Cellular Respiration and Fermentation

Importance of Oxygen in Cellular Respiration

  • Oxygen's Role: Essential for cellular respiration; allows Krebs cycle and electron transport chain to function.
  • Impact of Absence: Without oxygen, organisms cannot produce 36 ATP via aerobic processes.

Glycolysis: Anaerobic Energy Production

  • Glycolysis: An anaerobic process; can occur without oxygen.
    • Outputs: Produces ATP, NADH, and pyruvate.
    • Inputs: Requires glucose, ATP (converted from ADP and phosphate).
  • NADH's Function: Acts as an electron carrier.
    • NAD+: Electron acceptor necessary to regenerate NADH for continued glycolysis.

Fermentation: An Alternative Pathway

  • When Oxygen is Unavailable: Cells need to regenerate NAD+ for glycolysis through fermentation.
  • Oxidation of NADH: NADH loses electrons, turning back into NAD+.
Types of Fermentation
  1. Alcoholic Fermentation
    • Organisms: Utilized by yeasts (e.g., in bread and wine production).
    • Process: Pyruvate converts to ethanol and carbon dioxide.
    • Outcomes: Regenerates NAD+ from NADH.
      • Bread Example: CO2 produced causes bread to rise.
  2. Lactic Acid Fermentation
    • Applications: Used in yogurt production and during intense exercise in muscles.
    • Process: Pyruvate is converted into lactate (lactic acid).
    • Biological Relevance: Lactic acid accumulates in muscles during strenuous activity where oxygen supply is insufficient.
      • Aftermath: Lactic acid removed by blood circulation, converted back to pyruvate in the liver.

Overview of Energy Transformation

  • Glucose Origin: The glucose necessary for cellular respiration comes from photosynthesis.
  • Photosynthesis: Converts sunlight, water, and carbon dioxide into glucose and oxygen.
    • Opposite of Cellular Respiration: Where respiration breaks down glucose to release energy, photosynthesis builds it up.
    • Significance: Essential for energy source for plants and produces oxygen for respiration.