Biology Dictionary A

Meanings of biological terminology

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Words Prefixes Suffixes Roots
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A to Amplification

a (1) ampere; (2) anterior; (3) anode; (4) area; (5) artery.

A (1) adenine; (2) alanine.

Å Angstrom unit.

Ab Antibody.

Online Biology Dictionary (AB-)

abarticular /ab-are-TICK-yə-ler/ Away from the joint.

abasia /ab-BAY-zhə/ A lack of coordination in walking or an inability to walk due to incoordination.

abasic /ab-BAY-zik/ Of or pertaining to abasia.

abaxial /ab-ACKS-ee-əl/ (1) away, or facing away, from the axis or center line; (2) on the lower side (e.g. of a leaf). Compare: adaxial.

abdomen /AB-dō-men/ (1) in humans and tetrapods, the belly (that is, the region, not including the back, between the thorax and pelvis); (2) in non-arachnid arthropods, the posterior segment of the body, attached to the rear of the thorax; (3) in arachnids the posterior portion of the body which bears the legs and contains the digestive tract.

abdominal /ab-DAWM-ə-nəl/ Pertaining to the abdomen.

abdominal cavity /ab-DAWM-ə-nəl/ The large body cavity lying below the diaphragm and above the pelvis.

abdominogenital /ab-DAWM-ə-nō-JEN-ə-təl/ Of, or relating to, the abdomen and genital organs.

abiotic /ab-eye-AWT-ick/ Marked by the absence of life.

abomasum /ab-ō-MAY-səm/ (pl abomasa /ab-ō-MAY-sə/) The fourth stomach chamber of a ruminant. MORE INFORMATION

abscess /AB-sess/ A localized concentration of pus, anywhere in the body.

abscisic acid /ab-SIS-ick/ A plant hormone inhibiting growth; helps plants withstand adverse conditions.

absorption /ab-SORP-shən/ The taking in of water, along with its dissolved contents, through a cell membrane. Compare: ingestion.

abundance of an mRNA The mean number of copies of a particular mRNA molecule per cell.

abundant mRNAs Those mRNA molecules present at high copy number within a cell.

abyssal zone /ə-BIS-əl/ The cold, lightless zone in the depths of the sea where pressures are intense.

Ac-CoA Acetyl-coenzyme A.

acanthoid /ə-KAN-thoid/ Thorny, spiny, sharp.

Online Biology Dictionary (ACAR-)

acarine /ACK-ə-rine, -reen, -rən/ Relating to ticks and mites.

acarology /ack-er-AWL-ə-jee/ The study of ticks and mites.

ACAT Acyl-CoA:cholesterol acyl transferase.

acaulescent /AY-kawl-LESS-ənt/ Stemless.

acceptor splicing site Boundary between an intron's 3' end and the adjacent exon's 5' end — also known as the right (or 3') splicing junction.

accipitral /ack-SIP-ə-trəl/ Of or relating to a hawks.

acclimation /AK-lə-MAY-shən/ Adjustment of an organism to a change in some environmental factor.

acentric fragment /AY-sent-rick/ (also acentric chromosome) A centromereless portion of a broken eukaryotic chromosome.

Online Biology Dictionary (ACEPH-)

acephalia /AY-sə-FALL-ee-ə/ Headlessness.

acephalous /ay-SEFF-ə-ləs/ Lacking a head.

acephalus /ay-SEFF-ə-ləs, ə-/ A headless fetus.

acetabulum /ass-ə-TAB-yə-ləm/ The socket of the hip joint.

acetamide /ə-SEED-ə-mide, -AM-ide, -əd/ Amide of acetic acid.

acetic acid /ə-SEED-ick/ (also ethanoic acid /eth-ə-NŌ-ick/) The weak organic acid in vinegar. MORE INFORMATION

acetyl-coenzyme A (Ac-CoA) /ə-SEED-əl, ass-EED-, -EET-/ A molecule participating in many metabolic processes. Its most familiar function is in the Krebs cycle, which it initiates by transferring its two-carbon acetyl group to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate).

acetylcholine /ə-SEED-əl-kō-leen, -kawl-een, ass-EED-, -EET-/ (ACh) An ester of acetic acid and choline that functions as a neurotransmitter.

acetyl group /ə-SEET-əl/ A functional group, the acyl with chemical formula COCH₃, and often represented by the symbol Ac.

acheilia /ack-KIGH-lee-ə/ Congenital absence of one or both lips.

acheiria (also achiria) /ack-KIGH-ree-ə/ (1) congenital absence of one or both hands; (2) loss of sensation in, with a sense of actual loss, of one or both hands; (3) state of being unable to determine the side of the body to which a stimulus is being applied.

