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abiotic: physical, or nonliving factor that shapes an ecosystem

accesory pigment: compound other than chlorophyll that absorbs light at different wavelengths than chlorophyll

acid: compound that forms protons in solution

action potential: reversal of charges across the cell membrane of a neuron

activation energy: energy needed to get a reaction started

active transport: energy-requiring process that moves material across a cell membrane against its concentration gradient

adaptation: inherited characteristic that increases an organism's chance of survival

ATP: energy source for a cell

aerobic: process that requires oxygen

allele: one of a number of different forms of a gene

amino acid: compound with an amino group and a carboxyl group; monomer of proteins

amylase: enzyme in saliva that breaks down starches

anaerobic: process that occurs in the absence of oxygen

anaphase: third phase of mitosis during which chromatids separate to opposite poles

antibody: protein that helps destroy pathogens

anticodon: group of three bases on a tRNA molecule that are complementary to an mRNA codon

artificial selection: selection by humans for breeding of useful traits from the natural variation among living organisms

ATP synthase: large protein that uses energy from protons to bind ADP and a phosphate group together to produce ATP

autosome: chromosome that is not a sex chromosome

autotroph: organism that can capture energy from sunlight or chemicals and use it to produce its own food; producer



base: compound that produces hydroxide ions in solution

base pairing: principle that bonds in DNA can form only between adenine and thymine and guanine and cytosine

behavior: the way an organism reacts to changes in its internal condition or external environment

behavioral isolation: form of reproductive isolation in which two populations have differences in courtship rituals

bilateral symmetry: body plan which has two equal halves

binary fission: asexual reproduction in which an organism replicates its DNA and divides in half

biodiversity: biological diversity; sum total of the variety of organisms in the biosphere

biogeochemical cycle: process in which elements, chemical compounds, and other forms of matter are passed from one organism to another and from abiotic to biotic factors

biomass: total amount of living tissue within a given trophic level

biome: group of ecosystems that have the same climate and dominant communities

biosphere: part of Earth in which life exists including land, water and air or atmosphere

biotic factor: living influence on organisms within an ecosystem



Calvin Cycle: reactions of photsynthesis in which energy from ATP and NADPH is used to build sugars

cancer: disorder in which some of the body's own cells lose the ability to control growth

capsid: outer coat of a virus

carbohydrate: compound made up of carbon, hydrogen and oxygen atoms; major source of energy

carnivore: organism that obtains energy by eating animals

carrying capacity: largest number of individuals of a population that a given environment can support

catalyst: substance that speeds up the rate of a chemical reaction

cell: basic unit of all forms of life; separated by its surroundings by a cell membrane

cell cycle: series of events that cells go through as they grow and divide

cell division: process by which a cell divides into two new daughter cells

cell membrane: thin, flexible barrier around a cell; regulates what enters and leaves the cell

cell theory: idea that all living things are composed of cells, cells are the basic unit of life, and and new cells come from preexisting cells

cell wall: strong, supportive layer around a cell membrane in plants, algae and some bacteria

cellular respiration: process that releases energy by breaking down glucose and other food molecules in presence of oxygen

centriole: one of two tiny structures located in the cytoplasm of animal cells near the nuclear envelope; aids in cell division

centromere: area where the chromatids of a chromosome are attached

chemoautotroph: organism that makes organic carbon molecules from carbon dioxide using energy from chemical reactions

chemoheterotroph: organism that must take in organic molecules from both energy and carbon

chlorophyll: principal pigment of plants and other photosynthetic organisms; captures light energy

chloroplast: organelle found in cells of plants and some other organisms

chromatid: one of two identical sister parts of a duplicated chromosome

chromatin: material inside a cell nucleus; DNA tightly coiled around a protein

chromosome: threadlike structure within the nucleus containing the genetic information that is passed from one generation of cells to the next

cilium: short hairlike projections similar to flagellum; produces movement in many cells

codominance: situation in which both alleles of a gene contribute to the phenotype of an organism

codon: three nucleotide sequence on messenger RNA that codes for a single amino acid

community: group of populations together in an area

conjugation: form of sexual reproduction in which paramecia and bacteria exchange genetic information

consumer: organism that relies on other organisms for its energy and food supply; heterotroph

convergent evolution: process by which unrelated organisms independently evole similarities when adapting to similar environments

crossing over: process by which homologous chromosomes exchange portions of their chromatids during meiosis

cyclin: one of a family of closely related proteins that regulates the cell cycle

cytokinesis: division of the cytoplasm during cell division

cytoplasm: material inside the cell membrane and outside the nucleus to support the organelles

cytoskeleton: network of protein filaments within some cells that helps the cell maintain its shape and is involved in many forms of cell movement



decomposer: organism that breaks down and obtains energy from dead organic matter

denitrification: conversion of niitrates into nitrogen

density-dependent limiting factor: limiting factor that depends on population size

density-independent limiting factor: limiting factor that affects all populations in similar ways, regardless of population size

