Glossary

A  Located in the ventral cavity below the thoracic cavity and is separated from the thoracic cavity by the diaphragm; contains most other internal organs except the heart and the lungs. 416 Plant hormone that causes stomata to close and initiates and maintains dormancy. 358
 Dropping of leaves, fruits, or flowers from a plant. 358
 Method of birth control; the practice of not engaging in sexual intercourse. 519
 Neurotransmitter active in both the peripheral and central nervous systems. 476
 Enzyme that breaks down acetylcholine within a synapse. 476
 Molecule made up of a 2-carbon acetyl group attached to coenzyme A. During cellular respiration, the acetyl group enters the citric acid cycle for further breakdown. 102
 Molecules tending to raise the hydrogen ion concentration in a solution and to lower its pH numerically. 25
 Animals without a coelom, as in flatworms. 308
 
(see AIDS)
 Muscle protein making up the thin filaments in a sarcomere; its movement shortens the sarcomere, yielding muscle contraction. Actin filaments play a role in the movement of the cell and its organelles. 505
 Cytoskeletal filament of eukaryotic cells composed of the protein actin; also refers to the thin filaments of muscle cells. 62 Electrochemical changes that take place across the axomembrane; the nerve impulse. 475
 Resistance to disease due to the immune system’s response to a microorganism or a vaccine.  464
 Region on the surface of an enzyme where the substrate binds and where the reaction occurs. 76
 Use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy. 78
 Organism’s modification in structure, function, or behavior suitable to the environment. 4, 221
 Evolution of several species from a common ancestor into new ecological or geographical zones. 251
 Condition resulting from a deficiency of adrenal cortex hormones; characterized by low blood glucose, weight loss, and weakness. 487
 One of four nitrogen-containing bases in nucleotides composing the structure of DNA and RNA. 161
 Nucleotide with three phosphate groups. The breakdown of ATP into ADP + sP makes energy available for energy-requiring processes in cells. 60
 Junction between cells in which the adjacent plasma membra nes do not touch but are held together by intercellular filaments attached to buttonlike thickenings. 65
Located in the adrenal gland; produces the glucocorticoid and mineralocorticoid hormones. 487
Gland that lies atop a kidney; the adrenal medulla produces the hormones epinephrine and norepinephrine, and the adrenal cortex produces the glucocorticoid and mineralocorticoid hormones. 487
 Inner portion of the adrenal gland; secretes the hormones epinephrine and norepinephrine. 487
 Hormone secreted by the anterior lobe of the pituitary gland that stimulates activity in the adrenal cortex. 484
 In demographics, a display of the age groups of a population; a growing population has a pyramid-shaped diagram. 539
 Clumping of red blood cells due to a reaction between antigens on red blood cell plasma membranes and antibodies in the plasma. 461
 Disease caused by a retrovirus and transmitted via body fluids; characterized by failure of the immune system. 466, 522
 Type of protist that carries on photosynthesis; unicellular forms are a part of phytoplankton, and multicellular forms are called seaweed. 276
 Alternative form of a gene—alleles occur at the same locus on homologous chromosomes. 128, 145
 Foreign substance capable of stimulating an allergic response. 465
 Immune response to substances that usually are not recognized as foreign. 465
 Origin of new species between populations that are separated geographically. 250
 Life cycle, typical of plants, in which a diploid sporophyte alternates with a haploid gametophyte. 286, 362
 In humans, terminal, microscopic, grapelike air sac found in 
lungs. 423
 Brain disorder characterized by a general loss of mental abilities. 480
 Organic molecule composed of an amino group and an acid group; covalently bonds to produce peptide molecules. 39
 Procedure for removing amniotic fluid surrounding the developing fetus for testing of the fluid or cells within the fluid. 197
 Extraembryonic membrane of birds, reptiles, and mammals that forms an enclosing, fluid-filled sac. 526
 Cell that moves and engulfs debris with pseudopods. 278
 Member of a class of vertebrates that includes frogs, toads, and salamanders; they are still tied to a watery environment for reproduction. 323
 Structure that has a similar function in separate lineages but differs in anatomy and ancestry. 226, 257
Similarity of characters due to convergent evolution. 257
 Mitotic phase during which daughter chromosomes move toward the poles of the spindle. 115
 Formation of new blood vessels; one mechanism by which cancer spreads. 121, 190
 Flowering plant; the seeds are borne within a fruit. 286, 292
 Multicellular, heterotrophic organism belonging to the animal kingdom. 6
 Member of a phylum of invertebrates that contains segmented worms, such as the earthworm and the clam worm. 315
 Layer of wood (secondary xylem) usually produced during one growing 
season. 345
 Eating disorder characterized by a morbid fear of gaining weight. 448
 Portion of the pituitary gland that is controlled by the hypothalamus and produces six types of hormones, some of which control other endocrine glands. 484
 In flowering plants, pollen-bearing portion of stamen. 292, 363
 Group of primates that includes monkeys, apes, and humans. 328
 Protein produced in response to the presence of an antigen; each antibody combines with a specific antigen. 406, 456
 Three-base sequence in a transfer RNA molecule base that pairs with a complementary codon in mRNA. 168
 Hormone secreted by the posterior pituitary that increases the permeability of the collecting ducts in a kidney. 485
 Foreign substance, usually a protein or a polysaccharide, that stimulates the immune system to react, such as to produce antibodies. 406, 456
 Cell that displays the antigen to certain cells of the immune system so they can defend the body against that particular antigen. 462
 Substances, such as vitamins C, E, and A, which defend the body against free radicals. 442
 Outlet of the digestive tube. 420
 In humans, the major systemic artery that takes blood from the heart to the tissues. 
399, 402
 Structure located in the walls of the aorta; contains chemoreceptors sensitive to hydrogen ion and carbon dioxide concentrations in the blood. 424
 Influence of a terminal bud in suppressing the growth of lateral buds. 357
 In vascular plants, masses of cells in the root and shoot that reproduce and elongate as primary growth occurs. 341
 Programmed cell death involving a cascade of specific cellular events leading to death and destruction of the cell. 58, 120
 Part of the vertebrate skeleton forming the appendages, shoulder girdle, and hip girdle. 503
 In humans, small, tubular appendage that extends outward from the cecum of the large intestine. 419, 456
 Ecosystems that are freshwater ecosystems (rivers, streams, lakes, ponds) and saltwater (marine) ecosystems (oceans, coral reefs, saltwater marshes). 568
 Rock layers that contain water and will release it in appreciable quantities to wells or springs. 579
 Group of arthropods that contains spiders, scorpions, and ticks. 317
 One of the three domains of life; contains prokaryotic cells that often live in extreme habitats and have unique genetic, biochemical, and physiological characteristics; its members are sometimes referred to as archaea. 6, 261, 275
 Vessel that takes blood from an artery to capillaries. 401
 Blood vessel that transports blood away from the heart. 399, 401
 Member of a phylum of invertebrates that contains, among other groups, crustaceans and insects that have an exoskeleton and jointed appendages. 316
Individuals tend to mate with those that have the same phenotype with respect to certain characteristics. 236  Short, radiating fibers produced by the centrosomes in animal cells. 115
 Smallest particle of an element that displays the properties of the element. 17
 Number of protons within the nucleus of an atom. 17
 One or two letters that represent the name of an element—e.g., H stands for a hydrogen atom, and Na stands for a sodium atom. 17
 Enzyme that is part of an ATP synthase complex and functions in the production of ATP in chloroplasts and mitochondria. 89
 Heart valve located between an atrium and a ventricle. 399
 Chamber; particularly an upper chamber of the heart lying above a ventricle. 399
 One of several species of Australopithecus, a genus that contains the first generally recognized hominids. 330
 Disease that results when the immune system mistakenly attacks the body’s own tissues. 465
 Portion of the peripheral nervous system that regulates internal 
organs. 482
 Any chromosome other than the sex-determining pair. 129
 Organism that can capture energy and synthesize organic molecules from inorganic nutrients. 560
 Plant hormone regulating growth, particularly cell elongation; also called indoleacetic acid (IAA). 356
 Small region of neuromuscular tissue that transmits impulses received from the SA node to the ventricular walls. 400
 Part of the vertebrate skeleton forming the vertical support or axis, including the skull, the rib cage, and the vertebral column. 503
 Elongated portion of a neuron that conducts nerve impulses, typically from the cell body to the synapse. 474
B
 One of the three domains of life; contains prokaryotic cells that differ from archaea because they have their own unique genetic, biochemical, and physiological characteristics. 6, 261, 270
 Virus that infects bacteria. 267
 External part of a tree, containing cork, cork cambium, and phloem. 345
 Dark-staining body (discovered by M. Barr) in the nuclei of female mammals that contains a condensed, inactive X chromosome. 137
 Molecules tending to lower the hydrogen ion concentration in a solution and raise the pH numerically. 25
 Complex on the surface of a B cell that binds an antigen and stimulates the B cell. 460
 Ion that participates in buffering the blood, and the form in which carbon dioxide is transported in the bloodstream. 426
 Body plan having two corresponding or complementary halves. 308
 Secretion of the liver that is temporarily stored and concentrated in the gallbladder before being released into the small intestine, where it emulsifies fat. 418
 Splitting of a parent cell into two daughter cells; serves as an asexual form of reproduction in bacteria. 271
 Condition characterized by overeating episodes that are not followed by purging. 448
 Scientific name of an organism, the first part of which designates the genus and the second part of which designates the specific epithet. 7, 256
 Total number of species, the variability of their genes, and the communities in which they live. 7, 588
 Circulating pathway of elements such as carbon and nitrogen involving exchange pools, storage areas, and biotic communities. 564
 Study of the geographical distribution of organisms. 219
 Computer technologies used to study the genome. 209
 Process by which substances become more concentrated in organisms in the higher trophic levels of a food web. 587
 Scientific study of life. 8
 Weight of one or more organisms. 563
 Cleanup of the environment using bacteria to break down pollutants such as oil spills and Agent Orange. 273
 Zone of air, land, and water at the surface of the Earth in which organisms are found. 5, 546, 568
 Term that encompasses genetic engineering and other techniques that make use of natural biological systems to create a product or achieve a particular result desired by humans. 175
 Maximum population growth rate under ideal conditions. 540
 Walking erect on two feet. 329
 Endothermic vertebrate that has feathers and wings, is often adapted for flight, and lays hard-shelled eggs. 324
 Oral contraception containing estrogen and progesterone. 519
 Type of mollusc with a shell composed of two valves; includes clams, oysters, and scallops. 314
 Broad, expanded portion of a plant leaf that may be single or compound leaflets. 338
 Early stage of human embryonic development that consists of a hollow, fluid-filled ball of cells. 525
 Region of the retina, lacking rods or cones, where the optic nerve exits the retina. 500
 Fluid circulated by the heart through a closed system of vessels. 383, 405
 Force of blood pushing against the inside wall of blood vessels. 401
 Lymphocyte that matures in the bone marrow and, when stimulated by the presence of a specific antigen, gives rise to antibody-producing plasma cells. 457
 Calculation used to determine whether or not a person is overweight or obese. 444 Connective tissue having protein fibers and a hard matrix of inorganic salts, notably calcium salts. 383
 Member of a class of vertebrates (class Osteichthyes) containing numerous diverse fishes, with a bony rather than cartilaginous skeleton. 322
 Cause of genetic drift; occurs when a majority of genotypes are prevented from participating in the production of the next generation as a result of a natural disaster or human interference. 237
 In mammals; portion of the brain consisting of the medulla oblongata, pons, and midbrain. 479
 In terrestrial vertebrates, small tube that conducts air from a bronchus to the alveoli. 423
 In terrestrial vertebrates, branch of the trachea that leads to the lungs. 423
 Marine photosynthetic protists with a notable abundance of xanthophyll pigments; this group includes well-known seaweeds of northern rocky shores. 277
Member of one of three phyla of nonvascular plants—the mosses, liverworts, and hornworts; these plants have no vascular tissue and occur in moist locations. 304
 Substance or group of substances that tend to resist pH changes of a solution, thus stabilizing its relative acidity and basicity. 26
 Two small structures located below the prostate gland in males; add secretions to semen. 515
 Eating disorder characterized by binge eating followed by purging via self-induced vomiting or use of a laxative. 448 Saclike, fluid-filled structure, lined with synovial membrane, that occurs near a synovial joint. 506
C
 Plant that fixes carbon dioxide via the Calvin cycle; the first stable product of C3 photosynthesis is a 3-carbon compound. 92
 Plant that fixes carbon dioxide to produce a C4 molecule that releases carbon dioxide to the Calvin cycle. 92
 Hormone secreted by the thyroid gland that increases the blood calcium level. 486
 Amount of heat energy required to raise the temperature of water 1°C. 70
 Portion of photosynthesis that takes place in the stroma of chloroplasts and can occur in the dark; it uses the products of the light reactions to reduce CO2 to a carbohydrate. 86
 The sepals collectively; the outermost flower whorl. 292
Crassulacean-acid metabolism; plant fixes carbon dioxide at night to produce a C4 molecule that releases carbon dioxide to the Calvin cycle during the day. 93
 The dramatic appearance of animal fossils 543 mya; possibly related to each of the animal phyla during some 10 million years. 307
 Type of eye found in vertebrates and certain molluscs; a single lens focuses an image on closely packed photoreceptors. 499
 Malignant tumor whose nondifferentiated cells exhibit loss of contact inhibition, uncontrolled growth, and the ability to invade tissue and metastasize. 121