Acheulean (also Acheulian) /ə-CHEW-lee-ən/ An archaeological tool industry characteristic of certain early humans, particularly Homo erectus. MORE ABOUT ACHEULEAN TOOLS

achromia /ay-KROME-ee-ə/ Absence of normal pigment, particularly in erythrocytes or the skin.

Online Biology Dictionary (ACI-)

aciculate /ə-SICK-yə-lət/ Having or composed of needles or spines.

acid /ASS-id/ Any substance that increases a solution's hydrogen ion concentration. An acid can react with a base to produce a salt. In aqueous solution acids taste sour, redden litmus paper, and release hydrogen gas by reacting with metals such as iron or zinc. They are hydrogen-containing molecules or ions capable of giving up a proton to a base (or accepting an unshared pair of electrons from a base). An acid solution has a pH of less than 7. See: hydrogen ion concentrationacidic /ə-SEED-ick, ass-/

Acinonyx jubatus /ə-SIN-ə-nix JOO-but-əs/ Scientific name for the cheetah. GEOGRAPHIC DISTRIBUTION | PREY

Acipenseriformes /ass-ə-PENS-er-ə-FORM-eez/ The order of fish including the sturgeons and paddlefishes.

acoelomate /ay-SEEL-ə-MATE/ A solid-bodied organism lacking a cavity between the gut and body wall.

acoumeter /ə-KOO-mə-der, AH-koo-MEED-er/ An instrument for testing hearing.

ACP Acyl carrier protein.

acquired mutation See: somatic cell mutation.

Acrididae /ə-KRID-ə-dee/ A family of grasshoppers.

Online Biology Dictionary (ACRO-)

acrocentric chromosome /AK-row-CENT-rik/ A chromosome in which the centromere is located near the chromosome's end.

acrogenous Of, pertaining to, or being a plant that grows from its apical cells (at the apex of its stem).

acromiohumeral /ə-KRŌ-mee-ō-HUM-er-əl/ Pertaining to the acromion and humerus.

acromion /ə-KRŌ-mee-awn/ The projecting process of the scapula that forms the hard point of the shoulder. PICTURE

acrosome /AK-rə-sōm/ A vesicle at the tip of a sperm cell that allows it to penetrate the egg.

acrosome reaction /AK-rə-sōm/ The interaction between acrosome and egg that allows entry of the spermatozoon. MORE INFORMATION | ANIMATION OF ACROSOME REACTION

Online Biology Dictionary (ACTIN)

actin /AK-tin, -tən/ A family of proteins making up 5-10% of the total protein of the typical eukaryotic cell. Actin, which is 5-7 nm in diameter, is the material of which microfilaments, which perform a contractile function in the cytoskeleton, are composed. It is also present in the contractile, thin filaments of sarcomeres in muscle cells.

Actinophrys /ak-tə-NAWF-rəs/ A genus of protozoans with radial spines. PICTURE

Actinopterygii /ak-tə-nawp-ter-RIDGE-ee-eye/ Ray-finned fishes (fishes with fins supported by radiating spines).

action potential A rapid change in the electrical potential of a plasma membrane that occurs when the cell has been activated by a stimulus. It is caused by a selective closing and opening of voltage-sensitive ion channels.

activation energy The amount of energy (Eₐ) required to convert a stable molecule into a reactive one. It is the energy needed to produce the unstable condition in which the energy state of the bonds of the reactants is raised to a level corresponding to the unstable transition state that precedes a chemical reaction.

active immunity Immunity that arises in response to exposure to an antigen. See: passive immunity

active site The region of an enzyme where it binds to its substrate.

active transport The transport by a carrier protein of a molecule through a plasma-membrane against its concentration or electrochemical gradient.

