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AP Biology review: key concepts

AP Biology review flashcards covering biochemistry, cells, energetics, signalling, heredity, gene expression, evolution and ecology, with worked calculations.

42 cards7 topicsAbout 15 minutes a roundAP Biology style course content (introductory university biology for majors)

Independent study material written by StudyBrix. AP and SAT are trademarks of College Board and ACT is a trademark of ACT, Inc.; neither organisation is involved with or has reviewed this deck.

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About this deck

These cards are for students working through an AP Biology style course, or anyone who wants a structured review of first-year biology. They follow the big themes of the course: the chemistry of life, cell structure and transport, cellular energetics, cell communication and the cell cycle, heredity, gene expression and regulation, natural selection, and ecology.

You will get more from the deck if you already know basic chemistry vocabulary (atoms, bonds, pH) and can handle fractions, percentages and simple algebra. Several cards include the quantitative skills that show up in AP style questions: water potential, surface area to volume ratios, Hardy-Weinberg frequencies, chi-square tests and population growth rates. Do those on paper with a calculator before flipping.

A good way to study is to explain each process as a cause and effect chain out loud, then draw it. For example, sketch the flow of electrons in respiration or the steps of signal transduction. Questions often describe an experiment, so for each topic ask yourself what would change if one molecule or structure stopped working.

Common mistakes: saying plants do photosynthesis instead of respiration (they do both); describing evolution as individuals changing to adapt, when populations change because of differential survival and reproduction; mixing up a gene with an allele; and reading a chi-square result backwards. A large chi-square value relative to the critical value means the data differ significantly from the expected ratio.

Before you start: Grade 10 or 11 science, basic chemistry vocabulary, and comfort with fractions, percentages and simple algebra.

All 42 cards

Cover the definitions with a sheet of paper and test yourself, or use the study modes above.

Chemistry of life

Hydrogen bonding in water: Weak attractions between the slightly positive H of one water molecule and the slightly negative O of another; they explain cohesion, high specific heat and surface tension.Example: Cohesion lets a column of water be pulled up through xylem as water evaporates from leaves.
Dehydration synthesis: A reaction that joins two monomers by a covalent bond and releases one water molecule; it builds polymers.Example: Two glucose molecules (C6H12O6) join to form maltose (C12H22O11) plus H2O.
Hydrolysis: Breaking a polymer into smaller units by adding water across a bond; the reverse of building a polymer.Example: Digestive enzymes add water to break proteins into amino acids.
Levels of protein structure: Primary is the amino acid sequence; secondary is local folding (alpha helix, beta sheet) by backbone H bonds; tertiary is the overall 3D shape from R group interactions; quaternary is the arrangement of several chains.Example: Hemoglobin has quaternary structure: four polypeptide chains.
Antiparallel strands of DNA: The two strands of the double helix run in opposite directions (one 5' to 3', the other 3' to 5') and pair A with T and G with C.Example: The partner of 5' ATGC 3' is 3' TACG 5', written 5' GCAT 3'.
Competitive inhibition: An inhibitor that resembles the substrate binds the active site and blocks it; adding more substrate can overcome it.Example: Raising substrate concentration restores the maximum reaction rate in a competitive inhibition experiment.
Noncompetitive (allosteric) inhibition: An inhibitor binds a site other than the active site and changes the enzyme's shape, lowering activity; extra substrate cannot fully overcome it.Example: End products often switch off the first enzyme of a pathway this way (feedback inhibition).

Cells and transport

Surface area to volume ratio: As a cell grows, its volume rises faster than its surface area, so it has relatively less membrane for exchange; this limits cell size.Example: Cube of side 1 cm: 6/1 = 6. Side 3 cm: 54/27 = 2, a third of the exchange surface per unit volume.
Water potential (psi): A measure, in bars, of the tendency of water to move: psi = pressure potential + solute potential. Water flows from higher psi to lower psi.Example: Solute potential = -iCRT: 0.1 M sucrose at 295 K gives -(1)(0.1)(0.0831)(295), about -2.45 bar.
Hypotonic, hypertonic and isotonic: Compare solute concentration outside a cell with inside: hypotonic outside means water enters, hypertonic means water leaves, isotonic means no net movement.Example: A red blood cell in pure water swells and may burst; a plant cell becomes turgid instead.
Sodium-potassium pump: A membrane protein that uses ATP to move 3 Na+ out of the cell and 2 K+ in per cycle, against their gradients; an example of active transport.Example: The pump helps keep a neuron's resting potential near -70 mV.
Endomembrane system: The connected membranes of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, vesicles and lysosomes that make, modify and ship proteins and lipids.Example: A secreted protein: rough ER, then Golgi, then a vesicle that fuses with the plasma membrane.
Endosymbiotic theory: The idea that mitochondria and chloroplasts descend from free-living prokaryotes engulfed by an ancestral cell.Example: Evidence: both organelles have double membranes, circular DNA and their own ribosomes.

Cellular energetics

Chemiosmosis: ATP synthesis driven by H+ flowing down its gradient through ATP synthase; the gradient is built by an electron transport chain.Example: In mitochondria H+ is pumped into the intermembrane space and flows back into the matrix.
Light-dependent reactions: Stage of photosynthesis in the thylakoid membranes: light energy splits water, releases O2, and produces ATP and NADPH.Example: Labelling water with heavy oxygen shows the O2 released comes from water, not CO2.
Calvin cycle: Light-independent stage in the stroma that uses ATP and NADPH to fix CO2 (via rubisco) into sugar.Example: Three turns fix 3 CO2 to export one three-carbon G3P molecule.
Aerobic cellular respiration: Breakdown of glucose through glycolysis, pyruvate oxidation, the Krebs cycle and oxidative phosphorylation, with O2 as the final electron acceptor.Example: Blocking the electron transport chain with cyanide stops most ATP production.
Fermentation: Regenerates NAD+ without oxygen so glycolysis can continue; it yields only 2 ATP per glucose.Example: Muscle cells make lactate; yeast make ethanol and CO2.