DNA: nucleic acid that contains the sugar deoxyribose

detritivore: organism that feeds on plant and animal remains and other dead matter

diffusion: process by which molecules tend to move from an area of high concentration to an area of low concentration

diploid: term used to refer to a cell that contains both sets of homologous chromosomes

directional and disruptive selection: trends in natural selection where the population growth curve show a greater fitness of individuals at certain areas of the graph

DNA fingerprinting: analysis of sections of DNA that have little or no known function, but vary widely from one individual to another, in order to identify individuals

DNA polymerase: enzyme involved DNA replication that joins individual nucleotides to produce a DNA molecule



ecological pyramid: diagram that shows the relative amounts of energy or matter within each trophic level in a food chain or food web

ecological succession: gradual change in living communities that follows a disturbance

ecology: study of interactions among organisms and between organisms and their environment

ecosystem: collection of all the organisms that live in a particular place, together with their nonliving environment

electron transport chain: a series of proteins in which the high energy electrons from the Krebs cycle are used to convert ADP to ATP

emigration: movement of individuals out of an area

endocytosis: process by which a cell takes material into the cell by infolding of the cell membrane

endoplasmic reticulum: internal membrane system in cells in which lipid components of the cell membrane are made and proteins are modified

enzyme: protein that acts as a biological catalyst

eukaryote: organisms whose cells contain nuclei

evolution: change in a kind of organism over time; process by which modern organisms have descended from ancient organisms

exocytosis: process by which a cell releases large amounts of material

exon: expressed sequence of DNA; codes for a protein

exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate



facilitated diffusion: movement of specific molecules across cell membranes through protein channels

feedback inhibition: process in which the product or result stops or limits the process

fermentation: process by which cells release energy in the absence of oxygen

fitness: ability of an organism to survive and reproduce in its environment

food chain: series of steps in an ecosystem in which organisms transfer energy by eating and being eaten

food web: network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem

fossil: preserved remains or evidence of an ancient organism

fossil record: information about past life, including the structure of organism, what they ate, what ate them, in what environment they lived, and the order in which they lived

founder effect: change in allele frequencies as a result of the migration of a small subgroup of a population

frameshift mutation: mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide



gamete: specialized cell involved in sexual reproduction

gel electrophoresis: procedure used to separate and analyze DNA fragments by placing a mixture of DNA fragments at one end of a porous gel and applying an electrical voltage

gene: sequence of DNA that codes for a protein and thus determines a trait

gene map: diagram showing the relative locations of each known gene on a particular chromosome

gene pool: combined genetic information of all the members of a particular population

genetic diversity: sum total of all the different forms of genetic information carried by all organisms living on Earth

genetic drift: random change in allele frequencies that occurs in small populations

genetic engineering: process of making changes in the DNA code of living organisms

genetic equilibrium: situation in which allele frequencies remain constant

genetic marker: gene that makes it possible to distinguish bacteria that carry a plasmid with foreign DNA from those that do not have a plasmid

genetics: study of heredity

genotype: genetic makeup of an organism

geographic isolation: form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers or mountains

geologic time scale: scale used by paleontologists to represent evolutionary time

glycolysis: first step in releasing the energy of glucose, in which a molecule of glucose is broken into two molecules of pyruvic acid

