Glossary of Biology Campbell Glossary

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The broad region that corresponds to the length of the thick filaments.
A band
One of three binding sites for tRNA during translation, it holds the tRNA carrying the next amino acid to be added to the polypeptide chain; A stands for aminoacyl-tRNA site.
A site
The body cavity in mammals that primarily houses parts of the digestive, excretory, and reproductive systems. It is separated from the more cranial thoracic cavity by the diaphragm.
abdominal cavity
Nonliving chemical and physical factors in the environment.
abiotic components
Genetically determined classes of human blood that are based on the presence or absence of carbohydrates A and B on the surface of red blood cells. The ABO blood group phenotypes, also called blood types, are A, B, AB, and O.
ABO blood groups
A plant hormone that generally acts to inhibit growth, promote dormancy, and help the plant tolerate stressful conditions.
abscisic acid (ABA)
The uptake of small nutrient molecules by an organism's own body; the third main stage of food processing, following digestion.
The range of a pigment's ability to absorb various wavelengths of light.
absorption spectrum
The very deep benthic communities near the bottom of the ocean. This region is characterized by continuous cold, extremely high water pressure, low nutrients, and near or total absence of light.
abyssal zone
A group of ancient jawed fishes from the Devonian period.
Physiological adjustment to a change in an environmental factor.
The automatic adjustment of an eye to focus on near objects.
The entry compound for the Krebs cycle in cellular respiration; formed from a fragment of pyruvate attached to a coenzyme.
acetyl CoA (acetyl coenzyme A)
One of the most common neurotransmitters; functions by binding to receptors and altering the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane.
A substance that increases the hydrogen ion concentration of a solution.
A mixture of recently swallowed food and gastric juice.
acid chyme
Rain, snow, or fog that is more acidic than pH 5.6.
acid precipitation
A solid-bodied animal lacking a cavity between the gut and outer body wall.
The discharge of a sperm's acrosome when the sperm approaches an egg.
acrosomal reaction
An organelle at the tip of a sperm cell that helps the sperm penetrate the egg.
A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.
The class of lobe-finned fishes.
The class of ray-finned fishes.
A rapid change in the membrane potential of an excitable cell, caused by stimulus-triggered, selective opening and closing of voltage-sensitive gates in sodium and potassium ion channels.
action potential
A profile of the relative performance of different wavelengths of light.
action spectrum
The amount of energy that reactants must absorb before a chemical reaction will start.
activation energy
A transcription factor that binds to an enhancer and stimulates transcription of a gene.
Immunity conferred by recovering from an infectious disease.
active immunity
The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.
active site
The movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins.
active transport
Inherited characteristics that enhance the ability of an organism to survive and reproduce in a particular environment.
An equilibrium state in a population when the gene pool has allele frequencies that maximize the average fitness of a population's members.
adaptive peak
The emergence of numerous species from a common ancestor introduced into an environment, presenting a diversity of new opportunities and problems.
adaptive radiation
Also called the anterior pituitary, it consists of endocrine cells that synthesize and secrete several hormones directly into the blood.
An enzyme that converts ATP to cyclic AMP in response to a chemical signal.
adenylyl cyclase
The attraction between different kinds of molecules.
An endocrine gland located adjacent to the kidney in mammals; composed of two glandular portions: an outer cortex, which responds to endocrine signals in reacting to stress and effecting salt and water balance, and a central medulla, which responds to ne
adrenal gland
The central portion of an adrenal gland, controlled by nerve signals, that secretes the fight-or-flight hormones epinephrine and norepinephrine.
adrenal medulla
A peptide hormone released from the anterior pituitary, it stimulates the production and secretion of steroid hormones by the adrenal cortex.
adrenocorticotropic hormone
Roots extending from stems and leaves above ground.
Containing oxygen; referring to an organism, environment, or cellular process that requires oxygen.
The blood vessel supplying a nephron.
afferent arteriole
A branch of mammals that includes sloths, anteaters, and armadillos.
The relative number of individuals of each age in a population.
age structure
An antibody-mediated immune response in which bacteria or viruses are clumped together, effectively neutralized, and opsonized.
A fruit such as a blackberry that develops from a single flower that has several carpels.
aggregate fruit
A member of a jawless class of vertebrates represented today by the lampreys and hagfishes.
A type of behavior involving a contest of some kind that determines which competitor gains access to some resource, such as food or mates.
agonistic behavior
The name of the late stages of HIV infection; defined by a specified reduction of T cells and the appearance of characteristic secondary infections.
