Biology Encyclopedia

Biology Encyclopedia

If you would like to prepare for school subjects or simply increase your general knowledge, then enjoy our biology encyclopedia. We tried to focus only on very important terms and definitions. We also kept our terminology very brief so that you absorb the concept more quickly and easily.

Biology Glossary (Page 1)


(OS) COXA: Collectively, the hip bones (os = bone; cox = the hip).
A23187: Mobile-carrier calcium ionophore (allows Ca++ ions to cross cell membranes) originally isolated as an antibiotic from Streptomyces chartreusensis. Also known as Calcimycin, Antibiotic A23187.
ABDUCTOR: A muscle which moves a body part away from the midline of the body (ab = off, from, away; duct = to lead).
ABIOTIC: A term used to describe a process which occurs outside of the body of a living organism, occurring without involvement of a living organism (a- = not, without; bios = life).
ABLATION: Experimental removal or killing of some part of an organism; for example, in experimental embryology, used to determine what effect absence of the structure will have on development of the remaining embryo.
ACETABULARIA: Genus of unicellular marine algae. These organisms comprise an enormous single cell consisting of a cap, stalk and rhizoid and can be up to 10 cm in size.
ACETYL COENZYME A: A molecule of coenzyme A temporarily bonded to a 2-carbon (acetyl) group remaining from the break-down of pyruvic acid (aceto = vinegar).
ACETYLCHOLINESTERASE (ACHE): Enzyme that catalyzes hydrolysis of the neurotransmitter acetylcholine into acetate and choline. Expression of ache can serve as a marker of skeletal muscle differentiation.
ACHENE: A type of fruit, such as a dandelion fruit, which "looks like" a seed and does not burst open when ripe (a- = not, without; chen = yawn, open, gape).
ACHILLES TENDON: The tendon that ends the gastrocnemius (named after Achilles, who as a baby, was dipped into the River Styx to make him invincible - however, the person doing the dipping had hold of his ankle, so it didn't get wet, and he eventually was killed after an arrow pierced his ankle).
ACHONDROPLASIA: A dominant genetic disorder where the homozygote (AA) dies before birth, resulting in a miscarriage, and the heterozygote (Aa) is a dwarf (a- = not, without; chondro = cartilage; plasio = formed, molded).
ACROSOMAL VESICLE: Membrane-bound organelle in the sperm head derived from the golgi apparatus; the vesicle containing enzymes that digest proteins and complex sugars in the outer coverings of an egg. Fusion of the acrosomal vesicle with the plasma membrane of the sperm (in the "acrosome reaction") exposes receptors that bind to the egg surface and is necessary for fertilization.
ACTIN: Protein which when polymerized forms microfilaments, part of the cytoskeleton and necessary for cytokinesis and other cellular functions. Also well known as a major component of the contractile apparatus of muscle cells (along with myosin).
ADAPTATION: Changes in the genetics of individuals within a population that make them more fit for their environment (ad = to, toward; apt = fasten, adjust, fix; -tion = process of, action of).
ADAPTIVE RADIATION: The process of a species spreading into and making use of a new environment (ad = to, toward; apt = fasten, adjust, fix; radia = spoke, ray, radius).
ADDUCTOR: A muscle which moves a body part toward the midline of the body (ad = to, toward; duct = to lead).
ADENOSINE TRIPHOSPHATE (ATP): A molecule used by cells to store and transport energy (adeno = gland; tri = three).
ADRENAL GLANDS: Endocrine glands which are located on top of the kidneys and which secrete hormones such as cortisone and adrenaline (epinephrine) (ad- = to, toward; renal = kidney).
ADRENALINE: Hormone, also known as epinephrine, secreted by adrenal glands which triggers the "fight-or-flight" response (ad = to, toward; renal = kidney).
AETHER: The incorruptible, eternal matter which Aristotle thought composed the universe outside of the moon's orbit, including the sun, the stars, and the other planets (aether, ether = upper air).
