General

• Food chain


  Describes the feeding relationships between organisms and the resultant stages of biomass transfer
• Trophic levels


  The stages in a food chain
• Trophic levels

  • Represented by numbers, starting from 1
  • Numbered according to how far along the organism is in the food chain
• Trophic level 1

  Plants and algae which make their own food (through photosynthesis) - called producers
• Trophic level 2

  Herbivores which eat producers - called primary consumers
• Trophic level 3

  Carnivores that eat herbivores - called secondary consumers
• Trophic level 4

  Carnivores that eat other carnivores - called tertiary consumers
• Apex predator


  A carnivore with no predators
• How decomposers break down dead matter

  1. Decomposers release enzymes which catalyse the breakdown of dead material into smaller molecules

  2. Soluble small food molecules then diffuse into the microorganisms
• Biomass


  The dry mass of all of the living organisms in an area
• Dry mass is used for biomass because the wet mass varies as the volume of water in the organism varies
• How to calculate the efficiency of biomass transfer

  efficiency = (energy transferred / total energy available) × 100
• Producers transfer 1% of the incident energy from light for photosynthesis
• Approximately 10% of the biomass from one trophic level is transferred to the level above it in feeding
• Reasons why biomass transfers are not 100% efficient

  • Egestion (removal of faeces)
  • Excretion (removal of waste products e.g. urine containing urea and water)
  • Respiration (loss of carbon dioxide and water) in which large amounts of glucose are used
  • The production of inedible bones and shells
• The efficiency of biomass transfers

  Affects the number of trophic levels in a biomass pyramid
• Biomass pyramid


  A pyramid that shows the total dry mass of organisms at each trophic level, with trophic level 1 at the bottom
• Pyramid of numbers


  A pyramid that shows the number of organisms at each trophic level
• In the given pyramid of biomass, D is the producer
• Pyramids of numbers don't take size and mass of organisms into account, so they are not always pyramid shaped
• Calculate the efficiency of biomass transfer from the flowers to the caterpillar

  1. efficiency = (energy transferred / total energy available) × 100

  2. Total energy available = 800 kJ + 4000 kJ = 4800 kJ

  3. Energy transferred = 800 kJ

  4. 800/4800 x 100 = 16.67%