AP Biology UNIT 3: Cellular Energetics

IMPORTANT NOTE: Students under the age of 18, parents, caregivers and guardians are required to purchase this course and allow their students to benefit from it!

Unit 3 of AP Biology dives into one of the most exciting and essential themes in all of life science: how cells capture, transform, and use energy. Energy flow is the heartbeat of biology, and in this unit, we’ll uncover the processes that fuel every living system—from a single bacterium dividing in a hot spring to a neuron firing in the human brain.

We’ll begin by exploring the fundamentals of enzymes, the molecular catalysts that drive life’s chemical reactions with astonishing speed and precision. You’ll learn not only how enzymes lower activation energy but also how their activity is regulated, making them key players in the fine-tuned balance of metabolism.

From there, we’ll move into the great energy pathways: cellular respiration and photosynthesis. We’ll investigate how cells harvest energy from organic molecules in glycolysis, the Krebs cycle, and oxidative phosphorylation, and how plants and some bacteria capture light energy to build sugars in photosynthesis. Along the way, we’ll highlight the role of ATP as the universal energy currency of life.

By the end of this unit, you’ll see that cellular energetics is more than just memorizing steps of pathways—it’s the grand story of how energy moves through living systems. And understanding that story is the key to unlocking all higher processes of biology.