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Unit 3

3.0 Unit 3 Overview: Cellular Energetics

1 min readmay 30, 2020


Caroline Koffke

AP Biology 🧬

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All organisms require energy in order to function. This energy comes from a variety of sources, but all energy on earth originated in the sun. Energy is neither created nor destroyed, it is just transformed. All living things transfer energy between them. Photosynthesis is the process of converting light energy into chemical energy. 

Image courtesy of Giphy.

Cellular respiration is the process of breaking down organic compounds into cellular energy called ATP. Organisms get their energy from food sources and release energy through their metabolism as heat and waste products. Enzymes assist with the transformation of energy and allow organisms to sustain life by allowing reactions to occur with less energy.

Major Formulas

  • Cellular Respiration: C6H12O6 + O2 → H2O + CO2
  • Photosynthesis: H2O + CO2 → C6H12O6 + O2
  • Other key components
    • Electron carriers (NADH, FADH2, NADPH)
      • Electron carriers are responsible for carrying electrons in the form of a hydrogen ion. They drop these electrons either at the electron transport chain in order to make ATP or in the Calvin Cycle to contribute to bond formation.
    • ATP Synthase
      • ATP synthase is the enzyme responsible for synthesizing ATP. Remember that enzymes end in -ase. This enzyme harnesses the power of chemiosmosis in order to phosphorylate ADP into ATP.
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