B cell
A type of lymphocyte that is most important in the humoral immune response.
barrier reef
A coral reef that runs approximately parallel to the shore and is separated from the shore by a lagoon.
basal body
Also known as kinetosome and blepharoplast, a cylinder of nine triplets of microtubules found basal to a flagellum or cilium; same structure as a centriole.
base
A molecule that dissociates in solution to produce a hydroxide ion.
basis, basipodite
(Gr. basis, base,+ po, foot). The distal or second joint of the protopod of a crustacean appendage.
bathypelagic
(Gr. bathys, deep, + pelagos, open sea). Relating to or inhabiting the deep sea.
benthos
(Gr. depth of the sea). Organisms that live along the bottom of the seas and lakes; adj.,
benthic Also, the bottom itself.
bilirubin
(L. bilis, bile, + rubeo, to be red). A breakdown product of the heme group of hemoglobin, excreted in the bile.
binary fission
A mode of asexual reproduction in which the animal splits into two approximately equal offspring.
biogenesis
(Gr. bios, life, + genesis, birth). The doctrine that life originates only from preexisting life.
biological species concept
A reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.
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.
biomass
(Gr. bios, life,+ maza, lump or mass). The weight of total living organisms or of a species population per unit of area.
biome
(Gr. bios, life,+oma, abstract group suffix). Complex of plant and animal communities characterized by climatic and soil conditions; the largest ecological unit.
biosphere
(Gr. bios, life, + sphaira, globe). That part of earth containing living organisms.
biotic
(Gr. biotos, life, livable). Of or relating to life.
bipinnaria
(L. bi, dopinna, wing, + aria, like or connected with). Freeswimming, ciliated, bilateral larva of the asteroid echinoderms; develops into the brachiolaria larva.
biramous
(L. bi, double, +ramus, a branch). Adjective describing appendages with two distinct branches, contrasted with uniramous, unbranched.
bivalent
(L. bi, dovalen, strength, worth). The pairs of homologous chromosomes at synapsis in the first meiotic division, a tetrad.
blastocoel
(Gr. blastos, germ, + koilos, hollow). Cavity of the blastula.
blastocyst
(Gr. blastos, germ, +kystis, bladder). Mammalian embryo in the blastula stage.
blastomere
(Gr. blastos, germ, + meros, part). An early cleavage cell.
blastopore
(Gr. blastos, germ,+ poros, passage, pore). External opening of the archenteron in the gastrula.
blastula
(Gr. blastos, germ,+ L. ula, dim.). Early embryological stage of many animals; consists of a hollow mass of cells.
blending
See polygenic inheritance.
blepharoplast
(Gr. blepharon, eyelid, + plastos, formed). See basal body
blood plasma
The liqular fraction of blood, including dissolved substances.
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.
Bohr effect
A characteristic of hemoglobin that causes it to dissociate from oxygen in greater degree at higher concentrations of carbon dioxide.
boreal
(L. boreas, north wind). Relating to a northern biotic area characterized by a predominance of coniferous forests and tundra.
B.P
Before the present.
brachial
(L. brachium, forearm). Referring to the arm.
brachiation
(L. brachium, arm). Locomotion by swinging by the arms from one hold to another.
brachiolaria
(L. brachiola, little arm,+ aria, pertaining to). This asteroid larva develops from the bipinnaria larva and has three preoral holdfast processes.
bradyzoite
An individual coccidian (a singlecelled parasite) such as Toxoplasma gondii that is encased in a tissue cyst and divides slowly.
brain hormone
See
ecdysiotropin.
branchial
(Gr. branchia, gills). Referring to gills.
bronchiole
(Gr. bronchion, dim. of bronchos, windpipe). Small, thin-walled branch of the bronchus.
bronchus
pl. bronchi (Gr. bronchos, windpipe). Either of two primary divisions of the trachea that lead to the right and left lung.
brown fat
Mitochondria-rich, heat-generating adipose tissue of endothermic vertebrates.
buccal
(L. bucca, cheek). Referring to the mouth cavity.
budding
Reproduction in which the offspring arises as an outgrowth from the parent and is initially smaller than the parent. Failure of the offspring to separate from the parent leads to colony formation.
buffer
Any substance or chemical compound that tends to keep pH levels constant when acids or bases are added.
bursa
pl. bursae (M.L. bursa, pourse made of skin). A sac-like cavity. In ophiuroid echinoderms, pouches opening at bases of arms and functioning in respiration and reproduction (genitorespiratory bursae).
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