AP Biology · Unit 2
Cell Structure and Function
Begin with an optional chemistry refresher, then explore how cellular structures, membranes, transport, and compartmentalization allow cells to exchange matter and maintain distinct internal conditions.
Learning sequence
Choose a lesson
Optional chemistry review
Solutions, Polarity & Osmosis
Refresh the chemistry used to explain membrane permeability and water balance.
Topic 2.1
Cell Structures at Work
Connect organelle structure, location, and abundance to cellular function.
Topic 2.2
Size Sets Limits
Calculate surface area-to-volume ratio and predict exchange efficiency.
Topic 2.3
The Fluid Mosaic
Build a membrane and orient its lipids, proteins, and carbohydrates.
Topic 2.4
Who Crosses?
Predict permeability from molecular size, charge, and polarity.
Topics 2.5–2.6
Moving Across Membranes
Compare passive, active, protein-mediated, and bulk transport.
Topic 2.7
Water Balance
Model tonicity, water potential, and osmoregulation.
Topics 2.8–2.10
Gradients & Compartments
Connect ATP-powered pumps, internal membranes, and endosymbiosis.
Topics 2.1–2.10
Integrated AP-Style Practice
Complete 34 numbered MCQs and six evidence-based FRQs with calculations and data analysis.