CLEP Natural Sciences flashcards

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

Endosymbiotic theory

Mitochondria and chloroplasts descended from free-living bacteria engulfed by ancestral eukaryotic cells; evidence includes double membranes, circular DNA, and 70S ribosomes.

Hardy-Weinberg equilibrium

Allele and genotype frequencies stay constant across generations when there is no selection, mutation, migration, or drift and mating is random; p² + 2pq + q² = 1.

Three-domain classification

Woese's system dividing life into Bacteria, Archaea, and Eukarya based on ribosomal RNA sequence comparisons, replacing the older five-kingdom scheme.

Allopatric speciation

Formation of new species when a geographic barrier separates populations, blocking gene flow and allowing independent mutation, drift, and selection to diverge them.

Meiosis

Two successive nuclear divisions producing four haploid gametes; crossing over in prophase I and independent assortment in metaphase I create genetic variation.

Central dogma

Genetic information flows from DNA to RNA by transcription, then to protein by translation; codons of three bases specify amino acids, with AUG as start.

Glycolysis

Cytosolic pathway splitting one glucose into two pyruvate molecules, netting 2 ATP and 2 NADH without requiring oxygen; shared by aerobic and anaerobic metabolism.

Calvin cycle

Light-independent reactions in the chloroplast stroma where rubisco fixes CO2 using ATP and NADPH from light reactions to build three-carbon sugar precursors.

Competitive inhibition

An inhibitor binds the enzyme's active site, competing with substrate; it raises apparent Km but maximum velocity can still be reached at high substrate concentration.

Mendel's law of segregation

The two alleles of a gene separate during gamete formation so each gamete carries only one allele, restoring pairs at fertilization.

X-linked recessive inheritance

Traits carried on the X chromosome appear mostly in males, who have one X; affected fathers pass the allele to all daughters but no sons.

Negative feedback

A control mechanism in which a change triggers a response that reverses the change, stabilizing internal conditions such as blood glucose or body temperature.

Xylem and phloem

Vascular plant tissues: xylem carries water and minerals upward in dead cells driven by transpiration; phloem carries sugars in living sieve tubes by pressure flow.

Logistic growth

Population growth described by dN/dt = rN(K−N)/K, slowing as population N approaches carrying capacity K and producing an S-shaped curve.

Ten percent rule

Only about ten percent of energy at one trophic level is incorporated into the next; the rest is lost as heat and waste, limiting food chain length.

Competitive exclusion

Two species competing for the identical limiting resource cannot coexist indefinitely; the better competitor persists while the other is eliminated or shifts its niche.

Nitrogen fixation

Conversion of atmospheric N2 into ammonia by bacteria such as Rhizobium in root nodules or by lightning; makes nitrogen usable for amino acid and nucleic acid synthesis.

Half-life

Time required for half the nuclei in a radioactive sample to decay; after n half-lives the fraction remaining equals one-half raised to n.

Alpha decay

Radioactive emission of a helium-4 nucleus, lowering atomic number by two and mass number by four while producing a different element.

Mass defect

Difference between the mass of a nucleus and the sum of its separate nucleons; converted to nuclear binding energy by E = mc².

Hund's rule

Within a subshell, electrons occupy separate orbitals with parallel spins before pairing, minimizing electron repulsion and stabilizing the ground state.

VSEPR theory

Electron domains around a central atom repel and spread apart, predicting molecular geometry and bond angles from the number of bonds and lone pairs.

Hydrogen bonding

Strong dipole attraction between hydrogen bonded to N, O, or F and a lone pair on a nearby electronegative atom; raises boiling points and orders water structure.

Le Chatelier's principle

A system at equilibrium subjected to stress shifts in the direction that relieves the stress, such as changing concentration, pressure, or temperature.

pH scale

Negative logarithm of hydrogen ion concentration; values below 7 are acidic, 7 neutral, above 7 basic, with each unit representing a tenfold change.

First law of thermodynamics

Energy of a closed system changes by heat added minus work done (ΔU = Q − W); total energy is conserved, never created or destroyed.

Specific heat capacity

Heat needed to raise one gram of a substance by one degree Celsius; Q = mcΔT predicts temperature change for a given heat input.

Time dilation

Moving clocks run slower relative to stationary observers by factor t = t0 divided by the square root of one minus v²/c².

Ohm's law

Current through a conductor equals voltage divided by resistance (I = V/R); power dissipated equals voltage times current, or current squared times resistance.

Snell's law

Light bending at an interface obeys n1 sin θ1 = n2 sin θ2, where n is refractive index and angles are measured from the normal.

Stellar main sequence

Stage when a star fuses hydrogen into helium in its core; plotted diagonally on the Hertzsprung-Russell diagram, with massive stars hotter and more luminous.

Kepler's third law

The square of an orbital period is proportional to the cube of the semi-major axis; relates planet distance from the Sun to its orbital time.

Plate tectonics

Lithospheric plates move over the asthenosphere; divergent boundaries create new crust, convergent boundaries subduct or uplift, and transform boundaries slide past.