CLEP Biology cheat sheet

Enzymes lower activation energy but do not change the free-energy difference between reactants and products; Km is the substrate concentration at half-maximal velocity, and a low Km indicates high substrate affinity.

Competitive inhibitors raise apparent Km with unchanged Vmax; noncompetitive inhibitors lower Vmax with unchanged Km.

ATP yield per glucose: glycolysis nets 2 ATP and 2 NADH; pyruvate oxidation gives 2 NADH; the citric acid cycle gives 2 ATP, 6 NADH, and 2 FADH2; oxidative phosphorylation yields roughly 26-28 ATP.

Semiconservative DNA replication: helicase unwinds, primase lays RNA primers, DNA polymerase III extends 5' to 3', and ligase seals Okazaki fragments on the lagging strand.

Transcription in eukaryotes occurs in the nucleus and requires RNA polymerase plus transcription factors; translation occurs on ribosomes, with the start codon AUG coding for methionine.

Mitosis produces two genetically identical diploid cells; meiosis produces four haploid cells with crossing over in prophase I and independent assortment in metaphase I.

Membrane transport: simple diffusion and osmosis are passive; facilitated diffusion uses channels or carriers down a gradient; active transport (for example, the Na+/K+ pump) requires ATP and moves solute against its gradient.

Photosynthesis: light reactions in the thylakoid membrane generate ATP and NADPH and split water to release O2; the Calvin cycle in the stroma fixes CO2 using RuBisCO.

Cell cycle checkpoints (G1/S, G2/M, and spindle assembly) halt division on DNA damage; failure of tumor suppressors such as p53 permits uncontrolled proliferation.

Homeostasis is maintained by negative feedback loops (for example, insulin lowering blood glucose); positive feedback amplifies a change and is rare, as in oxytocin-driven labor contractions.

Mammalian circulation is a double circuit: the pulmonary circuit carries deoxygenated blood from the right ventricle to the lungs, and the systemic circuit carries oxygenated blood from the left ventricle to the body.

Vascular plants transport water and minerals upward in xylem (driven by transpiration) and distribute sugars in phloem (translocation, source to sink).

Gas exchange in mammals occurs in alveoli by diffusion; oxygen binds hemoglobin cooperatively, producing a sigmoid dissociation curve that shifts right with higher CO2, lower pH, or higher temperature.

Neurons transmit signals by action potentials: Na+ influx depolarizes, K+ efflux repolarizes, and the refractory period enforces one-way conduction; synapses transmit via neurotransmitters.

The vertebrate immune response has innate defenses (barriers, phagocytes, inflammation) and adaptive defenses (B cells producing antibodies, T cells mediating cell-mediated killing).

Osmoregulation in freshwater fish: water enters osmotically and salts are lost, so fish drink little, excrete dilute urine, and actively take up ions through gills.

Hormones act on target cells with specific receptors; steroid hormones cross membranes and bind intracellular receptors, while peptide hormones bind surface receptors and trigger second messengers.

Exponential growth follows N(t) = N0 * e^(rt); logistic growth follows dN/dt = rN(K - N)/K, where K is carrying capacity and growth is fastest at N = K/2.

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, no selection, and large population size; allele frequencies stay constant, and genotype frequencies are p^2, 2pq, and q^2.

Natural selection acts on heritable phenotypic variation; directional selection shifts the mean, stabilizing selection reduces variance, and disruptive selection favors both extremes.

Genetic drift is random allele-frequency change that is strongest in small populations; the bottleneck effect and founder effect both reduce genetic diversity.

Species interactions: mutualism (+,+), commensalism (+,0), parasitism and predation (+,-), and competition (-,-); competitive exclusion can lead to resource partitioning.

Energy transfer between trophic levels is roughly 10 percent efficient, so biomass pyramids typically narrow upward and food chains rarely exceed four or five levels.

Primary succession begins on bare substrate without soil; secondary succession follows a disturbance that leaves soil intact and generally proceeds faster.

Speciation: allopatric speciation involves geographic isolation; sympatric speciation occurs without geographic separation, often via polyploidy or behavioral isolation.

Population size estimation by mark-recapture uses the Lincoln-Petersen index: N = (M * C) / R, where M is marked, C is the total second sample, and R is recaptures.