AGGLUTINATION: The state of joining or clumping together by adhesion.
AGGREGATE (NOUN): Collection of units or particles (e.g., cells) forming a body or mass. (verb), to form such a body or mass.
ALBUMEN: The "white" of a bird's egg which provides both protein and water for the growing embryo.
ALBUMIN: The main protein in albumen, found in egg white (albumin = the white of an egg).
ALCOHOL: An organic molecule with at least one hydroxyl (-OH) group attached (from Arabic al kohl = powder of antimony).
ALDEHYDE: An organic molecule with a carbonyl group (-C=O, but note that the C needs a fourth bond, too) attached at one end of the molecule (from alcohol + dehydrogenatum where de- = from, down, out + hydrogen - recall that the corresponding alcohol would be -CH2OH).
ALEXANDER IVANOVICH OPARIN: Person who, in 1936, published The Origins of Life in which he described hypothetical conditions necessary for life to have arisen on early Earth.
ALFRED RUSSELL WALLACE: Person who lived about the same time as Charles Darwin and came up with a very similar theory of evolution.
ALIQUOT: A measured sub-volume of a solution taken used to prepare a dilution of that solution.
ALLANTOIS: Extra-embryonic membrane emerging as a sac from the hindgut's ventral wall; formed from the splanchnopleure (combination of endoderm and splanchnic mesoderm). Found in amniotes, it is one of the four extraembryonic membranes (chorion, amnion, allantois and yolk sac) that are adaptations of the terrestrial egg. It collects waste materials from the embryo, and as a part of the chorio-allantoic membrane can be a site of gas exchange.
ALLELES: Alternate forms for genes (allelo = one another, parallel).
ALLELOPATHY: When plants secrete chemicals to retard/inhibit the growth of other plants (allelo = one another, parallel; pathos = disease, suffering).
ALLOGENIC FACTORS: Causes of succession due to abiotic components (allo = other, different; gen = bear, produce).
ALLOMETRIC GROWTH OR ALLOMETRY: Phenomenon whereby parts of the same organism grow at different rates. Contrast with isometric growth.
ALLOPATRIC SPECIES: Species which occupy areas separated by space or time, therefore cannot come into contact with each other (allo = other, different; patri = fatherland, habitat).
ALLUVIAL SOIL: Water-deposited soil (alluvi = wash against, overflow, a pool).
ALVEOLUS: The tiny air sacs in the lungs in which gases are exchanged with the blood (alveol = cavity, pit, socket).
AMINE: An organic molecule with at least one amino (-NH2) group attached (amin, e, o = ammonia).
AMINO ACID: A carbon bonded to four different things, an amino group (-NH2), a carboxyl group (-COOH), a hydrogen (-H), and a side chain (symbolized by "-R") (amine = -NH2 chemical group; carboxylic acid = -COOH chemical group).
AMNIOCENTESIS: Prenatal diagnostic procedure in which amniotic fluid is withdrawn from amniotic sac in order to obtain fluid and fetal cells which are analyzed for metabolic and/or genetic disorders, and to test the maturity of the fetus' lungs.
AMNION: The innermost membranous sac enclosing the embryo of an amniote; it becomes filled with amniotic fluid. One of the four amniote extraembryonic membranes; derived from the somatopleure (combination of ectoderm and somatic mesoderm).
AMNIOTE: Higher vertebrate capable of terrestrial reproduction, and having an amnion during its development. Includes reptiles, birds and mammals, which share a common ancestor.
AMOEBA: Genus name for one-celled organisms which have pseudopodia and belong to Kingdom Protista; Division Rhizopoda (amoeb = change).
AMOEBIC DYSENTERY: Disease caused by the parasite, Entamoeba histolytica, a member of Division Rhizopoda (amoeb = change; dys = bad, malicious; ent = within, interior).
AMPLEXUS: [Latin, an embracing] form of sexual reproduction seen in frogs wherein the male grasps the female from behind and externally fertilizes the eggs as they are deposited.
