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AP Biology Total
| Question | Answer |
|---|---|
| 3' end | The end of a DNA or RNA molecule that has a free hydroxyl group. By convention, the end is considered the end with the last nucleotide. (p. 80) |
| 5' end | The end of a DNA or RNA molecule that has a free phosphate group. By convention, the end is considered the end with the first nucleotide. (p. 80) |
| abiotic | Pertaining to nonliving things. (p. 4) |
| acid | A molecule that donates ions to a solution. When the concentration of hydrogen ions is greater than the concentration of hydroxide ions, the pH is acidic. (p. 49) |
| activation energy | The energy input necessary to reach the transition state. (p. 199) |
| activator | A compound that increases the activity of an enzyme. (p. 205) |
| active site | The portion of an enzyme that binds substrate and converts it to product. (p. 202) |
| active transport | The movement of substances across a cell membrane against a concentration gradient requiring an input of energy. (p. 148) |
| adaptation | The close fit between an organism and its environment. (p. 561) |
| adaptive radiation | A period of unusually rapid evolutionary diversification in which natural selection accelerates the rate of speciation within a group, with new species adapted for specific niches. (p. 674) |
| addition rule of probability | Rule which states that the probability of two mutually exclusive events happening is the sum of their individual probabilities. (p. 372) |
| adenine (A) | A purine base. (p. 79) |
| adenosine diphosphate (ADP) | A chemical relative of ATP that is composed of the base adenine, the five-carbon sugar ribose, and two phosphate groups. ADP contains less chemical energy than ATP does. (p. 187) |
| adenosine triphosphate (ATP) | The molecule that provides energy in a form that all cells can readily use to perform the work of the cell. (p. 96) |
| adhesion | The tendency of water molecules to stick to other polar or charged molecules. (p. 44) |
| agonist | A ligand that binds a receptor and leads to a response. (p. 305) |
| alleles | Different forms of a gene, corresponding to different DNA sequences. (p. 369) |
| allopatric | Describes populations that are geographically separated from each other. (p. 668) |
| allosteric site | A site other than the active site of an enzyme. (p. 206) |
| alpha helix (α helix) | One of the two principal types of secondary structure found in proteins. (p. 70) |
| alternative hypothesis | A hypothesis that predicts that the independent variable in an experiment will have a real effect, and there will be a difference between the data collected from the control groups and experimental groups. (p. 11) |
| alternative splicing | The process by which exons are joined together and introns are removed during RNA processing. A single gene can be spliced in different ways to yield different mRNAs and different protein products. (p. 465) |
| amino acid | The subunit of proteins. (p. 38) |
| amplification | The process in which a small number of signaling molecules can generate a very large response. (p. 293) |
| anabolism | The set of chemical reactions that build molecules from smaller units utilizing an input of energy, usually in the form of ATP. Anabolic reactions result in net energy storage within cells and the organism. (p. 193) |
| anaphase | The phase of mitosis in which sister chromatids separate. (p. 328) |
| antagonist | A ligand that binds a receptor and inhibits a response. (p. 305) |
| anticodon | The sequence of three nucleotides in a tRNA molecule that base pairs with the corresponding codon in an mRNA molecule. (p. 471) |
| antiparallel | Oriented in opposite directions, like the two strands in a DNA molecule. (p. 82) |
| apoptosis | The genetically programmed death of a cell. (p. 340) |
| aquaporin | A channel protein that allows water to cross the cell membrane more readily than by diffusing through the lipid bilayer. (p. 147) |
| archaea | One of the three domains of life, consisting of unicellular organisms that differ from bacteria in many aspects of their cell and molecular biology. (p. 98) |
| artificial selection | A form of directional selection similar to natural selection, but with selection done intentionally by humans, usually with a specific goal in mind, such as increased milk yield in cattle. (p. 580) |
| asexual reproduction | The reproduction of organisms in which an offspring inherits its DNA from a single parent. (p. 323) |
| atom | The basic unit of matter. (p. 26) |
| atomic mass | The total mass of an atom; consists of the number of protons and neutrons in the atom. (p. 30) |
| atomic number | The number of protons in an element. (p. 30) |
| ATP synthase | An enzyme that couples the movement of protons through the enzyme with the synthesis of ATP. (p. 225) |
| autosome | A chromosome that is not a sex chromosome. (p. 352) |
| autotroph | Organism that obtains energy by photosynthesis or chemosynthesis. Also known as a producer. (p. 741) |
| bacteria | One of the three domains of life, consisting of unicellular organisms that differ from archaea in many aspects of their cell and molecular biology. (p. 98) |
| base | A molecule that accepts ions and removes them from solution. When the concentration of hydrogen ions is less than the concentration of hydroxide ions, the solution is basic or alkaline. (p. 49) |
| beta sheet (β sheet) | One of the two principal types of secondary structure found in proteins. (p. 71) |
| biodiversity | Biological diversity; the total number of species, or, more broadly, the diversity of genetic sequences, cell types, metabolism, life history, phylogenetic groups, communities, and ecosystems. (p. 562) |
| biological species concept (BSC) | As described by Ernst Mayr, the concept that “species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups.” The BSC is the most widely used and accepted definition of a species, but canno |
| biological system | A system made of both biological and physical entities that interact and, as a result, show complex properties. (p. 4) |
| biologist | A scientist who studies biology. (p. 1) |
| biology | The science of how life works. (p. 1) |
| biotic | Pertaining to life and living organisms. (p. 4) |
| bottleneck | An extreme, usually temporary, reduction in population size that may result in marked loss of genetic diversity and, in the process, genetic drift. (p. 603) |
| Calvin cycle | The process in which carbon dioxide is reduced to synthesize carbohydrates, with ATP and NADPH as the energy sources. (p. 217) |
| cancer | A condition of unregulated cell division, often resulting in the development of tumors and disease. (p. 336) |
| carbohydrate | A type of organic molecule. (p. 38) |
| carbon-14 | A radioactive isotope of carbon frequently used in radiometric dating. (p. 624) |
| carrier protein | A transport protein that facilitates movement of molecules across a cell membrane. (p. 147) |
| carrying capacity (K) | A limit on how many individuals can be supported in a given environment. (p. 760) |
| catabolism | The set of chemical reactions that break down molecules into smaller units and, in the process, produce ATP to meet the energy needs of the cell. (p. 193) |
| catalyst | A compound that increases the rate of a chemical reaction, but emerges from the process unaltered. (p. 197) |
| cell | The simplest self-reproducing entity that can exist as an independent unit of life. (p. 1) |
| cell cycle | |
| The collective name for the steps that make up the life cycle of a eukaryotic cell, including DNA replication and mitotic cell division. (p. 324) | |
| cell division | |
| The process by which a parent cell gives rise to two daughter cells. (p. 322) | |
| cell membrane | |
| The membrane that surrounds the cytoplasm of the cell, separating the inside of the cell from the outside of the cell; also known as plasma membrane. (p. 58) | |
| cell theory | |
