Explain the 10% rule in energy transfer between trophic levels and its ecological significance.

• A. About 10% of energy at one trophic level is transferred to the next; the rest is lost as heat or used for life processes.
• B. About 90% is transferred; only 10% is lost.
• C. Energy increases by 10% at each level.
• D. Energy transfer is 100% efficient at all levels.

Answer: (A)

Energy moves through ecosystems, but only a small portion of the energy available at one level becomes usable energy for the next. Most of it is lost as heat through metabolic processes, or used for daily activities and life processes, and some energy isn’t assimilated or is left in waste. That’s why roughly 10% of the energy at one trophic level is available to the next level as new biomass. This creates the characteristic energy pyramid: a lot of energy at the base (producers) and progressively less at higher levels (consumers). The ecological significance is that energy availability limits how many trophic levels an ecosystem can support and explains why top predators are more vulnerable to changes in energy supply upstream. In real ecosystems the transfer can vary, often around 5–20%, but the general idea is that energy transfer is inefficient and decreases at each step. The other options miss this core idea: energy is not transferred at 90% or more, it does not increase at higher levels, and it is not 100% efficient.