abiotic factors (a-bl-'a-tik fak-tsrz) Nonliving parts of an organism’s environment.

absorption (sb-'sorp-shsn) The movement of simple molecules from the digestive system to the circulatory system for dispersal throughout the body.

abyssal ecosystem (s-bi-ssl eco-sis-tsm) A benthic ecosystem that occurs at great depths in the ocean.

accessory pigments (ak-ses-uh-ree pig-msnt) Photosynthetic pigments other than the chlorophylls that enable an organism to use more colors of the visible light spectrum for photosynthesis (e.g., carotinoids [yellow, red, and orange]; phycoerythrins [red]; and phycocyanin [blue]).

acetyl (s-'se-ts) The 2-carbon remainder of the carbon skeleton of pyruvic acid (CH3CO-) that is able to enter the mitochondrion for oxidation in the Krebs cycle.

acetyl-CoA (s-'se-ts ko-'a) The 2-carbon

remainder of the carbon skeleton of pyruvic attached to a coenzyme A molecule.

acetylcholine (s-se-tsl-ko-len) A neurotransmitter secreted into the synapse by many axons and received by dendrites.

acetylcholinesterase (uh-seet-ko-ls-'nes-ts-'ras) An enzyme present in the synapse that destroys acetylcholine.

acid-base reactions (a-ssd bas re-'ak-shsn) When the ions of one compound (acid) interact with the ions of another compound (base), forming a salt and water.

acids (a-ssds) Compounds that release a hydrogen ion in a solution.

acoelomate (a-'se-ls-mat) Without a coelom; the internal organs have no spaces between them.

acquired characteristics (s-'kwl(-s)r ker-ik-ts- 'ris-tik) Characteristics of an organism gained during its lifetime, not determined genetically and therefore not transmitted to the offspring.

actin (ak-tsn) A protein found in the thin myofilaments of muscle fibers that binds to myosin.

actin filaments (ak-tsn fi-ls-msnts) Filaments composed of the protein actin that are part of a cell’s cytoskeleton.

activation energy (ak-ti-va'shun e-nsr-je) Energy required to start a reaction.

active site (ak-tiv sit) The place on the enzyme that causes the substrate to change.

active transport (ak-tiv trans-'port) The use of a carrier molecule to move molecules across a plasma membrane in a direction opposite that of the concentration gradient. The carrier requires an input of energy other than the kinetic energy of the molecules.

adaptive radiation (s-'dap-tiv ra-de-'a-shsn) A specific evolutionary pattern in which there is a rapid increase in the number of kinds of closely related species.

adenine (a-ds-nen) A double-ring nitrogenous-base molecule in DNA and RNA; the complementary base of thymine or uracil.

adenosine triphosphate (ATP) (s-'de-ns-sen tn-'fas-fat) A molecule formed from the building blocks of adenine, ribose, and phosphates; it functions as the primary energy carrier in the cell.

aerobic cellular respiration (er-'o-bik 'sel-ys-lsr res-ps-'ra-shsn) The biochemical pathway that requires oxygen and converts food, such as carbohydrates, to carbon dioxide and water. During this conversion, it releases the chemical- bond energy as ATP molecules.

aerobic exercise (er-'o-bik ek-ssr-siz) The level of exercise at which the level of exertion allows the heart and lungs to keep up with the oxygen needs of the muscles.

age distribution (aj dis-trs-'byu-shsn) The number of organisms of each age in the population.

alcoholic fermentation (al-ks-'ho-lik fsr- msn-'ta-shsn) The anaerobic respiration pathway in yeast cells; during this process, pyruvic acid from glycolysis is converted to ethanol and carbon dioxide.

algae ('al-gs) Protists that have cell walls and chlorophyll and can therefore carry on photosynthesis.

allele (s-'lel) An alternative form of a gene for a particular characteristic (e.g., attached earlobe and free earlobe are alternative alleles for ear shape).

allele frequency (s-'lel fre-kwsn(t)-se) A measure of how common a specific allele is, compared with other alleles for the same characteristic.

allergy ('a-lsr-je) An abnormal immune reaction to an antigen. Possibly the most familiar are allergies to foods, pollens, and drugs.

alternation of generations (ol-tsr-'na-shsn sv je-ns-'ra-shsnz) The aspect of the life cycle in which there are two distinctly different forms of an organism; each form is involved in the production of the other and only one form is involved in producing gametes; the cycling of a diploid sporophyte generation and a haploid gametophyte generation in plants.

alternative splicing (ol-'tsr-ns-tiv spll-sig) A process that selects which exons will be retained as part of the mature mRNA that will be used during translation. Alternative splicing allows for the possibility that a single gene can produce more than one type of protein.

altruism ('al-tru-i-zsm) Behavior in which an individual animal gives up an advantage or puts itself in danger to aid others.

alveoli (al-'ve-sle) Tiny sacs found in the lungs; where gas exchange takes place.

amino acid (s-'me-no 'a-ssd) A basic subunit of protein consisting of a short carbon skeleton that contains an amino group, a carboxylic acid group, and one of various side groups.

anabolism (s-'na-bs-li-zsm) Metabolic pathways that result in the synthesis of new, larger compounds (e.g., protein synthesis).

anaerobic cellular respiration (a-ns-'ro-bik 'sel-ys-lsr res-ps-'ra-shsn) A biochemical pathway that does not require oxygen for the production of ATP and does not use O2 as its ultimate hydrogen ion acceptor.

anaerobic exercise (a-ns-'ro-bik 'ek-ssr-slz) Bouts of exercise that are so intense that the muscles cannot get oxygen as fast as they need it.

analogous structures (s-'na-ls-gss 'strsk-chsr) Structures that have the same function (ex., the wing of a butterfly and the wing of a bird) but different evolutionary backgrounds.

anaphase ('a-ns-faz) The third stage of mitosis, characterized by division of the centromeres and movement of the chromosomes to the poles.

androgens ('an-drs-jsn) Male sex hormones, produced by the testes, that cause the differentiation of typical internal and external genital male anatomy.

angiosperms ('an-je-s-spsrmz) Plants that produce flowers, seeds, and fruits.

anorexia nervosa (a-ns-'rek-se-s nsr-'vo-ss) A nutritional deficiency disease characterized by severe, prolonged weight loss for fear of becoming obese; this eating disorder is thought to stem from sociocultural factors.

anther ('an-thsr) The sex organ in plants that produces the pollen that contains the sperm.

antheridium (an-ths-'ri-de-sm) The structure in lower plants that bears sperm.

anthropomorphism ('an-thrs-ps-mor- fi-zsm) The ascribing of human feelings, emotions, or meanings to the behavior of animals.

antibiotics (an-te-bi-'a-tiks) Drugs that

selectively kill or inhibit the growth of a particular cell type.

antibody ('an-ti-ba-de) A protein made by B-cells in response to a molecule known as the antigen.

anticodon (an-ti-'ko-dan) The trio of bases in the tRNA that is involved in base-pairing.

antidiuretic hormone (ADH) (an-ti-di-yu-'re- tik 'hOr-mon) The hormone produced by the pituitary gland that stimulates the kidney to reabsorb water.

antigen ('an-ti-jsn) A large organic molecule, usually a protein, which is able to stimulate the production of a specific defense response and becomes neutralized or destroyed by that response.

aorta (a-'Or-ts) The large blood vessel that carries blood from the left ventricle to the majority of the body.

apoptosis (a-psp-'to-sss) Death that has a genetic basis and not the result of injury.

Archaea (ar-'ke-s) one of two domains of prokaryotic organisms: Archaea and Bacteria. Distinguished from the domain Bacteria by differences in the nature of the DNA, cell wall, and cell membrane.

archegonium (ar-ki-'go-ne-sm) The structure in lower plants that bears eggs.

arteries ('ar-ts-rez) The blood vessels that carry blood away from the heart.

arterioles (ar-'tir-e-olz) Small arteries, located just before capillaries, that can expand and contract to regulate the flow of blood to parts of the body.

asexual reproduction (a-'sek-shwsl re-prs-'dsk-shsn) A form of duplication that requires only one parent and results in two organisms that are genetically identical to the parent.

assimilation (s-si-ms-'la-shsn) The physiological process that takes place in a living cell as it converts nutrients in food into specific molecules required by the organism.

association (s-so-se-'a-shsn) An animal learns that a particular outcome is associated with a particular stimulus.

aster ('as-tsr) Microtubules that extend from the centrioles to the plasma membrane of an animal cell.

asymmetry (a-'si-ms-tre) The characteristic of animals with no particular body shape.

atomic mass unit (s-'ta-mik 'mas 'yu-nst) A unit of measure used to describe the mass of atoms and is equal to 1.67 x 10-24 grams, approximately the mass of 1 proton.

atomic nucleus (s-'ta-mik 'nu-kle-ss) The central region of an atom.

atomic number (s-' ta-mik 'nsm-bsr) The number of protons in an atom.

atomic weight (s-'ta-mik 'wat) The weight of an atomic nucleus, expressed in atomic mass units (the sum of the protons and neutrons).

atoms ('a-tsmz) The fundamental units of matter; the smallest parts of an element that still act like that element.

atria (’a-tre-s) Thin-walled sacs of the heart that receive blood from the veins of the body and empty into the ventricles.

atrioventricular valves (a-tre-o-ven-'tri-kys- lsr 'valvz) Valves, located between the atria and ventricles of the heart, that prevent the blood from flowing backwards from the ventricles into the atria.

attachment site (s-'tach-msnt 'sit) A specific point on the surface of the enzyme where it can physically attach itself to the substrate; also called binding site.

autoimmune diseases ('O-to-i-'myun di-'zez) Disorders that result from the immune system turning against normal chemicals and cells of the body.

autosomes ('O-ts-somz) Chromosomes that typically carry genetic information used by an organism for characteristics other than the primary determination of sex.

autotrophs ('O-ts-trofs) Organisms that are

able to make their food molecules from inorganic raw materials by using basic energy sources, such as sunlight.

axon ('ak-san) A neuronal fiber that carries information away from the nerve cell body.



bacteria (bak-'tir-e-s) Noneukaryotic, unicellular organisms of the Domain Bacteria; formerly used to refer to members of both the Domain Bacteria and the Domain Archaea.

basal metabolic rate (BMR) ('ba-sslme-ts-'ba-lik 'rat) The amount of energy required to maintain normal body activity while at rest.

bases ('ba-sez) Compounds that release hydroxide ions or accept hydrogen ions in a solution.

basilar membrane ('ba-zs-lsr 'mem-bran) A membrane in the cochlea containing sensory cells that are stimulated by the vibrations caused by sound waves.

behavior (bi-'ha-vysr) How an organism acts, what it does, and how it does it.

behavioral isolating mechanisms (bi-'ha- vysr-rsl 'I-ss-lat-ing 'me-ks-ni- zsmz) Reproductive isolating mechanisms that prevent interbreeding between species because of differences in behavior.

benign tumor (bi-'nIn 'tu-msr) A cell mass that does not fragment and spread beyond its original area of growth.

benthic ('ben-thik) A term used to describe organisms that live in bodies of water, attached to the bottom or to objects in the water.

benthic ecosystem (‘ben-thik 'e-ko-sis-tsm) An aquatic ecosystem that exists on the bottom of a body of water.

bilateral symmetry (bI-'la-ts-rsl 'si-ms-tre) The characteristic of animals that are constructed along a plane running from a head to a tail region, so that only a cut along one plane of this axis results in two mirror halves.

bile ('bIl) The product of the liver, stored in the gallbladder, that is responsible for the emulsification of fats.

binary fission ('bI-ns-re 'fi-shsn) A method of asexual cell division used by noneukaryotic cells.

binding site (attachment site) ('bIn-dig 'sit) A specific point on the surface of the enzyme where it can physically attach itself to the substrate.

binomial system of nomenclature (bi-'no- me-sl 'sis-tsm 'sv 'no-msn-kla- chsr) A naming system that uses two Latin names, genus and specific epithet, for each species of organism.

biochemical isolating mechanisms (bi-o-'ke-mi-ksl 'I-ss-lat-ing 'me-ks-ni- zsmz) Differences in biochemical activities that prevent mating between individuals of different species.

biochemical pathway (metabolic pathway) (bI-o-’ke-mi-ksl 'path-wa) A major series of enzyme-controlled reactions linked together.

biochemistry (bI-o-'ke-ms-stre) The chemistry of living things, often called biological chemistry.

biogenesis (bI-o-'je-ns-sss) The concept that life originates only from preexisting life.

biological species concept (bI-o-'la-ji-ksl 'spe-shez 'kan-sept) The concept that species are distinguished from one another by their inability to interbreed.

biology (bI-'a-ls-je) The science that deals with the study of living things and how living entities interact with things around them.

biomagnification (bI-o-mag-ns-fs- 'ka-shsn) The accumulation of a compound in increasing concentrations in organisms at successively higher trophic levels.

biomass ('bI-o-mas) The dry weight of a collection of designated organisms.

biomes ('bI-omz) Large, regional communities primarily determined by climate.

bioremediation (‘bI-o-ri-me-de-'a-shsn) The use of living organisms to remove toxic agents from the environment.

biosphere ('bI-s-sfir) The worldwide ecosystem.

biotechnology (bI-o-tek-'na-ls-je) The science of gene manipulation.

biotic factors (bI-'a-tik 'fak-tsrz) Living

parts of an organism’s environment.

blood ('blsd) The fluid medium, consisting of cells and plasma, that assists in the transport of materials and heat.

bloom ('blum) A rapid increase in the

number of microorganisms in a body of water.

body mass index (BMI) ('ba-de 'mas 'in-deks) The weight of a person in kilograms divided by the person’s height in meters squared.