AIDS (acquired immunodeficiency syndrome)
The conversion of pyruvate to carbon dioxide and ethyl alcohol.
alcohol fermentation
Organic compounds containing hydroxyl groups.
An organic molecule with a carbonyl group located at the end of the carbon skeleton.
An adrenal hormone that acts on the distal tubules of the kidney to stimulate the reabsorption of sodium (Na+) and the passive flow of water from the filtrate.
A photosynthetic, plantlike protist.
A digestive tract consisting of a tube running between a mouth and an anus.
alimentary canal
One of four extra-embryonic membranes; serves as a repository for the embryo's nitrogenous waste.
Alternate versions of a gene.
The variation in the relative rates of growth of various parts of the body, which helps shape the organism.
allometric growth
A mode of speciation induced when the ancestral population becomes segregated by a geographic barrier.
allopatric speciation
A common type of polyploid species resulting from two different species interbreeding and combining their chromosomes.
An action that occurs either completely or not at all, such as the generation of an action potential by a neuron.
all-or-none event
A specific receptor site on some part of an enzyme molecule remote from the active site.
allosteric site
A spiral shape constituting one form of the secondary structure of proteins, arising from a specific hydrogen-bonding structure.
alpha helix
A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants.
alternation of generations
A type of regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript depending on which RNA segments are treated as exons and which as introns.
alternative RNA splicing
Behavior that reduces an individual's fitness while increasing the fitness of another individual.
The aiding of another individual at one's own risk or expense.
altruistic behavior
A protistan clade that includes dinoflagellates, apicomplexans, and the ciliates. Alveolates have small membrane-bounded cavities called alveoli under their cell surfaces. The function of alveoli is unknown.
(1) One of the deadend, multilobed air sacs that constitute the gas exchange surface of the lungs. (2) One of the milk-secreting sacs of epithelial tissue in the mammary glands.
Neurons of the retina that help integrate information before it is sent to the brain.
amacrine cell
An organic compound with one or more amino groups.
An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of proteins.
amino acid
A functional group that consists of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of +1.
amino group
An enzyme that joins each amino acid to the correct tRNA.
aminoacyl-tRNA synthetase
An enzyme found within the small intestine that splits off one amino acid at a time, beginning at the opposite end of the polypeptide containing a free carboxyl group.
A small and very toxic nitrogenous waste produced by metabolism.
Shelled cephalopod animals that were the dominant invertebrate predators for millions of years ending with the mass extinctions at the end of the Cretaceous period.
A technique for determining genetic abnormalities in a fetus by the presence of certain chemicals or defective fetal cells in the amniotic fluid, obtained by aspiration from a needle inserted into the uterus.
The innermost of four extraembryonic membranes; encloses a fluid-filled sac in which the embryo is suspended.
A vertebrate possessing an amnion surrounding the embryo; reptiles, birds, and mammals are amniotes.
A shelled, water-retaining egg that enables reptiles, birds, and egg-laying mammals to complete their life cycles on dry land.
amniotic egg
A type of protist characterized by great flexibility and the presence of pseudopodia.
An amoebalike cell that moves by pseudopodia, found in most animals; depending on the species, may digest and distribute food, dispose of wastes, form skeletal fibers, fight infections, and change into other cell types.
The vertebrate class of amphibians, represented by frogs, salamanders, and caecilians.
A molecule that has both a hydrophilic region and a hydrophobic region.
amphipathic molecule
The strengthening of stimulus energy that is otherwise too weak to be carried into the nervous system.
Lacking oxygen; referring to an organism, environment, or cellular process that lacks oxygen and may be poisoned by it.
A metabolic pathway that synthesizes a complex molecule from simpler compounds.
anabolic pathway
The use of inorganic molecules other than oxygen to accept electrons at the "downhill" end of electron transport chains.
anaerobic respiration
A pattern of evolutionary change involving the transformation of an entire population, sometimes to a state different enough from the ancestral population to justify renaming it as a separate species; also called phyletic evolution.
The similarity of structure between two species that are not closely related; attributable to convergent evolution.
The fourth subphase of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.
An acute, life-threatening, allergic response.
anaphylactic shock
One of three groups of amniotes based on key differences between their skulls.
Fully modern humans.
anatomically modern humans
The study of the structure of an organism.
