CIE Biology IGCSE - Topic 12: Respiration

Overview of Respiration

• Definition: Respiration is a chemical reaction occurring in almost all body cells to produce energy from nutrient molecules.
• Energy Utilization:
  • Muscle contraction
  • Protein synthesis
  • Cell division
  • Active transport
  • Growth
  • Nerve impulses
  • Maintaining body temperature
• Types of Respiration:
  • Aerobic Respiration: Requires oxygen
  • Anaerobic Respiration: Occurs in absence of oxygen, less efficient

Aerobic Respiration

• Process:
  • Takes place in the presence of oxygen.
  • Glucose is broken down into carbon dioxide, water, and energy with the help of oxygen.
  • Occurs in the cell's mitochondria; cells that require more energy, like muscle cells, have higher amounts of mitochondria.
• Chemical Equation:
  • Glucose + Oxygen → Carbon dioxide + Water
  • [C_6H_{12}O_6 + 6O_2 → 6CO_2 + 6H_2O]_

Anaerobic Respiration

• Process:
  • Occurs without oxygen.
  • Less energy is produced per glucose molecule compared to aerobic respiration.
  • Takes place in the cell cytoplasm and does not require mitochondria.
• Animal Cells:
  • Occurs during vigorous exercise when oxygen is insufficient.
  • Glucose breaks down into lactic acid, causing muscle fatigue.
  • Produces an "oxygen debt" which is repaid by breaking down lactic acid using oxygen.
  • High breathing and heart rates post-exercise facilitate this process.
• Microorganisms (Yeast):
  • Yeast undergoes anaerobic respiration to form alcohol and carbon dioxide instead of lactic acid.
• Chemical Equations:
  • In Yeast: Glucose → Alcohol + Carbon Dioxide
    • [C_6H_{12}O_6 → 2C_2H_5OH + 2CO_2]
  • In Animal Cells: Glucose → Lactic Acid_