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B cell | A type of lymphocyte that develops in the bone marrow and later produces antibodies, which mediate humoral immunity. |
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Bacteria | One of two prokaryotic domains, the other being the Archaea. |
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bacteriophage [L. bacterium + Gk. phagein, to eat] |
A virus that parasitizes a bacterial cell. |
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bacterium pl. bacteria |
A prokaryotic microorganism in Domain Bacteria. |
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balanced polymorphism |
A type of polymorphism in which the frequencies of the coexisting forms do not change noticeably over many generations. |
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bark | All tissues external to the vascular cambium in a plant growing in thickness, consisting of phloem, phelloderm, cork cambium, and cork. |
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Barr body | A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome. |
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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. |
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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. |
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base | A substance that reduces the hydrogen ion concentration in a solution. See Alkaline. |
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basement membrane | The floor of an epithelial membrane on which the basal cells rest. |
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base-pair substitution | A point mutation; the replacement of one nucleotide and its partner from the complementary DNA strand by another pair of nucleotides. |
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base-pairing principle | In the formation of nucleic acids, the requirement that adenine must always pair with thymine (or uracil) and guanine with cytosine. |
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basidium pl. basidia |
A reproductive appendage that produces sexual spores on the gills of mushrooms. The fungal division Basidiomycota is named for this structure. |
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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. |
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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. |
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behavioral ecology | A heuristic approach based on the expectation that Darwinian fitness (reproductive success) is improved by optimal behavior. |
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benthic zone | The bottom surfaces of aquatic environments. |
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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. |
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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. |
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bilateria (by-leh-teer-ee-uh) [L. bi, twice, two + lateris, side] |
Members of the branch of eumetazoans possessing bilateral symmetry. |
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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. |
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binary fission |
The type of cell division by which prokaryotes reproduce; each dividing daughter cell receives a copy of the single parental chromosome. |
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binomial [L. bi, twice, two + Gk. nomos, usage, law] |
The two-part Latinized name of a species, consisting of genus and specific epithet. |
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biochemical pathway [Gk. bios, life + ch |
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. |
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biodiversity hotspot |
A relatively small area with an exceptional concentration of species. |
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bioenergetics |
The study of how organisms manage their energy resources. |
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biogeochemical cycles [Gk. bios, life + ge + ch |
The various nutrient circuits, which involve both biotic and abiotic components of ecosystems. |
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biogeography |
The study of the past and present distribution of species. |
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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. |
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biological magnification |
A trophic process in which retained substances become more concentrated with each link in the food chain. |
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biological species |
A population or group of populations whose members have the potential to interbreed. |
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biomass [Gk. bios, life] |
The dry weight of organic matter comprising a group of organisms in a particular habitat. |
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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. |
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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. |
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biosynthesis [Gk. bios, life + synthesis, a putting together] |
Formation by living organisms of organic compounds from elements or simple compounds. |
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biotechnology |
The industrial use of living organisms or their components to improve human health and food production. |
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biotic (by-ot-ik) [Gk. bios, life] |
Pertaining to the living organisms in the environment. |
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bipedal [L. bi, twice, two + pes, foot] |
Walking upright on two feet. |
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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. |
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blastocoel (blas-toh-seel) [Gk. blastos, sprout + koilos, a hollow] |
The fluid-filled cavity that forms in the center of the blastula embryo. |
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blastocyst [Gk. blastos, sprout + kystis, sac] |
An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans. |
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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. |
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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. |
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blastula (blas-tyoo-la) [Gk. blastos, sprout] |
The hollow ball of cells marking the end stage of cleavage during early embryonic development. |
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blood |
A type of connective tissue with a fluid matrix called plasma in which blood cells are suspended. |
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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. |
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blood pressure |
The hydrostatic force that blood exerts against the wall of a vessel. |
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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. |
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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. |
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book lungs | Organs of gas exchange in spiders, consisting of stacked plates contained in an internal chamber. |
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botany [Gk. botanikos, of herbs] |
The study of plants. |
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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. |
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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. |
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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. |
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brain | The master control center in an animal; in vertebrates, the brain and spinal cord make up the central nervous system. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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bulb | A modified bud with thickened leaves adapted for underground food storage. |
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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. |
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bulk flow | The movement of water due to a difference in pressure between two locations. |
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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. |
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
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Glossary from Biology, Fifth Edition By Campbell, Reece, Mitchell © 1998, Benjamin Cummings. Reprinted with Permission. All Rights Reserved |