GACE Biology (710) cheat sheet

Hypothesis: a testable, falsifiable predicted relationship between variables; a theory is a broad, well-supported explanatory framework that generates further hypotheses, not an unproven guess.

Independent variable is manipulated by the researcher; dependent variable is measured; controlled variables are held constant to prevent confounding.

Control group receives no treatment or a placebo; it establishes the baseline against which the experimental group's change is compared.

Random assignment to groups reduces selection bias; random sampling improves external validity (generalizability) rather than internal validity.

Reliability = consistency of repeated measurements; validity = the measurement actually reflects the intended construct. A reliable instrument can still be invalid.

Correlation does not establish causation; causation requires controlled manipulation, temporal precedence, and ruling out confounders.

Peer review screens submissions for methodological soundness before publication but does not guarantee results are correct; replication is the stronger test.

Scientific claims are provisional and self-correcting; a single disconfirming result does not overturn a theory unless it is reproducible and unexplained.

Prokaryotes lack membrane-bound organelles and a nucleus; eukaryotes have a nucleus and compartmentalized organelles. Both have ribosomes, plasma membrane, and cytoplasm.

Endosymbiotic theory: mitochondria and chloroplasts derive from engulfed bacteria, evidenced by double membranes, own circular DNA, and 70S ribosomes.

Membrane structure is a phospholipid bilayer (fluid mosaic); small nonpolar molecules diffuse freely, while ions and polar molecules need channels or transporters.

Enzyme kinetics: Km is the substrate concentration at half Vmax (inverse index of affinity); Vmax rises with enzyme concentration; competitive inhibitors raise apparent Km, noncompetitive lower Vmax.

Glycolysis (cytosol) yields 2 ATP net and 2 NADH per glucose; the Krebs cycle and oxidative phosphorylation in mitochondria yield most ATP.

Photosynthesis: light reactions in thylakoids produce ATP and NADPH and split water releasing O2; the Calvin cycle in the stroma fixes CO2 via rubisco.

Central dogma: DNA to RNA (transcription) to protein (translation); ribosomes translate mRNA codons using tRNA anticodons, and the genetic code is degenerate but unambiguous.

Water properties follow from hydrogen bonding and polarity: high specific heat, high heat of vaporization, cohesion, and solvent capacity for ions and polar solutes.

Mendel's law of segregation: two alleles per gene separate during meiosis; law of independent assortment applies to genes on different chromosomes or far apart on the same one.

Monohybrid cross of heterozygotes gives 3:1 phenotype and 1:2:1 genotype; dihybrid heterozygote cross gives 9:3:3:1 with independent assortment.

DNA replication is semiconservative and proceeds 5' to 3' by DNA polymerase; the leading strand is continuous, the lagging strand is made in Okazaki fragments.

Mutations: substitution (missense, nonsense, silent), insertion or deletion causing frameshift; frameshifts usually are more damaging than substitutions.

Sex-linked (X-linked) recessive traits appear more often in males because they are hemizygous; affected fathers cannot pass X-linked alleles to sons.

Nondisjunction in meiosis produces aneuploid gametes (e.g., trisomy 21); crossing over in prophase I creates recombinant chromosomes and increases variation.

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, large population, and no selection; deviations indicate evolution is occurring.

PCR uses denaturation, primer annealing, and extension by a thermostable polymerase; gel electrophoresis separates DNA fragments by size, with smaller fragments moving farther.

Natural selection requires heritable variation, differential reproductive success, and environmental pressure; it acts on phenotypes, changing allele frequencies over generations.

Evidence for evolution includes the fossil record, homologous structures, embryological similarities, biogeography, and molecular sequence comparisons.

Homologous structures share ancestry but may differ in function (e.g., forelimbs); analogous structures share function but not ancestry (convergent evolution).

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

Reproductive isolating mechanisms (prezygotic: temporal, behavioral, mechanical; postzygotic: hybrid inviability or sterility) maintain species boundaries.

Genetic drift is random allele frequency change, strongest in small populations; the bottleneck and founder effects reduce genetic diversity.

Three domains (Bacteria, Archaea, Eukarya) replaced the five-kingdom scheme; Archaea differ biochemically from Bacteria despite prokaryotic form.

Binomial nomenclature: italicized genus (capitalized) plus specific epithet (lowercase); hierarchical ranks run domain to species.

Energy flows one way through trophic levels; the 10% rule means roughly 10% of energy transfers to the next level, so food chains rarely exceed 4-5 links.

Gross primary productivity is total energy fixed by producers; net primary productivity subtracts respiration and represents energy available to consumers.

Biogeochemical cycles: carbon and nitrogen have atmospheric reservoirs; phosphorus cycles through rock and soil and is often limiting in freshwater.

Nitrogen fixation by bacteria converts N2 to ammonia; nitrification and denitrification complete the cycle; legumes host nitrogen-fixing symbionts.

Population growth: exponential (J-shaped) under unlimited resources; logistic (S-shaped) approaches carrying capacity K, where growth rate is zero.

Density-dependent factors (competition, disease, predation) intensify with population size; density-independent factors (fire, drought) act regardless of density.

Species interactions: mutualism (+,+), commensalism (+,0), parasitism and predation (+,-), competition (-,-), the last driving resource partitioning or competitive exclusion.

Ecological succession: primary begins on bare substrate with pioneer species; secondary follows disturbance where soil remains, and often ends in a climax community.

Homeostasis uses negative feedback (a response reverses the deviation) as the dominant regulatory mechanism; positive feedback amplifies a change and is rare (e.g., childbirth, clotting).

Mammalian heart: right side pumps deoxygenated blood to lungs, left side pumps oxygenated blood to the body; the SA node sets the intrinsic rate.

Gas exchange occurs across thin, moist surfaces by diffusion; in mammals, alveoli provide large surface area and capillary proximity.

Nephron function: filtration in the glomerulus, reabsorption in the proximal tubule, and concentration in the loop of Henle and collecting duct, regulated by ADH.

Neurons transmit signals via action potentials (depolarization by Na+ influx, repolarization by K+ efflux); neurotransmitters cross the synaptic cleft.

Hormones: lipid-soluble steroids enter cells and alter gene expression; water-soluble hormones bind membrane receptors and act via second messengers.

Skeletal muscle contraction follows the sliding filament model: Ca2+ binds troponin, exposing actin-binding sites so myosin heads cross-bridge and pull actin.

Plant vascular tissue: xylem transports water and minerals upward by transpiration pull; phloem transports sugars bidirectionally under pressure flow.

Metric conversions: 1 L = 1000 mL, 1 mg = 1000 µg, 1 M = 1 mol/L; molarity = moles of solute divided by liters of solution.

Serial dilution: each step multiplies the prior concentration by the dilution factor, so a 1:10 series reaches 1/1000 by the third transfer.

Microscopy: magnification = ocular times objective; resolution improves as wavelength decreases; immersion oil reduces refraction and raises resolution.

Spectrophotometry uses Beer-Lambert law (absorbance proportional to concentration and path length) to quantify dissolved solutes.

Sterile technique: flame loops, work near the flame, keep lids off briefly, and autoclave biohazard waste at about 121 °C and 15 psi.

Chromatography separates molecules by differential affinity (paper: by solubility); centrifugation separates by density, with denser material forming the pellet.

Controls in lab design: negative controls detect contamination or false positives; blanks zero the instrument; positive controls confirm the assay works.

Graph choice: line graphs for continuous change, bar graphs for categorical comparisons, scatter plots for correlation between two continuous variables.