Energy Transfer and Productivity

• How much light energy is captured by green plants?

  As little as 1%-3%
• What do plants convert light energy into?

  Organic matter.
• Why is most of the sun's light energy not converted into organic matter by plants?

  Over 90% is reflected back into the atmosphere, not all wavelengths of light can be absorbed and used for photosynthesis, and the light may not fall onto the chlorophyll molecules.
• What is gross primary production?

  The total quantity of chemical energy store in plant biomass, in a given area and time.
• What is net primary production?

  The chemical energy store left in plant biomass after losses to respiration have been taken into account.
• What is the equation for net primary production?

  NPP = GPP - respiratory losses
• What causes a low percentage of energy transfer at each trophic level?

  Not all of the organism is ingested, some parts are not digested and are lost as feces, some energy is lost in excretory materials such as urine, and some energy losses occur as heat from respiration.
• What is the calculation for the net production of consumers?

  Net production = chemical energy store of ingested food - (energy lost in feces and urine + energy lost in respiration)
• Why do most food chains only have 4 or 5 trophic levels?

  There is insufficient energy available to support a large enough breeding population at trophic levels any higher.
• How much energy in producers is used by primary consumers?

  10%
• How much energy in primary consumers is used in secondary and tertiary consumers?

  Up to 20%
• How do you calculate the efficiency of energy transfers?

  Efficiency (%) = energy available after the transfer/energy available before the transfer *100