What does the 10% energy transfer rule state?

• A. Energy is transferred completely with no loss.
• B. Energy increases by about 10% at each transfer.
• C. Only about 10% of the energy at one trophic level is transferred to the next; the rest is lost as heat or used for life processes.
• D. Energy is stored indefinitely in the next level.

Answer: (C)

Energy transfer in food chains and why most of it isn’t passed on. In ecosystems, energy moves from producers to consumers, but only a fraction makes it to the next trophic level. The majority is lost as heat through metabolic processes, and some is used for life activities like movement, growth, and maintenance or remains in indigestible material. This is the idea behind the 10% rule: about 10% of the energy at one level becomes available to the next level. Because energy diminishes at each step, higher levels have less energy available and food chains are relatively short.

So the statement that only about 10% of the energy at one trophic level is transferred to the next, with the rest lost as heat or used for life processes, is the best description. The other ideas—energy transferring completely, increasing at each transfer, or being stored indefinitely—don’t fit how energy actually behaves in ecosystems.