AP Psychology — biological bases of behavior

Unit 1 of AP Psychology is where the course is at its most physical: neurons, brain regions, hormones, sleep, and the machinery of sensation. It is worth between 15 and 25 percent of the exam, and it supplies vocabulary that every later unit leans on. This set works through ten of its ideas, one question each.

Most of these are asked through a described consequence rather than a definition, because that is how the exam asks them and because recognizing a term is not the same as knowing what it does. A neuron loses its myelin: the answer is not that it stops firing but that it fires late, and the three wrong answers all describe a neuron that has stopped working altogether. A man's speech comes out in short effortful phrases while he follows everything said to him and grows frustrated at his own errors: two details settle it, because effortful production with intact comprehension separates Broca's area from Wernicke's, and answering on the word "language" alone will not do it. A crash behind you at night raises your heart rate, widens your pupils and dries your mouth: read the three signs together and they are all one thing, resources diverted towards immediate action.

Two questions are about what a measurement means rather than what a structure does. The threshold question gives a participant who notices 5 grams added to 100 but needs 20 grams added to 400 — the amount required quadruples with the weight, so what stays constant is the proportion, and that is the difference threshold behaving as Weber described. The heritability question is the one most often got wrong in the whole course: a heritability of 0.60 says that sixty percent of the VARIATION across a sampled population tracks genetic differences between people. It says nothing whatever about how much of one person's trait is inherited, because an individual has no variation to partition. It is also not a fixed property of the trait: make the environments in a sample more uniform and heritability rises, because there is less environmental variation left to account for anything.

Every distractor is a specific mistake and every explanation names it — agonist for antagonist, sympathetic for parasympathetic, trichromatic theory asked to explain an afterimage it has nothing to say about, a heritability estimate read as a fact about a person.

Two limits worth stating. Only a few items carry a drawing (a neuron, a synapse and a bar chart of the threshold data); real exam questions in this unit also use brain cross-sections and graphs of sleep stages, which are described in words here instead. And the free-response third of the exam is a different task entirely: two questions in seventy minutes, one analyzing a research article and one arguing from evidence, neither of which is trainable by recognizing a correct option.

• Explain what myelin does and what is lost when it degrades — speed of conduction rather than the capacity to fire
• Distinguish an agonist from an antagonist, and both from drugs that change how much neurotransmitter is present
• Infer the brain region implicated by a described deficit, separating Broca's area from Wernicke's by which side of language is affected
• Contrast endocrine and neural signaling by their delivery route, and derive the difference in speed and duration from it
• Identify the sympathetic and parasympathetic branches from a described pattern of bodily change
• Describe how REM and deep sleep trade places across a night's cycles
• Distinguish the difference threshold from the absolute threshold, and recognize that it scales in proportion to the original stimulus
• Say which observations the opponent-process theory explains and which belong to the trichromatic theory
• Separate top-down from bottom-up processing by asking where the information came from
• State what a heritability estimate measures, why it cannot describe an individual, and why it changes with the range of environments sampled

Built against the AP Psychology Course and Exam Description (College Board, revised framework first examined in May 2025): five units, each weighted between 15 and 25 percent of the exam, with Unit 1 covering the biological bases of behavior. The exam runs 2 hours 40 minutes in two sections — 75 multiple-choice questions in 1 hour 30 minutes for 67 percent of the score, then two free-response questions in 1 hour 10 minutes for the remaining 33 percent, an Article Analysis Question and an Evidence-Based Question. Every case, name and number in this material is invented and said to be invented in the question itself; no diagnostic criteria are reproduced from the DSM or ICD, and nothing is reproduced from any College Board publication, released exam or scoring guideline. Zestly is an independent study tool. It is not affiliated with the College Board, which owns the AP Psychology exam, and it is not an test center.