Which statement best describes energy transfer in ecosystems?

Which statement best describes energy transfer in ecosystems?

• A. Energy is recycled within ecosystems
• B. Energy increases as it moves through trophic levels
• C. Energy is lost as heat at each transfer
• D. Energy remains constant between levels

Answer: (C)

Energy flows through ecosystems from producers up to top consumers, and it is not recycled. When an organism uses energy for metabolism, movement, growth, or warmth, a large portion is released as heat. Only a fraction is stored in new biomass that the next trophic level can consume, so the amount of usable energy decreases at each step. This is why energy pyramids get smaller higher up the chain, and roughly only about 10% of the energy at one level is available to the next. In contrast, nutrients cycle, not energy, and energy does not stay constant or increase as you move through trophic levels.

Energy flows through ecosystems from producers up to top consumers, and it is not recycled. When an organism uses energy for metabolism, movement, growth, or warmth, a large portion is released as heat. Only a fraction is stored in new biomass that the next trophic level can consume, so the amount of usable energy decreases at each step. This is why energy pyramids get smaller higher up the chain, and roughly only about 10% of the energy at one level is available to the next. In contrast, nutrients cycle, not energy, and energy does not stay constant or increase as you move through trophic levels.