B cell
syn. B lymphocyte.
A type of
lymphocyte that develops in the bone marrow and later produces antibodies,
which mediate humoral immunity.
Bacteria
One of
two prokaryotic domains, the other being the Archaea.
bacteriophage
[L. bacterium +
Gk. phagein, to eat]
A virus that parasitizes a bacterial cell.
A virus that parasitizes a bacterial cell.
bacterium pl. bacteria
A
prokaryotic microorganism in Domain Bacteria.
balanced
polymorphism
A type of
polymorphism in which the frequencies of the coexisting forms do not change
noticeably over many generations.
bark
All
tissues external to the vascular cambium in a plant growing in thickness,
consisting of phloem, phelloderm, cork cambium, and cork.
Barr body
A dense
object lying along the inside of the nuclear envelope in female mammalian
cells, representing an inactivated X chromosome.
basal
body
[Gk. basis, foundation]
A eukaryotic cell organelle consisting of a 9 + 0 arrangement of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally identical to a centriole.
A eukaryotic cell organelle consisting of a 9 + 0 arrangement of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally identical to a centriole.
basal
metabolic rate (BMR)
[Gk. basis, foundation
+ metabole, change]
The minimal number of kilocalories a resting animal requires to fuel itself for a given time.
The minimal number of kilocalories a resting animal requires to fuel itself for a given time.
base
A
substance that reduces the hydrogen ion concentration in a solution. See Alkaline.
basement
membrane
The floor
of an epithelial membrane on which the basal cells rest.
base-pair
substitution
A point
mutation; the replacement of one nucleotide and its partner from the
complementary DNA strand by another pair of nucleotides.
base-pairing
principle
In the
formation of nucleic acids, the requirement that adenine must always pair with
thymine (or uracil) and guanine with cytosine.
basidium pl. basidia
A
reproductive appendage that produces sexual spores on the gills of mushrooms.
The fungal division Basidiomycota is named for this structure.
Batesian
mimicry
(baytz-ee-un mim-ih-kree)
A type of mimicry in which a harmless species looks like a different species that is poisonous or otherwise harmful to predators.
A type of mimicry in which a harmless species looks like a different species that is poisonous or otherwise harmful to predators.
behavior
All of
the acts an organism performs, as in, for example, seeking a suitable habitat,
obtaining food, avoiding predators, and seeking a mate and reproducing.
behavioral
ecology
A
heuristic approach based on the expectation that Darwinian fitness
(reproductive success) is improved by optimal behavior.
benthic
zone
The
bottom surfaces of aquatic environments.
biennial
(by-en-ee-ul)
[L. biennium, a space of two years; bi, twice
+ annus, year]
A plant that requires two years to complete its life cycle.
A plant that requires two years to complete its life cycle.
bilateral
symmetry
[L. bi, twice,
two + lateris, side; Gk. summetros, symmetry]
Characterizing a body form with a central longitudinal plane that divides the body into two equal but opposite halves.
Characterizing a body form with a central longitudinal plane that divides the body into two equal but opposite halves.
bilateria
(by-leh-teer-ee-uh)
[L. bi, twice, two + lateris, side]
Members of the branch of eumetazoans possessing bilateral symmetry.
Members of the branch of eumetazoans possessing bilateral symmetry.
bile
A yellow
secretion of the vertebrate liver, temporarily stored in the gallbladder and
composed of organic salts that emulsify fats in the small intestine.
binary
fission
The type
of cell division by which prokaryotes reproduce; each dividing daughter cell
receives a copy of the single parental chromosome.
binomial
[L. bi, twice,
two + Gk. nomos, usage, law]
The two-part Latinized name of a species, consisting of genus and specific epithet.
The two-part Latinized name of a species, consisting of genus and specific epithet.
biochemical
pathway
[Gk. bios, life
+ chemeia, alchemy]
An ordered series of chemical reactions in a living cell, in which each step is catalyzed by a specific enzyme; different biochemical pathways serve different functions in the life of the cell.
An ordered series of chemical reactions in a living cell, in which each step is catalyzed by a specific enzyme; different biochemical pathways serve different functions in the life of the cell.
biodiversity
hotspot
A
relatively small area with an exceptional concentration of species.
bioenergetics
The study
of how organisms manage their energy resources.
biogeochemical
cycles
[Gk. bios, life
+ geo, earth + chemeia, alchemy; kyklos, circle,
wheel]
The various nutrient circuits, which involve both biotic and abiotic components of ecosystems.
The various nutrient circuits, which involve both biotic and abiotic components of ecosystems.
biogeography
The study
of the past and present distribution of species.
biological
clock
[Gk. bios, life
+ logos, discourse]
Proposed internal factor(s) in organisms that governs functions that occur rhythmically in the absence of external stimuli.
Proposed internal factor(s) in organisms that governs functions that occur rhythmically in the absence of external stimuli.
biological
magnification
A trophic
process in which retained substances become more concentrated with each link in
the food chain.
biological
species
A population
or group of populations whose members have the potential to interbreed.
biomass
[Gk. bios, life]
The dry weight of organic matter comprising a group of organisms in a particular habitat.
The dry weight of organic matter comprising a group of organisms in a particular habitat.
biome
(by-ome)
One of the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment.
One of the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment.
biosphere
(by-oh-sfeer)
[Gk. bios, life + sphaira, globe]
The entire portion of Earth that is inhabited by life; the sum of all the planet's communities and ecosystems.