AMPULLA: Upper region of the mammalian oviduct, near the ovary. Fertilization typically takes place in this region.
AMYLASE: An enzyme which converts starch to maltose (amyl = starch; -ase = enzyme ending).
ANALOGOUS STRUCTURES: Structures having similar function or superficial appearance, but not necessarily sharing a common evolutionary origin (contrast with homologous structures).
ANAPHASE: The third stage of mitosis or meiosis in which the sister chromatids or chromosomes separate and move to the poles of the cell (ana = up, throughout, again).
ANATOMY: The study of body parts, their names, and locations (ana = up, throughout, again; tom = to cut).
ANAXIMANDER: Person who lived from 611 to 546 BC and is credited with the first written work on natural science, a classical poem entitled On Nature.
ANDROGENS: The collective name for male sex hormones, including testosterone (andro = a man; gen = bear, produce).
ANENCEPHALY: [Greek, no brain] condition of forebrain degeneration caused by failure of anterior neuropore closure and consequent prolonged contact of the forebrain with amniotic fluid. Although infants with this neural tube defect are sometimes born alive, the condition is invariably fatal within a few hours or days.
ANEUPLOIDY: Having an abnormal number of chromosomes (aneu = without; ploid = set of chromosomes).
ANGIOSPERMAE: Subdivision of plants within Division Spermatophyta which produce flowers and bear seeds enclosed in an ovary (angio = vessel, receptacle, container; sperma = seed).
ANIMAL HEMISPHERE: Half of an egg or embryo that contains less yolk and/or which divides more rapidly in comparison to the vegetal hemisphere. In eggs or embryos with considerable yolk, the animal hemisphere will be the upper half when the embryo is allowed to settle by gravity yolky cytoplasm being more dense than yolk-free cytoplasm.
ANTACIDS: Chemicals consumed by people to react with stomach acid to change the ph of the stomach contents to a neutral ph (anti = against, opposite; acid = sour, sharp).
ANTERIOR: Front or head end of an organism (ante = before).
ANTHER: Male plant structure in which male gametophytes (pollen) are produced and mature (anthe = flower).
ANTIBIOTIC: A chemical agent which directly or indirectly kills bacteria in a person's body (anti = against, opposite; bios = life).
ANTIBODY: A chemical produced by B-cells to "tag" foreign invaders (anti = against, opposite).
ANTIDIURETIC HORMONE: A hormone secreted by the pituitary gland which affects kidney function and prevents water loss, the production of which is inhibited by alcohol consumption, potentially resulting in dehydration (anti = against, opposite; diuret = to urinate).
ANTIGENS: Substances on the surfaces "foreign" cells that our immune systems use to distinguish "me" from a foreign invader (from "antibody generating"; anti = against, opposite; gen = bear, produce).
ANTON VAN LEEUWENHOEK: Person who lived in the 1600s and was the first person to see sperm cells, in which he thought he could see a homunculus.
APICOMPLEXA: Division of Protista which includes many parasites such as Plasmodium vivax which causes malaria (api = bee or apic = apex, summit, tip).
APOPTOSIS: Also known as programmed cell death (PCD); an active cellular process ("cell suicide") consisting of a stereotyped set of events including nuclear condensation, chromosome degradation, release of specific cellular proteases and signaling for phagocytosis. Apoptosis/PCD is a normal part of development in most or all tissues, aiding in regulating cell number and morphogenesis.
ARACEAE: A family of monocots whose flowers are in the form of a spathe and spadix (from the genus name Arum = "wake-robin" - note that while here in the US this common name is used to refer to Trillium sp., in Britain it is used to refer to plants related to Jack-in-the-Pulpit; -aceae = ending signifying plant family name).
ARCHENTERON: Cavity formed during gastrulation by invagination of the vegetal plate cells (in sea urchin) or involution of cells at the blastoporal lip (in amphibians); it will become the interior of the primitive gut. May also refer to the structure forming this cavity.
