In an energy pyramid, what happens to the available energy as you move up trophic levels?

• A. It increases
• B. It remains the same
• C. It decreases; typically about 10% is transferred to the next level
• D. It fluctuates randomly

Answer: (C)

Energy moves through an ecosystem in one direction, but the amount available at each higher trophic level gets smaller. This happens because organisms use energy for metabolism, movement, growth, and reproduction, and much of it is lost as heat or remains unavailable (undigested or not eaten). As a result, only a portion is converted into new biomass for the next level. In many ecosystems, about 10% of the energy from one level is transferred to the next, with the rest dissipated or locked away. For example, starting with 1000 energy units in producers, roughly 100 reach the next level, then about 10, and so on. So the correct idea is that energy decreases as you move up, with roughly a tenth transferred each step.