OAT Natural Sciences key terms

The net movement of water across a selectively permeable membrane from a region of lower solute concentration to one of higher solute concentration, driven by the water-potential gradient until equilibrium is reached.

Describes a solution with a higher solute concentration than the cell or compartment it is compared with, causing water to leave that cell and leading to shrinkage or crenation.

The outward hydrostatic force exerted by cell fluid pressing the plasma membrane against a rigid cell wall, keeping plant cells firm and helping drive cell expansion.

The potential energy of water per unit volume relative to pure water at atmospheric pressure; water flows from higher to lower water potential, and solutes lower it.

Movement of a solute across a membrane against its concentration gradient, requiring energy input such as ATP hydrolysis and usually a membrane protein pump.

Passive movement of a solute down its concentration gradient through a membrane protein channel or carrier, requiring no metabolic energy input.

The cytosolic pathway that splits one glucose into two pyruvate molecules, producing a net two ATP and two NADH without requiring oxygen.

The mitochondrial cycle that oxidizes acetyl-CoA to carbon dioxide, generating NADH, FADH2, and GTP while regenerating oxaloacetate for the next turn.

ATP production driven by an electron transport chain that pumps protons across the inner mitochondrial membrane, creating a gradient used by ATP synthase.

The use of a transmembrane proton gradient to drive ATP synthesis as protons flow back through ATP synthase, coupling electron transport to phosphorylation.

A membrane enzyme that uses the flow of protons down their electrochemical gradient to phosphorylate ADP into ATP, functioning as a rotary molecular motor.

Nuclear division producing two genetically identical daughter nuclei, proceeding through prophase, metaphase, anaphase, and telophase, followed by cytokinesis.

Two successive nuclear divisions that halve the chromosome number and generate genetic variation through independent assortment and crossing over, producing haploid gametes.

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

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

The condition in which allele and genotype frequencies in a population remain constant across generations absent mutation, migration, selection, drift, and nonrandom mating.

Random change in allele frequencies across generations due to sampling of gametes, strongest in small populations and capable of fixing or losing alleles by chance.

Differential survival and reproduction of individuals owing to heritable trait variation, causing alleles that improve fitness in a given environment to become more common.

Synthesis of an RNA molecule from a DNA template by RNA polymerase, producing messenger RNA that carries the coding sequence toward translation.

Ribosome-mediated assembly of a polypeptide, in which transfer RNA molecules match codons of messenger RNA to specific amino acids.

A sequence of three consecutive nucleotides in messenger RNA that specifies one amino acid or a stop signal during translation.

A concentration expression giving the number of moles of solute dissolved per liter of solution, abbreviated M and widely used in stoichiometric calculations.

The amount of substance containing Avogadro's number of particles, approximately 6.022 times 10 to the 23rd, used to convert between mass and particle count.

The mass in grams of one mole of a substance, numerically equal to its formula mass in atomic mass units and used to convert mass to moles.

The reactant that is completely consumed first in a chemical reaction, thereby determining the maximum amount of product that can form.

The actual mass of product obtained divided by the theoretical maximum mass predicted from stoichiometry, multiplied by one hundred.

The process of lowering a solution's concentration by adding solvent, described by the relationship that initial molarity times initial volume equals final molarity times final volume.

A quantitative procedure in which a solution of known concentration is added until the analyte is exactly consumed, often detected by an indicator color change.

The stage of a titration at which the moles of added titrant exactly match the stoichiometric requirement of the analyte, distinct from the observed endpoint.

A solution of a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists large pH changes upon addition of small amounts of acid or base.

The rule that a system at equilibrium shifts to partially offset a disturbance such as a change in concentration, pressure, or temperature.

The ratio of product concentrations to reactant concentrations at equilibrium, each raised to its stoichiometric coefficient; its value indicates whether products or reactants dominate.

The minimum energy that colliding reactant molecules must possess for a reaction to proceed, lowered by catalysts that provide an alternative pathway.

An equation expressing reaction rate as a function of reactant concentrations raised to experimentally determined orders, with an overall rate constant.

The time required for half of a reactant to be consumed in a reaction, or for half of a radioactive sample to decay; for first-order processes it is constant.

A species that donates a proton to another species in a reaction, leaving behind its conjugate base.

The species remaining after a Brønsted-Lowry acid loses a proton; together the acid and its conjugate base form a conjugate acid-base pair.

A logarithmic measure of hydrogen ion concentration, defined as the negative base-ten logarithm of the molar hydrogen ion concentration in a solution.

The property of an object or molecule that cannot be superimposed on its mirror image, typically arising from a carbon bonded to four different groups.

An atom bearing groups arranged so that interchanging any two produces a different stereoisomer, commonly a carbon with four distinct substituents.

One of a pair of stereoisomers that are non-superimposable mirror images of each other, with identical physical properties except direction of rotation of plane-polarized light.

A naming system assigning the spatial arrangement around a stereocenter by ranking substituents with the Cahn-Ingold-Prelog priority rules and noting the direction of priority 1 to 2 to 3.

An electron-rich species that donates an electron pair to form a new bond with an electron-poor carbon or other electrophilic center.

An electron-poor species that accepts an electron pair from a nucleophile, often a carbocation or a carbon bearing a partial positive charge.

A one-step nucleophilic substitution in which the nucleophile attacks the carbon as the leaving group departs, giving inversion of stereochemistry at that carbon.

A two-step nucleophilic substitution proceeding through a carbocation intermediate, whose formation is rate-determining and which leads to racemization at the reactive carbon.

A positively charged carbon species with only three bonds, stabilized by alkyl substitution and hyperconjugation; its stability order explains many substitution and elimination outcomes.

The atom or group that departs with a pair of electrons during a substitution or elimination reaction; weak bases are generally better leaving groups.

The guideline that addition of a hydrogen halide to an alkene places the hydrogen on the carbon with more hydrogens and the halogen on the more substituted carbon.

A carbonyl compound whose carbonyl carbon bears at least one hydrogen, making it readily oxidized to a carboxylic acid.

A carbonyl compound in which the carbonyl carbon is bonded to two carbon groups, resistant to mild oxidation and reactive toward nucleophilic addition.

A compound containing a carbonyl carbon bonded to a hydroxyl group, which is acidic and can be converted to esters, amides, and acid chlorides.

A compound formed when a carboxylic acid reacts with an alcohol, containing a carbonyl bonded to an oxygen that is attached to a carbon group.

Base-promoted hydrolysis of an ester that yields a carboxylate salt and an alcohol, the reaction by which triglycerides become soap.

The special stability of a planar, cyclic, fully conjugated system with 4n+2 pi electrons, exemplified by benzene.

The description of a molecule by two or more valid Lewis structures whose weighted average represents the actual delocalized electron distribution.