 Microscopic blood vessel; gases and other substances are exchanged across the walls of a capillary between blood and tissue fluid. 401
 Protective protein container of the genetic material of a virus. 266
 Gelatinous layer surrounding the cells of blue-green algae and certain bacteria. 50
 Class of organic compounds that includes monosaccharides, disaccharides, and polysaccharides. 33, 438
 Photosynthetic reaction in which carbon dioxide is attached to an organic compound. 90
 Development of cancer. 121
 One complete cycle of systole and diastole for all heart chambers. 400
 Striated, involuntary muscle tissue found only in the heart. 384
 Organ system in which blood vessels distribute blood under the pumping action of the heart. 386, 397
 Consumer in a food chain that eats other animals. 415, 560
 Yellow or orange pigment that serves as an accessory to chlorophyll in photosynthesis. 87
 Structure located at the branching of the carotid arteries; contain chemoreceptors sensitive to hydrogen ion and carbon dioxide concentrations in blood. 424
 Ovule-bearing unit that is a part of a pistil. 292, 363
 Heterozygous individual who has no apparent abnormality but can pass on an allele for a recessively inherited genetic disorder. 153
 Largest number of organisms of a particular species that can be maintained indefinitely by a given environment. 535
 Connective tissue in which the cells lie within lacunae embedded in a flexible, proteinaceous matrix. 383
 Member of a class of vertebrates (class Chondrichthyes) with a cartilaginous rather than bony skeleton; includes sharks, rays, and skates. 322
 Smallest unit that displays the properties of life; composed of cytoplasm surrounded by a plasma membrane. 2, 48
 Portion of a neuron that contains a nucleus and from which dendrites and an axon extend. 474
 Repeating sequence of events in eukaryotes that involves cell growth and nuclear division; consists of the stages G1, S, G2, and M. 114
 Structure across a dividing plant cell that signals the location of new plasma membranes and cell walls. 118
Mechanism used by a signal molecule leading to a signal transduction pathway, where a series of molecular changes converts a signal into a specific response in the cell. 187
 One of the major theories of biology, which states that all organisms are made up of cells; cells are capable of self-reproduction and come only from preexisting cells. 50
Metabolic reactions that use the energy from carbohydrates, fatty acid, or amino acid breakdown to produce ATP molecules. 61
 Polysaccharide that is the major complex carbohydrate in plant cell walls. 34
 Structure that surrounds a plant, protistan, fungal, or bacterial cell and maintains the cell’s shape and rigidity. 50, 64
 Portion of the nervous system consisting of the brain and spinal cord. 473
 Cell organelle, existing in pairs, that occurs in the centrosome and may help organize a mitotic spindle for chromosome movement during animal cell division. 62
 Central microtubule organizing center of cells. In animal cells, it contains two centrioles. 62, 115
 Having a well-recognized anterior head with a brain and sensory receptors. 308
 Type of mollusc in which a modified foot develops into the head region; includes squids, cuttlefish, octopuses, and nautiluses. 314
 In terrestrial vertebrates, portion of the brain that coordinates skeletal muscles to produce smooth, graceful motions. 479
 Outer layer of cerebral hemispheres; receives sensory information and controls motor activities. 478
 Birth control device made of latex or rubber in the shape of a cup which covers the cervix, considered a minidiaphragm. 520
 Narrow end of the uterus leading into the vagina. 516
 Tendency for characteristics to be more divergent when similar species belong to the same community than when they are isolated from one another. 557
In the cell cycle, one of several points where the cell cycle can stop or continue on, depending on the internal signal it receives; ensures that each step of the cell cycle is completed before the next one begins. 119
 Organism able to synthesize organic molecules by using carbon dioxide as the carbon source and the oxidation of an inorganic substance (such as hydrogen sulfide) as the energy source. 272
 Organism that is unable to reproduce its own organic molecules, and therefore requires organic nutrients in its diet. 272
 Strong but flexible nitrogenous polysaccharide found in the exoskeleton of arthropods. 34, 316
 Organic compounds containing carbon, chlorine, and fluorine atoms. CFCs such as Freon can deplete the ozone shield by releasing chlorine atoms in the upper atmosphere. 586
 Green pigment that absorbs solar energy and is important in algal and plant photosynthesis; occurs as chlorophyll a and chlorophyll b. 85, 87
 Membrane-bounded organelle in algae and plants with chlorophyll-containing membranous thylakoids; where photosynthesis takes place. 60, 85
 One of the major lipids found in animal plasma membranes; makes the membrane impermeable to many molecules. 37, 440
 Animal in the phylum Chordata that has a dorsal tubular nerve cord, a notochord, pharyngeal pouches, and postanal tail at some point in its life cycle. 320
 Treelike extensions of the chorion of the embryo; project into the maternal tissues at the placenta. 528
 Prenatal test in which a sample of chorionic villi cells is removed for diagnostic purposes. 197
 Network of fibrils consisting of DNA and associated proteins observed within a nucleus that is not dividing. 56, 113
 Alteration in the chromosome structure or number typical of the species. 198
 Structure consisting of DNA complexed with proteins that transmits genetic information from the previous generation of cells and organisms to the next generation. 56, 113
Sequence that shows the relative distance between gene loci on a chromosome. 154
 Thick, semiliquid food material that passes from the stomach to the small intestine. 418
 Complex unicellular protist that moves by means of cilia and digests food in food vacuoles. 278
 Short, hairlike projection from the plasma membrane, occurring usually in larger numbers. 63
 Cycle of reactions in mitochondria that begins with citric acid. It breaks down an acetyl group and produces CO2, ATP, NADH, and FADH2; also called the Krebs cycle. 99, 102
School of systematics that uses derived characters to determine monophyletic groups and construct cladograms. 259
 One of the categories, or taxa, used by taxonomists to group species; class is the taxon above the order level. 6, 256
 Cell division without cytoplasmic addition or enlargement; occurs during the first stage of animal development. 525
 In ecology, community that results when succession has come to an end. 554
 Cardiovascular system in all vertebrates and some invertebrates, which is composed of a muscular heart and blood vessels. 397
Spatial distribution of individuals in a population in which individuals are more dense in one area than in another. 538 
 Invertebrate in the phylum Cnidaria existing as either a polyp or medusa with two tissue layers and radial symmetry. 310
 Inheritance pattern in which both alleles of a gene are equally expressed. 149
 Three-base sequence in messenger RNA that causes the insertion of a particular amino acid into a protein, or termination of translation. 166
 Body cavity lying between the digestive tract and body wall that is completely lined by mesoderm. 308, 414
 Nonprotein organic molecule that aids the action of the enzyme to which it is loosely bound. 89
 Molecule that helps oxidate pyruvate in the preparatory (prep) reaction during cellular respiration. 99
 Joint evolution in which one species exerts selective pressure on the other species. 552
 Explanation for upward transport of water in xylem based upon transpiration-created tension and the cohesive properties of water molecules. 349
 Duct within the kidney that receives fluid from several nephrons; the reabsorption of water occurs here. 428
 Plant tissue composed of cells with unevenly thickened walls; supports growth of stems and petioles. 341
 Deficiency in one or more of the three kinds of cone cells responsible for color vision. 204
 Symbiotic relationship in which one species is benefited, and the other is neither harmed nor benefited. 556
 Ancestor held in common by at least two lines of descent. 247, 256
 Assemblage of populations interacting with one another within the same environment. 5, 546, 552
 Type of bone that contains osteons consisting of concentric layers of matrix and osteocytes in lacunae. 383, 504
 Interaction between two organisms in which both require the same limited resource, which results in harm to both. 542, 556
 Theory that no two species can occupy the same niche. 557
 Hydrogen bonding between particular purines and pyrimidines in DNA. 162
 Series of proteins in plasma that form a nonspecific defense mechanism against a pathogen invasion; it complements the antigen-antibody reaction. 459
 Substance having two or more different elements united chemically in a fixed ratio. 19
 Type of eye found in arthropods; it is composed of many independent visual units. 499
 Statement made following an experiment as to whether or not the results support the hypothesis. 9
 Birth control method that blocks the entrance of sperm to the uterus; also prevents STDs. 520
 Sheath used to cover the penis during sexual intercourse; used as a contraceptive and, if latex, to minimize the risk of transmitting infection. 520
 Deafness due to middle ear damage. 497
Photoreceptor cell in vertebrate eyes that responds to bright light and makes color vision possible. 500
In conifers, structure that bears either pollen (male gametophyte) or seeds (female gametophyte). 291
 Member of a group of cone-bearing gymnosperm plants that includes pine, cedar, and spruce trees. 291
 Transfer of genetic material from one cell to another. 272
 Type of animal tissue that binds structures together, provides support and protection, fills spaces, stores fat, and forms blood cells; adipose tissue, cartilage, bone, 
and blood are types of connective tissue. 382
 Organism that feeds on another organism in a food chain; primary consumers eat plants, and secondary consumers eat animals. 560
In cell culture, the point where cells stop dividing when they become a one-cell-thick sheet. 120
Dialysis which takes place inside the body using the peritoneum, the natural lining of the abdomen, as the dialysis membrane. 430
 Birth control method utilizing synthetic progesterone; prevents ovulation by disrupting the ovarian cycle. 519
 Birth control method utilizing progesterone or estrogen and progesterone; prevents ovulation by disrupting the ovarian cycle. 520 Under development, this birth control method immunizes against the hormone HCG, crucial to maintaining implantation of the embryo. 520 Sample that goes through all the steps of an experiment but does not contain the experimental variable being tested; a standard against which the results of an experiment are checked. 8
 Similarity in structure in distantly related groups due to adaptation to the environment. 257
Sexual union between a male and a female. 513
 Lateral meristem that produces cork. 345
 Dead cells found in the outer covering of the bark of trees; may be sloughed off. 345
 Transparent, anterior portion of the outer layer of the eyeball. 499
 Petals, collectively; usually the conspicuously colored flower whorl. 292
 Follicle that has released an egg and increases its secretion of progesterone. 517
 In plants, ground tissue bounded by the epidermis and vascular tissue in stems and roots; in animals, outer layer of an organ, such as the cortex of the kidney or adrenal gland. 347
 Seed leaf for embryo of a flowering plant; provides nutrient molecules for the developing plant before photosynthesis begins. 293, 340, 366
 Reaction that occurs simultaneously; one is an exergonic reaction that releases energy, and the other is an endergonic reaction that requires an input of energy in order to occur. 73
 Chemical bond in which atoms share one pair of electrons. 20
 Nerve that arises from the brain. 480
 Short, fingerlike projections formed by the folding of the inner membrane of mitochondria. 61
 Common name for the first fossils to be designated Homo sapiens. 332
 Exchange of segments between nonsister chromatids of a tetrad during meiosis. 131
 Member of a group of marine arthropods that contains, among others, shrimps, crabs, crayfish, and lobsters. 316
 Total pattern of human behavior; includes technology and the arts, and is dependent upon the capacity to speak and transmit knowledge. 330
 Condition resulting from hypersecretion of glucocorticoids; characterized by thin arms and legs and a “moon face,” and accompanied by high blood glucose and sodium levels. 487
 Sensory receptors for pressure and touch found in the dermis of the skin. 501
 Waxy layer covering the epidermis of plants that protects the plant against water loss and disease-causing organisms. 341
 Photosynthetic bacteria that contain chlorophyll and release O2; formerly called blue-green algae. 272 Protein that cycles in quantity as the cell cycle progresses; combines with and activates the kinases that function to promote the events of the cycle. 119, 189
cystic fibrosis Generalized, autosomal recessive disorder of infants and children, in which there is widespread dysfunction of the exocrine glands. 202
 Type of protein secreted by a T cell that attacks viruses, virally infected cells, and cancer cells. 463
 Division of the cytoplasm following mitosis and meiosis. 114
 Plant hormone that promotes cell division; often works in combination with auxin during organ development in plant embryos. 358
 Contents of a cell between the nucleus (nucleoid region of bacteria) and the plasma membrane. 50
 One of four nitrogen-containing bases in the nucleotides composing the structure of DNA and RNA; pairs with guanine. 161
 Internal framework of the cell, consisting of microtubules, actin filaments, and intermediate filaments. 55, 62
 cell that attacks and kills antigen-bearing cells. 462
D
 Facts or information collected through observation and/or experimentation. 9
 Plant whose flowering is not dependent on day length—e.g., tomato and cucumber. 360
 Shedding leaves annually. 339
 Organism, usually a bacterium or fungus, that breaks down organic matter into inorganic nutrients that can be recycled in the environment. 560
 Disorders caused by the lack of certain vitamins or minerals in the diet. Examples are bleeding gums, rickets (vitamin deficiencies); osteoporosis, anemia (mineral deficiencies). 436
 Removal of trees from a forest in a way that ever reduces the size of the forest. 578 Chemical reaction resulting in a covalent bond with the accompanying loss of a water molecule. 33
 Allergic response initiated at the site of the allergen by sensitized T cells, involving macrophages and regulated by cytokines. 465
 Change in chromosome structure in which the end of a chromosome breaks off or two simultaneous breaks lead to the loss of an internal segment; often causes abnormalities—e.g., cri du chat syndrome. 198
Study of human populations, their characteristics, and their changes. 539