Bowman’s capsule ('bo-msnz- 'kap-ssl) The saclike structure at the end of a nephron that surrounds the glomerulus.

breathing ('bre-thig) The process of pumping air into and out of the lungs.

bronchi ('brag-kI) Major branches of the trachea that ultimately deliver air to bronchioles in the lungs.

bronchioles ('brag-ke-olz) Small tubes that deliver air to the alveoli in the lungs.

budding ('bs-dig) A type of asexual reproduction in which the new organism is an outgrowth of the parent.

bulimia (bu-'le-me-s) A nutritional deficiency disease characterized by a binge-and- purge cycle of eating; it is thought to stem from psychological disorders.



calorie ('ka-ls-re) The amount of heat energy necessary to raise the temperature of 1 gram of water 1°C.

Calvin cycle ('kal-vsn- 'sI-ksl) A cyclic sequence of reactions that make up the light-independent reactions stage of photosynthesis.

capillary ('ka-ps-ler-e) The thinnest blood vessel that exchanges materials between the blood and tissues that surround these vessels.

carbohydrates (kar-bo-'hI-drats) One class of organic molecules composed of carbon, hydrogen, and oxygen in a ratio of 1:2:1; the basic building block of carbohydrates is a simple sugar (monosaccharide).

carbon cycle ('kar-bsn 'sI-ksl) The processes and pathways involved in capturing inorganic carbon-containing molecules, converting them into organic molecules that are used by organisms, and the ultimate release of inorganic carbon molecules back to the abiotic environment.

carbon skeleton ('kar-bsn 'ske-ls-tsn) The central portion of an organic molecule composed of rings or chains of carbon atoms.

carcinogens (kar-'si-ns-jsnz) Agents that cause cancer.

cardiovascular system ('kar-de-o-'vas-kys-lsr 'sis-tsm) The organ system of all vertebrates including humans that pumps blood around the body and consists of blood, the heart, and vessels.

carnivores ('kar-ns-vorz) Animals that eat other animals.

carrier proteins ('ker-e-sr 'pro-tenz) A category of proteins that pick up molecules at one place and transport them to another.

carrying capacity ('ka-re-ing ks-'pa-ss-te) The maximum sustainable population for an area.

catabolism (ks-'ta-bs-li-zsm) Metabolic pathways that result in the breakdown of compounds (e.g., glycolysis).

catalyst ('ka-ts-lsst) A chemical that speeds up a reaction but is not used up in the reaction.

cell cycle ('sel 'sI-ksl) All the stages of growth and division for a eukaryotic cell.

cell division ('sel ds-'vi-zhsn) The process in which a cell becomes two new cells.

cell plate ('sel 'plat) A plant-cell structure that begins to form in the center of the cell and proceeds to the cell membrane, resulting in cytokinesis.

cells ('selz) The basic structural units of all living things; the smallest units that display the characteristics of life.

cell theory ('sel 'the-s-re) The concept that all living things are made of cells.

cellular membranes ('sel-ys-lsr 'mem-branz) Thin sheets of material composed of phospholipids and proteins; some of the proteins have attached carbohydrates or fats.

cellular respiration ('sel-ys-lsr res-ps-'ra-shsn) A major biochemical pathway by which cells release the chemical-bond energy from food and convert it into a usable form (ATP).

cell wall ('sel 'wol) An outer covering on some cells; may be composed of cellulose, chitin, or peptidoglycan, depending on the kind of organism.

central nervous system ('sen-trsl 'nsr-vss 'sis-tsm) The portion of the nervous system consisting of the brain and spinal cord.

centriole ('sen-tre-ol) Two sets of nine short microtubules; each set of tubules is arranged in a cylinder.

centromere ('sen-trs-mir) The sequence of bases at the site where the sister chromatids are attached.

cerebellum (ser-s-'be-lsm) The region of the brain, connected to the medulla oblongata, that receives many kinds of sensory stimuli and coordinates muscle movement.

cerebrum (ss-'re-brsm) The region of the brain that surrounds most of the other parts of the brain and is involved in consciousness and thought.

chemical bonds ('ke-mi-ksl 'bandz) Forces that combine atoms or ions and hold them together.

chemical equation ('ke-mi-ksl i-'kwa-zhsn) A way of describing what happens in a chemical reaction.

chemical reaction ('ke-mi-ksl re-'ak-shsn) The formation or rearrangement of chemical bonds, usually indicated in an equation by an arrow from the reactants to the products.

chemicals ('ke-mi-kslz) Substances used or produced in processes that involve changes in matter.

chemistry ('ke-ms-stre) The science

concerned with the study of the composition, structure, and properties of matter and the changes it undergoes.

chemosynthesis ('ke-mo-'sin-ths-sss) The use of inorganic chemical reactions as a source of energy to make larger, organic molecules.

chlorophyll ('klor-s-fil) The green pigment located in the chloroplasts of plant cells associated with trapping light energy.

chloroplasts ('klor-s-plasts) Energyconverting, membranous, saclike organelles in plant cells containing the green pigment chlorophyll.

chromatid ('kro-ms-tsd) One of two

component parts of a chromosome formed by replication and attached at the centromere.

chromatin ('kro-ms-tsn) An area or a

structure within the nucleus of a cell composed of long molecules of deoxyribonucleic acid (DNA) in association with proteins.

chromosomal aberration ('kro-ms-som-al a-bs-'ra-shsn) A change in the structure of chromosomes that can affect the expression of genes (e.g., translocation, duplication mutations).

chromosomes (kro-ms-'somz) Doublestranded DNA molecules with attached protein (nucleoprotein) coiled into a short, compact unit.

cilia ('si-le-s) Numerous short, hairlike structures projecting from the cell surface that enable locomotion.

class ('klas) A group of closely related families within a phylum.

classical conditioning ('kla-si-ksl ksn-'di-sh- niq) Learning that occurs when an involuntary, natural, reflexive response to a natural stimulus is transferred from the natural stimulus to a new stimulus.

cleavage furrow ('kle-vij 'fsr-o) An indentation of the cell membrane of an animal cell that pinches the cytoplasm into two parts during cell division.

climax community ('kll-maks ks-'myu-ns-te) A relatively stable, long-lasting community.

clitoris ('kli-ts-rss) A small, elongated erectile structure located between and at the head of the labia; it is equivalent to the penis.

clone ('klon) Exact copies of biological entities such as genes, organisms, or cells.

cochlea ('ko-kle-s) The part of the ear that converts sound into nerve impulses.

coding strand ('ko-ding 'strand) One of the two DNA strands that serves as a template, or pattern, for the synthesis of RNA.

codominance (ko -'da-ms-nsns) A situation in which both alleles in a heterozygous organism express themselves.

codon ('ko-dan) A sequence of three nucleotides of an mRNA molecule that directs the placement of a particular amino acid during translation.

coelom ('se-lsm) A body cavity in which internal organs are suspended.

coenzyme (ko-'en-zlm) A molecule that works with an enzyme to enable the enzyme to function as a catalyst.

cofactor ('ko-fak-tsr) Inorganic ions or organic molecules that serve as enzyme helpers.

commensalism (ks-'men-ss-li-zsm) A relationship between two organisms in which one organism is helped and the other is not affected.

communication (ks-myu-ns-'ka-shsn) The use of signals to convey information from one animal to another.

community (ks-'myu-ns-te) Populations of different kinds of organisms that interact with one another in a particular place.

competition (kam-ps-'ti-shsn) A relationship between two organisms in which both organisms are harmed.

competitive exclusion principle (ksm-'pe-ts- tiv iks-'klu-zhsn 'prin-ss-psl) No two species can occupy the same niche at the same time.

competitive inhibition (ksm-'pe-ts-tiv in-hs- 'bi-shsn) The formation of a temporary enzyme-inhibitor complex that interferes with the normal formation of enzyme-substrate complexes, resulting in a decreased turnover.

complete proteins (ksm-'plet 'pro-tenz) Protein molecules that provide all the essential amino acids.

complex carbohydrates ('kam-pleks kar-bo- 'hl-drats) Macromolecules composed of simple sugars combined by dehydration synthesis to form a polymer.

compound (kam-'paund) A kind of matter that consists of a specific number of atoms (or ions) joined to each other in a particular way and held together by chemical bonds.

concentration gradient (diffusion gradient) (kan-ssn-'tra-shsn 'gra-de-snt) (di-'fyu-zhsn 'gra-de-snt) The gradual change in the number of molecules per unit of volume over distance.

conditioned response (ksn-'di-shsnd ri-'spans) The modified behavior displayed in which a new response is associated with a natural stimulus.

cones ('konz) Reproductive structures of gymnosperms that produce pollen in males or eggs in females.

consumers (ksn-'su-msrs) Organisms that must obtain energy in the form of organic matter.

control group (ksn-'trol 'grup) The situation used as the basis for comparison in a controlled experiment. The group in which there are no manipulated variables.

controlled experiment (ksn-'trold ik-'sper-s- msnt) An experiment that includes two groups, one in which the variable is manipulated in a particular way and one in which there is no manipulation.

control processes (ksn-'trl 'pra-se-ssz) Mechanisms that ensure an organism will carry out all life activities in the proper sequence (coordination) and at the proper rate (regulation).

convergent evolution (ksn-'vsr-jsnt e-vs-'lu- shsn) An evolutionary pattern in which widely different organisms show similar characteristics.

coral reef ecosystem ('kor-sl 'ref 'e-ko-sis- tsm) A benthic ecosystem in shallow water produced by coral animals that build cup-shaped external skeletons around themselves. A symbiotic relationship between corals and algae provides the organic matter that supports other kinds of organisms.

cotyledons (ka-ts-'le-dsn) Embryonic leaves that have food stored in them; also known as seed leaves.

covalent bond (ko-'va-lsnt 'band) The attractive force formed between two atoms that share a pair of electrons.

cristae ('kris-ts) Folded surfaces of the inner membranes of mitochondria.

critical period ('kri-ti-ksl 'pir-e-sd) The

period of time during the life of an animal when imprinting can take place.

crossing-over ('kro-sip 'o-vsr) The exchange of a part of a chromatid from 1 chromosome with an equivalent part of a chromatid from a homologous chromosome.

cryptorchidism (krip-'tor-ks-di-zsm) A developmental condition in which the testes do not migrate from the abdomen through the inguinal canal to the scrotum.

cytokinesis (sl-to-ks-'ne-sss) The division of the cytoplasm of one cell into two new cells.

cytoplasm ('sl-ts-pla-zsm) The portion of the protoplasm that surrounds the nucleus.

cytosine ('sl-ts-sen) A single-ring nitrogenous-base molecule in DNA and RNA; it is complementary to guanine.

cytoskeleton (sl-ts-'ske-ls-tsn) The internal framework of eukaryotic cells composed of intermediate filaments, microtubules, and microfilaments; provides the cell with a flexible shape, and the ability to move through the environment, to move molecules internally, and to respond to environmental changes.



death phase ('deth 'faz) The portion of some population growth curves in which the size of the population declines.

deceleration phase (de-se-ls-'ra-shen 'faz) A phase in the population growth curve during which the population growth rate begins to slow.

deciduous (di-'si-js-wss) A type of tree that loses its leaves at the end of the growing season.

decomposers (de-ksm-'po-zsrs) Organisms that use dead organic matter as a source of energy.

deductive reasoning (deduction) (di-'dsk-tiv 'rez-nip) (di-'dsk-shsn) The mental process of using accepted generalizations to predict the outcome of specific events; from the general to the specific.

dehydration synthesis reaction (de-bl-'dra- shsn 'sin-ths-sss re-'ak-shsn) A reaction that results in the formation of a macromolecule when water is removed from between the two smaller component parts.

deletion aberration (di-'le-shsn a-bs-'ra-shsn) A major change in DNA that can be observed at the level of the chromosome.

deletion mutation (di-'le-shsn myu-'ta-shsn) A change in the DNA that has resulted from the removal of one or more nucleotides.

denatured (de-'na-chsrd) Altered so that some of the protein’s original properties are diminished or eliminated.

dendrites ('den-drlts) Neuronal fibers that receive information from axons and carry it toward the nerve-cell body.

denitrifying bacteria (de-'m-trs-fl-ing bak-'tir-e-s) Several kinds of bacteria capable of converting nitrite to nitrogen gas.

density-dependent limiting factors ('den- ss-te di-'pen-dsnt 'li-ms-tip 'fak-tsrz) Population-limiting factors that become more effective as the size of the population increases.

density-independent limiting factors ('den- ss-te in-ds-'pen-dsnt 'li-ms-tip 'fak- tsrz) Population-controlling factors that are not related to the size of the population.

deoxyribonucleic acid (DNA) (de-'ak-si-n- bo-nu-kle-ik 'a-ssd) A polymer of nucleotides that serves as genetic information. In noneukaryotic cells, it is a double-stranded loop and contains attached HU proteins. In eukaryotic cells, it is found in strands with attached histone proteins. When tightly coiled, the DNA and histone structure is known as a chromosome.

dependent variable (di-'pen-dsnt 'ver-e-s-bsl) A variable that changes in direct response to (depends on) how another variable (independent variable) is manipulated.

depolarized (de-'po-ls-rizd) Having lost the electrical difference existing between two points or objects.

determination (di-tsr-ms-'na-shsn) The

process a cell goes through to select which genes it will eventually express on a more or less permanent basis.

diaphragm ('dl-s-fram) The muscle separating the lung cavity from the abdominal cavity; it is involved in exchanging the air in the lungs.

diastolic blood pressure (dl-s-'sta-lik 'blsd 'pre-shsr) The pressure present in a large artery when the heart is not contracting.

dicot ('dl-kat) An angiosperm whose embryo has two seed leaves.

diet ('dl-st) The food and drink consumed by a person from day to day.

dietary fiber ('dl-s-ter-e 'fi-bsr) Natural (plant) or industrially produced polysaccharides that are resistant to hydrolysis by human digestive enzymes.

