Online Biology Dictionary - B

b (1) base; (2) buccal.

B Boron.

Ba Barium.

Babesia /buh-BEEZH-yuh or -(ee)-uh/ A genus of protozoan blood parasites transmitted by ticks. Babesia infects humans, cattle, dogs, and many other vertebrates. The resulting disease is babesiosis /bah-buh-ZEE-oh-suhs/. LIFE CYCLE

BAC See: bacterial artificial chromosome.

bacillemia /bass-uhl-EEM-ee-yuh or -ee/ Presence of bacilli in the blood.

bacilli /buh-SILL-eye or -ee/ Plural of bacillus.

bacilliform /buh-SILL-uh-form/ Rod-shaped.

bacillus (pl bacilli) /buh-SILL-uhs; pl: -eye or -ee/ Any rod-shaped bacterium.

Bacillus anthracis (Gram stain) (click to enlarge)

Bacillus anthracis /buh-SILL-uhs AN-thruh-kiss/ A bacilliform bacterium; causative agent of anthrax.

backcross (1) a cross between a hybrid individual obtained by crossing two parental types and a second individual belonging one of those parental types; (2) to create a backcross individual or generation.

back mutation (also reverse mutation) A change in a mutant gene that allows it to once again produce its normal (wild type) product. See: forward mutation.

bacteremia /back-ter-EEM-ee-yuh/ Presence of bacteria in the blood.

bacteria (sing bacterium) /back-TEER-ee-uh; sing: -uhm/ (pronunciation) (1) prokaryotes; (2) strictly speaking, one of the two major types of prokaryotes, the other type being archaeans (more information). AGENTS OF COMMON BACTERIAL INFECTIONS

bacterial artificial chromosome (BAC) A vector used to clone DNA fragments in Escherichia coli cells. The fragments are typically 100- to 300-kb long (mean ~150 kb). The fragments are inserted in an F-factor plasmid found in E. coli. See also: cloning vector.

bacteriochlorophyll (BChl) Any one of the six types (a, b, c, d, e, and g) of chlorophyll found in bacteria.

bacteriophage (or simply phage) /back-TEER-ee-oh-fayj/ A virus that infects bacteria.

bacteriophage lambda (also phage lambda) /back-TEER-ee-oh-fayj LAM-duh/ A DNA virus, which infects E. coli, much used for the purpose of introducing genes into that bacterium.

bacteriophagy (also bacteriophagia) Consumption of bacteria, as by a bacteriophage.

Balanidae The family composed of the acorn barnacles.

balanopreputial Of or pertaining to the glans penis and prepuce.

Balbiani ring A very large puff at a particular band on a polytene chromosome.

Avalonia, Baltica, and Laurentia in the Middle Ordovician Credit: Ron Blakey

Baltica A separate continental plate (named for the Baltic Sea) that existed in the the Early Paleozoic. It later became part of Euramerica, then part of Pangea, and still later, part of Laurasia. Today it underlies parts of modern Scandinavia, European Russia and central Europe and the northern United Kingdom.

barium (Ba) /BEAR-ee-uhm/ Soft metallic element (atomic weight 137.34, atomic number 86); member of alkaline earth group. PERIODIC TABLE

barium sulphate Compound used in x-ray examinations. When ingested, it allows visualization the gastrointestinal tract.

barospirator /BAR-oh-spear-uh-ter/ A device that causes respiration by means of the application of alternating high and low air pressures.

barotactic /BAR-oh-TACK-tick/ Pertaining to barotaxis.

barotaxis /BAR-oh-TAX-uhs/ (pl barotaxes /BAR-oh-TAX-eez/) A taxis in which the stimulus is pressure.

Barr body An inactivated X chromosome. Under the microscope it is seen as a dense body lying near the nuclear envelope.

basal metabolism /BAY-suhl/ The quantity of energy required to maintain an organism when at complete rest.

base (1) in connection with DNA and RNA, one of the purine or pyrimidine nucleotide bases of which RNA and single-stranded RNA is composed. See: adenine, cytosine, guanine, thymine, and uracil); (2) any substance that reduces a solution's hydrogen ion concentration. See: acid.

basic /BAY-sick/ Chemistry: Tending to reduce a solution's hydrogen ion concentration. See: acid.

base pair (bp) A pair of hydrogen-bonded nitrogenous bases that join the two strands of the DNA double helix (click on figure at right for more details). A base pair is composed of a purine and a pyrimidine (guanine and cytosine or adenine and thymine).

base-pair substitution The substitution, in duplex DNA, of one pair of nucleotides for another, or the reversal of a pair of nucleotides with respect to the strands in which the two individual nucleotides reside. There are two types of base-pair substitutions: transitions, in which a purine substitutes for a purine in one strand and a pyrimidine substitutes for a pyrimidine in the other; and transversions in which a pyrimidine substitutes for a purine in one strand and a purine substitutes for a pyrimidine in the other.

base sequence The ordered sequence of nucleotide bases present in a particular DNA or RNA molecule.

base sequence analysis Any method for identifying the bases present in a particular nucleotide sequence.

basophil /BASE-uh-fill/ (also basophile /BASE-uh-file/ ) A leukocyte that stains dark purple with base dyes; appear in many types of inflammations, particularly allergic reactions.

