Biology Definitions

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definitions - chapter 01.txt
definitions - chapter 02.txt
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definitions - chapter 07.txt
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definitions - chapter 09.txt
definitions - chapter 10.txt
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definitions - chapter 17.txt
definitions - chapter 18.txt
definitions - chapter 19.txt
definitions - chapter 20.txt
definitions - chapter 21.txt
definitions - chapter 22.txt
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definitions - master.txt

abiotic factor					nonliving parts of an organism's environment.
acid							any substance that forms hydrogen ions (H^+) in water and has a pH below 7.
acid precipitation				rain, sleet, snow, or fog with a pH below 5.6.
active transport				energy-expending process by which cells transport materials across the cell membrane against a concentration gradient.
adaptation						evolution of a structure, behavior, or internal process that enables an organism to respond to environmental factors and live to produce offspring.
adenosine diphosphate			molecule formed from the breaking off of a phosphate group for ATP.
adenosine triphosphate			energy-storing molecule in cells composed of an adenosine molecule, a ribose sugar, and three phosphate groups.
age structure					proportions of a population that are at different age levels.
alcoholic fermentation			anaerobic process in which cells convert pyruvic acid into carbon dioxide and ethyl alcohol.
allele							alternative forms of a gene for each variation of a trait of an organism.
amino acid						basic building blocks of protein molecules.
anaerobic						chemical reactions that do not require the presence of oxygen.
anaphase						third phase of meitosis in which the centromeres split and the chromatic pairs of each chromosome are pulled apart by microtubules.
aphotic zone					deep water that never receives sunlight.
atom							smallest particle of an element that has the characteristics of that element.
autosomes						pairs of matching homologous chromosomes in somatic cells.
autotroph						organisms that use energy from the sun or energy stored in chemical compounds to manufacture their own nutrients.
base							any substance that forms hydroxide ions (OH^_) in water and has a pH above 7.
biodiversity					variety of life in an area.
biological community			a community made up of interacting populations in a certain area at a certain time.
biology							the study of life that seeks to provide an understanding of the natural world.
biomass							the total mass of all living matter in a given area.
biome							groups of ecosystems with the same climax communities.
biosphere						portion of Earth that supports life.
biotic factor					all the living organisms that inhabit an environment.
birthrate						number of live births per 1000 population in a given year.
Calvin cycle					series of reactions during the light-independent phase of photosynthesis in which simple sugars are formed from carbon dioxide using ATP and hydrogen from the light-dependent sources.
cancer							uncontrolled cell division that may be caused by environmental factors and/or changes in enzyme production in the cell cycle.
captivity						when members of a species are held by people in zoos or other conservation facilities.
carbohydrate					organic compound used by cells to store and release energy.
carrier							an individual heterozygous for a specific trait.
carrying capacity				number of organisms of one species that an environment can support indefinitely.
cell							basic unit of all organisms.
cell cycle						continuous sequence of growth (interphase) and division (mitosis) in a cell.
cell theory						the theory of cells.
cell wall						fairly rigid structure located outside of the plasma membrane of plants, fungi, and most bacteria.
cellular respiration			chemical process where mitochrondira break down food molecules to produce ATP.
centrioles						in animal cells, a pair of small cylindrcal structures composed of microtubules that duplicate during interphase and move to opposite ends of the cell during prophase.
centromere						cell structure that joins two sister chromatids of a chromosome. 
chlorophyll						light-absorbing pigment in plants and some protoists that is required for photosynthesis.
chloroplast						chlorophyll-containing organelles found in the cells of green plants.
chromatin						long strands of DNA found in the eukaryotic cell nucleus. 
chromosomal mutation			mutation that occurs at the chromosome level resulting in changes in the gene distribution to gametes during meiosis.
chromosomes						cell structures that carry the genetic material that is copied and passed from generation to generation of cells. 
cilia							short, numerous, hairlike projections composed of pairs of microtubules.