Dietary Reference Intakes ('dl-s-ter-e 're-fsrns 'in-taks) Published by the USDA, these guidelines provide information on the amounts of certain nutrients various members of the public should receive.

differentiation (dif-s-'ren-sbe-'a-sbsn) The process of forming specialized cells within a multicellular organism.

diffusion (di-'fyu-zbsn) The net movement of a kind of molecule from an area of higher concentration to an area of lesser concentration.

digestion (dl-'jes-cbsn) The breakdown of complex food molecules to simpler molecules; the chemical reaction of hydrolysis.

digestive system (dl-'jes-tiv 'sis-tsm) The organ system responsible for the processing and distribution of nutrients and consists of a muscular tube and glands that secrete digestive juices into the tube.

diploblastic (dip-lo-'blas-tik) A condition in which some simple animals consist of only two layers of cells.

diploid ('di-ploid) Having two sets of chromosomes: one set from the maternal parent and one set from the paternal parent.

directional selection (ds-'rek-sbnsl ss-'lek- sbsn) Selection that occurs when individuals at one extreme of the range of a characteristic are consistently selected for.

disruptive selection (dis-'rsp-tiv ss-'lek-sbsn) Selection that occurs when both extremes of a range for a charcteristic are selected for and the intermediate condition is selected against.

distal convoluted tubule ('dis-tsl 'kan-vs-lu- tsd 'tu-byul) The downstream end of the nephron of the kidney, primarily responsible for regulating the amount of hydrogen and potassium ions in the blood.

divergent evolution (ds-'vsr-jsnt e-vs-'lu-shsn) A basic evolutionary pattern in which individual speciation events cause many branches in the evolution of a group of organisms.

DNA fingerprinting (DNA 'fig-gsr-print-mg) A laboratory technique that detects differences in DNA to identify a unique individual; the differences in DNA are detected by using variable number tandem repeats, restriction enzymes, and electrophoresis.

DNA library (DNA 'H-brer-e) A collection of cloned DNA fragments that represent all the genetic information of an organism.

DNA replication (re-pls-'ka-sbsn) The process by which the genetic material (DNA) of the cell reproduces itself prior to its distribution to the next generation of cells.

domain (do-'man) The first (broadest) classification unit of organisms; there are three domains: Bacteria, Archaea, and Eucarya.

dominance hierarchy ('da-ms-nsns 'bl-rar-ke) A relatively stable, mutually understood order of priority within a group.

dominant allele ('da-ms-nsnt s-'lel) An allele that expresses itself and masks the effects of other alleles for the trait.

double bond ('ds-bsl 'band) A pair of covalent bonds formed between two atoms when they share two pairs of electrons.

double-factor cross ('ds-bsl 'fak-tsr 'kros) A genetic study in which two pairs of alleles are followed from the parental generation to the offspring.

Down syndrome ('daun 'sin-drom) A genetic disorder resulting from the presence of an extra chromosome 21. Symptoms include slightly slanted eyes, flattened facial features, a large tongue, and a tendency toward short stature and fingers. Individuals usually display mental retardation.

duodenum (du-s-'de-nsm) The first part of the small intestine, which receives food from the stomach and secretions from the liver and pancreas.

duplications (du-pli-'ka-shsnz) A form of chromosomal aberration in which a portion of a chromosome is replicated and attached to the original section in sequence.

dynamic equilibrium (dl-'na-mike-kws-'li-bre-sm) The condition in which molecules are equally dispersed; therefore, movement is equal in all directions.



ecology (i-'ka-ls-je) The branch of biology that studies the relationships between organisms and their environment.

ecosystem ('e-ko-sis-tsm) A unit consisting of a community of organisms (populations) and its interactions with the physical surroundings.

ectoderm ('ek-ts-dsrm) The outer embryonic layer.

ectotherms ('ek-ts-tbsrmz) Animals that are unable to regulate their body temperature by automatic physiological processes but can regulate their temperature by moving to places where they can be most comfortable.

ejaculation (i-ja-kys-'la-sbsn) The release of sperm cells and seminal fluid through the penis of a male.

electron (i-'lek-tran) A negatively charged particle moving at a distance from the nucleus of an atom; it balances the positive charges of the protons.

electron-transport system (ETS) (i-'lek-tran trans-'port 'sis-tsm) The series of oxidation-reduction reactions in aerobic cellular respiration in which the energy is removed from hydrogens and transferred to ATP.

electrophoresis (i-lek-trs-fs-'re-sss) A technique that separates DNA fragments, proteins, or other molecules on the basis of size.

elements ('e-ls-msnts) Fundamental chemical substances that are made up of collections of only one kind of atom.

emergent properties (i-'msr-jsnt 'pra-psr-tez) Never-before-seen features that result from the interaction of simple components when they form much more complex substances.

endocrine glands ('en-ds-krsn 'glandz) Glands that secrete into the circulatory system.

endocrine system ('en-ds-krsn 'sis-tsm) A number of glands that communicate with one another and other tissues through chemical messengers transported throughout the body by the circulatory system.

endocytosis (en-do-sl-'to-sss) The process cells use to wrap membrane around a particle (usually food) and engulf it.

endoderm ('en-ds-dsrm) The inner embryonic layer.

endoplasmic reticulum (ER) (en-ds-plaz-mik ri-'ti-kys-lsm) Folded membranes and tubes throughout the eukaryotic cell that provide a large surface on which chemical activities take place.

endoskeletons (en-do-'ske-ls-tsnz) Skeletons typical of vertebrates in which the skeleton is surrounded by muscles and other organs.

endospore ('en-do-spor) A unique bacterial structure with a low metabolic rate that germinates under favorable conditions to grow into a new cell.

endosymbiotic theory (en-do-sim-bl-'a-tik 'the-s-re) A theory suggesting that some organelles found in eukaryotic cells may have originated as free- living cells.

endotherms ('en-do-thsrmz) Animals that have internal temperature-regulating mechanisms and can maintain a relatively constant body temperature in spite of wide variations in the temperature of their environment.

energy ('e-nsr-je) The ability to do work or cause things to move.

energy level ('e-nsr-je 'le-vsl) A region surrounding an atomic nucleus that contains electrons moving at approximately the same speed and having approximately the same amount of kinetic energy.

enhancer sequence (in-'han-ssr 'se-kwsns) A DNA sequence that regulates gene expression by acting as a binding site for proteins that increase the ability of RNA polymerase to transcribe a specific protein.

environment (in-'vl-rs-msnt) Anything that affects an organism during its lifetime.

environmental resistance (in-'vl-rs-msn-tslri-'zis-tsns) The collective factors that limit population growth.

enzymatic competition (en-zs-'ma-tik kam- ps-'ti-shsn) Competition among several different available enzymes to combine with a given substrate material.

enzymes ('en-zlmz) Molecules, produced by organisms, that are able to control the rate at which chemical reactions occur.

enzyme-substrate complex ('en-zlm 'ssb- strat 'kam-pleks) A temporary molecule formed when an enzyme attaches itself to a substrate molecule.

epigenetics (e-pi-js-'ne-tiks) The study of changes in gene expression caused by factors other than alterations in a cell’s DNA.

epinephrine (e-ps-'ne-frsn) A hormone produced by the adrenal medulla and certain nerve cells that increases heart rate, blood pressure, and breathing rate.

epiphytes ('e-ps-fits) Plants that live on the surface of other plants without doing harm.

essential amino acids (i-'sen-shsl s-'me-no 'a-ssds) Amino acids that cannot be synthesized by the human body and must be part of the diet (e.g., lysine, tryptophan, and valine).

essential fatty acids (i-'sen-shsl 'fa-te 'a-ssds) The fatty acids linoleic and linolenic, which cannot be synthesized by the human body and must be part of the diet.

estrogen ('es-trs-jsn) One of the female sex hormones responsible for the growth and development of female sexual anatomy.

estuary ('es-chs-wer-e) A special category of aquatic ecosystem that consists of shallow, partially enclosed areas where freshwater enters the ocean; intermediate in saltiness between freshwater and the ocean.

Eucarya (yu'ka-re-ah) The domain of life that includes all organisms that have eukaryotic cells (plants, animals, fungi, protozoa, and algae).

eukaryotic cells (yu-ker-re-'a-tik 'sels) One of the two major types of cells; cells that have a true nucleus, as in plants, fungi, protists, and animals.

euphotic zone (yu-'fo-tik 'zon) The upper layer of the ocean, where the sun’s rays penetrate.

evolution (e-vs-'lu-shsn) A change in the frequency of genetically determined characteristics within a population over time.

excretory system ('ek-skrs-tor-e 'sis-tsm) The organ system responsible for the processing and elimination of metabolic waste products and consists of the kidneys, ureters, urinary bladder, and urethra.

exocrine glands ('ek-ss-krsn 'glandz) Glands that secrete through ducts to the surface of the body or into hollow organs of the body.

exocytosis (ek-so-sl-'to-sss) The process

cells use to wrap membrane around a particle (usually cell products or wastes) and eliminate it from a cell.

exon ('ek-san) Sequences of mRNA that are used to code for proteins.

exoskeletons (ek-so-'ske-ls-tsnz) Skeletons typical of many invertebrates, in which the skeleton is on the outside of the animal.

experiment (ik-'sper-s-msnt) A re-creation of an event that enables a scientist to gain valid and reliable empirical evidence.

experimental group (ik-sper-s-'men-tsl 'grup) The group in a controlled experiment that has a variable manipulated.

exponential growth phase (ek-sps-'nen-chsl 'groth 'faz) The period of time during population growth when the population increases at an accelerating rate.

expressivity (ek-spre-'si-vs-te) A term used to describe situations in which the gene expresses itself but not equally in all individuals that have it.

external parasites (ek-'stsr-nsl 'per-s-slts) Parasites that live on the outside of their hosts.

extinction (ik-'stip-shsn) The loss of a species.

extrinsic limiting factors (ik-'stip-shsn 'li-ms-tip 'fak-tsrz) Populationcontrolling factors that arise outside the population.



facilitated diffusion (fs-'si-ls-tat-ed di-'fyu-zhsn) Diffusion assisted by carrier molecules.

family ('fam-le) A group of closely related genera within an order.

fats ('fats) A class of water-insoluble macromolecules composed of a glycerol and fatty acids.

fatty acid ('fa-te 'a-ssd) One of the building blocks of a fat, composed of a long- chain carbon skeleton with a carboxylic acid functional group.

fermentation (fsr-msn-'ta-shsn) Pathways that oxidize glucose to generate ATP energy using something other than O2 as the ultimate hydrogen acceptor.

fertilization (fsr-ts-ls-'za-shsn) The joining of haploid nuclei, usually from an egg and a sperm cell, resulting in a diploid cell called a zygote.

filter feeders ('fil-tsr 'fe-dsrz) Animals that use cilia or other appendages to create water currents and filter food out of the water.

fitness ('fit-nss) The concept that those who are best adapted to their environment produce the most offspring. Nutritionally, a measure of how efficiently a person can function both physically and mentally.

flagella (fls-'je-ls) Long, hairlike structures, projecting from the cell surface, that enable locomotion.

flavin adenine dinucleotide (FAD) ('fla-vsn 'a-ds-nen dl-'nu-kle-s-tld) A hydrogen carrier used in respiration.

flower ('flaur) A complex plant reproductive structure made from modified stems and leaves that produces pollen and eggs.

fluid-mosaic model ('flu-sd mo-'za-ik 'ma-dsl) The concept that the cellular membrane is composed primarily of protein and phospholipid molecules that are able to shift and flow past one another.

follicles ('fa-li-kslz) Saclike structures near

the surface of the ovary, which encases the soon-to-be-released secondary oocyte.

follicle-stimulating hormone (FSH) ('fa-li-ksl 'stim-ys-la-tir] 'hor-mon) The pituitary secretion that causes the ovaries to begin to produce larger quantities of estrogen and to develop the follicle and prepare the egg for ovulation.

food chain ('fud 'chan) A sequence of organisms that feed on one another, resulting in a flow of energy from a producer through a series of consumers.

