OAE Biology cheat sheet

Scientific method sequence: observation, question, hypothesis, prediction, controlled experiment, data analysis, conclusion, peer review, replication.

Independent variable is manipulated by the researcher; dependent variable is measured; controlled variables are held constant across groups.

Control group receives no treatment or a placebo, establishing a baseline against which the experimental group is compared.

Validity: internal validity concerns whether the design supports causal claims; external validity concerns generalization beyond the study sample.

Reliability refers to consistency of repeated measurements; accuracy refers to closeness to the true value; precision refers to closeness among repeated measurements.

A theory is a well-tested explanatory framework supported by many lines of evidence; a hypothesis is a testable, falsifiable prediction; a law describes a consistent relationship.

Correlation does not establish causation; confounding variables and reverse causation are alternative explanations for an observed association.

Peer review screens manuscripts for methodological soundness before publication but does not guarantee correctness; replication remains the stronger check.

SI base units: meter (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), mole (amount), candela (luminous intensity).

Cell theory: all organisms are composed of cells, the cell is the basic unit of life, and cells arise from pre-existing cells.

Prokaryotes lack membrane-bound organelles and a nucleus; eukaryotes have a nucleus and membrane-bound organelles including mitochondria and endoplasmic reticulum.

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

Fluid mosaic model: phospholipid bilayer with embedded proteins, cholesterol modulating fluidity, and glycoproteins for recognition.

Enzymes lower activation energy without altering reaction equilibrium; activity depends on temperature, pH, substrate concentration, and inhibitors.

Competitive inhibitors bind the active site and are overcome by increased substrate; noncompetitive inhibitors bind elsewhere and reduce Vmax.

Cellular respiration: glycolysis (cytosol, net 2 ATP, 2 NADH), Krebs cycle (mitochondrial matrix), oxidative phosphorylation (inner membrane, ~30-32 ATP total).

Photosynthesis: light reactions in thylakoid membranes produce ATP and NADPH; the Calvin cycle in the stroma fixes CO2 via rubisco.

DNA replication is semiconservative; helicase unwinds, primase lays RNA primers, DNA polymerase III synthesizes 5' to 3', ligase seals nicks.

Mendel's laws: segregation (alleles separate during meiosis) and independent assortment (genes on different chromosomes assort independently).

Monohybrid cross Aa x Aa yields 3:1 phenotype and 1:2:1 genotype; dihybrid heterozygote cross yields 9:3:3:1.

Hardy-Weinberg equilibrium requires no mutation, no migration, no selection, infinite population size, and random mating; p + q = 1 and p² + 2pq + q² = 1.

Sex-linked traits: X-linked recessive disorders appear more often in males because they carry one X chromosome.

Central dogma: DNA to RNA via transcription, RNA to protein via translation; codons are triplet, degenerate, and non-overlapping.

Mutation types: silent, missense (amino acid substitution), nonsense (premature stop), and frameshift (insertion or deletion not in multiples of three).

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

Genetic drift is random allele frequency change, strongest in small populations; the bottleneck and founder effects are its classic cases.

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

Three domains: Bacteria, Archaea, Eukarya; Archaea differ biochemically from Bacteria, with ether-linked membrane lipids and distinct RNA polymerase.

Taxonomic hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species; binomial nomenclature italicizes genus and species.

Plants: bryophytes (no vascular tissue), ferns (vascular, no seeds), gymnosperms (naked seeds), angiosperms (flowers, fruit, double fertilization).

Animal phyla: Porifera (sponges, no true tissues), Cnidaria (radial symmetry, cnidocytes), Platyhelminthes (flatworms), Annelida (segmented), Arthropoda (exoskeleton, most species), Chordata (notochord, dorsal hollow nerve cord).

Vertebrate classes: fish (gills, ectothermic), amphibians (moist skin, metamorphosis), reptiles (amniotic eggs, scales), birds (feathers, endothermic), mammals (hair, mammary glands).

Fungi are heterotrophic absorbers with chitin cell walls; they form mycorrhizae and lichens and reproduce via spores.

Viruses are acellular obligate intracellular parasites with nucleic acid and a protein capsid; they are not classified in the three domains.

Homologous structures share ancestry but may differ in function; analogous structures share function but not ancestry, indicating convergent evolution.

Dichotomous keys use paired either-or choices to identify organisms; each step narrows the candidate set.

Trophic levels: producers, primary consumers, secondary consumers, tertiary consumers; decomposers recycle nutrients at every level.

The 10% rule: roughly 10% of energy transfers between trophic levels; energy is lost mainly as heat, so food chains rarely exceed four or five levels.

Population growth: exponential (J-shaped, unlimited resources) versus logistic (S-shaped, carrying capacity K); r-selected species favor rapid reproduction, K-selected favor competitive persistence.

Population size change equals (births + immigration) minus (deaths + emigration).

Symbiosis types: mutualism (both benefit), commensalism (one benefits, other unaffected), parasitism (one benefits, host harmed).

Primary succession begins on bare substrate without soil; secondary succession follows disturbance where soil and seeds remain.

Biogeochemical cycles: carbon (photosynthesis, respiration, combustion), nitrogen (fixation, nitrification, denitrification), phosphorus (no atmospheric phase).

Biomes are determined by temperature and precipitation; aquatic zones include photic, aphotic, benthic, and littoral.

Invasive species, habitat fragmentation, and pollution are leading causes of biodiversity loss; keystone species exert disproportionate ecosystem effects.

Scientific literacy includes distinguishing evidence from opinion, evaluating study design, and recognizing sources of bias and funding influence.

Bioethics principles: autonomy, beneficence, nonmaleficence, and justice guide decisions in medicine and research.

Informed consent requires disclosure, comprehension, voluntariness, and capacity; institutional review boards oversee human-subjects research.

Risk assessment combines hazard identification, dose-response, exposure assessment, and risk characterization.

Vaccination produces herd immunity when a sufficient proportion of a population is immune, protecting those who cannot be vaccinated.

Genetically modified organisms raise questions of allergenicity, gene flow, labeling, and biodiversity; regulation varies by country.

Antibiotic resistance develops through selection of resistant bacteria; misuse and overuse accelerate it, and stewardship reduces selection pressure.

Renewable energy sources (solar, wind, hydro, geothermal) versus nonrenewable (coal, oil, natural gas, nuclear fuel); each has distinct environmental trade-offs.

Science informs policy but policy also weighs economics, ethics, and public values; technology assessment evaluates intended and unintended consequences.