What is the overall cellular respiration equation, and where does it mostly occur in the cell?

• A. C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy; mostly in mitochondria
• B. C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O; occurs in chloroplasts
• C. 6 CO2 + 6 H2O -> C6H12O6 + O2; occurs in cytoplasm only
• D. Glucose -> lactic acid; occurs in ribosomes

Answer: (A)

Cellular respiration releases energy by breaking down glucose with oxygen to produce carbon dioxide, water, and energy stored as ATP. The overall equation is glucose plus oxygen yielding carbon dioxide, water, and energy. Most of the energy comes from the stages that occur in the mitochondria—the citric acid cycle and oxidative phosphorylation—while glycolysis happens in the cytoplasm and contributes less to the total ATP yield. The other options mix up the reactants and products or point to the wrong cellular locations (photosynthesis in chloroplasts, or fermentation in the cytoplasm), so they don’t fit the main process.