AP Biology course review

In this comprehensive AP Biology review, we'll cover units 1 through 8, highlighting key concepts and topics.

Unit 1: The Chemistry of Life

  1. Water: Its polarity, due to oxygen's electronegativity, leads to hydrogen bond formation. Key properties:

    • Cohesion & Adhesion: Water sticks to itself and other substances.

    • Temperature Moderation: High energy needed to break hydrogen bonds.

    • Density Reduction Upon Freezing: Ice floats, insulating water bodies.

    • Universal Solvent: Dissolves polar and charged substances.

  2. Carbon: Forms backbones of biological molecules with its four valence electrons, enabling diverse structures (chains, branches, rings, single/double/triple bonds).

    • Isomers & Enantiomers: Same formula, different structures; structure dictates function (e.g., right-hand vs. left-handed molecules).

  3. Macromolecules: Polymers (except lipids) made of monomers, formed via dehydration synthesis and broken down by hydrolysis.

    • Carbohydrates (C, H, O in 1:2:1 ratio):

      • Monosaccharides (e.g., glucose - \text{C}6\text{H}{12}\text{O}_6)

      • Polysaccharides: Starch (plant storage), glycogen (animal storage), cellulose (structural in plants, indigestible by animals without symbiotic microorganisms).

    • Lipids: Largely hydrophobic.

      • Fats/Oils: Glycerol + fatty acids; saturated (straight, solid) vs. unsaturated (kinked, liquid).

      • Phospholipids: Glycerol + 2 fatty acids + phosphate (hydrophilic head, hydrophobic tail); form bilayers in plasma membranes.

      • Steroids: Carbon rings; hormones (testosterone, estrogen) or cholesterol (membrane fluidity).

    • Proteins: Diverse structures from 20 amino acid monomers forming polypeptides via peptide bonds. R groups (polar, non-polar, charged) dictate folding and function.

      • Structures: Primary (sequence), secondary (alpha helices, beta sheets), tertiary (R group interactions like hydrophobic interactions, ionic & covalent bonding), quaternary (multiple polypeptides).

    • Nucleic Acids: Discussed in Unit 6.

Unit 2: Cell Biology

  1. Cell Structure: All cells have plasma membrane, cytoplasm, DNA (expressed via ribosomes), and are small due to surface area-to-volume ratio.

  2. Endomembrane System: Nucleus → ER (smooth & rough) → Golgi → Plasma membrane (± lysosomes); for protein excretion.

  3. Endosymbiosis: Mitochondria & chloroplasts originated as prokaryotes engulfed by eukaryotes.

    • Evidence: Double membrane, circular DNA, prokaryotic ribosomes.

  4. Cytoskeleton: Microtubules (spindle fibers in mitosis/meiosis); disruption (e.g., by taxol) inhibits cell division (cancer treatment).

  5. Plasma Membrane: Fluid mosaic model (phospholipids, proteins).

    • Fluidity: Regulated by saturated/unsaturated fatty acids, cholesterol.

  6. Membrane Transport:

    • Diffusion: High to low concentration.

    • Osmosis: Water moves from low to high solute concentration.

    • Simple Diffusion: Non-polar gases (\text{CO}2, \text{O}2).

    • Facilitated Diffusion: Channel proteins for ions/polar substances.

    • Active Transport: Pumps use ATP to move against the gradient (e.g., proton pump).

    • Chemiosmotic Potential: Energy stored in concentration gradients.

    • Aquaporins: Water channels.

    • Tonicity: Isotonic (equal), hypertonic (water out, cell shrinks/plasmolyzes), hypotonic (water in, cell lyses/turgid).

    • Bulk Transport: Endocytosis/exocytosis via vesicle formation.

Unit 3: Energy, Photosynthesis, and Cell Respiration

  1. Energy: Capacity to do work (transport, mechanical, chemical).

    • Exergonic Reactions: Release energy.

    • Endergonic Reactions: Require energy.

    • ATP: Energy currency (ATP → ADP + phosphate releases energy).

  2. Photosynthesis: Light energy converts CO_2 and water into glucose and oxygen.

    • Light Reaction (thylakoids): Photosystems absorb light, excite electrons, pump H+ ions, create ATP (via ATP synthase), and NADPH.

    • Calvin Cycle (stroma): RuBP + CO_2 (by rubisco) → 3PG → glyceraldehyde-3-phosphate (G3P) → sugar; regenerate RuBP.

    • C4 & CAM Pathways: Alternative carbon fixation methods.

  3. Cell Respiration: Glucose breakdown into CO_2 and water, releasing energy to recharge ATP.

    • Glycolysis (cytoplasm): Glucose → 2 pyruvate + 2 ATP + 2 NADH.

    • Pyruvate Oxidation (mitochondria): Pyruvate → Acetyl CoA + NADH.

    • Krebs Cycle (mitochondrial matrix): Acetyl CoA + oxaloacetate → citrate → release CO_2, NADH, FADH2, ATP.

    • Oxidative Phosphorylation (inner mitochondrial membrane): ETC uses electrons from NADH/FADH2 to pump protons, create ATP via ATP synthase.