Food Guide Pyramid ('fud 'gi d 'pir-s-mid) A tool developed by the U.S. Department of Agriculture to help the general public plan for good nutrition; it contains guidelines for required daily intake from each of the six food groups.

food web ('fud 'web) A system of interlocking food chains.

formed elements ('formd 'e-ls-msnts) Red, white blood cells and platelets suspended in a watery matrix called plasma.

formula ('for-mys-ls) Pertains to a chemical compound; describes what elements it contains (as indicated by a chemical symbol) and in what proportions they occur (as indicated by the subscript number).

fossil ('fa-ssl) Physical evidence of former life.

founder effect ('faun-dsr i-'fekt) The concept that small, newly established populations are likely to have reduced genetic diversity because of the small number of individuals in the founding population.

fovea centralis ('fo-ve-s sen-'tra-lss) The area of sharpest vision on the retina, containing only cones, where light is sharply focused.

frameshift mutation ('fram-shift myu-'ta-shsn) A form of mutation that occurs when insertions or deletions cause the ribosome to read the wrong sets of three nucleotides.

free-living nitrogen-fixing bacteria ('nl-trs-jsn 'fiks-sig bak-'tir-e-s) Soil bacteria that convert nitrogen gas molecules into nitrogen compounds plants can use.

fruit ('frut) The structure (mature ovary) in angiosperms that contains seeds.

functional groups ('fsrpshnsl 'grups) Specific combinations of atoms attached to the carbon skeleton that determine specific chemical properties.

fungus ('fsr-gss) The common name for members of the kingdom Fungi.



gallbladder ('gol-bla-dsr) The organ,

attached to the liver, that stores bile.

gametes ('ga-mets) Haploid sex cells.

gametogenesis (gs-me-ts-'je-ns-sss) The generating of gametes; the meiotic cell-division process that produces sex cells; oogenesis and spermatogenesis.

gametophyte (gs-'me-ts-fit) A haploid plant that produces gametes; it alternates with the sporophyte through the life cycle.

gametophyte generation (gs-'me-ts-fit je-ns- 'ra-shsn) A life cycle stage in plants in which a haploid sex cell is produced by mitosis.

gas ('gas) The phase of matter in which the molecules are more energetic than the molecules of a liquid, resulting in only a slight attraction for each other.

gastric juice ('gas-trik 'jus) The secretions

of the stomach; they contain enzymes and hydrochloric acid.

gene ('jen) Any molecule usually segments of DNA, able to (1) replicate by directing the manufacture of copies of themselves; (2) mutate, or chemically change, and transmit these changes to future generations; (3) store information that determines the characteristics of cells and organisms; and (4) use this information to direct the synthesis of structural and regulatory proteins.

gene expression ('jen ik-'spre-shsn) The cellular process of transcribing and translating genetic information.

gene flow ('jen 'flo) The movement of genes within a population because of migration or the movement of genes from one generation to the next by gene replication and reproduction.

gene frequency ('jen 'fre-kwsn-se) A measure of how often a specific gene shows up in the gametes of a population.

gene pool ('jen 'pul) All the genes of all the individuals of a species.

generative processes ('jen-rs-tiv 'pra-ses-es) Actions that increase the size of an individual organism (growth) or increase the number of individuals in a population (reproduction).

gene-regulator proteins ('jen 're-gys-la-tsr 'pro-tens) Chemical messengers within a cell that inform the genes as to whether protein-producing genes should be turned on or off or whether they should have their protein-producing activities increased or decreased (e.g., gene-repressor proteins and gene-activator proteins).

gene therapy ('jen 'ther-s-pe) A technique that introduces new genetic material into an organism to correct a genetic deficiency.

genetically modified (GM) (js-'ne-tik-le 'ma-ds-fid) Engineered to contain genes from at least one other species.

genetic bottleneck (js-'ne-tik 'ba-tsl- nek) The concept that, when populations are severely reduced in size, they may lose some of their genetic diversity.

genetic cross (js-'ne-tik 'kros) A planned breeding or mating between two organisms.

genetic diversity (js-'ne-tik ds-'vsr-ss-te) The degree to which individuals in a population possess alternative alleles for characteristics.

genetic drift (js-'ne-tik 'drift) A change in gene frequency that is not the result of natural selection; this typically occurs in a small population.

genetic recombination (js-'ne-tik re-kam-bs- 'na-shsn) The gene mixing that occurs during sexual reproduction.

genetics (js-'ne-tiks) The study of genes, how genes produce characteristics, and how the characteristics are inherited.

genome ('je-nom) A set of all the genes necessary to specify an organism’s complete list of characteristics.

genomics (je-'no-miks) A new field of

science that has developed since the sequencing of the human genome; the field looks at how genomes are organized and compares them with genomes of other organims.

genotype ('je-ns-tip) The catalog of genes of an organism, whether or not these genes are expressed.

genus ('je-nss) A group of closely related species within a family.

geographic isolation (je-s-'gra-fik I-ss-'la-shsn) A condition in which part of the gene pool is separated by geographic barriers from the rest of the population.

glands ('glandz) Organs that manufacture and secrete a material either through ducts or directly into the circulatory system.

glomerulus (gls-'mer-s-lss) A cluster of blood vessels, surrounded by Bowman’s capsule in the kidney.

glyceraldehyde-3-phosphate (gli-ss- 'ral-ds- hld 3 'fas-fat) A 3-carbon compound, produced during glycolysis and photosynthesis, that can be converted to other organic molecules.

glycerol ('gli-ss-rol) One of the building blocks of a fat, composed of a carbon skeleton that has three alcohol groups (OH) attached to it.

glycolysis (gli-'ka-ls-sss) The anaerobic first stage of cellular respiration, consisting of the enzymatic breakdown of a sugar into two molecules of pyruvic acid.

Golgi apparatus ('gol-je a-ps-'ra-tss) A stack of flattened, smooth, membranous sacs; the site of synthesis and packaging of certain molecules in eukaryotic cells.

gonads ('go-nads) Organs in which meiosis occurs to produce gametes; ovaries or testes.

gonadotropin-releasing hormone (GnRH) ('go-na-ds-'tro-psn ri-'le-siq 'hor-mon) A hormone released from the hypothalamus that stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

gradualism ('gra-js-ws-li-zsm) A model for evolutionary change that assumes that evolution occurred slowly by accumulating small changes over a long period of time.

grana ('gra-ns) Stacks of sacs of the chloroplast membrane (thylakoids) where chlorophyll molecules are concentrated.

granules ('gran-yul) Materials whose structure is not as well defined as that of other organelles.

growth-stimulating hormone (GSH) ('groth stim-ys-la-tir] 'hor-mon) The hormone produced by the anterior pituitary gland that stimulates tissues to grow.

guanine ('gwa-nen) A double-ring nitrogenous-base molecule in DNA and RNA; it is the complementary base of cytosine.

gymnosperms ('jim-ns-spsrmz) Plants that produce their seeds in cones.



habitat ('ha-bs-tat) The place or part of a

community occupied by an organism.

habitat preference (ecological isolating mechanisms) ('ha-bs-tat 'pre-fsrns) Reproductive isolating mechanisms that prevent interbreeding between species because they live in different areas.

habituation (hs-bi-chs-'wa-shsn) A change in behavior in which an animal ignores a stimulus after repeated exposure to it.

haploid ('ha-ploid) Having a single set of chromosomes, resulting from the reduction division of meiosis.

Hardy-Weinberg concept ('har-de 'wIn-bsrg 'kan-sept) Populations of organisms will maintain constant gene frequencies from generation to generation as long as mating is random, the population is large, mutation does not occur, migration does not occur, and no genes provide more advantageous characteristics than others.

heart ('hart) The muscular pump that forces blood through the blood vessels of the body.

heat (het) The total internal kinetic energy of molecules.

hemoglobin ('he-ms-glo-bsn) An iron- containing molecule found in red blood cells, to which oxygen molecules bind.

hepatic portal vein (hi-'pa-tik 'por-tsl 'van) A blood vessel that collects blood from capillaries in the intestine and delivers it to a second set of capillaries in the liver.

herbivores ('sr-bs-vorz) Animals that feed directly on plants.

heterotrophs ('he-ts-rs-trofs) Organisms that require a source of organic material from their environment; they cannot produce food on their own.

heterozygous ('he-ts-rs-o-zI-gus) Describes a diploid organism that has 2 different alleles for a particular characteristic.

high-energy phosphate bond ('hi 'e-nsr-je 'fas-fat 'band) The bond between two phosphates in an ADP or ATP molecule that readily releases its energy for cellular processes.

homeostasis (ho-me-o-'sta-sss) The maintenance of a constant internal environment.

homeotherms (ho-me-o-'thsrmz) Animals that maintain a constant body temperature.

homologous chromosomes (ho-'ma-ls-gss 'kro-ms-somz) A pair of chromosomes in a diploid cell that contain similar genes at corresponding loci throughout their length.

homologous structures (ho-'ma-ls-gss 'strsk- chsrz) Structures in different species that have been derived from a common ancestral structure.

homozygous (ho-ms-'zi-gss) Describes a diploid organism that has 2 identical alleles for a particular characteristic.

hormone ('hor-mon) A chemical messenger secreted by an endocrine gland to regulate other parts of the body.

host ('host) An organism that a parasite lives in or on and uses as a source of food.

hybrid inviability ('hi-brsd in-vi-s-'bi-ls-te) Mechanisms that prevent the offspring of two different species from continuing to reproduce.

hydrogen bonds ('hi-drs-jsn 'bandz) Weak attractive forces between molecules; important in determining how groups of molecules are arranged.

hydrolysis reactions (hi-'dra-ls-sss re-'ak- shsns) Processes that occur when large molecules are broken down into smaller parts by the addition of water.

hydrophilic (hi-drs-'fi-lik) Readily absorbing or dissolving in water.

hydrophobic (bI-drs-'fo-bik) Tending not to combine with, or incapable of dissolving in, water.

hydroxide ions (hI-'drak-sId 'I-snz) Negatively charged particles (OH-) composed of oxygen and hydrogen atoms released from a base when dissolved in water.

hypertonic (hI-psr-'ta-nik) A comparative term describing one of two solutions; a hypertonic solution is one with higher amount of dissolved material.

hypothalamus (hI-po-'tha-ls-mss) The region of the brain located in the floor of the thalamus and connected to the pituitary gland; it is involved in sleep and arousal; emotions, such as anger, fear, pleasure, hunger, sexual response, and pain; and automatic functions, such as temperature, blood pressure, and water balance.

hypothesis (hI-'pa-ths-sss) A possible answer to or explanation for a question that accounts for all the observed facts and that is testable.

hypotonic (hI-ps-'ta-nik) A comparative term describing one of two solutions; a hypotonic solution is one with a lower amount of dissolved material.


immune system (i-'myun 'sis-tsm) The system of white blood cells specialized to provide the body with resistance to disease.

immunity (i-'myu-ns-te) The ability to maintain homeostasis by resisting or defending against potentially harmful agents including microbes, toxins, and abnormal cells such as tumor cells.

immunization ('i-mys-ns-za -shsn) The technique used to induce the immune system to develop an acquired immunity to a specific disease by the use of a vaccine.

immunodeficiency diseases (i-mys-no-di-'fi- shsn-se di-'zez) Disorders that result from the immune system not having one or more component cells or chemicals.

imperfect flower (im-'psr-fikt 'flaur) A flower that contains either male (stamens) or female (pistil) reproductive structures, but not both.

imprinting ('im-prin-tig) A form of learning that occurs in a very young animal that is genetically primed to learn a specific behavior in a very short period.

inclusions (in-'klu-zhsns) Materials inside a cell that are usually not readily identifiable; stored materials.

incomplete dominance (in-ksm-'plet 'da-ms- nsns) Occurs when the phenotype of a hetrozygote is intermediate between the two homozygotes on a phenotypic gradient; that is, the phenotypes appear to be “blended” in heterozygotes.

incomplete proteins (in-ksm-'plet 'pro-tenz) Protein molecules that do not provide all the essential amino acids.

incus ('ig-kss) The ear bone that is located between the malleus and the stapes.

independent assortment (in-ds-'pen-dsnt s-sOrt-msnt) The segregation, or assortment, of one pair of homologous chromosomes independently of the segregation, or assortment, of any other pair of chromosomes.

independent variable (in-ds-'pen-dsnt 'ver-e-s-bsl) A variable that is purposely manipulated to determine how it will affect the outcome of an event.

inductive reasoning (induction) (in-'dsk-tiv 're-zs-nig) (in-'dsk-shsn) The mental process of examining many sets of facts and developing generalizations; from the specific to the general.

inflammation (in-fls-'ma-shsn) A nonspecific defense method that is a series of events that clear an area of harmful agents and damaged tissue.

ingestion (in-'jes-chsn) The process of taking food into the body through eating.

inguinal canal ('ig-gws-nsl ks-'nal) The opening in the floor of the abdominal cavity through which the testes in a human male fetus descend into the scrotum.

inhibitor (in-'hi-bs-tsr) A molecule that temporarily attaches itself to an enzyme, thereby interfering with the enzyme’s ability to form an enzyme- substrate complex.

inorganic molecules (in-or-'ga-nik 'ma-li-kyulz) Molecules that do not contain carbon atoms in rings or chains.

insertion mutation (in-'ssr-shsn myu-'ta-shsn) A change in DNA resulting from the addition of one or more nucleotides to the normal DNA sequence.

insight ('in-sIt) Learning in which past experiences are reorganized to solve new problems.

instinctive behavior (in-'stig-tiv bi-'ha-vysr) Automatic, preprogrammed, genetically determined behavior.

intermediate filaments (in-tsr-'me-de-st 'fi-ls-msnts) Protein fibers that connect microtubules and microfilaments as part of the cytoskeleton.

internal parasites (in-'tsr-nsl 'per-s-sIt) Parasites that live inside their hosts.

interphase ('in-tsr-faz) The stage between cell divisions in which the cell is engaged in metabolic activities.

interspecific competition (in-tsr-spi-'si-fik kam-ps-'ti-shsn) Interaction between two members of different species that is harmful to both organisms.

interspecific hybrids (in-tsr-spi-'si-fik 'hI-brsdz) Hybrids between two different species.

intraspecific competition (in-trs-spi-'si-fik kam-ps-'ti-shsn) Interaction between two members of the same species that is harmful to both organisms.

intraspecific hybrids (in-trs-spi-'si-fik 'hI-brsdz) Organisms that are produced by the controlled breeding of separate varieties of the same species.

intrinsic limiting factors (in-'trin-zik 'li-ms- tig 'fak-tsrz) Population-controlling factors that arise from within the population.

intron ('in-tran) Sequences of mRNA that do not code for protein.

inversion (in-'vsr-zhsn) A chromosomal aberration in which a chromosome is broken and a piece becomes reattached to its original chromosome, but in a flipped orientation.

invertebrates (in-'vsr-ts-brsts) Animals without backbones.

ion ('I-sn) Electrically unbalanced or charged atoms.

ionic bonds (I-'a-nik 'bandz) The attractive forces between ions of opposite charge.

isotonic (I-ss-'ta-nik) A term used to describe two solutions that have the same concentration of dissolved material.

isotope ('I-ss-top) An atom of the same element that differs only in the number of neutrons.



kidneys ('kid-nez) The primary organs involved in regulating blood levels of water, hydrogen ions, salts, and urea.

kilocalorie (kcal) ('ke-lo-ka-ls-re) A measure of heat energy 1,000 times larger than a calorie; food Calories are kilocalories.

kinetic energy (ks-'ne-tik 'e-nsr-je) Energy of motion.

kinetic molecular theory (ks-'ne-tik ms-'le- kys-lsr 'the-s-re) All matter is made up of tiny particles that are in constant motion.

kinetochore (ks-'ne-ts-kor) A multi-protein complex attached to each chromatid at the centromere.

kingdom ('kip-dsm) A classification category larger than a phylum and smaller than a domain.

