the reproductive success of males compared to females in relation to the number of mates they have.

Batesian mimicry Evolution by one species to resemble the coloration, body shape, or behavior of a related species that is protected from predators by a venomous stinger, bad taste, or some other adaptation.

Batesian mimics Palatable species that evolve morphologies and behaviors similar to those of unpalatable species.

bathyal zone The bottom between the shelf break and a depth of approximately 4,000 m (13,000 ft).

bathypelagic Relating to or inhabiting the deep sea.

bathypelagic zone The pelagic environment from a depth of 1,000 m

(3,000 ft) to 4,000 m (13,000 ft).

Bdelloidea A class of rotifers containing members where there are no males; anterior end retractile and bearing two disks; mastax adapted for grinding; paired ovaries; cylindrical body. Example: Rotaria.

beard worms (pogonophorans; phylum Pogonophora)Tube-dwelling invertebrates that lack a digestive system.

bedrock Unbroken, solid rock overlain by sand, gravel, or soil.

behavior genetics The study of the role that genes play in controlling behavior.

behavioral ecology A subdiscipline within animal behavior that deals with the ways in which animals interact with their environment and the survival value of behavior as well as its contribution to reproductive success.

behavioral isolating mechanisms Differences in behavior (usually courtship) that prevent genetic exchange between members of different populations or species.

behaviorism A view of the actions of animals that postulates that behavior can be analyzed functionally in terms of stimulus and response combinations. Thus, most of behavior is a function of the experience of the organism in this view.

benthic Pertaining to the bottom region of an ocean, lake, or pond.

benthic animals Refers to animals living in or on the bottom substrate of an ocean, lake, stream, or other body of water.

benthos Organisms that live along the bottom of the seas and lakes; adj., benthic. Also, the bottom itself.

berry A fleshy, two- or multiple-carpeled ovary, each carpel having many seeds.

best available, economically achievable technology (BAT) The best pollution control available; the Clean Water Act effectively negates this category by stipulating that equipment must be economically feasible.

best practical control technology (BPT) The best technology for pollution control available at reasonable cost and operable under normal conditions.

beta particles High-energy electrons released by radioactive decay.

beta-carotene Yellow to red pigment in plants; one of the most important of the carotenoids; converts to vitamin A in the body.

biantitropical distribution A pattern of a species' geographical distribution that extends across comparable bands of latitude in both the Northern Hemisphere and the Southern Hemisphere.

bicarbonate ion Carbonic acid ionizes to produce a bicarbonate ion, HCO₃ and a proton, H+ in rainfall.

biceps bi = two; L. ceps = head.

bicipital bi = two; L. cipit = head.

bicuspid bi = two; cuspi = point.

biennial Plant that completes its life cycle within two growing seasons; example: carrot.

big bang The theory proposing that the entire universe was created at one time.

big bang theory The theory that a hypothetical cosmic explosion resulted in clouds of dust and gas from which the earth and solar system originated.

bilateral body symmetry Animal body plan with mirror image left and right sides.

bilateral symmetry A form of symmetry in which only the midsagittal plane will divide an organism into mirror images; bilateral symmetry is characteristic of actively moving organisms that have definite anterior (head) and posterior (tail) ends.

bile A fluid secreted by the liver and poured into the small intestine via the bile duct; emulsifies fats.

bilharziasis Disease caused by Schistosoma spp. Also called schistosomiasis.

bilirubin A breakdown product of the heme group of hemoglobin, excreted in the bile.

bill A piece of legislation introduced in Congress and intended to become law.

bimodal breathing The ability of an organism to exchange respiratory gases simultaneously with both air and water; usually using gills for water breathing and lungs for air breathing.

binary fission Asexual reproduction in protists in which mitosis is followed by cytoplasmic division, producing two new organisms.

binomial The two names, genus and species, comprising the scientific name.

binomial nomenclature A system of naming species using two names, the first of which refers to the genus.

bioaccumulation Increasingly concentrated accumulation of substances, especially pollutants, at successively higher trophic levels in food chains.

bioassay A quantitative assay of a particular substance using a portion of or an entire living organism.

biocentric preservation A philosophy that emphasizes the fundamental right of living organisms to exist and to pursue their own goods.

biocentrism The belief that all creatures have rights and values; being centered on nature rather than humans.

biochemical taxonomy A biochemical approach to defining evolutionary relationships of organisms by determining molecular similarities and differences among organisms.

biochemistry The chemistry of living organisms and of vital processes; also known as physiological or biological chemistry. The study of the molecular basis of life.

biocide A broad-spectrum poison that kills a wide range of organisms.

biodegradable A chemical that can be broken down by bacteria or other organisms.

