Praxis Biology 5236 cheat sheet

The independent variable is deliberately manipulated by the researcher; the dependent variable is measured and is expected to respond to that manipulation.

A control group receives no treatment or an inactive placebo and provides the baseline against which the experimental group is compared.

Accuracy is closeness to the true value; precision is the closeness of repeated measurements to one another. A measurement can be precise but inaccurate.

Mean = (sum of all values) / n. Standard deviation describes the typical spread of values around the mean; larger values indicate greater variability.

A scientific hypothesis must be testable and falsifiable; a theory is a broad, well-supported explanatory framework that generates further hypotheses.

Correlation alone does not establish causation; causal claims require controlled experiments or randomized designs that rule out confounding variables.

Metric prefixes: kilo- = 10^3, centi- = 10^-2, milli- = 10^-3, micro- = 10^-6, nano- = 10^-9; convert by moving the decimal three places per prefix step.

pH = -log[H+]; each unit represents a tenfold change in hydrogen ion concentration, and values below 7 are acidic.

For significant figures, multiplication and division retain the least number of significant figures in the inputs; addition and subtraction retain the least number of decimal places.

Cell theory states that all organisms consist of cells, cells arise from pre-existing cells, and the cell is the basic unit of structure and function.

Prokaryotes lack a membrane-bound nucleus and membrane-bound organelles; eukaryotes possess a nucleus, endoplasmic reticulum, Golgi apparatus, and mitochondria.

The phospholipid bilayer is amphipathic; small nonpolar molecules diffuse across it freely, whereas ions and large polar molecules require channels or transporters.

Osmosis is the diffusion of water across a selectively permeable membrane from lower solute concentration (higher water potential) to higher solute concentration.

Enzymes lower activation energy, are not consumed by the reaction, are highly substrate-specific, and are denatured by excessive heat or extreme pH.

Aerobic respiration: C6H12O6 + 6O2 yields 6CO2 + 6H2O + ATP, with glycolysis in the cytosol and the Krebs cycle and electron transport chain in the mitochondria.

Photosynthesis: 6CO2 + 6H2O + light energy yields C6H12O6 + 6O2; light reactions occur in the thylakoid membranes and the Calvin cycle occurs in the stroma.

Mitosis produces two genetically identical diploid daughter cells for growth and repair; meiosis produces four genetically distinct haploid cells for gamete formation.

Transcription synthesizes mRNA from a DNA template in the nucleus; translation occurs on ribosomes, where mRNA codons pair with tRNA anticodons to assemble amino acids.

Hardy-Weinberg equations: p + q = 1 and p^2 + 2pq + q^2 = 1; equilibrium requires no mutation, no migration, random mating, no selection, and a large population.

Genotype is the combination of alleles an organism carries; phenotype is the observable trait produced by genotype interacting with the environment.

Incomplete dominance produces an intermediate heterozygous phenotype; codominance expresses both alleles fully, as in AB blood type.

A monohybrid cross between two heterozygotes yields a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio under complete dominance.

A dihybrid cross between heterozygotes for unlinked genes yields a 9:3:3:1 phenotypic ratio.

X-linked recessive traits appear more frequently in males because males carry only one X chromosome and therefore express the allele directly.

Natural selection acts on existing phenotypic variation: directional selection shifts the mean, stabilizing selection narrows variation, and disruptive selection favors both extremes.

Genetic drift is random change in allele frequency, strongest in small populations; gene flow is the movement of alleles between populations via migration.

Speciation requires reproductive isolation, which may arise geographically (allopatric) or within a shared range through polyploidy or behavioral divergence (sympatric).

The three domains are Bacteria, Archaea, and Eukarya; Archaea differ from Bacteria in cell membrane lipids and cell wall composition.

Taxonomic hierarchy from broadest to narrowest: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Binomial nomenclature gives each species a capitalized genus name and a lowercase specific epithet, both italicized in print or underlined when handwritten.

Viruses are acellular obligate intracellular parasites composed of nucleic acid and a protein capsid; they are not assigned to any of the three domains.

Fungi are heterotrophic eukaryotes with chitin cell walls that absorb nutrients externally and typically reproduce by spores.

Major plant innovations in evolutionary order: cuticle and vascular tissue, then seeds, then flowers and fruit.

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

Bacterial cell shapes are cocci (spheres), bacilli (rods), and spirilla (spirals); peptidoglycan composition distinguishes major bacterial groups.

Vertebrate classes are fishes, amphibians, reptiles, birds, and mammals, distinguished by skin covering, method of respiration, and mode of reproduction.

Exponential growth is described by dN/dt = rN; logistic growth is dN/dt = rN(K - N)/K, where K is the carrying capacity and growth slows as N approaches K.

Survivorship curves: Type I shows high survival early with late-life death, Type II shows constant mortality, and Type III shows heavy early mortality.

Energy transfer between trophic levels averages about 10 percent, with the remainder lost as heat; food chains therefore rarely exceed four or five levels.

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

A keystone species exerts influence on community structure disproportionate to its abundance; its removal triggers cascading changes through the food web.

Primary succession begins on bare substrate without soil, starting with pioneer species such as lichens; secondary succession begins where soil and propagules remain.

Density-dependent factors such as disease, competition, and predation intensify as population size rises; density-independent factors such as fire and storms do not.

Competitive exclusion states that two species cannot indefinitely occupy the same niche in the same place; coexistence requires resource partitioning.

The phosphorus cycle lacks a significant atmospheric phase, unlike the carbon and nitrogen cycles; nitrogen fixation, nitrification, assimilation, and denitrification move nitrogen among reservoirs.

Informed consent requires disclosure of purpose and risks, comprehension by the participant, voluntariness, and decision-making competence.

Antibiotic resistance arises by natural selection: mutations or horizontally transferred genes confer survival under drug pressure, and incomplete courses or agricultural overuse intensify selection.

Bioethical decision-making commonly applies four principles: autonomy, beneficence, nonmaleficence, and justice.

Genetically modified organisms are regulated by case-by-case assessment of the specific introduced trait and its ecological effects rather than by the technique alone.

Peer review screens manuscripts for methodological soundness before publication, but it does not guarantee that findings are correct or reproducible.

Science informs policy, while policy decisions also weigh economic cost, cultural values, feasibility, and competing stakeholder interests.

A technology-outcome correlation must be tested against confounding variables and comparison groups before a causal claim is warranted.

Stem cells are undifferentiated cells capable of self-renewal and differentiation; embryonic and adult sources raise distinct ethical and regulatory questions.

Risk assessment compares the probability and severity of harm from a technology with its expected benefits, and risk is communicated differently from hazard.