 Loss of an enzyme’s normal shape so that it no longer functions; caused by a less than optimal pH and temperature. 40
 Part of a neuron that sends signals toward the cell body. 474
 Type of connective tissue containing many collagen fibers packed together; found in tendons and ligaments, for example. 382
 Biotic factor, such as disease or competition, that affects population size according to the population’s density. 542
 Abiotic factor, such as fire or flood, that affects population size independent of the population’s density. 542
 Pentose sugar found in DNA that has one less hydroxyl group than ribose. 33
 Denuding and degrading a once-fertile land, initiating a desert-producing cycle that feeds on itself and causes long-term changes in the soil, climate, and biota of an area. 578
 Complex pattern of interlocking and crisscrossing food chains that begins with a population of detritivores. 562
 Organic matter produced by decomposition of substances such as tissues and animal wastes. 560
 Group of coelomate animals in which the second embryonic opening is associated with the mouth; the first embryonic opening, the blastopore, is associated with the anus. 313
 Condition characterized by a high blood glucose level and the appearance of glucose in the urine, due to a deficiency of insulin production and failure of cells to take up glucose. 488
 Material that passes through the membrane in dialysis. 430
 In mammals, dome-shaped muscularized sheet separating the thoracic cavity from the abdominal cavity. Also, a birth control device consisting of a soft rubber or latex cup that fits over the cervix. 424, 520
 Excessively frequent and watery bowel movements. 420
 Relaxation period of a heart chamber during the cardiac cycle. 400
A person’s typical food choices; a balanced diet contains all the nutrients in the right proportions to maintain a healthy body. 437
Nutrients and plant products (i.e., herbal teas, protein supplements) that are used to enhance health; do not need to undergo the same safety and effectiveness testing required for prescription drugs. 450
 Organ system that includes the mouth, esophagus, stomach, small intestine, and large intestine (colon) that receives food and digests it into nutrient molecules. Also has associated organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas. 386
 Individual that is heterozygous for two traits; shows the phenotype governed by the dominant alleles but carries the recessive alleles. 147
 Cell condition in which two of each type of chromosome are present. 129
 Outcome of natural selection in which an extreme phenotype is favored, usually in a changing environment. 239
 Sugar that contains two units of a monosaccharide; e.g., maltose. 33
 Outcome of natural selection in which the two extreme phenotypes are favored over the average phenotype, leading to more than one distinct form. 240
 Final portion of a nephron that joins with a collecting duct; associated with tubular secretion. 428
 Amount of each specific species in a community. 553
 Nucleic acid polymer produced from covalent bonding of nucleotide monomers that contain the sugar deoxyribose; the genetic material of nearly all organisms. 41
Very small glass square containing several rows of DNA probes. 205
 The use of DNA fragment lengths resulting from restriction enzyme cleavage to identify particular individuals. 174
 Enzyme that links DNA fragments; used during production of recombinant DNA to join foreign DNA to vector DNA. 173
 During replication, an enzyme that joins the nucleotides complementary to a DNA template. 164
 Piece of single-stranded DNA that will bind to a complementary piece of DNA. 205
 Synthesis of a new DNA double helix prior to mitosis and meiosis in eukaryotic cells and during prokaryotic fission in prokaryotic cells. 113, 164
Largest of the categories, or taxa, used by taxonomists to group species; the three domains are Archaea, Bacteria, and Eukarya. 6, 256
 Allele that exerts its phenotypic effect in the heterozygote; it masks the expression of the recessive allele. 145
 In plants, a cessation of growth under conditions that seem appropriate for growth. 357
 Mass of sensory neuron cell bodies located in the dorsal root of a spinal nerve. 481
 In flowering plants, one sperm nucleus unites with the egg nucleus, and a second sperm nucleus unites with the polar nuclei of an embryo sac. 293, 365
 Chronic progressive disease affecting the shoulder and hip (pelvic) girdles, commencing in early childhood; characterized by increasing weakness of the muscles followed by atrophy and a peculiar swaying gait with the legs kept wide apart. Transmitted as an X-linked trait; affected individuals, predominantly males, rarely survive to maturity. Death is usually due to respiratory weakness or heart failure. 204
First part of the small intestine where chyme enters from the stomach. 420
 Change in chromosome structure in which a particular segment is present more than once in the same chromosome. 198
Chromosome composed of two sister chromatids. 130
E
 Marine animals in phylum Echinodermata that include sea stars, sea urchins, and sand dollars; characterized by radial symmetry and a water vascular system. 319
 Role an organism plays in its community, including its habitat and its interactions with other organisms. 556
 Pictorial graph based on the biomass, number of organisms, or energy content of various trophic levels in a food web—from the producer to the final consumer populations. 563
 Gradual replacement of communities in an area following a disturbance (secondary succession) or the creation of new soil (primary succession). 554
 Study of the interactions of organisms with other organisms and with the physical and chemical environment. 546
 Biological community together with the associated abiotic environment; characterized by a flow of energy and a cycling of inorganic nutrients. 5, 546, 552
 Outermost primary tissue layer of an animal embryo; gives rise to the nervous system and the outer layer of the integument. 526
 Having a body temperature that varies according to the environmental temperature. 324
 Swelling due to tissue fluid accumulation in the intercellular spaces. 430
 Recording of the electrical activity associated with the heartbeat. 400
 Negative subatomic particle, moving about in an energy level around the nucleus of an atom. 17
 Ability of an atom to attract electrons toward itself in a chemical bond. 22
 Concentric energy levels in which electrons orbit. 18
 Passage of electrons along a series of electron carriers from a higher to lower energy level; the energy released is used for the synthesis of ATP. 88, 99
 Substance that cannot be broken down into substances with different properties; composed of only one type atom. 16
 Female gametophyte of flowering plants. 365
 Causative agent of a disease that is new or is demonstrating increased prevalence, such as the viruses that cause AIDS, SARS, and avian influenza. 269
 Breaking up of fat globules into smaller droplets by the action of bile salts or any other emulsifier. 418
 Ductless organ that secretes hormone(s) into the bloodstream. 420, 483
 Organ system involved in the coordination of body activities; uses hormones as chemical signals secreted into the bloodstream. 387
 Process by which substances are moved into the cell from the environment by phagocytosis (cellular eating) or pinocytosis (cellular drinking); includes receptor-mediated endocytosis. 79
 Innermost primary tissue layer of an animal embryo that gives rise to the linings of the digestive tract and associated structures. 526
 Internal plant root tissue forming a boundary between the cortex and the vascular cylinder. 347
 Collection of membranous structures involved in transport within the cell. 58
 Mucous membrane lining the interior surface of the uterus. 517
 System of membranous saccules and channels in the cytoplasm, often with attached ribosomes. 57
 Protective internal skeleton, as in vertebrates. 307, 502
 In flowering plants, nutritive storage tissue that is derived from the union of a sperm nucleus and polar nuclei in the embryo sac. 357
 Spore formed within a cell; certain bacteria form endospores. 272
 Maintenance of a constant body temperature independent of the environmental temperature. 325
 Capacity to do work and bring about change; occurs in a variety of forms. 3, 70
 Two laws explaining energy, and its relationships and exchanges. The first, also called the “law of conservation,” says that energy cannot be created or destroyed but can only be changed from one form to another; the second says that energy cannot be changed from one form to another without a loss of usable energy. 70
 Energy that must be added in order for molecules to react with one another. 75
 Elements that regulate transcription from nearby genes. Function by acting as binding sites for transcription factors. 186
 Measure of disorder or randomness. 71
 Organic catalyst, usually a protein, that speeds a reaction in cells due to its particular shape. 38, 75
 Means by which cells regulate enzyme activity; may be competitive or noncompetitive inhibition. 76
 (epidermis) In plants, tissue that covers roots, leaves, and stems of nonwoody organisms. 341
 Coiled tubule next to the testes where sperm mature and may be stored for a short time. 514
 Structure that covers the glottis and closes off the air tract during the process of swallowing. 416
 Hormone secreted by the adrenal medulla in times of stress; adrenaline. 487
 Tissue that lines hollow organs and covers surfaces. 380
 Population demonstrating a life history pattern in which members exhibit logistic population growth and the population size remains at or near the carrying capacity. Its members are large in size, slow to mature, have a long life span, have few offspring, and provide much care to offspring (e.g., bears, lions). 544
 Increase in blood flow to the penis during sexual arousal, causing the penis to stiffen and become erect. 515
 Muscular tube for moving swallowed food from the pharynx to the stomach. 416
 Substance in the diet that contributes to good health; must be supplied by the diet because the body either cannot synthesize it or makes insufficient amounts to meet the body’s needs. 437
 Female sex hormone that helps maintain sexual organs and secondary sex characteristics. 518
 Plant hormone that causes ripening of fruit and is also involved in abscission. 359
 Chromatin that is extended and accessible for transcription. 184
 Abbreviation of eudicotyledon. Flowering plant group; members have two embryonic leaves (cotyledons), net-veined leaves, vascular bundles in a ring, flower parts in fours or fives and their multiples, and other characteristics. 340
 One of the three domains of life, consisting of organisms with eukaryotic cells and further classified into the kingdoms Protista, Fungi, Plantae, and Animalia. 6, 261
 Type of cell that has a membrane-bounded nucleus and membranous organelles; found in organisms within the domain Eukarya. 50
 Enrichment of water by inorganic nutrients used by phytoplankton. Often, overenrichment caused by human activities leads to excessive bacterial growth and oxygen depletion. 565
Descent of organisms from common ancestors with the development of genetic and phenotypic changes over time that make them more suited to the environment. 4, 215
 Gland which discharges its secretion into ducts; the pancreas is an exocrine gland when it secretes pancreatic juice into the duodenum. 420 
 Process in which an intracellular vesicle fuses with the plasma membrane so that the vesicle’s contents are released outside the cell. 79
 Enlargement of the thyroid gland accompanied by an abnormal protrusion of the eyes. 486
 Protective external skeleton, as in arthropods. 307, 502
 Species that is new to a community, nonnative. 559
 Artificial situation devised to test a hypothesis. 8
 In a scientific experiment, a condition of the experiment that is deliberately changed. 8
 Growth, particularly of a population, in which the increase occurs in the same manner as compound interest. 540
 Fertilization of an egg by sperm that occurs outside of the body, as in aquatic animals. 512
 Total disappearance of a species or higher group. 7, 545
 Meshwork of polysaccharides and proteins that provides support for an animal cell and affects its behavior. 64
 Membranes that are not a part of the embryo but are necessary to the continued existence and health of the embryo. 513
F
 Passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a carrier. 77
familial hypercholesterolemia (FH) Inability to remove cholesterol from the bloodstream; predisposes individual to heart attack. 204
 One of the categories, or taxa, used by taxonomists to group species; the taxon above the genus level. 6, 256
 Organic molecule that contains glycerol and fatty acids and is found in adipose tissue of vertebrates. 35, 439
 Molecule that contains a hydrocarbon chain and ends with an acid group. 35
 Mechanism for regulating metabolic pathways in which the concentration of the product is kept within a certain range until binding shuts down the pathway, and no more product is produced. 76
 In seed plants, the gametophyte that produces an egg; in flowering plants, an embryo sac. Sometimes called a megagametophyte. 365 
 Anaerobic breakdown of glucose that results in a gain of two ATP and end products such as alcohol and lactate. 107
 Member of a group of plants that have large fronds; in the sexual life cycle, the independent gametophyte produces flagellated sperm, and the vascular sporophyte produces windblown spores. 289
 Fusion of sperm and egg nuclei, producing a zygote that develops into a new individual. 524
 Structure resembling a thread; also plant material that is nondigestible. 438
 Connective tissue cell that synthesizes fibers and ground substance. 382
 Structural protein with only a secondary structure (i.e., keratin, silk, 
collagen). 40
 End-to-end chains of cells that form as cell division occurs in only one plane; in plants, the elongated stalk of a stamen. 292, 363
 Method of obtaining nourishment by certain animals which strain minute organic particles from the water in a way that deposits them in the digestive tract. 310
 Movement of small molecules from a blood capillary into the nephron capsule due to the action of blood pressure. 428
In bacteria, small, bristle-like fibers on bacterial cell surface that enable bacteria to adhere to surfaces. 51, 516
 System of classification that contains the kingdoms Monera, Protista, Plantae, Animalia, and Fungi. 261
 Long, slender extension used for locomotion by some bacteria, protozoans, and sperm. 51, 63, 271
 Unsegmented worm lacking a body cavity; phylum Platyhelminthes. 311
 Reproductive organ of a flowering plant, consisting of several kinds of modified leaves arranged in concentric rings and attached to a modified stem called the receptacle. 285, 362
 Structure in the ovary of animals that contains an oocyte; site of oocyte production. 517
 First half of the ovarian cycle, during which the follicle matures and much estrogen (and some progesterone) is produced. 517
 Order in which one population feeds on another in an ecosystem, thereby showing the flow of energy from a detritivore (detrital food chain) or a producer (grazing food chain) to the final consumer. 563
