Why is only a portion of energy transferred from one trophic level to the next?

• A. Because all energy is stored within chemical bonds and never lost.
• B. Because producers refuse to share energy.
• C. Because energy is stored in the atmosphere.
• D. Because cellular respiration releases much energy as heat, leaving less for growth and transfer.

Answer: (D)

Energy moving from one trophic level to the next is limited because much of the energy organisms use for life processes is released as heat during cellular respiration, leaving less energy to be stored as biomass for the next level. Producers capture energy from the sun, and consumers obtain energy by eating them, but at every step organisms must fuel metabolism, movement, growth, and reproduction. The energy used for these activities becomes heat that dissipates into the environment, so only a fraction—often about 10%—is available to build new tissues for the next trophic level. Some energy is also lost in waste and in parts of the organism that cannot be digested. That's why energy transfer is inefficient and the amount available decreases as you move up the food chain.