B9.4 - metabolism and the liver

• Metabelisim

  The sum of all reactions that take place in a cell or in the body
• Common metabolic reactions

  • The conversion of glucose to starch, glycogen and cellulose
  • The formation of lipid molecules from glycerol molecules and 3 fatty acid molecules
  • The use of glucose and nitrate ions to form amino acids. Which then form proteins
  • The reactions of respiration
  • The reactions & photosynthesis
  • The breakdown of excess proteins in the liver to form urea
• The liver

  • It carries out many different functions
  • It's a very active organ with many metabolic functions
• Liver functions


  1. Detoxifying poisonous substances (such as ethane from alcoholic drinks)

  2. Passing breakdown products into the blood to they can be excreted in the urine via the kidneys

  3. Breaking down old worn out blood cells and storing iron until it's needed to synthesise more blood cells
• Lactic acid produced by anaerobic respiration in muscles

  • Blood flowing through the muscles transports the lactic acid to the liver and then it's converted back to glucose
  • The oxygen debt is then repaid once the lactic Acid has been converted back to glucose and broken down in aerobic respination forming CO₂ and water
  • If it isn't needed, the glucose could be converted into glycogen and stored in the liver until needed
• The liver is responsible for detoxifying substances that enter the body, such as alcohol.