Study Guide - AP Biology Course
A structured review of every unit in the AP Biology course. Use this guide for exam prep, quick revision, or as a reference while working through chapters and practice questions.
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Effective AP Biology study goes beyond memorization - build reasoning skills by connecting concepts and applying them to novel situations.
Read the concept
Understand the biological principle and its context
Connect across units
Link the idea to related topics in other units
Apply to scenarios
Use the concept to explain data or predict outcomes
Practice with questions
Test recall with MCQs and free-response prompts
Review and refine
Identify gaps, revisit weak areas, and repeat
| Term | Definition |
|---|---|
| Homeostasis | The maintenance of a stable internal environment through feedback mechanisms despite external changes |
| Macromolecule | Large organic molecule built from monomers - proteins, nucleic acids, carbohydrates, and lipids |
| Organelle | Membrane-bound or non-membrane-bound structure within a cell that performs a specific function |
| ATP | Adenosine triphosphate - the primary energy currency of cells, releasing energy when its terminal phosphate bond is hydrolyzed |
| Chemiosmosis | The movement of ions across a membrane down their electrochemical gradient, driving ATP synthesis via ATP synthase |
| Enzyme | A biological catalyst (usually a protein) that lowers activation energy to speed up a specific reaction |
| Signal transduction | The process by which a cell converts an extracellular signal into a functional cellular response through a cascade of molecular events |
| Mitosis | Nuclear division producing two genetically identical daughter nuclei - includes prophase, metaphase, anaphase, and telophase |
| Meiosis | Two-stage nuclear division that reduces chromosome number by half, producing four genetically unique haploid cells |
| Allele | An alternative form of a gene at a given locus, arising by mutation and contributing to phenotypic variation |
| Genotype | The genetic makeup of an organism at one or more loci - determines the range of possible phenotypes |
| Phenotype | The observable physical or biochemical characteristics of an organism, resulting from genotype and environment |
| Hardy-Weinberg equilibrium | A model predicting stable allele frequencies in a non-evolving population when five conditions are met (large population, random mating, no mutation, no migration, no selection) |
| Natural selection | Differential survival and reproduction of individuals with heritable traits that confer advantages in a given environment |
| Carrying capacity (K) | The maximum population size an environment can sustain indefinitely given available resources |
| Trophic level | A feeding position in a food web - producers, primary consumers, secondary consumers, and so on |
| Photosynthesis | The process by which autotrophs convert light energy, CO2, and water into glucose and O2 in chloroplasts |
| Cellular respiration | The metabolic pathway that oxidizes glucose to produce ATP - includes glycolysis, the citric acid cycle, and oxidative phosphorylation |
| Transcription | The synthesis of mRNA from a DNA template by RNA polymerase in the nucleus |
| Translation | The ribosome-mediated synthesis of a polypeptide chain from an mRNA template using tRNA and amino acids |
1. Introduction to AP Biology
Big Ideas, science practices, exam format
2. Chemistry of Life
Water, macromolecules, enzymes, pH
3. Cell Structure and Function
Organelles, membranes, transport
4. Cellular Energetics
Photosynthesis, respiration, ATP
5. Cell Communication and Cell Cycle
Signal transduction, mitosis, meiosis
6. Heredity and Genetics
Mendelian genetics, chi-square, linked genes
7. Gene Expression and Regulation
DNA replication, transcription, translation, operons
8. Evolution and Natural Selection
Hardy-Weinberg, speciation, phylogenetics
9. Ecology and Populations
Energy flow, nutrient cycles, community interactions
10. Cell Division
Mitotic and meiotic processes, genetic variation
| Concept A | Concept B | Connection |
|---|---|---|
| Photosynthesis | Cellular respiration | Products of one are reactants of the other - glucose and O2 cycle between the two pathways via the carbon and oxygen cycles |
| DNA mutations | Natural selection | Mutations create genetic variation; natural selection acts on phenotypic differences that affect fitness in a given environment |
| Signal transduction | Gene expression | Extracellular signals activate transcription factors through cascades, ultimately turning specific genes on or off |
| Meiosis | Genetic diversity | Crossing over and independent assortment during meiosis produce unique gamete combinations, driving variation in offspring |
| Enzyme structure | Homeostasis | Enzyme activity depends on temperature and pH; feedback inhibition of metabolic enzymes maintains stable internal conditions |
Approximate exam weight for each unit as published by the College Board. Use these to prioritize study time.
| Unit | Topic | Exam Weight |
|---|---|---|
| 1 | Chemistry of Life | 8-11% |
| 2 | Cell Structure and Function | 10-13% |
| 3 | Cellular Energetics | 12-16% |
| 4 | Cell Communication and Cell Cycle | 10-15% |
| 5 | Heredity | 8-11% |
| 6 | Gene Expression and Regulation | 12-16% |
| 7 | Natural Selection | 13-20% |
| 8 | Ecology | 10-15% |
Q1.Explain how the structure of water molecules contributes to water's role as a solvent in biological systems.
Water is a polar molecule with partial positive charges on hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water to form hydrogen bonds with other polar and charged molecules, dissolving them effectively. Ions are surrounded by hydration shells, and polar organic molecules interact with water through hydrogen bonding. This solvent property is critical for biochemical reactions, nutrient transport, and maintaining cellular environments.
Q2.Compare and contrast the light-dependent reactions and the Calvin cycle in terms of location, inputs, and outputs.
The light-dependent reactions occur in the thylakoid membranes and use light energy, water, ADP, and NADP+ to produce ATP, NADPH, and O2. The Calvin cycle occurs in the stroma and uses CO2, ATP, and NADPH to produce G3P (glyceraldehyde-3-phosphate), which is used to build glucose. The light reactions generate the energy carriers (ATP, NADPH) that the Calvin cycle consumes, coupling the two stages.
Q3.A population of beetles has two alleles for body color: B (dark, dominant) and b (light, recessive). If the frequency of the b allele is 0.3, what percentage of the population is expected to be heterozygous under Hardy-Weinberg equilibrium?
Under Hardy-Weinberg equilibrium, p + q = 1, so p = 0.7 and q = 0.3. The expected heterozygote frequency is 2pq = 2(0.7)(0.3) = 0.42, or 42% of the population. This calculation assumes the population is large, mating is random, and there is no selection, mutation, or migration acting on this locus.
Q4.Describe how a signal transduction pathway amplifies an extracellular signal and give one example of a cellular response.
Signal transduction pathways amplify signals through phosphorylation cascades. A single ligand binds a receptor, which activates a relay molecule. Each activated molecule in the cascade can activate many molecules at the next step, so the signal is multiplied at each stage. For example, epinephrine binding to a liver cell receptor triggers a cascade that activates glycogen phosphorylase, breaking down glycogen into glucose - a single molecule of epinephrine can lead to the release of millions of glucose molecules.
Q5.Explain why organisms at higher trophic levels generally have smaller populations than those at lower levels.
Energy transfer between trophic levels is inefficient - only about 10% of energy at one level is passed to the next. The remaining 90% is lost as heat through cellular respiration. Because less energy is available at each successive level, higher trophic levels can support fewer organisms and less total biomass. This is why food chains rarely exceed four or five levels and why top predators require large territories.
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