AP Biology: Unit-by-Unit Notes

Key Concepts:

• Water's unique properties arise from hydrogen bonding: cohesion, adhesion, high specific heat, solvent ability, and lower density as ice.
• The four macromolecules — carbohydrates, lipids, proteins, nucleic acids — are all polymers built from monomers via condensation reactions and broken apart by hydrolysis.
• Enzymes are biological catalysts that lower activation energy. They are affected by temperature, pH, and substrate concentration. Denaturation is usually irreversible.
• The induced-fit model: an enzyme's active site changes shape slightly to accommodate its substrate, forming the enzyme-substrate complex.

Must-Know Vocabulary: Monomer, polymer, dehydration synthesis, hydrolysis, activation energy, enzyme, substrate, active site, denaturation, pH, catalyst, polar/nonpolar

Common FRQ Topics: Describe the effect of temperature or pH on enzyme activity; explain why water is essential to life; compare the structures and functions of macromolecules.

Key Concepts:

• Prokaryotes lack membrane-bound organelles and a true nucleus. Eukaryotes have both, plus mitochondria, ER, Golgi, and other organelles.
• The fluid mosaic model: the cell membrane is a phospholipid bilayer with embedded proteins. Phospholipid heads are hydrophilic; tails are hydrophobic.
• Passive transport (diffusion, osmosis, facilitated diffusion) moves substances down their concentration gradient — no energy required. Active transport moves substances against the gradient using ATP (e.g., the sodium-potassium pump).
• Tonicity matters for osmosis: hypotonic solutions cause cells to swell (lysis in animal cells, turgor pressure in plants); hypertonic solutions cause shrinkage (crenation/plasmolysis).

Must-Know Vocabulary: Prokaryote, eukaryote, organelle, fluid mosaic model, phospholipid bilayer, diffusion, osmosis, tonicity, endocytosis, exocytosis, cell wall

Common FRQ Topics: Compare prokaryotic and eukaryotic cells; explain how membrane structure relates to selective permeability; predict the movement of water in osmosis scenarios.

Key Concepts:

• Photosynthesis has two stages: (1) Light reactions in the thylakoid membrane capture light energy to produce ATP, NADPH, and O₂ (water is split); (2) Calvin Cycle in the stroma uses ATP and NADPH to fix CO₂ into G3P (glucose precursor). The overall equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
• Cellular respiration has three stages: (1) Glycolysis in the cytoplasm (2 ATP net); (2) Krebs Cycle in the mitochondrial matrix (2 ATP + CO₂ + NADH); (3) Electron Transport Chain in the inner mitochondrial membrane (32–34 ATP via oxidative phosphorylation). Total theoretical yield: ~36–38 ATP per glucose.
• The ETC uses NADH and FADH₂ as electron carriers. Oxygen is the final electron acceptor, forming water. Chemiosmosis drives ATP synthase through proton gradient.

Must-Know Vocabulary: Chloroplast, thylakoid, stroma, Calvin Cycle, ATP synthase, mitochondria, glycolysis, Krebs Cycle, ETC, NADH, FADH₂, oxidative phosphorylation, chemiosmosis, fermentation

Common FRQ Topics: Compare photosynthesis and respiration; explain why the ETC produces more ATP than glycolysis; predict effects of mutations in specific enzymes.

Key Concepts:

• Signal transduction: receptor binds ligand → second messengers amplify signal (e.g., cAMP) → protein kinases phosphorylate target proteins → cellular response. Three stages: reception, transduction, response.
• The cell cycle: G1 (growth) → S (DNA synthesis) → G2 (preparation) → M (mitosis + cytokinesis). G0 is a non-dividing state.
• Mitosis produces two genetically identical diploid daughter cells. Phases: Prophase, Metaphase, Anaphase, Telophase (PMAT). Cytokinesis divides the cytoplasm.
• Cancer results from loss of cell cycle regulation — mutations in tumor suppressor genes (e.g., p53) or proto-oncogenes that convert them to oncogenes lead to uncontrolled division.

Must-Know Vocabulary: Signal transduction, ligand, receptor, second messenger, cAMP, G-protein, cell cycle, mitosis, cytokinesis, oncogene, tumor suppressor gene, checkpoint

Common FRQ Topics: Trace the path of a signal from receptor to cellular response; explain how checkpoints prevent cancer; compare mitosis and meiosis.

