GACE Biology (710) key terms

In an experiment, the set of subjects that receives no treatment or a sham treatment, used as a baseline for judging whether the independent variable actually caused the observed effect.

The factor that the researcher deliberately manipulates or selects among levels in an experiment; it is the presumed cause whose effect on the dependent variable is being measured.

The measured outcome in an experiment, expected to change in response to the independent variable. It must be operationally defined so results can be quantified and compared across treatment conditions.

A study in which all variables except the independent variable are held constant or randomized, allowing a causal claim about how that single factor affects the measured outcome.

A statement that no real difference or relationship exists between groups or variables; statistical tests evaluate whether observed data are unlikely enough under this assumption to reject it.

A result is statistically significant when the probability of obtaining it by chance alone, if the null hypothesis were true, falls below a chosen threshold such as 0.05.

A testable, falsifiable proposed explanation for an observation, phrased so that predictions can be derived and checked against evidence rather than accepted on belief alone.

A broad, well-supported explanation of a major natural pattern, built from many tested hypotheses and surviving repeated attempts at falsification; not a mere guess or tentative idea.

A concise statement, often mathematical, describing a consistent regularity observed in nature, such as a relationship among measurable quantities, without necessarily explaining the underlying mechanism.

The property of a scientific claim such that some conceivable observation could show it to be false; claims that cannot in principle be contradicted by evidence fall outside empirical science.

The consistency of a measurement or study: repeated measurements under the same conditions yield similar results. Reliable instruments reduce random error but do not guarantee that the right quantity is measured.

The extent to which a measurement or experimental design actually measures or tests what it claims to, so that conclusions drawn from the data are justified rather than artifacts of the method.

Evaluation of a manuscript by independent experts in the field before publication, intended to screen for methodological flaws, unsupported claims, and inadequate evidence, though it does not guarantee correctness.

A cell lacking a membrane-bound nucleus and membrane-bound organelles, with DNA typically in a single circular chromosome plus plasmids; bacteria and archaea are prokaryotes.

An organism whose cells contain a nucleus enclosing the chromosomes and membrane-bound organelles such as mitochondria and endoplasmic reticulum; includes protists, fungi, plants, and animals.

A double-membrane organelle where pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation occur, producing most of the cell's ATP; it contains its own DNA and ribosomes.

A complex of ribosomal RNA and protein that translates messenger RNA into polypeptide chains. Free ribosomes make cytosolic proteins; bound ribosomes on the rough ER make secreted and membrane proteins.

The widely supported explanation that mitochondria and chloroplasts descend from free-living bacteria engulfed by an ancestral host cell, evidenced by their own circular DNA, ribosomes, and double membranes.

Adenosine triphosphate, the universal energy currency of cells: hydrolysis of its terminal phosphate bond releases free energy that drives endergonic reactions, transport, and mechanical work.

A protein (or RNA) catalyst that speeds a biochemical reaction by lowering activation energy, typically through an active site whose shape confers substrate specificity; activity depends on temperature and pH.

The minimum energy input required for a reaction to proceed, corresponding to the energy barrier between reactants and products; catalysts lower it without changing the overall free-energy change.

Loss of a protein's functional three-dimensional shape caused by heat, extreme pH, or chaotropic agents disrupting hydrogen bonds and other noncovalent interactions, usually irreversible for the protein.

Net diffusion of water across a selectively permeable membrane from a region of higher water potential (lower solute concentration) to lower water potential, driven by a solute concentration gradient.

Spontaneous net movement of particles from regions of higher to lower concentration due to random thermal motion, a passive process requiring no cellular energy expenditure.

Passive movement of solutes across a membrane through channel or carrier proteins, down their concentration gradient and without ATP, but limited by the number of available transporters.

Reduction division producing four haploid gametes from one diploid cell through two consecutive divisions; crossing over in prophase I and independent assortment create genetic variation.

