DAT Natural Sciences key terms

The number of moles of solute dissolved in one liter of solution. It expresses concentration and is used to calculate how much reactant or product is present in a given volume during stoichiometric or equilibrium problems.

The calculation of relative quantities of reactants and products in a balanced chemical equation. It relies on mole ratios derived from coefficients and is used to predict yields, limiting reagents, and gas volumes.

The reactant that is completely consumed first in a chemical reaction, capping the maximum amount of product that can form. Identifying it requires comparing the mole ratio available to the ratio required by the balanced equation.

A rule stating that a system at equilibrium shifts to partially offset a disturbance such as a change in concentration, pressure, or temperature. It predicts the direction of shift but not the new equilibrium constant value.

The ratio of product concentrations to reactant concentrations at equilibrium, each raised to its coefficient power. Its magnitude indicates whether products or reactants are favored at a given temperature.

A value describing how strongly an acid donates a proton in water, defined as the equilibrium ratio of dissociated ions to undissociated acid. Larger values mean a stronger acid and a lower pH for a given concentration.

A solution of a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists large pH changes when small amounts of strong acid or base are added. It works near the acid's pKa.

The negative base-10 logarithm of hydrogen ion concentration, expressing how acidic or basic a solution is on a scale typically from 0 to 14. Each unit change represents a tenfold change in hydrogen ion concentration.

A reaction class in which electrons transfer between species: one is oxidized by losing electrons and another is reduced by gaining them. Oxidation states help track the electron flow and balance the overall equation.

A device that converts chemical energy into electrical energy, or the reverse, through separated oxidation and reduction half-reactions at two electrodes. Electrons flow through an external circuit while ions move through a salt bridge.

A chemical bond formed when two atoms share one or more pairs of electrons. Sharing occurs because both nuclei attract the same electrons, and unequal sharing produces polar bonds with partial charges.

A measure of how strongly an atom attracts shared electrons within a bond. Differences in this property between bonded atoms determine whether a bond is nonpolar covalent, polar covalent, or predominantly ionic.

A relatively strong attraction between a hydrogen atom covalently bonded to an electronegative atom such as oxygen or nitrogen and a lone pair on another electronegative atom. It explains water's high boiling point and DNA base pairing.

A specific cluster of atoms within an organic molecule that gives the molecule characteristic chemical properties and reactivity, such as hydroxyl, carboxyl, amino, or sulfhydryl groups. Recognizing them helps predict solubility and reactions.

One of two or more molecules with the same molecular formula but different arrangements of atoms, producing different structures and properties. Types include structural, geometric, and optical isomers.

An atom, usually carbon, bonded to four different groups so that exchanging two of them produces a different three-dimensional arrangement. It is the basis of chirality and optical isomerism in organic molecules.

A protein or RNA catalyst that speeds a biochemical reaction by lowering its activation energy without being consumed. Enzymes are usually specific to particular substrates and are regulated by pH, temperature, and inhibitors.

A model describing enzyme reaction rate as a function of substrate concentration, producing a hyperbolic curve that approaches a maximum velocity. The Michaelis constant Km reflects the substrate concentration giving half-maximal velocity.

Control of an enzyme's activity by a molecule binding at a site distinct from the active site, altering the enzyme's shape and therefore its affinity for substrate. It can be inhibitory or activating and often creates feedback loops.

The series of reactions in the cytoplasm that split one glucose molecule into two pyruvate molecules, producing a small net yield of ATP and reducing equivalents. It occurs with or without oxygen and is the first stage of cellular respiration.

A cyclic series of reactions in the mitochondrial matrix that oxidizes acetyl groups derived from pyruvate, releasing carbon dioxide and producing reduced electron carriers. It supplies intermediates for other metabolic pathways.

The final stage of aerobic respiration in which electron transport along the inner mitochondrial membrane pumps protons, and their return flow through ATP synthase drives most cellular ATP production. Oxygen serves as the terminal electron acceptor.