 In ecosystems, a complex pattern of linked and crisscrossing food chains. 562
 Protozoan; marine amoeba having a calcium carbonate skeleton, many of which make limestone formations such as the White Cliffs of Dover. 278
 Constituents of blood that are either cellular (red blood cells and white blood cells) or at least cellular in origin (platelets). 405
 Any past evidence of an organism that has been preserved in the Earth’s crust. 253
 Fuel such as oil, coal, and natural gas that is the result of partial decomposition of plants and animals coupled with exposure to heat and pressure for millions of years. 567, 583
 History of life recorded from remains from the past. 224
 Cause of genetic drift due to colonization by a limited number of individuals who, by chance, have different gene frequencies than the parent population. 238
Region of the retina consisting of densely packed cones; responsible for the greatest visual acuity. 500
 Alteration in a gene due to deletion of a base, so that the reading “frame” is shifted; can result in a nonfunctional protein. 172
 Fern leaf. 289
 In flowering plants, the structure that forms from an ovary and associated tissues and encloses seeds. 293, 366
 Specific cluster of atoms attached to the carbon skeleton of organic molecules that enters into reactions and behaves in a predictable way. 31
 Saprotrophic decomposer; the body is made up of filaments called hyphae that form a mass called a mycelium. 6, 296
G
 Organ attached to the liver that serves to store and concentrate bile. 418
 Haploid sex cell; e.g., egg and sperm. 521
 Haploid generation of the alternation of generations life cycle of a plant; produces gametes that unite to form a diploid zygote. 286, 362
 Collection or bundle of neuron cell bodies usually outside the central nervous system. 480
 Junction between cells formed by the joining of two adjacent plasma membranes; it lends strength and allows ions, sugars, and small molecules to pass between cells. 65
 Mollusc with a broad flat foot for crawling (e.g., snails and slugs). 314
 Stage of animal development during which the germ layers form, at least in part, by invagination. 526
 Formation of a gastrula from a blastula; characterized by an invagination of the cell layers to form a caplike structure. 526
 Unit of heredity existing as alleles on the chromosomes; in diploid organisms, typically two alleles are inherited—one from each parent. 4
 Sharing of genes between two populations through interbreeding. 236
Existence of several alleles on the same chromosome. 154
 Specific location of a particular gene on homologous chromosomes. 145
 Change in the sequence of bases in a gene. 172
 Total of all the genes of all the individuals in a population. 233
 Correction of a detrimental mutation by the addition of new DNA and its insertion in a genome. 210
 Plant that carries the genes of another organism as a result of DNA technology; also transgenic plant. 371
 Prospective parents consult a counselor who determines the genotype of each and whether an unborn child will have a genetic disorder. 196
 Mechanism of evolution due to random changes in the allelic frequencies of a population; more likely to occur in small populations or when only a few individuals of a large population reproduce. 237
 Alteration of genomes for medical or industrial purposes. 173
 Abnormality in the sequence of a base at a particular location on a chromosome signifying a disorder. 205
 An individual’s complete genotype, including any possible mutations. 209
 Genes of an organism for a particular trait or traits; often designated by letters—for example, BB or Aa. 145
 One of the categories, or taxa, used by taxonomists to group species; contains those species that are most closely related through evolution. 6, 256
 Beginning of growth of a seed, spore, or zygote, especially after a period of dormancy. 368
 Primary tissue layer of a vertebrate embryo—namely, ectoderm, mesoderm, or endoderm. 526
 Plant hormone promoting increased stem growth; also involved in flowering and seed germination. 357
 Predicted increase in the Earth’s temperature due to human activities that promote the greenhouse effect. 567
 Polypeptides in this protein have a tertiary structure (i.e., enzymes). 40
 Opening for airflow in the larynx. 423
 Hormone secreted by the pancreas which causes the liver to break down glycogen and raises the blood glucose level. 420, 487
 Type of hormone secreted by the adrenal cortex that influences carbohydrate, fat, and protein metabolism; see cortisol. 487
 Six-carbon sugar that organisms degrade as a source of energy during cellular respiration. 33
 Three-carbon carbohydrate with three hydroxyl groups attached; a component of fats and oils. 35
 Storage polysaccharide found in animals; composed of glucose molecules joined in a linear fashion but having numerous branches. 34
 Anaerobic breakdown of glucose that results in a gain of two ATP and the end product pyruvate. 99
Marine photosynthetic protist with elaborate shells of silica; represented by diatoms. 277 Organelle consisting of saccules and vesicles that processes, packages, and distributes molecules about or from the cell. 58
 Proprioceptor located in the joints; helps maintain equilibrium and posture. 50
 Substances secreted by the anterior pituitary that regulate the activity of the ovaries and testes; principally, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). 484
 Organs that produce gametes; the ovary produces eggs, and the testis produces 
sperm. 512
 Stack of chlorophyll-containing thylakoids in a chloroplast. 60, 85
 Maintenance of balance when the head and body are motionless. 498
 Growth response of roots and stems of plants to the Earth’s gravity; roots demonstrate positive gravitropism, and stems demonstrate negative gravitropism. 360
 Complex pattern of linked and crisscrossing food chains that begins with a population of photosynthesizers serving as producers. 562
 Member of a diverse group of photosynthetic protists that contains chlorophylls a and b and has other biochemical characteristics like those of plants. 277
 Reradiation of solar heat toward the Earth, caused by gases such as carbon dioxide, methane, nitrous oxide, water vapor, ozone, and nitrous oxide in the atmosphere. 567
 Gases in the atmosphere such as carbon dioxide, methane, nitrous oxide, water vapor, ozone, and nitrous oxide that are involved in the greenhouse effect. 583
 Tissue that constitutes most of the body of a plant; consists of parenchyma, collenchyma, and sclerenchyma cells that function in storage, basic metabolism, and support. 341
 Chemical signal that regulates mitosis and differentiation of cells that have receptors for it; important in such processes as fetal development, tissue maintenance and repair, and hematopoiesis; sometimes a contributing factor in cancer. 189
 Substance secreted by the anterior pituitary; controls size of an individual by promoting cell division, protein synthesis, and bone growth. 485
 One of four nitrogen-containing bases in nucleotides composing the structure of DNA and RNA; pairs with cytosine. 161
 Type of woody seed plant in which the seeds are not enclosed by fruit and are usually borne in cones, such as those of the conifers. 286, 291
H
Place where an organism lives and is able to survive and reproduce. 556
 Type of archaea that lives in extremely salty habitats. 275
 Cell condition in which only one of each type of chromosome is present. 129
 Muscular organ whose contraction causes blood to circulate in the body of an animal. 396 
 Damage to the myocardium due to blocked circulation in the coronary arteries; myocardial infarction. 404
 Clicking or swishy sounds, often due to leaky valves. 399
 Type of kinetic energy; captured solar energy eventually dissipates as heat in the environment. 71
 Secretes lymphokines, which stimulate all kinds of immune cells. 463
 Iron-containing group found in hemoglobin. 426
 Cleansing of blood by using an artificial membrane that causes substances to diffuse from blood into a dialysis fluid. 430
Iron-containing respiratory pigment occurring in vertebrate red blood cells and in the blood plasma of some invertebrates. 
38, 405
 Most common of the severe clotting disorders caused by the absence of a blood clotting factor. 204
 Nonwoody stem. 344
 Primary consumer in a grazing food chain; a plant eater. 415, 560
 Type of animal that has both male and female sex organs. 312, 512
 Highly compacted chromatin that is not accessible for transcription. 184
 Organism that cannot synthesize organic compounds from inorganic substances, and therefore must take in organic food. 560
 Possessing unlike alleles for a particular trait. 145
 Portion of the vertebrate skeleton to which the lower (hind) limbs are attached; consists of the coxal bones. 503
 Substance, produced by basophils in blood and mast cells in connective tissue, that causes capillaries to dilate. 458
 Protein molecule responsible for packing chromatin. 113
 Virus responsible for AIDS. 466, 522
 Maintenance of normal internal conditions in a cell or an organism by means of self-regulating mechanisms. 3, 388
 Member of the family Hominidae, which contains australopithecines and humans. 329
 Hominid who used fire and migrated out of Africa to Europe and Asia. 330
 Hominid of two million years ago who is believed to have been the first tool user. 330
 Member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division; a homologue. 128
 In evolution, a structure that is similar in different types of organisms because these organisms are derived from a common ancestor. 226, 257
 Member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division; a homologous chromosome. 128
 Modern humans. 331
 Possessing two identical alleles for a particular trait. 145
Huntington disease Genetic disease marked by progressive deterioration of the nervous system due to deficiency of a neurotransmitter.  203
 Cartilage whose cells lie in lacunae separated by a white translucent matrix containing very fine collagen fibers. 383
 Crossing of different species. 370
 Weak bond that arises between a slightly positive hydrogen atom of one molecule and a slightly negative atom of another molecule or between parts of the same molecule. 22
 Hydrogen atom that has lost its electron and therefore bears a positive charge (H1). 25
 Splitting of a compound by the addition of water, with the H being incorporated in one fragment and the OH in the other. 33
 Type of molecule that interacts with water by dissolving in water and/or by forming hydrogen bonds with water molecules. 23, 31
 Type of molecule that does not interact with water because it is nonpolar. 23, 31
 Fluid-filled body compartment that provides support for muscle contraction resulting in movement; seen in cnidarians, flatworms, roundworms, and segmented worms. 503
 One of two ions that results when a water molecule dissociates; it has gained an electron, and therefore bears a negative charge (OH). 25
 Elevated blood pressure, particularly the diastolic pressure. 403
 Higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis. 78
 One of many hormones produced by the hypothalamus that stimulates the secretion of an anterior pituitary hormone. 484
 In vertebrates, part of the brain that helps regulate the internal environment of the body—for example, heart rate, body temperature, and water balance. 479, 484
 Supposition established by reasoning after consideration of available evidence; it can be tested by obtaining more data, often by experimentation. 8
 Lower solute (more water) concentration than the cytoplasm of a cell; causes cell to gain water by osmosis. 78
I
 Allergic response that occurs within seconds of contact with an allergen; caused by the attachment of the allergen to IgE antibodies. 465
 All the cells in the body that protect the body against foreign organisms and substances and also against cancerous cells. 387, 456
 Ability of the body to protect itself from foreign substances and cells, including disease-causing agents. 456
Inheritance pattern in which the offspring has an intermediate phenotype, as when a red-flowered plant and a white-flowered plant produce pink-flowered offspring. 149
 Change in the shape of an enzyme’s active site that enhances the fit between the active site and its substrate(s). 76
 Ability of a chemical or a tissue to influence the development of another tissue. 526
 Using specific observations and the process of logic and reasoning to arrive at a hypothesis. 8
 Increased frequency of darkly pigmented (melanic) forms in a population when soot and pollution make lightly pigmented forms easier for predators to see against a pigmented background. 234
 Inability to have as many children as desired. 520
 Tissue response to injury that is characterized by redness, swelling, pain, and heat. 458
The study of compounds not having a carbon basis; chemistry of the nonliving world. 30
 Type of arthropod. The head has antennae, compound eyes, and simple eyes; the thorax has three pairs of legs and often wings; and the abdomen has internal organs. 318
 Hormone secreted by the pancreas that lowers the blood glucose level by promoting the uptake of glucose by cells and the conversion of glucose to glycogen by the liver and skeletal muscles. 420, 487
 Summing up of excitatory and inhibitory signals by a neuron or by some part of the brain. 476
 Organ system consisting of skin various organs, such as hair, which are found in skin. 387
 Region that holds adjacent cardiac muscle cells together; disks appear as dense bands at right angles to the muscle striations. 384
 Period of time between meiosis I and meiosis II during which no DNA replication takes place. 133
 Space that occurs between the outer and inner membrane of a mitochondrion. 105
 Neuron located within the central nervous system that conveys messages between parts of the central nervous system. 474
 In vascular plants, the region of a stem between two successive nodes. 339
 Stages of the cell cycle (G1, S, G2) during which growth and DNA synthesis occur when the nucleus is not actively dividing. 114
 Enzyme, produced by the epithelial cells on the surface of villi, which functions in the digestion of small organic molecules. 418
  Birth-control device consisting of a small piece of molded plastic inserted into the uterus, and believed to alter the uterine environment so that fertilization does not occur. 520
Change in chromosome structure in which a segment of a chromosome is turned around 180°; this reversed sequence of genes can lead to altered gene activity and abnormalities. 198
 Charged particle that carries a negative or positive charge. 20
 Chemical bond in which ions are attracted to one another by opposite 
charges. 20
 Muscular ring that surrounds the pupil and regulates the passage of light through this opening. 499
 Molecules with the same molecular formula but a different structure, and therefore a different shape. 31
 Solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis. 78
 Atom of the same element having the same atomic number but a different mass number due to the number of neutrons. 18
J
 Type of fish(es) that have no jaws, includes today’s hagfishes and lampreys. 322
K
 Chromosomes arranged by pairs according to their size, shape, and general appearance in mitotic metaphase. 196