Krebs cycle ('krebz 'sl-ksl) The series of reactions in aerobic cellular respiration that results in the production of two carbon dioxides, the release of four pairs of hydrogens, and the formation of an ATP molecule.

kwashiorkor (kwa-she-'or-ksr) A protein- deficiency disease, common in malnourished children, caused by prolonged protein starvation leading to reduced body size, lethargy, and low mental ability.



lacteal ('lak-te-sl) A tiny lymphatic vessel located in a villus.

lactic acid fermentation ('lak-tik 'a-ssd fsr- msn-'ta-shsn) A process during which the pyruvic acid (CH3COCOOH) that results from glycolysis is converted to lactic acid (CH3CHOHCOOH) by the transfer of electrons that had been removed from the original glucose.

lag phase ('lag 'faz) The period of time following colonization when a population remains small or increases slowly.

large intestine (also colon) ('larj in-'tes-tsn) The last portion of the food tube; it is primarily involved in reabsorbing water.

law of conservation of energy ('lo sv kan- ssr-'va-shsn sv 'e-nsr-je) The law that states that energy is never created or destroyed.

Law of Dominance ('lo sv 'da-ms-nsns) When an organism has 2 different alleles for a trait, the allele that is expressed and overshadows the expression of the other allele is said to be dominant; the allele whose expression is overshadowed is said to be recessive.

Law of Independent Assortment ('lo svin-ds-'pen-dsnt s-'sort-msnt) Members of one allelic pair will separate from each other independently of the members of other allele pairs.

Law of Segregation ('lo sv se-gri-'ga-shsn) When haploid gametes are formed by a diploid organism, the 2 alleles that control a trait separate from one another into different gametes, retaining their individuality.

leaf ('lef) Plant structure specialized for carrying out the process of photosynthesis.

learned behavior ('lsrnd bi-'ha-vysr) A change in behavior as a result of experience.

learning ('lsrn-ip) A change in behavior as a result of experience.

lichen ('li-chsn) An organism comprised of a fungus and an alga protist or cyanobacterium existing in a mutualistic relationship.

light-capturing events ('lit 'kap-chsr-ipi-'vent) The first stage in photosynthesis; involves photosynthetic pigments capturing light energy in the form of excited electrons.

light-dependent reactions ('lit di-'pen-dsnt re-'ak-shsns) The second stage in photosynthesis, during which excited electrons from the light-capturing events are used to make ATP, and water is broken down to hydrogen and oxygen. The hydrogens are transferred to electron carrier coenzymes, NADP+.

light-independent reactions ('lit in-di-'pen- dsnt re-'ak-shsns) The third stage of photosynthesis; involves cells using ATP and NADPH from the light- dependent reactions to attach CO2 to 5-carbon starter molecules to manufacture organic molecules (e.g., glucose [C6H12O6]).

limiting factors ('li-ms-tip 'fak-tsrz) Environmental influences that limit population growth.

limnetic zone (lim-'ne-tik 'zon) In freshwater ecosystems, the portion of a lake that does not have rooted vegetation.

linkage ('lip-kij) A situation in which the genes for different characteristics are inherited together more frequently than would be predicted by probability.

linkage group ('lip-kij 'grup) A group of genes located on the same chromosome that tend to be inherited together.

lipids ('li-psdz) Large organic molecules that do not easily dissolve in water; classes include true (neutral) fats, phospholipids, and steroids.

liquid ('li-kwsd) The phase of matter in which the molecules are strongly attracted to each other, but, because they have more energy and are farther apart than in a solid, they move past each other more freely.

littoral zone ('li-ts-rsl 'zon) In freshwater ecosystems, the region with rooted vegetation.

locus ('lo-kss) The spot on a chromosome where an allele is located.

loop of Henle ('lup 'sv 'hen-le) The middle portion of the nephron; primarily involved in regulating the amount of water lost from the kidney.

lung ('lsp) Organs of the body that allow gas exchange to take place between the air and blood.

luteinizing hormone (LH) (lu-te-sn-i-zip 'hor-mon) A hormone produced by the anterior pituitary gland, which stimulates ovulation.

lymph ('limf) Liquid material that leaves the circulatory system to surround cells.

lymphatic system (lim-'fa-tik 'sis-tsm) A collection of thin-walled tubes that collect, filter, and return lymph from the body to the circulatory system.

lymph nodes ('limf 'nodz) Small encapsulated bodies found along the lymph vessels that contain large numbers of white blood cells (WBCs), macrophages, and lymphocytes that remove microorganisms and foreign particles from the lymph.

lysosomes ('li-ss-somz) Specialized, submicroscopic organelles that hold a mixture of hydrolytic enzymes.



macromolecules (ma-kro- 'ma-li-kyulz) Very large molecules, many of which are composed of many smaller, similar monomers that are chemically bonded together.

malignant tumors (ms-'lig-nsnt 'tu-msrz) Nonencapsulated growths of tumor cells that are harmful; they may spread to or invade other parts of the body.

malleus ('ma-le-ss) The ear bone that is attached to the tympanum.

mass number ('mas 'nsm-bsr) The weight of an atomic nucleus expressed in atomic mass units (the sum of the protons and neutrons).

masturbation (mas-tsr-'ba-shsn) Stimulation of one’s own sex organs.

matter ('ma-tsr) Anything that has weight (mass) and takes up space (volume).

mechanical (morphological) isolating

mechanisms (mi-'ka-ni-ksl [mor-'fa-la- ji-ksl] 'I-ss-la-tig 'me-ks-ni-zsm) Structural differences that prevent mating between members of different species.

medulla oblongata (ms-'ds-ls a-blog-'ga-ts) The region of the more primitive portion of the brain, connected to the spinal cord, that controls such automatic functions as blood pressure, breathing, and heart rate.

medusa (mi-'du-ss) A free-swimming adult stage in the phylum Cnidaria that reproduces sexually.

meiosis (mI-'o-sss) The specialized pair of cell divisions that reduces the chromosome number from diploid (2n) to haploid (n).

meiosis I (mI-'o-sss 'wsn) The first stage in a form of cell division involved in the production of gametes; results in the reduction of the number of chromosomes from 2n (diploid) to n (haploid).

meiosis II (mI-'o-sss 'tu) The second stage in a form of cell division involved in the production of gametes; results in the doubling of the number of newly produced haploid cells from meiosis I.

Mendelian genetics (men-'de-le-sn js-'ne-tiks) The pattern of inheriting characteristics that follows the laws formulated by Gregor Mendel.

menopause ('me-ns-poz) The period beginning at about age 50 when the ovaries stop producing viable secondary oocytes and ovarian hormones.

menstrual cycle ('men-stru-sl 'sI-ksl) The repeated building up and shedding of the lining of the uterus.

mesenteries ('me-zsn-ter-ez) Connective tissues that hold the organs in place and serve as support for blood vessels connecting the various organs.

mesoderm ('me-zs-dsrm) The middle embryonic layer.

messenger RNA (mRNA) ('me-ssn-jsr) A molecule composed of ribonucleotides that functions as a copy of the gene and is used in the cytoplasm of the cell during protein synthesis.

metabolism (ms-'ta-bs-li-zsm) The total of all the chemical reactions and energy changes that take place in an organism.

metaphase ('me-ts-faz) The second stage in mitosis, characterized by alignment of the chromosomes at the equatorial plane.

metastasize (ms-'tas-ts-sIz) The process by which cells of tumors move from the original site and establish new colonies in other regions of the body.

microfilaments (mI-kro-'fi-ls-msnts) Long, fiberlike, submicroscopic structures made of protein and found in cells, often in close association with the microtubules; provide structural support and enable movement.

microorganism (microbe) (mI-kro-'or-gs-ni- zsm) A small organism that cannot be seen without magnification.

microtubules (mI-kro-'tu-byuls)Submicroscopic, hollow tubes of protein that function throughout the cytoplasm to provide structural support and enable movement.

minerals ('min-rslz) Inorganic elements that cannot be manufactured by the body but are required in low concentrations; essential to metabolism.

missense mutation ('mis-sens myu-'ta-shsn) A change in the DNA at a single point that causes the wrong amino acid to be used in making a protein.

mitochondria (mI-ts-'kan-dre-s) Membranous organelles resembling small bags with a larger bag inside that is folded back on itself; serve as the site of aerobic cellular respiration.

mitosis (mI-'to-sss) A process that results in equal and identical distribution of replicated chromosomes into two newly formed nuclei.

mixture ('miks-chsr) Matter that contains two or more substances not in set proportions.

molecules ('ma-li-kyul) The smallest particles of a chemical compound; the smallest naturally occurring parts of an element or a compound.

monocot ('ma-ns-kat) An angiosperm whose embryo has one seed leaf (cotyledon).

monoculture ('ma-ns-ksl-chsr) The agricultural practice of planting the same varieties of a species over large expanses of land.

monohybrid cross (ma-no-'hI-brsd 'kros) A mating between two organisms that are both heterozygous for the one observed gene.

monosomy (ma-ns-'so-me) A cell with only 1 of the 2 chromosomes of a homologous pair.

mortality (mor-'ta-ls-te) The number of individuals leaving the population by death per thousand individuals in the population.

motor neurons (' mo-tsr 'nu-ranz) Neurons that carry information from the central nervous system to muscles or glands.

motor unit ('mo-tsr 'yu-nst) All the muscle cells stimulated by a single neuron.

multigene families ('msl-ts-jen 'fam-lez) A type of variation in an organism’s DNA sequence; this variation consists of several different genes that produce different proteins that are related in function.

multiple alleles ('msl-ts-psl s-'lelz) Several different alleles for a particular characteristic within a population, not just 2.

multiregional hypothesis ('msl-ts-rej-nsl hI-'pa-ths-sss) The concept that Homo erectus migrated to Europe and Asia from Africa and evolved into Homo sapiens.

mutagens ('myu-ts-jsn) Agents that mutate, or chemically damage, DNA.

mutation (myu-'ta-shsn) Any change in the genetic information of a cell.

mutualism ('myu-chs-ws-li-zsm) A relationship between two organisms in which both organisms benefit.

mycorrhizae (mI-ks-'rI-ze) Symbiotic relationships between fungi and plant roots.

mycotoxins (mI-ks-'tak-ssnz) Deadly poisons produced by fungi.

myosin ('mI-s-ssn) The protein molecule, found in the thick filaments of muscle fibers, that attaches to actin, bends, and moves actin molecules along its length, causing the muscle fiber to shorten.



natality (na-'ta-ls-te) The number of individuals entering the population by reproduction per thousand individuals in the population.

negative-feedback inhibition ('ne-gs-tiv'fed-bak in-hs-'bi-shsn) A regulatory

mechanism in which an increase in the stimulus causes a decrease of the response and results in homeostasis.

nekton ('nek-tsn) Many kinds of aquatic animals that are large enough and strong enough to be able to swim against currents and tides and go where they want to.

nephrons ('ne-franz) Tiny tubules that are the functional units of kidneys.

nerve cell ('nsrv 'sel) The basic unit of the nervous system that consists of a central body and several long fibrous extensions.

nerve impulse ('nsrv 'im-psls) A series of changes that take place in the neuron, resulting in a wave of depolarization, which passes from one end of the neuron to the other.

nerves ('nsrvz) Bundles of neuronal fibers.

nervous system ('nsr-vss 'sis-tsm) A network of neurons that carry information from sense organs to the central nervous system and from the central nervous system to muscles and glands.

net movement ('net 'muv-msnt) Movement in one direction minus the movement in the other.

neuron (nerve cell) ('nu-ran) The cellular unit consisting of a cell body and fibers that makes up the nervous system.

neurotransmitter (nur-o-trans-'mi-tsr) A molecule released by the axons of neurons that stimulates other cells.

neutron ('nu-tran) A particle in the nucleus of an atom that has no electrical charge; named neutron to reflect this lack of electrical charge.

niche ('nich) An organisms specific functional role in its community.

