Which term describes each step in a food chain or food web, with energy decreasing as you move up?

• A. Biomass
• B. Trophic Cascade
• C. Trophic Level
• D. Keystone Species

Answer: (C)

Energy moves through ecosystems in steps called trophic levels—the positions organisms occupy as energy passes from producers up to apex predators. At each step, only a fraction of the energy available at the level below is transferred onward because organisms use energy for their metabolism and much is lost as heat, so the amount of usable energy declines as you move up. This is what the question describes. Biomass refers to the total mass of living matter at a given level, which can change independently of the idea of a step. A trophic cascade describes indirect effects across multiple levels, not a single step. Keystone species are influential due to their role in the ecosystem, not because of the energy-transfer step. So the term that best fits describing each step with energy decreasing as you move up is trophic level.