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Volume I · MMXXVI AP Biology
Library› AP Biology› Unit 2: Cell Structure and Function
⁂   AP Biology · Unit 2

2. Cell Structure and Function

10–13% of the AP exam. 7 key topics. 4 common errors analyzed.

10–13% exam weight 12 instructional periods

Unit 2: Cell Structure and Function

Unit 2 covers cell structure and function — a core component of the AP Biology curriculum. Master these concepts to build the mechanistic vocabulary the FRQ rubrics demand.

Key topics in this unit

  1. Prokaryotic vs. eukaryotic cell structure and compartmentalization
  2. Cell membrane: fluid mosaic model, phospholipid bilayer, membrane proteins
  3. Passive transport: simple diffusion, facilitated diffusion, osmosis
  4. Active transport: pumps, endocytosis, exocytosis
  5. Organelle structure-function relationships: mitochondria, chloroplast, endoplasmic reticulum, Golgi apparatus, ribosomes, nucleus, vacuoles, lysosomes
  6. Cell size constraints: surface area-to-volume ratio
  7. Endomembrane system and vesicle trafficking

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Reversing the direction of osmosis — water moves toward higher solute concentration (lower water potential), not away from it

Common error

Claiming active transport does not require a protein carrier, or confusing facilitated diffusion (no ATP) with active transport (ATP required)

Common error

Misattributing ATP synthesis to the mitochondrial matrix rather than the inner mitochondrial membrane (ATP synthase location)

Common error

Forgetting that a smaller cell has a more favorable surface area-to-volume ratio for nutrient/waste exchange, not a larger one

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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Our worked solutions and practice questions are original instructional content created by Tian2 AP. They are aligned to the concepts and skills described in College Board’s Course and Exam Description and are not reproductions of, or affiliated with, College Board’s official materials.