What is covered in AP Psychology Unit 1?

Unit 1, Biological Bases of Behavior, covers heredity and environment, the neuron and neurotransmitters, the nervous and endocrine systems, the structures of the brain and the tools used to study it, sleep and consciousness, and sensation and perception.

Is Unit 1 of AP Psychology hard?

Unit 1 is the most vocabulary-heavy unit because of the neuroscience and brain anatomy terms. It's very learnable with steady review and diagrams, but it rewards memorizing precise definitions — the difference between the sympathetic and parasympathetic systems, for example.

AP Psychology · Unit 1

AP Psychology Unit 1: Biological Bases of Behavior

Unit 1 is the biology beneath every other unit — how neurons fire, how the brain is organized, and how your senses turn the world into experience. It's the most term-dense unit, so this guide lays out exactly what to know and where the exam focuses.

What Unit 1 Covers

The College Board groups Unit 1 into a few big areas: the interaction of heredity and environment, the nervous and endocrine systems, neural firing, the brain, sleep and consciousness, and sensation and perception. Together they answer one question: how does biology produce behavior and experience?

The Neuron and Neural Firing

Know the parts of the neuron — dendrites receive signals, the cell body integrates them, the axon carries the impulse, and the myelin sheath speeds it up. A neuron fires in an all-or-none action potential once it crosses threshold; at rest it sits at a negative resting potential. Signals jump the synapse via neurotransmitters. Memorize the big ones and their roles: dopamine (reward, movement), serotonin (mood, sleep), acetylcholine (muscle movement, memory), GABA (inhibition), glutamate (excitation), and endorphins (pain relief).

The Nervous and Endocrine Systems

The nervous system splits into the central (brain and spinal cord) and peripheral systems. The peripheral divides into the somatic (voluntary muscles) and autonomic, which itself splits into the sympathetic (arouses — fight or flight) and parasympathetic (calms) branches. The endocrine system uses hormones for slower, longer-lasting effects; know the pituitary ("master gland") and the adrenal glands (adrenaline).

The Brain

Work from the bottom up: the brainstem and medulla (heartbeat, breathing), the cerebellum (balance, coordination), the thalamus (sensory relay), the hypothalamus (hunger, thirst, temperature, the endocrine link), and the limbic system — the amygdala (emotion, fear) and hippocampus (memory formation). The cerebral cortex has four lobes: frontal (planning, movement, judgment), parietal (touch), occipital (vision), and temporal (hearing). Know research tools too — the EEG, fMRI, and lesion studies, plus plasticity and the split-brain work of Sperry and Gazzaniga.

Sleep and Consciousness

Understand the circadian rhythm, the NREM sleep stages, and REM sleep (vivid dreams, near-paralysis). Be ready to compare theories of why we sleep and dream, and to identify common sleep disorders like insomnia and narcolepsy.

Sensation and Perception

Sensation is detecting stimuli; perception is interpreting them. Key ideas: transduction (turning stimulus energy into neural signals), the absolute threshold, the difference threshold (just-noticeable difference, Weber's law), and sensory adaptation. Know the basics of vision and hearing, plus top-down vs. bottom-up processing and Gestalt grouping principles.

How to Study Unit 1

This unit rewards diagrams and flashcards — draw the neuron, label the brain, and quiz the neurotransmitters until they're automatic. Then test yourself with mixed questions on the practice test. When you're ready to move on, Unit 2 builds directly on this foundation: see AP Psychology Unit 2: Cognition or the full units overview.

Test Your Unit 1 Recall

Mixed practice questions with instant explanations across all five units.

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