biodegradable plastics Plastics that can be decomposed by microorganisms.

biodiversity The genetic, species, and ecological diversity of the organisms in a given area.

biogenesis The doctrine that life originates only from preexisting life.

biogenous sediment The type of sediment that is made up of the skeletons and shells of marine organisms. Also see calcareous and siliceous ooze.

biogeochemical cycles Movement of matter within or between ecosystems; caused by living organisms, geological forces, or chemical reactions. The cycling of nitrogen, carbon, sulfur, oxygen, phosphorus, and water are examples.

biogeographical area An entire self-contained natural ecosystem and its associated land, water, air, and wildlife resources.

biogeography The study of the distribution of life on earth.

biological clock An internal timing mechanism that involves both an internal self-sustaining pacemaker and cyclic environmental synchronizers.

biological communication An action by one organism (or cell) that causes a reaction from another organism (or cell) in a fashion adaptive to either one or both of the participants.

biological community The populations of plants, animals, and microorganisms living and interacting in a certain area at a given time.

biological controls Use of natural predators, pathogens, or competitors to regulate pest populations.

biological magnification The increased concentration of nonbiodegradable chemicals in the higher levels of the food chain.

biological or biotic factors Organisms and products of organisms that are part of the environment and potentially affect the life of other organisms.

biological oxygen demand (BOD) A standard test for measuring the amount of dissolved oxygen utilized by aquatic microorganisms over a five-day period.

biological pests Organisms that reduce the availability, quality, or value of resources useful to humans.

biological resources The earth's organisms.

biological rhythm A cyclical pattern of behavior, occurring at some regular period (e.g., diurnal). See biological clock.

biological species concept A reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.

biological vector Vector in which a disease organism lives or develops. Contrast with mechanical vector.

biology The study of all living organisms.

bioluminescence. Method of light production by living organisms in which usually certain proteins (luciferins), in the presence of oxygen and an enzyme (luciferase), are converted to oxyluciferins with the liberation of light.

biomagnification Increase in concentration of certain stable chemicals (for example, heavy metals or fat-soluble pesticides) in successively higher trophic levels of a food chain or web.

biomass The weight of total living organisms or of a species population per unit of area.

biomass fuel Organic material produced by plants, animals, or microorganisms that can be burned directly as a heat source or converted into a gaseous or liquid fuel.

biomass pyramid A metaphor or diagram that explains the relationship between the amounts of biomass at different trophic levels.

biomes Distinctive associations of plant and animal populations; characterized by certain geographical boundaries and specific climatic and geographical features.

bioregionalism Organization of human activities according to natural geographic or ecological boundaries and associations. This philosophy emphasizes a sense of place and living within the resources of one's local ecosystem.

biosphere The earth and all of its ecological interactions considered as a single system.

biosphere reserves World heritage sites identified by the IUCN as worthy for national park or wildlife refuge status because of high biological diversity or unique ecological features.

biota All organisms in a given area.

biotechnology The use of living organisms to provide products for humanity; using genetic engineering to create organisms with useful traits.

biotic Of or relating to life.

biotic factor Living component in the environment.

biotic potential The maximum reproductive rate of an organism, given unlimited resources and ideal environmental conditions. Compare with environmental resistance.

bipinnaria Free-swimming, ciliated, bilateral larva of the asteroid echinoderms; develops into the brachiolaria larva.

biramous Adjective describing appendages with two distinct branches, contrasted with uniramous, unbranched.

biramous appendage (Appendage with two main branches from a common basal joint, characteristic of Crustacea, although not all appendages of a crustacean may be biramous.

birds Vertebrates that have feathers and lay eggs with calcified shells on land.

birth control Any method used to reduce births, including celibacy, delayed marriage, contraception; devices or medication that prevent implantation of fertilized zygotes, and induced abortions.

bisexual A flower having both stamens and pistil (both sexes); a perfect flower.

bivalent The pairs of homologous chromosomes at synapsis in the first meiotic division, a tetrad.

bivalves The clams, mussels, and other molluscs that possess a two-valved shell, filtering gills, and a shovel-like foot.

Bivalvia The class of molluscs whose members are enclosed in a shell consisting of two dorsally hinged valves, lack a radula, and possess a wedge-shaped foot. Clams, mussels, oysters.