An anaerobic pathway that regenerates oxidized electron carriers by transferring electrons to organic molecules such as pyruvate, allowing glycolysis to continue. It yields far less ATP than aerobic respiration and produces lactate or ethanol.

The division of a cell nucleus producing two daughter nuclei with the same chromosome number as the parent. Its stages are prophase, metaphase, anaphase, and telophase, typically followed by cytokinesis.

A two-round form of nuclear division that halves the chromosome number and produces four genetically varied gametes. Crossing over and independent assortment during meiosis generate genetic diversity.

The random orientation of homologous chromosome pairs at the metaphase plate during meiosis, so alleles for different genes are distributed into gametes independently. It increases genetic variation among offspring.

Patterns of trait transmission explained by segregation of paired alleles and dominance relationships between them. Predictions use Punnett squares and ratios such as 3:1 for monohybrid crosses of heterozygotes.

The use of a family tree diagram to infer the mode of inheritance of a trait, such as autosomal dominant, autosomal recessive, or X-linked. Affected individuals, carriers, and sexes are tracked across generations to test hypotheses.

The process by which heritable traits that improve survival or reproduction become more common in a population over generations. It requires variation, differential fitness, and inheritance of that variation.

A model predicting that allele and genotype frequencies in a population remain constant when there is no mutation, migration, selection, or genetic drift and mating is random. Deviations suggest that one of these forces is acting.

The maintenance of stable internal conditions, such as temperature, pH, and blood glucose, despite changes in the external environment. It typically relies on negative feedback loops that reverse deviations from a set point.

A signaling molecule secreted by endocrine cells that travels through the bloodstream to affect target cells bearing specific receptors. Hormones regulate metabolism, growth, reproduction, and stress responses.

A rapid electrical change in a neuron's membrane caused by sequential opening of ion channels, generating a depolarization followed by repolarization. It propagates along the axon and triggers neurotransmitter release at terminals.

The junction where a neuron communicates with another cell across a small gap called the synaptic cleft. Chemical messengers released from the presynaptic terminal bind receptors on the postsynaptic membrane.

A two-dimensional representation of land surface features using contour lines that connect points of equal elevation. Closely spaced contours indicate steep slopes, and V-shaped contours typically point upstream along valleys.

A line on a map joining points of equal elevation above a reference level. The interval between adjacent contours indicates vertical change, and the spacing between them indicates the steepness of the terrain.

A perceptual ability task requiring you to order several angles from smallest to largest when the angles differ only slightly. It tests visual acuity for subtle orientation differences rather than calculation.

A perceptual task in which a sheet is folded and holes are punched, and you must determine the unfolded pattern. It requires tracking symmetry and mirroring of holes across each fold line.

A perceptual task in which you count the number of painted or unpainted faces on cubes in a stacked figure, including hidden supporting cubes. It tests spatial reasoning about occlusion and three-dimensional structure.

The central point or overall message that a passage develops, which the other details support or illustrate. Identifying it helps distinguish essential content from examples and tangents.

A conclusion drawn from evidence in a passage rather than stated directly. Valid inferences must follow necessarily from the text, not merely seem plausible or match outside knowledge.

A specific fact, example, or reason in a passage that explains or strengthens a broader claim. It is often the target of questions asking why the author mentioned something.

A comparison of two quantities and an equation stating that two such comparisons are equal. Proportions let you solve for an unknown quantity when scaling rates, mixtures, or similar figures.

A rate expressed as a quantity per single unit of another quantity, such as miles per hour or cost per item. Converting to a unit rate makes comparisons and multi-step calculations simpler.

The measure of how likely an event is, calculated as favorable outcomes divided by total equally likely outcomes. For independent events, individual probabilities multiply to give the chance both occur.

Counting methods for selecting items from a group: permutations count arrangements where order matters, while combinations count selections where order does not. Factorials underlie both formulas.

An equation of the form ax squared plus bx plus c equals zero, whose solutions are found by factoring, completing the square, or the quadratic formula. Its graph is a parabola.

A rule assigning exactly one output value to each input value in its domain. Graphs, tables, and equations can represent functions, and transformations shift or stretch their graphs.