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nonliving, as in the physical environment


the process by which water and dissolved substances pass through a membrane


a transmitter substance released from the axons of nerve cells at the synapse

active immunity

protective immunity to a disease in which the individual produces antibodies as a result of previous exposure to the antigen


a behavioral or biological change that enables an organism to adjust to its environment

adaptive radiation

the production of a number of different species from a single ancestral species

adenosine phosphate

adenosine diphosphate (ADP) and adenosine triphosphate (ATP), which are energy storage molecules

ADH (vassopressin)

a hormone that regulates water reabsorption


fatty tissue, fat-storing tissue, or fat within cells

adrenal cortex

the outer part of the adrenal gland that secretes many hormones, including cortisone and aldosterone

adrenal medulla

the inner part of the adrenal gland that secretes adrenalin

adrenaline (epinephrin)

an "emergency" hormone stimulated by anger or fear; increase blood pressure and heart rate in order to supply the emergency needs of the muscles

adrenocorticotrophic hormone

usually referred to as ACTH and secreted by the anterior lobe of the pituitary gland; stimulates the adrenal cortex to produce its characteristic hormones


an organism that requires oxygen for respiration and can live only in the presence of oxygen


requiring free oxygen from the atmosphere for normal activity and respiration


hormone active in osmoregulation; a mineral corticoid produced by the adrenal cortex; stimulates reabsorption of Na+ and secretion of K+

alimentary canal

an organ (group of organs) centrally involved in the human digestive system


the extraembyonic membrane of birds, reptiles and mammals that serves as an area of gaseous exchange and as a site for the storage of noxious excretion products (think umbilical cord)


one or two or more types of genes, each representing a particular trait; many alleles exist for a specific gene locus

alternation of generations

the description of a plant life cycle that consists of a diploid, asexual, sporophyte generation and a haploid, sexual, gametrophyte generation


an air sac in the lung; the site of respiratory exchange, involving diffusion of oxygen and carbon dioxide between the air in the alveolus and the blood in the capillaries


the extraembryonic membrane in birds, reptiles and mammals that surrounds the embryo, forming an amniotic sac

amoeboid movement

movement involving the flowing of cytoplasm into pseudopods, as in amoeba


an organism that does not require free oxygen in order to respire


living or active in the absence of free oxygen; pertaining to respiration that is independent of oxygen


describes structures that have similar function but different evolutionary origins; e.g., a bird's wing and a moth's wing


the stage in mitosis that is characterized by the migration of chromatids to opposite ends of the cell; the stage in meiosis during which homologus pairs migrate (Anaphase I), and the stage in meiosis during which chromatids migrate to different ends of the cell (Anaphase II)


a male sex hormone (e.g., testosterone)


a flowering plant; a plant of the class Angiospermae that produces seeds enclosed in an ovary and is characterized by the possession of fruits and flowers


the phylum to which segmented worms belong


the part of the male reproductive organ (the stamen) that produces and stores pollen


an antipathogenic substance (e.g., penicillin)


globular proteins produced by tissues that destroy or inactivate antigens, Y shaped


a foreign protein that stimulates the production of antibodies when introduced into the body of an organism


the largest artery; carries blood from the left ventricle

aortic arch

blood vessels located between ascending and descending aortas that deliver blood to most of the upper body


a structure that extends from the trunk of an organism and is capable of active movements

aqueous humor

fluid in the eye, found between the cornea and the lens


a class of arthropods that includes scorpions, spiders, mites and ticks


a blood vessel that carries blood away from the heart


the phylum to which jointed-legged invertebrates belong, including insects, arachnids and crustaceans

asexual reproduction

the production of daughter cells by means other than the sexual union of gametes (as in budding and binary fission)


the conversion of digested foods and other materials into forms usable by the body (i.e., the conversion of amino acids into proteins)

assortative mating

the type of mating that occurs when an organism selects a mating partner that resembles itself


