In an ecosystem energy pyramid, if producers contain 50,000 kJ and 10% is transferred to the first consumer level with another 10% transferred to the second, how much energy is available to primary and secondary consumers?

• A. Primary 5,000 kJ; Secondary 500 kJ
• B. Primary 50,000 kJ; Secondary 5,000 kJ
• C. Primary 500 kJ; Secondary 50 kJ
• D. Primary 25,000 kJ; Secondary 2,500 kJ

Answer: (A)

Energy moves through trophic levels in roughly a 10% rule pattern: only about one-tenth of the energy at one level is available to the next level. Starting with producers at 50,000 kJ, the first consumer can access 10% of that, which is 5,000 kJ. The second consumer then gets 10% of the energy that was available to the first consumer, which is 500 kJ. So primary consumers have 5,000 kJ and secondary consumers have 500 kJ. This aligns with the idea that energy decreases at each step in the pyramid due to losses like heat and metabolic use.