🧬 AP Biology Cheat Sheet 2025

Water Properties:

• 💧 Hydrogen bonding creates cohesion (water-water), adhesion (water-other)
• 🌡️ High specific heat & heat of vaporization (temperature regulation)
• 🧊 Less dense as solid (ice floats, insulates aquatic life)
• 🕷️ Surface tension allows small organisms to walk on water

Macromolecules:

• 🍯 Carbohydrates: monosaccharides, disaccharides, polysaccharides (glucose, starch, cellulose, glycogen)
• 🥑 Lipids: fats, phospholipids, steroids (energy storage, membranes, signaling)
• 🥩 Proteins: 20 amino acids, 4 levels of structure (primary, secondary, tertiary, quaternary)
• 🧬 Nucleic acids: DNA (deoxyribose), RNA (ribose), purines (A,G), pyrimidines (C,T,U)

Chemical Bonds & pH:

• ⚡ Ionic (electron transfer), Covalent (electron sharing), Hydrogen (weak attraction)
• 📊 pH scale 0-14, acids <7, bases >7, buffers resist pH changes
• 🔗 Dehydration synthesis forms bonds, hydrolysis breaks bonds

Cell Theory & Types:

• 🔬 All living things made of cells, cells = basic unit of life, cells from pre-existing cells
• 🦠 Prokaryotes: no nucleus, bacteria & archaea
• 🧬 Eukaryotes: nucleus present, plants, animals, fungi, protists

Organelles:

• 🧠 Nucleus: DNA storage, ribosome assembly, nuclear envelope with pores
• 🏭 Ribosomes: protein synthesis (free or ER-bound)
• 🚚 ER: Rough (ribosomes, protein modification), Smooth (lipid synthesis, detox)
• 📦 Golgi: protein processing, packaging, shipping
• ⚡ Mitochondria: ATP production, cellular respiration, double membrane
• 🗑️ Lysosomes: digestion, waste removal, autophagy
• 🌱 Chloroplasts: photosynthesis, thylakoids, stroma (plants only)

Transport:

• 🚪 Fluid mosaic model: phospholipids, proteins, cholesterol
• ⬇️ Passive: diffusion, osmosis, facilitated diffusion (no ATP)
• ⬆️ Active: pumps, cotransport (requires ATP)
• 📦 Bulk: endocytosis, exocytosis, phagocytosis, pinocytosis

ATP & Energy:

• ⚡ ATP = adenosine + 3 phosphates, energy currency of cells
• 🔄 ATP ↔ ADP + Pi + energy (hydrolysis/phosphorylation)
• 🌡️ 1st Law: energy conserved, 2nd Law: entropy increases

Enzymes:

• 🔗 Lower activation energy, not consumed, substrate specific
• 🎯 Active site fits substrate (induced fit model)
• 🌡️ Temperature, pH, concentration affect activity
• 🚫 Competitive (active site), noncompetitive (allosteric) inhibition

Photosynthesis:

• 🌱 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂
• ☀️ Light reactions: photosystems I & II, electron transport, ATP/NADPH
• 🔄 Calvin cycle: CO₂ fixation, reduction, regeneration (RuBP)
• 🌿 C4 & CAM plants adapt to hot/dry conditions

Cellular Respiration:

• 🔥 C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
• 1️⃣ Glycolysis: glucose → pyruvate (cytoplasm, 2 ATP)
• 2️⃣ Krebs cycle: pyruvate → CO₂ + NADH/FADH₂ (mitochondria)
• 3️⃣ Electron transport: NADH/FADH₂ → ATP (~32 total)
• 🍺 Fermentation: without oxygen (alcoholic, lactic acid)

Signal Transduction:

• 📡 Reception → Transduction → Response pathway
• 🎯 Paracrine (local), endocrine (hormonal), autocrine (self)
• 🚪 Receptors: ligand-gated channels, G-protein coupled, enzyme-linked
• 📢 Signal amplification through cascades
• 💬 Second messengers: cAMP, IP₃, DAG, Ca²⁺

Feedback Systems:

• ➖ Negative feedback: homeostasis (insulin/glucose, thermostat)
• ➕ Positive feedback: amplifies response (oxytocin, blood clotting)

Cell Cycle:

• 🔄 G₁ (growth), S (synthesis), G₂ (preparation), M (mitosis)
• 🛡️ Checkpoints: G₁/S, G₂/M, spindle (prevent errors)
• ⚱️ Apoptosis: programmed cell death
• 🦠 Cancer: uncontrolled division, oncogenes, tumor suppressors

Mitosis Phases:

• 1️⃣ Prophase: chromatin condenses, nuclear envelope breaks
• 2️⃣ Metaphase: chromosomes align at cell center
• 3️⃣ Anaphase: sister chromatids separate
• 4️⃣ Telophase: nuclei reform, cytokinesis

Meiosis:

• 🧬 Diploid (2n) → haploid (n), sexual reproduction
• 1️⃣ Meiosis I: homologs separate (reduction division)
• 2️⃣ Meiosis II: sister chromatids separate
• 🔀 Crossing over: genetic recombination in prophase I
• 🎲 Independent assortment: random chromosome orientation

Mendelian Genetics:

