FY13CE Biology cheat sheet

Water is polar: hydrogen bonds give it high specific heat, high heat of vaporization, cohesion, and solvent power for ionic and polar solutes; nonpolar substances do not dissolve.

Macromolecules are built by dehydration synthesis (condensation) and broken by hydrolysis: carbohydrates (monosaccharides → glycosidic bonds), proteins (amino acids → peptide bonds), nucleic acids (nucleotides → phosphodiester bonds), lipids (glycerol + fatty acids → ester bonds).

Enzymes lower activation energy but do not change ΔG or equilibrium position; they are not consumed. Rate rises with substrate concentration until saturation (Vmax), and each enzyme has an optimum pH and temperature.

Competitive inhibitors raise apparent Km without changing Vmax; noncompetitive/allosteric inhibitors lower Vmax without changing Km.

Membrane structure is a phospholipid bilayer with embedded proteins (fluid mosaic). Small nonpolar molecules (O2, CO2) diffuse freely; ions and polar molecules need channels or carriers.

Osmosis: water moves from low to high solute concentration. Hypertonic solution → cell shrinks (plasmolysis in plants); hypotonic → animal cell lyses, plant cell becomes turgid.

ATP hydrolysis (ATP → ADP + Pi) releases energy that drives endergonic reactions; ATP is regenerated by cellular respiration.

Photosynthesis: light reactions in thylakoid membranes produce ATP and NADPH and split water, releasing O2; the Calvin cycle in the stroma fixes CO2 using RuBisCO.

Cellular respiration: glycolysis (cytoplasm, net 2 ATP, 2 NADH) → pyruvate oxidation and Krebs cycle (mitochondrial matrix, yields NADH, FADH2, CO2) → oxidative phosphorylation at the inner membrane (most ATP, O2 as final electron acceptor).

DNA replication is semiconservative: helicase unwinds, primase lays RNA primers, DNA polymerase III adds nucleotides 5'→3', and ligase seals Okazaki fragments on the lagging strand.

Central dogma: DNA → RNA (transcription, RNA polymerase) → protein (translation at ribosomes; mRNA codons read 5'→3' against tRNA anticodons).

Mendel's law of segregation: two alleles separate during meiosis; law of independent assortment applies to genes on different chromosomes.

Monohybrid cross Aa × Aa gives 1 AA : 2 Aa : 1 aa, i.e., 3:1 phenotype. Dihybrid heterozygote cross gives 9:3:3:1. Testcross (× homozygous recessive) reveals an unknown genotype.

Incomplete dominance gives an intermediate phenotype; codominance expresses both alleles; multiple alleles (ABO blood groups: IA, IB, i) and polygenic traits produce varied phenotypes.

Sex-linked (X-linked) recessive traits appear more often in males because males have only one X; an affected father cannot pass an X-linked allele to sons.

Meiosis produces four haploid cells; crossing over in prophase I and independent assortment in metaphase I generate genetic variation. Nondisjunction causes aneuploidy (e.g., trisomy 21).

Mutations: substitutions may be silent, missense, or nonsense; insertions/deletions of non-multiples of three cause frameshifts. Mutations are the ultimate source of new alleles.

Pedigree rules: a trait appearing in offspring of unaffected parents is recessive; if it appears only in males and skips generations, suspect X-linked recessive.

Natural selection requires heritable variation in fitness. It acts on phenotypes, not directly on genotypes, and populations evolve, not individuals.

Hardy–Weinberg equilibrium (p + q = 1; p² + 2pq + q² = 1) holds only with no mutation, no migration, random mating, infinite population size, and no selection. Deviations indicate evolution.

Five mechanisms of microevolution: mutation, gene flow, genetic drift (bottleneck, founder effect), nonrandom mating, and natural selection.

Species concept: biological species = interbreeding populations reproductively isolated; prezygotic barriers (habitat, temporal, behavioral, mechanical, gametic) and postzygotic barriers (hybrid inviability, sterility) maintain isolation.

Evidence for evolution: fossil record, homologous structures (common ancestry), analogous structures (convergent evolution), vestigial structures, biogeography, and molecular (DNA/protein) similarities.

