Aerobic and Anaerobic

• Organisms need energy for


  • Chemical reactions to build larger molecules from smaller molecules
  • Muscle contraction to allow movement
  • Keeping warm (to maintain a constant temperature suitable for enzyme activity)
• Anaerobic Respiration in Animals


  1. Respiration in cells can take place anaerobically (without oxygen), to transfer energy

  2. Involves the incomplete breakdown of glucose into lactic acid
• Word equation for anaerobic respiration in animals

  Glucose → Lactic acid + Energy
• Anaerobic respiration takes place without the need of oxygen
• Fermentation


  Economically important in the manufacture of bread (where the production of carbon dioxide makes dough rise) and alcoholic drinks (as ethanol is a type of alcohol)
• Anaerobic respiration in yeast

  Glucose → ethanol + carbon dioxide + energy released
• Comparison of aerobic and anaerobic respiration


  • Aerobic: Presence of oxygen, Complete oxidation of glucose, Products are carbon dioxide and water, Relatively large amount of energy released
  • Anaerobic: Absence or short supply of oxygen, Incomplete oxidation of glucose, Products are lactic acid (in mammals), ethanol and carbon dioxide (in yeast and some plants), Small amount of energy released but quickly
• Respiration


  Happens in cells, not to be confused with breathing which is ventilation
• Respiration is only around 40 per cent efficient
• Yeast


  Used to make alcoholic drinks
• Yeast respiration during beer or wine production


  1. Yeast cells reproducing rapidly

  2. Oxygen runs out

  3. Yeast switches to anaerobic respiration

  4. Ethanol and carbon dioxide are produced
• Yeast used to produce bread


  1. Yeast respires using sugar added to the dough

  2. Bubbles of carbon dioxide make the bread rise

  3. Alcohol produced evaporates as the bread is baked