Comprehensive AP Biology Exam Review Notes

Study Strategy and the Stoplight Method

  • The Review Plan: To prioritize studying for the AP Biology exam, students are encouraged to download a checklist from apbiosuccess.com/checklist.

  • The Stoplight Method: This technique uses three highlighters to categorize knowledge levels:     * Green: Topics known well.     * Yellow: Topics with partial understanding.     * Red: Topics not understood at all.

  • Prioritization Logic: Focus on red items first, followed by yellow, and review green items periodically to keep the information fresh.

Unit 1: Chemistry of Life

  • Water and Hydrogen Bonding (Topic 1.1):     * Polarity: Water is a polar molecule, meaning it has an uneven distribution of charges.     * Hydrogen Bonds: These are weak intermolecular bonds that form between water molecules.     * Universal Solvent: Because of its polarity and hydrogen bonding, water acts as a universal solvent.     * Thermal and Physical Properties: Water exhibits cohesion, adhesion, surface tension, and a high specific heat.     * Wider Biological Context: Hydrogen bonding is not restricted to water; it is foundational in DNA, is responsible for specific RNA shapes, and occurs in protein folding and various intermolecular interactions.

  • Elements of Life (Topics 1.2–1.3):     * Polymerization: The molecules of life are built from monomers that combine into polymers.     * Dehydration Synthesis: This process combines monomers into polymers.     * Hydrolysis: This process takes polymers apart.

  • Carbohydrates:     * Functions include energy storage and key structures.     * Monosaccharides: Simple sugars.     * Disaccharides: Used for energy transport.     * Polysaccharides: Include storage molecules like starch and structural molecules like cellulose (found in cell walls).

  • Lipids:     * Nature: Lipids are nonpolar molecules.     * Fatty Acids: The key component. They can be Saturated (solid at room temperature) or Unsaturated (liquid at room temperature, containing bends and kinks).     * Functions: Energy storage (fats and oils), waterproofing (waxes), membrane formation (phospholipids), and signaling (steroids).     * Phospholipids: Possess a dual nature with a hydrophilic polar head and a hydrophobic nonpolar tail. When mixed with water, they naturally form a phospholipid bilayer, creating a water-free zone between the tails.

  • Proteins:     * Diverse Functions: Motion (muscle tissue), enzymes, structure building, transport, energy storage, and signaling.     * Monomer: Amino acids, which consist of an amino group, a carboxyl group, and a variable R-group (side chain).     * Four Levels of Structure:         * Primary Structure: The genetically determined linear sequence of amino acids.         * Secondary Structure: Alpha helices and beta-pleated sheets formed by interactions in the polypeptide backbone.         * Tertiary Structure: Complex turns and loops formed by R-group interactions (hydrogen bonds, covalent bonds, hydrophobic interactions, and ionic bonds).         * Quaternary Structure: The aggregation of multiple polypeptide chains.

  • Nucleic Acids:     * Molecules of Heredity: DNA plays the central role in cells. RNA can be hereditary material in some viruses but typically serves as an information transfer molecule (mRNA).     * RNA Catalysis: RNA can catalyze reactions (acting like enzymes) in ribosomes, spliceosomes, and microRNAs.     * Monomer: Nucleotides, consisting of a five-carbon sugar, a nitrogenous base, and a phosphate group.     * Comparison of DNA and RNA:         * Sugars: Deoxyribose in DNA; Ribose in RNA.         * Bases: Adenine, Thymine, Cytosine, Guanine (ATCG) in DNA; Adenine, Uracil, Cytosine, Guanine (AUCG) in RNA.     * DNA Structure: A double-stranded double helix with a sugar-phosphate backbone. Base pairing rules are Adenine with Thymine and Cytosine with Guanine. It has an anti-parallel structure with 5′5' and 3′3' ends running in opposite directions.

Unit 2: Cell Structure and Function

  • Cell Types: Distinction between prokaryotic and eukaryotic cells regarding size, structure, and DNA packaging.

  • Cell Size and SA:V Ratio (Topic 2.2):     * Maximizing Efficiency: Cells must be small to maximize their surface-area-to-volume (SA:V) ratio, allowing for efficient diffusion.     * Adaptations for Surface Area: Gills, elephant ears, mitochondrial inner foldings, and the intestinal lining.     * Counter-Adaptations: Large animals like whales evolve low surface area to minimize heat loss.

  • Relative Metabolic Rate (Metabolic Scaling):     * In mammals, the amount of energy burned per gram of tissue (relative metabolic rate) is significantly higher in small animals than in large ones. This correlates with heart rate and lifespan.

  • Membrane Structure and Function:     * Selective Permeability: The membrane controls what enters and exits the cell.     * Fluid Mosaic Model: The membrane consists of phospholipids, proteins, and cholesterol in motion.     * Cholesterol: Acts as a fluidity buffer, keeping the membrane stable at high temperatures and fluid at low temperatures.     * Proteins: Involved in transport, cytoskeleton attachment, enzymatic activity, signal transduction, and cell-cell recognition.

