Energy and ATP

• Energy

  • the ability to do work
  • variety of forms
  • transferred from one form to another
  • cannot be created or destroyed
  • measured in joules
• why do organisms need energy?

  • metabolism- all the reactions that take place in living organisms
  • movement
  • active transport
  • maintenance, repair and division of cells
  • production of substances
  • maintenance of body temperature
• The flow of energy through living systems


  1. light energy is converted by plants into chemical energy during photosynthesis
  2. the chemical energy from photosynthesis in the form of organic molecules, is converted into ATP during respiration
  3. ATP is used by cells as the energy source to perform useful work
• ATP is made of adenine (base), ribose (pentose sugar), 3 phosphate groups
• why is ATP is useful


  • universal - many processes, all cells all organisms
  • small release of energy is manageable
  • immediate release of energy
• how ATP releases energy


  • the 3 phosphate groups are joined together by 2 high energy bonds
  • ATP can be hydrolysed to break a bond which releases a large amount of energy
  • hydrolysis of ATP to ADP and inorganic phosphate Pi
• ADP + Pi -> ATP 


  • Photophosphorylation- occurs in chlorophyll during photosynthesis
  • oxidative phosphorylation- occurs in the mitochondria during the electron transport chain
  • substrate-level phosphorylation- when phosphate groups are transferred when donor molecules to ADP
• • the energy released from the splitting of ATP into ADP releases energy in small, manageable bursts
  • hydrolysis of ATP to ADP is a single reaction, glucose breakdown requires a long series of reaction
• Advantages of ATP


  • instant source of energy in the cell
  • releases energy in small amounts is needed
  • it is a mobile and transports chemical energy to where it is needed in the cell
  • universal energy carrier and can be used in many different chemical reactions
• metabolic processes

  • ATP provides the energy to build up macromolecules from their basic units e.g. polysaccharides from monosaccharides, polypeptides from amino acids, DNA from nucleotides.

  Movement -

  • ATP provides energy for muscles contraction
• Activation of molecules


  when a phosphate molecule is transferred from ATP to another molecule it makes it more reactive. ATP therefore allows enzyme-catalysed reactions to occur more quickly