The requirement that to divide, a cell must be attached to the substratum.
anchorage dependence
Adhesive junctions that link cells together into tissues.
anchoring junctions
The principal male steroid hormones, such as testosterone, which stimulate the development and maintenance of the male reproductive system and secondary sex characteristics.
A chromosomal aberration in which certain chromosomes are present in extra copies or are deficient in number.
A flowering plant, which forms seeds inside a protective chamber called an ovary.
The ability to survive in a dormant state when an organism's habitat dries up. Also called cryptobiosis.
The portion of the egg where the least yolk is concentrated. Opposite of vegetal pole.
animal pole
A negatively charged ion.
A plant that completes its entire life cycle in a single year or growing season.
Sensory appendages found in uniramians and crustaceans.
Also called the adenohypophysis, it consists of endocrine cells that synthesize and secrete several hormones directly into the blood.
anterior pituitary
Referring to the head end of a bilaterally symmetrical animal.
The terminal pollen sac of a stamen, inside which pollen grains with male gametes form in the flower of an angiosperm.
In plants, the male gametangium, a moist chamber in which gametes develop.
The phylum of hornworts, small herbaceous (non-woody) plants.
The phylum containing all angiosperms.
A member of a primate group made up of the apes (gibbon, orangutan, gorilla, chimpanzee, and bonobo), monkeys, and humans.
A chemical that kills bacteria or inhibits their growth.
An antigen-binding immunoglobulin, produced by B cells, that functions as the effector in an immune response.
A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.
A hormone that is part of an elaborate feedback scheme that helps regulate the osmolarity of the blood.
antidiuretic hormone
A foreign macromolecule that does not belong to the host organism and that elicits an immune response.
The process by which an MHC molecule cradles a fragment of an intracellular protein antigen in its hammocklike groove, carries it to the cell surface, and "presents" the protein to an antigen receptor on a nearby T cell.
antigen presentation
Transmembrane versions of antibody molecules that B cells and T cells use to recognize specific antigens. Also called membrane antibodies.
antigen receptor
Cells that ingest bacteria and viruses and then destroy them. Class II MHC molecules in these cells collect peptide remnants of this degradation and present them to helper T cells.
antigen-presenting cell (APCs)
The order of frogs and toads that includes tailless tetrapod amphibians.
The group of frogs and toads.
The part of the ocean beneath the photic zone, where light does not penetrate sufficiently for photosynthesis to occur.
aphotic zone
Concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growth.
apical dominance
A limb-bud organizing region consisting of a thickened area of ectoderm at the tip of a limb bud.
apical ectodermal ridge
Embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the plant to grow in length.
apical meristem
One of a group of parasitic protozoans, some of which cause human diseases.
The order of caecilians that includes legless amphibians.
The group of caecilians.
The asexual production of seeds.
A derived phenotypic character, or homology, that evolved after a branch diverged from a phylogenetic tree.
apomorphic character
In plants, the nonliving continuum formed by the extracellular pathway provided by the continuous matrix of cell walls.
Programmed cell death brought about by signals that trigger the activation of a cascade of "suicide" proteins in the cells destined to die.
The bright coloration of animals with effective physical or chemical defenses that acts as a warning to predators.
aposematic coloration
A small, fingerlike extension of the vertebrate cecum; contains a mass of white blood cells that contribute to immunity.
A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).
Plasmalike liquid in the space between the lens and the cornea in the vertebrate eye; helps maintain the shape of the eye, supplies nutrients and oxygen to its tissues, and disposes of its wastes.
aqueous humor
A solution in which water is the solvent.
aqueous solution
The animal class that includes scorpions, spiders, ticks, and mites.
One of two prokaryotic domains, the other being the Bacteria.
Primitive eukaryotic group that includes diplomonads, such as Giardia; some systematists assign kingdom status to archezoans.
In plants, the female gametangium, a moist chamber in which gametes develop.
The endoderm-lined cavity, formed during the gastrulation process, that develops into the digestive tract of an animal.
The reptilian group that includes crocodiles, alligators, dinosaurs, and birds.
A vessel that conveys blood between an artery and a capillary bed.
A cardiovascular disease caused by the formation of hard plaques within the arteries.
A vessel that carries blood away from the heart to organs throughout the body.
Segmented coelomates with exoskeletons and jointed appendages.
The most diverse phylum in the animal kingdom; includes the horseshoe crab, arachnids (e.g., spiders, ticks, scorpions, and mites), crustaceans (e.g., crayfish, lobsters, crabs, barnacles), millipedes, centipedes, and insects. Arthropods are characterize
The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.
artificial selection
Macroscopic fruiting bodies of sac fungi.