  • Membrane Transport:     * Passive Transport: Diffusion from high to low concentration without energy input. Simple diffusion is for small nonpolar molecules (oxygen, CO2CO_2) and lipids (steroids, fats). Facilitated diffusion uses protein channels for polar molecules and ions.     * Active Transport: Movement against a concentration gradient (low to high). Requires energy in the form of ATP, which is broken down into ADP to power pumps.     * Bulk Transport: Endocytosis (membrane buckles in to form a vesicle) and Exocytosis (vesicles fuse with membrane to dump contents outside).

  • Osmosis and Water Potential:     * Definition: The diffusion of water down its concentration gradient (hypotonic to hypertonic).     * Water Potential Equation: Ψ=Ψs+Ψp\Psi = \Psi_s + \Psi_p     * Principles: Adding solute decreases solute potential (and thus water potential). Adding pressure increases water potential. Water flows from high Ψ\Psi to low Ψ\Psi.     * Cellular Effects: Plant cells prefer hypotonic environments (turgid). Animal cells in hypotonic environments may burst.

  • Compartmentalization:     * Internal Compartments: Allow for specialized pH and chemistry for specific reactions.     * Endomembrane System: Includes the nuclear membrane, rough and smooth ER, vesicles, Golgi, and lysosomes.     * Endosymbionts: Mitochondria and chloroplasts evolved from free-living bacteria. Evidence: Circular DNA, bacterial-like ribosomes, binary fission, and double membranes.

Unit 3: Cellular Energetics

  • Enzymes:     * Catalysts: Proteins that lower activation energy.     * Active Site: Highly specific binding site for substrates.     * Denaturation: Changes in pH or temperature can change the active site shape, stopping activity.     * Inhibition:         * Competitive: Molecule competes for the active site.         * Noncompetitive/Allosteric: Molecule binds to a second site (allosteric site), changing the active site shape.

  • Metabolic Pathways: Series of reactions where the product of one is the reactant for the next. Can be linear (Glycolysis) or cyclical (Krebs or Calvin cycle).

  • Energy Coupling:     * Exergonic Reactions: Release energy to drive work.     * Endergonic Reactions: Require energy input.     * ATP: Consists of ribose, a nitrogenous base, and three phosphates. Energy from respiration powers ATP creation (ADP+P→ATPADP + P \rightarrow ATP). Hydrolyzing ATP releases energy for cellular work.

  • Photosynthesis:     * Process: Photoautotrophs use light to combine Carbon Dioxide and water into carbohydrates, releasing oxygen.     * Formula: 6CO2+6H2O+light energy→C6H12O6+6O26CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2     * Light Reactions: Occur in the thylakoid. Light powers an electrical current that pumps protons into the thylakoid space. Diffusion through ATP synthase generates ATP. Water is split to provide electrons, releasing oxygen. NADP+ is reduced to NADPH.     * Calvin Cycle: Occurs in the stroma. Fixes CO2CO_2 into G3P (glyceraldehyde 3-phosphate). Includes carbon fixation, energy investment (using ATP/NADPH), and RuBP regeneration.

  • Cellular Respiration:     * Stages: Glycolysis, Link Reaction, Krebs Cycle, Electron Transport Chain (ETC).     * Oxidation: Food is oxidized to create mobile electron carriers (NADH and FADH2).     * Oxidative Phosphorylation: Occurs in the inner mitochondrial membrane. ETC powers proton pumps (matrix to intermembrane space). Protons flow through ATP synthase to create ATP. Oxygen is the final electron acceptor.     * Anaerobic Respiration: Occurs without oxygen. Includes glycolysis (yielding 2 ATP) and fermentation (regenerates NAD+ so glycolysis can continue).

Unit 4: Cell Communication, Feedback, and the Cell Cycle

  • Cell Communication:     * Ligands: Signal molecules complementary to specific receptors.     * Three Phases: Reception, Signal Transduction (often including amplification), and Response (gene or enzyme activation).     * Steroid Hormones: Nonpolar; they diffuse through the bilayer, bind to cytoplasmic receptors, enter the nucleus, and activate genes.

  • Homeostasis and Feedback:     * Negative Feedback: The output slows down the system (e.g., Insulin lowers blood sugar, Glucagon raises it).     * Positive Feedback: Output accelerates internal changes (e.g., Oxytocin during childbirth, Ethylene during fruit ripening).

  • The Cell Cycle:     * Phases: Interphase (G1, S, G2) and M phase (Prophase, Metaphase, Anaphase, Telophase, Cytokinesis).     * Regulation: Controlled by checkpoints and internal signals like Cyclin and Cyclin-Dependent Kinase (CDK).     * Cancer: Result of unregulated cell division due to mutations in proto-oncogenes (act like a gas pedal) or tumor-suppressor genes (act like brakes), leading to metastasis.

