Pyramids of Energy: Skills (HL IB Biology)

• Pyramids of energy illustrate the energy contained within the biomass of organisms at each trophic level
• The length of each box, or bar, represents the energy present
  • Pyramids of energy should be drawn to scale so that each bar is proportional in size to the energy that it represents
  • In some situations, however, a pyramid of energy may be an approximate sketch where each bar is a rough representation of the energy contained
• These pyramids are always widest at the base and decrease in size as they go up
  • The base is wide due to there being more energy contained within the biomass of producers
• Pyramids of energy show a stepped decrease in the energy contained at each level of the food chain, rather than appearing as a pyramid with smooth sides
• The levels of a pyramid of energy should be labelled producer, primary consumer, secondary consumer, and so on
• The units used should be the energy, per unit area, per year e.g. kJ m^-2 year^-1
• As you move up the pyramid to higher trophic levels, the energy available decreases as not all energy is transferred to the biomass of the next trophic level
  • Roughly 10 % of the energy is passed on at each trophic level
• Energy is lost at each trophic level due to
  • Incomplete consumption
  • Incomplete digestion
  • Loss of heat energy to the environment during respiration
  • Excretion of the waste products of metabolism e.g. carbon dioxide, water, and urea
• As a result of this the biomass at each trophic level will also decrease as energy availability decreases

Pyramid of energy diagram

The energy stored in the biomass of organisms can be represented by a pyramid of energy