      • Oxygen acts as final electron acceptor, forming water.

    • Anaerobic Respiration: Glycolysis + fermentation (ethanol or lactic acid) to regenerate NAD+.

  4. Enzymes: Proteins catalyze reactions by lowering activation energy.

    • Inhibitors: Competitive (bind to active site) vs. non-competitive (alter active site).

    • Regulation: Modifying active site.

Unit 4: Cell Communication and Cell Division

  1. Cell Communication: Signal transduction (reception, transduction, response).

    • Reception: Ligand binds to membrane-bound receptor (e.g., G-protein coupled receptor).

    • Transduction: Second messengers (e.g., cyclic AMP) activate protein kinases, amplifying the signal via phosphorylation cascade.

    • Response: Cytoplasmic responses (activate enzymes) or transcription initiation (protein production).

    • Non-polar signals: Pass through membrane, bind intracellular receptors.

  2. Cell Division: Continuity via genetic information.

    • Diploid Species: Two copies of each chromosome (one from each parent).

    • Cell Cycle: G1 (growth), S (DNA synthesis/replication), G2 (checks), M (mitosis).

    • Mitosis: Prophase (chromosomes condense), prometaphase (nuclear envelope dissolves), metaphase (chromosomes align), anaphase (sister chromatids separate), telophase (chromosomes relax, nucleus reforms).

    • Cytokinesis: Physical separation of daughter cells.

    • Regulation: Cyclins/kinases, growth factors, density-dependent inhibition; errors → cancer.

Unit 5: Heredity

  1. Chromosomes and Genes: Genes on chromosomes encode proteins.

    • Diploid organisms have two copies of each gene (alleles).

    • Meiosis: Produces haploid gametes (sperm/eggs) via two divisions.

    • Meiosis I: Prophase I (crossing over), metaphase I (random assortment), anaphase I (chromosome separation).

    • Meiosis II: Prophase II, metaphase II (single file alignment), anaphase II (chromatid separation) → 4 haploid cells.

    • Variation arises from crossing over, random assortment, and fertilization.

  2. Mendelian Genetics: Discrete heritable units (genes, alleles).

    • Laws: Segregation (alleles separate in meiosis), dominance (dominant allele masks recessive), independent assortment (genes on different chromosomes assort independently).

    • Punnett Squares: Predict probabilities of inheritance.

    • Atypical Inheritance: Epistasis, polygenic inheritance, environmental effects.

    • Pedigrees: Track inheritance patterns (autosomal recessive/dominant, X-linked, mitochondrial).

  3. Linkage: Genes close on chromosome don't assort independently.

    • Recombination Frequency: (Recombinant offspring / total offspring) x 100 = map units.

Unit 6: Gene Expression

  1. DNA Structure: Nucleotide (base, deoxyribose sugar, phosphate).

    • Double Helix: Anti-parallel strands (5' to 3' and 3' to 5').

    • Base Pairing: A-T, G-C (hydrogen bonds).

    • Semiconservative Replication: Each new DNA has one original strand.

  2. DNA Replication: Replication bubble, helicase (unwinds), primase (RNA primer), DNA polymerase (adds nucleotides 5' to 3').

    • Leading Strand: Continuous replication.

    • Lagging Strand: Discontinuous (Okazaki fragments), ligase (joins fragments).

  3. Gene Expression: DNA → mRNA → protein.

    • Gene Structure: Promoter (initiation), coding region (data).

    • Transcription: Initiation (transcription factors bind, RNA polymerase binds), elongation (RNA monomers match template), termination.

    • mRNA Processing (eukaryotes): 5' cap, poly-A tail, intron splicing (exons remain).

    • Translation: Ribosome, tRNA, codons (genetic code).

    • Process: Initiator tRNA (AUG), tRNA matches mRNA, amino acids polymerize, stop codon reached.

  4. Gene Regulation: Responding to environment, resource efficiency.

    • Bacterial Operons: Inducible (lac operon) vs. repressible (trp operon).

    • Translational Regulation (eukaryotes): mRNA present but not translated.

Unit 7: Evolution

  1. Darwin's Theory: Natural selection (variation, heritability, differential survival/reproduction).

    • Adaptations: Arise through adaptive radiation.

  2. Evidence for Evolution: Real-time natural selection (antibiotic resistance), homologous structures, vestigial structures.

  3. Microevolution: Change in allele frequency.

    • Mechanisms: Mutation, gene flow, genetic drift (bottleneck/founder effect), sexual selection.

  4. Macroevolution: Speciation (divergence of species).

    • Species Definition: Interbreeding, fertile offspring.

    • Reproductive Isolation: Key to speciation.

    • Allopatric Speciation: Geographic barrier separates populations.

    • Sympatric Speciation: New habitat within same area.

    • Prezygotic Barriers: Habitat, temporal, behavioral, mechanical, gametic isolation.

    • Postzygotic Barriers: Reduced hybrid viability/fertility.

    • Cladograms: Show evolutionary relationships.

Unit 8: Ecology

  1. Abiotic Factors: Carbon, nitrogen cycles.

    • Energy Flow: Producers (plants) → consumers