Key Concepts:

• Meiosis produces four genetically unique haploid cells from one diploid cell. Crossing over during Prophase I and independent assortment during Metaphase I generate genetic variation.
• Mendel's Laws: Law of Segregation (alleles separate during meiosis) and Law of Independent Assortment (genes on different chromosomes sort independently).
• Non-Mendelian inheritance: codominance (both alleles fully expressed — AB blood type), incomplete dominance (intermediate phenotype), sex-linked traits (X-linked recessive more common in males), polygenic inheritance (multiple gene loci).
• Chi-square analysis tests whether observed ratios differ significantly from expected — AP Bio frequently asks you to perform or interpret this test.

Must-Know Vocabulary: Meiosis, crossing over, independent assortment, genotype, phenotype, dominant, recessive, heterozygous, homozygous, codominance, sex-linked, pedigree, chi-square

Common FRQ Topics: Punnett squares and probability calculations; pedigree analysis to determine inheritance patterns; chi-square test interpretation.

Key Concepts:

• DNA replication is semiconservative — each new double helix contains one old and one new strand. Key enzymes: helicase (unwinds), primase (RNA primer), DNA polymerase (adds nucleotides 5'→3'), ligase (seals gaps).
• Transcription (DNA → mRNA) occurs in the nucleus. Translation (mRNA → protein) occurs at ribosomes. The central dogma: DNA → RNA → Protein.
• Gene regulation in eukaryotes: transcription factors bind promoter regions; enhancers and silencers act at a distance. Chromatin remodeling (histone modification) controls access to DNA.
• Types of mutations: substitution, insertion, deletion, frameshift (insertions/deletions shift reading frame). Silent mutations don't change amino acid; missense changes one; nonsense creates premature stop codon.

Must-Know Vocabulary: DNA polymerase, helicase, ligase, mRNA, tRNA, ribosome, codon, anticodon, promoter, transcription factor, frameshift mutation, point mutation, epigenetics

Common FRQ Topics: Translate a DNA sequence to mRNA to amino acids; explain how gene expression differs between cell types with identical DNA; describe the effect of a specific mutation.

Key Concepts:

• Hardy-Weinberg equilibrium: allele frequencies remain constant if no evolution occurs. Conditions: no mutation, no gene flow, random mating, no genetic drift, no natural selection. Equations: p + q = 1 and p² + 2pq + q² = 1. Use to calculate allele/genotype frequencies.
• Mechanisms of evolution: natural selection, genetic drift (bottleneck and founder effects), gene flow, mutation. Only natural selection is adaptive.
• Types of natural selection: directional (favors one extreme), stabilizing (favors intermediate), disruptive (favors both extremes).
• Phylogenetics: shared derived characteristics (synapomorphies) are used to build cladograms. Outgroups and parsimony are key concepts.

Must-Know Vocabulary: Natural selection, fitness, adaptation, Hardy-Weinberg, genetic drift, bottleneck, founder effect, gene flow, speciation, allopatric, sympatric, phylogeny, cladogram, synapomorphy

Common FRQ Topics: Hardy-Weinberg calculations; explain why a population is or is not in HW equilibrium; interpret a cladogram to determine evolutionary relationships.

Key Concepts:

• Population ecology: logistic growth (S-curve) includes carrying capacity (K) and limiting factors. Exponential growth (J-curve) occurs only when resources are unlimited.
• Community ecology: competition (-/-), predation (+/-), mutualism (+/+), commensalism (+/0), parasitism (+/-). Competitive exclusion principle: two species cannot occupy identical niches indefinitely.
• Energy flows through ecosystems in one direction; matter cycles. Only ~10% of energy transfers between trophic levels (the 10% rule). Primary producers → primary consumers → secondary consumers → tertiary consumers.
• Biogeochemical cycles: Carbon cycle (photosynthesis/respiration/decomposition), Nitrogen cycle (fixation by bacteria, nitrification, denitrification), Water cycle (evaporation, precipitation, transpiration).

Must-Know Vocabulary: Population, community, ecosystem, carrying capacity, logistic growth, ecological niche, keystone species, primary succession, secondary succession, trophic level, food web, biogeochemical cycle, nitrogen fixation

Common FRQ Topics: Interpret a population growth curve and identify limiting factors; describe energy loss between trophic levels; explain how human activities disrupt biogeochemical cycles.