the thin-walled anterior chamber of the heart (also called the auricle)


self-digestion occurring in plant and animal tissues, particularly after they have ceased to function properly

autonomic nervous system

the part of the nervous system that regulates the involuntary muscles, such as the walls of the alimentary canal; includes the parasympathetic and sympathetic nervous systems


any chromosome that is not a sex chromosome


an organism that utilizes the energy of inorganic materials such as water and carbon dioxide or the sun to manufacture organic materials


a plant growth hormone


a nerve fiber


bacteria that are rod shaped


a type of virus that can destroy bacteria by infecting, parasitizing and eventually killing them


an emulsifying agent secreted by the liver

bile salts

compounds in bile that aid in emulsification

binary fission

asexual reproduction; in this process, the parent organism splits into two equal daughter cells

binomial nomenclature

the system of naming an organism by its genus and species name


a habitat zone, such as desert, grassland or tundra


living, as in living organisms in the environment


a stage of embryonic development in which the embryo consists of a hollow ball of cells

Bowman's capsule

part of the nephron in the kidney; involved in excretion


in plants, an area of undifferentiated tissue covered by embryonic leaves


a process of asexual reproduction in which the offspring develop from an outgrowth of the plant or animal


a substance that prevents appreciable changes in pH in solutions to which small quantities of acids or bases are added


a unit of heat; the amount of heat required to raise the temperature of one gram of water by one degree centigrade (note: the uppercase Calorie=1000 calories)

Calvin cycle

cycle in photosynthesis that reduces fixed carbon to carbohydrates through the addition of electrons ("dark cycle")


undifferentiated tissue in the stem of a plant that aids growth in width


a tube one cell thick that carries blood from artery to vein; the site of material exchange between the blood and tissues of the body


a bony or chitinous case or shield covering the back or part of the back of an animal (shell of a crab)


an organic compound to which hydrogen and oxygen are attached; the hydrogen and oxygen are in a 2:1 ratio; examples include sugars, starches and cellulose

carbon cycle

the recycling of carbon from decaying organisms for use in future generations


a flesh-eating animal; a holotrophic animal that subsists on other animals or parts of animals


an orange plant pigment that is the precursor of vitamin A


an ion with a positive charge, or an ion that migrates towards the cathode (negative electrode) in an electric field

cell wall

a wall composed of cellulose that is external to the cell membrane in plants; it is primarily involved in support and in the maintenance of proper internal pressure

cell wall plate

in mitosis of higher plants, the structure that forms between the divided nuclei of the two daughter cells and eventually becomes the cell wall

central nervous system (CNS)

encompasses the brain and the spinal cord


the small granular body within the centrosome to which the spindle fibers attach


the place of attachment of the mitotic fiber to the chromosome


a structure in animal cells containing centrioles from which the spindle fibers develop


pertaining to the head


the hindbrain region that controls equilibrium and muscular coordination

cerebral cortex

the outer layer of cerebral hemispheres in the forebrain, consisting of gray matter

cerebral hemisphere

one of the paired lateral divisions of the forebrain


the largest portion of the human brain; it is believed to be the center of intelligence, conscious thought and sensation


the process by which carbohydrates are formed through chemical energy; found in bacteria


the orientation of cells or organisms in relation to chemical stimuli; the growth or movement response of organisms to chemical stimuli


a white or colorless, amorphous, horny substance that forms part of the outer integument of insects, crustaceans and some other invertebrates; it also occurs in certain fungi


a green pigment that performs essential functions as an electron donor and light "entrapper" in photosynthesis


a plastid (organelle) containing chlorophyll


an animal phylum in which all members have a notochord, dorsal nerve cord and pharyngeal gill slits at some embryonic stage; includes the Cephalochordata and the Vertebrates


the outermost, extra-embryonic membrane of reptiles and birds


one of the two strands that constitute a chromosome; chromatids are held together by the centromere


