In energy flow within ecosystems, what happens to most of the solar energy that enters?

• A. Most energy is lost as heat, with only a portion transferred to higher trophic levels.
• B. All energy is stored as biomass with no loss.
• C. Energy is recycled by decomposers back to producers.
• D. Energy is created at higher trophic levels from inorganic sources.

Answer: (A)

Energy flowing through ecosystems begins with sunlight captured by producers, but most of that energy is used for the organisms’ own metabolism and released as heat. Only a portion becomes stored chemical energy in biomass that can be passed to the next trophic level, and of that, even less moves upward again. This means energy transfer between levels is inefficient—roughly only a fraction, often cited around 10%, makes it to the next level while the rest is lost as heat or used for maintenance. Because energy is lost as heat at each step, top trophic levels receive much less energy and supporting large amounts of biomass at higher levels becomes impractical. Energy cannot be recycled back to producers or created anew at higher levels from inorganic sources; decomposers recycle nutrients, not usable energy, and the energy originally from the sun is ultimately dissipated as heat.