Respiration

• If insufficient oxygen is supplied, anaerobic respiration takes place in muscles. The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt. During long periods of vigorous activity, muscles become fatigued and stop contracting efficiently.
• Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose. Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
• Metabolism includes:

  • Conversion of glucose to starch, glycogen, and cellulose
  • The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids
  • The use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins
  • Respiration
  • Breakdown of excess proteins to form urea for excretion