Biventer bi = two; L. vent = belly, underside.

black corals Colonial anthozoans that secrete a black protein skeleton.

black fly fever Combination of symptoms resulting from sensitization to bites by black flies (Simuliidae).

black lung disease Inflammation and fibrosis caused by accumulation of coal dust in the lungs or airways. See respiratory fibrotic agents.

black smoker A chimney-like accumulation of mineral deposits that is found at hydrothermal vents.

blackhead Disease of turkeys caused by the protozoan Histomonas meleagridis. Also called histomoniasis or infectious enterohepatitis.

bladder worm The unilocular hydatid cyst of a tapeworm. See cysticercus.

blade Flat, green part of a leaf; expanded or flattened portion of a brown alga.

blastocoel The internal cavity commonly formed by cell division early in embryonic development, prior to gastrulation.

blastocyst An early stage of embryonic development consisting of a hollow ball of cells;a small ball of cells representing an early stage of embryonic development.

blastoderm "Primary epithelium" formed in early embryonic development of many arthropods when the nuclei migrate to the periphery and undergo superficial cleavage; usually encloses the central yolk mass.

blastomeres Any of the cells produced by cleavage of a zygote.

blastopore External opening of the archenteron in the gastrula.

blastula An early stage in the development of an embryo; it consists of a sphere of cells enclosing a fluid-filled cavity (blastocoel).

bleaching The expulsion of zooxanthellae by reef corals in response to stress.

blending See polygenic inheritance.

blepharoplast See basal body.

blood A type of connective tissue with a fluid matrix called plasma in which blood cells are suspended. The fluid that circulates through the heart, arteries, capillaries, and veins.

blood plasma The liquid, noncellular fraction of blood, including dissolved substances.

blood pressure The force (energy) with which blood is pushed against the walls of blood vessels and circulated throughout the body when the heart contracts.

blood type Characteristic of human blood given by the particular antigens on the membranes of the erythrocytes, genetically determined, causing agglutination when incompatible groups are mixed; the blood types are designated A, B, O, AB, Rh negative, Rh positive, and others.

bloom A dense concentration of phytoplankton that occurs in response to optimum growth conditions.

blowhole The nostrils, or nasal openings, of cetaceans.

blubber The fat found between the skin and muscle of whales and other cetaceans, from which oil is made.

blue revolution New techniques of fish farming that may contribute as much to human nutrition as miracle cereal grains but also may create social and environmental problems. Commercial fish farming already is a $5 billion per year industry, and domestic fish ponds supply as much as two-thirds of the protein consumed by subsistence farmers in many countries.

blue-green algae Prokaryote organisms with photosynthetic phycobilin pigments.

bluetongue Virus disease of ruminants transmitted by biting midges (Ceratopogonidae).

bog An area of waterlogged soil that tends to be peaty; fed mainly by precipitation; low productivity; some bogs are acidic.

Bohr effect. A characteristic of hemoglobin that causes it to dissociate from oxygen in greater degree at higher concentrations of carbon dioxide.

bomb calorimeter An instrument used for measuring the caloric content of any organic material; measures energy release in combusting organic materials to CO₂ and H₂O.

bone cells The hard, rigid form of connective tissue constituting most of the skeleton of vertebrates; composed chiefly of calcium salts. Also called bone (osseous) tissue.

Bone os, G. osteon = bone.

bony fishes Fishes with a skeleton made mostly of bone; they also have gill covers.

book gill Modifications of a horseshoe crab's exoskeleton into a series of leaflike plates that serve as a surface for gas exchange between the arthropod and the water (phylum Arthropoda, class Merostomata).

book lung Modification of the arthropod exoskeleton into a series of internal plates that provide surfaces for exchange of gases between the blood and air.

boreal forest A broad band of mixed coniferous and deciduous trees that stretches across northern North America (and also Europe and Asia); its northernmost edge, the taiga, intergrades with the arctic tundra.

boreal forest Northern coniferous forest biome, also called the taiga, located south of the tundra and dominated by conifers.

boreal (L. boreas, north wind). Relating to a northern biotic area characterized by a predominance of coniferous forests and tundra.

boring sponges Sponges that bore through calcareous skeletons and shells.

botany The study of plants.

bothria Dorsal or ventral grooves, which may be variously modified, on the scolex of a cestode.

bothridium Muscular lappet on the dorsal or ventral side of the scolex of a tapeworm. Bothridia are often highly specialized, with many types of adaptations for adhesion.

bothrium Dorsal or ventral groove, which may be variously modified, on the scolex of a cestode.

bottleneck effect Changes in gene frequency that result when numbers in a population are drastically reduced, and genetic variability is reduced as a result of the population being built up again from relatively few surviving individuals.

bottom layer See deep layer.

BPT See best practical control technology.

Brachial brachialis = arm.

brachiolaria This asteroid larva develops from the bipinnaria larva and has three preoral holdfast processes.