| The set of ideas that places the cell at the center of life. It states that the cell is the fundamental unit of life, that organisms are made up of one or more cells, and that cells arise from preexisting cells. (p. 93) | |
| cellular respiration | |
| A series of chemical reactions in which organic molecules are oxidized to carbon dioxide, converting the energy stored in organic molecules to ATP. (p. 110) | |
| central dogma | |
| The idea that information in a cell usually flows from DNA to RNA to protein. (p. 84) | |
| centromere | |
| A region of DNA where sister chromatids can be held together, it is also the place where the mitotic spindle attaches to drive chromosome movement during mitosis. (p. 325) | |
| centrosome | |
| A compact structure that is the microtubule organizing center for animal cells. (p. 326) | |
| channel protein | |
| A transport protein with a passage that allows the movement of molecules through it. (p. 147) | |
| character | |
| An anatomical, physiological, or molecular feature of an organism that varies among taxa. (p. 651) | |
| checkpoint | |
| A point of transition between one phase of the cell cycle and the next phase of the cell cycle. (p. 338) | |
| chemical bond | |
| A form of attraction between atoms that holds them together. (p. 33) | |
| chemical energy | |
| A form of potential energy held in the chemical bonds between pairs of atoms in a molecule. (p. 185) | |
| chemical reaction | |
| A process by which molecules are transformed into different molecules. (p. 35) | |
| chemiosmosis | |
| The movement of ions, such as hydrogen ions (protons), from a region of high concentration to a region of low concentration across a selectively permeable membrane, similar to the movement of water by osmosis. In mitochondria and chloroplasts, chemiosmosi | |
| chemosynthesis | |
| The biochemical process in which the energy of chemical compounds is used to build sugars. (p. 740) | |
| Chi-square test | |
| A statistical test that determines whether the number of observed events in different categories differs from an expected number of events. (p. 374) | |
| chlorophyll | |
| The major photosynthetic pigment contained in the photosynthetic membranes; it plays a key role in the cell’s ability to capture energy from sunlight. (p. 112) | |
| chloroplast | |
| An organelle in photosynthetic eukaryotes that converts energy of sunlight into chemical energy by synthesizing simple sugars. (p. 111) | |
| chromatin | |
| Inside the eukaryotic nucleus, chromatin refers to the assemblage of DNA, RNA, and protein that fills the nucleus. (p. 326) | |
| chromosome | |
| A cellular structure containing the genetic material in cells, consisting of a single DNA molecule with associated proteins. (p. 324) | |
| cladogram | |
| A type of phylogenetic tree that shows clades, or monophyletic groups. (p. 650) | |
| codon | |
| A group of three adjacent nucleotides in mRNA that specifies an amino acid in a protein or that terminates protein synthesis. (p. 471) | |
| cohesion | |
| Tendency of water molecules to stick to one another due to hydrogen bonding with one another. (p. 44) | |
| commensalism | |
| An interaction in which one species receives a benefit while the other species is neither harmed nor helped. (p. 787) | |
| competition | |
| An interaction between species that require the same limited resource. (p. 786) | |
| complementary | |
| Describes the relationship of purine and pyrimidine bases, in which the base A pairs only with T, and G pairs only with C. (p. 83) | |
| complex carbohydrate | |
| A long, branched chain of monosaccharides. (p. 57) | |
| concentration gradient | |
| A difference in concentration of a substance, with regions of higher and lower concentration. (p. 146) | |
| conjugation | |
| The direct cell-to-cell transfer of DNA, usually a plasmid; a form of horizontal gene transfer. (p. 520) | |
| contractile vacuole | |
| An organelle in some protists that actively takes up and expels water that enters the cell by osmosis. (p. 159) | |
| control group | |
| A group that is not exposed to the independent variable in an experiment and therefore is not expected to show a change; also known as a negative control, or control for short. (p. 7) | |
| controlled experiment | |
| An experiment in which there are at least two groups to be tested and the conditions and setup are almost identical for the groups except that one group (the test or experimental group) deliberately has a variable introduced, whereas the other (control) g | |
| convergent evolution | |
| The independent evolution of similar traits in different species as a result of similar environments or selective pressures. (p. 577) | |
| cooperative behavior | |
| A behavior that helps a member of the same species improve another individual’s fitness. (p. 731) | |
| covalent bond | |
| A bond in which two atoms share a pair of electrons. (p. 33) | |
| crossing over | |
| A process in prophase I in meiosis when each chromatid can break at the chiasma and then connect to a non-sister chromatid. Also known as recombination. (p. 354) | |
| cyclic adenosine monophosphate (cAMP) | |
| Derived from ATP and serves as an intracellular second messenger in many signal transduction pathways. (p. 293) | |
| cyclin-dependent kinase (CDK) | |
| An enzyme that is activated by binding to the appropriate cyclin partner, gaining the ability to transfer a phosphate group to a target protein. (p. 337) | |
| cyclins | |
| A family of several different proteins that are produced in different amounts during different phases of the cell cycle so that they can bind to and regulate cyclin-dependent kinases, thus cueing the progression of the cell cycle. (p. 337) | |
| cytokinesis | |
| The stage of M phase in which the cytosol, organelles, and duplicated nuclei from one eukaryotic cell divide into two daughter cells. (p. 324) | |
| cytoplasm | |
| The region of the cell outside of the nucleus. (p. 98) | |
| cytosine (C) | |
| A pyrimidine base. (p. 79) | |
| cytoskeleton | |
| An internal protein scaffold that helps cells to maintain their shape. (p. 112) | |
| cytosol | |
| The region of the cell inside the cell membrane but outside the organelles; the jelly-like internal environment that surrounds the organelles. (p. 101) | |
| dehydration synthesis reaction | |
| A reaction in which a water molecule is released by the two reacting molecules as a new covalent bond is formed between them. Dehydration synthesis reactions build large molecules from smaller subunits. Also called dehydration reaction. (p. 50) | |
| denature | |
| Unfold, as a protein. A protein that unfolds loses its function, as the shape of a protein is closely connected to its function. (p. 204) | |
| density-dependent factor | |
| Factors that limit population growth as its size increases. (p. 766) | |
| density-independent factor | |
| Factors that reduce density regardless of a population’s size. (p. 765) | |
| deoxyribonucleic acid (DNA) | |
| The carrier molecule of genetic information for all organisms. (p. 4) | |
| deoxyribose | |
| The pentose sugar component of DNA. (p. 56) | |
| dependent variable | |
| The variable that is being tested, observed, or measured, and that may change due to the independent variable. (p. 8) | |
| derived character | |
| A character or trait that is newly evolved; an evolutionary innovation. (p. 652) | |
| differentiation | |
| The process by which cells become progressively more specialized as a result of gene regulation. (p. 499) | |
| diffusion | |
| The net movement of molecules from areas of higher to lower concentration of the molecules due to random motion. (p. 124) | |
| dihybrid cross | |
| A mating in which hybrid individuals differ in two traits that are coded by two different genes. (p. 378) | |
| diploid | |
| A cell with two sets of chromosomes (denoted as 2n). (p. 351) | |
| directionality | |
| An asymmetry such that one end of a structure differs from the other. Also known as polarity. (p. 80) | |
| disaccharide | |
| Two simple sugars joined by a covalent bond; an example is sucrose. (p. 57) | |
