OAT Natural Sciences flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cell theory

All living organisms are composed of one or more cells, the cell is the basic unit of structure and function, and all cells arise from pre-existing cells through division.

Prokaryote vs eukaryote

Prokaryotes lack a membrane-bound nucleus and organelles, having circular DNA and 70S ribosomes; eukaryotes have a nucleus, linear chromosomes, membrane-bound organelles, and 80S ribosomes.

Osmosis direction

Water diffuses across a semipermeable membrane from the region of lower solute concentration to the region of higher solute concentration, equalizing water potential until equilibrium is reached.

Km meaning

Km is the substrate concentration at which an enzyme reaches half its maximum velocity; a low Km indicates high substrate affinity, while a high Km indicates low affinity.

Competitive inhibition effect

A competitive inhibitor binds the active site, raising apparent Km because more substrate is needed, but Vmax stays unchanged since high substrate outcompetes the inhibitor.

Semiconservative replication

Each new DNA double helix contains one original parental strand and one newly synthesized strand; DNA polymerase adds nucleotides to the 3' end, so synthesis proceeds 5' to 3'.

Dihybrid cross ratio

Crossing two heterozygotes for two independently assorting genes produces a 9:3:3:1 phenotypic ratio in the offspring, reflecting independent assortment of alleles during meiosis.

Glycolysis net yield

Glycolysis converts one glucose into two pyruvate in the cytoplasm, with a net gain of two ATP and two NADH; it requires no oxygen and occurs in all cells.

Mitochondrial function

Mitochondria generate ATP through the Krebs cycle in the matrix and oxidative phosphorylation on the inner membrane, and they contain their own circular DNA and ribosomes.

Ideal gas law

PV = nRT relates pressure, volume, moles, and temperature; R is 0.0821 L·atm/(mol·K), and at STP one mole of ideal gas occupies 22.4 liters.

Molarity definition

Molarity equals moles of solute divided by liters of solution; it changes with temperature because solution volume expands, whereas molality based on solvent mass does not.

pH formula

pH equals the negative log of hydrogen ion concentration; at 25 °C, pH plus pOH equals 14, and each unit change represents a tenfold change in hydrogen ion concentration.

Henderson-Hasselbalch equation

pH = pKa + log([conjugate base]/[weak acid]) predicts buffer pH; a buffer resists pH change best when the acid and base concentrations are equal and pH equals pKa.

Le Chatelier pressure effect

Increasing pressure on a gaseous equilibrium shifts the reaction toward the side with fewer moles of gas; adding an inert gas at constant volume has no effect.

Equilibrium constant meaning

K expresses the ratio of product to reactant activities at equilibrium; K greater than one favors products, K less than one favors reactants, and pure solids and liquids are omitted.

Gibbs free energy equation

ΔG = ΔH - TΔS determines spontaneity; a negative ΔG means the process is spontaneous, and ΔG equals zero at equilibrium where ΔG° = -RT ln K.

Periodic atomic radius trend

Atomic radius decreases left to right across a period as nuclear charge pulls electrons closer, and increases down a group as additional electron shells are added.

Colligative properties

Boiling point elevation and freezing point depression depend on the number of dissolved particles, not identity; formulas are ΔTb = iKb·m and ΔTf = iKf·m.

Strong versus weak acid

A strong acid dissociates completely in water, giving a large Ka and low pH; a weak acid partially dissociates and requires an equilibrium expression with its Ka value.

Oxidation number rules

Fluorine is always -1, oxygen is usually -2, hydrogen is +1 with nonmetals, and the sum of oxidation numbers equals the ion charge or zero for neutral molecules.

Limiting reactant

The limiting reactant is consumed first and determines maximum product yield; compare moles of each reactant divided by its stoichiometric coefficient to identify it.

Hybridization geometry

Four electron groups give sp3 hybridization and tetrahedral 109.5° geometry; three groups give sp2 and trigonal planar 120°; two groups give sp and linear 180°.

Functional group priority

For IUPAC naming, carboxylic acid outranks ester, amide, aldehyde, ketone, alcohol, amine, alkene, alkyne, and alkane; the highest-priority group determines the suffix.

SN1 mechanism

SN1 is a two-step substitution with a carbocation intermediate, favored by tertiary substrates and polar protic solvents; stereochemistry is racemized and rate depends only on substrate.

SN2 mechanism

SN2 is a one-step concerted substitution with backside attack, favored by primary substrates and polar aprotic solvents; it gives inversion of configuration and rate depends on both reactants.

E2 elimination requirements

E2 is a concerted elimination requiring a strong base and anti-periplanar hydrogen and leaving group; it follows Zaitsev's rule to give the more substituted alkene.

Markovnikov's rule

In addition of HX to an alkene, hydrogen adds to the carbon with more hydrogens, placing the halogen on the more substituted carbon; peroxides reverse this regiochemistry for HBr.

Alcohol oxidation products

Primary alcohols oxidize to aldehydes then carboxylic acids, secondary alcohols oxidize to ketones, and tertiary alcohols resist oxidation because the carbon lacks a hydrogen.

Hückel aromaticity rule

An aromatic ring must be cyclic, planar, fully conjugated, and contain 4n+2 pi electrons; benzene with six pi electrons satisfies this and is aromatic.

Chirality and R/S

A carbon with four different substituents is chiral; R/S assignment ranks substituents by atomic number using Cahn-Ingold-Prelog rules and views the lowest priority group away.

Esterification reaction

A carboxylic acid reacts with an alcohol in the presence of acid catalyst to form an ester and water; the reaction is reversible and equilibrium favors products with excess alcohol.