nicotinamide adenine dinucleotide (NAD+) (ni-ks-'te-ns-mld 'a-ds-nen dl-'nu-kle-s- tld) An electron acceptor and hydrogen carrier used in respiration.

nitrifying bacteria ('m-trs-fi-ig bak-'tir-e-s) Several kinds of bacteria capable of converting ammonia to nitrite, or nitrite to nitrate.

nitrogen cycle ('nl-trs-jsn 'sl-ksl) The cycling of nitrogen atoms between the abiotic and biotic components and among the organisms in an ecosystem.

nitrogen-fixing bacteria ('m-trs-jsn 'fik-sig bak-'tir-e-s) Bacteria that are able to convert the nitrogen gas (N2) that enters the soil into ammonia that plants can use.

non-coding strand (nan-'ko-dig 'strand) The strand of DNA that is not read directly by the enzymes.

nondeciduous (nan-di-'si-js-wss) A type of tree that does not lose its leaves all at once.

nondisjunction (nan-dis-'jsg-shsn) An abnormal meiotic division that results in sex cells with too many or too few chromosomes.

noneukaryotic (nan-ker-e-'a-tik) One of two general types of living cells: eukaryotic and noneukaryotic. Two forms of noneukaryotic organisms are recognized: Bacteria and Archaea.

non-homologous chromosomes (nan-ho- 'ma-ls-gss 'kro-ms-somz) Chromosomes that have different genes on their DNA.

nonsense mutation ('nan-sens myu-'ta-shsn) A type of point mutation that causes a ribosome to stop protein synthesis by introducing a stop codon too early.

norepinephrine (nor-e-ps-'ne-frsn) The hormone produced by the adrenal medulla and certain nerve cells that increases heart rate, blood pressure, and breathing rate.

nuclear membrane ('nu-kle-sr 'mem-bran) The structure surrounding the nucleus that separates the nucleoplasm from the cytoplasm.

nucleic acids (nu-'kle-ik 'a-ssdz) Complex molecules that store and transfer information within a cell. They are constructed of fundamental monomers known as nucleotides.

nucleolus (nu-'kle-s-lss) A nuclear structure composed of completed or partially completed ribosomes and the specific parts of chromosomes that contain the information for their construction.

nucleoplasm ('nu-kle-s-pla-zsm) The liquid matrix of the nucleus, composed of a mixture of water and the molecules used in the construction of the rest of the nuclear structures.

nucleoprotein (nu-kle-o-'pro-ten) DNA strands with attached proteins that become visible during cell division.

nucleosome (nu-kle-o-som) Histone protein with their encircling DNA.

nucleotides ('nu-kle-s-tldz) Fundamental subunits of nucleic acid constructed of a phosphate group, a sugar, and an organic nitrogenous base.

nucleus ('nu-kle-ss) The central body that contains the information system for the cell; also the central part of an atom, containing protons and neutrons.

nutrients ('nu-tre-snts) Molecules required by organisms for growth, reproduction, or repair.

nutrition (nu-'tri-shsn) Collectively, the processes involved in taking in, assimilating, and utilizing nutrients.



obesity (o-'be-ss-te) The condition of being overweight to the extent that a person’s health, quality of life, and life span are adversely affected.

observation (ab-ssr-'va-shsn) The process of using the senses or extensions of the senses to record events.

observational learning (imitation) (ab-ssr- 'va-shsn-sl 'lsrn-ig) A form of association that involves a complex set of associations used in watching another animal being rewarded for performing a particular behavior and then performing the same behavior oneself.

offspring ('of-sprig) Descendants of a set of parents.

olfactory epithelium (al-'fak-tre e-ps-'the- le-sm) The cells of the nasal cavity that respond to chemicals.

omnivores ('am-ni-v(jrz) Animals that are carnivores at some times and herbivores at others.

oogenesis (o-s-'je-ns-sss) The gametogenesis process that leads to the formation of eggs.

operant (instrumental) conditioning ('a-ps- rsnt ksn-'di-shnig) A change in behavior that results from associating a stimulus with a response by either rewarding or punishing the behavior after it has occurred.

order ('or-dsr) A group of closely related classes within a phylum.

organ ('or-gsn) A structure composed of groups of tissues that perform particular functions.

organelles (or-gs-'nelz) Cellular structures that perform specific functions in the cell; the function of organelles is directly related to their structure.

organic molecules (or-'ga-nik 'ma-li-kyulz) Complex molecules whose basic building blocks are carbon atoms in chains or rings.

organism ('or-gs-ni-zsm) An independent living unit.

organ system ('or-gsn 'sis-tsm) A structure composed of groups of organs that perform particular functions.

orgasm ('or-ga-zsm) The complex series of responses to sexual stimulation that results in an intense frenzy of sexual excitement.

osmosis (az-'mo-sss) The net movement of water molecules through a selectively permeable membrane.

osteoporosis (as-te-o-ps-'ro-sss) A disease condition resulting from the demineralization of the bone, resulting in pain, deformities, and fractures; related to a loss of calcium.

out-of-Africa hypothesis ('aiit sv 'a-fri-ks hl-'pa-ths-sss) The concept that modern humans (Homo sapiens) originated in Africa and migrated from Africa to Europe and Asia and displaced existing hominins.

oval window ('o-vsl 'win-do) The membrane-covered opening of the cochlea, to which the stapes is attached.

ovaries ('o-vs-rez) Female sex organs, which produce haploid sex cells, called eggs.

oviduct ('o-vs-dskt) The tube (fallopian tube) that carries the egg to the uterus.

ovulation (av-ys-'la-shsn) The release of a secondary oocyte from the surface of the ovary.

oxidation-reduction reaction (ak-ss-'da-shsn ri-'dsk-shsn re-'ak-shsn) An electron- transport reaction in which the molecules losing electrons become oxidized and those gaining electrons become reduced.

oxidizing atmosphere ('ak-ss-dlz-ig 'at-ms- sfir) An atmosphere that contains molecular oxygen.

oxytocin (ak-se-'to-ssn) The hormone, released from the posterior pituitary, that causes contraction of the uterus.



pancreas ('pag-kre-ss) The organ of the body that secretes many kinds of digestive enzymes into the duodenum.

panspermia ('pan-spsr-me-s) A hypothesis by Svante Arrhenius in the early 1900s that life arose outside the Earth and that living things were transported to Earth to seed the planet with life.

parasite ('per-s-slt) An organism that lives in or on another organism and derives nourishment from it.

parasitism ('per-s-ss-ti-zsm) A relationship between two organisms that involves one organism living in or on another organism and deriving nourishment from it.

pathogens ('pa-ths-jsnz) Agents that cause specific diseases.

pelagic (ps-'la-jik) Aquatic organisms that are not attached to the bottom.

pelagic ecosystem (ps-'la-jik 'e-ko-sis-tsm) An aquatic ecosystem which exists in open water in which the organisms are not attached to the bottom.

penetrance ('pe-ns-trsns) A term used to describe how often an allele expresses itself when present.

pepsin ('pep-ssn) The enzyme, produced by the stomach, that is responsible for beginning the digestion of proteins.

perception (psr-'sep-shsn) Recognition by the brain that a stimulus has been received.

perfect flower ('psr-fikt 'flaur) A flower that contains both male (stamen) and female (pistil) reproductive structures.

peripheral nervous system (ps-'ri-frsl 'nsr- vss 'sis-tsm) The fibers that communicate between the central nervous system and other parts of the body.

peroxisomes (ps-'rak-ss-somz) Membrane- bound, submicroscopic organelles that hold enzymes capable of producing hydrogen peroxide that aids in the control of infections and other dangerous compounds.

petals ('pe-tsls) Modified leaves of angiosperms; accessory structures of a flower.

pH A scale used to indicate the concentration of an acid or a base.

phagocytosis (fa-gs-ss-'to-sss) The process by which the cell wraps around a particle and engulfs it.

pharynx ('fa-rigs) The region at the back of the mouth cavity; the throat.

phases of matter ('fazez sv 'ma-tsr) Physical conditions of matter (solid, liquid, and gas) determined by the relative amounts of energy of the molecules.

phenotype ('fe-ns-tlp) The physical, chemical, and behavioral expression of the genes possessed by an organism.

pheromones ('fer-s-monz) Chemicals

produced by an animal and released into the environment to trigger behavioral or developmental processes in another animal of the same species.

phloem ('flo-em) One kind of vascular tissue found in higher plants; it transports food materials from the leaves to other parts of the plant.

phospholipids (fas-fo-'li-psdz) A class of water-insoluble molecules that resembles fats but contains a phosphate group (PO4) in its structure.

phosphorylation reaction (fas-for-s-'la-shsn re-'ak-shsn) The reaction that takes place when a cluster of atoms, known as a phosphate group, is added to another molecule.

photoperiod (fo-to-'pir-e-sd) The length of the light part of the day.

photosynthesis (fo-to-'sin-ths-sss) A series of reactions that take place in chloro- plasts and results in the storage of sunlight energy in the form of chemical-bond energy.

photosystems (fo-to-'sis-tsmz) Clusters of photosynthetic pigments (e.g., chlorophyll) that serve as energygathering or energy-concentrating mechanisms; used during the lightcapturing events of photosynthesis.

phylogeny (fi-'la-js-ne) The science that explores the evolutionary relationships among organisms and seeks to reconstruct evolutionary history.

phylum ('fi-lsm) A subdivision of a kingdom.

phytoplankton (fi-to-'plag-tsn) Microscopic, photosynthetic species that form the basis for most aquatic food chains.

pinocytosis (pi-ns-ss-'to-sss) The process by which a cell engulfs some molecules dissolved in water.

pioneer community (pl-s-'nir ks-'myu-ns-te) The first community of organisms in the successional process established in a previously uninhabited area.

pioneer organisms (pl-s-'nir 'or-gs-ni-zsms) The first organisms in the succes- sional process.

pistil ('pis-tsl) The female reproductive structure in flowers; contains the ovary, which produces eggs.

pituitary gland (ps-'tu-s-ter-e 'gland) The gland at the base of the brain that controls the functioning of other glands throughout the organism.

placenta (pls-'sen-ts) An organ made up of tissues from the embryo and the uterus of the mother; allows for the exchange of materials between the mother’s bloodstream and the embryo’s bloodstream; also produces hormones.

plankton ('plarptsn) Small, floating or weakly swimming organisms.

plasma ('plaz-ms) The watery matrix that contains the molecules and cells of the blood.

plasma membrane (cell membrane) ('plaz-ms 'mem-bran) The outer boundary membrane of the cell.

plasmid ('plaz-msd) A plasmid is a circular piece of DNA that is found free in the cytoplasm of some bacteria.

platelets ('plat-lsts) Fragments of specific kinds of white blood cells; important in blood clotting.

pleiotropy ('pll-a-trs-pe) The multiple effects that a gene may have on the phenotype of an organism.

poikilotherms (poi-'ke-ls-thsrmz) Animals with a variable body temperature that changes with the external environment.

point mutation ('point myu-'ta-shsn) A change in the DNA of a cell as a result of a loss or change in a nitrogenous-base sequence.

polar body ('po-lsr 'ba-de) The smaller of two cells formed by unequal meiotic division during oogenesis.

pollen ('pa-lsn) The male gametophyte in gymnosperms and angiosperms.

pollination (pa-ls-'na-shsn) The transfer of pollen in gymnosperms and angiosperms.

polygenic inheritance ('pa-le-jen in-'her-s- tsns) The concept that a number of different pairs of alleles may combine their efforts to determine a characteristic.

polymerase chain reaction (PCR) (ps-'lim-s- ras 'chan re-'ak-shsn) A laboratory technique that is able to generate useful quantities of DNA from very small amounts of DNA.

polymers ('pa-ls-msrs) Combinations of

many smaller, similar building blocks called monomers (mono = single) bonded together.

polyp ('pa-lsp) A sessile larval stage in the phylum Cnidaria that reproduces asexually.

polypeptide (pa-le-'pep-tld) A macromolecule composed of a specific sequence of amino acids.

polyploidy ('pa-le-ploid) A condition in which cells contain multiple sets of chromosomes.

pons ('panz) The region of the brain, immediately anterior to the medulla oblongata, that connects to the cerebellum and higher regions of the brain and controls several sensory and motor functions of the head and face.

population (pa-pys-'la-shsn) A group of

organisms of the same species located in the same place at the same time.

population density (pa-pys-'la-shsn 'den- ss-te) The number of organisms of a species per unit area.

population distribution (pa-pys-'la-shsn dis- trs-'byu-shsn) The way individuals within a population are arranged with respect to one another.

population genetics (pa-pys-'la-shsn js-'ne- tiks) The study of the kinds of genes within a population, their relative numbers, and how these numbers change over time.

population growth curve (pa-pys-'la-shsn 'groth 'ksrv) A graph of the change in population size over time.

population pressure (pa-pys-'la-shsn 'pre- shsr) Intense competition as a result of high population density that leads to changes in the environment and the dispersal of organisms.

positive feedback ('pa-zs-tiv 'fed-bak) A regulatory mechanism in which an increase in the stimulus causes an increase of the response and does not result in homeostasis.

potential energy (ps-'ten-shsl 'e-nsr-je) The energy an object has because of its position.

predation (pri-'da-shsn) A relationship between two organisms that involves the capturing, killing, and eating of one by the other.

predator ('pre-ds-tsr) An organism that captures, kills, and eats another animal.

prey ('pra) An organism captured, killed, and eaten by a predator.

primary carnivores ('pn-mer-e 'kar-ns-vorz) Carnivores that eat herbivores and are therefore on the third trophic level.