Online Biology Dictionary (ACU-)

aculeolate /ak-yə-LEE-ə-lət/ Having tiny prickles.

acuminate /ə-KYOOM-ə-nət, -nate/ Tapering or pointed.

acusection /ak-yoo-SEK-shən/ To cut with an electrosurgical needle.

acutifoliate /ə-KYOOT-ə-FŌL-ee-ət/ Having sharp leaves.

acyl-CoA:cholesterol acyl transferase (ACAT) /ASS-əl, ASS-eel/ A member of the class of enzymes known as acyltransferases. ACAT transfers amino-acyl groups from one molecule to another.

acyl carrier protein (ACP) /ASS-əl, ASS-eel/ A protein involved in every step of fatty acid synthesis. It consists of a polypeptide chain and an essential prosthetic group, 4'-phosphopantetheine, linked to a serine residue by a phosphodiester bond.

acyl group /ASS-əl, ASS-eel/ A functional group (RCO—) resulting from the removal of all hydroxyl groups from an organic acid.

acyltransferase /ASS-əl-TRANS-fer-aze/ A transferase enzyme that acts on acyl groups.

Online Biology Dictionary (ADAPT)

adaptation /ad-ap-TAY-shən/ (1) a genetic process whereby a population or at type of organism is thought to have become better suited to its environment; (2) a trait considered to be the product of such a process.

adaptive peak /ə-DAPT-iv/ A hypothetical state of a population in which the combination of alleles present in the population are better suited to the environment than would be any other combination.

adaptive radiation /ə-DAPT-iv raid-ee-AY-shən/ A hypothetical process whereby an originally generalized form gives rise to a number of specialized types. MORE INFORMATION

adaptive zone /ə-DAPT-iv/ A set of ecological niches that may be occupied by various distinct types of organisms exploiting the identical resources in a like manner.

adaxial /ad-ACKS-ee-əl/ (1) toward, or facing toward, the axis or center line; (2) on the upper side (e.g. of a leaf). Compare: abaxial.

addiction /ə-DICK-shən, ad-/ A condition in which the affected individual has a compulsive need for some habit-forming drug.

additive genetic effects (also additive effects) Effects of alleles at different loci that are equal, when combined, to the sum of their individual effects. See also: anticipation, complex trait.

adducent /ad-D(Y)OO-sənt/ Leading or conducting toward.

Online Biology Dictionary (ADEN-)

adenine (A) /ADD-ə-neen/ A purine base found in nucleic acids. In DNA it is one member of the base pair AT (adenine-thymine). See also: nucleotide.

adenocarcinoma /AD-ə-nō-kar-sin-NŌ-mə/ A malignant neoplasm of a glandular epithelium.

adenoma /ad-ə-NŌ-mə/ Any neoplasm of a glandular epithelium.

adenosine diphosphate (ADP) /ə-DEN-ō-seen die-FOSS-fate/ The product of ATP dephosphorylation by ATPases. ADP is converted into ATP by ATP synthases.

adenosine triphosphate (ATP) /ə-DEN-ō-seen try-FOSS-fate/ A nucleotide with multiple functions. In its phosphate bonds it stores energy produced by photosynthesis and cellular respiration. This energy is consumed by various metabolic processes when ATP is hydrolyzed into ADP. MOLECULAR STRUCTURE

adenylate cyclase /ad-DEN-ə-late SIGH-klaze/ The enzyme that catalyzes the conversion of cAMP to ATP.

ADH Alcohol dehydrogenase.

adipose /AD-ə-pōs/ Pertaining to or being animal fat.

adiposis /ad-ə-PŌS-səs, -sis/ (1) obesity; (2) infiltration of an organ or other body part by fat.

AdoMet S-adenosyl methionine.

