Energy Pyramids: Showing Energy at Each Trophic Level to ScaleAn energy pyramid shows the energy available at each trophic level in an ecosystem.Energy is expressed per unit area per unit time, in kilojoules per square metre per year (kJ m⁻² yr⁻¹).Each bar is drawn to scale, with its length proportional to the energy at that level.An energy pyramid is always upright because energy falls at each successive level, with the mechanism of that loss covered in C4.2.12.An energy pyramidHow to Construct an Energy PyramidIdentify the trophic levels by sorting organisms into producers, primary consumers, secondary consumers, and tertiary consumers.Find the energy at each level in kJ m⁻² yr⁻¹ from the available data.Draw horizontal bars stacked with producers at the base and each higher level above.Scale the length of every bar in proportion to its energy value.Label each bar with its trophic level and energy value.Worked Example: A Grassland EcosystemProducers: grass at 50,000 kJ m⁻² yr⁻¹ forms the widest bar at the base.Primary consumers: herbivores such as rabbits at 7,000 kJ m⁻² yr⁻¹.Secondary consumers: predators such as foxes at 3,000 kJ m⁻² yr⁻¹.HintBecause the bars shrink upward, an energy pyramid can never be inverted, unlike some pyramids of numbers or biomass.Active recallWhat quantity does each bar of an energy pyramid represent, and in what units?Why must the length of each bar be drawn to scale?Why is an energy pyramid always upright?
