Lesson 2.5 - Anaerobic Respiration

Cellular Respiration and Fermentation

  • Anaerobic Cellular Respiration: A metabolic process that occurs in the absence of oxygen.

    • Involves glycolysis to convert glucose into ATP and lactic acid or ethanol depending on the organism.

    • Anaerobic respiration produces significantly less ATP compared to aerobic respiration (36 ATP).

Fermentation Processes

  • General Overview: In the absence of oxygen, cells have to recycle NADH back to NAD+ to continue ATP production via glycolysis.

    • There are two primary types of fermentation: Lactic Acid Fermentation and Ethanol Fermentation.

Lactic Acid Fermentation

  • Occurrence: Common in animal cells and during high-intensity exercise.

    • Produces lactate, leading to an acidic environment which may inhibit muscle function and cause a burning sensation.

    • Once exercise subsides, lactate is often converted back to pyruvate and reused in aerobic respiration, aiding recovery.

    • Net Production: 2 ATP molecules and 2 NAD+ molecules recycled.

Ethanol Fermentation

  • Occurrence: Performed by yeast and some bacteria (facultative anaerobes).

    • Converts pyruvate into ethanol and carbon dioxide; primarily used in making bread and alcoholic beverages.

    • Net Production: 2 ATP molecules, 2 ethanol molecules, and 2 CO2 molecules produced.

Historical Context

  • During WWI, fermentation helped produce acetone from wood in the absence of oxygen, showcasing an alternative to petrochemical sources.

    • Efficient fermentation of starches (from molasses or grain) to produce high yields of chemicals.

Experimental Application: Fermentation in a Bag

  • Materials:

    • 1 tsp dry active yeast

    • 1 tsp sugar

    • 100 mL warm water

  • Procedure: Combine the above in a zip-lock bag for observation of fermentation activity.

Other Strategies for Anaerobic Respiration

  • Some organisms have developed specialized metabolic adaptations to survive in low oxygen environments.

    • For example, E. coli can use nitrate ions as an electron acceptor in the absence of oxygen.

    • Methanogens: A group of organisms that produce methane from CO2 and other substrates in anaerobic conditions.