ARCHEOCYTE: Somatic cell of sponge that can differentiate into all three other cell types of the organism.
ARISTOTLE: Person who lived from 343 to 322 BC, and contributed ideas such as the Scala Naturae and the idea that the Earth was round and surrounded by the other spheres of matter.
ASCLEPIADACEAE: Plant family with milky juice and flowers with a corona and reflexed petals (Asclepius = Greek god of healing and medicine; -aceae = ending signifying plant family name).
ASCORBIC ACID: A chemical name for vitamin C - when present in adequate amounts, this prevents scurvy (a- = not, without; scorbus = scurvy).
ASEPTICAL: Without bacteria, sterile, under sterile conditions (a- = not, without; sepsis = rotten, putrid).
ASTER: [Latin, star] radiating formation of microtubules at each pole of a spindle apparatus, formed during mitosis.
ASTEROID: Smaller, planet-like objects whose orbits lie between Mars and Jupiter (aster = star; -oid = like, resembling).
ASTHMA: An allergy-induced constriction of the bronchiole muscles, thereby reducing the air passages (asthma = panting, gasping).
ATMOSPHERE: The gaseous mass (air) surrounding a planet (atmo = smoke, vapor; sphere = a ball).
ATOM: One particle, one piece of an element (a = not, without; tom = to cut).
AUSTRALIAN REALM: The biogeographical realm including the continent of Australia and some of the surrounding islands (austr(ali) = southern).
AUTECOLOGY: The study of the relationship of an individual or a species to its environment (auto = self; eco, oikus = house; logy = to study, the study of).
AUTOGENIC FACTORS: Causes of succession due to the plants, themselves (auto = self; gen = bear, produce).
AUTONOMIC NS: The functional part of the NS which controls visceral and cardiac muscles; includes sympathetic and parasympathetic NS (auto = self; nomos = law; autonomos = independent, self-governing).
AUTONOMOUS SPECIFICATION: Determination of cell fate by material acquired during mitosis, independent of interactions with neighboring cells (for example, by 'cytoplasmic segregation' of factors into one daughter cell but not the other.).
AUTORADIOGRAPHY: Photographic process used to detect location of radioactive material.
AUTOSOMES: All the chromosomes other than the X and Y chromosomes (auto = self; soma = body).
AUTOTROPH: An organism, such as a plant, which makes its own food (auto = self; troph = food, nourish, nourishment).
AXONEME: Motor section of flagellum constructed of microtubules emanating from the centriole at the base of the flagellum.
AZIMUTH: The distance in angular degrees in a clockwise direction from north (from Arabic as-samut, the plural of as-samt = the way, direction, path).
BACILLUS: A bacterial cell that is rod-shaped (i.e. Longer than it is wide).
BACTERIOPHAGE: A type of virus that invades, lives in, and kills a host species of bacterium (phago = to eat).
BACTERIOPHAGES: A type of virus that infects bacteria. Infection with a bacteriophage may or may not lead to the death of the bacterium, depending on the phage and sometimes on conditions. Each bacteriophage is specific to one form of bacterium.
BARK: The living tissue outside the vascular cambium in a woody stem. It is composed of phloem tissues, which occur as living inner and dead outer zones.
BAROMETER: An instrument for measuring air pressure (baro = pressure, a burden, heavy; meter = to measure).
BASIDIUM: A reproductive appendage that produces sexual spores on the gills of mushrooms. The fungal division Basidiomycota is named for this structure.
BATHYPELAGIC ZONE: Equivalent of hypolimnion, bottom layer of water in the ocean (bathy = deep, high; pelago = the sea).
BELLY: The central portion of a muscle.
BENTHIC ZONE: The bottom mud in a lake or ocean (benthos = the depths of the sea).
BICEPS: A group of muscles present in the upper forelimb of tetrapods, which are flexors of the elbow joint. In the hind limb, the biceps femoris is a flexor of the knee and an elevator of the femur.

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