citric acid cycle				in cellular respiration, series of chemical reactions that break down glucose and produce ATP.
climax community				a stable, mature community that undergoes little or no change in species over time.
clones							genetically identical copies of an organism or gene.
codominant alleles				pattern where phenotypes of both homozygous parents are produced in heterozygous offspring so that both alleles are equally expressed.
codon							set of three nitrogenous bases that represents an amino acid.
commmensalism					symbiotic relationship in which one species benefits and the other species is neither harmed nor benefited.
compound						substance composed of atoms of two or more different elements that are chemically combined.
compound light microscope		instrument that uses light and a series of lenses to magnify objects in steps. 
conservation biology			field of biology that studies methods and implements plans to protect biodiversity.
control							in an experiment, the standard against which results are judged.
covalent bond					chemical bond formed when two atoms share electrons.
crossing over					exchange of genetic material between nonsister chromatids from homologous chromosomes during prophase 1 of meiosis.
cytokinesis						cell process following meiosis or mitosis in which the cell's cytoplasm divides and separates into new cells.
cytoplasm						clear, gelatinous fluid in cells that is the site of numerous chemical reactions.
cytoskeleton					cellular framework found within the cytoplasm composed of microtubules and microfilaments.
data							information obtained from experiments, sometimes called experimental results.
death rate						number of deaths per 1000 population in a given year.
decomposers						organisms, such as fungi and bacteria, that break down and absorb nutrients from dead organisms.
demography						study of population characteristics.
density-dependent factor		limiting factors that affect the growth of a population.
density-independent factor		factor that affects all populations, regardless of density.
dependent variable				in an experiment, the condition that results from changes in the independent variable.
desert							arid region with sparse to almost nonexistent plant life.
development						all of the changes that take place during the life of an organism; a characteristic of all living things.
diffusion						random movement of particles from an area of higher concentration to an area of lower concentration, eventually resulting on even distribution.
diploid							cell with two of each kinds of chromosome.
DNA replication					process in which chromosomal DNA is copied before mitosis or meiosis.
dominant						observed trait of an organism that masks the recessive form of a trait.
double helix					shape of a DNA molecule formed when two twisted DNA strands are coiled together into a springlike structure and held together by hydrogen bonds between the bases.
doubling time					time needed for a population to double in size.
dynamic equilibrium				result of diffusion where there is continuous movement of particles but no overall change in concentration.
ecology							scientific study between organisms and their environments.
ecosystem						interactions among populations in a community.
edge effect						different environmental conditions that occur along the edges of an ecosystem.
egg								haploid female sex cell produced my meiosis.
electron transport chain		series of proteins embedded in a membrane along which energized electrons are transported.
element							substance that cannot be broken down into simpler chemical substances.
endangered species				a species in which the number of individuals falls so low that extinction is possible.
endocytosis						active transport process where a cell engulfs materials with a portion of the cell's plasma membrane and releases the contents inside of the cell.
endoplasmic reticulum			organelle in eukaryotic cells with a series of highly folded membranes surrounded by cytoplasm.
energy							the ability to cause change; organisms use energy to perform biological functions.
environment						biotic and abiotic surroundings to which an organism must constantly adjust. 
enzymes							type of protein found in all living things that changes the rate of chemical reactions.
estuary							coastal body of water where saltwater and freshwater mix.
ethics							the moral principals and values held by humans.
eukaryote						organisms composed of eukaryotic cells.
evolution						gradual change in a species through adaptations over time.
exocytosis						active transport process by which materials are secreted or expelled from a cell.
exotic species					nonnative species in an area.
experiment						procedure that tests a hypothesis by collecting data under controlled conditions.
exponential growth				growth pattern where a population grows faster as it increases in size.
extinction						the disappearance of a species when the last of its members dies.
facilitated diffusion			passive transport of materials across a plasma membrane by transport proteins embedded in the plasma membrane. 
fertilization					fusion of male and female gametes.
fetus							a developing mammal from 9 weeks to birth.
