Energy Flow

• biomass - dry mass of tissue at a given time in a given area
• GPP - chemical energy present in biomass in a given area at a given time
• GPP - R = NPP
• Producers only absorb 1-3% of light as...

  • some light misses the chloroplast
  • wrong wavelength of light
  • other limiting factors
  • converted into heat
• Primary Consumers have an efficiency of 10%

  NP = I - (F+R)
• Efficiency transfer is usually calculated in kJ m-2 yr-1
• Producers - convert light energy into chemical energy via photosynthesis. This energy is then available to other trophic levels. e.g. phytoplankton & algae.
• Food Web - A diagram showing the flow of energy through different trophic levels of a community
• Efficiency of energy transfers - the percentage of energy which is transferred between trophic levels.
• Detritivores - small animals break down large organic compounds from dead organisms into small ones.
• The saprobionts break down these further, making mineral ions e.g. NO3-, available via extracellular enzymes.
• Pyramids of numbers - Communities can be represented by pyramids as energy is lost at each trophic level. Pyramids of numbers are often pyramidal except for when there is 1 big producer - i.e. a tree
• Pyramids of biomass - can be derived from weighing tissue after heating repeatedly until constant masses occur. This is done for each trophic level of a community and should result in a pyramid.
• Eutrophication:

  • mineral ions are leached from fields - particularly those where soluble, artificial fertilisers are used, into water sources.
  • this overcomes limiting factors in lakes/rivers
  • algal blooms occur and block out sunlight from penetrating the surface.
  • aquatic plants die, as they can't photosynthesise, reducing O2 conc.
  • aerobic saprobionts reduce O2 conc. as they decompose the dead plants.
  • these anaerobic conditions kill aquatic animals.
  • the saprobionts aerobically respire more as the animals are decomposed. The environment is now anaerobic.