KBIT-2 cheat sheet

Prokaryotic cells lack membrane-bound organelles and a nucleus; eukaryotic cells compartmentalize glycolysis (cytosol) from oxidative phosphorylation (inner mitochondrial membrane).

Membrane fluidity rises with shorter fatty acyl chains and more cis-unsaturated bonds; cholesterol buffers fluidity, decreasing it at high temperature and opposing packing at low temperature.

Na+/K+-ATPase exports 3 Na+ and imports 2 K+ per ATP hydrolyzed, producing an electrogenic current that maintains resting membrane potential.

Michaelis-Menten: v = Vmax[S]/(Km+[S]); Km equals the substrate concentration at half-maximal velocity and is inversely related to enzyme-substrate affinity.

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

Allosteric enzymes show sigmoidal kinetics and are regulated by effectors shifting the T (tense, low-affinity) and R (relaxed, high-affinity) equilibrium.

Glycolysis nets 2 ATP and 2 NADH per glucose; complete aerobic oxidation yields about 30-32 ATP, with most ATP from oxidative phosphorylation.

First law of thermodynamics: energy is conserved; second law: each energy transfer increases entropy, so coupled reactions must have a net negative delta-G to proceed spontaneously.

DNA replication is semiconservative and bidirectional from origins; DNA polymerase synthesizes 5' to 3' and requires a primer, so the lagging strand is made in Okazaki fragments.

Transcription in eukaryotes: RNA polymerase II makes mRNA, requires general transcription factors, and its product is capped, polyadenylated, and spliced.

The genetic code is degenerate and non-overlapping; 64 codons encode 20 amino acids plus 3 stop codons (UAA, UAG, UGA).

Mendelian monohybrid F2 phenotypic ratio is 3:1; dihybrid F2 is 9:3:3:1 when genes assort independently and show complete dominance.

Recombination frequency equals map distance in centimorgans for linked genes below roughly 50%; at 50% the loci behave as unlinked.

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

X-linked recessive traits appear more often in males, who are hemizygous; an affected father cannot pass such a trait to his sons.

Sanger sequencing terminates chains with dideoxynucleotides; PCR uses a thermostable polymerase, two primers, and repeated denaturation-annealing-extension cycles.

Cardiac output = heart rate x stroke volume; stroke volume depends on preload, afterload, and contractility (Frank-Starling relationship).

Blood flows from high to low pressure; resistance varies inversely with the fourth power of vessel radius, so small radius changes produce large flow changes.

SA node pacemaker potential arises from funny current (If) plus Ca2+ influx; parasympathetic vagal tone slows it, sympathetic activity accelerates it.

In the nephron, the proximal tubule reabsorbs most filtered Na+, water, and glucose; the loop of Henle generates the medullary osmotic gradient for concentrating urine.

Alveolar gas exchange follows partial-pressure gradients; oxygen is carried mainly bound to hemoglobin, and the oxygen-hemoglobin dissociation curve shifts right with higher CO2, H+, and temperature.

Resting membrane potential of a typical neuron is about -70 mV, set mainly by K+ permeability; an action potential fires when threshold near -55 mV is reached.

The autonomic nervous system uses acetylcholine at preganglionic synapses; sympathetic postganglionic fibers mostly release norepinephrine, parasympathetic ones acetylcholine.

Negative feedback (e.g., thyroid hormone suppressing TSH) stabilizes a regulated variable; positive feedback (e.g., oxytocin in labor) amplifies a change until a terminating event.

Exponential growth: dN/dt = rN; logistic growth: dN/dt = rN(1 - N/K), where K is carrying capacity and growth is fastest at N = K/2.

Energy transfer between trophic levels averages about 10%; the rest is lost to respiration and heat, so food chains rarely exceed 4-5 levels.

Net primary productivity = gross primary productivity minus autotrophic respiration; it sets the energy available to consumers.

Interspecific interactions: competition (-/-), predation and parasitism (+/-), mutualism (+/+), commensalism (+/0).

Primary succession begins on bare substrate without soil; secondary succession follows disturbance that leaves soil and propagules intact.

Population growth can be limited by density-dependent factors (competition, disease) or density-independent factors (fire, storms, temperature extremes).

The water cycle is driven by evapotranspiration and precipitation; the carbon cycle couples photosynthesis, respiration, combustion, and ocean uptake.

Species richness counts species present, while species evenness describes relative abundance; both contribute to Shannon diversity.

Natural selection requires heritable variation, differential reproductive success, and a selective pressure; it acts on phenotypes and changes allele frequencies across generations.

Genetic drift is random allele-frequency change, strongest in small populations; a bottleneck or founder event sharply reduces diversity.

