The Energy Budget of Respiration

Energy Production in Respiration:

  • ATP Yield: The primary goal of respiration is to produce ATP, the cell's energy currency.

  • Electron Transport Chain: The electron transport chain is the major source of ATP, utilizing NADH and FADH2 generated in glycolysis and the Krebs cycle.

  • ATP Production: Each NADH molecule produces 3 ATP, while each FADH2 produces 2 ATP.

  • Glycolysis ATP: Glycolysis itself produces a net of 2 ATP molecules.

Energy Budget Calculations:

  • Aerobic Respiration:

    • Glycolysis: 2 ATP

    • Krebs Cycle: 2 ATP (per pyruvate), so 4 ATP total (2 pyruvate molecules)

    • NADH: 10 NADH molecules produced, yielding 30 ATP (10 x 3)

    • FADH2: 2 FADH2 molecules produced, yielding 4 ATP (2 x 2)

    • Total ATP: 2 + 4 + 30 + 4 = 38 ATP per glucose molecule.

  • Anaerobic Respiration:

    • Glycolysis: 2 ATP

    • No further ATP production due to the absence of the Krebs cycle and electron transport chain.

    • Total ATP: 2 ATP per glucose molecule.

Key Points:

  • ATP Yield: Aerobic respiration produces significantly more ATP than anaerobic respiration.

  • Energy Efficiency: Aerobic respiration is a much more efficient process for extracting energy from glucose.

  • Oxygen Requirement: The availability of oxygen determines whether aerobic or anaerobic respiration occurs.


In summary, the energy budget of respiration reflects the efficiency of energy extraction from glucose. Aerobic respiration, with its complete oxidation of glucose and ATP production through the electron transport chain, is a highly efficient process.

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