primary consumers ('prl-mer-e ksn-'su-msrz) Organisms that feed directly on plants—herbivores.

primary succession ('pn-mer-e ssk-'se-shsn) The orderly series of changes that begins in a previously uninhabited area and leads to a climax community.

prions ('pn-anz) Infectious protein particles responsible for diseases such as Creutzfeldt-Jakob disease and bovine spongiform encephalitis.

probability (pra-bs-'bi-ls-te) The chance that an event will happen, expressed as a percentage or fraction.

producers (prs-'du-ssrz) Organisms that produce new organic material from inorganic material with the aid of sunlight.

productivity (pro-dsk-'ti-vs-te) The rate at which an ecosystem can accumulate new organic matter.

products ('pra-dskts) New molecules resulting from a chemical reaction.

prokaryotes (pro-'ka-re-ots) Organisms that do not have a nucleus in their cells; Bacteria and Archaea.

prokaryotic cells (pro-ka-re-'a-tik 'sels) One of the two major types of cells; now referred to as noneukaryotic cells. They do not have a typical nucleus bound by a nuclear membrane and lack many of the other membranous cellular organelles—for example, members of Bacteria and Archaea.

promoter sequences (prs-'mo-tsr 'se-kwsns) Specific sequences of DNA nucleotides that RNA polymerase uses to find a protein-coding region of DNA and to identify which of the two DNA strands is the coding strand.

prophase ('pro-faz) The first phase of mitosis, during which individual chromosomes become visible.

proteins ('pro-tenz) Macromolecules made up of one or more polypepides attached to each other by bonds.

protein-sparing ('pro-ten 'spe-rip) The conservation of proteins by first oxidizing carbohydrates and fats as a source of ATP energy.

proteomics (pro-te-'o-miks) A new field of science that has developed since the sequencing of the human genome; it groups proteins by similarities to help explain their function and how they may have evolved.

proton ('pro-tan) The particle in the nucleus of an atom that has a positive electrical charge.

proto-oncogene (pro-to-'ap-ko-jen) Genes that code for proteins that provide signals to the cell that encourage cell division.

protoplasm ('pro-ts-pla-zsm) The living portion of a cell, as distinguished from the nonliving cell wall.

protozoa (pro-ts-'zo-a) Heterotrophic, eukaryotic, unicellular organisms.

proximal convoluted tubule ('prak-ss-msl 'kan-vs-lu-tsd 'tu-byul) The upstream end of the nephron of the kidney; is responsible for reabsorbing most of the valuable molecules filtered from the glomerulus into Bowman’s capsule.

pseudocoelom (su-do-'se-lsm) A body cavity located between the lining of the gut and the outer body wall and does not have muscles around the digestive system; the word means false body cavity.

pseudoscience (su-do-'si-sns) An activity that uses the appearance or language of science to convince or mislead people into thinking that something has scientific validity.

puberty ('pyu-bsr-te) A time in the life of a developing individual characterized by the increasing production of sex hormones, which cause it to reach sexual maturity.

pulmonary artery ('pul-ms-ner-e 'ar-ts-re) The major blood vessel that carries blood from the right ventricle to the lungs.

pulmonary circulation ('pul-ms-ner-e ssr- kys-'la-shsn) The flow of blood through certain chambers of the heart and blood vessels to the lungs and back to the heart.

punctuated equilibrium ('pspk-chs-wa-tsd e-kws-'li-bre-sm) The theory stating that evolution occurs in spurts, between which there are long periods with little evolutionary change.

Punnett square ('ps-nst 'skwer) A method used to determine the probabilities of allele combinations in a zygote.

pyloric sphincter (pi-'lor-ik 'sfip-tsr) The valve located at the end of the stomach that regulates the flow of food from the stomach to the duodenum.



radial symmetry ('ra-de-sl 'si-ms-tre) The characteristic of an animal with a body constructed around a central axis; any division of the body along this axis results in two similar halves.

reactants (re-'aktsnts) Materials that will be changed in a chemical reaction.

receptor mediated endocytosis (ri-'sep-tsr 'me-de-a-tsd en-do-si-'to-sss) The process in which molecules from the cell’s surroundings bind to receptor molecules on the plasma membrane, followed by the membrane folding into the cell so that the cell engulfs these molecules.

recessive allele (ri-'se-siv s-'lel) An allele that, when present with its homolog, does not express itself and is masked by the effect of the other allele.

recombinant DNA (re-'kam-bs-nsnt) DNA that has been constructed by inserting new pieces of DNA into the DNA of an organism.

red blood cells (rbcs) ('red 'blsd 'sels) Small, disk-shaped cells that lack a nucleus and contain the iron- containing pigment hemoglobin.

reducing atmosphere (ri-'dus-ip 'at-ms- sfir) An atmosphere that does not contain molecular oxygen (O2).

reduction division (ri-'dsk-shsn ds-'vi-zhsn) A type of cell division in which daughter cells get only half the chromosomes from the parent cell.

regulator proteins ('re-gys-la-tsr 'pro-tenz) Proteins that influence the activities that occur in an organism—for example, enzymes and some hormones.

reproductive capacity (biotic potential) (re-prs-'dsk-tiv ks-'pa-ss-te) The theoretical maximum rate of reproduction.

reproductive (genetic) isolating mechanisms (re-prs-'dsk-tiv 'I-ss-la-tip 'me-ks-ni- zsmz) Mechanisms that prevent interbreeding between species.

respiratory system ('res-prs-tor-e 'sis-tsm) The organ system that moves air into and out of the body and consists of lungs, trachea, the air-transport pathway, and diaphragm.

response (ri-'spans) The reaction of an organism to a stimulus.

responsive processes (ri-'span-siv 'pra-se-ssz) Abilities to react to external and internal changes in the environment— for example, irritability, individual adaptation, and evolution.

restriction enzymes (ri-'strik-shsn 'en-zImz) Proteins that catalyze the cutting of the DNA helix; these proteins cut the DNA helix into two pieces at specific DNA sequences.

restriction fragments (ri-'strik-shsn 'frag- msnts) Pieces of DNA that are created by cutting DNA with restriction enzymes; restriction fragments are used in cloning and characterizing DNA.

restriction sites (ri-'strik-shsn 'sits) The DNA sequence that is recognized by a restriction enzyme; the restriction enzyme cuts at this sequence, generating two DNA fragments.

retina ('re-ts-ns) The light-sensitive region of the eye.

rhodopsin (ro-'dap-ssn) A light-sensitive pigment found in the rods of the retina.

ribonucleic acid (RNA) (ri-bo-nu-'kle-ik 'a-ssd) A polymer of nucleotides formed on the template surface of DNA by transcription; three forms are mRNA, rRNA, and tRNA.

ribosomal RNA (rRNA) (ri-bs-'so-msl) A globular form of RNA; a part of ribosomes.

ribosomes ('ri-bs-somz) Small structures composed of two protein and ribonucleic acid subunits, involved in the assembly of proteins from amino acids.

ribulose ('rI-bys-los) A 5-carbon sugar molecule used in photosynthesis.

ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBisCO) ('rI-bys-los bi-'fas-fat kar-'bak-ss-las 'ak-si-js-nas) An enzyme found in the stroma of chloroplast that speeds the combining of the CO2 with an already present 5-carbon carbohydrate, ribulose.

RNA polymerase (ps-'lim-s-ras) An enzyme that bonds RNA nucleotides together during transcription after they have aligned on the DNA.

rods ('radz) Light-sensitive cells in the retina of the eye that respond to low- intensity light but do not respond to different colors of light.

root ('rut) Underground structures that anchor the plant and absorb water and minerals.

root hairs ('rut 'hers) Tiny cellular outgrowths of roots that improve the ability of plants to absorb water and minerals.


salivary glands ('sa-ls-ver-e 'glandz) Glands that produce saliva.

salts ('stilts) Ionic compounds formed from a reaction between an acid and a base.

saprophytes ('sa-prs-fIts) Organisms that obtain energy by the decomposition of dead organic material.

saturated ('sa-chs-ra-tsd) A term used to describe the carbon skeleton of a fatty acid that contains no double bonds between carbons.

science ('sI-sns) A process used to solve problems or develop an understanding of natural events.

scientific law (sI-sn-'ti-fik 'lo) A uniform or constant fact that describes what happens in nature.

scientific method (sl-sn-'ti-fik 'me-thsd) A way of gaining information (facts) about the world around you that involves observation, hypothesis formation, testing of hypotheses, theory formation, and law formation.

seasonal isolating mechanisms ('sez-nsl 'I-ss-la-tip 'me-ks-ni-zsmz) Reproductive isolating mechanisms that prevent interbreeding between species because they reproduce at different times of the year.

secondary carnivores ('se-ksn-der-e 'kar-ns- vorz) Carnivores that feed on primary carnivores and are therefore at the fourth trophic level.

secondary consumers ('se-ksn-der-e ksn-'su-msrz) Animals that eat other animals—carnivores.

secondary sexual characteristics ('se-ksn-der-e 'sek-shwsl ker-ik-ts-'ris-tiks) Characteristics of the adult male or female, including the typical shape that develops at puberty: broader shoulders; heavier long-bone muscles; development of facial hair, axillary hair, and chest hair; and changes in the shape of the larynx in the male; rounding of the pelvis and breasts and changes in deposition of fat in the female.

secondary succession ('se-ksn-der-e ssk-'se- shsn) The orderly series of changes that begins with the disturbance of an existing community and leads to a climax community.

seed ('sed) A specialized structure that contains an embryo along with stored food enclosed in a protective covering called the seed coat.

seed leaves ('sed 'levz) Cotyledons; embryonic leaves in seeds.

segmental duplications (seg-'men-tsl du-pli-'ka-shsnz) A type of variation in an organism’s DNA sequence; this variation occurs when a segment of DNA, which may contain several genes, occurs twice in the genome.

segmentation (seg-msn-'ta-shsn) The separation of the body of an animal into a number of recognizable units from the anterior to the posterior end of the animal.

segregation (se-gri-'ga-shsn) The separation and movement of homologous chromosomes to the opposite poles of the cell.

selecting agents (ss-'lek-tip 'a-jsnts) Factors that affect the probability that a gene will be passed on to the next generation.

selectively permeable (ss-'lek-tiv-le 'psr-me- s-bsl) The property of a membrane that allows certain molecules to pass through it but interferes with the passage of others.

semen ('se-msn) The sperm-carrying fluid produced by the seminal vesicles, prostate gland, and bulbourethral glands of males.

semicircular canals (se-me-'ssr-kys-lsr ks-'nalz) A set of tubular organs, associated with the cochlea, that sense changes in the movement or position of the head.

semilunar valves (se-me-'lu-nsr 'valvz) Valves, located in the pulmonary artery and aorta, that prevent the flow of blood backwards, into the ventricles.

seminiferous tubules (se-ms-'ni-frss 'tu-byulz) Sperm-producing tubes in the testes.

sensory neurons ('sens-re 'nu-ranz) Neurons that send information from sense organs to the central nervous system.

sepals ('se-psls) Accessory structures of flowers.

sessile ('se-sIl) Firmly attached.

sex ('seks) The nature of the biological differences between males and females.

sex chromosomes ('seks 'kro-ms-somz) Chromosomes that carry genes that determine the sex of an individual (X and Y in humans).

sex-determining chromosomes ('seks di- 'tsr-ms-nip 'kro-ms-somz) The chromosomes X and Y, which are primarily responsible for determining if an individual will develop as a male or a female.

sex linkage ('seks 'lip-kij) Refers to genes that are located on the chromosomes that determine the sex of an individual.

sex ratio ('seks 'ra-sho) The number of males in a population compared with the number of females.

sexual reproduction ('sek-shwsl re-prs-'dsk- shsn) The propagation of organisms involving the union of gametes from two parents.

sexual selection ('sek-shwsl ss-'lek-shsn) Selection that is the result of specific individuals being chosen by members of the opposite sex for mating purposes.

sexuality (sek-shs-'wa-ls-te) All the factors that contribute to one’s female or male nature.

signal transduction ('sig-nsl trans-'dsk- shsn) The process by which cells detect specific signals and transmit those signals to the cell’s interior.

silencer sequence ('sI-lsn-ssr 'se-kwsns) A DNA sequence that regulates gene expression by acting as a binding site for proteins that decrease the ability of RNA polymerase to transcribe a specific protein.

silent mutation ('sI-lsnt myu-'ta-shsn) A change of a single mucleotide that does not cause a change in the amino acids used to build a protein.

single-factor cross ('sip-gsl 'fak-tsr 'kros) A genetic study in which a single characteristic is followed from the parental generation to the offspring.

sister chromatids ('sis-tsr 'kro-ms-tsdz) The 2 chromatids of a chromosome that were produced by replication and that contain the identical DNA.

skeleton ('ske-ls-tsn) The part of an organism that provides structural support.

small intestine ('smol in-'tes-tsn) The portion of the digestive system immediately following the stomach; it is responsible for digestion and absorption.

society (ss-'sI-s-te) Interacting groups of animals of the same species that show division of labor.

sociobiology (so-se-o-bI-'a-ls-je) The systematic study of all forms of social behavior, both human and nonhuman.

solid ('sa-lsd) The phase of matter in which the molecules are packed tightly together; they vibrate in place.

solute ('sal-yut) The component that dissolves in a solvent.

solution (ss-'lu-shsn) A homogeneous mixture of ions or molecules of two or more substances.

solvent ('sal-vsnt) The component present in the larger amount.