Golgi apparatus: stack of membranes in the cell that modifies, sorts and packages proteins from the endoplasmic reticulum

greenhouse effect: natural situation in which heat is retained in Earth's atmosphere by carbon dioxide, methane, water vapor and other gases



habitat: the area where an organism lives, including the abiotic and biotic factors that affect it

half-life: length of time required for half of the radioactive atoms in a sample to decay

haploid: term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes

Hardy-Weinberg principle: principle that allele frequencies in a population willremain constant unless one or more factors cause the frequencies to change

herbivore: organism that obtains energy from eating plants

heterotroph: organism that obtains energy from the foods it consumes; consumer

heterozygous: term used to refer to an organism that has two different alleles from the same trait

histone: protein molecule around which DNA is coiled in chromatin

homeostasis: process by which organisms maintain a relatively stable internal environment

homologous: term used to refer to chromosomes that each have corresponding chromosomes from the other parent

homologous structures: structures that have different mature forms in different organisms but develop from the same embryonic tissues

homozygous: term used to refer to an organism that has two identical alleles for a particular trait

hybrid: offspring of crosses between parents with different traits

hybridization: breeding technique that involves crossing dissimilar individuals to bring together the best traits of both organisms

hypertonic: when comparing two solutions, the solution with the greater concentration of solutes

hypotonic: when comparing two solutions, the solution with the lesser concentration of solutes



immigration: movement of individuals into an area occupied by an existing population

immunity: ability of the body to resist a specific pathogen

incomplete dominance: situation in which one allele is not completely dominant over the other

independent assortment: independent segregation of genes during the formation of gametes

index fossil: distinctive fossil used to compare the relative ages of fossils

interphase: period of the cell cycle between cell divisions

intron: sequence of DNA that is not involved in coding for a protein

isotonic: concentrations of two solutions is the same





karyotype: photograph of chromosomes grouped in order in pairs

Krebs cycle: second stage of cellular respiration; pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions



light-dependent reactions: reactions of photosynthesis that use energy from light to produce ATP and NADPH

limiting factor: factor that causes the growth of a population to decrease

lipid: macromolecule made mainly from carbon and hydrogen atoms; fats, waxes, oils

lipid bilayer: double-layered sheet that forms the core of nearly all cell membranes

logistic growth: growth pattern in which a population's growth rate slows or stops following a period of exponential growth

lysosome: cell organelle filled with enzymes needed to break down certain materials in a cell



macroevolution: large-scale evolutionary changes that take place over long periods of time

mass extinction: event in which many types of living things became extinct at the same time

meiosis: process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

messenger RNA: RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell

metabolism: set of chemical reactions through which an organism builds up or breaks down materials as it carries out life processes

metaphase: second stage of mitosis; chromosomes line up in the center of the cell

mitochondrion: cell organelle that converts the chemical energy stored in food into compounds that are more convenient for the cell to use

mitosis: part of eukaryotic cell division during which the cell nucleus divides

molecular clock: model that uses DNA comparisions to estimate the length of time that two species have been evolving independently

monomer: small unit that can join together with other small units to create polymers, or macromolecules

monosaccharide: single sugar molecule

multiple alleles: three or more alleles of the same gene

mutation: change in a DNA sequence that affects genetic information



NAD: electron carrier involved in glycolysis

NADP: one of carrier molecules that transfers high energy electrons from chlorophyll to other molecules

natural selection: process by which individuals that are better suited to their environment survive and reproduce most successfully

niche: full range of physical and biological conditions in which an organism lives and the way in which the organism uses those conditions

nitrogen fixation: process of converting nitrogen gas into ammonia

nondisjunction: error in meiosis in which homologous chromosomes fail to separate

nuclear envelope: layer of two membranes that surrounds the nucleus of the cell

nucleic acid: macromolecule containing hydrogen, oxygen, nitrogen, carbon and phosphorous atoms; genetic information

nucleolus: small, dense region within most nuclei in which the assembly of proteins begins with the assembly of ribosomes

nucleotide: monomer of nucleic acids madue up of a 5-carbon sugar, a phosphate group, and a nitrogen base

nucleus: the structure that contains the cell's genetic information and controls the cell's activities



omnivore: organism that obtains energy by eating both plants and animals

operator: region of chromosome in an operon to which the repressor binds when the operon is "turned off"

operon: group of genes operating together

organelle: specialized structure that performs important cellular functions within a eukaryotic cell

osmosis: diffusion of water through a selectively permeable membrane



pathogen: disease-causing agent

pedigree: chart that shows the relationships within a family

period: unit of time into which eras are subdivided

phagocytosis: process in which extensions of cytoplasm surround and engulf large particles and take them into the cell

