OAT key terms

The net movement of water across a semipermeable membrane from a region of lower solute concentration to one of higher solute concentration, driven by a difference in water potential.

A solution whose solute concentration exceeds that inside a cell, so water leaves the cell and it shrinks or shrivels. In plant cells the membrane pulls away from the wall.

The ability of an external solution to cause water to move into or out of a cell, determined by the concentration of nonpenetrating solutes relative to the cytoplasm.

Enzyme inhibition in which a molecule resembling the substrate binds the active site and blocks substrate entry; raising substrate concentration can overcome it, and maximum velocity is unchanged.

Control of enzyme activity by a molecule binding a site other than the active site, shifting the enzyme between active and inactive conformations. It may activate or inhibit and is common in feedback control.

A control mechanism in which the end product of a metabolic pathway inhibits an earlier enzyme in that pathway, slowing production when the product accumulates.

The substrate concentration at which an enzyme works at half its maximum velocity. A small value indicates high affinity of enzyme for substrate.

Pairs of reactions in which the energy released by one spontaneous reaction drives another nonspontaneous one, typically by shared intermediates such as ATP hydrolysis.

Synthesis of ATP driven by a proton gradient across a membrane, as protons flow through ATP synthase. It powers oxidative phosphorylation and photophosphorylation.

Exchange of corresponding chromosome segments between homologous chromatids during prophase I of meiosis, producing new combinations of alleles on a chromosome.

The random orientation of homologous chromosome pairs at metaphase I, so alleles of genes on different chromosomes are distributed to gametes independently of one another.

A pair of chromosomes, one inherited from each parent, that carry the same genes in the same order at corresponding loci but may carry different alleles.

The condition in which allele and genotype frequencies in a population stay constant across generations, requiring no mutation, no migration, random mating, large population, and no selection.

A concentration unit equal to the number of moles of solute dissolved per liter of solution. Because volume changes with temperature, molarity is slightly temperature dependent.

A concentration unit equal to moles of solute per kilogram of solvent. It is temperature independent and is preferred for colligative property calculations.

Properties of a solution that depend on the number of dissolved particles rather than their identity: vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

The number of particles a formula unit of solute produces in solution, used to correct colligative property calculations. It is ideally 1 for glucose and 2 for sodium chloride.

The reactant that is completely consumed first in a chemical reaction, fixing the maximum amount of product that can form from the given quantities.

The amount of substance containing Avogadro's number (about 6.022 x 10^23) of representative particles, with a mass in grams equal to the molar mass.

The actual mass of product obtained divided by the theoretical mass predicted from stoichiometry, multiplied by 100 to express it as a percentage.

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partially offsets the disturbance.

The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient, at equilibrium. Its value depends on temperature and indicates the extent of reaction.

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.

The relationship pH = pKa + log([conjugate base]/[weak acid]), used to calculate the pH of a buffer or the ratio of acid to base at a chosen pH.

The property of a molecule that cannot be superimposed on its mirror image, usually because a carbon bears four different groups. Chiral molecules rotate plane-polarized light.

An atom bearing groups arranged so that interchanging two of them produces a different stereoisomer. A carbon with four different substituents is the most common example.

Stereoisomers that are nonsuperimposable mirror images of each other. They have identical physical properties except for the direction they rotate polarized light and their behavior in chiral environments.

Stereoisomers that are not mirror images of each other, such as cis and trans isomers. They differ in physical properties and can be separated by ordinary methods.

A species that donates an electron pair to form a new bond, often an anion or a molecule with a lone pair. It attacks electron-poor centers such as carbonyl carbons.

A species that accepts an electron pair to form a new bond and is attracted to electron-rich regions. Carbocations and the carbonyl carbon are common examples.

A one-step nucleophilic substitution in which the nucleophile attacks as the leaving group departs, giving inversion of configuration and a rate depending on both substrate and nucleophile.

A two-step nucleophilic substitution that proceeds through a carbocation intermediate, giving a rate that depends only on the substrate and producing racemization at the reacting carbon.

In addition of a hydrogen halide to an alkene, the hydrogen adds to the carbon with more hydrogens, placing the halogen on the more substituted carbon because the more stable carbocation forms.

Delocalization of electrons described by two or more valid Lewis structures, with the real structure a hybrid of them. It stabilizes molecules and affects acidity and reactivity.

The central claim or point a passage is built to support. It is broader than any single detail and is often stated in the first or last paragraph.

A conclusion that follows logically from stated information without being stated directly. Correct inferences require textual support rather than personal opinion.

The author's attitude toward the subject, conveyed through word choice and emphasis, such as critical, neutral, or admiring. It differs from the mood the passage creates in a reader.

A specific fact, example, or reason in a passage that explains or backs up the main idea. Detail questions ask what the passage states explicitly.

Two-dimensional motion of an object under only gravity, analyzed by treating horizontal velocity as constant and vertical motion as uniformly accelerated.

Motion under gravity alone, with air resistance ignored, so every object accelerates downward at the same rate g, about 9.8 m/s^2 near Earth's surface.

The projections of a vector along perpendicular axes, found with sine and cosine, that allow a two-dimensional problem to be solved as two independent one-dimensional problems.

The principle that total momentum of an isolated system stays constant, so in a collision the vector sum of momenta before equals that after.

A collision in which both momentum and kinetic energy are conserved. In one dimension between equal masses, the bodies exchange velocities.

A wave pattern formed by interference of two waves of equal frequency traveling in opposite directions, with fixed nodes and antinodes; only certain wavelengths fit a given length.

A natural frequency at which a system oscillates with large amplitude for a small driving force, producing standing waves in strings and pipes and maximum energy transfer.

The relationship n1 sin(theta1) = n2 sin(theta2) governing refraction at an interface, where n is refractive index and angles are measured from the normal.

The ratio of the speed of light in vacuum to its speed in a medium, always at least 1. It determines how much light bends when entering a material.

The relationship V = IR for a resistor, stating that voltage across a conductor equals current through it times resistance, valid when resistance is constant.

A circuit in which components are connected in one path, so the same current flows through each and the total resistance is the sum of the individual resistances.

A circuit in which components connect across the same two nodes, so each has the same voltage and the total resistance is less than the smallest branch resistance.

A problem-solving method that uses unit conversions as fractions equal to one, canceling units until only the desired unit remains, which also checks whether an answer is plausible.

Rewriting a measured quantity in different units by multiplying by a ratio equal to one, such as 1000 mL per 1 L, without changing the actual value.

The likelihood of an event, computed as favorable outcomes divided by total equally likely outcomes, or as the fraction of times an event occurs in repeated trials.

A selection of items from a group in which order does not matter, counted by n! divided by r!(n-r)!, where n is the group size and r the number chosen.

An arrangement of items in which order matters, counted by n! divided by (n-r)! when choosing and ordering r items from n distinct items.

The exponent to which a base must be raised to produce a given number. Common rules let products become sums and powers become multipliers, useful for solving exponential equations.

Increase in a quantity at a rate proportional to its current size, described by y = a(b)^x with b greater than 1, producing a curve that steepens steadily.

Equations true for all angles that relate sine, cosine, and tangent, such as sin^2 x + cos^2 x = 1, used to simplify expressions and solve equations.

A circle of radius 1 centered at the origin; a point at angle theta on it has coordinates (cos theta, sin theta), which defines the trigonometric functions for all angles.