soma ('so-ms) The cell body of a neuron, which contains the nucleus.

somatic cell nuclear transfer (so-'ma-tik 'sel 'nu-kle-sr trans-'fsr) A laboratory technique in which the nucleus of a cell is placed into an unfertilized egg cell; the cell may then be stimulated to grow; cells that are generated from this growth will have the same genetic information as the cell that donated the nucleus.

speciation (spe-she-'a-shsn) The process of generating new species.

species ('spe-shez) A population of organisms potentially capable of breeding naturally among themselves and having offspring that also interbreed. Also, the smallest irreversible unit of evolution; a group of organisms that shares a common ancestor with other species, but is set off from those others by having newer, genetically unique traits.

specific dynamic action (SDA) (spi-'si-fik dl-'na-mik 'ak-shsn) The amount of energy required to digest and assimilate food. SDA is equal to approximately 10% of total daily kilocalorie intake.

specific epithet (spi-'si-fik 'e-ps-thet) A word added to the genus name to identify which one of several species within the genus is being identified (i.e., Homo sapiens: Homo is the genus name and sapiens is the specific epithet).

sperm ('spsrm) The haploid sex cells produced by sexually mature males.

spermatogenesis (spsr-ma-ts-'je-ns-sss) The gametogenesis process that leads to the formation of sperm.

spinal cord ('spl-nsl 'kord) A collection of nerve fibers surrounded by the vertebrae that conveys information to and from the brain.

spindle ('spin-dsl) An array of microtubules extending from pole to pole; used in the movement of chromosomes.

spindle fiber ('spin-dsl 'fi-bsrs) Microtubules that are individual strands of the spindle.

spontaneous generation (span-'ta-ne-ss je-ns-'ra-shsn) The idea that living organisms arose from nonliving material.

spontaneous mutations (span-'ta-ne-ss myu- 'ta-shsnz) Natural changes in the DNA caused by unidentified environmental factors.

spore ('spor) In the kingdom Fungi, a cell with a tough protective cell wall that can resist extreme conditions.

sporophyte generation (or stage) ('spor-s-fit je-ns-'ra-shsn) A stage in the life cycle of plants in which this diploid (2n) plant, which has special plant parts where meiosis takes place, produces haploid (n) spores.

sporophyte stage ('spor-s-fit 'staj) A life cycle stage in plants in which a haploid spore is produced by meiosis.

stabilizing selection ('sta-bs-ll-zir] ss-'lek- shsn) Selection that occurs when individuals at the extremes of the range of a characteristic are consistently selected against.

stable equilibrium phase ('sta-bsl e-kws-'li- bre-sm 'faz) The period of time during population growth when the number of individuals entering a population and the number leaving the population are equal, resulting in a stable population size.

stamens ('sta-msnz) Male reproductive structures of a flower.

stapes ('sta-pez) The ear bone that is attached to the oval window.

stem ('stem) Plant structures that connect the roots with the leaves and position the leaves so that they receive sunlight.

stem cells ('stem 'selz) Cells that can differentiate into any type of cell, including liver cells, skin cells, and brain cells; embryonic and hematopoietic cells.

steroids ('stir-oidz) One of the three kinds of lipid molecules characterized by their arrangement of interlocking rings of carbon.

stimulus ('stim-ys-lss) Any change in the internal or external environment of an organism that it can detect.

stroma ('stro-ms) The region within a chloroplast that has no chlorphyll.

structural proteins ('strsk-chs-rsl 'pro-tenz) Proteins that are important for holding cells and organisms together, such as the proteins that make up the cell membrane, muscles, tendons, and blood.

subspecies (breeds, varieties, strains, races) ('ssb-spe-shez) Regional groups within a species that are significantly different structurally, physiologically, or behaviorally yet are capable of exchanging genes by interbreeding.

substrate ('ssb-strat) A reactant molecule with which the enzyme combines.

succession (ssk-'se-shsn) The process of changing one type of community to another.

successional (stage) (successional community) (ssk-'se-shs-nsl 'staj) An intermediate stage in succession.

symbiosis (sim-be-'o-sss) A close physical relationship between two kinds of organisms; parasitism, commensalism, and mutualism are examples of symbiosis.

symbiotic nitrogen-fixing bacteria (sim-be- 'o-tik 'nl-trs-jsn 'fik-sig bak-'tir-e-s) Bacteria that live in the roots of certain kinds of plants, where they convert nitrogen gas molecules into compounds that plants can use.

synapse ('si-naps) The space between the axon of one neuron and the dendrite of the next, where chemicals are secreted to cause an impulse to be initiated in the second neuron.

synapsis (ss-'nap-sss) The condition in which the two members of a pair of homologous chromosomes come to lie close to one another.

systemic circulation (sis-'te-mik ssr-kys-'la- shsn) The flow of blood through certain chambers of the heart and blood vessels to the general body and back to the heart.

systolic blood pressure ('sis-ts-lik 'blsd 'pre-shsr) The pressure generated in a large artery when the ventricles of the heart are contracting.



tandem clusters ('tan-dsm 'klss-tsrs) A type of variation in an organism’s DNA sequence; this variation occurs when a gene is duplicated several times in the same region of DNA.

taxonomy (tak-'sa-ns-me) The science of classifying and naming organisms.

telomere ('te-ls-mir) A chromosome cap composed of repeated, specific sequences of nucleotide pairs; its activity or inactivity is associated with cell aging and cancer.

telophase ('te-ls-faz) The last phase in mitosis, characterized by the formation of daughter nuclei.

temperature ('tem-ps-chur) A measure of molecular energy of motion.

termination sequences (tsr-ms-'na-shsn 'se-kwsns) DNA nucleotide sequences that indicate when RNA polymerase should finish making an RNA molecule.

territorial behavior (ter-s-'tor-e-sl bi-'ha- vysr) Behavior involved in establishing, defending, and maintaining a territory for food, mating, or other purposes.

territory ('ter-s-tor-e) A space that an animal defends against others of the same species.

testes ('tes-tsz) The male sex organs, which produce haploid cells—sperm.

testosterone (tes-'tas-ts-ron) The male sex hormone, produced in the testes, that controls male sexual development.

thalamus ('tha-ls-mss) The region of

the brain that relays information between the cerebrum and lower portions of the brain; it also provides some level of awareness in that it determines pleasant and unpleasant stimuli and is involved in sleep and arousal.

theory ('the-s-re) A widely accepted, plausible generalization about fundamental concepts in science that is supported by many experiments and explains why things happen in nature.

theory of natural selection ('the-s-re sv 'na-chs-rsl ss-'lek-shsn) In a species of genetically differing organisms, the organisms with the genes that enable them to survive better in the environment and thus reproduce more offspring than others will transmit more of their genes to the next generation.

thinking ('thiq-kiq) A mental process that involves memory, a concept of self, and an ability to reorganize information.

thylakoid ('thl-ls-koid) A membranous sac found within chloroplasts of plant cells that contains chlorophyll and is the site of the light-capturing events and the light-dependent reactions of photosynthesis; a stack of thylakoids is known as a granum.

thymine ('thl-men) A single-ring, nitrogenous-base molecule in DNA but not in RNA; it is complementary to adenine.

tissue ('ti-shu) A group of specialized cells that work together to perform a specific function.

tissue fluid ('ti-shu 'flu-sd) The liquid that baths the body’s cells and contains

the same chemicals as plasma but smaller amounts of the blood protein albumin.

trachea ('tra-ke-s) The major tube, supported by cartilage rings, that carries air to the bronchi; also known as the windpipe.

transcription (tran-'skrip-shsn) The process of manufacturing RNA from the template surface of DNA; three forms of RNA that can be produced are mRNA, rRNA, and tRNA.

transcription factors (tran-'skrip-shsn 'fak- tsrz) Proteins that help control the transcription process by binding DNA or other transcription factors and regulating when RNA polymerase begins transcription.

transcriptomics (tran-skript-'ta-miks) A new field of science developed since the sequencing of the human genome; it looks at when and how much of a particular transcript is made by an organism.

transfer RNA (tRNA) (trans-'fsr) A molecule composed of ribonucleic acid. It is responsible for transporting a specific amino acid into a ribosome for assembly into a protein.

transformation (trans-fsr-'ma-shsn) A technique or process in which an organism gains new genetic information from its environment; this is known to happen to bacteria and is used to introduce DNA fragments to bacteria during the DNA cloning process.

translation (trans-'la-shsn) A chromosomal aberration in which one broken segment of DNA becomes integrated into a different chromosome.

translocation (trans-lo-'ka-shsn) The process whereby tRNA uses mRNA as a guide to arrange the amino acids in their proper sequence according to the genetic information in the chemical code of DNA.

transpiration (trans-ps-'ra-shsn) In plants, the transportation of water from the soil by way of the roots to the leaves, where it evaporates.

triploblastic (tri-plo-'blas-tik) A condition typical of most animals in which their bodies consist of three layers of cells.

trisomy ('tn-so-me) The presence of 3 chromosomes instead of the normal 2, resulting from the nondisjunction of homologous chromosomes during meiosis—as in Down syndrome.

trophic level ('tro-fik 'le-vsl) A step in the flow of energy through an ecosystem.

tropism ('tro-pi-zsm) Any reaction to a particular stimulus in which the organism orients toward or away from the stimulus.

tropomyosin (tra-ps-'ml-s-ssn) A molecule, found in thin myofilaments of muscle, that helps regulate when muscle cells contract.

troponin ('tro-ps-nsn) A molecule, found in thin myofilaments of muscle, that helps regulate when muscle cells contract.

true (neutral) fats ('tru 'fats) Important organic molecules composed of glycerol and fatty acids that are used to provide energy.

tumor ('tu-msr) A mass of undifferentiated cells not normally found in a certain portion of the body.

tumor-suppressor gene ('tu-msr ss-'pre-ssr 'jen) Code for proteins that provide signals that discourage cell division.

turnover number ('tsrn-o-vsr 'nsm-bsr) The number of molecules of substrate with which a single molecule of enzyme can react in a given time.

tympanum ('tim-ps-nsm) The eardrum.



unique structural organization (yii-'nek 'strsk-chs-rsl or-gs-ns-'za-shsn) One of five traits displayed by living things and not shown by nonliving things; can be seen at the molecular, cellular, and organism levels.

unsaturated (sn-'sa-chs-ra-tsd) A term used to describe the carbon skeleton of a fatty acid containing carbons that are double-bonded to each other at one or more points.

uracil ('yur-s-sil) A single-ring nitrogenous- base molecule in RNA but not in DNA; it is complementary to adenine.



vaccines (vak-'sens) Antigens made so they can start an active immunity without causing disease.

vacuoles ('va-kys-wolz) Large sacs within the cytoplasm of a cell, composed of a single membrane.

variable number tandem repeats (VNTRs) ('ver-e-s-bsl 'nsm-bsr 'tan-dsm ri-'petz) A type of variation in an organism’s DNA sequence that is a repeated sequence; different individuals may have the sequence repeated a different number of times; this variation can occur in regions of the DNA that do not code for genes.

variables ('ver-e-s-bslz) Factors in an experimental situation or other circumstance that are changeable.

vascular cambium ('vas-kys-lsr 'kam-be-sm) A layer of cells between the xylem and phloem in trees that is responsible for the increase in diameter of a stem.

vascular tissue ('vas-kys-lsr 'ti-shu) Consists of tube-like cells that allow plants to efficiently transport water and nutrients about the plant.

vector ('vek-tsr) An organism that carries a disease or parasite from one host to the next.

veins ('vanz) The blood vessels that return blood to the heart.

ventricles ('ven-tri-kslz) The powerful muscular chambers of the heart whose contractions force blood to flow through the arteries to all parts of the body.

vertebrates ('vsr-ts-brsts) Animals with backbones.

vesicles ('ve-si-ksls) Small, intracellular, membrane-bound sacs in which various substances are stored.

villi ('vi-ll) Tiny, fingerlike projections in the lining of the small intestine that increase the surface area for absorption.

viroid ('vl-roid) An infectious particle composed solely of singlestranded RNA.

virus ('vl-rss) A nucleic acid particle coated with protein that functions as an obligate intracellular parasite.

vitamin-deficiency disease ('vl-ts-msn di-'fi- shsn-se di-'zez) Poor health caused by the lack of a certain vitamin in the diet—for example, scurvy from lack of vitamin C.

vitamins ('vl-ts-msnz) Organic molecules that cannot be manufactured by the body but are required in very low concentrations for good health.

voltage ('vol-tij) A measure of the electrical difference between two points or objects.



white blood cells (wbcs) ('hwlt 'blsd 'selz) Formed elements in the blood that lack hemoglobin, are larger than RBCs, and have a nucleus; also called leukocytes.

wood ('wud) The accumulation of the xylem in the trunk of gymnosperms.



X chromosome ('eks 'kro-ms-som) The chromosome in a human female egg (and in one-half of sperm cells) that is associated with the determination of sexual characteristics.

X-linked genes ('eks-'lipt 'jenz) Genes located on the sex-determining X chromosome.

xylem ('zl-lsm) A kind of vascular tissue that transports water from the roots to other parts of the plant.



Y chromosome ('w! 'kro-ms-som) The sex determining chromosome in one-half the sperm cells of human males responsible for determining maleness.

Y-linked genes ('wl-'lipt 'jenz) Genes found only on the Y chromosome.



zooplankton (zo-s-'plap-tsn) Nonphotosynthetic aquatic protozoa and tiny animals.

zygote ('z!-got) A diploid cell that results from the union of an egg and a sperm.