 Species whose activities significantly affect community structure. 558
 Paired organs of the vertebrate urinary system that regulate the chemical composition of the blood and produce a waste product called urine. 427
 Caloric value of food; 1,000 calories. 70
 Enzyme that activates another enzyme by adding a phosphate group. 119
 Energy associated with motion. 70
 One of the categories, or taxa, used by taxonomists to group species; the taxon above phylum. 6, 256
 Condition caused by the inheritance of XXY chromosomes. 137
L
 Lymphatic vessel in an intestinal villus; aids in the absorption of fats. 418
 Small pit or hollow cavity, as in bone or cartilage, where a cell or cells are located. 383
 Invertebrate chordate with a body that resembles a lancet and has the four chordate characteristics as an adult. 320
 In vertebrates, portion of the digestive tract that follows the small intestine; in humans, consists of the cecum, colon, rectum, and anal canal. 419
 Cartilaginous organ located between the pharynx and the trachea; in humans, contains the vocal cords; sometimes called the voice box. 423
 Site on a stem where lateral branches grow. 339
 Canal system containing sensory receptors that allow fishes and amphibians to detect water currents and pressure waves from nearby objects. 498
 Theory that is generally accepted by an overwhelming number of scientists. 9
 Alleles of unlinked genes assort independently of 
each other during meiosis so that the gametes contain all possible combinations 
of alleles. 146
 Separation of alleles from each other during meiosis so that the gametes contain one from each pair. Each resulting gamete has an equal chance of receiving either allele. 145
 Lateral appendage of a stem, highly variable in structure, often containing cells that carry out photosynthesis. 338
 Vascular tissue within a leaf. 340
 Blood-sucking annelid, usually found in fresh water, with a sucker at each end of a segmented body. 315
 Clear, membranelike structure found in the vertebrate eye behind the iris; brings objects into focus. 499
 Country that is becoming industrialized; typically, population growth is expanding rapidly, and the majority of people live in poverty. 535
 Symbiotic relationship between certain fungi and algae, in which the fungi possibly provide inorganic food or water and the algae provide organic food. 299
 Recurring pattern of genetically programmed events by which individuals grow, develop, maintain themselves, and reproduce. 129
 Adaptations in characteristics that influence an organism’s biology, such as how many offspring it produces, its survival, and factors such as age and size that determine its reproductive maturity. 544
 Tough cord or band of dense fibrous tissue that binds bone to bone at a joint. 382, 506
 Portion of photosynthesis that captures solar energy and takes place in thylakoid membranes of chloroplasts; it produces ATP and NADPH. 86
 Chemical that hardens the cell walls of plants. 288
 In humans, functional association of various brain centers, including the amygdala and hippocampus; governs learning and memory and various emotions such as pleasure, fear, and happiness. 480
 Evolutionary line of descent. 328
 Alleles of different genes that are located on the same chromosome and tend to be inherited together. 154
 Fat-digesting enzyme secreted by the pancreas. 418
 Class of organic compounds that tends to be soluble in nonpolar solvents; includes fats and oils. 35
 Large, dark red internal organ that produces urea and bile, detoxifies the blood, stores glycogen, and produces the plasma proteins, among other functions. 418
 Type of fish(es) with limblike fins. 323
 Population increase that results in an S-shaped curve; growth is slow at first, steepens, and then levels off due to environmental resistance. 541
 Plant that flowers when day length is longer than a critical length; e.g., wheat, barley, clover, and spinach. 360
 Tissue composed mainly of fibroblasts widely separated by a matrix containing collagen and elastic fibers. 382
 Internal respiratory organs containing moist surfaces for gas exchange. 323, 422
 Second half of the ovarian cycle, during which the corpus luteum develops and much progesterone (and some estrogen) is produced. 517
 Fluid, derived from tissue fluid, that is carried in lymphatic vessels. 403
 Organs other than a lymphatic vessel that are part of the lymphatic system; the lymphatic organs are the lymph nodes, tonsils, spleen, thymus gland, and bone marrow. 456
 Organ system consisting of lymphatic vessels and lymphatic organs; transports lymph and lipids, and aids the immune system. 386, 403
 Vessel that carries lymph. 403
 Mass of lymphatic tissue located along the course of a lymphatic vessel. 457
 Specialized white blood cell that functions in specific defense; occurs in two forms—T lymphocytes and B lymphocytes. 406
 Bacteriophage life cycle in which the virus incorporates its DNA into that of a bacterium; occurs preliminary to the lytic cycle. 267
 Membrane-bounded vesicle that contains hydrolytic enzymes for digesting macromolecules. 58
 Bacteriophage life cycle in which the virus takes over the operation of the bacterium immediately upon entering it and subsequently destroys the bacterium. 267
M
 Large-scale evolutionary change, such as the formation of new species. 246
 Essential element needed in large amounts by plants and humans. In plants, nitrogen, calcium, and sulfur are needed for plant growth; in humans, carbohydrates, lipids, and proteins supply the body’s energy needs. 437
 In vertebrates, large phagocytic cell derived from a monocyte that ingests microbes and debris. 406, 457
 In seed plants, the gameto-phyte that produces sperm; a pollen grain. Sometimes called a microgametophyte. 364
 Blind, threadlike excretory tubule near the anterior end of an insect’s hindgut. 429
 Endothermic vertebrate characterized especially by the presence of hair and mammary glands. 326
 Congenital disorder of connective tissue characterized by abnormal length of the extremities. 203
 Member of a group of mammals bearing immature young nursed in a marsupium, or pouch—for example, kangaroo and opossum. 326
 Episode of large-scale extinction in which large numbers of species disappear in a few million years or less. 254
 Sum of the number of protons and neutrons in an atom’s nucleus. 17
 Connective tissue cell that releases histamine in allergic reactions. 458
 Unstructured semifluid substance that fills the space between cells in connective tissues or inside organelles. 61, 382
 Anything that takes up space and has mass. 16
 In vertebrates, part of the brain stem that is continuous with the spinal cord; controls heartbeat, blood pressure, breathing, and other vital functions. 479
 One of the two types of spores produced by seed plants; develops into a female gametophyte (embryo sac). 362, 364
 Type of nuclear division that occurs as part of sexual reproduction in which the daughter cells receive the haploid number of chromosomes in varied combinations. 129, 130
 Capacity of the brain to store and retrieve information about past sensations and perceptions; essential to learning. 480
 Cartilaginous wedges that separate the surfaces of bones in synovial joints. 506
 Termination of the ovarian and menstrual cycles in older women. 518
 Flow of blood during menstruation. 518
 Cycle that runs concurrently with the ovarian cycle; it prepares the uterus to receive a developing zygote. 518
 Periodic shedding of tissue and blood from the inner lining of the uterus in primates. 518
 Undifferentiated embryonic tissue in the active growth regions of plants. 341
 Middle primary tissue layer of an animal embryo that gives rise to muscle, several internal organs, and connective tissue layers. 526
 Inner, thickest layer of a leaf consisting of palisade and spongy mesophyll; the site of most of photosynthesis. 342
 Type of RNA formed from a DNA template and bearing coded information for the amino acid sequence of a polypeptide. 165
 Faithful copy of the sequence of bases in DNA. 167
 Series of linked reactions, beginning with a particular reactant and terminating with an end product. 75
 All of the chemical reactions that occur in a cell during growth and repair. 3
 Mitotic phase during which chromosomes are aligned at the spindle equator. 115
 Spread of cancer from the place of origin throughout the body; caused by the ability of cancer cells to migrate and invade tissues. 121, 190
 Type of archaea that lives in oxygen-free habitats, such as swamps, and releases methane gas. 275
 Change in gene frequencies between populations of a species over time. 232
 Essential element needed in small amounts by plants and humans. In plants, boron, copper, and zinc are needed for plant growth; in humans, vitamins and minerals help regulate metabolism and physiological development. 437
 One of the two types of spores produced by seed plants; develops into a male gametophyte (pollen grain). 362, 364
 Small, cylindrical organelle composed of tubulin protein around an empty central core; present in the cytoplasm, centrioles, cilia, and flagella. 62
 Cylindrical process that extends from an epithelial cell of a villus and serves to increase the surface area of the cell. 418
 Naturally occurring inorganic substance containing one or more elements; certain minerals are needed in the diet. As raw materials in the Earth, they are nonrenewable resources. 441, 586
 Hormones secreted by the adrenal cortex that regulate salt and water balance, leading to increases in blood volume and blood pressure. 487
 Membrane-bounded organelle in which ATP molecules are produced during the process of cellular respiration. 60
 Process in which a parent nucleus produces two daughter nuclei, each having the same number and kinds of chromosomes as the parent nucleus. 114
 Simulation of a process that aids conceptual understanding until the process can be studied firsthand; a hypothesis that describes how a particular process could possibly be carried out. 8
 Union of two or more atoms of the same element; also, the smallest part of a compound that retains the properties of the compound. 19
 Periodic shedding of the exoskeleton in arthropods. 316
 Abbreviation of monocotyledon. Flowering plant group; members have one embryonic leaf (cotyledon), parallel-veined leaves, scattered vascular bundles, flower parts in threes or multiples of three, and other characteristics. 340
 Type of a granular leukocyte that functions as a phagocyte, particularly after it becomes a macrophage.  406
 Small molecule that is a subunit of a polymer—e.g., glucose is a monomer of starch. 32
 Simple sugar; a carbohydrate that cannot be decomposed by hydrolysis—e.g., glucose. 33
 Egg-laying mammal—e.g., duckbill platypus and spiny anteater. 326
 Country that is industrialized; typically, population growth is low, and the people enjoy a good standard of living. 535
 Spherical mass of cells resulting from cleavage during animal development prior to the blastula stage. 525
 Concept that human characteristics did not evolve at the same rate; for example, some body parts are more humanlike than others in early hominids. 330
 Nerve cell that conducts nerve impulses away from the central nervous system and innervates effectors (muscle and glands). 474
 In humans, organ of the digestive tract where food is chewed and mixed with saliva. 415
Organism composed of many cells; usually has organized tissues, organs, and organ systems. 2
 Trait controlled by polygenes subject to environmental influences; each dominant allele contributes to the phenotype in an additive and like manner. 150
 Proposal that modern humans evolved separately in at least three different places: Asia, Africa, and Europe. 331
 Mental state where a person thinks his or her body is underdeveloped, and becomes preoccupied with body-building and diet; affects more men than women. 448
 Proprioceptor wrapped around a few muscle cells within a connective tissue sheath; can respond to changes in muscle length. 501
 System of muscles that produces movement, both within the body and of its limbs; principal components are skeletal muscle, smooth muscle, and cardiac muscle. 387
 Type of animal tissue composed of fibers that shorten and lengthen to produce movements. 384
 Agent, such as radiation or a chemical, that brings about a mutation in DNA. 172
 Alternation in chromosome structure or number and also an alteration in a gene due to a change in DNA composition. 235
 Symbiotic relationship in which both species benefit in terms of growth and reproduction. 556
 Tangled mass of hyphal filaments composing the vegetative body of a fungus. 296
 Mutualistic relationship between fungal hyphae and roots of vascular plants. 299, 348
 White, fatty material—derived from the membranes of tightly spiraled cells—that forms a covering for nerve fibers. 474
 Specific muscle cell organelle containing a linear arrangement of sarcomeres, which shorten to produce muscle contraction. 505
 Muscle protein making up the thick filaments in a sarcomere; it pulls actin to shorten the sarcomere, yielding muscle contraction. 505
N
 One of two canals in the nose, separated by a septum. 422
 Indigenous species that colonize an area without human assistance. 559
 The study of how organisms are influenced by factors such as climate, predation, competition, and evolution; uses field observations instead of experimentation. 547
 Lymphocyte that causes an infected or cancerous cell to burst. 459
 Mechanism of evolution caused by environmental selection of organisms most fit to reproduce; results in adaptation to the environment. 4, 221, 238
 Hominid with a sturdy build that lived during the last Ice Age in Europe and the Middle East; hunted large game and left evidence of being culturally advanced. 332
 Mechanism of homeostatic response by which the output of a system suppresses or inhibits activity of the system. 
389, 486
 In cnidarians, a capsule that contains a threadlike fiber, the release of which aids in the capture of prey. 311
 Segmentally arranged, paired excretory tubules of many invertebrates, as in the earthworm. 315
 Microscopic kidney unit that regulates blood composition by filtration, reabsorption, and secretion. 427
 Cuplike structure that is the initial portion of a nephron. 428
 Portion of a nephron between the proximal and distal tubules; functions in water reabsorption. 428
 Bundle of long axons outside the central nervous system. 385, 480
 Deafness due to spiral organ damage. 497
 Organ system consisting of the brain, spinal cord, and associated nerves that coordinates the other organ systems of the body. 387
 Tissue that contains nerve cells (neurons), which conduct impulses, and neuroglia, which support, protect, and provide nutrients to neurons. 385
 Region of the dorsal surface of the chordate embryo that marks the future location of the neural tube. 526
 Tube formed by closure of the neural groove during development. In vertebrates, the neural tube develops into the spinal cord and brain. 526
 Nonconducting nerve cells that are intimately associated with neurons and function in a supportive capacity. 385
 Nerve cell that characteristically has three parts: dendrites, cell body, and an axon. 
