Respiration

Respiration is the metabolic pathway by which cells release energy from organic molecules (primarily glucose) to synthesise ATP — the universal energy currency of cells. It occurs in all living cells, continuously, and can be aerobic (requiring oxygen) or anaerobic (without oxygen). Respiration is not simply the reverse of photosynthesis — it involves different enzymes, different intermediates, and occurs in different organelles.

Key Definition: Respiration is the enzyme-controlled release of energy from organic molecules (respiratory substrates) to produce ATP. It occurs in every living cell.

Overall equation for aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (+ heat)

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Overview of the Four Stages