Brachiopoda A phylum of marine animals whose members possess a bivalved calcareous and/or chitinous shell that is secreted by a mantle and encloses nearly all of the body. Unlike the molluscs, the valves are dorsal and ventral. Possess a lophophore. Lampshells.

brachiopods See lamp shells.

Brachium The arm from shoulder to elbow.

bract A modified leaf or leaflike structure, usually much reduced in size.

bradycardia Marked slowing of the heartbeat rate during a breath-hold dive.

bradyzoite Small stage in various coccidia of the Isospora group that develops in a zoitocyst; similar to a merozoite.

brain hormone. See ecdysiotropin.

bran The husk of a cereal grain; including the pericarp and seed coat of a cereal grain. The bran is removed in the processing of refined grains.

branch roots Lateral roots arising from the pericycle of a

branchial Referring to gills.

breaching Leaping into the air by whales.

breakbone fever Another name for dengue, a virus disease transmitted by mosquitoes.

breeder reactor A nuclear reactor that produces fuel by bombarding isotopes of uranium and thorium with high-energy neutrons that convert inert atoms to fissionable ones. These reactors are inherently less stable and more dangerous than normal nuclear reactors.

brittle stars Echinoderms with five flexible arms that radiate from a conspicuous central disk and tube feet that are used in feeding.

broadcast spawners Marine animals that reproduce by releasing eggs and sperm into the water.

broadcast spawning The release of gametes into the water, allowing external fertilization to occur.

bronchi The paired ventilatory tubes of a vertebrate that branch into each lung at the lower end of the trachea.

bronchiole Small, thin-walled branch of the bronchus.

bronchitis An inflammation of bronchial linings that causes persistent cough, copious production of sputum, and involuntary muscle spasms that constrict airways.

bronchus Either of two primary divisions of the trachea that lead to the right and left lung.

brood patch The patch of feathers used by birds to incubate eggs; also known as incubation patch.

brooding Parental care of developing young.

brown algae (division Phaeophyta)Seaweeds with a predominance of yellow and brown pigments.

brown fat Mitochondria-rich, heat-generating adipose tissue of endothermic vertebrates.

Bruce effect In mice, the effect of a strange male, or his odor, that causes females to abort and become receptive.

bryophytes A group of nonvascular plants consisting of the hornworts, liverworts,

bryozoans Colonial invertebrates in which the anus is located outside the edge of a lophophore.

bubo Swollen lymph node.

buccal cone Portion of the mouthparts of acarines composed of hypostome and labrum.

buccal pump The mechanism by which lung ventilation occurs in amphibians; muscles of the mouth and pharynx create positive pressure to force air into the lungs.

buccal Referring to the mouth cavity.

buccopharyngeal respiration The diffusion of gases across moist linings of the mouth and pharynx of amphibians.

bud An apical meristem and the appendages which surround and enclose it. Also refers to the asexual reproductive outgrowth in yeasts and some bacteria.

budding A form of asexual reproduction in which new individuals develop from a portion of the parent, as in all bryozoans and in many protozoans, cnidarians, and polychaetes.

bud scales Modified leaves surrounding and protecting a bud.

bud scale scar A scar or impression encircling the twig caused by the abscission of bud scales.

buffer Any substance or chemical compound that tends to keep pH levels constant when acids or bases are added.

bulb of Krause A sensory receptor in the skin believed to be the sensor for touch-pressure; also called bulbous corpuscle.

bulb An underground storage organ characterized by fleshy leaves attached to a stem base.

Bulbo- A bulb.

bulbourethral gland Gland that secretes a viscous fluid into the male urethra during sexual excitement.

bulla Nonliving structure serving as an anchor to which the maxillae are permanently attached; secreted by head and maxillary glands of female copepods in the family Lernaeopodidae.

bulliform cell A large epidermal cell found on the upper surface of many grass leaves; turgor pressure in these cells controls the lateral rolling of the leaves during water stress.

bundle sheath Sheath of parenchyma or sclerenchyma cells surrounding the vascular bundles in leaves.

bundle sheath cell Cells surrounding the vascular bundle in C₄ plants.

bursa A sac-like cavity. In ophiuroid echinoderms, pouches opening at bases of arms and functioning in respiration and reproduction (genitorespiratory bursae).

bursa of Fabricius The lymphoid organ of birds that, like the thymus, develops as an outpouching of the gut near the cloaca rather than the foregut.

buttocks Prominence formed by the gluteal muscles.

buttress Seaward face of a coral reef, extending from a depth of about 20 m to just below the low tide line.

buttressing A stem modification in which the diameter is larger near the ground, giving additional mechanical support.

by-catch The less valuable catch that is captured while fishing for a more valuable catch.

byssal thread a strong elastic fiber used by mussels to attach themselves to a solid substrate