385, 474
 Chemical stored at the ends of axons that is responsible for transmission across a synapse. 476
 Development of the central nervous system organs in an embryo. 526
 Neutral subatomic particle, located in the nucleus and assigned one atomic mass unit. 17
 Granular leukocyte that is the most abundant of the white blood cells; first to respond to infection. 406, 458
 In plants, the place where one or more leaves attach to a stem. 339
 Failure of homologous chromosomes or daughter chromosomes to separate during meiosis I and meiosis II, respectively. 136
 Mating among individuals on the basis of their phenotypic similarities or differences, rather than mating on a random basis. 236
 Minerals, fossil fuels, and other materials present in essentially fixed amounts (within human time scale) in our environment. 576
 Bryophytes such as mosses that have no vascular tissue and either occur in moist locations or have special adaptations for living in dry locations. 287
 Neurotransmitter of the postganglionic fibers in the sympathetic division of the autonomic system; also, a hormone produced by the adrenal medulla. 476, 487
 Cartilaginous-like supportive dorsal rod in all chordates sometime in their life cycle; replaced by vertebrae in vertebrates. 320, 526
 Double membrane that surrounds the nucleus in eukaryotic cells and is connected to the endoplasmic reticulum; has pores that allow substances to pass between the nucleus and the cytoplasm. 57
 Opening in the nuclear envelope that permits the passage of proteins into the nucleus and ribosomal subunits out of the nucleus. 57
 Enzyme that catalyzes decomposition of nucleic acids. 418
 Polymer of nucleotides; both DNA and RNA are nucleic acids. 41
 Region of prokaryotic cells where DNA is located; it is not bounded by a nuclear envelope. 51, 271
 Dark-staining, spherical body in the nucleus that produces ribosomal subunits. 56
 In the nucleus of a eukaryotic cell, a unit composed of DNA wound around a core of eight histone proteins, giving the appearance of a string of beads. 113 
 Monomer of DNA and RNA consisting of a 5-carbon sugar bonded to a nitrogenous base and a phosphate group. 41
 Membrane-bounded organelle within a eukaryotic cell that contains chromosomes and controls the structure and function of the cell. 17, 54
 Chemical substances in foods that are essential to the diet and contribute to good health. 436
 The Council on Food and Nutrition of the American Medical Association defines nutrition as “the science of food; the nutrients and the substances therein; their action, interaction, and balance in relation to health and disease; and the process by which the organism (i.e., body) ingests, digests, absorbs, transports, utilizes, and excretes food substances.” 436
O
 Characterized by excess adipose tissue; exceeding desirable weight by more than 20%. 439 Step in the scientific method by which data are collected before a conclusion is drawn. 8
 States that an atom other than hydrogen tends to form bonds until it has eight electrons in its outer shell; an atom that already has eight electrons in its outer shell does not react and is inert. 19
 Triglyceride, usually of plant origin, that is composed of glycerol and three fatty acids and is liquid in consistency due to many unsaturated bonds in the hydrocarbon chains of the fatty acids. 35
 Organism in a food chain that feeds on both plants and animals. 415, 560
 Cancer-causing gene. 189
 Production of eggs in females by the process of meiosis and maturation. 129
Circulatory system, such as that found in a grasshopper, where a tubular heart pumps hemolymph through channels and body cavities. 396
 Group of structural and regulating genes that function as a single unit. 182
 Population demonstrating a life history pattern in which members exhibit exponential population growth. Its members are small in size, mature early, have a short life span, produce many offspring, and provide little or no care to offspring (e.g., dandelions). 544
 One of the categories, or taxa, used by taxonomists to group species; the taxon above the family level. 6, 256
 Combination of two or more different tissues performing a common function. 2
 Small, often membranous structure in the cytoplasm having a specific structure and function. 54
Molecule that always contains carbon and hydrogen, and often contains oxygen as well; organic molecules are associated with living things. 30
The study of carbon compounds; chemistry of the living world. 30
 Individual living thing. 2, 30, 546
 Group of related organs working together. 2
 Physiological and psychological sensations that occur at the climax of sexual stimulation. 515
 Diffusion of water through a differentially permeable membrane. 77
 Bone-forming cell. 504
 Cell that causes erosion of bone. 504
 Cylindrical-shaped unit containing bone cells that surround an osteonic canal; also called Haversian system. 504 
 Condition in which bones break easily because calcium is removed from them faster than it is replaced. 504
 Proposal that modern humans originated only in Africa; then they migrated and supplanted populations of Homo in Asia and Europe about 100,000 years ago. 331
 Female gonad in animals that produces an egg and female sex hormones; in flowering plants, the enlarged, ovule-bearing portion of the carpel that develops into a fruit. 292, 363, 512
 Bursting of a follicle when a secondary oocyte is released from the ovary; if fertilization occurs, the secondary oocyte becomes an egg. 517
 In seed plants, a structure that contains the female gametophyte and has the potential to develop into a seed. 290, 363
 Amount of oxygen needed to metabolize lactate, a compound that accumulates during vigorous exercise. 107
 Hormone released by the posterior pituitary that causes contraction of uterus and milk letdown. 484
P
 Study of fossils that results in knowledge about the history of life. 253
 Layer of tissue in a plant leaf containing elongated cells with many chloroplasts. 342
 Internal organ that produces digestive enzymes and the hormones insulin and glucagon. 418, 487
 Enzyme that digests starch to maltose. 418
 Masses of cells that constitute the endocrine portion of the pancreas. 487
 Similarity in structure in related groups that cannot be traced to a common ancestor. 257
Symbiotic relationship in which one species (the ) benefits in terms of growth and reproduction to the detriment of the other species (the ). 556
 Division of the autonomic system that is active under normal conditions; uses acetylcholine as a neurotransmitter. 482
 Gland embedded in the posterior surface of the thyroid gland; it produces parathyroid hormone. 486
 Hormone secreted by the four parathyroid glands that increases the blood calcium level and decreases the phosphate level. 486
 Plant tissue composed of the least-specialized of all plant cells; found in all organs of a plant. 341
 Development of an egg cell into a whole organism without fertilization. 512
 Protection against infection acquired by transfer of antibodies to a susceptible individual. 464
 Disease-causing agent such as viruses, parasitic bacteria, fungi, and animals. 274
 Chart showing the relationships of relatives and which ones have a particular trait. 200
 Latent infection of gonorrhea or chlamydia in the vasa deferentia or uterine tubes. 523
 Male copulatory organ; in humans, the male organ of sexual intercourse. 514
 Enzyme secreted by gastric glands that digests proteins to peptides. 417
 Two or more amino acids joined together by covalent bonding. 40
 Type of covalent bond that joins two amino acids. 39
 Type of hormone that is a protein, a peptide, or derived from an amino acid. 484
 Unique molecule found in bacterial cell walls. 271
 Flowering plant that lives more than one growing season because the underground parts regrow each season. 339
 Layer of cells surrounding the vascular tissue of roots; produces branch roots. 347
 Nerves and ganglia that lie outside the central nervous system. 473
 Wavelike contractions that propel substances along a tubular structure such as the esophagus. 416
 Flower part that occurs just inside the sepals; often conspicuously colored to attract pollinators. 292, 363
 Part of a plant leaf that connects the blade to the stem. 338
Hydrogen ion concentration. 26
 Process by which amoeboid-type cells engulf large substances, forming an intracellular vacuole. 79
 In vertebrates, common passageway for both food intake and air movement; located between the mouth and the esophagus. 
416, 423
 Visible expression of a genotype—e.g., brown eyes or attached earlobes. 145
 Result of accumulation of phenylalanine characterized by mental retardation, light pigmentation, eczema, and neurological manifestations unless treated by a diet low in phenylalanine. 202
Vascular tissue that conducts organic solutes in plants; contains sieve-tube members and companion cells. 288, 340
 Molecule that forms the   of plasma membranes has a polar, hydrophilic head bonded to two nonpolar, hydrophobic tails. 36
 Organism able to synthesize organic molecules by using carbon dioxide as the carbon source and sunlight as the energy source. 272
 Relative lengths of daylight and darkness that affect the physiology and behavior of an organism. 360
 Sensory receptor that responds to light stimuli. 499
 Process occurring usually within chloroplasts whereby chlorophyll-containing organelles trap solar energy to reduce carbon dioxide to carbohydrate. 3, 84
 Photosynthetic unit where solar energy is absorbed and high-energy electrons are generated; contains a pigment complex and an electron acceptor; occurs as PS (photosystem) I and PS II. 88
 Growth response of plant stems to light; stems demonstrate positive phototropism. 360
 Energy-conversion device that captures solar energy and directly converts it to electrical current. 585
 Measurement scale for hydrogen ion concentration. 26
 Diagram that indicates common ancestors and lines of descent among a group of organisms. 256
 Evolutionary history of a group of organisms. 256
 One of the categories, or taxa, used by taxonomists to group species; the taxon above the class level. 6, 256
 Photoreversible plant pigment that is involved in photoperiodism and other responses of plants, such as etiolation. 361
 Process by which vesicle formation brings macromolecules into the cell. 79
 Parenchyma tissue in the center of some stems and roots. 347
 Small gland that lies just inferior to the hypothalamus; consists of the anterior and posterior pituitary, both of which produce hormones. 484
 Organ formed during the development of placental mammals from the chorion and the uterine wall; allows the embryo, and then the fetus, to acquire nutrients and rid itself of wastes; produces hormones that regulate pregnancy. 513
 Mammal characterized by the presence of a placenta during the development of an offspring. 327
 Free-living flatworm with a ladder-like nervous system. 311
 Multicellular, usually photosynthetic, organism belonging to the plant kingdom. 6
 Accumulation of soft masses of fatty material, particularly cholesterol, beneath the inner linings of the arteries. 404
 In vertebrates, the liquid portion of blood; contains nutrients, wastes, salts, and proteins. 405
 Membrane surrounding the cytoplasm that consists of a phospholipid bilayer with embedded proteins; functions to regulate the entrance and exit of molecules from cell. 52
 Self-duplicating ring of accessory DNA in the cytoplasm of bacteria. 271
 In plants, cytoplasmic strands that extend through pores in the cell wall and connect the cytoplasm of two adjacent cells. 64
 Contraction of the cell contents due to the loss of water. 78
 Component of blood that is necessary to blood clotting. 383, 406
 Inheritance pattern in which one gene affects many phenotypic characteristics of the individual. 151
 Alteration in a gene due to a change in a single nucleotide; results of this mutation vary. 172
 In chemistry, bond in which the sharing of electrons between atoms is unequal. 22
 In seed plants, structure that is derived from a microspore and develops into a male gametophyte. 290, 364
 In seed plants, a tube that forms when a pollen grain lands on the stigma and germinates. The tube grows, passing between the cells of the stigma and the style to reach the egg inside an ovule, where fertilization occurs. 293
 In gymnosperms, the transfer of pollen from pollen cone to seed cone; in angiosperms, the transfer of pollen from anther to stigma. 290, 365
 Any environmental change that adversely affects the lives and health of living things. 576
 Pattern of inheritance in which a trait is controlled by several allelic pairs; each dominant allele contributes to the phenotype in an additive and like manner. 150
 Macromolecule consisting of covalently bonded monomers; for example, a polypeptide is a polymer of monomers called amino acids. 32
 Technique that uses the enzyme DNA polymerase to produce millions of copies of a particular piece of DNA. 174
 Genes that have more than one wild-type allele. 241
 Small, abnormal growth that arises from the epithelial lining. 420
 Polymer of many amino acids linked by peptide bonds. 40
 String of ribosomes simultaneously translating regions of the same mRNA strand during protein synthesis. 57, 169
 Polymer made from sugar monomers; the polysaccharides starch and glycogen are polymers of glucose monomers. 34
 Group of organisms of the samespecies occupying a certain area and sharing a common gene pool. 5, 232, 546
 The number of individuals per unit area or volume living in a particular habitat. 538
 Pathway of blood flow that begins and ends in capillaries, such as the portal system located between the small intestine and liver. 403
 Portion of the pituitary gland that stores and secretes oxytocin and antidiuretic hormone produced by the hypothalamus. 485
 Anatomical or physiological difference between two species that prevents successful reproduction after mating has taken place. 249
 Stored energy as a result of location or spatial arrangement. 70
 Interaction in which one organism (the predator) uses another (the prey) as a food source. 543, 556
 Association area in the frontal lobe that receives information from other association areas and uses it to reason and plan actions. 479
 Reaction that oxidizes pyruvate with the release of carbon dioxide; results in acetyl CoA and connects glycolysis to the citric acid cycle. 99, 102
 Explanation for phloem transport; osmotic pressure following active transport of sugar into phloem brings a flow of sap from a source to a sink. 350
 Anatomical or behavioral difference between two species that prevents the possibility of mating. 248
 Area in the frontal lobe where voluntary commands begin; each section controls a part of the body. 478
 Amount of biomass produced primarily by photosynthesizers. 570
 Area located in the parietal lobe where sensory information arrives from the skin and skeletal muscles. 478
 Stage in ecological succession, which involves the creation of new soil. 554 Theory that is generally accepted by an overwhelming number of scientists; also called a law. 9
 Infectious particle consisting of protein only and no nucleic acid. 270
 Photosynthetic organism at the start of a grazing food chain that makes its own food—e.g., green plants on land and algae in water. 560
 Substance that forms as a result of a reaction. 21
 Female sex hormone that helps maintain sexual organs and secondary sex characteristics. 518
 Organism that lacks the membrane-bounded nucleus and membranous organelles typical of eukaryotes. 270
 Lacking a membrane-bounded nucleus and organelles; the cell type within the domains Bacteria and Archaea. 50
 Hormone secreted by the anterior pituitary that stimulates the production of milk from the mammary glands. 484
 In an operon, a sequence of DNA where RNA polymerase binds prior to transcription. 167
 Mitotic phase during which chromatin condenses so that chromosomes appear; chromosomes are scattered. 115
 Sensory receptor that assists the brain in knowing the position of the limbs. 501
 Group of primates that includes lemurs and tarsiers, and may resemble the first primates to have evolved. 328
 Gland located around the male urethra below the urinary bladder; adds secretions to semen. 515
 Molecule consisting of one or more polypeptides; a macronutrient in the diet that is digested to amino acids used by cells to synthesize cellular proteins. 38, 440
Collection of proteins resulting from the translation of genes into proteins. 209
Study of the structure, function, and interaction of proteins. 209
 Member of the kingdom Protista. 6, 276
 Positive subatomic particle located in the nucleus and assigned one atomic mass unit. 17
 Normal gene that can become an oncogene through mutation. 189
 Group of coelomate animals in which the first embryonic opening (the blastopore) is associated with the mouth. 313
 Heterotrophic, unicellular protist that moves by flagella, cilia, or pseudopodia, or is immobile. 276
 Portion of a nephron following the nephron capsule where reabsorption of filtrate occurs. 428
 Body cavity lying between the digestive tract and body wall that is incompletely lined by mesoderm. 309