| distribution | |
| A description which typically takes the form of a list or graph of all of the possible values of a particular variable and their frequencies. The distribution describes the spread of the data and how often each value occurs. (p. 21) | |
| divergent evolution | |
| The process by which two groups of organisms become genetically and physically different from each other over time. (p. 668) | |
| DNA editing | |
| Techniques used to “rewrite” a nucleotide sequence so that specific mutations can be introduced into genes to better understand their function, or to correct mutant versions of genes to restore normal function. (p. 536) | |
| DNA ligase | |
| An enzyme that joins two DNA fragments together. (p. 454) | |
| DNA polymerase | |
| An enzyme that is a critical component of a large protein complex that carries out DNA replication. (p. 451) | |
| DNA replication | |
| The process of duplicating a DNA molecule, during which the parental strands separate and new partner strands are made. (p. 339) | |
| domain | |
| One of the three largest limbs of the tree of life: Eukarya, Bacteria, or Archaea. (p. 98) | |
| dominant | |
| Describes an allele or trait that is expressed in heterozygotes. Only one dominant allele is needed to express the phenotype. (p. 369) | |
| double bond | |
| A covalent bond in which two atoms share two pairs of electrons. (p. 33) | |
| double helix | |
| The structure formed by two strands of complementary nucleotides that coil around each other. (p. 81) | |
| Down syndrome | |
| A condition in humans caused by an extra chromosome 21. (p. 425) | |
| ectotherm | |
| An animal that obtains most of its heat to warm its body from the environment. (p. 737) | |
| electron | |
| An atomic particle that moves around the nucleus and carries a negative charge. (p. 30) | |
| electron shell | |
| See energy level. (p. 31) | |
| electronegativity | |
| Difference in the ability of atoms to attract electrons. (p. 34) | |
| element | |
| A chemical that cannot be split into other chemicals. (p. 30) | |
| emerging disease | |
| An infectious disease that has appeared recently and/or spread rapidly. (p. 547) | |
| endergonic | |
| Describes reactions with a positive ∆G that are not spontaneous and so require an input of energy. (p. 191) | |
| endocytosis | |
| The process in which a vesicle buds off from the cell membrane, bringing material from outside the cell into that vesicle, which can then fuse with other membranes. (p. 151) | |
| endomembrane system | |
| A cellular system present in eukaryotic cells that includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, the cell membrane, and the vesicles that move between them. (p. 106) | |
| endoplasmic reticulum (ER) | |
| An organelle composed of a network of membranes that is involved in the synthesis of proteins and lipids. (p. 107) | |
| endosymbiosis | |
| A symbiosis in which one partner lives within the other. (p. 173) | |
| endotherm | |
| An animal that produces most of its heat as a by-product of metabolic reactions to maintain a warm and steady body temperature. (p. 736) | |
| energetic coupling | |
| The driving of a non-spontaneous reaction by a spontaneous reaction. (p. 192) | |
| energetics | |
| The science of the properties of energy and how energy is distributed in biological, chemical, and physical processes. (p. 4) | |
| energy | |
| The ability to do work. (p. 4) | |
| energy level | |
| An area in space where electrons circle around the nucleus. Also called an electron shell. (p. 31) | |
| entropy | |
| The amount of disorder, or the number of possible positions and motions of molecules, in a system. (p. 188) | |
| enzyme | |
| A protein that functions as a catalyst to accelerate the rate of a chemical reaction. (p. 107) | |
| epigenetic | |
| Describes effects on gene expression due to differences in DNA packaging and chromosome organization, such as modifications in histones or chromatin structure. (p. 493) | |
| eukarya | |
| One of the three domains of life, in which cells have a nucleus. (p. 101) | |
| eukaryotic | |
| Describes a cell that has a nucleus; used to refer collectively to animals, plants, fungi, and protists. (p. 98) | |
| evolution | |
| A change in the genetic makeup of a population over time. (p. 2) | |
| evolutionarily conserved | |
| Characteristics that persist relatively unchanged through diversification of a group of organisms and therefore remain similar in related species. (p. 503) | |
| exergonic | |
| Describes reactions with a negative ∆G that proceed spontaneously and release energy. (p. 191) | |
| exocytosis | |
| The process in which a vesicle fuses with the cell membrane and empties its contents into the extracellular space or delivers proteins to the cell membrane. (p. 150) | |
| exon | |
| A sequence that is left intact in mRNA after RNA splicing, and is therefore expressed in the protein. (p. 465) | |
| experimental group | |
| See Test group. (p. 7) | |
| exponential growth model | |
| A model of a population that continues to grow rapidly over time in an exponential manner. (p. 758) | |
| extinction | |
| The loss of a group of organisms, typically a species. (p. 682) | |
| facilitated diffusion | |
| Diffusion across a cell membrane through a transmembrane protein, such as a channel or carrier. (p. 147) | |
| fatty acid | |
| A long chain of carbons attached to a carboxyl group; three fatty acid chains attached to glycerol form a triacylglycerol, a lipid used for energy storage. (p. 58) | |
| fermentation | |
| A variety of metabolic pathways that produce ATP from the partial oxidation of organic molecules without oxidative phosphorylation or an electron acceptor, such as oxygen. (p. 254) | |
| first law of thermodynamics | |
| The law of conservation of energy, which states that energy can be neither created nor destroyed; it can only be transformed from one form into another. (p. 188) | |
| fitness | |
| A measure of the ability of an individual to survive and reproduce in a particular environment; the extent to which the individual’s genotype is represented in the next generation. (p. 262) | |
| fluid mosaic model | |
| A model proposing that the lipid bilayer is a dynamic structure that allows molecules to move laterally within the membrane and is a mosaic, or mixture, of several components, including lipids, proteins, and carbohydrates. (p. 141) | |
| fossil | |
| The remains of a once-living organism. (p. 620) | |
| founder effect | |
| A type of genetic drift that occurs when only a few individuals establish a new population. (p. 603) | |
| functional group | |
| A group of one or more atoms that has a particular chemical property on its own, regardless of what it is attached to. (p. 55) | |
| G protein-coupled receptor | |
| A receptor protein in cell membranes that is associated with a G protein that in turn alters activity of adenylyl cyclase and other generators of second messengers in responding cells. (p. 293) | |
| phase | |
| The phase in the cell cycle in which cells pause between M phase and S phase; it may last for periods ranging from days to more than a year. (p. 326) | |
| phase | |
| The phase during interphase in which the cell synthesizes regulatory proteins controlling the eukaryotic cell cycle. (p. 325) | |
| phase | |
| The phase during interphase after DNA has been replicated, characterized by increases in cell size and protein contents. (p. 325) | |
| gamete | |
| A reproductive haploid cell; gametes fuse to form a diploid zygote. In many species, there are two types of gametes: eggs in females, sperm in males. (p. 356) | |
| gel electrophoresis | |
| A technique that is used to separate DNA and RNA based on size, and proteins based on size and charge, using an electric current passed through a jelly-like substance. (p. 529) | |
| gene | |
| The unit of heredity affecting one or more traits of an organism; the DNA sequence that corresponds to a specific protein or noncoding RNA. (p. 1) | |
