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Padilla Biology

AP Biology

Study AP Biology unit by unit, then practice until it sticks.

Pick a unit, get real explanations on every question, and watch your weak spots turn into strengths.

Start practicingBrowse the units

Course units

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Unit 1Chemistry of Life8–11%Unit 2Cells10–13%Unit 3Cellular Energetics12–16%Unit 4Cell Communication and Cell Cycle10–15%Unit 5Heredity8–11%Unit 6Gene Expression and Regulation12–16%Unit 7Natural Selection13–20%Unit 8Ecology10–15%

How to use this site

  1. Review a unit

    Read the unit's key concepts and terms before you practice, or jump straight in if you're already comfortable with the content.

  2. Practice with explanations

    Work through multiple-choice and free-response questions. Every choice has an explanation, not just the correct one.

  3. Track what's weak

    Your dashboard shows accuracy by unit and flags the topics you keep missing, so you know what to review next.

🧫 Interactive model

Explore a full cell simulation

Walk through organelles, the secretory pathway, and central dogma interactions when a diagram alone isn't enough.

Open the simulation →