flagella						long structures composed of microtubules.
fluid mosaic model				structural model of the plasma membrane where molecules are free to move sideways within a lipid bilayer.
food chain						simple model that shows how matter and energy move through an ecosystem.
food web						complex model that shows all possible feeding relationships at each trophic level in a community.
frameshift mutation				mutation that occurs when a single base is added or deleted from DNA.
gametes							male and female sex cells.
gene							segment of DNA that controls the protein production and the cell cycle.
gene therapy					insertion of normal genes into cells to correct genetic disorders.
genetic engineering				method of cutting DNA from one organism and inserting the DNA fragment into a host organism.
genetic recombination			major source of genetic variation among organisms caused by reassortment or crossing over during meiosis.
genetics						branch of biology that studies heredity.
genotype						combination of genes in an organism.
glycolysis						in cellular respiration, series of anaerobic chemical reactions in the cytoplasm that break down glucose into pyruvic acid.
Golgi apparatus					organelle in eukaryotic cells with a system of flattened tubular membranes.
grassland						biome composed of large communities covered with rich soil, grasses, and similar small plants.
growth							increase in the amount of living material and formation of new structures in an organism.
habitat							place where an organism lives out its life.
habitat corridors				natural strips of land that allow the migration of organisms from one wilderness area to another.
habitat degradation				damage to a habitat by air, water, and land pollution.
habitat fragmentation			separation of wilderness areas from each other.
haploid							cell with one of each kind of chromosome.
heredity						passing on of characteristics from parents to offspring.
heterotrophs					organisms that cannot make their own food and must feed on other organisms for energy and nutrients.
heterozygous					when there are two different alleles for a trait.
homeostasis						organism's regulations of its internal environment to maintain conditions suitable for survival.
homologous chromosomes			paired chromosomes with genes for the same traits arranged in the same order.
homozygous						when there are two identical alleles for a trait.
human genome					map of the approximately 80,000 genes on 46 human chromosomes.
hybrid							offspring formed by parents having different forms of a trait.
hydrogen bond					weak chemical bond formed by the attraction of positively charged atoms to other negatively charged atoms.
hypertonic solution				in cells, solution in which the concentration of dissolved substances outside the cell is higher than the concentration inside the cell.
hypothesis						explanation for a question or a problem that can be formally tested.
hypotonic solution				in cells, solution in which the concentration of dissolved substances is lower in the solution outside the cell than the concentration inside the cell.
inbreeding						mating between closely related individuals.
incomplete dominance			inheritance pattern where the phenotype of a heterozygote is intermediate between those of two homozygotes.
independent variable			in an experiment, the condition that is tested because it affects the outcome of the experiment.
interphase						cell growth phase where a cell increases in size, carries on metabolism, and duplicates chromosomes prior to division.
intertidal zone					portion of the shoreline that lies between high and low tide zones.
ion								atom or group of atoms that gain or lose electrons.
ionic bond						chemical bond formed by the attractive forces between two ions of opposite charge.
isomers							compounds with the same simple formula but different three-dimensional structures resulting in different physical and chemical properties.
isotonic solution				in cells, solution in which the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside a cell.
isotopes						atoms of the same element that have different numbers of neutrons in the nucleus.
karyotype						chart of metaphase chromosome pairs arranged according to length and location of the centromere.
lactic acid fermentation		series of anaerobic chemical reactions in which pyruvic acid uses NADH to form lactic acid and NAD+, which is then used in glycolysis.
law of independent assortment	Mendelian principle stating that genes for different traits are inherited independently from each other.
law of segregation				Mendelian principal explaining that because each plant has two different alleles, it can produce two different types of gametes.
life-history pattern			an organism's pattern of reproduction.
light-dependent reactions		phase of photosynthesis where light energy is converted to chemical energy in the form of ATP.
light-independent reactions		phase of photosynthesis where energy from light-dependent reactions is used to produce glucose and additional ATP molecules.