 Cytoplasmic extension of amoeboid protists; used for locomotion and engulfing food. 278
 Period of life when secondary sex changes occur in humans; marked by the onset of menses in females and sperm production in males. 516
 Blood vessel that takes blood away from the heart to the lungs. 399
 Circulatory pathway between the lungs and the heart. 398
 Large blood vessel that divides into the pulmonary arteries; takes blood away from the heart to the lungs. 399 
 Blood vessel that takes blood to the heart from the lungs. 399
 Vibration felt in arterial walls due to expansion of the aorta following ventricle contraction. 400
 Grid used to calculate the expected results of simple genetic crosses. 144
 Opening in the center of the iris of the vertebrate eye. 499
R
 Body plan in which similar parts are arranged around a central axis, like spokes of a wheel. 308
 Protozoan; marine amoeba having a calcium carbonate skeleton, many of which make limestone formations such as the White Cliffs of Dover. 278
Spatial distribution of individuals in a population in which individuals have an equal chance of living anywhere within an area. 538
 That portion of the globe where a certain species can be found. 538
 Group of bony fishes with fins supported by parallel bony rays connected by webs of thin tissue. 322
 Movement of primarily nutrient molecules and water from the contents of the nephron into blood at the proximal tubule. 428
 Substance that participates in a reaction. 21
 Area where a flower attaches to a floral stalk. 362
 Selective uptake of molecules into a cell by vacuole formation after they bind to specific receptor proteins in the plasma membrane. 79
 Allele that exerts its phenotypic effect only in the homozygote; its expression is masked by a dominant allele. 145
 DNA that contains genes from more than one source. 173
New combination of alleles incorporated into a gamete during crossing-over. 154
 Marine photosynthetic protist with a notable abundance of phycobilin pigments; includes coralline algae of coral reefs. 277
 Erythrocyte; contains hemoglobin and carries oxygen from the lungs or gills to the tissues in vertebrates. 383, 405
 Vascularized, modified connective tissue that is sometimes found in the cavities of spongy bone; site of blood cell formation. 457, 504
 Automatic, involuntary response of an organism to a stimulus. 481
 Ability of sponges and echinoderms to “generate” into another organism if separated into pieces. 512
 In an operon, a gene that codes for a protein that regulates the expression of other genes. 183
 Outer portion of the kidney that appears granular. 427
 Inner portion of the kidney that consists of renal pyramids. 427
 Hollow chamber in the kidney that lies inside the renal medulla and receives freshly prepared urine from the collecting ducts. 427
 Resources normally replaced or replenished by natural processes; resources not depleted by moderate use. Examples include solar energy, biological resources, such as forests and fisheries, biological organisms, and some biogeo-chemical cycles. 576
 In an operon, protein molecule that binds to an operator, preventing transcription of structural genes. 183
 To produce a new individual of the same kind. 3
 Genetically identical to the original individual. 180
 Organ system that contains male or female organs and specializes in the production of offspring. 387
 Member of a class of terrestrial invertebrates with internal fertilization, scaly skin, and an egg with a leathery shell; includes snakes, lizards, turtles, and crocodiles. 324
 In economic terms, anything with potential use in creating wealth or giving satisfaction. 538
 Mechanism that increases the number of niches by apportioning the supply of a resource such as food or living space between species. 557
 Sequence of events that results in gas exchange between the cells of the body and the environment. 422
 Organ system consisting of the lungs and tubes that bring oxygen into the lungs and take carbon dioxide out. 386
 Bacterial enzyme that stops viral reproduction by cleaving viral DNA; used to cut DNA at specific points during production of recombinant DNA. 173
 Innermost layer of the vertebrate eyeball containing the photoreceptors—rods and cones. 499
 RNA virus containing the enzyme reverse transcriptase that carries out RNA/DNA transcription. 268
 Light-absorbing molecule in rods and cones that contains a pigment and the protein opsin. 500
 Pentose sugar found in RNA. 33
 Type of RNA found in ribosomes that translate messenger RNAs to produce proteins. 165
 RNA and protein in two subunits; site of protein synthesis in the cytoplasm. 51, 
56, 165
 Nucleic acid produced from covalent bonding of nucleotide monomers that contain the sugar ribose; occurs in three forms: messenger RNA, ribosomal RNA, and transfer RNA. 41, 164
 During transcription, an enzyme that joins nucleotides complementary to a DNA template. 167
Photoreceptor in vertebrate eyes that responds to dim light. 500
 Protective cover of the root tip, whose cells are constantly replaced as they are ground off when the root pushes through rough soil particles. 347
 Extension of a root epidermal cell that collectively increases the surface area for the absorption of water and minerals. 339
 Structure on plant root that contains nitrogen-fixing bacteria. 348
 Includes the main root and any and all of its lateral (side) branches. 338
 Maintenance of balance when the head and body are suddenly moved or rotated. 498
 Membranous system of tubules, vesicles, and sacs in cells; has attached ribosomes. 58
 Member of the phylum Nematoda with a cylindrical body that has a complete digestive tract and a pseudocoelom; some forms are free-living in water and soil, and many are parasitic. 312
 Enzyme that is required for carbon dioxide fixation (atmospheric CO2 attaches to RuBP) in the Calvin cycle. 90
The chance of two (or more) independent events occurring together is the product of their chance occurring separately. 147
S
 Saclike cavity in the vestibule of the vertebrate inner ear; contains sensory receptors for gravitational equilibrium. 498
 Process in which mineral salts accumulate in the soil, killing plants; occurs when soils in dry climates are irrigated profusely. 581
 In humans, enzyme in saliva that digests starch to maltose. 416
 In humans, gland associated with the mouth that secretes saliva. 416
 Compound produced by a reaction between an acid and a base. 20
 Movement of nerve impulses from one neurofibral node to another along a myelinated axon. 475
 Movement of saltwater into freshwater aquifers in coastal areas where groundwater is withdrawn faster than it is replenished. 579
 Small region of neuromuscular tissue that initiates the heartbeat; also called the pacemaker. 400
 Organism that secretes digestive enzymes and absorbs the resulting nutrients back across the plasma membrane. 272, 298
 One of many units, arranged linearly within a myofibril, whose contraction produces muscle contraction. 505
 Fatty acid molecule that lacks double bonds between the carbons of its hydrocarbon chain. The chain bears the maximum number of hydrogens possible. 36
 Concept supported by a broad range of observations, experiments, and data. 9
 Plant tissue composed of cells with heavily lignified cell walls; functions in support. 341
 Trait that is sometimes helpful but not absolutely necessary for reproduction and is maintained by the sex hormones in males and females. 516
 In ecological succession, the stage which is the gradual replacement of communities in an area following a disturbance. 554
 In the cell, release of a substance by exocytosis from a cell that may be a gland or part of a gland; in the urinary system, movement of certain molecules from blood into the distal tubule of a nephron so that they are added to urine. 58, 428
 Mature ovule that contains an embryo, with stored food enclosed in a protective coat. 
285, 366
 Repetition of body units as seen in the earthworm. 309
 Thick, whitish fluid consisting of sperm and secretions from several glands of the male reproductive tract. 515
Duplication of DNA resulting in two double helix molecules, each having one parental and one new strand. 164
 Valve resembling a half moon located between the ventricles and their attached vessels. 399
 Convoluted, saclike structure attached to the vas deferens near the base of the urinary bladder in males; adds secretions to semen. 515
 Long, coiled structure contained within chambers of the testis where sperm are produced. 515
 Sum of the processes involving aging, decline, and eventual death of a plant or plant part. 358
 Nerve cell that transmits nerve impulses to the central nervous system after a sensory receptor has been stimulated. 474
 Outermost leaflike covering of the flower; usually green in color. 292, 363
 Partition or wall that divides two areas; the septum in the heart separates the right half from the left half. 399
 Chromosome that determines the sex of an individual; in humans, females have two X chromosomes, and males have an X and a Y chromosome. 129
 In a bacterium, elongated, hollow appendage used to transfer DNA to other cells. 51
 Changes in males and females, often due to male competition and female selectivity, leading to increased fitness. 236
 Aboveground portion of a plant consisting of the stem, leaves, and flowers. 338
 Plant that flowers when day length is shorter than a critical length—e.g., cocklebur, poinsettia, and chrysanthemum. 360
 Portion of the vertebrate skeleton that provides support and attachment for the upper (fore) limbs; consists of the scapula and clavicle on each side of the body. 503
sickle cell disease Hereditary disease in which red blood cells are narrow and curved so that they are unable to pass through capillaries and are destroyed; causes chronic anemia. 203
 Member that joins with others in the phloem tissue of plants as a means of transport for nutrient sap. 342
Molecule that stimulates or inhibits an event in the cell cycle. 119 
 Activation and inhibition of intracellular targets after binding of growth factors. 187
 Movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution. 77 
 Condition in which an enlarged thyroid produces low levels of thyroxine. 486
 Cavity or hollow space in an organ such as the skull. 422
 One of two genetically identical chromosomal units that are the result of DNA replication and are attached to each other at the centromere. 113
 Striated, voluntary muscle tissue that comprises skeletal muscles; also called striated muscle. 384
 System of bones, cartilage, and ligaments that works with the muscular system to protect the body and provide support for locomotion and movement. 387
 An explanation for muscle contraction based on the movement 
of actin filaments in relation to myosin filaments. 505
 Protists that decompose dead material and feed on bacteria by phagocytosis; vegetative state is mobile and amoeboid. 279
 In vertebrates, the portion of the digestive tract that precedes the large intestine; in humans, consists of the duodenum, jejunum, and ileum. 418
  Membranous system of tubules, vesicles, and sacs in eukaryotic cells; lacks attached ribosomes. 58
 Nonstriated, involuntary muscles found in the walls of internal organs. 384
 Carrier protein in the plasma membrane that moves sodium ions out of and potassium ions into animal cells; important in nerve and muscle cells. 79
 Substance that is dissolved in a solvent, forming a solution. 77
 Fluid (the solvent) that contains a dissolved solid (the solute). 77
 Liquid portion of a solution that serves to dissolve a solute. 77
 Body cell; excludes cells that undergo meiosis and become sperm or egg. 120
 Portion of the peripheral nervous system containing motor neurons that control skeletal muscles. 481
 Origin of new species due to the evolutionary process of descent with modification. 220, 246
 Group of similarly constructed organisms capable of interbreeding and producing fertile offspring; organisms that share a common gene pool; the taxon at the lowest level of classification. 4, 6, 256
 List of difference species in a community. 553
 In the binomial system of taxonomy, the second part of an organism’s name; it may be descriptive. 256
 Production of sperm in males by the process of meiosis and maturation. 129
In vertebrates, the nerve cord that is continuous with the base of the brain and housed within the vertebral column. 478
 Nerves that arises from the spinal cord. 481
 Microtubule structure that brings about chromosomal movement during nuclear division. 115
 Disk formed during metaphase in which all of a cell’s chromosomes lie in a single plane at right angles to the spindle fibers. 115
 Structure in the vertebrate inner ear that contains auditory receptors (also called organ of Corti). 496
 Large, glandular organ located in the upper left region of the abdomen; stores and purifies blood. 457
 Invertebrate animal of the phylum Porifera; pore-bearing filter feeder whose inner body wall is lined by collar cells. 310
 Type of bone that has an irregular, meshlike arrangement of thin plates of bone. 504
 Layer of tissue in a plant leaf containing loosely packed cells, increasing the amount of surface area for gas exchange. 342
 Asexual reproductive or resting cell capable of developing into a new organism without fusion with another cell, in contrast to a gamete. 286
 Diploid generation of the alternation of generations life cycle of a plant; produces haploid spores that develop into the haploid generation. 286, 362
 Spore-forming protist that has no means of locomotion and is typically a parasite with a complex life cycle having  Outcome of natural selection in which extreme phenotypes are eliminated and the average phenotype is conserved. 240
 In flowering plants, the portion of the flower that consists of a filament and an anther containing pollen sacs where pollen is produced. 292, 363
 Storage polysaccharide found in plants that is composed of glucose molecules joined in a linear fashion with few side chains. 34
 Gravitational equilibrium organ found in some invertebrates; give information about head position. 498 Usually the upright, vertical portion of a plant that transports substances to and from the leaves. 339
 Type of lipid molecule having a complex of four carbon rings—e.g., cholesterol, estrogen, progesterone, and testosterone. 37
 Type of hormone that has the same complex of four carbon rings, but each one has different side chains. 483
 In flowering plants, portion of the carpel where pollen grains adhere and germinate before fertilization can occur. 292, 363
 Small opening between two guard cells on the underside of leaf epidermis through which gases pass. 85, 341
 In vertebrates, muscular sac that mixes food with gastric juices to form chyme, which enters the small intestine. 417
 Having bands; in cardiac and skeletal muscle, alternating light and dark bands produced by the distribution of contractile proteins. 384
 Condition resulting when an arteriole in the brain bursts or becomes blocked by an embolism; cerebrovascular accident. 404
 Fluid within a chloroplast that contains enzymes involved in the synthesis of carbohydrates during photosynthesis. 60, 85
 Elongated, central portion of the carpel between the ovary and stigma. 292, 363
 Occurs when a portion of the Earth’s surface gradually settles downward. 579
 Reactant in a reaction controlled by an enzyme. 75
 Ratio of a cell’s outside area to its internal volume. 49
 Probability of newborn individuals of a cohort surviving to particular ages. 539
 Ability of a society or ecosystem to maintain itself while also providing services to human beings. 592
 Relationship that occurs when two different species live together in a unique way; it may be beneficial, neutral, or detrimental to one and/or the other species. 273
 Division of the autonomic system that is active when an organism is under stress; uses norepinephrine as a neurotransmitter. 482
Origin of new species in populations that overlap geographically. 250
 Junction between neurons consisting of the axon membrane, the synaptic cleft, and a dendrite. 476
 Pairing of homologous chromosomes during meiosis I. 130
 Small gap between membranes of a synapse. 476
 Freely moving joint in which two bones are separated by a cavity. 506
Study of the diversity of organisms to classify them and determine their evolutionary relationships. 256
 Circulatory pathway of blood flow between the tissues and the heart. 398, 402
 Contraction period of the heart during the cardiac cycle. 400
T
 Structures in the vertebrate mouth containing sensory receptors for taste; in humans, most taste buds are on the tongue. 495
 Group of organisms that fills a particular classification category. 256
 Branch of biology concerned with identifying, describing, and naming organisms. 6, 256
Tay-Sachs disease Lethal genetic disease in which the newborn has a faulty lysosomal digestive enzyme. 202
 Receptor on the T cell surface consisting of two antigen-binding peptide chains; it is associated with a large number of other glycoproteins. Binding of antigen to the TCR, usually in association with MHC, activates the T cell. 462
Long, repeating DNA sequence at the ends of chromosomes; function like a cap and chromosomes from fusing with each other. 