A saclike spore capsule located at the tip of the ascocarp in dikaryotic hyphae; defining feature of the Ascomycota division of fungi.
A type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts.
asexual reproduction
An amino acid that functions as a CNS neurotransmitter.
The acquired ability to associate one stimulus with another; also called classical conditioning.
associative learning
A type of nonrandom mating in which mating partners resemble each other in certain phenotypic characters.
assortative mating
Glial cells that provide structural and metabolic support for neurons.
A carbon atom covalently bonded to four different atoms or groups of atoms.
asymmetric carbon
Cell division in which one daughter cell receives more cytoplasm than the other during mitosis.
asymmetric cell division
A cardiovascular disease in which growths called plaques develop on the inner walls of the arteries, narrowing their inner diameters.
The smallest unit of matter that retains the properties of an element.
An atom's central core, containing protons and neutrons.
atomic nucleus
The number of protons in the nucleus of an atom, unique for each element and designated by a subscript to the left of the elemental symbol.
atomic number
The total atomic mass, which is the mass in grams of one mole of the atom.
atomic weight
An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
ATP (adenosine triphosphate)
A cluster of several membrane proteins found in the mitochondrial crista (and bacterial plasma membrane) that function in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion concentration gradient to make ATP. ATP syn
ATP synthase
A peptide hormone that opposes the renin-angiotensin-aldosterone system (RAAS).
atrial natriuretic factor
A region of specialized muscle tissue between the right atrium and right ventricle. It generates electrical impulses that primarily cause the ventricles to contract.
atrioventricular (AV) node
A valve in the heart between each atrium and ventricle that prevents a backflow of blood when the ventricles contract.
atrioventricular valve
A chamber that receives blood returning to the vertebrate heart.
According to this model, eukaryotic cells evolved by the specialization of internal membranes originally derived from prokaryotic plasma membranes.
autogenesis model
An immunological disorder in which the immune system turns against itself.
autoimmune disease
A subdivision of the motor nervous system of vertebrates that regulates the internal environment; consists of the sympathetic and parasympathetic divisions.
autonomic nervous system
A type of polyploid species resulting from one species doubling its chromosome number to become tetraploid, which may self-fertilize or mate with other tetraploids.
A chromosome that is not directly involved in determining sex, as opposed to a sex chromosome.
An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms. Autotrophs use energy from the sun or from the oxidation of inorganic substances to make organic molecules from inorganic ones.
A class of plant hormones, including indoleacetic acid (IAA), having a variety of effects, such as phototropic response through the stimulation of cell elongation, stimulation of secondary growth, and the development of leaf traces and fruit.
A nutritional mutant that is unable to synthesize and that cannot grow on media lacking certain essential molecules normally synthesized by wild-type strains of the same species.
The vertebrate class of birds, characterized by feathers and other flight adaptations.
An embryonic shoot present in the angle formed by a leaf and stem.
axillary bud
A typically long extension, or process, from a neuron that carries nerve impulses away from the cell body toward target cells.
A type of lymphocyte that develops in the bone marrow and later produces antibodies, which mediate humoral immunity.
B lymphocyte (B cell)
One of two prokaryotic domains, the other being the Archaea.
An artificial version of a bacterial chromosome that can carry inserts of 100,000–500,000 base pairs.
bacterial artificial chromosome (BAC)
A virus that infects bacteria; also called a phage. See phage.
A photosynthetic pigment found in halophiles. It is very similar to the visual pigments in the retinas of our eyes.
A prokaryotic microorganism in Domain Bacteria.
A form of Rhizobium contained within the vesicles formed by the root cells of a root nodule.
A bone that is contained in, and helps stiffen, the penis of rodents, raccoons, walruses, and several other mammals.
The ability of natural selection to maintain diversity in a population.
balanced polymorphism
All tissues external to the vascular cambium in a plant growing in thickness, consisting of phloem, phelloderm, cork cambium, and cork.
A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.
Barr body
Contraception that relies upon a physical barrier to block the passage of sperm. Examples include condoms and diaphragms.
barrier methods
Glands near the vaginal opening in a human female that secrete lubricating fluid during sexual arousal.
Bartholin's glands
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 body
The minimal number of kilocalories a resting animal requires to fuel itself for a given time.
basal metabolic rate (BMR)
A cluster of nuclei deep within the white matter of the cerebrum.
basal nuclei
A substance that reduces the hydrogen ion concentration of a solution.