limiting factor					any biotic or abiotic factor that restricts the existence, numbers, reproduction, or distribution of organisms.
linkage map						genetic map that shows the location of genes on a chromosome.
lipid							large organic compounds made mostly of carbon and hydrogen with a small amount of oxygen.
lysosome						organelle that contains digestive enzymes.
meiosis							type of cell division where one body cell produces four gametes, each containing half the number of chromosomes as a parent's body cell.
messenger RNA					RNA that transports information from DNA in the nucleus to the cell's cytoplasm.
metabolism						all of the chemical reactions that occur within an organism.
metaphase						short second phase of mitosis where doubled chromosomes move to the equator of the spindle and chromatids are attached by centromeres to a separate spindle fiber.
microfilaments					thin, solid protein fibers that provide structural support for eukaryotic cells.
microtubules					thin, hollow cylinders made of protein that provide structural support for eukaryotic cells.
mitochondria					eukaryotic membrane-bound organelles that transform energy stored in food molecules.
mitosis							period of nuclear cell division in which two daughter cells are formed, each containing a complete set of chromosomes.
mixture							combination of substances in which individual components retain their own properties.
molecule						group of atoms held together by covalent bonds.
multiple alleles				presence of more than two alleles for a genetic trait.
mutagen							any agent that needs can cause a change in DNA.
mutation						any change or random error in a DNA sequence.
mutualism						a symbiotic relationship in which both species benefit.
NADP+							nicotinamide adenine dicucleotide phosphate; electron carrier molecule.
natural resources				the parts of an environment that are useful for living organisms.
niche							role or position a species has in its environment.
nitrogenous base				carbon ring structure found in DNA or RNA that supports one or more atoms of nitrogen.
nondisjunction					failure of homologous chromosomes to separate properly during meiosis.
nucleic acid					complex biomolecules that store cellular information in cells in the form of code.
nucleolus						organelle in eukaryotic cell nucleus that produces ribosomes.
nucleotides						subunits of nucleic acid formed by from a simple sugar, a phosphate group, and a nitrogenous base.
nucleus							positively charged center of an atom composed of neutrons and positively charged protons, and surrounded by negatively charged electrons.
organ							group of two or more tissues organized to perform complex activities within an organism.
organ system					multiple organs that work together to perform a specific life function. 
organelle						membrane-bound structures with particular functions within eukaryotic cells.
organism						anything that possesses all of the characteristics of life.
organization					orderly structure of cells in an organism.
osmosis							diffusion of water across a selectively permeable membrane depending on the concentration of solutes on either side of the membrane.
ozone layer						layer of the atmosphere that helps to protect living organisms on Earth's surface from damaging doses of ultraviolet radiation from the sun.
parasitism						symbiotic relationship in which one organism benefits at the expense of another.
passive transport				movement of particles across cell membranes by diffusion or osmosis. 
pedigree						graphic representation of genetic inheritance used by geneticists to map genetic traits.
peptide bond					covalent bond formed between amino acids.
pH								measure of how acidic or basic a solution is.
phenotype						outward appearance of an organism regardless of its genes.
phospholipids					lipids with an attached phosphate group.
photic zone						portion of the marine biome that is shallow enough for sunlight to penetrate.
photolysis						reaction taking place in the thylakoid membranes of a chroloplast during light-dependent reactions where two molecules of water are split to form oxygen, hydrogen ions, and electrons.
photosynthesis					process by which autotrophs trap energy from sunlight with chlorophyll and use this energy to convert carbon dioxide and water into simple sugars.
pigments						molecules that absorb specific wavelengths of light.
plankton						small organisms that drift and float in the waters of the photic zone.
plasma membrane					flexible boundary between that cell and it's environment.
plasmid							small ring of DNA found in a bacterial cell that is used as a bacterial vector.
plastids						group of plant organelles that are used for storage of starches, lipids, or pigments.
point mutation					mutation in a DNA sequence.
polar molecule					molecule with an unequal distribution of charge, resulting in the molecule having a positive end and a negative end.
