(1) Aerobic vs Anaerobic Respiration - Lactic Acid and Ethanol Fermentation

Aerobic vs. Anaerobic Respiration

  • Key Difference:

    • Aerobic respiration occurs in the presence of oxygen.

    • Anaerobic respiration occurs without oxygen.

Aerobic Respiration

  • Definition:

    • A process converting glucose into carbon dioxide and water using oxygen.

    • Example of aerobic respiration includes cellular respiration.

  • Process Overview:

    1. Glycolysis:

      • Glucose (C6H12O6) is converted into two molecules of pyruvate.

      • Glycolysis does not require oxygen.

    2. Pyruvic Oxidation:

      • Pyruvate is converted into acetyl coenzyme A.

    3. Krebs Cycle:

      • Acetyl coenzyme A is oxidized to produce two CO2 molecules.

      • NAD+ is reduced to NADH and FAD is reduced to FADH2.

    4. Electron Transport Chain:

      • NADH and FADH2 donate electrons to oxygen, resulting in water production.

  • Overall Reaction:

    • 1 Glucose + 6 O2 → 6 CO2 + 6 H2O

    • Total CO2 produced: 6 molecules.

Anaerobic Respiration

  • Definition:

    • Metabolic process that converts glucose into different end products without oxygen.

  • Types of Anaerobic Respiration:

    1. Ethanol Fermentation:

      • Occurs in yeasts, specifically when glucose is available but O2 is not.

      • Process:

        • Glycolysis converts glucose to pyruvate (producing 2 ATP).

        • Pyruvate is decarboxylated to form acetaldehyde (loss of CO2).

        • Acetaldehyde is reduced to ethanol, regenerating NAD+ from NADH.

      • Overall Yield:

        • 2 ATP from one glucose.

    2. Lactic Acid Fermentation:

      • Occurs in muscle cells when oxygen is depleted during intense exercise.

      • Process:

        • Glycolysis converts glucose to two pyruvate (producing 2 ATP).

        • Pyruvate is reduced to lactate, regenerating NAD+ from NADH.

      • Overall Yield:

        • 2 ATP from one glucose.

Summary of key points for each fermentation type

  • Ethanol Fermentation:

    • Steps: Glycolysis → 2 Pyruvate → 2 Acetaldehyde → 2 Ethanol (with CO2 released).

  • Lactic Acid Fermentation:

    • Steps: Glycolysis → 2 Pyruvate → 2 Lactate (no CO2 released).

Review Questions

  1. ATP Yield in Lactic Acid Fermentation:

    • Answer: 2 ATP per glucose.

  2. False Statement Identification for Anaerobic Processes:

    • Correct Answers:

      • D: Lactic acid fermentation produces CO2 (It does not!).

      • E: Ethanol fermentation occurs in four steps (It occurs in three steps!).

Conclusion

  • Aerobic Respiration: occurs with oxygen

  • Anaerobic Respiration: occurs without oxygen; includes ethanol and lactic acid fermentation.