The floor of an epithelial membrane on which the basal cells rest.
basement membrane
A point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides.
base-pair substitution
Elaborate fruiting bodies of a dikaryotic mycelium of a club fungus.
A reproductive appendage that produces sexual spores on the gills of mushrooms. The fungal division Basidiomycota is named for this structure.
A circulating leukocyte that produces histamine.
A type of mimicry in which a harmless species looks like a species that is poisonous or otherwise harmful to predators.
Batesian mimicry
What an animal does and how it does it.
A heuristic approach based on the expectation that Darwinian fitness (reproductive success) is improved by optimal behavior.
behavioral ecology
A mass of abnormal cells that remains at the site of origin.
benign tumor
The bottom surfaces of aquatic environments.
benthic zone
The communites of organisms living in the benthic zone of an aquatic biome.
The source of insulin within the islets of Langerhans, nestled within the pancreas.
beta cell
A metabolic sequence that breaks fatty acids down to two-carbon fragments which enter the Krebs cycle as acetyl CoA.
beta oxidation
One form of the secondary structure of proteins in which the polypeptide chain folds back and forth, or where two regions of the chain lie parallel to each other and are held together by hydrogen bonds.
beta (b) pleated sheet
A plant that requires two years to complete its life cycle.
A life history in which adults have but a single reproductive opportunity to produce large numbers of offspring, such as the life history of the Pacific salmon. Also known as semelparity.
big-bang reproduction
Characterizing a body form with a central longitudinal plane that divides the body into two equal but opposite halves.
bilateral symmetry
Members of the branch of eumetazoans possessing bilateral symmetry.
A mixture of substances that is produced in the liver, stored in the gall bladder, and acts as a detergent to aid in the digestion and absorption of fats.
The type of cell division by which prokaryotes reproduce. Each dividing daughter cell receives a copy of the single parental chromosome.
binary fission
The two-part latinized name of a species, consisting of genus and specific epithet.
All of the variety of life; usually refers to the variety of species that make up a community; concerns both species richness (the total number of different species) and the relative abundance of the different species.
The current rapid decline in the variety of life on Earth, largely due to the effects of human culture.
biodiversity crisis
A relatively small area with an exceptional concentration of endemic species.
biodiversity hot spot
The study of how organisms manage their energy resources.
The principle that all life arises by the reproduction of preexisting life.
Neurotransmitters derived from amino acids.
biogenic amines
Any of the various nutrient circuits, which involve both biotic and abiotic components of ecosystems.
biogeochemical cycles
The study of the past and present distribution of species.
An internal timekeeper that controls an organism's biological rhythms; marks time with or without environmental cues but often requires signals from the environment to remain tuned to an appropriate period. See also circadian rhythm.
biological clock
A trophic process in which retained substances become more concentrated with each link in the food chain.
biological magnification
The definition of a species as a population or group of populations whose members have the potential in nature to interbreed and produce fertile offspring; a biological species is also called a sexual species.
biological species concept
The dry weight of organic matter comprising a group of organisms in a particular habitat.
One of the world's major ecosystems, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment.
The use of living organisms to detoxify and restore polluted and degraded ecosystems.
The entire portion of Earth inhabited by life; the sum of all the planet's ecosystems.
The manipulation of living organisms or their components to produce useful products.
Pertaining to the living organisms in the environment.
All the organisms that are part of the environment.
biotic components
Neurons that synapse with the axons of rods and cones in the retina of the eye.
bipolar cell
Any of a class of warm-blooded vertebrates distinguished by having the body more or less completely covered with feathers and the forelimbs modified as wings.
Chemical contraceptives that inhibit ovulation, retard follicular development, or alter a woman's cervical mucus to prevent sperm from entering the uterus.
birth control pills
A flower equipped with both stamens and carpels.
bisexual flower
A leaflike structure of a seaweed that provides most of the surface area for photosynthesis.
The fluid-filled cavity that forms in the center of the blastula embryo.
An embryonic stage in mammals; a hollow ball of cells produced one week after fertilization in humans.
An embryonic cap of dividing cells resting on a large undivided yolk.
Small cells of an early embryo.
The opening of the archenteron in the gastrula that develops into the mouth in protostomes and the anus in deuterostomes.
The hollow ball of cells marking the end stage of cleavage during early embryonic development.
A type of connective tissue with a fluid matrix called plasma in which blood cells are suspended.

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