| gene expression | |
| The production of a functional gene product, such as a protein; the “turning on” of a gene. (p. 436) | |
| gene flow | |
| The movement of alleles from one population to another through interbreeding between members of each population. (p. 605) | |
| gene regulation | |
| The various ways in which cells control gene expression. (p. 440) | |
| genetic code | |
| The correspondence between codons and amino acids, in which 20 amino acids are specified by 64 codons. (p. 473) | |
| genetic drift | |
| A random change in the frequency of an allele due to chance. (p. 603) | |
| genetic variation | |
| The range of different genotypes found among individuals. (p. 351) | |
| genetically modified organism (GMO) | |
| An organism that has been genetically engineered, such as modified viruses and bacteria, laboratory organisms, agricultural crops, and domestic animals; also called a transgenic organism. (p. 535) | |
| genome | |
| All of the genetic information that an individual, or a species, contains. (p. 1) | |
| genotype | |
| The set of genes that an organism carries. (p. 350) | |
| Gibbs free energy (G) | |
| The amount of energy available to do work. (p. 191) | |
| glycerol | |
| A 3-carbon molecule with hydroxyl groups attached to each carbon; a component of triacylglycerol. (p. 58) | |
| glycolipid | |
| A carbohydrate that is covalently linked to a lipid. (p. 141) | |
| glycolysis | |
| The breakdown of glucose to pyruvate; the first stage of cellular respiration. (p. 237) | |
| glycoprotein | |
| A carbohydrate that is covalently linked to a protein. (p. 141) | |
| Golgi apparatus | |
| An organelle that modifies proteins and lipids produced by the endoplasmic reticulum and acts as a sorting station as they move to their final destinations. (p. 108) | |
| gradualism | |
| The idea that species change slowly over time. (p. 676) | |
| grana (singular, granum) | |
| Interlinked stacks of thylakoids in chloroplasts. (p. 111) | |
| GTP cap | |
| The modification of the end of the primary transcript by the addition of a special nucleotide attached in an unusual chemical linkage; also called a cap. (p. 464) | |
| guanine (G) | |
| A purine base. (p. 79) | |
| half-life | |
| The time it takes for an amount of a substance to reach half its original value. Radioactive half-life is the time it takes for half of the atoms in a given sample of a substance to decay. (p. 625) | |
| haploid | |
| A cell with one set of chromosomes (denoted as 1n). (p. 352) | |
| Hardy–Weinberg equilibrium | |
| A state in which allele and genotype frequencies do not change over time, implying the absence of evolutionary forces. It also specifies a mathematical relationship between allele frequencies and genotype frequencies. (p. 607) | |
| helicase | |
| An enzyme that separates the two DNA strands at the replication fork so that each strand can be copied during DNA replication. (p. 451) | |
| heterotroph | |
| An organism that obtains energy by eating other organisms. Also known as a consumer. (p. 741) | |
| heterozygous | |
| A condition in which an individual possesses two different alleles for a given gene. (p. 317) | |
| homeostasis | |
| The active regulation and maintenance of a stable internal physiological state in the face of a changing external environment. (p. 95) | |
| homologous chromosomes | |
| Two chromosomes that are similar in size and shape, and that carry the same genes. (p. 352) | |
| homozygous | |
| A condition in which an individual possesses two identical alleles for a given gene. (p. 370) | |
| horizontal gene transfer | |
| The transfer of genetic material between organisms that are not parent and offspring. (p. 520) | |
| hormone | |
| A signaling molecule that is transported in the circulatory system by endocrine signaling. (p. 279) | |
| hydrogen bond | |
| An interaction between a hydrogen atom with a slight positive charge and an electronegative atom of another molecule. In the case of water, hydrogen bonds form between the hydrogen atom of one water molecule and oxygen atom of another water molecule. (p. | |
| hydrolysis reaction | |
| A reaction that adds water across a covalent bond and breaks the covalent bond. Hydrolysis reactions break down larger molecules into smaller, simpler molecules. (p. 51) | |
| hydrophilic | |
| “Water loving”; describes polar molecules that readily dissolve in water. (p. 38) | |
| hydrophobic | |
| “Water fearing”; describes nonpolar molecules that do not dissolve well in water. (p. 38) | |
| hypertonic | |
| Describes a solution having a higher solute concentration (lower water potential) than another solution. (p. 159) | |
| hypothesis | |
| A tentative explanation for one or more observations that make predictions that can be tested by experimentation or additional observations. (p. 6) | |
| hypotonic | |
| Describes a solution having a lower solute concentration (higher water potential) than another solution. (p. 159) | |
| independent variable | |
| The variable that is manipulated or added to an experimental group to test a hypothesis. (p. 8) | |
| inhibitor | |
| A compound that decreases the activity of an enzyme. (p. 205) | |
| innate behavior | |
| A behavior that is performed without any previous experience. (p. 728) | |
| integral membrane protein | |
| A protein that is permanently associated with the cell membrane and cannot be separated from the membrane experimentally without destroying the membrane itself. (p. 139) | |
| interphase | |
| One of two major phases of the eukaryotic cell cycle, in which the cell copies its DNA and synthesizes proteins necessary for mitosis. (p. 324) | |
| intron | |
| An intervening sequence that is removed from the primary transcript during RNA splicing. (p. 465) | |
| invasive species | |
| Non-native species that become established in new ecosystems. (p. 628) | |
| ion | |
| An electrically charged atom. (p. 31) | |
| ionic bond | |
| A bond in which two ions with opposite electrical charges associate with each other. (p. 34) | |
| isotonic | |
| Describes a solution having the same solute concentration (same water potential) as another solution. (p. 159) | |
| isotope | |
| One of two or more forms of the same element with different numbers of neutrons. (p. 30) | |
| karyotype | |
| A visual display of the pairs of chromosomes. (p. 352) | |
| keystone species | |
| Pivotal populations that affect other members of the community in ways that are disproportionate to their abundance or biomass. (p. 788) | |
| kinase | |
| An enzyme that catalyzes the transfer of a phosphate group from ATP to another molecule. (p. 293) | |
| kinetic energy | |
| The energy of motion. (p. 185) | |
| kinetochore | |
| The protein complex on a chromatid where the mitotic spindle attaches. (p. 328) | |
| Krebs cycle | |
| The third stage of cellular respiration, in which acetyl-CoA is broken down and carbon dioxide is released; also called the citric acid cycle. (p. 237) | |
| lagging strand | |
| A daughter strand that has its end pointed toward the replication fork, so as the parental double helix unwinds, a new DNA piece is initiated at intervals, and each new piece is elongated at its end until it reaches the piece in front of it. (p. 453) | |
| law of independent assortment | |
| The principle that segregation of one set of alleles for one gene is independent of the segregation of a second set of alleles for a different gene. (p. 378) | |
| law of segregation | |
| The principle that half of the gametes receive one allele of a gene and half receive the other allele. This principle is explained by meiosis, in which the maternal and paternal homologous chromosomes separate during anaphase I. (p. 370) | |
| leading strand | |
| A daughter strand that has its end pointed toward the replication fork, so as the parental double helix unwinds, this daughter strand can be synthesized as one long, continuous polymer. (p. 453) | |
| learned behavior | |
