4.2 Energy Flow

• Energy is stored in the organic compounds (biomass) of organisms.

  Approximately 90% of the energy is lost between trophic levels due

  to:

  • Living organisms use organic molecules for respiration, with energy lost as heat.
  • Some organisms die before they are eaten so the energy is lost from the food chain.
  • Some parts of organisms are not eaten, such as hair and bones.
  • Some parts of organisms are indigestible such as cellulose in cell walls.
• Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.
• • The process of respiration converts organic compounds to ATP, but energy is lost in the form heat from all living organisms.
  • Living organisms cannot convert heat energy to other forms of energy, therefore heat energy is lost from ecosystems.
• Organisms require energy for:

  • Synthesizing large molecules such as DNA and proteins
  • Active transport
  • Moving things around within cells (vesicles and chromosomes)
  • Moving tissues – muscles
• Trophic Level - The position an organism occupies within a feeding sequence is known as its trophic level
• A food chain shows the feeding relationship between organisms in an ecosystem.
• • 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.
• • 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.
• In food webs which process produces the chemical energy found in carbon compounds? Photosynthesis
• Which of these cannot be recycled in an ecosystem? Heat
• What are the units of energy used in quantitative representations of energy flow using pyramids of energy? kJ m-2 year-1
•  What is the main factor that restricts the length of food chains in an ecosystem? Energy loss
• In most terrestrial ecosystems what happens to each trophic level as you move through a food chain? A decrease in biomass and energy
• What percentage of energy is usually lost between trophic levels? 90%
• Which of the following forms of energy is the least useful in an ecosystem? Heat energy
• Which of the following statements about pyramids of energy are not correct? Energy is passed on as kinetic energy