Online Biology Dictionary (ADREN-)

adrenal /ə-DREE-nəl/ (1) next to the kidney; (2) the adrenal gland; (3) of or pertaining to the adrenal gland.

adrenal gland (also: suprarenal gland) /ə-DREE-nəl/ A gland lying atop either kidney; it releases hormones in response to stress via the synthesis of corticosteroids (e.g., cortisol) and catecholamines (e.g., epinephrine). These glands influence kidney function via the secretion of aldosterone, which increases reabsorption of ions and water in the kidney (it also increases blood volume and, consequently, blood pressure).

adrenosterone /ə-DREE-nō-stə-RONE/ An androgen secreted by the adrenal gland.

adventitious /ad-ven-TISH-əs/ Arising or occurring in some location other than the usual one.

AED Automated external defibrillator.

Aegyptopithecus /ee-JIP-tō-PITH-ə-kəs/ An ancient primate discovered in the Fayum Formation in Egypt and widely considered an ancestor of both modern monkeys and apes. MORE INFORMATION

aerobic respiration /air-ROBE-ick/ See: respiration.

aerobiology /AIR-ō-bī-AWL-ə-jee/ n. The study of airborne organic particles. aetiology /ET-ee-AWL-ə-jee, EET-/ See: etiology.

Afar Depression /ə-FAR/ A geological depression, the source of many hominid fossils, formed by the junction of the East African Rift with the two spreading ridges that have formed the Red Sea and the Gulf of Aden. MORE INFORMATION

affected relative pair Pair of genetically related individuals that both have a trait (i.e., that are both affected by the gene causing that trait). Examples are affected sibling, cousin, and avuncular pairs. See also: avuncular relationship.

afferent /AF-fer-ənt/ adj. Leading toward (opposite of efferent).

afterbirth /AF-ter-berth/ n. The placenta and other tissues discharged from the uterus after the birth of the offspring.

Online Biology Dictionary (AG-)

Ag (1) antigen; (2) chem. symbol for silver.

A/G ratio Albumin/globulin ratio; ratio of albumin to globulin in blood serum (normal ratio: ~1.55).

agamospermy /ay-GAM-ə-SPERM-ee/ n. Reproduction in which the embryo develops without fertilization. MORE INFORMATION

Lake Agassiz An immense prehistoric lake that once existed in northern North America. MORE INFORMATION

agglutination /ag-GAM-ə-sperm-ee, AG-gə-mə-sperm-ee/ n. A uniting or adhering; within a biological context: a clumping of dispersed cells or microorganisms.

agglutinable /ə-GLOOT-ə-nə-bəl/ adj. Capable of undergoing agglutination.

aggregation technique /ag-rə-GAY-shən/ A procedure in which two separate embryos are pushed together at the 8-cell stage of development to produce a single embryo.

Online Biology Dictionary (AGNATH-)

agnathans /ag-NAY-thuns/ Jawless fishes, such as lampreys and hagfishes.

agonistic behavior /ag-ə-NIST-ick/ Behavior involving a contest over some resource, such as territory or mates.

agriculture /AG-rə-kəl-cher/ The science of crop and livestock production.

AIDS Acquired immune deficiency syndrome.

Online Biology Dictionary (AL-)

Al Chemical symbol for aluminum.

ala /AL-ə/ (1) alanine; (2) wing or winglike part.

ALA d-aminolevulinic acid.

alanine (A or ala) /AL-ə-neen/ n. A nonessential amino acid. CODONS | MOLECULAR STRUCTURE | SYNTHESIS

albumin /al-BYOO-min/ n. A class of simple proteins that are (1) water soluble, (2) moderately soluble in concentrated salt solutions, and (3) coagulate on heating (due to denaturation). Albumins make up about one percent of body weight in humans — albuminous /al-BYOO-min-nəs/. Compare: globulins

albuminuria /alb-yoo-mən-ER-ee-ə/ n. Abnormally high levels of albumin in the urine; commonly the result either of impaired kidney function or of intense exercise.

albumose /alb-yoo-mən-ER-ee-ə/ Any of various protein derivatives produced during digestion by the action of hydrolytic enzymes, particularly pepsin, on proteins.

alcohol /ALK-ə-hall/ Any organic compound with a hydroxyl group (-OH) bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple alcohol is CnH2n+1OH.

alcohol dehydrogenases (ADH) /ALK-ə-hall dee-high-DRAW-jə-naze, də-/ n. A group of dehydrogenases that interconvert alcohols and aldehydes or ketones with the reduction of NAD⁺. In animals, they break down toxic alcohols. In yeast and many other microorganisms they reverse the process, producing alcohols via fermentation.

aldehyde /ALD-ə-hide/ n. A member of the class of organic compounds with the formula CnH2nO and having a terminal carbonyl group.

algae (Latin pl. of alga) /AL-jee/ n. A general term applied to simple photosynthetic organisms living in water.

algesia /al-JEE-zhə, -ze-ə/ n. Hypersensitivity to pain.

alive adj. Living; being in the state of life, as opposed to dead.