a nuclear protein of chromosomes that stains readily


a short, stubby rod consisting of chromatin that is found in the nucleus of the cells; contains the genetic or hereditary component of cells (in the form of genes)


partially digested food in the stomach

circadian rhythms

daily cycles of behavior


the division in animal cell cytoplasm caused by the pinching in of the cell membrane

climax community

the stable, biotic part of the ecosystem in which populations exist in balance with each other and with the environment


the coagulation of blood caused by the rupture of platelets and the interaction of fibrin, fibrinogen, thrombin, prothrombin and calcium ions


the chamber in the alimentary canal of certain vertebrates located below the large intestine, into which the ureter and reproductive organs empty (as in frogs)


the sensory organ of the inner ear of mammals; it is coiled and contains the organ of corti


the state in which two genetic traits are fully expressed and neither dominates

Coelentrata (Cnidarians)

an invertebrate animal phylum in which animals possess a single alimentary opening and tentacles with stinging cells


the space between the mesodermal layers that forms the body cavity of some animal phyla


an organic cofactor required for enzyme activity


the large intestine


describes an organism that lives symbiotically with a host; this host neither benefits nor suffers from the association


the association of physical, visceral response with an environmental stimulus with which it is not naturally associated; a learned response


a cell in the retina that is sensitive to colors and is responsible for color vision


organism that consumes food from outside itself instead of producing it

contractile vacuole

a specialized structure that controls osmotic pressure by removing water from the cell


the outer, transparent layer of the eye

corpus callosum

a tract of nerve fibers connecting the two cerebral hemispheres

corpus luteum

a remnant of follicle after ovulation that secretes the hormone progesterone


in plants, the tissue between the epidermis and the vascular cylinder in the roots and stems of plants; in animals, the outer tissue of some organs


a hormonal secretion of the adrenal cortex


a "seed leaf"; responsible for food digestion and storage in plant embryo


a thyroid deficiency that results in stunted growth and feeblemindedness

crossing over

the exchange of parts of homologous chromosomes during meiosis


the pollination of the pistil of one flower with pollen from the stamen of a different flower of the same species


a large class of arthropods, including crabs and lobsters


a waxy protective layer secreted by the outer surface of plants, insects, etcetera


a hydrogen carrier containing iron that functions in many cellular processes, including respiration


a process by which the cytoplasm and the organelles of the cell divide; the final stage of mitosis


the cell body of a neuron


the living matter of a cell, located between the cell membrane and the nucleus


the organelle that provides mechanical support and carries out motility functions for the cell


a nitrogen base that is present in nucleotides and nucleic acids; it is paired with guanine


the removal of an amino group from an organism, particularly from an amino acid


the loss of all or part of a chromosome


a small, local population


the part of the neuron that transmits impulses to the cell body


a five carbon sugar that has one oxygen atom less than ribose; a component of DNA


the passive, rhythmical expansion or dilation of the cavities of the heart (atria or ventricles) that allows these organs to fill with blood; preceded and followed by systole (contraction)


a plant that has two seed leaves or cotyledons


the hind portion of the forebrain of vertebrates


a progressive change from which a permanently more mature or advanced state results


the movement of particles from one place to another as a result of their random motion


the process of breaking down large organic molecules into smaller ones


an organism that is heterozygous for two different traits


the instance of polymorphism in which there is a difference of form between two members of a species, as between males and females


describes cells that have a double set of chromosomes in homologous pairs (2n)


a sugar composed of two combined monosaccharides


the separation of homologous pairs of chromosomes following meiotic synapsis


deoxyribonucleic acid; found in cell nucleus, its basic unit is the nucleotide; contains coded genetic information; can replicate on the basis of heredity


a dominant allele suppresses the expression of the other member of an allele pair when both members are present

dorsal root

the sensory branch of each spinal nerve


the most anterior portion of the small intestine of vertebrates, adjacent to the stomach; the continuation of the stomach into which the bile duct and pancreatic duct empty

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