AP Psychology, AP exams

Unit 1: Biological Bases of Behavior

Unit 1 covers the nervous system, genetics and environment, consciousness and sleep, and sensation. It is the most technical unit in the course and the one where vocabulary precision matters most. Students should be able to describe a neural or sensory process step by step rather than recognizing terms in isolation.

Position: 1 of 5 units
Topics covered: 7 topics in this guide

What is covered

Topics inside this unit.

These topics describe the scope students most often review for this part of AP Psychology. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Heredity and environment: Nature and nurture interaction, twin and adoption studies, and evolutionary explanations of behavior.
The nervous and endocrine systems: Central and peripheral divisions, the autonomic nervous system, and hormonal influences on behavior.
Neurons and neural firing: Resting and action potentials, the all-or-none principle, synaptic transmission, and major neurotransmitters.
The brain: Structures and their functions, hemispheric specialization, plasticity, and imaging methods such as EEG and fMRI.
Consciousness and sleep: Sleep stages and cycles, circadian rhythms, theories of dreaming, and common sleep disorders.
Psychoactive drugs: Depressants, stimulants, and hallucinogens, plus tolerance, withdrawal, and effects on neurotransmission.
Sensation: Transduction, absolute and difference thresholds, sensory adaptation, and the mechanics of vision, hearing, and the body senses.

Study tips

How to practice Biological Bases.

Section-specific guidance that follows from how this material is usually tested.

Draw the neuron and the action potential from memory until the sequence is automatic.
Pair each brain structure with one function and one consequence of damage.
Separate sensation from perception explicitly; the exam tests the boundary between Units 1 and 2.

Where this fits

Unit 1: Biological Bases of Behavior is 1 of 5 units in the AP Psychology guide. Use the full guide to balance it against everything else you have to review.

Back to the AP Psychology guide Official exam information

Sample Biological Bases questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
Which principle states that once a neuron reaches its threshold it fires at full strength, and that a stronger stimulus does not produce a stronger impulse?
1. AThe all-or-none principle
2. BThe refractory period
3. CReuptake
4. DSensory adaptation
Show answer
Answer: A. The all-or-none principle
A neuron either fires completely or not at all, so intensity is communicated by how often neurons fire and how many fire, not by the size of a single impulse. The refractory period is the tempting distractor, but it names the brief interval after firing during which the neuron cannot fire again.
Key insight: Neurons signal intensity by rate and number, never by amplitude of a single action potential.
Question 2Foundational
Which division of the nervous system arouses the body for action during stress by raising heart rate, dilating pupils, and releasing glucose?
1. AThe sympathetic nervous system
2. BThe parasympathetic nervous system
3. CThe somatic nervous system
4. DThe central nervous system
Show answer
Answer: A. The sympathetic nervous system
The sympathetic branch of the autonomic nervous system mobilizes energy for fight or flight. The parasympathetic branch is the tempting distractor because it belongs to the same autonomic system, but its job is the opposite: conserving energy and returning the body to baseline once the threat passes.
Key insight: Sympathetic arouses and parasympathetic calms; both run automatically without conscious control.
Question 3Intermediate
During which stage of sleep do vivid storylike dreaming, darting eye movements, and near-paralysis of the voluntary muscles occur together?
1. AREM sleep
2. BNREM Stage 1
3. CNREM Stage 2
4. DNREM Stage 3
Show answer
Answer: A. REM sleep
REM combines an active, awake-looking brain with a motionless body, which is why it is also called paradoxical sleep. NREM Stage 3 is the tempting distractor because it is the deepest sleep, but it is dominated by slow delta waves and is associated with sleepwalking and night terrors rather than vivid narrative dreams.
Key insight: In REM the brain is busy and the body is still, and REM periods lengthen across the night.
Question 4Intermediate
What is the term for the process by which sensory receptors convert physical energy such as light or sound waves into neural impulses the brain can use?
1. ATransduction
2. BSensory adaptation
3. CPerception
4. DAccommodation
Show answer
Answer: A. Transduction
Transduction is the conversion step that turns environmental energy into the electrochemical language of the nervous system. Perception is the tempting distractor, but it is the later interpretation and organization of those signals rather than their conversion.
Key insight: Sensation converts energy into signals, and perception is what the brain then makes of them.
Question 5Advanced
What is the term for the smallest change between two stimuli that a person can detect half of the time?
1. AThe difference threshold
2. BThe absolute threshold
3. CSensory adaptation
4. DThe perceptual set
Show answer
Answer: A. The difference threshold
The difference threshold, also called the just noticeable difference, measures how much two stimuli must differ before the change is detectable, and it grows proportionally with stimulus intensity under Weber's law. The absolute threshold is the tempting distractor, but it is the minimum stimulation needed to detect a stimulus at all rather than a change between two of them.
Key insight: Absolute threshold asks whether you notice anything; difference threshold asks whether you notice a change.

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Unit 1: Biological Bases of Behavior