The entire portion of Earth that is inhabited by life; the sum of all the planet's communities and ecosystems.
biosynthesis
[Gk. bios, life
+ synthesis, a putting together]
Formation by living organisms of organic compounds from elements or simple compounds.
Formation by living organisms of organic compounds from elements or simple compounds.
biotechnology
The
industrial use of living organisms or their components to improve human health
and food production.
biotic
(by-ot-ik)
[Gk. bios, life]
Pertaining to the living organisms in the environment.
Pertaining to the living organisms in the environment.
bipedal
[L. bi, twice,
two + pes, foot]
Walking upright on two feet.
Walking upright on two feet.
blade
(1) The
broad, expanded part of a leaf. (2) The broad, expanded photosynthetic part of
the thallus of a multicellular alga or a simple plant.
blastocoel
(blas-toh-seel)
[Gk. blastos, sprout + koilos, a hollow]
The fluid-filled cavity that forms in the center of the blastula embryo.
The fluid-filled cavity that forms in the center of the blastula embryo.
blastocyst
[Gk. blastos, sprout
+ kystis, sac]
An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans.
An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans.
blastodisc
[Gk. blastos, sprout
+ discos, a round plate]
Disklike area on the surface of a large, yolky egg that undergoes cleavage and gives rise to the embryo.
Disklike area on the surface of a large, yolky egg that undergoes cleavage and gives rise to the embryo.
blastopore
(blas-toh-por)
[Gk. blastos, sprout + poros, a way, means,
path]
The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes.
The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes.
blastula
(blas-tyoo-la)
[Gk. blastos, sprout]
The hollow ball of cells marking the end stage of cleavage during early embryonic development.
The hollow ball of cells marking the end stage of cleavage during early embryonic development.
blood
A type of
connective tissue with a fluid matrix called plasma in which blood cells are
suspended.
blood-brain
barrier
A
specialized capillary arrangement in the brain that restricts the passage of
most substances into the brain, thereby preventing dramatic fluctuations in the
brain's environment.
blood
pressure
The
hydrostatic force that blood exerts against the wall of a vessel.
bond
energy
The
quantity of energy that must be absorbed to break a particular kind of chemical
bond; equal to the quantity of energy the bond releases when it forms.
bond
strength
The
strength with which a chemical bond holds two atoms together; conventionally
measured in terms of the amount of energy, in kilocalories per mole, required
to break the bond.
book
lungs
Organs of
gas exchange in spiders, consisting of stacked plates contained in an internal
chamber.
botany
[Gk. botanikos, of
herbs]
The study of plants.
The study of plants.
bottleneck
effect
Genetic
drift resulting from the reduction of a population, typically by a natural
disaster, such that the surviving population is no longer genetically
representative of the original population.
Bowman's
capsule
A
cup-shaped receptacle in the vertebrate kidney that is the initial, expanded
segment of the nephron where filtrate enters from the blood.
box
A small
portion of a gene or protein that appears in many genes or proteins that are
related in structure; the box usually has some specific function, sometimes
called a "motif", like binding DNA or interacting with specific
proteins or other molecules.
brain
The
master control center in an animal; in vertebrates, the brain and spinal cord
make up the central nervous system.
brainstem
The
hindbrain and midbrain of the vertebrate central nervous system. In humans, it
forms a cap on the anterior end of the spinal cord, extending to about the
middle of the brain.
bryophyte
(bry-oh-fites)
The mosses, liverworts, and hornworts; a group of nonvascular plants that inhabit the land but lack many of the terrestrial adaptations of vascular plants.
The mosses, liverworts, and hornworts; a group of nonvascular plants that inhabit the land but lack many of the terrestrial adaptations of vascular plants.
bronchus pl. bronchi
(bronk-us, bronk-
eye) [Gk. bronchos, windpipe]
One of a pair of respiratory tubes branching into either lung at the lower end of the trachea; it subdivides into progressively finer passageways, the bronchioles, culminating in the alveoli.
One of a pair of respiratory tubes branching into either lung at the lower end of the trachea; it subdivides into progressively finer passageways, the bronchioles, culminating in the alveoli.
bud
(1) In
plants, an embryonic shoot, including rudimentary leaves, often protected by
special bud scales. (2) In animals, an asexually produced outgrowth that
develops into a new individual.
budding
An
asexual means of propagation in which outgrowths from the parent form and pinch
off to live independently or else remain attached to eventually form extensive
colonies.
buffer
A
substance that consists of acid and base forms in solution and that minimizes
changes in pH when extraneous acids or bases are added to the solution.
bulb
A
modified bud with thickened leaves adapted for underground food storage.
bulbourethral
gland
(bul-bo-you-ree-thral)
One of a pair of glands near the base of the penis in the human male that secrete fluid that lubricates and neutralizes acids in the urethra during sexual arousal.
One of a pair of glands near the base of the penis in the human male that secrete fluid that lubricates and neutralizes acids in the urethra during sexual arousal.
bulk flow
The
movement of water due to a difference in pressure between two locations.
bundle of
His
In the
vertebrate heart, a group of muscle fibers that carry impulses from the
atrioventricular node to the walls of the ventricles; the only electrical bridge
between the atria and the ventricles.
Tags:
bacteriophage
Barr body
biological clock
biological magnification
blastodisc
Bowman's capsule
bundle of His