phenotype: physical characteristics of an organism

photoautotroph: organism that uses energy from sunlight to convert carbon dioxide and water to carbon compounds

photoheterotroph: organism that is photosynthetic but needs organic compounds as an energy source

photosynthesis: process by which plants use light energy to convert water and carbon dioxide into oxygen and high energy carbohydrates such as sugars and starches

photosystem: light-collecting units of the chloroplast

phylogeny: study of evolutionary relationships among organisms

pigment: light-absorbing molecule

pinocytosis: process by which a cell takes in liquid from the surrounding environment

pioneer species: first species to populate an area during primary succession

plasmid: small circular piece of DNA

point mutation: gene mutation involving changes in one or a few nucleotides

polygenic trait: trait controlled by two or more genes

polymer: large compound formed from combinations of many monomers; macromolecule

PCR: technique that allows molecular biologists to make many copies of a particular gene

polyploidy: condition in which an organism has extra sets of chromosomes; results from nondisjunction

polysaccharide: large macromolecule formed from simple sugars

population: group of individuals of the same species that live in the same area

population density: number of individuals per unit of area

predation: interaction in which one organism captures and feeds on another organism

predator-prey relationship: mechanism of population control in which a population is regulated by predation

primary succession: successsion that occurs on surfaces where no soil exists

prion: infectious particle made up of protein rather than DNA or RNA

producer: organism that can capture energy from sunlight or chemicals and use it to produce food from inorganic compounds; autotroph

product: element or compound produced by a chemical reaction

prokaryote: unicellular organism lacking a nucleus

promoter: region of DNA that indicates to an enzyme where to bind to make RNA

prophage: viral DNA that is embedded into the host cell's DNA

prophase: first and longest phase of mitosis; chromosomes become visible and the centrioles separate and move to opposite sides of the cell

protein: macromolecule that contains carbon, hydrogen, oxygen and nitrogen; needed by the body for growth and repair and to make up enzymes

punctuated equilibrium: pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

Punnett square: diagram showing the gene combinations that might result from a genetic cross






radioactive dating: technique in which scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains

recombinant DNA: DNA produced by combining DNA from different sources

reactant: element or compound that enters into a chemical reaction

relative dating: method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock

relative frequency: number of times an allele occur in a gene pool compared with the number of times other alleles occur

replication: copying process by which a cell duplicates its DNA

reproductive isolation: separation of species or populations so that they cannot interbreed and produce fertile offspring

restriction enzyme: enzyme that cuts DNA at a specific sequence of nucleotides

retrovirus: virus that contains RNA as its genetic information

RNA: single-stranded nucleic acid that contains the sugar ribose

ribosomal RNA: type of RNA that make up the major part of a ribosome

RNA polymerase: enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription



secondary succesion: succession following a disturbance that destroys a community without destroying the soil

segregation: separation of alleles during gamete formation

selective breeding: method of breeding that allows only those individual organisms with desired characcteristics to produce the next generation

sex chromosome: one of two chromosomes that determine an individual's sex

sex-linked gene: gene located on the X or Y chromosome

solute: substance that is dissolved in a solvent to make a solution

solution: mixture of two or more substances in which the molecules of the substances are evenly distributed

solvent: substance in which a solute is dissolved to form a solution

species: group of similar organisms that can breed and produce fertile offspring; created through speciation

spindle: fanlike microtubule structure that helps separate the chromosomes during mitosis

stabilizing selection: form of natural selection by which the center of the curve remains a bell-shaped curve

substrate: reactant of an enzyme-catalyzed reaction



telophase: fourth and final phase of mitosis; chromosomes begin to disperse into a tangle of dense material

trait: specific characteristic that varies from one individual to another

transcription: process in which part of the nucleotide sequence of DNA is copied into a complementary sequence of RNA

transfer RNA: type of RNA molecule that transfers amino acids to ribosomes during protein synthesis

transformation: process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria

transgenic: term used to refer to an organism that contains genes from other organisms

translation: decoding of a mRNA message into a polypeptide (protein) chain

trophic level: step in a food chain or food web





vacuole: cell organelle that stores materials such water, salts, proteins and carbohydrates

vector: animal that carries pathogens from person to person

virus: particle made up of nucleic acid, protein, and in some cases lipids that can replicate only by infecting living cells










Glossary definitions courtesy of Prentice-Hall Biology by Miller and Levine