Batesian mimicry /BAIT-see-uhn/ A type of mimicry where a harmless organism looks like some other type of organism that is poisonous or harmful in some other way.

bathypelagic /bath-uh-puh-LAJ-ik/ Pertaining to ocean levels that are deep, but above the abyssal zone.

B cell or B lymphocytes A type of lymphocyte that differentiates in the bone marrow in mammals and in bursa of Fabricius in birds (the B in B cell originally stood for bursa since these cells were discovered in birds, but now generally under stood to refer to bone marrow); after contact with an antigen, B cells differentiate into antibody-secreting plasma cells.

BChl Bacteriochlorophyll.

Beagle (H.M.S.) The ship on which Darwin took a five-year voyage in his youth. MORE ABOUT THE VOYAGE OF THE BEAGLE

Before Present (BP or B.P.) years is a time scale used in geology, archaeology, and other branches of science to indicate the number of years back to past events. Since the present time changes, this system of time measurement has been standardized to use January 1, 1950 as the zero mark on the scale. For example, 1200 BP means 1200 years before 1950 (i.e., the year 850).

behavioral genetics The study of genes influencing behavior.

Beijing Man See: Homo erectus.

John Tyndall (1820-1893)

Belfast Address A famous speech delivered by John Tyndall in Belfast, Ireland on August 19, 1874. The president of the British Association, the country's leading scientific organization, Tyndall explicitly predicted in his address that scientific explanation would replace religious revelation in the long run, in particular with regard to the nature of human origins. He also said that "the promise and potency of every form and quality of life" can be found in matter, without reference to a divine creator, an assertion that provoked a storm of objection from religious conservatives. FULL TEXT OF BELFAST ADDRESS

Belemnite guards

belemnite (or belemnoid) /buh-LEM-night, buh-LEM-noid/ A member of the extinct group Belemnoidea composed of certain cephalopods similar to the modern squid and cuttlefish. They are abundant as fossils. The portion of a belemnite usually fossilized is the rear portion of the internal skeleton, the guard or rostrum, which is cylindrical and rounded or pointed on one end. Fossil range: Early Devonian–Late Cretaceous

benthic zone /BEN-thick/ The seafloor, as an environment or habitat.

bile A substance produced by the liver. It contains bile salts (sodium glycocholate and sodium taurocholate) and aids in the absorption of fats by facilitating their digestion and emulsification.

bilirubin /bill-ee-ROOB-uhn/ An orangish-yellow pigment in bile. A catabolite of hemoglobin breakdown, bilirubin is carried to the liver where it is chemically converted and excreted in the bile into the duodenum.

biochemistry /BYE-oh-KEM-uh-stree/ The study of life at the chemical level, in particular the chemistry of proteins, carbohydrates, and nucleic acids.

bioengineering (also biological engineering) /BYE-oh-en-guh-NEAR-ing/ A hybrid field of scientific research that uses the principles of biology and the techniques of engineering to produce useful products.

biogeography /BYE-oh-gee-AWG-ruh-phee/ The study of the geographic distributions of living organisms.

bioinformatics /BYE-oh-in-fer-MAT-iks/ The use of computers to manage and analyze biological data.

biology /bye-AWL-uh-jee/ (1) the scientific study of life; (2) the life processes of a particular organism or class of organisms (e.g., the biology of plants).

biomass /BYE-oh-mass/ All of the living material in a given region.

biomathematics (also mathematical biology) /BYE-oh-math-MAT-iks/ An interdisciplinary field of study that attempts to model biological processes using mathematical techniques.

biome /BYE-ome/ A major type of ecological community (as savanna, sahel, or taiga).

biophysics (also biological physics) /BYE-oh-FIZZ-iks/ An interdisciplinary science applying the theories and methods of physics to biological questions.

biota /bye-OH-tuh/ The flora and fauna of an era, geographic region, or biome.

biotechnology /BYE-oh-tek-NAWL-uh-jee/ The practical application of biological science; particularly applied research and product development that uses recombinant DNA, cell fusion, and various other modern bioprocessing techniques.

biotic /bye-AWT-ick/ Pertaining to living things.

biparous /BIP-uh-ruhs/ Producing two offspring per birth.

bipedal /bye-PEED-uhl/ Walking upright on two legs (as does a human or a bird).

bird A winged, feathered, endothermic, bipedal vertebrate that lays eggs. Like mammals, birds have a complete double circulatory system.

bisexual /bye-SEX-yoo-uhl/ Pertaining to a type of organism in which two different sexes occur; (2) pertaining to an individual having both male and female sexual organs.

bivalent /bye-VALE-uhnt/ A pair of homologous, synapsed chromosomes; this configration occurs during meiotic prophase I. Also known as a "tetrad."