Cell communication and cell cycle

Signal transduction pathway: The sequence of reception (ligand binds receptor), transduction (relay molecules, often phosphorylation cascades) and response (a change in the cell).Example: Epinephrine binds a G protein coupled receptor, cAMP rises, and liver cells release glucose.
Negative feedback: A response that counteracts a change and returns a variable toward its set point.Example: High blood glucose triggers insulin release, which lowers blood glucose.
Positive feedback: A response that amplifies the original change until some endpoint is reached.Example: During childbirth, oxytocin increases contractions, which trigger more oxytocin.
Cell cycle checkpoints: Control points (in G1, G2 and M) where the cell checks DNA integrity, size and chromosome attachment before continuing; cyclins and CDKs drive progress.Example: A cell with damaged DNA is held at the G1 checkpoint; failure of this control can lead to cancer.
Meiosis: Two divisions that turn one diploid cell into four genetically different haploid cells; crossing over and independent assortment add variation.Example: A human cell with 46 chromosomes produces gametes with 23.
Nondisjunction: Failure of homologous chromosomes or sister chromatids to separate properly, producing gametes with too many or too few chromosomes.Example: A gamete with an extra chromosome 21 can lead to trisomy 21.

Heredity and gene expression

Monohybrid cross: A cross that follows one gene; two heterozygotes give a 1:2:1 genotype ratio and a 3:1 phenotype ratio for complete dominance.Example: Aa x Aa: 1 AA, 2 Aa, 1 aa, so 3/4 show the dominant trait.
Dihybrid cross: A cross following two independently assorting genes; two double heterozygotes give a 9:3:3:1 phenotype ratio.Example: AaBb x AaBb: P(aabb) = 1/4 x 1/4 = 1/16.
X-linked recessive inheritance: Traits on the X chromosome show up more in males, who have one X; a carrier mother passes the allele to half her sons on average.Example: Carrier mother and unaffected father: each son has a 1/2 chance of being affected.
Chi-square goodness of fit: Statistic sum of (O - E)^2/E that measures how far observed counts are from expected ones; compare with a critical value for df = categories - 1.Example: Observed 290:110, expected 300:100: 100/300 + 100/100 = 1.33 < 3.84 (df 1, p = 0.05), so do not reject.
Semiconservative replication: Each new DNA double helix keeps one original strand and one new strand; DNA polymerase adds nucleotides only to the 3' end.Example: The lagging strand is made in short Okazaki fragments joined by ligase.
Transcription: Synthesis of RNA from a DNA template by RNA polymerase; in eukaryotes the pre-mRNA gets a cap, a poly-A tail and has introns spliced out.Example: Template DNA 3' TAC 5' is copied into mRNA 5' AUG 3'.
Translation: Ribosomes read mRNA codons and tRNAs bring matching amino acids, building a polypeptide from start codon to stop codon.Example: mRNA AUG UUU UAA codes Met then Phe, then stops.
Lac operon: An inducible set of genes in E. coli: a repressor blocks transcription unless lactose (as allolactose) binds and removes it.Example: With lactose present and glucose low, the genes for lactose breakdown are transcribed.
Frameshift mutation: An insertion or deletion of nucleotides not in a multiple of three; every codon after it is read differently.Example: Deleting one base from THE CAT ATE gives THC ATA TE, a garbled message.

Evolution

Natural selection: Heritable variation exists, more offspring are produced than survive, and individuals with traits better suited to the environment leave more offspring, so allele frequencies change.Example: In a drought, finches with deeper beaks cracked hard seeds and left more offspring.
Hardy-Weinberg equilibrium: With no selection, mutation, migration or drift and random mating, allele frequencies stay constant: p + q = 1 and p^2 + 2pq + q^2 = 1.Example: If 9% are recessive, q^2 = 0.09, q = 0.3, p = 0.7 and carriers 2pq = 0.42.
Genetic drift: Random change in allele frequencies from chance events, strongest in small populations; includes bottleneck and founder effects.Example: A storm kills most of a small island population, leaving survivors with a random subset of alleles.
Reading a phylogenetic tree: Branch points (nodes) show common ancestors; the closest relatives share the most recent common ancestor, regardless of how near they sit on the page.Example: If lizards and birds share a node not shared with mammals, they are more closely related to each other.
Prezygotic barrier: Something that blocks reproduction before fertilization: habitat, temporal, behavioural, mechanical or gametic isolation.Example: Two frog species that breed in different months are temporally isolated.

Ecology

Ten percent rule: Roughly 10% of the energy at one trophic level is passed to the next; the rest is lost mostly as heat from respiration.Example: 10 000 kcal in producers supports about 1000 in primary, 100 in secondary and 10 in tertiary consumers.
Exponential population growth: Growth with no limits, dN/dt = r N, giving a J shaped curve.Example: r = 0.2 per year and N = 500: dN/dt = 100 individuals per year.
Logistic population growth: Growth that slows as the population nears carrying capacity K: dN/dt = r N (K - N)/K, giving an S shaped curve.Example: r = 0.5, N = 200, K = 1000: 0.5 x 200 x 800/1000 = 80 per year.
Keystone species: A species whose effect on community structure is far larger than its abundance suggests; removing it changes the whole community.Example: Sea otters eat urchins; without otters, urchins can strip kelp forests.