Unit 5: Heredity

  • Meiosis:     * Produces haploid gametes from diploid germ cells.     * Meiosis I: Homologous pairs separate.     * Meiosis II: Sister chromatids separate.     * Diversity Generators: Independent assortment, crossing over (prophase I), and random fertilization.

  • Sex Determination:     * Mammals: XX/XY system.     * Birds: ZW/ZZ system.     * Insects (Bees/Wasps): Males are haploid; females are diploid.     * Environmental: Temperature during development in reptiles.

  • Genetic Disorders: Nondisjunction (failure of chromosomes to separate) leads to Trisomy (Down Syndrome) or Monosomy (Turner Syndrome).

  • Mendelian Genetics:     * Law of Segregation: Alleles separate during gamete formation.     * Dihybrid Cross Ratio: 9:3:3:19:3:3:1.     * Rules of Probability: Use general rules like the Rule of Multiplication for multiple genes.

  • Complex Genetics:     * X-Linked Traits: Genes on X-chromosomes (e.g., color blindness, hemophilia). Males express traits with only one recessive allele.     * Linked Genes: Genes on the same chromosome. Can be separated by crossing over; recombination frequency helps map chromosomes.     * Non-nuclear Inheritance: Genes found in mitochondria.     * Genotype-Environment Interaction: Identical genotypes can have different phenotypes depending on soil pH or other factors.     * Pleiotropy: One gene influencing multiple traits (e.g., sickle cell anemia, cystic fibrosis).

Unit 6: Gene Expression and Regulation

  • DNA Replication:     * Semi-conservative: Each daughter strand is half-new and half-old.     * Enzymes: Helicase (unwinds), DNA Polymerase (synthesizes), Primase (primes), Ligase (seals).     * Directionality: Synthesis only occurs 5′→3′5' \rightarrow 3'. Leading strand is continuous; lagging strand has Okazaki fragments.

  • Gene Regulation:     * Eukaryotes: All cells are genetically equivalent but express different genes.     * Epigenetics: Chemical modifications like Acetylation (turns genes on) and Methylation (turns genes off).     * Alternative Splicing: Eukaryotic genes have Introns (removed) and Exons (expressed), allowing for phenotypic variation from the same gene.

  • Mutations:     * Point Mutations: Substitutions like Silent (redundancy), Nonsense (early stop), or Missense (different amino acid).     * Frameshift: Insertions or deletions that shift the reading frame.

  • Biotechnology: Includes PCR (amplification), Restriction Enzymes, Gel Electrophoresis, Plasmids (for insulin production), and DNA sequencing.

Unit 7: Natural Selection and Evolution

  • Selection Types: Natural selection (survival of the fittest), Artificial selection (human-driven), and Sexual selection (reproductive advantage).

  • Population Genetics:     * Misconception: Dominant alleles are not necessarily more common (e.g., Achondroplasia).     * Hardy-Weinberg Equations: p+q=1p + q = 1 and p2+2pq+q2=1p^2 + 2pq + q^2 = 1.

  • Factors Leading to Evolution: Genetic Drift (bottleneck/founder effect), Natural Selection, Gene Flow, and Mutation.

  • Evidence for Evolution: Fossils, homologies (anatomical and molecular), vestigial structures, and observed resistance (antibiotics/pesticides).

  • Speciation: Biological species concept defines species by interbreeding. Barries include prezygotic (behavioral) and postzygotic (sterility). Speciation can be allopatric (geographic barrier) or sympatric (no barrier).

  • Origin of Life:     * Miller-Urey Experiment: Simulated early Earth to synthesize amino acids abiotically.     * RNA World: RNA likely the first genetic molecule because it is informational and catalytic (ribozymes).

Unit 8: Ecology

  • Energy Flow: Trophic levels follow a 10% energy transfer rule. Producers have the most energy, followed by primary and secondary consumers.

  • Biogeochemical Cycles: Movements between biotic and abiotic reservoirs. Includes Carbon, Nitrogen, Water, and Phosphorus cycles.

  • Population Growth:     * Models: Exponential and Logistic (reaches carrying capacity KK).     * Factors: Density-dependent (competition) and density-independent (weather).

  • Community Ecology: Includes symbiosis (parasitism, mutualism, commensalism) and niche partitioning. Keystone species maintain biodiversity by controlling herbivore populations.

  • Biodiversity indices: Measured by Simpson’s diversity index to account for richness and evenness.

  • Human Impact:     * Eutrophication: Phosphorus/Nitrogen runoff leads to algae blooms and ecosystem disruption.     * Biomagnification: Toxins (like DDT) concentrate at higher trophic levels.     * Habitat Fragmentation and Invasive Species: Reduce genetic diversity, potentially creating an extinction vortex.