IB Biology SL

Revision Notes

2.1.2 Metabolism


Metabolism means ALL the reactions that take place in organisms

  • Metabolism is a catch-all term to group 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 pathway
  • Metabolic reactions can be classified broadly as anabolic or catabolic


Anabolic reactions

  • Are involved with building up 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
  • Often for the purposes of releasing energy for cellular processes and for 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



Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top