4.2  Energy Flow

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Essential Idea:

Ecosystems require a continuous supply of energy 

to fuel life processes and to replace energy lost as heat


  • Most ecosystems rely on a supply of energy from sunlight
  • Light energy is converted to chemical energy in carbon compounds by photosynthesis
  • Chemical energy in carbon compounds flows through food chains by means of feeding
  • Energy released from carbon compounds by respiration is used in living organisms and converted to heat
  • Living organisms cannot convert heat to other forms of energy
  • Heat is lost from ecosystems
  • Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels


  • Quantitative representations of energy flow using pyramids of energy