Glossary
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A
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
B
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
C
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
D
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
E
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
F
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
G
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
H
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
I
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
J
K
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
L
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
M
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
N
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
O
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
P
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
Q
R
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
S
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
T
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
U
V
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
W
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