| A behavior in which the individual’s experience in its environment plays a large role. (p. 728) | |
| ligand | |
| A signaling molecule with a molecular shape and distribution of charge that allows it to match up with and bind to a complementary receptor protein. (p. 277) | |
| ligand-gated channel | |
| Receptor proteins in cell membranes that alter membrane permeability to ions after binding to an extracellular hydrophilic signaling molecule. (p. 299) | |
| light reactions | |
| The series of chemical reactions during photosynthesis in which the energy of sunlight is used to synthesize NADPH and ATP. (p. 217) | |
| linked genes | |
| Genes that are physically located near each other on the same chromosome. (p. 398) | |
| lipid | |
| A type of organic molecule that is hydrophobic; lipids make up the barrier between the cell and its environment, store energy, and act as signaling molecules. (p. 38) | |
| lipid bilayer | |
| A two-layered structure of the cell membrane made up of lipids with hydrophilic heads pointing outward toward the aqueous environment and hydrophobic tails oriented inward away from water. (p. 133) | |
| logistic growth model | |
| A growth model that describes population growth when there is a density-dependent carrying capacity. (p. 768) | |
| lysosome | |
| A vesicle derived from the Golgi apparatus that contains enzymes that break down macromolecules such as proteins, nucleic acids, lipids, and carbohydrates. (p. 109) | |
| M phase | |
| One of two major phases of the eukaryotic cell cycle, consisting of mitosis and cytokinesis. (p. 324) | |
| maternal inheritance | |
| A type of inheritance in which the organelles in the offspring cells derive from those in the mother. (p. 401) | |
| matter | |
| Material that makes physical objects. (p. 26) | |
| maximum per capita growth rate | |
| The maximum growth rate possible for a population living without any constraints. (p. 758) | |
| mean | |
| A measure of the average of a set of numbers. The mean is determined by adding all the values and dividing by the number of values. (p. 20) | |
| median | |
| The middle number in a set of numbers when ordered from lowest to highest. (p. 20) | |
| meiosis | |
| A form of cell division in which a parental cell divides in two stages to produce four daughter cells. (p. 352) | |
| meiosis I | |
| The first step in meiosis in which homologous chromosomes are separated from each other. (p. 353) | |
| meiosis II | |
| The second step in meiosis in which sister chromatids are separated from each other. (p. 353) | |
| messenger RNA (mRNA) | |
| The RNA molecule that combines with a ribosome to direct protein synthesis; it carries the genetic “message” from the DNA to the ribosome. (p. 463) | |
| metabolic pathway | |
| A series of chemical reactions that build or break down molecules in cells. (p. 186) | |
| metabolic rate | |
| The number of calories burned by an organism over time while at rest. (p. 738) | |
| metabolism | |
| The chemical reactions occurring within cells that convert one molecule into another and transfer energy in living organisms. (p. 96) | |
| metaphase | |
| The phase of mitosis in which the chromosomes align in the middle of the dividing cell. (p. 328) | |
| migration | |
| The movement of individuals from one population to another or to areas with no prior population. (p. 604) | |
| mitochondria (singular, mitochondrium) | |
| Specialized organelles that are the site of cellular respiration in eukaryotic cells, oxidizing chemical compounds such as sugars to carbon dioxide and transferring their chemical energy to ATP. (p. 110) | |
| mitochondrial matrix | |
| The space enclosed by the inner membrane of the mitochondria. (p. 110) | |
| mitosis | |
| The stage of M phase that produces two identical nuclei during the eukaryotic cell cycle. (p. 324) | |
| mitotic spindle | |
| A structure in the cytosol made up predominantly of microtubules that pull the chromosomes into separate daughter cells. (p. 326) | |
| mode | |
| The most common number in a set of numbers. (p. 21) | |
| molarity | |
| The amount of a solute in a volume of solution, expressed as moles of a solute per liter of solution. Also called molar concentration. (p. 156) | |
| molecular clock | |
| The observation that the extent of genetic divergence between two groups is a reflection of the time since the groups shared a common ancestor. (p. 618) | |
| molecule | |
| A chemical formed of two or more atoms. (p. 26) | |
| monohybrid cross | |
| A cross between two individuals that are hybrids for a single gene, meaning they possess two different alleles. (p. 369) | |
| monomer | |
| A single molecule that can bond chemically with similar molecules in a polymer. (p. 37) | |
| morphological homology | |
| An anatomical structure that is similar in two groups of organisms because it was present in the common ancestor of the two groups and retained over evolutionary time. (p. 616) | |
| multiplication rule of probability | |
| A rule which states that the probability of two independent events both happening is the product of their individual probabilities. (p. 372) | |
| mutagen | |
| An agent that increases the probability of mutation. (p. 520) | |
| mutation | |
| Any heritable change in the genetic material, usually a change in the nucleotide sequence of a gene. (p. 305) | |
| mutualism | |
| A special type of symbiosis in which both species benefit in regard to their growth or reproduction. (p. 787) | |
| natural selection | |
| A mechanism of evolution that occurs when there is genetic variation in a population of organisms and the variants best suited for survival and reproduction in a particular environment contribute disproportionately to future generations. Of all the evolut | |
| negative control | |
| See control. (p. 8) | |
| negative feedback | |
| A process in which the response or output of a system opposes the initial stimulus, resulting in steady conditions, or homeostasis. (p. 285) | |
| negative regulatory molecule | |
| A molecule, such as a repressor, that binds to the DNA at a site near the gene to prevent transcription. (p. 486) | |
| neutron | |
| An atomic particle of the nucleus that carries no charge. (p. 30) | |
| niche | |
| A complete description of the role a species plays in its environment, and of its requirements, both abiotic and biotic. (p. 665) | |
| nicotinamide adenine dinucleotide phosphate (NADPH) | |
| An electron carrier in many biochemical reactions; the reducing agent used in the Calvin cycle during photosynthesis. (p. 214) | |
| nitrogenous base | |
| A nitrogen-containing compound that makes up part of a nucleotide. (p. 78) | |
| node | |
| In phylogenetic trees, the point where a branch splits, representing the common ancestor from which the descendant species diverged. (p. 564) | |
| non-sister chromatids | |
| Chromatids that are not connected by a centromere. (p. 354) | |
| nondisjunction | |
| The failure of a chromosome to separate during anaphase of cell division. (p. 423) | |
| nonpolar covalent bond | |
| A bond that results when electrons are shared equally, or nearly equally, between two atoms. (p. 34) | |
| nonrandom mating | |
| Mate selection that is not random, but instead is based on genotype or relatedness. (p. 606) | |
| nontemplate strand | |
| The strand of DNA that is not used as a template, or model, for RNA synthesis during transcription. The nontemplate strand is the reverse complement of the template strand. The nontemplate strand is also called the coding, sense, and plus strand. (p. 460) | |
| normal distribution | |
| A symmetric distribution or bell curve in which most of the values cluster in the middle and fewer values are found at the extremes. In a normal distribution, approximately 68% of the values lie within one standard deviation on either side of the mean, an | |
| nuclear envelope | |
| The two membranes, inner and outer, that define the boundary of the nucleus. (p. 106) | |
| nucleic acid | |
| A type of organic molecule that encodes and transmits genetic information. (p. 38) | |