Exchange of corresponding chromosome segments between nonsister chromatids of homologous chromosomes during prophase I of meiosis, producing recombinant chromosomes and new allele combinations.

Mendel's principle that alleles of different genes on separate chromosome pairs segregate into gametes independently, generating 2^n possible gamete combinations for n heterozygous pairs.

One of two or more alternative forms of a gene at a given locus, differing in DNA sequence; an individual may carry identical or different alleles on its two homologous chromosomes.

The particular combination of alleles an organism carries at one or more loci, which together with environmental influences and interactions among genes determines the observable phenotype.

The observable traits of an organism, such as morphology, physiology, or behavior, resulting from the interaction of its genotype with environmental conditions during development.

Synthesis of an RNA molecule from a DNA template by RNA polymerase, occurring in the nucleus of eukaryotes and coupled to translation in prokaryotes.

The process at the ribosome in which messenger RNA codons are read and matched to transfer RNAs, assembling amino acids into a polypeptide in the order specified by the genetic code.

Differential survival and reproduction of individuals whose heritable traits make them better suited to their environment, causing those alleles to increase in frequency over generations.

A heritable trait that improves an organism's fitness in a particular environment, or the evolutionary process by which such traits arise and spread within a population.

Random change in allele frequencies from generation to generation due to sampling of gametes, especially strong in small populations; it can fix or eliminate alleles regardless of their effect on fitness.

Movement of alleles between populations through migration and interbreeding, which tends to reduce genetic differences among populations and can counteract the effects of selection and drift.

The relative contribution an individual makes to the next generation's gene pool, usually measured as survival and reproductive success compared with other phenotypes in the same environment.

The evolutionary process by which populations diverge to become reproductively isolated species, often initiated by geographic separation (allopatric) or by polyploidy or assortative mating (sympatric).

The maximum population size an environment can sustain indefinitely given available food, water, space, and other limiting resources; growth slows as the population approaches this ceiling.

Population growth that initially accelerates but slows as density rises and resources become scarce, producing an S-shaped curve that levels off at the environment's carrying capacity.

Any resource or condition whose scarcity restricts population growth or distribution, such as nitrogen availability for plants or nesting sites for birds.

A feeding position within a food web, such as primary producer, primary consumer, or secondary consumer; energy available decreases substantially at each successive level.

A diagram showing that only about 10 percent of energy at one trophic level is transferred to the next, the rest being lost as heat through metabolism and excretion.

An autotroph, usually a photosynthetic plant, alga, or cyanobacterium, that converts inorganic carbon into organic compounds and forms the base of every food web.

Maintenance of a relatively stable internal environment, such as temperature, pH, and blood glucose, through negative feedback loops that detect deviations and trigger corrective responses.

A regulatory mechanism in which a change in a variable triggers a response that counteracts the change, returning the system toward its set point; the dominant control mode in physiology.

A signaling molecule secreted by endocrine cells into the bloodstream, traveling to distant target cells whose receptors recognize it and trigger specific physiological responses.

A specialized cell that receives, integrates, and transmits electrical signals; it has dendrites for input, a cell body, and an axon whose terminals release neurotransmitters.

A rapid, self-propagating change in membrane voltage caused by sequential opening of voltage-gated sodium and potassium channels, carrying signals along axons over long distances.

The junction where a neuron communicates with another cell, typically releasing neurotransmitter across a narrow cleft to excite or inhibit the postsynaptic membrane.

A graph plotting a measured signal against known concentrations of a substance, used to determine the concentration of an unknown sample by interpolation from its measured response.

A laboratory instrument that aspirates and dispenses precise microliter volumes using a disposable tip; correct technique prevents contamination and volume error in assays and dilutions.

A stepwise series of dilutions in which each tube's concentration is reduced by a constant factor, producing a wide range of known concentrations from a single stock solution.

A technique that separates charged molecules such as DNA fragments or proteins through a gel matrix under an electric field, with smaller or more highly charged molecules migrating farther.