Energy Transfer in Ecosystems

• Energy flow in ecosystems:

  • Energy enters an ecosystem as light.
  • Light energy is used to produce organic molecules from CO2 and water.
  • Energy in organic molecules is passed to consumers.
• Photosynthesis Efficiency:

  • Some light is the wrong wavelength and is not used.
  • Some light is reflected off the leaf.
  • Some light passes through the leaf without hitting a chloroplast.
• Photosynthesis Efficiency = (energy in carbohydrate / light energy falling on plant) x 100
• The amount of energy in carbohydrate made by photosynthesis in a given area or volume in a given time is termed gross primary production.
• Net Productivity = Gross Productivity - Respiratory Losses.

  NPP = GPP - R
• The NPP is available to the plant for growth and available other trophic levels - primary consumers and decomposers.
• Net productivity (NPP) can fall due to succession. This is due to less light reaching lower levels or more biomass respiring.
• The chemical energy store in dry biomass can be estimated using calorimetry.
• Energy = Mass x 4.2 x Temp. increase.
• Efficiency= Energy in biomass (of consumer) / Energy consumed.
• Only about 10% of energy is transferred between trophic levels.
• Eficiency between trophic levels:

  1. Not all plant/ animals matter is consumed and absorbed.
  2. Some energy is lost as metabolic waste.
  3. Respiratory losses.

  N= I - (F+R)