Directional, stabilizing, and disruptive selection respectively shift the mean, reduce variance, or favor both extremes of a trait distribution.

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

Allopatric speciation requires geographic isolation; sympatric speciation occurs without it, for example via polyploidy or host shifts.

Biological species concept: members interbreed in nature and produce fertile offspring; it does not apply to asexual organisms, so morphological or phylogenetic concepts are used.

Binomial nomenclature uses genus and species, italicized, with the genus capitalized; taxonomic ranks run domain, kingdom, phylum, class, order, family, genus, species.

Mass extinctions remove many lineages and open ecological niches, often followed by adaptive radiation of surviving groups.

Photosynthesis: light reactions in thylakoid membranes split water, release O2, and make ATP and NADPH; the Calvin cycle in the stroma fixes CO2 via rubisco.

C3 plants fix CO2 directly; C4 plants separate initial fixation and the Calvin cycle spatially; CAM plants separate them temporally to conserve water.

Xylem moves water and minerals upward under tension driven by transpiration; phloem transports sugars bidirectionally by pressure flow.

Stomata open when guard cells take up K+ and water, become turgid, and bow outward; ABA triggers closure under drought stress.

Plant hormones: auxin promotes elongation and apical dominance; gibberellin promotes stem growth and germination; cytokinin promotes cell division; ethylene promotes ripening and abscission.

Alternation of generations: the diploid sporophyte produces haploid spores by meiosis; the gametophyte produces gametes by mitosis.

Monocots have one cotyledon, parallel venation, and scattered vascular bundles; dicots have two cotyledons, netted venation, and bundles in a ring.

Root hairs and mycorrhizae increase absorptive surface area; nitrogen fixation by rhizobia supplies usable nitrogen for legumes.

Gram-positive bacteria retain crystal violet due to a thick peptidoglycan layer; Gram-negative cells have a thin layer plus an outer membrane with lipopolysaccharide.

Bacterial growth phases: lag, exponential (log), stationary, and death; generation time is constant only in log phase.

Viruses are obligate intracellular parasites with nucleic acid plus a protein capsid; they lack ribosomes and cannot replicate independently.

Innate immunity is rapid and nonspecific (barriers, phagocytes, complement, inflammation); adaptive immunity is slower, specific, and creates memory.

B cells produce antibodies and differentiate into plasma cells; helper T cells (CD4+) activate B cells and cytotoxic T cells (CD8+), which kill infected cells.

Antibody classes: IgM is the first response and largest; IgG is most abundant and crosses the placenta; IgA protects mucosa; IgE mediates allergy.

Antigenic variation and horizontal gene transfer (transformation, transduction, conjugation) drive pathogen escape and antibiotic resistance.

Sterilization kills all microbes including endospores; disinfection reduces pathogens on surfaces; antibiotics target bacterial structures such as cell walls and ribosomes, not viruses.

Neurons signal via action potentials: depolarization opens voltage-gated Na+ channels, repolarization follows K+ efflux, and the refractory period enforces one-way conduction.

Synaptic transmission: an action potential opens Ca2+ channels, vesicles release neurotransmitter, and it binds receptors on the postsynaptic cell, causing excitation or inhibition.

Innate behaviors are developmentally fixed (reflexes, fixed action patterns); learned behaviors include habituation, classical conditioning, and operant conditioning.

Fixed action patterns are triggered by a sign stimulus and run to completion once initiated, even if the stimulus is removed.

Imprinting occurs during a sensitive period and is largely irreversible; it is a form of learning with a critical window.

Kin selection favors altruism when Hamilton's rule holds: rB > C, where r is relatedness, B is benefit to recipient, and C is cost to actor.

Optimal foraging theory predicts animals maximize net energy gain per unit time, balancing energy intake against search and handling costs.

Circadian rhythms are endogenous ~24-hour cycles entrained by external cues such as light; the suprachiasmatic nucleus is the mammalian master clock.

A controlled experiment changes one independent variable while holding others constant; a control group establishes the baseline for comparison.

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

A hypothesis must be testable and falsifiable; predictions state what observation would follow if the hypothesis is true.

Reliability concerns consistency of measurement; validity concerns whether the measurement actually reflects the intended variable.

Mean is sensitive to outliers; median and interquartile range are more robust summaries for skewed distributions.

Standard error of the mean decreases with sample size (SE = s/sqrt(n)); a p-value is the probability of data at least this extreme given the null hypothesis, not the probability the null is true.

Statistical significance is not practical significance; effect size and confidence intervals convey magnitude and precision.

In a graph, the independent variable goes on the x-axis and the dependent variable on the y-axis; a line of best fit summarizes trend, and error bars show variability or uncertainty.