| nucleotide | |
| A subunit of nucleic acids, consisting of a 5-carbon sugar, a nitrogen-containing base, and one or more phosphate groups. (p. 38) | |
| nucleus | |
| The dense, central part of an atom. (p. 30) | |
| nucleus (of a cell) | |
| The compartment of the cell that houses the DNA in chromosomes. (p. 98) | |
| null hypothesis | |
| A hypothesis that predicts that the independent variable in a controlled experiment will not have a real effect, and any difference between the data collected from the control groups and experimental groups is due to chance. (p. 11) | |
| observation | |
| The act of viewing the world around us. (p. 5) | |
| operon | |
| A group of functionally related genes located in tandem along DNA and transcribed as a single unit from one promoter in prokaryotes. (p. 478) | |
| organelle | |
| Any one of several compartments in a eukaryotic cell that divides the cell contents into smaller spaces specialized for different functions. (p. 101) | |
| organic molecule | |
| A molecule made of carbon. (p. 26) | |
| organism | |
| A living individual entity that displays the properties of life. (p. 1) | |
| osmoregulation | |
| The regulation of water and solute levels to control osmotic pressure. (p. 163) | |
| osmosis | |
| The net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration. (p. 156) | |
| osmotic pressure | |
| The pressure needed to prevent water from moving from one solution into another by osmosis. (p. 157) | |
| outgroup | |
| A group of organisms that has an older common ancestor than the common ancestor of the group of interest, and therefore serves as a reference for evolutionary relationships within the group of interest. (p. 654) | |
| oxidation | |
| A chemical reaction in which a molecule loses electrons and energy. (p. 214) | |
| oxidative phosphorylation | |
| A set of chemical reactions that occurs by passing electrons along an electron transport chain to a final electron acceptor, oxygen, pumping protons across a membrane, and using the proton electrochemical gradient to drive the synthesis of ATP. (p. 236) | |
| parasitism | |
| An interaction in which one species lives in or on another organism, known as the host. (p. 785) | |
| passive transport | |
| The movement of molecules across a cell membrane by diffusion. (p. 146) | |
| paternal inheritance | |
| A type of inheritance in which the organelles in the offspring cells derive from those in the father. (p. 401) | |
| pedigree | |
| A visual mapping of phenotypes using ancestral relationships. (p. 380) | |
| peptide | |
| A molecule made by joining amino acids together by peptide bonds. Peptides may range from as few as two to many hundreds of amino acids linked together. (p. 69) | |
| peptide bond | |
| The bond between the carboxyl end of an amino acid and the amino end of another amino acid that creates a peptide. (p. 69) | |
| per capita growth rate (r) | |
| The rate of population change divided by the size of the population. (p. 756) | |
| periodic table of the elements | |
| A table in which the elements are indicated by their chemical symbols and arranged in order of increasing atomic number. (p. 31) | |
| peripheral membrane protein | |
| A protein that is temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions. (p. 139) | |
| pH scale | |
| A measure of the acidity of a solution. The pH scale ranges from 0 to 14 and is calculated by the negative logarithm of the hydrogen ion concentration. (p. 49) | |
| phenotype | |
| The set of traits that an organism expresses, such as hair color or eye color. (p. 350) | |
| phenotypic plasticity | |
| The ability of a single genotype to produce different phenotypes in different environments. (p. 406) | |
| phospholipid | |
| A type of lipid and a major component of the cell membrane. (p. 61) | |
| photophosphorylation | |
| The process by which energy from sunlight drives the movement of electrons along an electron transport chain, which leads to the synthesis of ATP. (p. 226) | |
| photosynthesis | |
| The biochemical process in which the energy of sunlight is used to synthesize carbohydrates from carbon dioxide and water. (p. 111) | |
| photosynthetic electron transport chain | |
| A series of redox reactions in which light energy absorbed by chlorophyll is used to power the movement of electrons; in oxygenic photosynthesis, the electrons ultimately come from water, and the terminal electron acceptor is . (p. 217) | |
| photosystem | |
| A protein–pigment complex that absorbs light energy to drive redox reactions and thereby sets the photosynthetic electron transport chain in motion. (p. 224) | |
| phylogenetic tree | |
| A tree-like diagram representing a hypothesis about the evolutionary relationships among populations or species. (p. 563) | |
| phylogeny | |
| The history of descent with modification and the accumulation of change over time. (p. 645) | |
| plasma membrane | |
| See cell membrane. | |
| plasmid | |
| In bacteria, a small circular molecule of DNA carrying a small number of genes that replicates independently of the DNA in the bacterium’s circular chromosome. (p. 442) | |
| plasmodesmata | |
| Connections between two adjacent plant cells that permit molecules and other substances to pass directly from the cytoplasm of one cell to the cytoplasm of another. (p. 282) | |
| polar (molecule) | |
| A molecule that has regions of positive and negative charge. (p. 43) | |
| polar covalent bond | |
| A bond that results when electrons are shared unequally between two atoms. (p. 34) | |
| polarity | |
| See directionality. (p. 80) | |
| poly(A) tail | |
| The adenine (A) nucleotides added to the end of the primary transcript. (p. 465) | |
| polymer | |
| A large molecule composed of many smaller subunits. (p. 37) | |
| polymerase chain reaction (PCR) | |
| A selective and highly sensitive method for making copies of a piece of DNA, which allows a targeted region of a DNA molecule to be replicated into as many copies as desired. (p. 526) | |
| polypeptide | |
| A polymer of amino acids connected by peptide bonds. (p. 69) | |
| polyploidy | |
| The condition of having more than two complete sets of chromosomes in the genome. (p. 517) | |
| polysaccharide | |
| A polymer of simple sugars. Polysaccharides provide long-term energy storage or structural support. (p. 57) | |
| population | |
| All the individuals of a given species that live and reproduce in a particular place; one of several interbreeding groups of organisms of the same species living in the same geographical area. (p. 276) | |
| positive control | |
| A sample or group that receives a treatment or variable with a known effect in a controlled experiment and therefore is expected to show a predictable change. (p. 8) | |
| positive feedback | |
| A pattern of response in which the output or signal of a communication system increases the activity in the same system that produced the signal. (p. 285) | |
| positive regulatory molecule | |
| A molecule, such as an activator, that binds to DNA at a site near a gene so that transcription can take place. (p. 486) | |
| postzygotic | |
| Describes factors that cause the failure of a fertilized egg to develop into a fertile individual. (p. 666) | |
| potential energy | |
| Stored energy related to an object’s structure or position. (p. 185) | |
| predation | |
| An interaction that involves one species killing and consuming another. (p. 784) | |
| pressure potential | |
| The effect of pressure in the movement of water. (p. 160) | |
| prezygotic | |
| Describes factors that prevent the fertilization of an egg. (p. 666) | |
| primary active transport | |
| Active transport that uses the energy of ATP directly. (p. 148) | |
| primary structure | |
| The sequence of amino acids in a peptide or a protein. (p. 70) | |
| primary transcript | |
| The initial RNA molecule that comes off the template DNA strand. (p. 463) | |
| primer | |
| A short strand of DNA or RNA; in DNA replication, RNA is used as a primer for DNA synthesis. (p. 451) | |
