Respiration

• Respiration: chemical reactions that break down nutrient molecules in living cells to release energy.
• Uses of energy in the body of humans: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature.
• Respiration involves the action of enzymes in cells
• Aerobic respiration: release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen.
• Aerobic respiration:

  Glucose + oxygen -> carbondioxide + water

  $C_6H_{12}O_6\ \rightarrow6CO_2+$$6H_2O$
• Anaerobic Respiration: release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen.
• Anaerobic respiration in muscles:

  Glucose -> Lactic Acid

  $C_6H_{12}O_6\rightarrow2C_3H_6O_3$
• Anaerobic respiration in yeast:

  Glucose -> Ethanol + Carbon Dioxide

  $C_6H_{12}O_6\rightarrow2C_2H_5OH+$$2CO_2$
• Disadvantages of anaerobic respiration:

  • Only produces 1/20 of the energy per glucose molecule that aerobic respiration would
  • Produces poisonous lactic acid
• Lactic acid:

  • Transported in blood to heart, liver and kidneys, which oxidize it
  • The heart, liver and kidneys need extra oxygen to do this which causes you to continue breathing heavily after exercise.
  • The extra oxygen is called the oxygen debt.