IB DP Biology: SL复习笔记2.1.2 Metabolism


  • Metabolism is a catch-all term used to describe all the chemical reactions that take place within cells and organisms
  • Metabolism can be thought of as the chemical reactions of life
    • The molecules involved are metabolites
  • Many reactions of metabolism take place in multiple stages
    • Each stage is catalysed by a separate enzyme
  • A series of interlinked metabolic reactions is called a metabolic pathway
  • Metabolic reactions can be classified broadly as anabolic or catabolic


  • Anabolic reactions are involved with the building of large molecules from smaller ones
  • Examples include;
    • Photosynthesis, where CO2 and water are built up into complex sugars
    • Protein synthesis, where amino acids are joined together in sequence
    • The buildup of fat stores ahead of animal hibernation
  • Anabolic reactions often include condensation reactions
  • Anabolic reactions are endergonic (they require an input of energy to take place)
    • Energy-storing products are the end result


  • Catabolic reactions are involved with breaking down large molecules into smaller ones
  • These reactions are often carried out to release energy for cellular processes and for the excretion of waste
  • Examples include:
    • Respiration, where CO2 and water are produced from the breakdown of sugars
    • Deamination of proteins to release urea
    • The depletion of fat stores during animal hibernation
  • Catabolic reactions often include hydrolysis reactions
  • Catabolic reactions are exergonic (free energy is released for cellular processes or as excess heat)

Comparison of Anabolism and Catabolism Table


Exam Tip

You may be familiar with the concept of anabolic steroid drugs used by bodybuilders. This is to build muscle mass and so is a good example to remember when trying to remember the difference between anabolic and catabolic reactions.