| probability | |
| The likelihood of an event happening. (p. 372) | |
| product | |
| Atoms or molecules that are made in a chemical reaction. (p. 35) | |
| prokaryotic | |
| Describes a cell that does not have a nucleus; used to refer collectively to archaeons and bacteria. (p. 98) | |
| prometaphase | |
| The phase of mitosis in which the nuclear envelope breaks down and the microtubules of the mitotic spindle attach to chromosomes. (p. 328) | |
| promoter | |
| A regulatory region where RNA polymerase and associated proteins bind to the DNA molecule in the process of transcription. (p. 461) | |
| proofreading | |
| The process in which a DNA polymerase can immediately correct its own errors by excising and replacing a mismatched base. (p. 455) | |
| prophase | |
| The phase of mitosis in which the chromosomes condense and become visible through the microscope. (p. 326) | |
| protein | |
| A type of organic molecule that provides structural support for the cell and speeds up chemical reactions. (p. 37) | |
| proton | |
| An atomic particle of the nucleus that carries a positive charge. (p. 30) | |
| punctuated equilibrium | |
| The idea that species go through periods of relatively little change, which are interrupted by short periods of rapid change and diversification. (p. 676) | |
| purine | |
| In nucleic acids, either of the bases adenine and guanine, which have a double-ring structure. (p. 78) | |
| pyrimidine | |
| In nucleic acids, any of the bases thymine, cytosine, and uracil, which have a single-ring structure. (p. 79) | |
| quaternary structure | |
| The level of protein structure that arises from the interaction of two or more polypeptide chains or subunits, each with its own tertiary structure. (p. 72) | |
| quorum sensing | |
| Density-dependent production of signal molecules in bacteria that leads to population responses, such as bioluminescence or DNA uptake. (p. 278) | |
| radiometric dating | |
| Dating ancient materials using the decay of radioisotopes as a yardstick, including the decay of radioactive to nitrogen for time intervals up to a few tens of thousands of years, and the decay of radioactive uranium to lead for most of Earth history. (p | |
| range | |
| A measure of how spread out numbers in a set of numbers are. The range is calculated by determining the difference between the highest and lowest numbers in a set of numbers. (p. 22) | |
| reactant | |
| Atoms or molecules that are changed in a chemical reaction. (p. 35) | |
| reaction center | |
| Specially configured chlorophyll molecules where light energy is converted into electron transport. (p. 223) | |
| receptor protein | |
| A molecule that binds to a signaling molecule and triggers a response in a target cell. (p. 138) | |
| receptor-protein kinase | |
| A receptor protein in cell membranes that have kinase activity that is activated after binding to an extracellular signaling molecule. (p. 294) | |
| recessive | |
| Describes an allele or trait that is only expressed in homozygotes, and not expressed in heterozygotes. Two recessive alleles are needed to express the phenotype. (p. 369) | |
| recombination | |
| See crossing over. | |
| reduction | |
| A chemical reaction in which a molecule gains electrons and energy. (p. 214) | |
| replication fork | |
| The site where the parental DNA strands separate as the DNA duplex unwinds. (p. 448) | |
| reverse transcriptase | |
| An RNA-dependent DNA polymerase that uses a single-stranded RNA as a template to synthesize a DNA strand that is complementary in sequence to the RNA. (p. 544) | |
| ribonucleic acid (RNA) | |
| A molecule chemically related to DNA that is synthesized from a DNA template and is involved in protein synthesis, among other functions. (p. 38) | |
| ribose | |
| A pentose sugar commonly found in RNA. (p. 56) | |
| ribosomal RNA (rRNA) | |
| Noncoding RNA found in all ribosomes that aid in translation. (p. 465) | |
| ribosome | |
| A complex structure of RNA and protein that synthesizes proteins from mRNA. (p. 96) | |
| RNA polymerase | |
| The enzyme that synthesizes an RNA transcript from a DNA template. (p. 460) | |
| RNA processing | |
| A chemical modification that converts the primary transcript into mature mRNA, enabling the RNA molecule to be transported to the cytoplasm and recognized by the translational machinery. (p. 463) | |
| RNA splicing | |
| The process of joining exons and removing introns from the primary transcript. (p. 465) | |
| RNA world hypothesis | |
| The idea that the earliest cells relied on RNA for both information storage and catalysis. (p. 709) | |
| root | |
| The base of a phylogenetic tree, representing the common ancestor or group from which all the organisms on the tree evolved. (p. 564) | |
| S phase | |
| The phase during interphase in which the cell copies its DNA; the S phase follows the phase but precedes the phase. (p. 325) | |
| saturated | |
| Describes fatty acids that do not contain double bonds; the maximum number of hydrogen atoms is attached to each carbon atom, “saturating” the carbons with hydrogen atoms. (p. 58) | |
| scientific inquiry | |
| A deliberate, systematic, careful, and unbiased way of learning about the natural world; the process used to ask questions and seek answers about the natural world in a deliberate and ordered way. (p. 5) | |
| second law of thermodynamics | |
| The principle that the transformation of energy is associated with an increase in the degree of disorder in the universe. (p. 189) | |
| second messenger | |
| An intermediate signaling molecule that amplifies a response inside a cell. (p. 293) | |
| secondary active transport | |
| Active transport that uses the energy of an electrochemical gradient to drive the movement of molecules. (p. 148) | |
| secondary structure | |
| The structure that results from hydrogen bonding in the polypeptide backbone. Two kinds of secondary structures are the alpha helix (α helix) and the beta sheet (β sheet). (p. 70) | |
| selective pressure | |
| The full set of environmental conditions, both abiotic and biotic, that influence the evolution of a population by natural selection. (p. 576) | |
| semiconservative replication | |
| The mechanism of DNA replication in which each strand of a parental DNA molecule serves as a template for the synthesis of a new daughter strand. (p. 448) | |
| sensor | |
| In homeostasis, the component that detects a stimulus. (p. 284) | |
| set point | |
| In homeostasis, the typical physiological value of a particular parameter, such as body temperature or blood glucose levels, which is actively maintained by the body with very little fluctuation. (p. 284) | |
| sex chromosome | |
| A chromosome associated with sex determination. (p. 352) | |
| sex-linked gene | |
| A gene that is only located on one of the two sex chromosomes. (p. 394) | |
| sexual reproduction | |
| The process of producing offspring that receive genetic material from two parents; in eukaryotes, the process occurs through meiotic cell division and fertilization. (p. 351) | |
| sexual selection | |
| A form of selection that promotes traits that increase an individual’s ability to find and attract mates. (p. 582) | |
| shared character | |
| A character or trait that is present in two or more groups of organisms. (p. 651) | |
| signal transduction | |
| The process by which an external signal is converted to an internal response. (p. 290) | |
| signaling cascade | |
| A series of chemical reactions inside of a cell that are initiated by a signal and are typically amplified to produce a large cellular response. (p. 294) | |
| signaling molecule | |
| A chemical messenger that functions in cell communication by affecting activities of other cells. (p. 277) | |
| Simpson’s diversity index | |
| An equation that quantifies the diversity of species in a community. (p. 779) | |
| single bond | |
| A covalent bond in which two atoms share two electrons. (p. 33) | |
| sister chromatids | |
