Anaerobic Respiration (Leaving Cert Biology): Revision Notes

Anaerobic Respiration

• Anaerobic respiration occurs in the cytosol.
• It does not require oxygen, but it can occur in the presence of oxygen.
• Anaerobic respiration produces only a small amount of energy because glucose is not fully broken down.
• There are two types of fermentation:
  1. Lactic acid fermentation
  2. Alcohol fermentation

Lactic Acid Fermentation

Lactic acid fermentation occurs in some bacteria and fungi and in mammal muscle when it is short of oxygen.

What Happens:

• Glucose is converted into lactic acid and a small amount of energy: Glucose → 2 lactic acid + small amount of energy

When It Occurs:

• During strenuous exercise, when muscles do not get enough oxygen.

Effects:

• Lactic acid builds up in the muscles, causing cramp and leading to an oxygen debt.
• The oxygen debt is repaid when the person breathes deeply and rapidly after exercise.
• Lactic acid is transported to the liver, where it is broken down.

Uses in Industry:

• Lactic acid fermentation is used by bacteria to:
  • Make milk sour.
  • Produce silage.
  • Create dairy products like cheese and yoghourt.

Alcohol Fermentation

What Happens:

• Glucose is converted into ethanol (alcohol), carbon dioxide (CO₂), and a small amount of energy: Glucose → 2 ethanol + 2 CO₂ + small amount of energy

C₆H₁₂O₆ → 2C₂H₅OH + 2 CO₂ + small amount of energy

• Yeast (a single celled fungus) respires the glucose in the absence of oxygen to produce ethanol and carbon dioxide as waste products.

Where It Occurs:

• In plants (in the absence of oxygen) and in some bacteria and fungi.

Uses in Industry:

• Alcohol fermentation is the basis of:
  • The brewing industry (to produce beer and wine).
  • The baking industry (to make bread rise).

Key Points of Anaerobic Respiration

• Produces less energy than aerobic respiration because glucose is only partially broken down.
• In humans, lactic acid fermentation occurs during exercise when oxygen is limited.
• Alcohol fermentation is widely used in food and drink industries.