• 👨‍🔬 Mendel's laws: segregation, independent assortment
• 🧬 Genotype (genetic makeup) vs phenotype (observable traits)
• 🔢 Monohybrid (3:1), dihybrid (9:3:3:1) ratios
• 👑 Dominant (expressed when present) vs recessive (masked)

Beyond Simple Dominance:

• 🌈 Incomplete dominance: blended phenotype
• 🩸 Codominance: both alleles expressed (ABO blood)
• 🧬 Multiple alleles: >2 alleles per gene
• 📊 Polygenic: multiple genes affect one trait
• ♂️♀️ Sex-linked traits: genes on X or Y chromosomes

Chromosomal Abnormalities:

• ❌ Nondisjunction: chromosomes don't separate properly
• ➕ Trisomy: extra chromosome (Down syndrome = trisomy 21)
• ➖ Monosomy: missing chromosome (Turner syndrome)

Central Dogma:

• 🧬 DNA → RNA → Protein (replication, transcription, translation)
• 📄 DNA: template, permanent; RNA: temporary, variable

DNA Replication:

• 🔄 Semi-conservative: each strand serves as template
• ➡️ 5' to 3' direction only
• 🧰 Helicase (unwind), primase (primer), DNA polymerase (synthesis)
• 🔗 Leading strand (continuous), lagging strand (Okazaki fragments)
• ✂️ Ligase joins fragments, telomerase extends telomeres

Transcription:

• 📝 DNA → mRNA by RNA polymerase
• 🎬 Promoter (start), terminator (stop)
• ✂️ RNA processing: 5' cap, 3' poly-A tail, splicing (remove introns)

Translation:

• 🏭 mRNA → protein at ribosomes
• 🔤 Genetic code: 64 codons, 20 amino acids
• 🚀 Start codon (AUG), stop codons (UAG, UAA, UGA)
• 🔄 tRNA brings amino acids, anticodon pairs with codon

Gene Regulation:

• 🦠 Prokaryotes: operons (lac, trp), negative/positive control
• 🧬 Eukaryotes: transcription factors, enhancers, silencers
• 🎛️ Epigenetics: DNA methylation, histone modification

Mutations & Biotechnology:

• 🎯 Point mutations: silent, missense, nonsense
• 🧪 PCR amplifies DNA, gel electrophoresis separates
• 🔬 Transformation: introduce DNA into bacteria

Darwin's Theory:

• 🧬 Descent with modification from common ancestor
• 🏆 Natural selection: variation, heritability, differential reproduction
• 💪 Fitness = reproductive success (not physical strength)

Types of Selection:

• 📈 Directional: favors one extreme
• 🎯 Stabilizing: favors average
• 📊 Disruptive: favors both extremes
• ⚡ Sexual selection: traits for mating success

Population Genetics:

• 📐 Hardy-Weinberg: p² + 2pq + q² = 1
• ⚖️ Equilibrium conditions: no mutation, selection, migration, drift
• 🎲 Genetic drift: random allele frequency changes
• 🌊 Gene flow: migration between populations

Speciation:

• 🏔️ Allopatric: geographic separation
• 🧬 Sympatric: reproductive isolation without separation
• 🚫 Reproductive barriers: prezygotic, postzygotic

Evidence for Evolution:

• 🦴 Fossils: chronological record
• 🦴 Comparative anatomy: homologous, analogous structures
• 🧬 Molecular evidence: DNA/protein similarities
• 👶 Embryology: similar development patterns
• 🌍 Biogeography: distribution patterns

Phylogenetics:

• 🌳 Phylogenetic trees show evolutionary relationships
• 🔗 Cladograms based on shared derived characters
• 👑 Outgroup: reference for ancestral traits

Population Ecology:

• 📈 Exponential growth: J-curve (unlimited resources)
• 📊 Logistic growth: S-curve (carrying capacity)
• 🛑 Limiting factors: density-dependent, density-independent
• 👥 Age structure: reproductive potential

Community Interactions:

• 🤝 Mutualism: both benefit (+/+)
• 🏠 Commensalism: one benefits, other neutral (+/0)
• 🦠 Parasitism: one benefits, other harmed (+/-)
• 🦁 Predation: predator benefits, prey harmed (+/-)
• ⚡ Competition: both harmed (-/-)

Ecosystem Structure:

• 🌱 Producers (autotrophs): make own food
• 🐰 Primary consumers: herbivores
• 🐺 Secondary/tertiary consumers: carnivores
• 🍄 Decomposers: break down dead matter
• ⚡ 10% rule: energy transfer between levels

Biogeochemical Cycles:

• 💧 Water cycle: evaporation, precipitation, transpiration
• 🌱 Carbon cycle: photosynthesis, respiration, fossil fuels
• 🧪 Nitrogen cycle: fixation, nitrification, denitrification
• 💀 Phosphorus cycle: no atmospheric phase

Biodiversity & Conservation:

• 🌈 Genetic, species, ecosystem diversity
• 🔢 Simpson's diversity index measures community diversity
• ⚖️ More diversity = greater stability and resilience
• 🌍 Human impacts: habitat loss, pollution, climate change

Homeostasis:

• ⚖️ Maintain internal equilibrium despite external changes
• 🔥 Thermoregulation: endotherms vs ectotherms
• 💧 Osmoregulation: water and salt balance
• 🍯 Blood glucose regulation: insulin and glucagon