Online Biology Dictionary (ALKAL-)

alkali /AL-kə-LIE/ n. Any metallic hydroxide other than ammonia that can join with an acid to form a salt (or with an oil to form a soap).

alkaline /AL-kə-lin, AL-kə-line/ adj. Like an alkali; basic.

alkane /AL-kane/ n. A paraffin or saturated hydrocarbon.

alkene /AL-keen/ n. An unsaturated chemical compound containing one or more carbon-to-carbon double bonds.

alkyl /AL-kill/ n. A univalent radical composed of a chain of hydrogen and carbon atoms having the general formula CnH2n+1. For example, the ethyl radical is the alkyl with formula C₂H₅.

Online Biology Dictionary (ALL-)

allantois /ə-LAN-tə-wəs/ n. One of the four membranes enclosing an embryo. It sequesters the nitrogenous wastes produced by the embryo.

allatum hormones Juvenile hormones.

allele frequency (also gene frequency) /ə-LEEL/ For a particular allele at a specified locus, the proportion of all alleles occurring in a population at that locus.

alleles /ə-LEELS/ Alternative forms of a gene occurring at the same locus.

allelic exclusion /ə-LEEL-ick/ The expression in some particular lymphocyte of just one of the alleles that code for the expressed immunoglobulin.

allelic genes /ə-LEEL-ick/ Alleles.

Online Biology Dictionary (ALLO-)

allogeneic /al-lō-jə-NAY-ick/ Having allelic variation between the members of a population.

allolactose /al-lō-LACK-tose, al-lə-/ A disaccharide, similar to lactose, that inhibits the lac repressor's ability to bind DNA. MOLECULAR STRUCTURE

allometry /al-LAWM-ə-tree/ (or allometric growth) /al-lə-MET-trick/ Growth of a part that differs in rate from that of some other part, or from that of the whole organism. Compare: isometry

allopatric /al-lō-PAT-trick/ Of two populations: Occupying different, non-contiguous geographic regions.

allopolyploid /AL-ō-PAWL-ee-ploid/ A polyploid that combines two distinct chromosome sets from different sources. Allopolyploids are produced by hybridization. Compare: autopolyploid.

allosteric control /al-lō-STARE-ick/ Regulation of the activity of one site of a protein by interactions at some other site on the protein.

allozymes /AL-lō-zimes/ Enzymes produced by the same locus, but differing in molecular structure. They are coded for by distinct alleles.

Online Biology Dictionary (ALPHA-)

α-amantin /AL-fə ə-MAWN-tən/ A compound inhibiting transcription of eukaryotic RNA polymerases. RNA polymerase II is inhibited by very low concentrations of α-amantin, while RNA polymerase I is not. It is obtained from the poisonous mushroom Amanita phalloides.

alpha-helix /AL-fə HEE-licks/ A spiral secondary structure occurring in many proteins. An alpha-helix allows maximum intramolecular bonding between H-N and C=O groups, and therefore water exclusion.

alpha-particle /AL-fə/ A helium nucleus; composed of two neutrons and two protons and therefore has a double positive charge.

Online Biology Dictionary (ALT-)

Altamira /alt-ah-MEE-rah/ A cave in northern Spain; site of some of the most famous paleolithic cave paintings. MORE INFORMATION

alternation of generations The cyclic alternation, seen in the life cycles of sexual organisms, between a haploid and a diploid form.

alternative splicings Alternative ways of combining a gene's exons to make variant proteins.

altrices /all-TRY-seez/ See: altricial.

altricial /alt-TRISH-əl/ Slow developing; needing long nursing. Altricial birds or mammals ("altrices") are those with newly hatched or born young being more dependent on their parents (i.e., ones that cannot move about or open their eyes, and that lack down or hair). Compare: precocial.

altruism /AL-troo-iz-əm/ Unselfish behavior; within a biological context, behavior that assists others to survive and reproduce, but that does not benefit the individual engaging in the behavior.