pollination						from male reproductive organs to female reproductive organs of plants, usually within the same species.
polygenic inheritance			inheritance pattern of a trait controlled by controlled by two or more genes.
polymer							large molecule formed when many smaller molecules bond together.
population						group of organisms all of the same species, which interbreed and live in the same place at the same time.
primary succession				colonization of barren land by pioneer organisms.
prokaryotes						unicellular organisms, such as bacteria, each of which is composed of a prokaryotic cell.
prophase						first and longest phase of mitosis where chromatin coils into visible chromosomes.
protein							large, complex polymer essential to all life.
recessive						trait of an organism that can be masked by the dominant form of a trait.
recombinant DNA					DNA made by recombining fragments of DNA from different sources.
reintroduction programs			programs that release organisms into an area where their species once lived in hopes of reestablishing naturally reproducing populations.
reproduction					production of an offspring by an organism.
response						an organisms reaction to a change in its internal or external environment.
restriction enzymes				DNA-cutting enzymes that can cut both strands of a DNA molecule at a specific nucleotide sequence.
ribosomal RNA					RNA that makes up the ribosomes.
ribosomes						nonmembrane-bound organelles in the nucleus where proteins are assembled.
safety symbol					symbol that warns you about a danger that may exist from experimental procedures.
scientific methods				procedures that biologists and other scientists use to gather information and answer questions.
secondary succession			sequence of changes that take place ofter a community is disrupted.
selective permeability			feature of the plasma membrane that maintains homeostasis within a cell by allowing some molecules into the cell while keeping others out.
sex chromosomes					in humans, the 23rd pair of chromosomes; determine the sex of an individual and carry sex-linked characteristics.
sex-linked traits				traits controlled by genes located on sex chromosomes.
sexual reproduction				pattern of reproduction that involves the production of and subsequent fusion of haploid sex cells.
sister chromatid				identical halves of a duplicated parent chromosome formed during the prophase stage of mitosis. 
solution						mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent).
species							group of organisms that can interbreed and produce fertile offspring in nature.
sperm							haploid male sex cells produced by meiosis.
spindle							cell structures composed of microtubule fibers.
stimulus						anything in an organism's internal or external environment that causes the organism to react.
succession						orderly, natural changes and species replacements over time.
sustainable use					philosophy that promotes letting people use resources in wilderness areas in ways that will not damage the ecosystem.
symbiosis						permanent, close association between two or more organisms of different species.
taiga							biome just south of the tundra.
technology						application of scientific research to society's needs and problems.
telophase						final phase of mitosis during which new cells prepare for their own independent existence.
temperate/deciduous 			forest biome composed of forests of broad-leaved hardwood trees that lose their foliage annually.
test cross						mating of an individual of unknown genotypes with an individual of known genotypes.
theory							explanation of natural phenomenon supported by a large body of scientific evidence obtained from many different investigations and sources.
threatened species				when the population of a species is likely to become endangered.
tissue							groups of cells that work together to perform a specific function.
tolerance						the ability of an organism to withstand fluctuations in biotic and abiotic environmental factors.
trait							characteristic that is inherited.
transcription					process in the cell nucleus where enzymes make an RNA copy of a DNA strand.
transfer RNA					RNA that transports amino acids to the ribosomes to be assembled into proteins.
transgenic organisms			organisms that contain functional recombinant DNA from a different organism.
translation						process of converting information in mRNA into a sequence of amino acids in a protein.
transport proteins				proteins that span the plasma membrane creating a selectively permeable membrane that regulates which molecules enter and leave a cell.
trophic level					organism that represents a feeding step in the movement of energy and materials through an ecosystem.
tropical rain forest			biome near the equator.
tundra							biome that surrounds the north and south poles.
vacuole							membrane-bound space in the cytoplasm of cells used for the temporary storage of materials.
vector							means by which DNA from another species can be carried into the host cell.
zygote							diploid cell formed when a sperm fertilized an egg.

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