AEPA Biology (NT305) cheat sheet

Independent variable is manipulated by the researcher; dependent variable is measured and expected to respond.

Control group receives no treatment or a placebo so the effect of the independent variable can be isolated.

A hypothesis must be testable and falsifiable; a claim that cannot be disproved is outside empirical science.

Correlation does not establish causation; only controlled manipulation or strong converging evidence supports causal claims.

Reliability = consistency of repeated measurements; validity = the measurement actually reflects the intended variable.

Scientific law describes a consistent observed relationship; theory is a well-tested explanatory framework supported by many lines of evidence.

Random assignment reduces systematic bias between groups; random sampling improves generalizability to a population.

Peer review and replication are the primary error-checking mechanisms that separate scientific claims from anecdote.

Standard error decreases as sample size increases (SE = s / sqrt(n)), so larger samples give more precise estimates.

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

Mitochondria and chloroplasts carry their own circular DNA and ribosomes, consistent with endosymbiotic origin.

Enzymes lower activation energy; they do not change the equilibrium constant or the overall free-energy change of a reaction.

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

Net ATP yield from aerobic cellular respiration is about 30-32 per glucose; glycolysis alone yields 2 ATP and 2 NADH.

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

Water moves by osmosis from lower to higher solute concentration across a selectively permeable membrane.

Phospholipid bilayer is amphipathic; membrane fluidity rises with unsaturated fatty acids and falls with cholesterol at high temperature.

DNA replication is semiconservative; DNA polymerase synthesizes 5' to 3' and requires a primer.

Transcription makes mRNA from the template strand; translation reads codons 5' to 3' at the ribosome using tRNA anticodons.

Mendelian monohybrid F2 phenotypic ratio is 3:1; dihybrid ratio for unlinked genes is 9:3:3:1.

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, no selection, and large population size.

Natural selection acts on phenotypic variation that is heritable and affects differential reproductive success.

Genetic drift is strongest in small populations; founder effect and bottleneck are its two classic forms.

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

Mutation is the ultimate source of new alleles; recombination and gene flow redistribute existing variation.

Surface area to volume ratio decreases as organism size increases, limiting diffusion-based exchange in large bodies.

Vascular plants: xylem transports water and minerals upward; phloem transports sugars bidirectionally.

Mammalian circulation is a four-chambered double circuit: pulmonary to the lungs, systemic to the body.

Negative feedback maintains homeostasis; positive feedback amplifies a change until a terminating event.

Body plan symmetry: radial in cnidarians, bilateral in most animals with cephalization and paired sensory organs.

Fungi are heterotrophic absorbers with chitinous cell walls; they are more closely related to animals than to plants.

Arthropods are characterized by jointed appendages, chitinous exoskeleton, and segmented bodies.

Vertebrate classes differ in skin, respiration, and reproduction: amphibians rely on moist skin and aquatic larvae; reptiles have amniotic eggs.

Energy flows unidirectionally through trophic levels; only about 10% transfers between levels, so food chains rarely exceed 4-5 levels.

Matter cycles (carbon, nitrogen, phosphorus, water); energy does not cycle.

Primary succession starts on bare substrate with no soil; secondary succession begins after disturbance where soil remains.

Carrying capacity (K) is the maximum population size an environment sustains; logistic growth approaches K asymptotically.

Exponential growth (dN/dt = rN) applies when resources are unlimited; r is the intrinsic rate of increase.

Species interactions: mutualism (+,+), commensalism (+,0), parasitism (+,−), competition (−,−), predation (+,−).

Keystone species exert disproportionate influence relative to abundance; removing them can collapse community structure.

Nitrogen fixation, nitrification, and denitrification are the key microbial steps of the nitrogen cycle.

Biodiversity hotspots and habitat fragmentation: smaller, isolated patches lose species faster due to area and edge effects.