Three domains: Bacteria, Archaea, Eukarya. Kingdom-level classification within Eukarya includes Protista (paraphyletic grouping), Fungi (absorptive heterotrophs, chitin walls), Plantae (cellulose walls, photosynthesis), Animalia (ingestive heterotrophs).

Endosymbiotic theory: mitochondria and chloroplasts descended from engulfed prokaryotes, supported by their own circular DNA, 70S ribosomes, and double membranes.

Viruses are acellular obligate intracellular parasites: nucleic acid core plus capsid; they reproduce only inside host cells and are not classified as living by all criteria.

Binomial nomenclature: genus capitalized, species lowercase, both italicized or underlined (e.g., Homo sapiens).

Homeostasis uses negative feedback (deviation triggers correction, e.g., thermoregulation, blood glucose via insulin/glucagon) and positive feedback (amplifies change, e.g., oxytocin in childbirth).

Neuron signaling: resting potential ≈ −70 mV; depolarization opens Na+ channels, repolarization involves K+ efflux; the action potential is all-or-none, and myelin speeds conduction.

Synaptic transmission is chemical: neurotransmitter released by exocytosis crosses the cleft and binds receptors; acetylcholinesterase terminates the signal.

Human circulation is a double circuit (pulmonary and systemic); arteries carry blood away from the heart, veins toward it; the SA node sets heart rhythm.

Gas exchange: O2 and CO2 diffuse across thin, moist surfaces (alveoli, gills, leaves). Hemoglobin binds O2 cooperatively; CO2 is carried mainly as bicarbonate.

Kidneys filter blood by nephrons: filtration in the glomerulus, reabsorption in the proximal tubule, and concentration via the loop of Henle; ADH increases water reabsorption.

Plant transport: xylem carries water and minerals upward driven by transpiration and cohesion-tension; phloem translocates sugars from source to sink under pressure flow.

Plant hormones: auxin (cell elongation, phototropism), gibberellins (stem growth, seed germination), cytokinins (cell division), abscisic acid (stomatal closure, dormancy), ethylene (ripening, senescence).

Immune defenses: innate (barriers, phagocytes, inflammation) versus adaptive (B cells → antibodies, humoral; T cells → cell-mediated). Memory cells give a faster secondary response.

Trophic levels: producers → primary consumers → secondary consumers → tertiary consumers; only about 10% of energy transfers between levels, so biomass pyramids narrow upward.

Food webs differ from food chains by showing multiple interacting pathways; removing a keystone species causes disproportionate community change.

Population growth: exponential (dN/dt = rN) occurs with unlimited resources; logistic (dN/dt = rN(K − N)/K) approaches carrying capacity K.

Survivorship curves: Type I (high early survival, e.g., humans), Type II (constant mortality, e.g., birds), Type III (high early mortality, e.g., many fish, oysters).

Species interactions: competition (−/−), predation and parasitism (+/−), mutualism (+/+), commensalism (+/0). Competitive exclusion occurs when niches overlap fully.

Primary succession begins on bare rock or lava (lichens, then mosses); secondary succession follows disturbance where soil remains.

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

Biodiversity includes genetic, species, and ecosystem diversity; habitat loss is the leading cause of species endangerment.

Biomes are defined by climate and dominant vegetation; temperature and precipitation determine their distribution.

Controlled experiments test one independent variable against a dependent variable while holding all other factors constant; a control group receives no treatment or a placebo.

Correlation does not establish causation; a controlled manipulation is needed to infer cause and effect.

Reliability increases with sample size, repetition, and randomization; bias arises from nonrandom sampling or unblinded measurement.

Descriptive statistics: mean (average), median (middle value, resistant to outliers), mode (most frequent); standard deviation measures spread around the mean.

Standard error of the mean = SD/√n; larger n narrows the confidence interval. Error bars typically show SD, SE, or 95% confidence intervals.

A graph's slope represents a rate; a linear relationship indicates a constant rate, and the y-intercept gives the value at x = 0.

A hypothesis must be testable and falsifiable; a theory is a well-supported explanatory framework, not a guess.

Microscopy: magnification = objective lens × ocular lens; resolution improves with shorter wavelengths and higher numerical aperture.

Significant figures and unit conversions: report values to the precision of the instrument, and convert units consistently before calculating rates.