During energy transfer in ecosystems, what happens to most of the energy that is not stored in organisms?

• A. Energy is stored indefinitely in biomass.
• B. Energy is recycled by producers.
• C. It is lost as heat.
• D. It becomes water and carbon dioxide.

Answer: (C)

Energy that isn’t stored in organisms mostly goes into powering life processes and is released as heat. When organisms perform metabolism—growth, movement, maintaining body temperature, and other activities—they burn chemical energy to do work, and most of that energy leaves as heat to the surroundings. Energy can’t be recycled efficiently in ecosystems; only a small fraction is stored as new biomass for the next trophic level, while the rest is lost as heat. CO2 and H2O are produced during respiration, but the energy tied up in those molecules is released as heat rather than preserved as usable energy. That’s why most of the energy not stored is lost as heat.