7.4

• What are trophic levels?

  The stages in a food chain
• What does a food chain show?

  It describes the feeding relationships between organisms and the resultant stages of biomass transfer.
• How are trophic levels represented?

  Trophic levels are represented by numbers, starting from 1.
• What is trophic level 1?

  Plants and algae which make their own food (through photosynthesis) - called producers.
• What is trophic level 2?

  Herbivores which eat producers - called primary consumers.
• What is trophic level 3?

  Carnivores that eat herbivores - called secondary consumers.
• What is trophic level 4?

  Carnivores that eat other carnivores - called tertiary consumers.
• What is an apex predator?

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

  Decomposers release enzymes which catalyse the breakdown of dead material into smaller molecules.
• Why is dry mass used for biomass?

  Because the wet mass varies as the volume of water in the organism varies.
• What is biomass?

  The dry mass of all of the living organisms in an area.
• How do you calculate the efficiency of biomass transfer?

  $\text{efficiency} =$$\left(\frac{\text{energy transferred}}{\text{total energy available}}\right) \times 100$
• What percentage of the incident energy from light for photosynthesis do producers transfer?

  1%
• Why are biomass transfers not 100% efficient?

  Energy is lost through egestion, excretion, respiration, and the production of inedible bones and shells.
• What percentage of the biomass from one trophic level is transferred to the level above it in feeding?

  Approximately 10%
• How does the efficiency of biomass transfers affect the number of trophic levels in a biomass pyramid?

  The less efficient the transfers, the fewer trophic levels and the fewer organisms in higher trophic levels.
• What is a biomass pyramid?

  • A pyramid that shows the total dry mass of organisms at each trophic level
  • Trophic level 1 is at the bottom of the pyramid
• Identify the producer in this pyramid of biomass.

  D is the producer.
• What is a pyramid of numbers?

  • A pyramid of numbers shows the number of organisms at each trophic level.
• Why is this pyramid of numbers not pyramid shaped?

  Pyramids of numbers don’t take size and mass of organisms into account.
• Calculate the efficiency of the biomass transfer from the flowers to the caterpillar.

  $\text{efficiency} =$$\left(\frac{800 \text{ kJ}}{4800 \text{ kJ}}\right) \times 100 =$$16.67\%$