| The two copies of a chromosome resulting from DNA duplication that remain connected at the centromere. (p. 325) | |
| solute | |
| A dissolved molecule such as the ions, amino acids, and sugars often found in a solvent such as water. (p. 156) | |
| solute potential | |
| The effect of solutes on the movement of water. (p. 160) | |
| solvent | |
| A substance that can dissolve another substance. (p. 48) | |
| speciation | |
| The process whereby new species are produced. (p. 668) | |
| species | |
| A group of individuals that are capable of interbreeding and producing viable, fertile offspring. (p. 2) | |
| specific heat | |
| The amount of heat required per unit mass of a substance to raise the temperature of the mass by 1 degree Celsius. (p. 46) | |
| standard deviation | |
| A measure of how spread out numbers in a set of numbers are. The standard deviation is calculated by taking the square root of the variance, or the average of the squared differences from the mean. (p. 22) | |
| standard error of the mean | |
| A measure of how far the mean of a sample is from the true mean of the whole population. The standard error of the mean is calculated by dividing the standard deviation by the square root of the number of values in a sample. (p. 24) | |
| steroid | |
| A type of lipid; the precursor molecule for cholesterol and steroid hormones. (p. 60) | |
| stroma | |
| The region of the chloroplast that surrounds the thylakoid, where the Calvin cycle takes place. (p. 218) | |
| substrate (S) | |
| A molecule acted upon by an enzyme; also called a reactant. (p. 200) | |
| substrate-level phosphorylation | |
| A way of generating ATP in which a phosphate group is transferred to ADP from an organic molecule, which acts as a phosphate donor or substrate. (p. 235) | |
| surface area | |
| The total area of the outside surface of an object. (p. 105) | |
| surface tension | |
| A measure of the difficulty of breaking the surface of a liquid. (p. 44) | |
| symbiosis (plural, symbioses) | |
| A close interaction that has evolved between species that live together, often interdependently. (p. 172) | |
| sympatric | |
| Describes populations that are in the same geographic location. (p. 673) | |
| system | |
| A group of entities that function together. A system may be living or nonliving. (p. 4) | |
| target cell | |
| A cell that has receptor proteins that can bind to a specific signaling molecule. (p. 277) | |
| telophase | |
| The phase of mitosis in which the nuclei of the daughter cells are formed and the chromosomes uncoil to their original state. (p. 328) | |
| template strand | |
| The strand of DNA that is used as a template, or model, for RNA synthesis during transcription. The template strand is also called the noncoding, antisense, and minus strand. (p. 460) | |
| tertiary structure | |
| The three-dimensional shape of a single polypeptide chain, usually made up of several secondary structure elements. (p. 71) | |
| test group | |
| The group that is exposed to the independent variable in an experiment. Also known as the experimental group. (p. 7) | |
| theory | |
| A general explanation of the world supported by a large body of experiments and observations. (p. 13) | |
| thylakoid | |
| A flattened sac within the chloroplast that is bounded by membranes where the light-dependent reactions of photosynthesis occur. (p. 111) | |
| thymine (T) | |
| A pyrimidine base. (p. 79) | |
| tonicity | |
| A measure of osmotic pressure; the higher the osmotic pressure, the higher the tonicity. (p. 158) | |
| topoisomerase | |
| An enzyme that relieves stress on the DNA double helix that results from overwinding or underwinding during DNA replication and transcription. (p. 451) | |
| transcription | |
| The synthesis of RNA from a DNA template. (p. 440) | |
| transcription factor | |
| A protein that binds to the promoter of a gene and is necessary for transcription to take place. (p. 489) | |
| transduction | |
| The transfer of DNA from cell to cell by means of a virus; a form of horizontal gene transfer. (p. 521) | |
| transfer RNA (tRNA) | |
| Noncoding RNA that carries individual amino acids for use in translation. (p. 465) | |
| transformation | |
| The conversion of cells from one state to another, as from nonvirulent to virulent, when DNA released to the environment by cell breakdown is taken up by recipient cells. In recombinant DNA technology, the introduction of recombinant DNA into a recipient | |
| transition state | |
| The brief time in a chemical reaction in which chemical bonds in the reactants are broken and new bonds in the product are formed. (p. 198) | |
| translation | |
| The synthesis of a polypeptide chain corresponding to the coding sequence present in a molecule of messenger RNA. (p. 440) | |
| translation elongation | |
| The process by which successive amino acids are added one by one to a growing polypeptide chain during translation. (p. 475) | |
| translation initiation | |
| The process by which translation begins. During initiation, the initiator AUG codon is recognized, and Met is established as the first amino acid in the new polypeptide chain. (p. 475) | |
| translation termination | |
| The process by which the addition of amino acids stops during translation and the completed polypeptide chain is released from the ribosome. (p. 475) | |
| transmembrane protein | |
| A protein that spans the entire lipid bilayer; most integral membrane proteins are transmembrane proteins. (p. 139) | |
| transport protein | |
| A membrane protein that moves molecules across the cell membrane. (p. 138) | |
| transposition | |
| The process by which a DNA sequence moves from one location to another in a DNA molecule. (p. 515) | |
| triacylglycerol | |
| A lipid composed of a glycerol backbone and three fatty acids. (p. 58) | |
| triploidy | |
| The condition of having three complete sets of chromosomes in the genome. (p. 517) | |
| trophic cascade | |
| When indirect effects are initiated by the presence of a predator. (p. 789) | |
| trophic levels | |
| An arrangement of producers and consumers into successive levels that represents the movement of energy. (p. 741) | |
| turgor pressure | |
| Pressure within a cell resulting from the movement of water into the cell by osmosis. (p. 114) | |
| Turner syndrome | |
| A condition in humans in which females have only one X chromosome. (p. 426) | |
| unsaturated | |
| Describes fatty acids that contain carbon–carbon double bonds. (p. 59) | |
| uracil (U) | |
| A pyrimidine base in RNA, where it replaces thymine found in DNA. (p. 84) | |
| vacuole | |
| A membrane-bound organelle present in some cells, including plant and fungal cells, that contains fluid, ions, and other molecules; in some cases, it absorbs water and contributes to turgor pressure. (p. 114) | |
| valence electron | |
| An electron in the outermost energy level of an atom. (p. 31) | |
| van der Waals force | |
| An interaction of temporarily polarized molecules because of the attraction of opposite charges. (p. 59) | |
| vesicle | |
| A small membrane-enclosed sac that transports substances within the cell. (p. 105) | |
| vestigial structure | |
| A structure that has lost its original function over time and is now much reduced in size. (p. 619) | |
| virus | |
| A small infectious agent that contains a nucleic acid genome packaged inside a protein coat called a capsid; some viruses also have a phospholipid envelope. (p. 541) | |
| visible light | |
| The portion of the electromagnetic spectrum apparent to our eyes. (p. 221) | |
| volume | |
| The amount of space an object occupies. (p. 120) | |
| water potential | |
| A parameter that combines all the physical and chemical factors that influence the movement of water, such as pressure, osmosis, and gravity; water moves from regions of higher water potential to regions of lower water potential. (p. 157) | |
| zygote | |
| The diploid cell formed by the fusion of two gametes. (p. 360) |
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