A bivalve: Atlantic sea scallop Placopecten magellanicus (Click to enlarge)

bivalves /BYE-valves/ Members of Class Bivalvia of Phylum Mollusca. Familiar representatives of this class are clams, oysters, and scallops.

BLAST A computer program that finds similar nucleotide or protein sequences in sequence data bases. BLAST stands for Basic Local Alignment Search Tool.

blastocoel /BLAST-uh-seal/ The cavity within a blastula.

blastocyst /BLAST-uh-sist/ Embryo at the time of implantation in the wall of the uterus. PICTURE

blastula /BLAST-yuh-luh/ A hollow ball of cells that occurs early in embryonic development.

Blattaria /bluht-TAR-ee-yuh, -TER-/ The insect order that consists of the roaches.

blepharoplast /BLEF-er-oh-plast/ Basal granule of a flagellate.

bond energy The amount of energy required to break a given type of chemical bond.

boron (B) /BORE-on/ Nonmetallic chemical element; atomic weight 10.811, atomic number 5. Boron is required by plants as a nutrient, in particular for maintenance of their cell walls. It does not, however, appear to be necessary in the diets of animals. PERIODIC TABLE

Borrelia /bore-RELL-yuh/ A genus of spirochetes, among which are the causative agents of Lyme disease (Borrelia burgdorferi), louse-borne relapsing fever (Borrelia recurrentis), and tick-borne relapsing fever (Borrelia hermsii). PHOTOMICROGRAPH OF BORRELIA BURDORFERI

botany /BAWT-uhn-ee/ The study of plants.

bp See: Base pair.

BP or B.P See: Before Present.

BPG D-2,3-bisphosphoglycerate.

BPheo Bacteriopheophytin (same as bacteriochlorophyll less its magnesium residue).

BPTI Bovine pancreatic trypsin inhibitor; also known as aprotinin.

bradytelic /BRAID-uh-tel-ick/ Pertaining to evolution that occurs at a slower than usual rate.

branchiate /BRANK-ee-uht, -ate/ (also branchiferous /brang-KIF-er-ruhs/) Possessing gills.

breccia /BRECH-yuh/ A sedimentary rock composed of coarse rock fragments embedded in a matrix of finer-grained material.

brevifoliate /brehv-uh-FOAL-ee-uht/ Short-leaved.

bronchus /BRAWNK-uhs/ (pl bronchi /BRAWNK-ee, BRONK-eye/ ) Either of the two tubes into which the trachea divides.

Brownian motion Movement visible under the microscope of particles; due to collisions with the surrounding molecules.

browser An animal that feeds on the twigs, shoots, leaves, and fruits of bushes and trees.

bryology /bry-AWL-uh-jee/ The study of bryophytes.

bryophytes /BRY-uh-fites/ A group of nonvascular plants comprising the mosses, hornworts, and liverworts.

bubble The region where a duplex strand of DNA is separated to admit an enzymeenzyme during initiation of transcription or replication.

buccal /BUCK-uhl/ Of or pertaining to the mouth or cheeks.

buccogingival /BUCK-uh-JIN-juh-vuhl/ Of or pertaining to the cheeks and gums.

bucnemia /buck-NEEM-ee-yuh, NEEM-yuh/ Elephantiasis; broadly: inflammation of the leg.

budding A form of reproduction in which outgrowths from the parent separate from the parent and continue to live as separate individuals.

Bufo /BYOO-foe/ A genus of toads.

bulbourethral glands /BULB-oh-yer-REETH-ruhl/ Cowper's glands.

bullate /BULL-ate/ Like a bubble or blister.

BUN Blood urea nitrogen.

bunodont /BYOON-uh-dawnt/ Molar teeth, or having molar teeth, with rounded cusps.

bursa /BER-suh/ (pl bursae /BER-sigh, BER-see/ or bursas /BER-suhs/) A cushionlike sac nearby a joint. Bursae contain synovial fluid, a lubricant easing friction between tendons and bone.

burst size The mean number of phages released from a lysed bacterial host.

byssus /BISS-uhs/ A tough strand of filaments attaching certain bivalves to their substrate.