10.2

• How is energy transferred between trophic levels?

  Only a small amount of the energy available to an organism is transferred to the next trophic level. Some is never taken in, some is lost before being transferred.
• What is meant by net primary productivity?

  Energy transferred into biomass (available to the next trophic level)
• What is meant by gross primary productivity?

  Energy taken in by primary consumers
• Why is some energy never taken in at each trophic level?

  • Some parts of food aren't eaten
  • Some parts of food are indigestible
  • Plants can't use all light energy as some is in the wrong wavelength
• Why is some energy lost at each trophic level?

  Respiration; it is lost as heat
• How are nutrients recycled within an ecosystem?

  By microorganisms
• Outline the roles of microorganisms in the nitrogen cycle

  1. Nitrogen-fixing bacteria in roots/soil convert gaseous nitrogen into ammonia

  2. Saprobionts decompose nitrogenous waste into ammonium compounds

  3. Nitrifying bacteria convert ammonium compounds into nitrates and nitrites
• Net primary productivity = gross primary productivity - energy loss due to respiration
• What is nitrification?

  The conversion of ammonium ions to nitrate ions by nitrifying bacteria. This takes place in two stages:

  1. ammonium ions are oxidised to nitrite ions
  2. nitrite ions are oxidised to nitrate ions
• What is nitrifying bacteria?

  Microorganisms found un the soil responsible for the oxidation of ammonium ions to nitrate ions
• What is the nitrogen cycle?


  The cycle through which nitrogen moves between living organisms and the environment, involving ammonification, nitrification, nitrogen fixation and denitrification
• What is nitrogen fixation?


  The conversion of atmospheric nitrogen gas into nitrogen-containing compounds by nitrogen-fixing bacteria in the soil or nodules of legumes. Into a form that can be used by plants.
• How do you do calculate the efficiency of energy transfer between different trophic levels and account for the loss of energy at each level?

  Higher level / lower level x 100 = % biomass transferred