Alu-equivalent family /AL-oo/ A term used to refer to the Alu-related repetitive sequences present in the genomes non-human mammals.

Alu family /AL-oo/ A set of dispersed repetitive DNA sequences in the genomes of humans and related organisms. Each repeat is about 300 bp long. They are named for the Alu cleavage sites that flank them.

aluminum (Al) /ə-LOOM-ə-nəm, British: al-loo-MIN-ee-əm/ Metallic element; atomic number 13, atomic weight 26.9185. PERIODIC TABLE

alveoli (sing alveolus) /al-VEE-ō-lie, -lee/ (1) the minute air cells within the lungs where gas exchange occurs; (2) general: a small hollow, sac, socket, follicle, or depression.

amalgam /ə-MAL-gəm/ A compound containing mercury.

Online Biology Dictionary (AMBI-)

ambilateral /am-bə-LAT-er-əl/ Occurring on both sides.

ambitus /AM-bə-təs/ The outer edge or periphery of a biological structure, such as a leaf or shell.

amblyopia /am-blee-OPE-ee-yə/ Impaired vision due to poor transmission by the optic nerve; usually occurs in only one eye.

Amblypygi /am-BLIP-ə-jigh/ An order of arachnids composed of the whip spiders. MORE INFORMATION

Online Biology Dictionary (AMBUL-)

ambulant /AM-byəl-lənt/ Able to walk.

ambulatory /AM-byə-lə-tore-ee/ Able to walk.

Ambulocetus A hypothesized ancestor of whales, which lived during the early Eocene, about 50 million years ago. MORE INFORMATION

amelia /am-EEL-yəh/ Congenital absence of one or more limbs.

aminoacetic acid /ə-MEEN-ō-ə-SEAT-ick/ A synonym for glycine.

amino acid /ə-MEEN-ō/ One of 20 organic molecules serving as the monomers of proteins. An amino acid has both carboxyl and amino groups. The various amino acids differ only in what is attached to the 4th bond of the α carbon. This variable attachment, or side-chain, is generally indicated by the letter R. The properties of the side chain determine the unique properties of an amino acid.

amino group /ə-MEEN-ō/ The chemical group —NH₂ (the amino group is hydrophilic).

ammonite /AM-mə-nite/ A member of the order Ammonoidea, extinct cephalopods similar to the extant chambered nautilus. Fossil range: Early DevonianLate Cretaceous. PICTURE 1 | PICTURE 2 | PICTURE 3 | PICTURE 4 | PICTURE 5 | PICTURE 6

ammonium /ə-MONE-ee-əm/ The radical NH₄+.

Online Biology Dictionary (AMNIO-)

amnion /AM-nee-ən/ The innermost of the four membranes enclosing the embryo of a reptile, bird, or mammal.

amniorrhexis /am-nee-ə-REKS-əs/ Rupture of the amnion ("breaking of the waters").

amniote /AM-nee-ōt/ Any vertebrate having an amnion during embryonic development, as in the case of a reptile, bird or mammal.

amniotic egg /am-nee-AWT-ick/ The egg of an amniote. The presence of an amnion prevents drying and allows amniotic eggs to be laid on land.

amphibian /am-FIB-ee-ən/ (1) an animal, such as a frog, newt, or salamander belonging to the vertebrate class Amphibia. Amphibians differ from reptiles in that they lay their eggs (which lack an amnion to prevent their drying) in water and pass through an aquatic larval stage, followed by metamorphosis into an often marked distinct adult form; (2) like or being a member of Class Amphibia.

amphimixis /AMF-ə-MIX-əs/ Sexual reproduction.

amplexifoliate /am-pleks-ə-FŌL-ee-ət/ Having grasping leaves.

amplification /am-plə-fə-KAY-shən/ Increase in the copy number of a DNA fragment. Amplification can occur either in vivo or in vitro. See also: cloning, polymerase chain reaction.

A to Amplification

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