120, 190
Mitotic phase during which daughter cells are located at each pole. 115
 Parental strand of DNA that serves as a guide for the complementary daughter strand produced during DNA replication. 164
 Strap of fibrous connective tissue that connects skeletal muscle to bone. 382
 Bud that develops at the apex of a shoot. 338
 Also called biomes, these are the tundra, the taiga, temperate forests, tropical grasslands (savanna), temperate grasslands (prairie), deserts, and tropical rain forests. 568
 Cross between an individual with the dominant phenotype and an individual with the recessive phenotype. The resulting phenotypic ratio indicates whether the dominant phenotype is homozygous or heterozygous. 144
 Male gonad that produces sperm and the male sex hormones. 512, 514
 Male sex hormone that helps maintain sexual organs and secondary sex characteristics. 516
 Severe twitching caused by involuntary contraction of the skeletal muscles due to a calcium imbalance. 486
 Homologous chromosomes, each having sister chromatids that are joined during meiosis; also called bivalent. 130
 In vertebrates, the portion of the diencephalon that passes on selected sensory information to the cerebrum. 479
 Used to create mature cells of various cell types. Also, used to learn about specialization of cells and provide cells and tissue to treat human illnesses. 181
 Type of archaea that lives in hot, acidic, aquatic habitats, such as hot springs or near hydrothermal vents. 275
 Located in the ventral cavity above the abdominal cavity and is separated from the abdominal cavity by the diaphragm; contains the heart and the lungs. 416
 System of classification that recognizes three domains: Bacteria, Archaea, and Eukarya. 261
 Enzyme that converts fibrinogen to fibrin threads during blood clotting. 407
 Flattened sac within a granum whose membrane contains chlorophyll and where the light reactions of photosynthesis occur. 60, 85
  One of four nitrogen-containing bases in nucleotides composing the structure of DNA; pairs with adenine. 161
 Lymphatic organ involved in the development and functioning of the immune system; T cells mature in the thymus gland. 457
 Large gland in the neck that produces several important hormones, including thyroxine, triiodothyronine, and calcitonin. 486
 Substance produced by the anterior pituitary that causes the thyroid to secrete thyroxine and triiodothyronine. 484
 Hormone secreted from the thyroid gland that promotes growth and development; in general, it increases the metabolic rate in cells. 486
 Junction between cells when adjacent plasma membrane proteins join to form an impermeable barrier. 65
 Group of similar cells combined to perform a common function. 2, 378
 Process of growing tissue artificially, usually in a liquid medium in laboratory glassware. 369
 Fluid that surrounds the body’s cells; consists of dissolved substances that leave the blood capillaries by filtration and diffusion. 386
 Lymphocyte that matures in the thymus and exists in four varieties, one of which kills antigen-bearing cells outright. 457
 Partially encapsulated lymph nodules located in the pharynx. 456
 Cell that has the full genetic potential of the organism, including the potential to develop into a complete organism. 369
 Substance having an attached radioactive isotope that allows a researcher to track its whereabouts in a biological system. 18
 In tetrapod vertebrates, air tube (windpipe) that runs between the larynx and the bronchi. 423
 In vascular plants, type of cell in xylem that has tapered ends and pits through which water and minerals flow. 342
 Bundles of myelinated axons in the central nervous system. 478
 School of systematics that takes into consideration the degree of difference between derived characters to construct phylogenetic trees. 256 
 Process whereby a DNA strand serves as a template for the formation of mRNA. 166
 Protein that speeds transcription. 186
 In eukaryotes, protein required for the initiation of transcription by RNA polymerase. 186
 Exchange of DNA between bacteria by means of a bacteriophage. 272
 Amount of a substance that moves from one component of the environment to another within a specified period of time. 565
 Type of RNA that transfers a particular amino acid to a ribosome during protein synthesis; at one end, it binds to the amino acid, and at the other end it has an anticodon that binds to an mRNA codon. 165
 Taking up of extraneous genetic material from the environment by bacteria. 272
 Free-living organism in the environment that has had a foreign gene inserted into it. 173
 Plant that carries the genes of another organism as a result of DNA technology; also genetically modified plant. 371
 Process whereby ribosomes use the sequence of codons in mRNA to produce a polypeptide with a particular sequence of amino acids. 166
 Movement of a chromosomal segment from one chromosome to another nonhomologous chromosome, leading to abnormalities—e.g., Down syndrome. 170, 199
 Plant’s loss of water to the atmosphere, mainly through evaporation at leaf stomata. 349
 DNA sequence capable of randomly moving from one site to another in the genome. 172
 Sexually transmitted disease caused by the parasitic protozoan Trichomonas vaginalis. 523
 Neutral fat composed of glycerol and three fatty acids. 439
 During gene expression, each sequence of three nucleotide bases stands for a particular amino acid. 167
 Feeding level of one or more populations in a food web. 563
 In plants, a growth response toward or away from a directional stimulus. 360
 Parasitic zooflagellate that causes severe disease in human beings and domestic animals, including a condition called sleeping sickness. 278
 Protein-digesting enzyme secreted by the pancreas. 418
 Cells derived from a single mutated cell that has repeatedly undergone cell division; benign tumors remain at the site of origin, while malignant tumors metastasize. 121
 Gene that codes for a protein that ordinarily suppresses cell division; inactivity can lead to a tumor. 189
 Type of primitive invertebrate chordate. 320
 Condition caused by the inheritance of a single X chromosome. 137
U
 Cord connecting the fetus to the placenta through which blood vessels pass. 527
 Made up of but a single cell, as in the bacteria. 2
Spatial distribution of individuals in a population in which individuals are dispersed uniformly through the area. 538 
 Belief espoused by James Hutton that geological forces act at a continuous, uniform rate. 219
 Fatty acid molecule that has one or more double bonds between the carbons of its hydrocarbon chain. The chain bears fewer hydrogens than the maximum number possible. 36
 Pyrimidine base that replaces thymine in RNA; pairs with adenine. 164
 Tubular structure conducting urine from the kidney to the urinary bladder. 427
 Tubular structure that receives urine from the bladder and carries it to the outside of the body. 427
 Organ where urine is stored. 427
 Organ system consisting of the kidneys and urinary bladder; rids the body of nitrogenous wastes and helps regulate the water-salt balance of the blood. 386
 Liquid waste product made by the nephrons of the vertebrate kidney through the processes of filtration, reabsorption, and secretion. 427
 In mammals, expanded portion of the female reproductive tract through which eggs pass to the environment or in which an embryo develops and is nourished before birth. 516
 Saclike cavity in the vestibule of the vertebrate inner ear; contains sensory receptors for gravitational equilibrium. 498
V
 Antigens prepared in such a way that they can promote active immunity without causing disease. 464
 Membrane-bounded sac, larger than a vesicle; usually functions in storage and can contain a variety of substances. In plants, the central vacuole fills much of the interior of the cell. 59
 Outer shell of an atom. 19
 In plants, primary phloem and primary xylem enclosed by a bundle sheath. 340
 In plants, lateral meristem that produces secondary phloem and secondary xylem. 341
 Plant that has vascular tissue (xylem and phloem); includes seedless vascular plants (e.g., ferns) and seed plants (gymnosperms and angiosperms). 288
 Transport tissue in plants, consisting of xylem and phloem. 285, 341
 Tube that leads from the epididymis to the urethra in males. 514
 Piece of DNA that can have a foreign DNA attached to it; a common vector is a plasmid. 173
 Blood vessel that arises from venules and transports blood toward the heart. 399, 401
 Large systemic vein that returns blood to the right atrium of the heart in tetrapods; either the superior or inferior vena cava. 399, 402
 Cavity in an organ, such as a lower chamber of the heart or the ventricles of the brain. 399
 Vessel that takes blood from capillaries to a vein. 399
Portion of the vertebrate endoskeleton that houses the spinal cord; consists of many vertebrae separated by intervertebral disks. 503
 Chordate in which the notochord is replaced by a vertebral column. 320
 Small, membrane-bounded sac that stores substances within a cell. 58
 Cell that joins with others to form a major conducting tube found in xylem. 342
 Remains of a structure that was functional in some ancestor but is no longer functional in the organism in question. 226
 Small, fingerlike projection of the inner small intestinal wall. 418
 Infectious strand of RNA devoid of a capsid and much smaller than a virus. 270
 Noncellular parasitic agent consisting of an outer capsid and an inner core of nucleic acid. 266
 Essential requirement in the diet, needed in small amounts. Vitamins are often part of coenzymes. 442
 In humans, folds of tissue within the larynx; create vocal sounds when they vibrate. 423
W
 Filamentous organisms having cell walls made of cellulose; typically decomposers of dead freshwater organisms, but some are parasites of aquatic or terrestrial organisms. 279
 Leukocyte, of which there are several types, each having a specific function in protecting the body from invasion by foreign substances and organisms. 383, 406
 Allele or phenotype that is the most common for a certain gene in a population. 146
 Secondary xylem that builds up year after year in woody plants and becomes the annual rings. 345
X
 Allele that is located on an X chromosome but may control a trait that has nothing to do with the sex characteristics of an animal. 152
 Vascular tissue that transports water and mineral solutes upward through the plant body; it contains vessel elements and tracheids. 288, 340
Z
 Nonphotosynthetic protist that moves by flagella; typically zooflagellates enter into symbiotic relationships, and some are parasitic. 278
 Diploid cell formed by the union of two gametes; the product of fertilization. 129, 512